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Fraser
2004-Aug-10, 04:15 PM
SUMMARY: The Japanese Institute of Space and Astronautical Science has succeeded in launching and deploying the first ever solar sail into space. A solar sail is a thin metallic film pushed by light from the Sun - like a sail on Earth is pushed by the wind - it requires no engine. The 7.5 micrometers thick sail was carried on board an S-310 rocket launched from the Uchinoura Space Center, and deployed at 122 km (75 miles) altitude.

What do you think about this story? Post your comments below.

TuTone
2004-Aug-10, 04:37 PM
I wonder how fast the sail will travel.

Planetwatcher
2004-Aug-10, 07:36 PM
I wonder how fast the sail will travel. I think the current solar light sail technology can reach speeds of up to 5 1/2 times faster then rockets currently in use.
The potental is certainly there to some day travel a significant fraction of the speed of light.

However, I do not aggree that the solar light sail holds any real promise of intersteller travel. It's application will be limited to inner, and middle solar system travel.
(Inner is defined as between the Sun and asteroid belt, and middle includes the asteroid belt out to almost the orbit of Neptune.

And even the middle regions may not provide enough sunlight for light sails to be effective.
This makes solar light sails beyond Neptune less then likely, and travel to the edge of the Orrt Cloud bleak.
Attempts at intersteller travel using solar light sails alone would be fool hardy.

However, solar wind sails could maintain acceleration out to the helopause, and simply coast from there. This could take us out beyond the Orrt Clould, but intersteller would still be out of the question.

Now if you had a space craft which used both solar sails and ion drive technology, and achieved your maximum solar sail speed while still in the solar system, The ion drive will take you the rest of the way to most any star we want to visit, but the journey will still take decades to the nearest half dozen star systems, and centuries to anything farther.

But this doesn't make solar sails useless by a long shot.

The 6 month journey to Mars could be made in just over a month, the moon would be about a 12 hour trip, The planet Venus would be a week or two,
Jupiter about 4 months, Saturn less then a year.

A probe to Pluto using a solar sail boost, then coasting could reach it's goal in two or three years, rather then the 9 or 10 planned using current rocket technology.

Shadoglare
2004-Aug-10, 10:00 PM
This is very, very cool.

I'm curious though if there's anything to it other than just the sails - is there any instrumentation on board that will send back speeds? Is it being sent anywhere interesting?
I would have liked to find out more about it other than just the fact it was launched...

antoniseb
2004-Aug-10, 10:17 PM
Originally posted by Planetwatcher@Aug 10 2004, 07:36 PM
I do not aggree that the solar light sail holds any real promise of intersteller travel.
Solar Sails are a cool low power idea. They will not mix very well with ion drives because the reactor needed for deep-space ion drives will be very heavy.

The general idea about solar sail usage for a probe to interstellar space would be that the probe would first be used to take away solar orbital velocity so that it could plunge to well inside the orbit of Mercury [getting as close to the sun as it can get without being damaged by the heat and radiation, and then orienting the sail to catch as much light and wind as it can grab to rapidly accelerate out. The possible speed that could be achieved depends on the surface area to mass ratio, but can't exceed the speed of the solar wind.

tgbotg
2004-Aug-10, 10:53 PM
Was it such a good idea to launch that thin solar sail now, with the Perseids upon us? Isn't the likelihood of that 7.5 micron sail getting torn much higher with that cometary debris we're running into? Personally, I would've launched next week, or even next month, to avoid that onslaught. But I don't know how much more likely it was and if the risks were acceptable. Are they?

James Friesen
2004-Aug-10, 11:21 PM
I'll bet the sails aren't really funtional or intended to go anywhere. I think their purpose was to test various factors, like deployment techniques, and probably didn't have much instrumentation, if any aboard. It is also possible that they were deployed simply as a form of kite and then released after the tests were completed. In this case, they would have quickly collapsed into a random mass of plastic and slowly reentered the atmosphere and either burned up or floated down to unknown locations on the Earth.

I'd also like to hear more about the tests.

joetommasi
2004-Aug-11, 02:56 AM
I'm sure the back side of the sail was painted black to minimize the push in the opposite direction from stars. I'm surprised they didn't make it in the shape of a fan so it could turn in space. That would keep it pointed toward the sun.

Tom2Mars
2004-Aug-11, 03:41 AM
Well, more power to 'em, more solar power that is. :D

This is a good site: Advanced Propulsion Concepts (http://www.islandone.org/APC/index.html)

Sails of all types is in the index, and check out> Solar Thermal Propulsion under the heading "Beamed" and Solar Thermal-Electric Hybrids is in there somewhere.

Planetwatcher, Re-
It's application will be limited to inner, and middle solar system travel.


Unlike chemical rockets, which build up speed very quickly, and then coast to the goal, a solar sail can build up speed for quite a while, and coast just as well as a coasting, chemically accelerated rocket. So, the outer planets should be very reachable. I think Antoniseb provided the set-up for that scenario very well:


it could plunge to well inside the orbit of Mercury [getting as close to the sun as it can...to rapidly accelerate out

Way back in another post there was a link to a French Solar Sail site that mentioned a large sail with a microminiaturized probe payload that could reach Jupiter in a week.

Although,
Attempts at intersteller travel using solar light sails alone would be fool hardy.

That would be very true!!

One has to admit, Solar Sails are different, and very inexpensive. It will certainly be interesting to see if the data returned agrees with the expectations.

Oh, and tgbotg! Re-
Was it such a good idea to launch that thin solar sail now, with the Perseids upon us?...Personally, I would've launched next week, or even next month, to avoid that onslaught.

