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absael
2012-Dec-28, 09:52 PM
I saw this article (http://www.gizmag.com/next-ion-record/25570/) about NASA's NEXT ion thruster setting a record for continuous operation. I was curious what speed a spaceship using this thruster could attain. I found the Tsiolkovsky rocket equation (http://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation), but I'm missing a couple of values. I couldn't find the effective exhaust velocity, so I was going to compute it from the specific impulse and standard gravity. I found out here (http://esto.nasa.gov/conferences/nstc2007/papers/Patterson_Michael_D10P3_NSTC-07-0014.pdf) that the engine has a specific impulse of 4100 seconds, but I'm not familiar with the term and I don't know if this is the correct value to use in the equation. And I don't understand what the specific gravity is in this context.

Assuming an initial spacecraft mass of 3000 kg, and an engine operating time of 5 years with fuel consumption of 770 kg (the numbers used in the article), can someone show me how to figure out the speed?

IsaacKuo
2012-Dec-28, 10:04 PM
When specific impulse is given in "seconds", you multiply by g (9.8m/s/s) in order to get average exhaust velocity. So, for example, a specific impulse of 4100s is an average exhaust velocity of 4100s * 9.8m/s/s = 40km/s (to two significant digits). 40km/s is a typical value for the exhaust velocity of a modern ion thruster. This value is what you plug into the rocket equation.

With a starting mass of 3000kg and a fuel consumption of 770kg, you end up with a final mass of 2230kg. This corresponds to a mass ratio of 3000/2230 = 1.35. Using the rocket equation, we end up with a delta-v of log(1.35)*40km/s = 12km/s.

This does not actually translate to a "speed" of 12km/s in a real life space mission, due to the various effects of orbital mechanics. The gravity of the Earth and Sun have important implications, as well as the initial speed of the Earth itself with respect to the Sun. For better or worse, there is no simple way to translate that delta-v value into a "speed" that a real life space mission can reach.

absael
2012-Dec-28, 11:03 PM
Thanks! It occurred to me that the initial mass that I chose was on the high side for a robotic spacecraft. The mass of Voyager 1 is only 722 kg, so if we chose that number as the dry weight of the spacecraft, with the same fuel consumption, the delta-v would be 29 km/s. Even keeping in mind your point about actual velocity vs calculated speed, it seems that this would be much faster than Voyager's current velocity of 17 kms/s relative to the sun, and if the NEXT engine had been available when Voyager 1 was launched, it would now be well outside the heliosphere.

Glom
2012-Dec-28, 11:10 PM
This does not actually translate to a "speed" of 12km/s in a real life space mission, due to the various effects of orbital mechanics. The gravity of the Earth and Sun have important implications, as well as the initial speed of the Earth itself with respect to the Sun. For better or worse, there is no simple way to translate that delta-v value into a "speed" that a real life space mission can reach.

I guess the situation with ion drive is a little different.

Delta-v is a concept best applied to a more old school form of mission design where a brief punch of a few minutes puts the spacecraft into an orbit in which it will coast for days/months/years. For example, we might talk about the delta-v of a burn from LEO to get into a lunar transfer orbit or a Mars transfer orbit.

Once we get into an architecture where the spacecraft is in powered flight for a large part of its journey, things get a little different. I'm not sure what the equivalent metrics would be.

IsaacKuo
2012-Dec-28, 11:32 PM
Thanks! It occurred to me that the initial mass that I chose was on the high side for a robotic spacecraft. The mass of Voyager 1 is only 722 kg, so if we chose that number as the dry weight of the spacecraft, with the same fuel consumption, the delta-v would be 29 km/s. Even keeping in mind your point about actual velocity vs calculated speed, it seems that this would be much faster than Voyager's current velocity of 17 kms/s relative to the sun, and if the NEXT engine had been available when Voyager 1 was launched, it would now be well outside the heliosphere.
Like I said, it's not so simple. If the spacecraft starts from low Earth orbit, then it would consume about 8km/s delta-v just spiraling out to escape Earth. Then it would slowly spiral out from Earth's orbit, consuming another 16km/s delta-v to spiral out to Jupiter. Without a Jupiter assist, this doesn't actually leave enough juice left over to escape the Sun's gravity. With a Jupiter assist, it could escape the Sun's gravity, but ironically it would do so with less speed than Voyager. Voyager picked up a LOT of speed from its multiple gravity assist maneuvers.

You can do much better if you fiddle around with the mission design. It's a very complicated interaction between delta-v, acceleration, and clever orbital mechanics. But generally, electric propulsion is most compelling when the destination is something like a typical asteroid. This is why the Dawn mission to Vesta and Ceres used electric propulsion.

absael
2012-Dec-29, 12:16 AM
Like I said, it's not so simple. If the spacecraft starts from low Earth orbit, then it would consume about 8km/s delta-v just spiraling out to escape Earth. Then it would slowly spiral out from Earth's orbit, consuming another 16km/s delta-v to spiral out to Jupiter. Without a Jupiter assist, this doesn't actually leave enough juice left over to escape the Sun's gravity. With a Jupiter assist, it could escape the Sun's gravity, but ironically it would do so with less speed than Voyager. Voyager picked up a LOT of speed from its multiple gravity assist maneuvers.

You can do much better if you fiddle around with the mission design. It's a very complicated interaction between delta-v, acceleration, and clever orbital mechanics. But generally, electric propulsion is most compelling when the destination is something like a typical asteroid. This is why the Dawn mission to Vesta and Ceres used electric propulsion.

Hmmm... I'm still stuck on the idea of using ion propulsion for very long-distance missions. What if Voyager had also used an ion thruster, but didn't turn it on until it had attained an appreciable distance from the sun, say outside of Neptune's orbit? Do you think that this would have resulted in significantly greater velocity?

cjameshuff
2012-Dec-29, 01:02 AM
Hmmm... I'm still stuck on the idea of using ion propulsion for very long-distance missions. What if Voyager had also used an ion thruster, but didn't turn it on until it had attained an appreciable distance from the sun, say outside of Neptune's orbit? Do you think that this would have resulted in significantly greater velocity?

That's actually the opposite of what you want to do. If you make a given delta-v when you still have a higher orbital velocity, you actually make a larger change in orbital specific energy which leaves you with more velocity left over. Applied delta-v adds to velocity, while orbital energy scales with the square of velocity. Ideally, you'd apply it all at once when you were still at the deepest in the gravity well and moving the fastest.

Rather than applying it continuously to spiraling out, going into an elliptical solar orbit and using repeated burns at perihelion to make your orbit more and more elliptical until you get into an escape trajectory might be more efficient, but it will take a long time if your thrust is too low to do it in small number of passes. Ion engines are really better suited to going between small bodies with little gravitation, making many adjustments to the orbit around a planet over time, or setting up for maneuvers using higher thrust engines.

djellison
2013-Jan-07, 07:45 AM
You're all missing the punchline here guys.

The NEXT engine requires 7kw of electricity. Where do you get it from?

At launch - the RTG's of Voyager produced only 0.47kw

You could perhaps use solar arrays - let's take the huge solar arrays from the Juno spacecraft. They way more than 300kg - and even using high efficiency modern cells ( twice as efficient as what was available in the 70's) - they produce 18kw at Earth. but only 450 watts at Jupiter

Take the solar arrays of the International Space Station - several tons of hardware.... 84kw of power produced.

By the time you're at Jupiter - that 84kw would be less than 4kw. By the time you're at Neptune..... Those 84kw arrays would produce only 92 watts.

Running that engine for 40,000 hours....that's 5 years. The Voyager spacecraft were past the orbit of Jupiter in 18 months.

It just doesn't work I'm afraid.

Jens
2013-Jan-07, 07:54 AM
You're all missing the punchline here guys.

The NEXT engine requires 7kw of electricity. Where do you get it from?

What about a nuclear reactor? Or would that just make it too heavy?

djellison
2013-Jan-07, 08:04 AM
What nuclear reactor was available in the 70's that could go on Voyager?

I believe the sort of things being planned for JIMO were on the order of a couple of tons.

Jens
2013-Jan-07, 08:16 AM
I took the question to be a hypothetical one, i.e. what if we were to launch a rocket either in the past or today with that thruster, how fast could it go?

cjameshuff
2013-Jan-07, 02:00 PM
What nuclear reactor was available in the 70's that could go on Voyager?

