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m1omg
2007-Sep-29, 06:02 PM
What is the best ion drive that we can construct now?And what is the currently the best electric propulsion system?Could we add more strenght and efficiency to it if we'll use nuclear reactor as electricity source instead of solar power (I know, anti-nuclear groups will protest like crazy, but I would advise any space agency to say them "shut up" otherwise we will never have any really useable interlanetary engine {some groups, like Greenpeace, are even against fusion power!})?
I once read somewhere on the net that there are compact nuclear reactor with weights only around 350 kg and with around 150 KW power!That should imo revolutionarise space travel if the NASA and others will say shut up to anti nuclear fanatics.
The reasons why I think that the nuclear power would be best used in an advanced ion engine are:

1.Nuclear thermal rockets (solid core) are not much more efficient than conventional chemical rocket engines, and thus do not provide enough advantage over chem. rockets, + the exhaust is highly radioactive.
And he liquid and gas core systems were never constructed or tested, they are just on the paper.

2.Nuclear salt-water, I know, many of you belive that they are very good, but they are just theory now, safety is almost zero, and their exhaust is extremely radioactive waste... (+EDIT-there is debate on that if it even would work)

3.Ion engines were tested from the 1950s and they were suscessfully tested in multiple space probes and they are starting to be widely used in satelite managing and attitude control, and their exhaust is harmless and inert xenon gas.

KaiYeves
2007-Sep-29, 06:20 PM
I consider their successful use on space probes evidence of the energy potential of both solar and nuclear power.

m1omg
2007-Sep-29, 06:31 PM
Then why they did not launched any nuclear powered spacecraft with an ion engine, for example, to the outer Solar system?Just because some Greeenpeace hates anythings nuclear and thinks "nuclear" is a dirty word even if they do not know anything other about it than "it is evil"?
The nuclear powered ion engine could open the doors to more efficient and complex space exploration and eventually colonisation of our Solar system.

antoniseb
2007-Sep-29, 07:54 PM
Just because some Greeenpeace hates anythings nuclear and thinks "nuclear" is a dirty word even if they do not know anything other about it than "it is evil"?
m1omg, please back this statement up with some facts, or apologize to those of us in Greenpeace. I'm pretty offended that you've said I know nothing about nuclear other than it is evil.

m1omg
2007-Sep-29, 08:05 PM
Sorry, I did not mean to offend you, just those cranks that are shouting that nuclear power is bad and blahblahblah while not knowing anything about it, not the entire Greepeace,I actually like some of their arguments about things other than nuclear power.

I apologise.

ciderman
2007-Sep-29, 08:17 PM
I like the look of this :)

NASA will accelerate missions featuring space nuclear power
found here;
http://www.spaceref.com/news/viewnews.html?id=1237


Ps please feel free to spilt this off into a new thread if warranted....

KaiYeves
2007-Sep-29, 09:51 PM
I wasn't saying anything about how much they used it, just that it's sucessful use on Viking and Voyager convinced me that it was powerful. Perhaps not as safe as other alternatives here on Earth, but a very good idea for space travel.

IsaacKuo
2007-Sep-29, 10:06 PM
What is the best ion drive that we can construct now? And what is the currently the best electric propulsion system?

It depends on your definition of "best". If you just want a thruster which can provide the highest power, highest thrust, and highest performance...probably VASIMR or double helicon thruster. Both of these exist in the lab and offer high performance in those terms. However, these are just laboratory beasts. It will take years before either is ready for spaceflight. The thruster is impressive...but we don't have space power systems suitable for them.

So, this definition of "best" is perhaps flawed. What good is an amazing thruster which can't actually be flown because we lack the required power source?


Could we add more strenght and efficiency to it if we'll use nuclear reactor as electricity source instead of solar power (I know, anti-nuclear groups will protest like crazy, but I would advise any space agency to say them "shut up" otherwise we will never have any really useable interlanetary engine {some groups, like Greenpeace, are even against fusion power!})?

Nuclear reactors may actually be of limited use in space travel. They're a good fit for deep space exploration missions to the outer solar system, but they actually do NOT provide more energy than solar panels for inner solar system missions. And solar panels are a lot less expensive, and they're a lower technology risk. But the most compelling thing in favor of solar panels--they scale down to small probes, which is all we're currently interested in flying.

What about when we want honking big manned spacecraft flying around the solar system, then? Well, nuclear might still not be the best idea. Nuclear power is still more expensive than solar. The best way to "pump up" the power level of manned spacecraft may actually be to use solar power indirectly. Rather than accelerate those big and heavy solar panels, you use sunlight to power orbital solar pumped lasers, and shine those lasers at the spacecraft.

Laser power stations are great because they can offer big returns on their investment. A spacecraft flying between planets spends most of its time drifting at minimal power. If you use nuclear reactors, then most of the time that expensive reactor is sitting around idle. In contrast, a laser power station can be running at full blast 24/7. As soon as it finishes boosting one spacecraft, it can switch to boosting another spacecraft. The spacecraft may spend most of their time drifting across interplanetary space, but the laser station spends most of its time doing work--getting a return on the initial investment.