There's a lot of empty space between those particles, so the sail, even if it is big, is probably safe. Also, it operates on total surface area, so it could peppered with literally millions of microscopic holes and keep on sailing. In fact, if you had big grains of sand, say 5 grains per mm, or .2 mm across, 1 million holes would only take up an area of 400 cm2 (20 cm by20 cm)or, about 0.04 meter2. That's not too much area to lose. And, I doubt that the sail would take more than a single hit.

tgbotg
2004-Aug-11, 04:41 AM
Thanks Tom2Mars. I know space is big and there is a lot of space between the meteors, but I figured the risk would be less (albeit not much less) if they launched at a different time. And I didn't know the sail would allow objects such as that to pass through it without causing any problems for the spacecraft. Thanks again. :)

Maybe I should look up this spacecraft on Google .... :unsure:

Greg
2004-Aug-11, 07:07 AM
Hmm. I read an article on this technology a while back. The author scoffed at the whole idea of solar sail being able to convert photons into acceleration. Apparently such laboratory work in a vacuum indicated that the mirror on the sail would convert a significant portion of the photons into heat. The end result was that the material in the sail accelerated very little but did in fact get very hot.

antoniseb
2004-Aug-11, 10:49 AM
Originally posted by tgbotg@Aug 10 2004, 10:53 PM
Was it such a good idea to launch that thin solar sail now, with the Perseids upon us?
I had the impression from the article that this was a test flight. They launched it in a rocket that made a mostly straight-up sub-orbital flight. The sail was out for a few sconds, took some measurements, and then came back to Earth more or less immediately. There was no time for the Perseids to do any meaningful damage to this thing.

That doesn't make the whole mission less cool. It made it a cheap way to test the technology before trying to make a bigger one.

Guest
2004-Aug-11, 04:06 PM
Sails ? you gotta be kidding



news links
http://www.badastronomy.com/phpBB/viewtopi...pic.php?t=14572 (http://www.badastronomy.com/phpBB/viewtopic.php?t=14572)


is it any wonder the Japan space agency is on the verge of bankruptcy

ASEI
2004-Aug-11, 04:30 PM
Solar sails carrying any significant mass would either have to be several miles wide, or would take hundreds of years to accelerate. On the other hand, a good ion drive is about as complicated as a picture tube, weighs less, and you can point it in any direction you want provided you have a nice power source. It accelerates the same no matter where you are in the solar system.
I think that project prometheus is the way to do probes in the future. Nuclear ion drive.

Greg
2004-Aug-11, 10:20 PM
I second that opinion. Ion drive with perhaps a little chemical or nuclear boost is the way to get about the solar system in the future.

Tom2Mars
2004-Aug-12, 01:20 AM
ASEI, re-
Solar sails carrying any significant mass would either have to be several miles wide, or would take hundreds of years to accelerate.

More like months, not hundreds of years. Sunlight is a constant pressure, and out away from Earth, it is present 24/7. The force on a square kilometer of sail will accelerate one kilogram at 1/2 a Gee. A total mass of sail and payload of 5000kg will reduce the acceleration to only 0.0001 Gee. At two weeks, the sail and payload would have been accelerated to one kilometer per second.

Check out the math, it gets very interesting from there. Plus, it gives the greenies nothing to do but watch your launch and grumble amongst themselves.

Planetwatcher
2004-Aug-12, 07:43 PM
Solar Sails are a cool low power idea. They will not mix very well with ion drives because the reactor needed for deep-space ion drives will be very heavy. That would be true of a nuclear reactor, but what about one that is not nuclear? Such as the SMART 1 currently enroute to the Moon?


The possible speed that could be achieved depends on the surface area to mass ratio, but can't exceed the speed of the solar wind. While solar wind sails can't even match let alone exceed the speed of the solar wind, they could reach a significant fraction of light speed if it were a light sail.
But that depends on the payload and the size of the sails, which has already been said in this string.


Unlike chemical rockets, which build up speed very quickly, and then coast to the goal, a solar sail can build up speed for quite a while, and coast just as well as a coasting, chemically accelerated rocket. So, the outer planets should be very reachable. I think Antoniseb provided the set-up for that scenario very well: They don't build up speed as quick as a rocket, but a whole lot quicker then an ion drive does. And while you could use that method to get to the outer planets, it's a one way, one time trip. Unless you have an adjusted trijectory to swing by once and visit several other places in one voyage.

In other word, yes you could use a solar sail out to the middle regions of the solar system, and coast from there to say Pluto, and get there in just a couple years as opposed to ten years with current technology, but once you land there, what if you want to check out Quanor? Or return home.
There isn't sufficent light for propulsion to a new destination, so without an additional means of propulsion, you would be morooned on Pluto.

Even if you had some kind of combo sail which will allow solar winds to propell it, you couldn't get home because the winds are blowing outward, not inward.
So you would have to just wait 8 or 10 years for somebody to come out with a rocket to put on your *** to get you home.

Tom2Mars
2004-Aug-13, 03:02 AM
Planetwatcher, re-
Even if you had some kind of combo sail which will allow solar winds to propell it, you couldn't get home because the winds are blowing outward, not inward.
So you would have to just wait 8 or 10 years for somebody to come out with a rocket to put on your *** to get you home

Actually, no butt-Rocket required. I'm looking at a diagram from a space book(photocopy...can't tell which book it is from), and it appears that you can tack a solar sail, just like a sailboat, and the sunlight will brake the spacecraft and it will spiral back in, to the inner planets.

I also found these links today:

Solar Sails at Asteroids: Close Proximity Operations for Scientific Missions (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000DPS....32.1410M)

Apparently, they can match up speeds with asteroids quite well...

Multiple rendezvous and sample return missions to near-Earth objects using solar sailcraft (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2003lcpm.conf..351D)

And, a single sail can rendevous with multiple targets in succession.

Wow, they're simple, cheap, versatile...I wonder if you can baste a Turkey with the material? :P

ASEI
2004-Aug-13, 03:39 AM
Simple, huh? How do you control a giant multiple mile wide film of metal thinner and far weaker than tissue paper? How does it transfer it's load to the spacecraft without tearing?

Even a solar electric ion drive is more robust because it can be pointed in different directions readily, and solar panels are less fragile and stiffer. Ion drives can produce whole millinewtons of thrust. If you apply more power, or more fuel flow, you can get a lot more thrust.

Tom2Mars
2004-Aug-13, 04:36 AM
ASEI, re-
How do you control a giant multiple mile wide film of metal thinner and far weaker than tissue paper?