Availability in the 70s doesn't appear to be a requirement. The SAFE-400 (http://en.wikipedia.org/wiki/Safe_Affordable_Fission_Engine) gives 100 kW electrical power at a mass of 512 kg.

djellison
2013-Jan-07, 03:00 PM
Post number 6 in this thread explicitly states fitting this engine to Voyager

TooMany
2013-Jan-08, 04:40 PM
Availability in the 70s doesn't appear to be a requirement. The SAFE-400 (http://en.wikipedia.org/wiki/Safe_Affordable_Fission_Engine) gives 100 kW electrical power at a mass of 512 kg.

I don't think that includes the weight of the radiator. Also, it's only about 25% efficient. Temperature is 1000K; heat engines can do better than that, at least with combined cycle 50% is possible which would make the radiator a lot smaller.

cjameshuff
2013-Jan-08, 04:54 PM
I don't think that includes the weight of the radiator. Also, it's only about 25% efficient. Temperature is 1000K; heat engines can do better than that, at least with combined cycle 50% is possible which would make the radiator a lot smaller.

It is likely inefficient because it has a small radiator. If it doesn't include the radiator, talking about efficiency is fairly meaningless, as it is largely determined by the cold side temperature which is set by the radiator size...that overall conversion efficiency is stated and fairly low makes me think the mass likely includes the radiator.

Despite this, the efficiency is still much higher than for thermoelectric conversion, which generally converts just a few percent of the thermal power to electrical power. There may be other compromises that trade efficiency for longevity...efficiency is not the highest priority (as evidenced by the use of thermoelectric conversion in other systems).

TooMany
2013-Jan-08, 10:12 PM
Despite this, the efficiency is still much higher than for thermoelectric conversion, which generally converts just a few percent of the thermal power to electrical power. There may be other compromises that trade efficiency for longevity...efficiency is not the highest priority (as evidenced by the use of thermoelectric conversion in other systems).

It's not bad at all. But at 50% efficiency you only need to radiate 1/3 as much heat as at 25%. Isaac's been claiming that nuclear isn't any good because it's too heavy and whatnot. Solar gets so weak at Jupiter's distance, I'm surprised that they decided to use it for Juno. I supposed that solar is so well developed that engineering wise it is the simplest solution if you don't need a lot of power.

Didn't know about SAFE-400. The name says a lot about the public support risks that NASA takes when they try to use nuclear.

cjameshuff
2013-Jan-08, 10:57 PM
It's not bad at all. But at 50% efficiency you only need to radiate 1/3 as much heat as at 25%.

But you need to radiate it at 2/3 the temperature, which takes about 5/3 times the radiator area (taking into account the reduced thermal power needed), all else being equal. And all else isn't equal...cooler radiators will have a harder time with solar heating, larger radiators complicate deployment and heat transport issues, etc. It may not be meaningfully easier or cheaper to make a lower powered reactor, and going for ultra high efficiency right from the start means higher development costs and risks and a system that requires extensive redevelopment to expand into higher powers in the future.

It need only be better than what was available before, they can make it perfect later.

TooMany
2013-Jan-09, 12:39 AM
But you need to radiate it at 2/3 the temperature, which takes about 5/3 times the radiator area (taking into account the reduced thermal power needed), all else being equal. And all else isn't equal...cooler radiators will have a harder time with solar heating, larger radiators complicate deployment and heat transport issues, etc. It may not be meaningfully easier or cheaper to make a lower powered reactor, and going for ultra high efficiency right from the start means higher development costs and risks and a system that requires extensive redevelopment to expand into higher powers in the future.

It need only be better than what was available before, they can make it perfect later.

Of course (just trying to convince Isaac that nuclear is good for space).

If you want to keep the radiator light, you want to run the radiator as hot as possible because of the T^4 radiation rate. I suppose you would sacrifice efficiency for that reason, you have more heat to get rid of, but it's easier to dump because of the higher temp. Energy is not so much an issue with nuclear. I read that a soda can full of Uranium has more energy than the Shuttle's hydrogen tank which is enormous in comparison.

IsaacKuo
2013-Jan-09, 01:14 AM
Of course (just trying to convince Isaac that nuclear is good for space).
Umm...you forget that I gave plenty of examples of atomic power being used in actual space missions. It's good for electrical power in various situations, including outer system missions to Saturn and beyond. It's not so useful for space propulsion.

The web comic i write is set on a spacecraft in the Oort cloud. It is atomic powered. The character's last stop before leaving the solar system was the Titan station--also atomic powered. You apparently think I'm against atomic power, but in fact I'm not.

TooMany
2013-Jan-09, 07:19 PM
Umm...you forget that I gave plenty of examples of atomic power being used in actual space missions. It's good for electrical power in various situations, including outer system missions to Saturn and beyond. It's not so useful for space propulsion.

The web comic i write is set on a spacecraft in the Oort cloud. It is atomic powered. The character's last stop before leaving the solar system was the Titan station--also atomic powered. You apparently think I'm against atomic power, but in fact I'm not.

OK, you're just denying any value in nuclear propulsion.

IsaacKuo
2013-Jan-09, 08:24 PM
OK, you're just denying any value in nuclear propulsion.
Certainly nuclear thermal rockets don't seem to be promising for any missions, and nuclear electric is of limited potential for near term missions.

The problem with nuclear electric is cost vs benefit. For inner system missions, solar electric is better due to superior cost, mass, and maturity. Thus, nuclear electric propulsion is only a potential benefit for outer system missions--and these are few and far between. Furthermore, the majority of outer system missions would do better with chemical rocket propulsion rather than electric propulsion, limiting the potential benefit even further.

That's not to say there is no potential benefit at all. It's just limited, and not worth the costs. The JIMO mission was originally designed around nuclear electric propulsion (a case of a hammer looking for a nail, but regardless of the reason it was a real mission with a real budget). JIMO was slashed and ultimately cut from NASA completely due to the excessive costs, long development times, and technology risk. The ESA side continued, scaling it back to the JUICE mission--chemical rocket propulsion with solar power. JUICE will study three of the four moons JIMO would have studied, but at a fraction of the cost.

Nevertheless, nuclear electric propulsion would seem to be the most practical option for an eventual Pluto system orbiter, or a multiple KBO mission. Neither of these are in the cards yet, due to the fabulous costs of such missions compared to other comparable missions (Uranus and Neptune, Jupiter trojans, asteroid belt, etc).

Ara Pacis
2013-Jan-10, 01:59 AM
I'm curious how useful solar concentrators would be for solar-electric or solar thermal for the missions suggested above?

cjameshuff
2013-Jan-10, 02:42 AM
I'm curious how useful solar concentrators would be for solar-electric or solar thermal for the missions suggested above?

Solar concentration requires more accurate pointing, with rapid loss of power as the collector angles away from the sun, and the concentrators and required heat-spreading structures probably considerably outmass a simple un-concentrated panel. I see concentrated solar as best used for stationary applications where mass and pointing are less of an issue, but potentially quite valuable there...a concentrating mirror is easier to make from orbital resources than a solar panel.

Ara Pacis
2013-Jan-10, 07:46 AM
Solar concentration requires more accurate pointing, with rapid loss of power as the collector angles away from the sun, and the concentrators and required heat-spreading structures probably considerably outmass a simple un-concentrated panel. I see concentrated solar as best used for stationary applications where mass and pointing are less of an issue, but potentially quite valuable there...a concentrating mirror is easier to make from orbital resources than a solar panel.

I thought that solar sails were supposed to be doable, and lightweight. And the comparison is not against non-concentrated panels but against nuclear power, since it would be used farther away form the sun.

cjameshuff
2013-Jan-10, 04:27 PM
I thought that solar sails were supposed to be doable, and lightweight.

What do solar sails have to do with this? They don't need to concentrate or convert light, just reflect it in mostly the right direction.

And the comparison is not against non-concentrated panels but against nuclear power, since it would be used farther away form the sun.

If concentrated solar panels compare poorly against non-concentrated solar panels for spacecraft, they aren't going to suddenly do better than those systems when compared against nuclear.

IsaacKuo
2013-Jan-10, 04:30 PM
Based on various discussions I've read on NASASpaceflight, I gather that the near term progress in solar power is in thin film PV, with concentrated solar having lost favor all around. Thin film PV is getting so lightweight that it makes more sense to simply make a really large sheet of it than to try and make a large reflector (which isn't lighter and requires rigidity).