IsaacKuo
2007-Sep-29, 10:10 PM
I wasn't saying anything about how much they used it, just that it's sucessful use on Viking and Voyager convinced me that it was powerful. Perhaps not as safe as other alternatives here on Earth, but a very good idea for space travel.

Viking and Voyager used rather weak radio-isotope decay powered cells, not powerful fission reactors. These power systems were adequate for their missions, but I wouldn't call them "powerful".

m1omg
2007-Sep-30, 09:14 AM
Dawn is powered by 10 KW solar cells.
A light space nucear reactor can do around several hundred KW.
And I am not taking about use in small inner solar system probes, but medium sized outer solar system orbiters like the cancelled JIMO.
And I said, the more power will go to ion engine, providing more thrust and shortening the time required and enabling it to orbit multiple moons and carry more power hungry instruments.
I mean, construct a more powerful ion engine that uses more power and power it by small nuclear reactor.

Super ion engine; http://www.centauri-dreams.org/?p=506
"Public fear"; http://www.wired.com/science/space/news/2007/09/space_nukes

m1omg
2007-Sep-30, 09:24 AM
VASIMR, MPD...not feasible, because we do not have nuclear reactors that are light enough and simultanously powerful enough to pump enough power to these engines.
But scaling ion engines to more powerful nuclear reactor powered versions is something completely different.

m1omg
2007-Sep-30, 09:25 AM
I like the look of this :)

found here;
http://www.spaceref.com/news/viewnews.html?id=1237


Ps please feel free to spilt this off into a new thread if warranted....

That is good news at least :).I hope that public protests will not ruin the project.

IsaacKuo
2007-Sep-30, 02:24 PM
Dawn is powered by 10 KW solar cells.
A light space nucear reactor can do around several hundred KW.

Ah, but how heavy is it? You've got to look at how powerful a reactor would be if it only had as much mass as the solar cells (if such a reactor even has sufficient mass). And don't forget that solar cells get more powerful if you get closer to to the Sun.


And I am not taking about use in small inner solar system probes, but medium sized outer solar system orbiters like the cancelled JIMO.

As I noted, nuclear power is a better fit for outer solar system work. However, even then it'd be better to use laser power than nuclear after we have developed the required laser systems. In the long term, laser power is more economical than nuclear power.


And I said, the more power will go to ion engine, providing more thrust and shortening the time required and enabling it to orbit multiple moons and carry more power hungry instruments.
I mean, construct a more powerful ion engine that uses more power and power it by small nuclear reactor.

Producing more thrust doesn't produce more acceleration if the reactor is that much heavier. It's the thrust-to-weight ratio which matters.

Electrostatic ion thrusters also have hard physics charge density limitations which inherently limit them to a particular low thrust, but in the near term these limitations aren't such a big deal. It does mean they will be superceded by better technologies that don't suffer those limitations, though.

Ilya
2007-Sep-30, 09:43 PM
Then why they did not launched any nuclear powered spacecraft with an ion engine, for example, to the outer Solar system?

Because RTG's produce about one order of magnitude less power for their weight than ion engine needs.

Ronald Brak
2007-Oct-01, 02:35 AM
Rather than accelerate those big and heavy solar panels, you use sunlight to power orbital solar pumped lasers, and shine those lasers at the spacecraft.

This is very practical. An even cheaper and simpler method is to use mirrors to shine sunlight onto solar powered probes or ships.

eburacum45
2007-Oct-01, 02:53 AM
I really like the idea of laser and particle beam powered spacecraft myself - but there will surely be some sort of political and cultural resistance to the idea of building such powerful lasers.

A beam weapon is extraordinarily useful in warfare; if someone knows where the target is, the target can be reliably destroyed in practically no time at all, given a powerful enough laser. How can the international community be persuaded that is a good idea?

On a different note- I once had the idea of maser-powered craft, with a rectenna converting microwaves into ion thrust. Any thoughts on that one? Of course it doesn't necessarily need to be microwaves, but the rectenna idea appealed to me.

Ronald Brak
2007-Oct-01, 03:05 AM
At the moment there is only so much energy that a photelectric surface can absorb (if the lasers are being used for electrical power) so they might not be all that deadly. Sure someone could try to focus the laser array onto one spot to cause some damage, but you can use sunlight to do that as well. I suppose a really nasty person could try and blind people with it.

IsaacKuo
2007-Oct-01, 04:31 PM
This is very practical. An even cheaper and simpler method is to use mirrors to shine sunlight onto solar powered probes or ships.

This doesn't work. Consider any small spot of a mirror. The light from the sun will be reflected by this spot into a cone rather than a narrow ray. For example, if the image of the Sun as seen by this spot is 0.5 degrees across, the reflected image will also be 0.5 degrees across. This is an unavoidable amount of conical spread, in addition to any other spreading effects (like imperfect mirror surfaces or diffraction spread).