In Zero-Gee, the structural components can be lighter. Bucky Fuller and Kenneth Snelson's Tensegrity concepts and designs can come in handy, lots of structure, mostly in tension, and compression elements made up of tensegrity elements which are mostly empty space and mostly tension elements(good book, "The Dymaxion World of Buckminster Fuller" 1960, ISBN 0-385-01804-5).

Most of the applications I've seen for solar sails are for smaller payloads, or miniaturized payloads to reduce total sail size. Bigger payloads and sails miles across would probably happen over time...baby steps?

And, might need some little robot space spiders.


How does it transfer it's load to the spacecraft without tearing?

At 1/10,000 Gee acceleration, there wouldn't be much of a "load". No drag race here for sure.

I once saw a presentation by the astronaut Rusty Schweikert where he asked "How does one move a huge mass, like a giant steel ball 100 feet across?" He gave the answer, "You could run at it...and squash yourself. Or, you could just lean against it...and wait".


Even a solar electric ion drive is more robust because it can be pointed in different directions readily, and solar panels are less fragile and stiffer. Ion drives can produce whole millinewtons of thrust. If you apply more power, or more fuel flow, you can get a lot more thrust.


True, but I think the appeal of solar sails for some is that they are fuel-less. A transitional technology would be Solar Concentrating systems for solar electric power, that would replace most of the solar panels with a lightweight reflective material in a parabolic shape, or section of a parabola. So, practicing with these materials could provide learning experiences for other techniques and hybridizations.

As a next step, Solar Concentrating Thermal-Electric would yield more power for an Ion Drive.

And, maybe we could try out a Solar Concentrating, Thermal-Electric, Solar Sail Assisted Ion Drive Hybrid? Add a touch of charged Argon to a plasma made from the CH4(methane) obtained from the Methane Digester (waste treatment system from the Life support system) in a human transport ship. I am resisting the urge to name such a system... :lol:

Plus, on the "lot more thrust" thought. There may be lots of missions that can be done cheaply, where "speed" is not so important. Humans can plan ahead. Some parents start college funds when their baby is born, people plan/save for retirement. Some people prefer long ocean cruises or slow-moving train trips to a fast plane ride.

And, if budgets get cut, or interest for space wanes, who knows what inexpensive techniques will be embraced?

ASEI
2004-Aug-13, 04:58 AM
I think big, or to be more specific massive. I want to see humans do things in space involving colonization and habitation, and all these solar based things are too weak and slow for my tastes. That's why I like nuclear electric/nuclear thermal/fission plasma technology. It's big, it's brutal, and it's lightning fast, but it is also simple and get's the job done (high dV, high thrust with low fuel masses).

I suppose solar electric would work for sattelites and probes in the inner solar system. Solar sails also (but why bother with the complexity)?

Tom2Mars
2004-Aug-15, 05:17 AM
ASEI, I could spend a couple of hours replying to this, but I'll try to hold myself back...a little.

re-
I think big, or to be more specific massive. I want to see humans do things in space involving colonization and habitation, and all these solar based things are too weak and slow for my tastes.
I like to think big too! In fact, you should see the NASA researchers' jaws drop when I mention that the first colony on the Moon and Mars should be big enough for over 500 people. Delivered in one package! I'm talking about almost 4 million cubic feet, or, over 113,000 cubic meters. And that includes full radiation shielding.

How is that possible? Well, right now, I am listed as a Space Architect in a NASA contract that had passed the first hurdles for funding. The goal is to build a machine that would take indigenous soil, process it for material, which is then used to fabricate structural components that are assembled into very large structures and covered with the leftover process material (and some additional soil) that acts as a radiation shield. The whole manufacturing package can fit into a space the size of a couple of minivans.

Solar propulsion could handle it just fine.


That's why I like nuclear electric/nuclear thermal/fission plasma technology. It's big, it's brutal
With a little clever design for the habitats, big, brutal technology may be overkill.

The costs for our whole project, including deployment and autonomous operation and assembly of the structures(for later human occupation) would be less than the development costs for a nuclear propulsion system alone.

Re-
and it's lightning fast
It wouldn't matter if you could make a nuclear engine that could get something to Mars in 1 week. The funding for such a nuclear propulsion program and a Mars Colonization program (made up of conventional style habitat technology) isn't likely to be there for awhile. Some say decades.

On the other hand, with some innovation and some off-the-shelf techniques (inexpensive ones by the way) NASA or some private companies could have big bases on the Moon or Mars within the decade. And solar propulsion systems can be part of that low-cost approach.

See, it's kind of like the 'Tortoise and the Hare' story(Aesop's Fables). The Hare is very fast, but he gets sidetracked, while the tortoise is slow and steady, and wins the race.

Then there's the hurdle of the environmentalists to get over. They will not be happy about the development and launch of "big brutal" nuclear systems. But, don't blame them for holding technology back. You know the expression, "it's a poor workman who blames his tools"?

Well, I think it's a poor systems designer who blames "environmentalists". Step over them. It's easy enough to work around them with available technology like Solar Sails that they can't complain about.

You are perfectly welcome to get distracted and fight them for a couple of decades while trying to get those big powerful nuclear rocket systems built. But, there's the Tortoise and Hare thing again. And time might just be of the essence.

Re- Nuclear being
simple
One measure of how simple something is would be the cost, and nuclear technology is much more expensive than a piece of foil. As a challenge for you, try writing down all the steps required to make a nuclear rocket, starting with mining the ore and processing it, and refining it down to fuel rods, and isolating the materials from the workers, and terrorists, and the problems related to shipping the materials and dealing with the waste products, and the special conditions for testing the rockets. It has been done in the 50's and 60's and the test track area was so irradiated, it was not safe for humans afterwards.

Anyway, remember, a nuclear rocket is just heat, and it basically would heat up hydrogen gas to several thousand degrees F, and exhaust it at high velocity out of a nozzle.

Solar is also just heat, and solar concentrators can heat hydrogen gas to several thousand degrees F, and exhaust it at high velocity out of a nozzle.