That said, ISRU might change the game in space. Even if a large reflector might require more mass than thin film PV, a reflector might be made out of locally produced aluminum. The overall system mass may be larger, but the amount of mass which needed to be lifted from Earth might be smaller.

Another unknown factor is how durable thin film PV will be in practice, in space environments.

In any case, an undeniable reality is that the amount of solar power available for a given size goes down with distance from the Sun. At some distance, alternative power sources will be superior.

NEOWatcher
2013-Jan-10, 04:32 PM
What do solar sails have to do with this? They don't need to concentrate or convert light, just reflect it in mostly the right direction.
I can see it applicable when comparing the mass of a flat solar panel against a reflector that captures the same cross section of sunlight. If the solar panels are a weight issue, then a very lightweight reflector which is built in the same fashion as a solar sail helps alleviate that problem.
Although; I don't know how that compares to all the other issues.

cjameshuff
2013-Jan-10, 06:15 PM
I can see it applicable when comparing the mass of a flat solar panel against a reflector that captures the same cross section of sunlight. If the solar panels are a weight issue, then a very lightweight reflector which is built in the same fashion as a solar sail helps alleviate that problem.

Again, solar sails don't need to concentrate light. Merely reflecting light isn't enough for concentrated solar power. Concentrating reflectors might be a lot lighter in space than anything used on Earth, but they have requirements for structure, geometry, and optical quality that simply aren't comparable to solar sails.

Thin film solar cells are more comparable to solar sails than concentrated solar, and in fact can be combined with them, as was done with IKAROS.

Ara Pacis
2013-Jan-11, 12:39 AM
What do solar sails have to do with this? They don't need to concentrate or convert light, just reflect it in mostly the right direction.Some solar sail materials are reflective, such as mylar and mylar makes a decent solar reflector and concentrator for many earth-side applications. space sourced aluminum foil might work in a pinch. Like you write about a solar sail, a concentrator needs to "just reflect it in mostly the right direction, which is roughly parabolic, though a faceted tube would probably work as well since you don't need to to come to a focus, but to spread it across a flat area. Sure, that would some very lightweight structure (or half of the inside of an inflatable transparent balloon), but it shouldn't mass much. The inverse square law kicks in here fairly well so if you make the concentrator merely twice as long and wide, then you've quadrupled your area and using the inverse square law again, that means that the reflector will be able to double the usable range (distance from the sun) of the solar panel.

If concentrated solar panels compare poorly against non-concentrated solar panels for spacecraft, they aren't going to suddenly do better than those systems when compared against nuclear.

What are you talking about? Who said a concentrated panel would fair more poorly than a non-concentrated panel? All you need to do to a non-concentrated panel is add a few grams/meter2 of reflector and supports, and rotate it 180°. The only downside of using a concentrator is that you don't want to use it until the craft is far enough from the sun need it, or else you may overheat and damage the solar panel. The mass of a reflector for even a large solar array would seem to be less than the minimum mass of a nuclear reactor for a smallish craft.

djellison
2013-Jan-11, 01:04 AM
You're missing the complexities of solar array performance. It also drops of in very cold temperatures, they're damaged by radiation etc etc.

Plus - a thin film reflector isn't going to be a great reflector - http://en.wikipedia.org/wiki/File:Inflatable_Antenna_Experiment.jpg - a smooth better performing reflector will involve a lot of substrcuture - structure that's complex, expensive, and potentially far heavier than just a thin film array that doesn't need such a rigid substrate. If an array is off a few degrees you barely loose any energy. If the reflector is off a few degrees, you drop to zero.

cjameshuff
2013-Jan-11, 02:53 AM
Some solar sail materials are reflective, such as mylar and mylar makes a decent solar reflector and concentrator for many earth-side applications. space sourced aluminum foil might work in a pinch. Like you write about a solar sail, a concentrator needs to "just reflect it in mostly the right direction,

No, it needs to reflect it consistently in a very particular direction. Wrinkles that cause minor cosine losses from irregular reflection angles in a solar sail will cause severe losses if you attempt to make a concentrator with a similar quality reflector. A completely diffuse reflector will still make an effective solar sail, but be useless for a concentrator. Even a flat black absorber has some use for photon sails. The optical requirements of solar sails and solar concentrators are not comparable.

What are you talking about? Who said a concentrated panel would fair more poorly than a non-concentrated panel?

I did.

All you need to do to a non-concentrated panel is add a few grams/meter2 of reflector and supports, and rotate it 180°. The only downside of using a concentrator is that you don't want to use it until the craft is far enough from the sun need it, or else you may overheat and damage the solar panel. The mass of a reflector for even a large solar array would seem to be less than the minimum mass of a nuclear reactor for a smallish craft.

The reflector is going to mass a good deal more than a few grams per meter...that's toward the optimistic end of the feasible range for solar sails, which again have looser optical requirements. In fact, the only solar sail material that lightweight only reflects a fraction of the light that hits it, it is a sparse carbon fiber material that mostly absorbs what light doesn't simply go through (http://mix.msfc.nasa.gov/IMAGES/MEDIUM/0002024.jpg). And that's just the sail material, with no structure, no photovoltaics.

It's certainly not likely to be less than the mass of an equivalent nuclear reactor, especially if it needs the additional structure to withstand being mounted on a spacecraft. At the distance of Saturn, given 30% collection and conversion efficiency, you need about 25000 m^2 of collection area to equal the 100 kWe from the SAFE-400. To beat the SAFE-400's 512 kg mass, you need less than 21 g/m^2. A solar sail may manage that, I don't see a concentrating solar power system coming anywhere close.

The benefit of concentrating solar isn't mass of the completed system, it's that the reflectors can be made from local materials, reducing the mass of photovoltaics you need to import.

Ara Pacis
2013-Jan-11, 08:21 AM
You're missing the complexities of solar array performance. It also drops of in very cold temperatures, they're damaged by radiation etc etc.From what I've read, the LILT cells designed for Juno actually work better at lower temperatures (NASA pdf 2007, p.5 (http://www.lpi.usra.edu/opag/nov_2007_meeting/presentations/solar_power.pdf)).

Plus - a thin film reflector isn't going to be a great reflector - http://en.wikipedia.org/wiki/File:Inflatable_Antenna_Experiment.jpg - a smooth better performing reflector will involve a lot of substrcuture - structure that's complex, expensive, and potentially far heavier than just a thin film array that doesn't need such a rigid substrate. If an array is off a few degrees you barely loose any energy. If the reflector is off a few degrees, you drop to zero.Then use something other than inflationor something thicker. I've read that 2mil metalized Mylar (BOPET) is fairly good in this role with decent physical properties and capable of up to 99% reflectance. I'm not sure how much that masses (I've been Googling for a while with poor results) but from what I see, I think it's somewhere between 50-to-100 gsm. If the insolation at Jupiter is 25x less than at Earth then you'd need a reflector 25 times the area of the solar panel. The 3 Juno Solar panels each are 2.65 m x 9 m, so the reflector area might be 73.59 m x 27 m (a quarter tube) and mass 198.69 kg (assuming 100 gsm, give or take). Better yet, add 2.55 solar panels and a longer solar reflector of 73.6 m x 50 m (massing 367.95 kg), because with each panel generating ~18kW at Earth and with a concentrator, those extra panels would generate 100 kW, just like the SAFE.

The questions I still have are the mass of the Juno solar panels, batteries and tracking mechanism, which I couldn't find. I'm also not sure how much the support structure should mass, but it could be held in tension against some wire stringers to create a faceted tube instead of trying to keep the cross section circular/parabolic, although it might not be that much mass to create a more rounded tube using stiffer stringers oriented circumferentially instead of longitudinally. Instead of putting the solar panels at the focus, it might be better to put them in the middle of the tube and use another reflector at the focus (like a Cassegrain reflector) so that if the array did move off axis, the solar panels would be able to see the sun directly and still provide some power. There might be other ways of adding reflectors at other locations and geometries to help if the array moves off-axis, but that would increase the mass.

Of course, that was merely about solar PV. I still wonder if we could use it to power a heat pump with less mass than the SAFE nuclear heat pump.