This means that a solar reflector can't project the Sun's energy onto a small spot, at useful distances. In contrast, a solar pumped fiber laser can be focused onto a small spot.

IsaacKuo
2007-Oct-01, 04:53 PM
I really like the idea of laser and particle beam powered spacecraft myself - but there will surely be some sort of political and cultural resistance to the idea of building such powerful lasers.

A beam weapon is extraordinarily useful in warfare; if someone knows where the target is, the target can be reliably destroyed in practically no time at all, given a powerful enough laser. How can the international community be persuaded that is a good idea?

This is one of those glass half-empty vs half-full things. Consider the flip side of the political equation--you can get funding for this powerful laser from those who want to have a ballistic missile defense weapon. And that's likely to prompt other major powers to want one also...

Whether or not it's a good thing for world peace, an arms race can certainly drum up huge budgets like nothing else.


On a different note- I once had the idea of maser-powered craft, with a rectenna converting microwaves into ion thrust. Any thoughts on that one? Of course it doesn't necessarily need to be microwaves, but the rectenna idea appealed to me.

The main downside to microwaves is that microwave beams spread much more than shorter wavelength beams. This isn't so much of a problem if you scale up the microwave array enough--a 100km wide phased array emitting 1mm microwaves could shine onto 1m wide spot at 100,000km. This is a huge engineering project, but there aren't any show-stoppers besides the fabulous cost.

But higher frequency lasers could be far more compact and scale down to less expensive projects better. There's good potential for solid state lasers tuned to silicon transition energies to efficiently transmit and receive electrical power. This would eliminate most of the potential advantages microwaves might have.

m1omg
2007-Oct-02, 12:56 PM
Because RTG's produce about one order of magnitude less power for their weight than ion engine needs.

I said NUCLEAR REACTOR, not some weakish RTG.
And small nuke reactor can weight only about 350 kg.
If the Soviet Russia was able to launch spy satelites with real nuclear reactors onboard, NOT RTGs , why NASA would not be able to use neaclear reactors on it's probes.

Ronald Brak
2007-Oct-02, 01:15 PM
This doesn't work. Consider any small spot of a mirror. The light from the sun will be reflected by this spot into a cone rather than a narrow ray. For example, if the image of the Sun as seen by this spot is 0.5 degrees across, the reflected image will also be 0.5 degrees across. This is an unavoidable amount of conical spread, in addition to any other spreading effects (like imperfect mirror surfaces or diffraction spread).

I hadn't considered that. Thanks for pointing it out. I can't think of any way for a cheap mirror system to overcome that drawback.

genericdefect
2007-Oct-03, 07:19 AM
I think the best "out-there" plan would involve high-orbit solar sats powering lasers with advanced targeting and tracking technology.

The key to laser powered flight is that lasers can accelerate the expansion of released neutral gases or other particles in a "combustion" (expansion) chamber much more quickly than other conventional methods afaik. The weight of the traveling satellite is thus reduced. Perhaps large parabolic focusing arrays might make things a bit easier in terms of targeting.

Even better, the laser platform can be reused over and over, and it is both failure redundant, serviceable, and upgradeable. It can also be used for more efficient orbital maintenance on our future local or lunar satellite fleet in lieu of a permanent orbital ferry, although one of those would be handy too.

publiusr
2007-Oct-12, 06:27 PM
I really like the idea of laser and particle beam powered spacecraft myself - but there will surely be some sort of political and cultural resistance to the idea of building such powerful lasers.

A beam weapon is extraordinarily useful in warfare; if someone knows where the target is, the target can be reliably destroyed in practically no time at all, given a powerful enough laser. How can the international community be persuaded that is a good idea?

On a different note- I once had the idea of maser-powered craft, with a rectenna converting microwaves into ion thrust. Any thoughts on that one? Of course it doesn't necessarily need to be microwaves, but the rectenna idea appealed to me.


Well, the same tech needed for solar power satellites and large orbital radio telescopes would also make ideal lens material

Such lens can tack toward positions around the sun, then reflect power to a cental spike type design--to focus many beams into one. This is then reflected onto a sail-craft and off you go.


You need many hundreds of tons of memory metal and something that can fold--like the active 'scope technology for earthbound scopes to keep them focused.


No moving parts--very little computer power--but a lot of sunlight power.

Materiels research is needed on heat resistance. The disks would have to spin to keep from melting into blobs.

IsaacKuo
2007-Oct-12, 08:48 PM
This doesn't work. Consider any small spot of the lens. The light from the sun will be bent by this spot into a cone rather than a narrow ray. For example, if the image of the Sun as seen by this spot is 0.5 degrees across, the reflected image will also be 0.5 degrees across. This is an unavoidable amount of conical spread, in addition to any other spreading effects (like imperfect lens surfaces or diffraction spread).

In contrast, using sunlight to pump solar fiber lasers might be a practical and inexpensive concept for powering laser thermal rockets. The light from a solar fiber laser CAN be aimed/focused across respectable distances.