Solar Sails are even simpler than concentrator systems and can provide a continuous, lightweight, zero-fuel technique to get to where you want to go. I just can't see how a piece of foil is more "complex" than a nuclear propulsion system considering all the time and money and political effort that would be involved to make a nuclear system work.

In summary, I can think of many applications for nuclear power in space. I am not against it. However, I do think it will be a lengthy, uphill battle. For the short term, it might be easier and cheaper to get human colonies started in space using other techniques, and Solar Sails look like an enticing option to have in our repertoire B)

ASEI
2004-Aug-15, 02:44 PM
Then there's the hurdle of the environmentalists to get over. They will not be happy about the development and launch of "big brutal" nuclear systems. But, don't blame them for holding technology back. You know the expression, "it's a poor workman who blames his tools"?

Yeah, but in this case it is more like telling a medievel sailor that he is expected to get across an ocean, then denying him the use of sails, or even oars. (And internal combustion isn't invented yet) If you deny your workman too many tools, you can't expect him to get the job done.

A lot of the problems with anything nuclear boils down to red tape, white-knuckled security regulations, and ignorant fear in the public mind. The technology itself consists of a few strips of metal exposed to each other's radiation and heated to thousands of degrees, passing their heat to propellant. You can deal with nuclear waste by putting it in a barrel and putting the barrel in the ground, honestly. You could even use water as your propellant if you don't mind sacrificing specific impulse.


continuous, lightweight, zero-fuel technique Assuming 100% reflective efficiency, you are talking about 6*10^-6 N/m^2. If you had ion drives you could carry a few pounds of fuel and tens of newtons of thrust. Thousands if you had a decent reactor.

Suppose you had a 500 ton colony load (for reference, the completed ISS was supposed to be 500 tons) you wanted to get to Mars. You want to get a 20 kps dv change. With a circular solar sail with a diameter of 2000 meters, you would have to wait 16.8 years to get up to speed. You could do the same task with a nuclear thermal engine (1200+ sec Isp) and 2200 tons of fuel (less if you stage correctly) and get up to speed in just 11 days. Or with an ion drive and 113 tons of fuel, and a good power source you could be up to speed in a few months.

Tom2Mars
2004-Aug-16, 12:21 AM
ASEI, this is just a quick reply as I'm pressed for time this evening. Re-
Yeah, but in this case it is more like telling a medievel sailor that he is expected to get across an ocean, then denying him the use of sails, or even oars. (And internal combustion isn't invented yet) If you deny your workman too many tools, you can't expect him to get the job done.


Actually, I looked over my previous posts on this topic alone, and I mentioned something positive about using Sails, Solar Sails and made reference to Sails and tacking with them just like sailors do with real old fashioned cloth Sails, about 19 times. I think that as an analogy and metaphor, the comparison is precise and appropriate.

I would earnestly encourage the medievel sailor to use a sail. I wouldn't ask him to wait for the internal combustion engine or the nuclear reactor for the engine room connected to the modern hydrodynamically engineered propeller.

I'd say "go ahead and use the force (of the wind) Luke".

Anyway, tonight I am adding my part to that NASA proposal I'm involved with re- sending a 10 ton package to the Moon(or Mars) that could build a habitat 50 times larger than the ISS. Let's see, that's 50 times larger at 50 times less weight(500 tons-Iss divided by 10 tons-our hab-building machine), which is an overall improvement of 2500 times over your suggestion.

Afterwards, I want to check out some math and I'll get back to the rest of this later, I promise.

jitte
2004-Aug-16, 01:32 AM
I know they used a rocket to get the MUSES-C mission into orbit and their ion engine to get to the asteroid. Once there, they plan to land on it to take a sample and a booster to lift off the asteroid before they fire up the ion engine again for the return flight. Maybe they plan on using the same basic strategy of a multi-system propulsion for solar sail missions.

I'm not sure what their ion engine weighs, but the spacecraft has a 1.5 m x 1.5m x 1.2m box-shaped main body with launch mass of about 500kg and on-orbit dry mass of about 272kg.

Tom2Mars
2004-Aug-16, 03:26 PM
Jitte, Thanks for the data on the ion engine size/weights, I'll work those numbers into my response.

ASEI, re-
Suppose you had a 500 ton colony load (for reference, the completed ISS was supposed to be 500 tons) you wanted to get to Mars. You want to get a 20 kps dv change. With a circular solar sail with a diameter of 2000 meters, you would have to wait 16.8 years to get up to speed.
Well, what I wanted to move the Moon to Saturn using a Solar Sail the size of a hankerchief? :P

Really, just exagerating a bit here. But, it does seem like you picked the largest possible payload for an example, using one of the smallest sails I've heard of, and an over-the-top Delta-Vee.

First off, I looked up the Delta-Vee for a trip to Mars. Starting from LEO (because absolutely no one is considering launching from the surface of the Earth with a Nuke, so, all things being equal from LEO...) , I ran across a range of Delta-V's from 3.7 km's/sec to 6.8+ km/sec.

Delta Vee for orbital transfer from Earth to Mars (http://www.theculture.org/rich/sharpblue/archives/000057.html)
This page also discusses a nuclear fission version as well. And yes, you can go faster, but then you are on a hyperbolic trajectory which is more energy wasteful, instead of an efficient elliptical Hohmann transfer orbit. The Nuke/Hyperbolic mission requires too much speed, so you would have to turn around half-way and slow down, which you don't have to do with the Hohmann, since the velocities of Mars and the Mission Package are nearly identical at the Mars Insertion Point.

One reference referred to the Nuclear dragster technique as "an Impulsive Burn".

The 6.8+ km/sec reference is at:Transfer Orbits for Dummies! A Hilbilly tutorial. (http://www.physicsforums.com/showpost.php?p=249113&postcount=36) With deeper math at:Transfer Orbits for Dummies! Full Hillbilly Tutorial (http://www.physicsforums.com/showthread.php?t=29524)
It turns out that Robert Heinlein not only wrote good SciFi, but also did the math. Neat Guy!