Ara Pacis
2013-Jan-11, 08:45 AM
No, it needs to reflect it consistently in a very particular direction. Wrinkles that cause minor cosine losses from irregular reflection angles in a solar sail will cause severe losses if you attempt to make a concentrator with a similar quality reflector. A completely diffuse reflector will still make an effective solar sail, but be useless for a concentrator. Even a flat black absorber has some use for photon sails. The optical requirements of solar sails and solar concentrators are not comparable.Never mind, you're taking the reference to solar sails too specifically.

I did.But you fail to explain why you think the modification would decrease the utility instead of increase it, as I explained in another post. The reflectors, if they are of a lower mass than the panels mean that the power density increases non-linearly.

The reflector is going to mass a good deal more than a few grams per meter...that's toward the optimistic end of the feasible range for solar sails, which again have looser optical requirements. In fact, the only solar sail material that lightweight only reflects a fraction of the light that hits it, it is a sparse carbon fiber material that mostly absorbs what light doesn't simply go through (http://mix.msfc.nasa.gov/IMAGES/MEDIUM/0002024.jpg). And that's just the sail material, with no structure, no photovoltaics.Again, I think you're taking the reference too specifically. I don't think it's in Strawman territory yet, but you seem to be taking the most extreme assumptions from a vague analogy.

It's certainly not likely to be less than the mass of an equivalent nuclear reactor, especially if it needs the additional structure to withstand being mounted on a spacecraft. At the distance of Saturn, given 30% collection and conversion efficiency, you need about 25000 m^2 of collection area to equal the 100 kWe from the SAFE-400. To beat the SAFE-400's 512 kg mass, you need less than 21 g/m^2. A solar sail may manage that, I don't see a concentrating solar power system coming anywhere close.What sort of accelerations are you referring to? Also, If I the insolation at Saturn is 1/90 at Earth, then you'd need a reflector with 90x the area if it was ~100% reflective to recreate 1 AU insolation levels. Mylar can be 99%, so for a Juno class solar array capable of 100 kW, you'd only need around 12,000 m2, or 25,000 as you suggest, if you're using aluminum foil with ~50% reflectivity. However, metalized Mylar at 100 gsm would mass at least double the SAFE

The benefit of concentrating solar isn't mass of the completed system, it's that the reflectors can be made from local materials, reducing the mass of photovoltaics you need to import.

Depends on insolation. In some cases, it might be less massy.

cjameshuff
2013-Jan-11, 03:36 PM
But you fail to explain why you think the modification would decrease the utility instead of increase it,

I did so in my first post on the matter in this thread!

The reflectors, if they are of a lower mass than the panels mean that the power density increases non-linearly.

But they aren't of lower mass. Thin film photovoltaics are perhaps a few times the mass of the base plastic film, are insensitive to imperfect shape, pointing direction, etc, and have already been deployed on a solar sail. Concentrator mirrors need to hold a precise shape and orientation that is incompatible with solar sail structures, requiring structural mass to hold that shape, and they require a high optical quality reflective surface...not just high reflectivity.

Again, I think you're taking the reference too specifically. I don't think it's in Strawman territory yet, but you seem to be taking the most extreme assumptions from a vague analogy.

What other way is there to to take it? You're assuming solar sail masses...fairly exotic ones in fact, currently only matched by what's apparently an absorptive microwave sail material...for something that has much more stringent requirements. This is an obviously wrong assumption.

What sort of accelerations are you referring to?

For a reflector system with solar sail masses? Any acceleration! You need to avoid distorting the concentrator and keep it pointed precisely at the sun. Solar sails don't have these needs and aren't built for them. If you have the mass of a solar sail, you don't have the structure you need to withstand any maneuvering, you're doing a miraculous job just concentrating light at all...you've evidently found a way to hold the sail material in a good quality, smooth and wrinkle-free parabolic curve without adding any structural mass.

Also, If I the insolation at Saturn is 1/90 at Earth, then you'd need a reflector with 90x the area if it was ~100% reflective to recreate 1 AU insolation levels. Mylar can be 99%, so for a Juno class solar array capable of 100 kW, you'd only need around 12,000 m2, or 25,000 as you suggest, if you're using aluminum foil with ~50% reflectivity. However, metalized Mylar at 100 gsm would mass at least double the SAFE

Once again, yes, aluminized films can be highly reflective, the issue is where they reflect it, you are simply not going to get 99% light gathering efficiency out of a large mylar concentrator mirror. And no, I was assuming reflectivity in the 90% range, not 50%. Your 12000 m^2 reflector's only going to intercept about 200 kW of raw sunlight at Saturn's perihelion, and only 160 kW at aphelion, you're not going to get 100 kWe out of it.

Depends on insolation. In some cases, it might be less massy.

Except it's looking like any reasonable concentrators will outmass thin film photovoltaics per unit area, so no, it doesn't depend on insolation.

djellison
2013-Jan-11, 06:07 PM
From what I've read, the LILT cells designed for Juno actually work better at lower temperatures (NASA pdf 2007, p.5 (http://www.lpi.usra.edu/opag/nov_2007_meeting/presentations/solar_power.pdf)).

Note - their cold testing shows a drop off at outer solarsystem levels. Get out to beyond saturn and you'll see increasing trouble.

Moreover - all those designs of solar arrays in that document....not one suggests thin film reflectors. They just use thin film arrays instead. Even wondered why that is?

This simple line "If the insolation at Jupiter is 25x less than at Earth then you'd need a reflector 25 times the area of the solar panel. " does not account for.....

Reflection efficiency
Accuracy in reflector pointing
Diffuse reflection
etc etc etc. So many things wrong with just saying that 1/25th the sunlight requires a 25x reflector.

I add my voice to all of cjameshuff's comments above and also - I add these points also

These huge reflectors of yours are now solar sails. Are you accounting for the delta-V you'll have to take with you to counteract the significant delta-v thes. You can't try and use the Delta-V of the sail for maneuvers as you HAVE to be sun pointed at ALL times. Moreover - it has to be be centered on the center of mass of the whole vehicle or you will impart a torque to the vehicle that will require reaction wheels that will quickly saturate and require prop to desaturate.

You've still not even begun to grasp the complexity and implications of what you're proposing.

Sardonicone
2013-Jan-12, 02:09 AM
Certainly nuclear thermal rockets don't seem to be promising for any missions, and nuclear electric is of limited potential for near term missions.

The problem with nuclear electric is cost vs benefit. For inner system missions, solar electric is better due to superior cost, mass, and maturity. Thus, nuclear electric propulsion is only a potential benefit for outer system missions--and these are few and far between. Furthermore, the majority of outer system missions would do better with chemical rocket propulsion rather than electric propulsion, limiting the potential benefit even further.

That's not to say there is no potential benefit at all. It's just limited, and not worth the costs. The JIMO mission was originally designed around nuclear electric propulsion (a case of a hammer looking for a nail, but regardless of the reason it was a real mission with a real budget). JIMO was slashed and ultimately cut from NASA completely due to the excessive costs, long development times, and technology risk. The ESA side continued, scaling it back to the JUICE mission--chemical rocket propulsion with solar power. JUICE will study three of the four moons JIMO would have studied, but at a fraction of the cost.

Nevertheless, nuclear electric propulsion would seem to be the most practical option for an eventual Pluto system orbiter, or a multiple KBO mission. Neither of these are in the cards yet, due to the fabulous costs of such missions compared to other comparable missions (Uranus and Neptune, Jupiter trojans, asteroid belt, etc).

I have to nitpick about JIMO, and specifically the Prometheus project as a whole.
They were cancelled in favor of Manned missions, not due to the cost. In 2004 400 mill was awarded to Northrop. By 2005 all funding was stopped, with 84 mill being spent in cancellation costs.

It was not cut for excessive costs, at all. It was cut simply due to favoring manned missions in the VSE.

TooMany
2013-Jan-12, 02:53 AM
That's not to say there is no potential benefit at all. It's just limited, and not worth the costs. The JIMO mission was originally designed around nuclear electric propulsion (a case of a hammer looking for a nail, but regardless of the reason it was a real mission with a real budget). JIMO was slashed and ultimately cut from NASA completely due to the excessive costs, long development times, and technology risk. The ESA side continued, scaling it back to the JUICE mission--chemical rocket propulsion with solar power. JUICE will study three of the four moons JIMO would have studied, but at a fraction of the cost.

How do you decide what is worth the cost in innovation and development? NASA doesn't have a lot of money for innovation. Innovation is one of the first things that gets cut. The nuclear thermal program was cut in 1972 when Apollo petered out and NASA spending was slashed. As far as I'm aware no serious work on it has followed although it has been considered for manned Mars missions.

Apparently some people think that JIMO was cancelled in favor of arguably the most cost-inefficient way to explore the solar system ever suggested - manned space craft.

IsaacKuo
2013-Jan-12, 06:31 AM
I have to nitpick about JIMO, and specifically the Prometheus project as a whole.
They were cancelled in favor of Manned missions, not due to the cost.
How does this even make sense? Even if the planetary and manned programs shared the same budget, the only reason for cancelling one in favor of another would be because the combined costs were too high. I just can't see how cost isn't a critical factor.

The way it works is that flagship programs are the ones which are highest cost and which are sacrificed first when necessary. That way, the remaining programs don't get lost due to a single program's runaway budget. This is why there has been such a big running stink over the James Webb Space telescope.

It was not cut for excessive costs, at all. It was cut simply due to favoring manned missions in the VSE.
It's true that the VSE shifted budget priorities from planetary to manned spaceflight, but it's not like President Bush directed anyone to cut JIMO or Prometheus specifically. Rather, the shrinking planetary budget affected the regular decision making process, which slashes expensive flagship programs so the majority of programs (cheaper, quicker, do-more-with-less) can survive.

IsaacKuo
2013-Jan-12, 07:05 AM
How do you decide what is worth the cost in innovation and development?
Personally, I make that judgement based on what missions are enabled and/or benefited, compared to the alternatives. This is only half of the equation, though--there's still the question of how valuable each of those missions are.

Naturally, I have my own ideas about how valuable various missions are, and in particular my own ideas about the balance between manned and unmanned missions. But in this case I generally weight missions according to pubic opinion and the space enthusiast community's opinions rather than just my own. In particular, I personally have little interest in a manned Mars mission, but it's a popular goal so I consider the value of developing Mars mission technology and hardware according to those goals rather than my own.

Apparently some people think that JIMO was cancelled in favor of arguably the most cost-inefficient way to explore the solar system ever suggested - manned space craft.
If your only criteria is scientific data, then manned space exploration doesn't look good at all. That's not the only criteria for the space enthusiast community in general, or the public as a whole.

JIMO was nowhere near anything cost efficient for exploration either. It was basically something for the nuclear electric propulsion project to do, with not a whole lot else for it to potentially do. In a budget contest between JIMO and James Webb Space Telescope, it's a no-brainer. Now, whether or not the latter should have been allowed to crush planetary programs for so long...

Anyway, the VSE may have been flawed and you may disagree with its priorities, but unless you want to get rid of manned spaceflight entirely, you have to remember what forced its hand--The Columbia disaster. Things HAD to change after Columbia's loss. The Space Shuttle was dead. It needed a replacement. That was going to cost!

So, if you want to blame the first domino to fall, blame it on Columbia. But really, there were going to be ups and downs in planetary's budget for some reason or another. That's why NASA has regular policies and procedures on how to plan for and deal with it. JIMO was iffy anyway.

Ara Pacis
2013-Jan-12, 12:21 PM
I did so in my first post on the matter in this thread!Which was about solar panels, not reflectors.

But they aren't of lower mass. Thin film photovoltaics are perhaps a few times the mass of the base plastic film, are insensitive to imperfect shape, pointing direction, etc, and have already been deployed on a solar sail. Concentrator mirrors need to hold a precise shape and orientation...I've been loking for data on the mass of the Juno solar panels, but I couldn't find any. I don't know if they are only a few times the mass of the base plastic film.

...that is incompatible with solar sail structures, requiring structural mass to hold that shape, and they require a high optical quality reflective surface...not just high reflectivity.

What other way is there to to take it? You're assuming solar sail masses...fairly exotic ones in fact, currently only matched by what's apparently an absorptive microwave sail material...for something that has much more stringent requirements. This is an obviously wrong assumption.

For a reflector system with solar sail masses? Any acceleration! You need to avoid distorting the concentrator and keep it pointed precisely at the sun. Solar sails don't have these needs and aren't built for them. If you have the mass of a solar sail, you don't have the structure you need to withstand any maneuvering, you're doing a miraculous job just concentrating light at all...you've evidently found a way to hold the sail material in a good quality, smooth and wrinkle-free parabolic curve without adding any structural mass.You're still nitpicking about solar sails. Do you think I'm trying to promote some idea? I'm not. I asked a question and was hoping someone could answer it and explain why, but since no one did I'm having to try to figure it out myself.

Metalized BOPET is available at 12micron thicknesses massing 10-20 gsm. I don't know if they could be used or if they would be too fragile or have a lower reflectance, but material with those properties is not exactly uncommon.

Once again, yes, aluminized films can be highly reflective, the issue is where they reflect it, you are simply not going to get 99% light gathering efficiency out of a large mylar concentrator mirror. And no, I was assuming reflectivity in the 90% range, not 50%. Your 12000 m^2 reflector's only going to intercept about 200 kW of raw sunlight at Saturn's perihelion, and only 160 kW at aphelion, you're not going to get 100 kWe out of it.I admit I'm using back of the envelope calculations. Better numbers mean better results, and I found a chart that lists w/m2.. You're right, the collector area would be roughly double. But when I run the numbers, 15 w/m2 is ~1/90 earth insolation... but why doesn't 90x the surface area calculation work? I seem to be failing some basic math here and I'm not sure what I'm missing/forgetting.

Why won't a mylar mirror work? I suggested 2mil (~50 microns thickness) as it seems to have better optical properties from what I've read. I don't know if that's good enough, but it's a start.

Except it's looking like any reasonable concentrators will outmass thin film photovoltaics per unit area, so no, it doesn't depend on insolation.But can we/are we using or plan to use thin films in space. What is the mass of thin films? Are thin films reliable in deep space?

Ara Pacis
2013-Jan-12, 12:40 PM
Note - their cold testing shows a drop off at outer solarsystem levels. Get out to beyond saturn and you'll see increasing trouble.

Moreover - all those designs of solar arrays in that document....not one suggests thin film reflectors. They just use thin film arrays instead. Even wondered why that is?Yes, but I found no information. However, I guessed it involved limitations based on Earth surface-launch and orbital-deployment of solar panels in Near Earth space, and injection rocket acceleration, and even aerodynamic drag in LEO and other planets it might make a slingshot around, and also interference with communications dishes, astrogation equipment, various cameras and sensors and decreased temperature on the lee of the reflector. I consider those issues separate from whether or not a collector will work or not with regards to the solar cells and in comparison to the mass of the reference nuclear reactor.

This simple line "If the insolation at Jupiter is 25x less than at Earth then you'd need a reflector 25 times the area of the solar panel. " does not account for.....

Reflection efficiency
Accuracy in reflector pointing
Diffuse reflection
etc etc etc. So many things wrong with just saying that 1/25th the sunlight requires a 25x reflector.My spherical cow says "moo".

I add my voice to all of cjameshuff's comments above and also - I add these points also

These huge reflectors of yours are now solar sails. Are you accounting for the delta-V you'll have to take with you to counteract the significant delta-v thes. You can't try and use the Delta-V of the sail for maneuvers as you HAVE to be sun pointed at ALL times. Moreover - it has to be be centered on the center of mass of the whole vehicle or you will impart a torque to the vehicle that will require reaction wheels that will quickly saturate and require prop to desaturate.One thing at a time. And no, you would not need to be pointing at the sun the whole time. You'd only need to be pointing at it when you need maximum power.

You've still not even begun to grasp the complexity and implications of what you're proposing.

If by "have not begun to grasp" you mean I haven not populated my questions with answers, then you are correct... That's why I asked the question in the first place. If you mean that I am not even aware of the questions, then you are wrong, which should be obvious by the fact that I'm asking for explanations. Also, you should note that I'm not proposing anything here, I asked a very simple question and didn't get enough detail in response.

publiusr
2013-Jan-12, 07:42 PM
This is why I prefer nuclear power. The radiators aren't as finicky as solar panels and reflectors as to where they are pointing. In fact, they would prefer to "see" the sun edge on as to dump heat.