Also, regarding some more realistic mission opportunities: Solar Sails- Potential Mission Applications (http://www.inspacepropulsion.com/tech/sails_missionapps.html) and the PDF file for these references is at:Solar Sails Potential Mission Applications-PDF File (http://www.inspacepropulsion.com/tech/sail_mission.pdf)

Mission planning can take years. New propulsion technology, like nuclear rockets can take decades. If we are only talking about a difference of a few months travel time between a nuclear mission and a solar sail mission, why wait decades to have a race? The point is we can do some interesting things now, and save decades in waiting. We might even discover things along the way that would foster more public support for the kind of faster Human missions that you are interested in. And, in the long run, that might shave off some of those decades before you get to see 'Big' nuclear propulsion have its day in the sun (huge pun intended!). :D

ASEI
2004-Aug-16, 04:52 PM
True, the dv was over the top. I suppose hohman transfers would suffice for cargo missions. If you have people though, you would want to get them there in a small amount of time. Acceleration that is too small wouldn't allow for a high dV transfer. (In fact, acceleration that is too small would result in a very slow outward spiral that could take decades to get anywhere).

Nuclear thermal propulsion won't take decades to develop. We had working engines in the 1970's for pete's sake! The technology is the height of simplicity and would allow very flexible and fast missions.

Tom2Mars
2004-Aug-16, 07:20 PM
ASEI, OK...point-by-point-
I suppose hohman transfers would suffice for cargo missions.I'm glad we can agree on something.

If you have people though, you would want to get them there in a small amount of time.
Why?

Acceleration that is too small wouldn't allow for a high dV transfer.
Again, how high a DV do you think is needed, and why?

Now, on one hand, I'm glad that you have changed your estimate of hundreds of years to accelerate:
Solar sails carrying any significant mass would either have to be several miles wide, or would take hundreds of years to accelerate.down to decades:
(In fact, acceleration that is too small would result in a very slow outward spiral that could take decades to get anywhere)., but how exactly do you arrive at "decades to get anywhere".

From all the sources I could find and google up(a couple thousand came up on google), with the exception of interstellar missions, all the missions planned and researched for solar sails have a travel time of months.

Also regarding-
Nuclear thermal propulsion won't take decades to develop. We had working engines in the 1970's for pete's sake!
Well, it has been decades from the 70's, hasn't it? There were some serious problems with the "working engines" from that time. And, I don't think there was any anti-nuclear rocket engine lobby at the time either. My father was in the Air Force, and was a missile instructor and a nuclear weapons and technology specialist/instructor, and I can guarantee you that there are some significant reasons that we don't use nuclear rockets everyday now.


The technology is the height of simplicity

My response to your claim of "simplicity" before was:
One measure of how simple something is would be the cost, and nuclear technology is much more expensive than a piece of foil. As a challenge for you, try writing down all the steps required to make a nuclear rocket, starting with mining the ore and processing it, and refining it down to fuel rods, and isolating the materials from the workers, and terrorists, and the problems related to shipping the materials and dealing with the waste products, and the special conditions for testing the rockets. It has been done in the 50's and 60's and the test track area was so irradiated, it was not safe for humans afterwards.

Any response to any of those points? How is any single part of the life-cycle of any nuclear technology more simple than reflective foil?

And again, heat is heat, whether is from a hot nuclear core, or from a solar concentrator. So, how is nuclear any more simple than solar?

Planetwatcher
2004-Aug-16, 08:44 PM
I'd like to expand on Jitte's idea. Go ahead and have your payload the size of the ISS, and lets put some good sized solar sails on it, but we're not done yet.

Now let's attatch 4 or 5 solid rocket boosters, like the kind used for the space shuttle. One long burn at full power, use up the solid propellent, and let the sails take it from there. After a good rocket burn, the sails shouldn't take very long at all to reach full power.

I'm all for nuclear power and see no reason to not devlop both technologies.
However right now solar has so many advantages over nuclear that it makes nuclear a lot less then feasible at the current time. The nuclear fuel alone in mass is enough to detour a lot of determination, but the single biggest factor is the current method of nuclear propulsion is a total waste of that form of energy.
Current nuclear fission propulsion is based on a glorified boiling water reactor principle used in the 1960s with nuclear power plants.

Those reactors superheated water to create steam to turn the turbines to produce electrcity. It is the most expensive and inefficient way ever devised to boil water, and using a nuclear reaction to superheat hydrogen is little different.

But it is an important step towards harnessing the real power in the reaction itself.
Only when we directly harness the power of the reaction will we see nuclear fission used properly. In a couple hundred years, our current nuclear technology will be seen much like we now view the covered wagons which once traveled through the western United States.

I think better possibilities yet exist in nuclear fussion, but that development will be at least half a century after we get a good grip on fission potental.

Tinaa
2004-Aug-16, 10:07 PM
What is delta V?

antoniseb
2004-Aug-16, 10:49 PM
Originally posted by Tinaa@Aug 16 2004, 10:07 PM
What is delta V?
That's a shorthand way of naming the vector representing the total change in velocity.

Planetwatcher
2004-Aug-17, 01:55 AM
Which means what?

ASEI
2004-Aug-17, 04:23 AM
dV is more of a scalar in this case. It is a reference to the total change in velocity that your rocket makes (based on an ideal rocket and linear motion). Some trajectories are more dV efficient than others, the hohman transfer being one of the most efficient trajectories assuming that your velocity changes are instantaneous.

Tom2Mars, I did exxagerate the acceleration time of solar sails.

I will maintain this, though: Having manned missions, or moving cargo for manned development of space does require moving large amounts of mass. In-situ resource utilization is the goal, but a lot of equipment needs to come from earth to make it possible - the base machinery to crack what is needed from the soil will not be weight inexpensive in the long run. And startup supplies will weigh a lot. Furthermore, wouldn't you rather get men to mars and back as fast as possible. A hohman transit to mars takes something like seven months, right? High velocity transfers could take as little as one month with nuclear engines providing the needed dV (and acceleration to make the dV within the desired time). When your orbital plot looks like a tight spiral, and you have only ascended a few thousand miles after hundreds of hours of acceleration, you aren't going anywhere fast enough for manned space-flight. For heavy cargo missions, you would want heavy thrust so that you could have a halfway decent acceleration. Imagine building a station on mars, where your colonists have to wait decades for replacement equipment.