TooMany
2013-Jan-13, 06:52 AM
Naturally, I have my own ideas about how valuable various missions are, and in particular my own ideas about the balance between manned and unmanned missions. But in this case I generally weight missions according to pubic opinion and the space enthusiast community's opinions rather than just my own. In particular, I personally have little interest in a manned Mars mission, but it's a popular goal so I consider the value of developing Mars mission technology and hardware according to those goals rather than my own.

If we must have manned space missions in order to attract funding, so be it. I want the continuation of the explorers like the HST, Curiosity, Galileo, Cassini, Voyager, Hershel and so on. But now, because manned space has taken roughly 300 G bucks via the shuttle and ISS, JWST is not going to be launched until 2018. I believe it was originally supposed to be launched this year. Other innovative things (space-based interferometer, gravity wave detector, etc) are sacrificed left and right to this Buck Rogers nonsense. It's really sad that there is little public interest in the Universe unless some space jockey is involved. That's a failure of our educational system to inspire children.

If your only criteria is scientific data, then manned space exploration doesn't look good at all. That's not the only criteria for the space enthusiast community in general, or the public as a whole.

Yep the public. If it was up to the public there would be no science.

JIMO was nowhere near anything cost efficient for exploration either. It was basically something for the nuclear electric propulsion project to do, with not a whole lot else for it to potentially do. In a budget contest between JIMO and James Webb Space Telescope, it's a no-brainer. Now, whether or not the latter should have been allowed to crush planetary programs for so long...

But the money wasn't there because one shuttle fight costs that much and that got priority.

Anyway, the VSE may have been flawed and you may disagree with its priorities, but unless you want to get rid of manned spaceflight entirely, you have to remember what forced its hand--The Columbia disaster. Things HAD to change after Columbia's loss. The Space Shuttle was dead. It needed a replacement. That was going to cost!

So, if you want to blame the first domino to fall, blame it on Columbia. But really, there were going to be ups and downs in planetary's budget for some reason or another. That's why NASA has regular policies and procedures on how to plan for and deal with it. JIMO was iffy anyway.

Challenger and Columbia should have been a reminders of the impractical nature of human space flight. What is gained by human space flight? Realizing fantasies from the 40's and 50's about men zooming around in space ships and walking on planets? I think it's time to grow up and admit it does not make sense.

I'll make a bet with you (but I won't live long enough to collect). If we do send men to Mars, their will be a few trips (like Apollo) and then the whole idea will be dropped (for the very good reason that it does not make sense to send men).

djellison
2013-Jan-13, 07:53 AM
(for the very good reason that it does not make sense to send men).

Forgive me if I'll disagree with you. I'll side with arguably the most experienced and brilliant mind in the robotic exploration of Mars

Watch it. All of it.

Ara Pacis
2013-Jan-13, 08:31 AM
It's really sad that there is little public interest in the Universe unless some space jockey is involved.Sad, perhaps, but humans evolved to be social animals and that's just how it is. That's how it's always been.

That's a failure of our educational system to inspire children.What's inspiring about what you propose? And how can that be translated in a way that's accessible to most children instead of some fraction of a percent (if you can manage to get even that many inspired)?

Yep the public. If it was up to the public there would be no science.You have to make it accessible, or at least interesting. It's poor marketing and salesmanship.

Challenger and Columbia should have been a reminders of the impractical nature of human space flight.Challenger and Columbia were examples of hybrid military-manned-cargo-class-vehicle spaceflight. I agree, we shouldn't do it that way. We should specialize our vehicles like normal flight services, which also fail on occasion.

What is gained by human space flight? Realizing fantasies from the 40's and 50's about men zooming around in space ships and walking on planets? I think it's time to grow up and admit it does not make sense.What is gained by being human, by living? I've known people who felt that way before. I refer them to a prevention hotline.

TooMany
2013-Jan-13, 11:57 PM
Forgive me if I'll disagree with you. I'll side with arguably the most experienced and brilliant mind in the robotic exploration of Mars

Watch it. All of it.

Sure I watched the entire video. I agree that if we did put men (e.g. a geologist and astrobiologist) on Mars with suitable mobility etc., that they could do a far better job of selecting interesting things in a short period of time than any currently conceived robot. Nevertheless I don't think it makes good sense to do this. The reason is that the cost to send men is enormous (even ignoring their safety).

Someone on the panel suggested \$80 billion over a decade to put together a manned mars mission. I doubt it will be that cheap; I would say that estimate is misleading (to be kind). Shuttle flights were \$1.6 billion each and that's distributing the development cost over 135 flights. Manned Mars vehicles will be far more complex than the shuttle. I'm not sure that human life preservation technology that we already have is adequate (because the mission is so long, radiation and food are issues). The mission itself (at least given the plans I have seen) is highly complex involving pre-trip launches of supplies and the transport environment, multiple rendezvous, perhaps an ISRU lander etc.

Now let's look at accomplishing the same ends without men. We already have a good start. Although exploration by the rovers is slow, the slowness is not an issue. Curiosity is expected to operate for at least 2 years and Opportunity is going on toward 9 years! We will not in the near future have the ability for men to stay very long, for multiple reasons.

Steve Squyres suggested that men on Mars are needed to find the appropriate samples for sample-return. I do not think that is correct. Rovers of the future will give us better and better information about what is interesting. After all, with existing and future rovers, men are on Mars in the sense of their tele-presence. From a shirtsleeve environment on Earth they can direct exploration for years on end.

Future rovers will have the ability to do many things it is currently claimed that men are needed to do. Future rovers can do some autonomous guidance to cover more ground, if need be. Future rovers can turn over a rock, hit it with a hammer, see how heavy, how hard it is, crack it open and dig holes. The rover we have already has a microscope and many other instruments. Future rovers might pick up samples and even subject them to electron microscopy. At our leisure we command these rovers as proxies for ourselves and through them we can carefully search for years.

It occurred to me looking at Curiosity's recent findings, that we can map out where the interesting samples are using existing and future no-return rovers. We can then send a relatively uncomplicated sample/return rover to just pick up the interesting rocks and bring them back to earth. This I believe is far easier and more practical than sending men to get samples.

The advantages of the robotic route are obvious (especially cost wise) and that is why it is in fact currently the only route being directly pursued.

Sorry, I listened to his argument very carefully, but I couldn't help wondering if he actually believed it. There were no critical questions asked following his speech, instead he was fed questions to try to help him express more of his enthusiasm for the idea. Frankly, I feel like man-in-space is a sacrifice of resources that must be made by NASA in order to continue to get funding from the public. I would not be surprised if public speech against manned-space within the NASA circle is discouraged. As member publiusr put it (paraphrasing), man-in-space is to space exploration what football teams are to universities.

However, perhaps what Steve is saying makes perfect sense strategically. Plan for a manned Mars mission, but point out that we need to pave the way by sending more rovers and testing a sample return mission (to verify round-trip technology). Keep the funds coming from the manned-space enthusiasts, but do the job robotically first and then see what public opinion is about a manned mission, perhaps a couple of decades from now.

TooMany
2013-Jan-14, 12:05 AM
What is gained by being human, by living? I've known people who felt that way before. I refer them to a prevention hotline.

Ara, be fair, I made no such implication. I'm more excited about space exploration now than I was as a kid (and I was very enthusiastic supporter of Apollo). I've just learned to be practical and accept that the best way to do it is by robotic proxy. I've come to understand that we don't need to physically be there to explore the place. Neither do we need to be there to be excited by the exploration; we can be space pioneers while our bodies are still on Earth.

Sardonicone
2013-Jan-14, 02:53 AM
How does this even make sense? Even if the planetary and manned programs shared the same budget, the only reason for cancelling one in favor of another would be because the combined costs were too high. I just can't see how cost isn't a critical factor.

The way it works is that flagship programs are the ones which are highest cost and which are sacrificed first when necessary. That way, the remaining programs don't get lost due to a single program's runaway budget. This is why there has been such a big running stink over the James Webb Space telescope.

It's true that the VSE shifted budget priorities from planetary to manned spaceflight, but it's not like President Bush directed anyone to cut JIMO or Prometheus specifically. Rather, the shrinking planetary budget affected the regular decision making process, which slashes expensive flagship programs so the majority of programs (cheaper, quicker, do-more-with-less) can survive.

My apologies. We're saying the same thing, just in two different ways. It remains to be seen what could have been done since they gave it one year, then scrapped it.

IsaacKuo
2013-Jan-14, 05:02 PM
If we must have manned space missions in order to attract funding, so be it. I want the continuation of the explorers like the HST, Curiosity, Galileo, Cassini, Voyager, Hershel and so on. But now, because manned space has taken roughly 300 G bucks via the shuttle and ISS, JWST is not going to be launched until 2018. I believe it was originally supposed to be launched this year. Other innovative things (space-based interferometer, gravity wave detector, etc) are sacrificed left and right to this Buck Rogers nonsense. It's really sad that there is little public interest in the Universe unless some space jockey is involved. That's a failure of our educational system to inspire children.
I understand your attitude, but I do not share it. Personally, I am more interested in the technology of spaceflight than the science of astronomy. My priorities are on the potential for humanity to exploit space resources and expand into space (whether manned or unmanned). For me, science missions are mainly a convenient way to fund the development of the technology required to do these things. For me, manned spaceflight is also mainly a convenient way to fund the development of this technology.

Now, I am indeed a fan of unmanned missions, but it's not because I think they're the best investment for science returns. I desire exploitation of space resources and expansion into space, and I see unmanned missions as the best way to reach those goals.

Different space enthusiasts are interested in space technology and science for different reasons.

djellison
2013-Jan-14, 05:52 PM
Or maybe, just maybe, we can have a sustainable program of exploration with humans, and robots, working in harmony, to achieve far more than either could on their own.

Nahh - too much to ask, right?

R.A.F.
2013-Jan-14, 08:06 PM
... I've just learned to be practical and accept that the best way to do it is by robotic proxy.

Robotics is safer, and cheaper, but the "best" way?....hardly.

TooMany
2013-Jan-15, 06:30 PM
I understand your attitude, but I do not share it. Personally, I am more interested in the technology of spaceflight than the science of astronomy. My priorities are on the potential for humanity to exploit space resources and expand into space (whether manned or unmanned). For me, science missions are mainly a convenient way to fund the development of the technology required to do these things. For me, manned spaceflight is also mainly a convenient way to fund the development of this technology.

Now, I am indeed a fan of unmanned missions, but it's not because I think they're the best investment for science returns. I desire exploitation of space resources and expansion into space, and I see unmanned missions as the best way to reach those goals.

Different space enthusiasts are interested in space technology and science for different reasons.

Yes, I admit that, as is quite clear from opinions expressed here. As pointed out by Steve Squyres, robotic missions and robotic assistance is important for manned space missions to Mars, so there is synergy. That's the way it is and "peaceful coexistence" is possible. I believe manned-space missions have consumed the majority of the available bucks (Apollo, Shuttle, ISS). Please correct me if I'm wrong. I've been trying to get figures on this for a while. What frustrates me are cancellations and delays in science programs like JWST to feed shuttle flights and ISS which seem to accomplish nothing new at huge expense.

djellison
2013-Jan-15, 07:33 PM
The compartmentalization of the NASA budget is actually very strong (and very well published - the figures are very easy to find). I don't know of any instance where, for example, ISS or Shuttle has caused JWST delays. JWST's problems are of its own making and have had a catastrophic effect on the rest of the SMD, but not the wider NASA budget It takes no effort whatsoever to find the very detailed breakdown of NASA's budget - I really don't know how you can have been 'trying to get figures on this for a while' without finding the budgets that are publicly available. I mean... http://lmgtfy.com/?q=nasa+budget ??? Top hit. Right there.

Simple top linefigures in the 2013 budget request....

http://www.nasa.gov/pdf/632697main_NASA_FY13_Budget_Summary-508.pdf

Science ( Earth, Planetary, Astrophys, JWST, Helio) 4.911B
Aeronautics 0.551B
Space Tech - 0.7B
Exploration 3.9B
Operations ( ISS etc) 4B
Education 0.1B
And then construction, management etc caccounts for a further 2.8B + 0.62B

The total budget for 2013 is 17.7B of which Manned accound for approx 7.9B - just under half - certainly not the 'majority'

Also - claiming the completion of ISS is 'nothing new' is just, well, wrong.

R.A.F.
2013-Jan-15, 09:55 PM
What frustrates me are cancellations and delays in science programs like JWST to feed shuttle flights and ISS which seem to accomplish nothing new at huge expense.

Why do you believe it is an "either/or" situation?

TooMany
2013-Jan-16, 01:09 AM
The compartmentalization of the NASA budget is actually very strong (and very well published - the figures are very easy to find). I don't know of any instance where, for example, ISS or Shuttle has caused JWST delays. JWST's problems are of its own making and have had a catastrophic effect on the rest of the SMD, but not the wider NASA budget.

But... (emphasis mine)

The mission had been working towards a launch date in 2014, but during the summer of 2010 an independent review panel determined that 2015 was the earliest possible launch date, and even that would require a significant influx of additional funding.[46] Notably, this review commended the JWST project for being in excellent technical shape with most flight hardware making good progress to completion. The delay and cost overruns are due to an unrealistic original budget and insufficient program management. In response, NASA instituted significant management changes in the JWST project, but the need for increased funding has led to a substantial mission delay. As of June 2011, it appears likely that JWST will launch no sooner than 2017 [47] or 2018.[48] A more specific launch date plan should become determined by the end of 2011, pending the FY2012 US federal budget process.[49]

"Unrealistic initial budget" should have a familiar ring when it comes to Shuttle trips.

The total cost of JWST and operation for five years is now predicted to be about \$9 billion. Shuttle & ISS: \$300 billion and still spending. If JWST succeeds, what we will learn about our universe is priceless.

It takes no effort whatsoever to find the very detailed breakdown of NASA's budget - I really don't know how you can have been 'trying to get figures on this for a while' without finding the budgets that are publicly available. I mean... http://lmgtfy.com/?q=nasa+budget ??? Top hit. Right there.

Simple top linefigures in the 2013 budget request....

http://www.nasa.gov/pdf/632697main_NASA_FY13_Budget_Summary-508.pdf

Science ( Earth, Planetary, Astrophys, JWST, Helio) 4.911B
Aeronautics 0.551B
Space Tech - 0.7B
Exploration 3.9B
Operations ( ISS etc) 4B
Education 0.1B
And then construction, management etc caccounts for a further 2.8B + 0.62B

The total budget for 2013 is 17.7B of which Manned accound for approx 7.9B - just under half - certainly not the 'majority'

Also - claiming the completion of ISS is 'nothing new' is just, well, wrong.

I did find budget numbers but they were not classified in terms of whether the expenses were related to manned or unmanned efforts (certainly there is some overlap too). Yes it may be half this year, but we are not doing any shuttle flights. I was more interested in total spending over the last two or three decades.

Concerning the scientific or technical value of ISS, beyond studying what happens to men in weightlessness and a few other experiments, it's not much return (scientifically or technologically) for \$100 billion, not even counting the \$100 billion spent ferrying people back and forth from this LOE outpost.

(The google wisecrack really wasn't necessary nor appreciated. Can you just be polite when disagreeing and I'll try to be too?)

TooMany
2013-Jan-16, 01:16 AM
Why do you believe it is an "either/or" situation?

Not sure what you mean, but there is one pot of money and many projects, so money is distributed among them. If a dollar goes to manned there is one dollar less for unmanned and vice versa. Since the manned space program is so popular, I admit that it is going to get a big share of the funds, but how much is this big share? That's the problem that NASA has to manage.

R.A.F.
2013-Jan-16, 01:58 AM
Not sure what you mean...

I acknowledge that you don't know what I mean....lets leave it at that...:)

djellison
2013-Jan-16, 02:04 AM
I did find budget numbers but they were not classified in terms of whether the expenses were related to manned or unmanned efforts

Well clearly the google 'wisecrack' WAS required - as the VERY FIRST HIT when you google for NASA budget includes multiple documents that explicitly and accurate split the budget across the programms - manned and unmanned. You've clearly not gone and looked at the budget docs - the info is RIGHT THERE.

Yes it may be half this year, but we are not doing any shuttle flights. I was more interested in total spending over the last two or three decades.

Not 'maybe half this year' - 17.7B budget. 7.9B on manned. It's 45%.

Do I have to get out LMGTFY again? Did you not see on the very first hit..