Solar sails are simple in terms of structure, but are they any hard to control. Any load on them would tear the sail. If you angle them away from maximum sunlight incidence, they lose their already meager acceleration. Atmospheric drag would prevent their use in low and mid earth orbits. Thin films don't even have 100% reflectivity. Your probe would have a lot less headaches if it used solar powered or mini-reactor powered ion drives. Solar panels can angle towards the sun while the ion drive points where it pleases. Isp is high enough that fuel is barely a concern. Solar panels are stiffer, and you would require a lot less area and mass to manage.

The only appeal I can see for solar sails in place of ion drives is that they make good imagery for powerpoint presentations and artists concept drawings.

*For reference, I ran an orbital ascent simulation in MATLAB using the starting conditions described below:
400 km circular (within simulation accuracy) orbit
2E-7 m/sec^2 acceleration tangent to earth's surface
(This comes from the 500 ton system, 1000 m radius sail, though I realize that solar sails should be carrying smaller payloads)
The final conditions of the simulation show that the sail ascended 20000 km in 130 hours and didn't look very close to breaking away.
(Timestep - 20 seconds using 1st order Euler state variable simulation, it was sloppy, I only spent 15 minutes on it using an old simulation for a concept of mine, but you get the general idea if not a NASA quality course plot)

Tom2Mars
2004-Aug-19, 04:46 AM
Planetwatcher, That was a good suggestion...
After a good rocket burn, the sails shouldn't take very long at all to reach full power.

Techniques like that could help out with the acSAILeration. :P

And ASEI,
In-situ resource utilization is the goal, but a lot of equipment needs to come from earth to make it possible - the base machinery to crack what is needed from the soil will not be weight inexpensive in the long run.
I'm working with engineers on in-situ resource utilization right now. There are some very efficient processes and the machinery shouldn't weigh 500 tons. Initially, soil processing and habitat building will be automated, and the humans can come later. The equipment and hardware can be sent ahead using some kind of cost/fuel effective solar thermal/electric technology or even sail technology.

I would like to emphasize that lower-cost techniques such as solar sails might give private entrepreneurs an advantage, and a head-start on colonization efforts.

Re-The tight spiral. I have mentioned in several other posts the concept of Buzz Aldrin's about a cycling orbiter. Once it is up to speed, it can fly back and forth between Earth and Mars, needing only enough fuel for small course corrections. The cycling orbiter will swing past each planet, and persons or cargo can be dropped off, and people/cargo getting on would need to hop on with a running start, like jumping onto the sideboard of a car/truck, or a trolley car. Years ago, here in Florida, kids used to have "Skimboards", flat fiberglassed disks of plywood. They would spin them like a Frisbee at the surf coming up the beach, the disks would hydroplane, and the kid would run and jump on it and skim across the beach.

If by chance, the only means of transportation to Mars for Humans was to use Solar Sails, I'm sure it would be very practical to "hop on board" after the vehicles had built up sufficient velocity.

Re-
Imagine building a station on mars, where your colonists have to wait decades for replacement equipment.

While it would handicap the argument for solar sails by suggesting that a small sail try to move the mass equivalent of the the ISS, I doubt that any 'replacement equipment' would weigh as much as the entire initial base that was sent to Mars. Subsequent trips of supplies and cargo will probably have lower mass.

Re-
Solar sails are simple in terms of structure, but are they any hard to control.
Really? Have you ever done any sailing? I used to be a sailing instructor at a Yacht Club at a Navy Base. The principles of solar sailing are similar to 'cloth-and-mast' sailing which humans have been experiencing for thousands of years.
Re-
Any load on them would tear the sail.
I have asked you about this before. If the acceleration is very small, what is the nature of this "load"?

I do very much agree with you on the possibility of using Solar-Electric propulsion. Which is why I think that Planetwatcher and jitte made some positive comments.

re-
Atmospheric drag would prevent their use in low and mid earth orbits.

Re- Your MATLAB simulation. Part of the reason sails aren't considered for use that close to Earth isn't just the atmospheric drag, but the fact that the sail may be in shadow around 40% of the time that close to Earth. (See, I don't mind bringing up a bad point about sails!) And, except for some initial tests, I haven't heard of anyone suggesting using solar sails close to Earth for that very reason.

Secondly, the rule of thumb is that the payload be reduced if possible. That might come from a different mission design, and a corresponding payload reduction. But a more simple way to handle large payloads is to break them up into several smaller payloads( I see you mentioned that). Each smaller payload gets its own sail, one that can handle the trip in less than decades. Another option is to make the sails larger, and that would come from experience, and from fabricating them in space.

Re-
The final conditions of the simulation show that the sail ascended 20000 km in 130 hours and didn't look very close to breaking away.

Imagine Werner Von Braun explaining that the Saturn V multi-stage vehicle would be tossing aside it's big first stage after only reaching a fraction of the escape velocity. It wouldn't be fair to point out that the largest portion of fuel had been expended, and the vehicle/payload had barely moved away from the launch tower. Things do get better!

There are 5,208 hours in a 7 month trip. You only ran your simulation for 130 hours, 2.5% of the total acceleration time possible. Of course it didn't look very close to breaking away!

Please, just humor me on this, next time you are going to have a long lunch, or go to a movie or something, let the simulation run for 5,208 hours (of simulated time), and let us know how far the vehicle gets. And just to be fair, please plug a more recognized acceleration rate of 1E-4 m/sec^2. Oh, what the heck...if you could, maybe you could run each of the following:
1E-4 m/sec^2
1E-5 m/sec^2
1E-6 m/sec^2
...and then your worst case 500 ton mission, 1000 m radius sail @
2E-7 m/sec^2

I'd be curious to know what your program comes up with. I wouldn't even mind if you started with a 500(?) km circular orbit, and allowed for an average of 35% reduction in acceleration up to 10,000 km due to time spent in Earth's shadow, and also assuming that it is a slightly inclined orbit (to catch more sunlight), which should put the sail on the same orbital plane for the trip to Mars.