Previous Years' Budgets
› FY 2012 | › FY 2011 | › FY 2010 | › FY 2009 | › FY 2008 | › FY 2007
› FY 2006 | › FY 2005 | › FY 2004 | › FY 2003 and Earlier

All the way to 1997 is archived, broken down in the same way. That's 16 years for you.

Your other arguments are straw men you're building just to have an argument with me regarding ISS / STS / JWST. I not interested in having that argument with you. I'm just bringing the facts to the table... facts that are incredibly easy to find....facts you have demonstrated you're incapable of finding for yourself.

ExoZZ
2013-Jan-16, 01:49 PM
Not sure what you mean, but there is one pot of money and many projects, so money is distributed among them. If a dollar goes to manned there is one dollar less for unmanned and vice versa. Since the manned space program is so popular, I admit that it is going to get a big share of the funds, but how much is this big share? That's the problem that NASA has to manage.

If you read the links djellison provided you will see the budget broken down into categories. If you read the enabling appropriations bill you will find the same categories with the authorized budget numbers. Congress does NOT provide one pot of money that NASA can decide what to do with, Congress specifies a number of different pots of money and NASA has no authority to move money between those pots.

R.A.F.
2013-Jan-16, 10:59 PM
What frustrates me are cancellations and delays in science programs like JWST to feed shuttle flights and ISS...

TooMany...after reading the links, provided, do you agree that this statement was an error?

TooMany
2013-Jan-18, 06:22 PM
TooMany...after reading the links, provided, do you agree that this statement was an error?

No matter how you look at the budgeting process whether it is flexible or inflexible, separately allocated with separate budgets or a single budget, government revenue is allocated either to unmanned science or to manned projects in some proportion.

Anyhow, if it is so easy to google it, then in the last twenty years how much money was spent on manned and unmanned?

In the 2013 request I see in billions:

Science 4.9
Exploration 3.9 (seems to be manned)
Cross agency support 2.8 (neutral?)

Space Ops 4.2 (manned)
Aeornautics 0.55 (neutral?)

Totals:

Science 4.9
Manned 8.1
Miscellaneous 3.35
All 16.35 (excludes some neutral costs)

R.A.F.
2013-Jan-18, 06:38 PM
No matter how you look at the budgeting process whether it is flexible or inflexible, separately allocated with separate budgets or a single budget, government revenue is allocated either to unmanned science or to manned projects in some proportion.

So your answer would be no...you don't consider your statement to be "in error".

Just wanted to see what you were willing to admit....now I know...

TooMany
2013-Jan-18, 06:53 PM
So your answer would be no...you don't consider your statement to be "in error".

Just wanted to see what you were willing to admit....now I know...

Defensive about manned-space much? What have I not admitted? That they have separate budgets so you cannot take from one and give to the other? Your point isn't clear, but you annoyance is.

djellison: How do you assign all of those miscellaneous costs to unmanned or science? This year it's 30% science, 50% manned and 20% don't know.

djellison
2013-Jan-18, 07:02 PM
Clearly you can assign them in whichever way suits the agenda you're pedaling. You've still not bothered to read the documentation we've highlighted for you - very very explicitly details budget lines are available...you're just not doing the homework. We're not going to do it for you.

Your claim regarding Manned stealing from JWST is utterly false. What JWST has done is steal from other missions in the SMD - hence the near death of the highly efficient discovery program.

R.A.F.
2013-Jan-18, 07:02 PM
What have I not admitted?

In my opinion, stating that the ISS and the Shuttle were "delaying/cancelling" robotic missions (for instance) the JWST is a mistake.

Your inability to admit that mistake is the only reason I continue "harping" about it...

TooMany
2013-Jan-18, 07:38 PM
In my opinion, stating that the ISS and the Shuttle were "delaying/cancelling" robotic missions (for instance) the JWST is a mistake.

Your inability to admit that mistake is the only reason I continue "harping" about it...

OK. You want me to admit that manned space spending has absolutely nothing to do with getting more money for JWST (as was found to be needed after an analysis of the program was done a couple of years back). NASA decided that no additional money was available for the program, so they delayed the launch from 2015 to 2018 (to simply get more science-budget money over time). So I guess what you want me to admit is, that there is no relationship between money spent on ISS/Shuttle versus JWST, because the money was already allocated to those manned space endeavors but the JWST had overrun it's budget and is not allowed to take money away from the manned budget. Yes, I will admit to that. OK?

Would you like to admit that the Shuttle hugely overran it's budget, but got the money anyway for 135 launches at \$1.5 billion per launch?

TooMany
2013-Jan-18, 08:12 PM
You've still not bothered to read the documentation we've highlighted for you - very very explicitly details budget lines are available...you're just not doing the homework. We're not going to do it for you.

Can you explain how I have not bothered to look at it but put up a condensed table from 2013 budget? You are coping out on the question of how much has been spent on manned versus unmanned in the past 20 years because you don't know? or perhaps you do know it's not easy to find? short of adding up 20 years of budgets and guessing what is really manned versus unmanned spending. Well I'll give it a try.

Your claim regarding Manned stealing from JWST is utterly false. What JWST has done is steal from other missions in the SMD - hence the near death of the highly efficient discovery program.

What missions are you referring to and why can't they get the money by cutting a couple of trips to ISS instead of cutting SMD? Because it's against the rules? It's seems that you are saying that each pool must be completely independent and that there is no relationship between the monies at all. But how can that be? This is all NASA funding and someone makes decisions about how much goes where.

Is it for example impossible to cut military budget and redirect that to domestic infrastructure so that we must say that there is no relationship between military spending and infrastructure spending?

It seems to me this is getting to be a game hair-splitting semantics. There is a limited amount of money allocated and it is divided. That division is artificial. It's a choice, not a necessity. We have made a choice about how much manned gets versus unmanned and manned definitely gets the big end of the stick.

Rides into LEO, ISS operations and work toward future manned missions current eat up well over half of the funding, providing us with exactly what that we could not get from unmanned satellites and deep space robotic craft? While unmanned continues to do actual new exploration and valuable science of all sorts: earth, solar, planetary exploration and astronomical exploration.

I guess you would have to argue that the manned projects (like ISS) being done now has it's value in still more manned missions in the future?

R.A.F.
2013-Jan-18, 08:15 PM
This is all NASA funding and someone makes decisions about how much goes where.

...and apparently you do not understand how that process "works".

djellison
2013-Jan-18, 08:32 PM
Nailed it R.A.F.

The budget numbers are clear, yet TooMany is still making the 'well over half' claim. He's accusing me of a pro-manned bias...I work at the worlds leading center for robotic exploration of the solar system. I think the irony is lost.

TooMany
2013-Jan-19, 05:22 PM
Nailed it R.A.F.

The budget numbers are clear, yet TooMany is still making the 'well over half' claim. He's accusing me of a pro-manned bias...I work at the worlds leading center for robotic exploration of the solar system. I think the irony is lost.

What I'm claiming (and I showed you the figures that I got from the 2013 budget) is that 20% is neutral (can't tell), 50% is manned and 30% is unmanned science. If I've done something wrong please explain.

P.S. I'm not accusing you of anything. You seem to be doing all the accusing here.

ravens_cry
2013-Jan-19, 05:42 PM
Geeze, he's here too?
I am honestly starting to wonder how someone so adverse to learning learned how to read and write in the first place.

R.A.F.
2013-Jan-19, 08:29 PM
I'm not accusing you of anything.

Technically not. It was "I" who you said was "defensive about manned space".

However I do completely agree with djellison's reasoning, so I fail to see much of a distingtion.

You seem to be doing all the accusing here.

As I just pointed out...obviously not.

publiusr
2013-Jan-19, 09:14 PM
He's accusing me of a pro-manned bias...I work at the worlds leading center for robotic exploration of the solar system.

Well, you will never have to worry about me doing that at least :)

That's okay. A lot of people think we never went to the moon because they disbelieve in simple plumbing (which works) and think we have a secret space program of flying saucers (that don't.)

Or they think milspace is more advanced than it is when space advocates actually rank below the janitor in the Pentagon...

Jim
2013-Jan-20, 08:46 PM
The discussion of Heiwa's problem has been moved to here (http://cosmoquest.org/forum/showthread.php/141335-Heiwa-s-thread).