And, if you could, I'd also be curious about 1E-4 m/sec^2 acceleration with a 10 to 20 ton payload.

Thanks, this would be very interesting to see some numbers.

Guest
2004-Aug-20, 01:01 AM
I have a few concerns about solar sails.

1) Once you accelerate to 10 million mph, how do you slow down enough to be captured by a planets gravity? If you can decelerate from that speed with rockets, why not use rockets to attain that speed in the first place? Ok, so that's a rhetorical question, but solar sails are one way tickets.

2) Does a sail use the solar wind(particles) or the solar light(photons) as fuel. Anyone that has touched metal left in the blazing sun knows that light can easily heat reflective surfaces. But the particles likely carry much more energy(momentum in this case).

3) Could a solar sail and ion drive be used simultaneously? What are the accelerations of both technologies, currently speaking. Hopefully, the solar sail is ahead of the ion drive.

Tom2Mars
2004-Aug-20, 03:50 AM
Hi Guest! I'll try to give this a shot.


1) Once you accelerate to 10 million mph, how do you slow down enough to be captured by a planets gravity?
1.1- You can spill the "wind" early on, and settle into an eliptical transfer orbit, let the planet grab you and aerobrake in, if you were a probe.

1.2- You can "tack" and change the orientation of the sail, and the solar wind will de-accelerate you and slow you down.

So, Solar Sails aren't a "one-way" propulsion system, so you can speed up and slow down, and change course.
1.3:

If you can decelerate from that speed with rockets, why not use rockets to attain that speed in the first place?

Planetwatcher mentioned:
I think the current solar light sail technology can reach speeds of up to 5 1/2 times faster then rockets currently in use. After the sail has you up to speed, it could be a big job to decelerate with rockets. Would probably need to use the same sail system to slow down.

Guest, re #2:
2) Does a sail use the solar wind(particles) or the solar light(photons) as fuel. Anyone that has touched metal left in the blazing sun knows that light can easily heat reflective surfaces. But the particles likely carry much more energy(momentum in this case).


Now this one. you need to ask someone else about. Momentum sounds right, but I've seen it mentioned here and other places, that there is controversy about what is really causing the effect. Two things I've seen, 1- There was a documentary once showing an infrared photograph of Salt Lake City, and the coldest thing in the picture was the roof of the Mormon Tabernacle(Auditorium?) that had a reflective Aluminum roof. It was reflecting away most of the heat. Dark metal gets hot, but reflective metal seems to stay cooler, so whatever energy level was there is reflected.

Another thing that is interesting is that years ago I bought a radiometer at a World's Fair. It's a small glass bulb, evacuated of air, with a little rotating part with 4 vanes on it. Looks like a small weathervane on top of an old barn. One side of the vanes are painted white, and the other side of the vanes are black. Anyway, when you shine a light on it, or place it in the sun, it spins like crazy. So, while some researchers may challenge the idea that light can't "push" foil, you can watch the radiometer spin around and realize that something is pushing those little vanes around.

The astronomer Johannes Kepler, noticed that the tails of comets were getting "blown" away from the sun, and realized that there might be a solar "wind" and that the solar wind might someday push vessels around the solar system, and came up with the concept of solar sails.
Sailing to the Stars (http://liftoff.msfc.nasa.gov/News/2000/News-SolarSail.asp)

And about question #3:
3) Could a solar sail and ion drive be used simultaneously?
I would think that the accelerations would be additive. Have you ever been on one of those people movers at the airports, I can't help but walk at a brisk pace when they are moving me forward, seems like I get to go really fast. I suppose a better analogy would be walking up the escalator in a store, or mall. You get to the top of the gravity well a lot faster that way than just walking up stairs, or, being "taken" up by the escalator alone. I'd have to look up the precise accelerations for both sails and ion drives, but there are advantages to both, and disadvantages to both.

Working together would probably make for a nice system, with more speed, smaller sails, less fuel and an extra bit of redundancy(back-up for each other) that the space guys like when they think of sending important probes, or, maybe even people, to far-away places.

Good questions! Sorry I don't have more scientifically precise answers. :P

Guest
2004-Aug-20, 06:15 AM
For the longest time, I believed that photons pushed solar sails. Even if it is particles supplying the necessary momentum, how can you possible decelarate using a solar sail? The definition of a solar sail involves a force radially from the sun. It pushes in one direction, and solar sails use strings to keep the sail taught. Sails are like muscles, they pull, but cannot push.

I just don't see how you would use a solar sail to slow your velocity(radially from the sun).

ASEI
2004-Aug-20, 04:50 PM
I've run some more simulations. It took a while to reprogram my simulator for improved efficiency and speed.

I ran a simulation starting in 500 km circular earth orbit, accelerating at 1E-4 and 1E-3 m/sec^2.

The 1E-4 m/sec equates to 1N of thrust with a 10 ton probe. Using this acceleration, the probe spiraled around until it finally broke free of Earth's gravity on day 303.
I also ran a solar simulation where it accelerated between a 1 AU and 1.5 AU circular orbit. (I realize that Mars is offset by an angle, and has some slight orbital eccentricity, but this is a simpler model and gives the general idea). The probe took an additional 670.160 days to travel from Earth solar orbit to Mars solar orbit.

I also tried 1E-3 m/sec^2. This would equate to a 10N thrust. This one took only 40 days to break earth's orbit, and 136.084 days to complete the orbital transfer

For each of these simulations, the timestep was 30 seconds.



I have asked you about this before. If the acceleration is very small, what is the nature of this "load"?


The sail itself, floating out in space, probably wouldn't feel much of a load because the solar pressure is distributed evenly across the surface (unless it is curved or something). However, when the sail is attached to a probe, the manner of its attachment becomes extremely important. The load applied by the attachment members applies a stress to the sail. The integration of the pressure from the center to the attachment members around the edge could add up to a sail-tearing shear stress. (The sail pulls apart around the attachment members and floats away) It could also mean that the sail would try to fold up, making it a tangled mess to work with. I am assuming that for the sake of weight, only tension members would be present, and no compression members. Either that, or you would have to figure out a way to have an extremely large lightweight compression member to hold the sail. BTW, wouldn't you need some form of electric propulsion anyway to maneuver and angle the solar sail? After all, it doesn't angle itself.

Alright. I recant. <_< :P Solar sail may be workable as a form of spacecraft propulsion. They don&#39;t require decades of transit time, merely years. (Of course, chemical thrusters only require seven months to reach mars as well.)


I&#39;m working with engineers on in-situ resource utilization right now. There are some very efficient processes and the machinery shouldn&#39;t weigh 500 tons. Initially, soil processing and habitat building will be automated, and the humans can come later. The equipment and hardware can be sent ahead using some kind of cost/fuel effective solar thermal/electric technology or even sail technology.

I&#39;m curious as to what processes you&#39;ve come up with to make this more efficient. (Though I suppose that should go on another thread.

It always seemed to me that it would be at least a few hundred tons in terms of equipment weight. After all, you need soil miners, soil processors, reactors to power the miners and processors, cranes and transportation rigs, smelters, and microwave chemical plants to turn worthless dirt into a lunar base. Not to mention replacement parts, because anything dealing with so much drilling, crunching, and crushing, frying, ect will enevitably wear out and break down.



BTW, I have been using metric tons (because I&#39;m lazy and don&#39;t want to do the proper conversion)

Tom2Mars
2004-Aug-24, 02:53 AM
ASEI, Wow&#33; Thanks for taking the time to work up those simulations. I have to admit, I like the idea of the 1E-3 m/sec^2 acceleration,
I also tried 1E-3 m/sec^2. This would equate to a 10N thrust. This one took only 40 days to break earth&#39;s orbit, and 136.084 days to complete the orbital transfer That&#39;s almost exactly half-a-year. And a 10 ton load is a good-sized payload, even bigger as a metric ton&#33;

Even if the trips were a bit longer, there could be more of them, spaced apart by a month or two. So, once supplies and equipment started arriving at Mars, for instance, another &#39;package&#39; would be along shortly.

Re-
However, when the sail is attached to a probe, the manner of its attachment becomes extremely important. I ran across a link for a new sail material being developed made up of Carbon Fiber &#39;fluffy&#39; stuff, can&#39;t locate it now, will get it to you when I scour my files again. Robert Goddard&#39;s first rockets didn&#39;t get too high at first, but if bright folks get a chance to work with real sails in space someday, I&#39;m sure they&#39;ll improve them too.

Re, In-Situ resource utilization-
I&#39;m curious as to what processes you&#39;ve come up with to make this more efficient. (Though I suppose that should go on another thread. Yeah, probably best in another topic. Although...I did run across some papers about the fact that on Earth, big equipment is useful in mining because the weight of the machine helps to hold it in place, and lever/lift/pull the loads up and move them around, like the big cranes. The weight of the machine acts as a counter-balance. However, sending massive, counterbalance style machines to the Moon or Mars would be cost-prohibitive. Using local material as a counterweight helps. But, it was noted that much of the Regolith on the Moon and Mars has been quite pulverized.

Something called a "slush bucket" was considered a lightweight alternative. Basically, it is pulled along by an anchored winch, scooping up the surface materials to a collection spot, a lot easier than dead-lifting with a crane. And, most of the material is very fine to begin with, and less crushing and grinding would be needed. So, hopefully, as folks design for these different environments, they can incorporate new ways of solving the problems, with a mind towards keeping the weight down, and the sails could be smaller, as would conventional fuel and propulsion systems

Also, Guest&#33;&#33;(And ASEI) Re turning and tacking.
Sails are like muscles, they pull, but cannot push...I just don&#39;t see how you would use a solar sail to slow your velocity(radially from the sun).A sailboat can sail with the wind, or into the wind. You can use a sail to speed up, or slow down. In fact, sometimes, you can even sail faster than the wind. Much of these abilities are due to having a keel or a centerboard, to resist the water. In space, there is nothing to resist against. However, because of the low mass of the sail, the center of gravity of the whole vehicle system is very close to the main payload mass. It is possible to use a small portion of the solar energy available to create electricity and turn a gyroscope(momemtum wheel) and provide sufficient "resistance" and turn the vehicle/sail into the desired tack. Then the sun is pushing against the sail in the opposite direction, and the vehicle speed will slow down.

Or, pull on one set of "strings" and let out the opposite set.

See Figure 12 at this link:Solar Sailing (http://aerospace.wcc.hawaii.edu/sail.html)

(Where&#39;s that Smilie/emoticon with the one eye and the pirate patch when you need it?)

PS- ASEI, thanks again for spending the time on the numbers, I appreciate the effort. :)

Planetwatcher
2004-Aug-25, 12:03 AM
For the longest time, I believed that photons pushed solar sails. Even if it is particles supplying the necessary momentum, how can you possible decelarate using a solar sail? There are two methods of solar propulsion being discussed here, and they are being confused.

1 Solar wind sails.
2 Solar light sails.

Solar wind sails use particles. This technology is simpler to use, and likely to undergo early development faster. It is a stronger, and faster acceleration then light sails, but it&#39;s top speed is limited to the speed of the solar wind, which is much much slower then light, and the way these sails work is more akin to the sails in the old wooden boats of the middle ages. Everyone who has ever driven a sail boat, or sail boards, knows that no matter which direction the wind comes from, you can go in any other direction, except directly against the wind.

Solar light sails are more compicated. They use light photons in a way I don&#39;t understand well enough to explain myself. They can go in any direction, especially if you have an onboard source of light to direct at the sails, execpt for against a stronger source of light.

The acceleration is much slower then solar wind sails but still way faster then all but the most advanced ion propulsion devices. Even those will be exceeded with time.
Maximum speed in theory is just somewhat slower then light, provided you have a small enough payload, large enough sails, and no other strong sources of light to interfear with acceleration. But, it will take a very very long time to reach such speeds.

Deceleraton for both is actually easier then achieving full speed, and if you don&#39;t get slowed down enough when you reach your destination, you can simply loop around and continue to slow down until you reach your desired speed.