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neviden

Banned

Registered: 2004-05-06

Posts: 99

Re: Use LEO’s residual atmosfere for propelants? - Just use ramjet to colect atmosfere..

The main problem for space travel is fuel. Just to get to LEO we use rockets that are 95% fuel. And then when we are in orbit we use more propelants.. either chemichal rocket, ion rocket, nuclear.. all basicly throw stuff at the back end to push spaceship forward. To get faster/futher we need more propelants, which means more tanks, which means biger ship, which means still more propelants..

There is no problem with amount of propelants we can get. We have oceans of water, and all you need is electicety to get H2 and O2. But to get this to LEO we use rockets.

Why do we use progress and ATV, to bring to ISS water and propelants - to compensate for resedual ATMOSFERICAL drag?   ???

Why not use this?

All you basicly need is spaceship (which would be permamently in space) wich can scoop this small atmosfere, seperate gasses and presto. You have O2, H2, N2, H2O,.. If atmosfere is to thin, then lower altitue to 100 km, gather gasses for few days, then deliver usefull gases (H2O and O2) to ISS, use solar panels and we have rocket fuel.

This would basicly mean that fuel is free and unlimited. If you need more, you go and scoop it up. That would make ISS actually usefull.
- Hubble not working? send tugboat, get it, repear it at ISS, send Hubble back.
- ISS at wrong orbit? Burn fuel.
- Want to go Mars? Build battlestar galatica - big, roomy, spinning, safe.. with big empty tanks. Refuel, go to mars, go back, park at ISS, fix if broken, refuel and go again.
- Want to go to Moon? The same.. just smaller.
- Want to mine asteorids? The same.. just bigger.

or.. Am I missing something?

Euler

Member

From: Corvallis, OR

Registered: 2003-02-06

Posts: 922

Re: Use LEO’s residual atmosfere for propelants? - Just use ramjet to colect atmosfere..

Colecting the atmosphere would create more drag, and you would lose more momentum than you would gain from burning the fuel.

neviden

Banned

Registered: 2004-05-06

Posts: 99

Re: Use LEO’s residual atmosfere for propelants? - Just use ramjet to colect atmosfere..

Not if you use solar energy to compensate for drag. Let say we build something that looks like stingray. Flat with solar wings, wide mouth to 'scoop' atmosfere, seperate, eject unneeded parts (N2 probobly) with some kind of thruster (with energy from the sun).

Euler

Member

From: Corvallis, OR

Registered: 2003-02-06

Posts: 922

Re: Use LEO’s residual atmosfere for propelants? - Just use ramjet to colect atmosfere..

ISS has an orbital velocity of about 7.6 km/s.  Current H2/O2 rocket engines cannot produce an exhaust velocity above 4.5 km/s.  This means collecting H2 and O2 would cause more drag than propulsion, unless you had some sort of scramjet.  Hydrogen and Oxygen are not the only gasses in the atmosphere either, which makes the drag even worse.

neviden

Banned

Registered: 2004-05-06

Posts: 99

Re: Use LEO’s residual atmosfere for propelants? - Just use ramjet to colect atmosfere..

O2/H2 rocket has maximum ISP of 450. Hall Thruster has ISP up to 2000, Ion up to 10000. (so exhaust speeds could reach 100 km/s). All you need is power.. lots of power..

http://www.spacetethers.com/cc1.regolit … olith.html
http://www.permanent.com/t-el-iov.htm]h … el-iov.htm

Euler

Member

From: Corvallis, OR

Registered: 2003-02-06

Posts: 922

Re: Use LEO’s residual atmosfere for propelants? - Just use ramjet to colect atmosfere..

Most ion engines use Xenon.  You won't find much Xenon in the atmosphere.

neviden

Banned

Registered: 2004-05-06

Posts: 99

Re: Use LEO’s residual atmosfere for propelants? - Just use ramjet to colect atmosfere..

Yes, I know.. but they use Xenon because it's inert and easy to keep for long time. As far as I can tell Hall thrusters can use any gass including O2 (the most reactive).

I have looked up data on Smart-1. It has 2 KW solar pannel, Ion drive which has 70 kg of Xenon and ISP 1640. It will use all of it in 200 days.

So If we would have to use half of gasses for thrusting, and we would have 2 MW solar pannels, then we would get 100 tons of usefull gasses / year. More power = more gasses.

Euler

Member

From: Corvallis, OR

Registered: 2003-02-06

Posts: 922

Re: Use LEO’s residual atmosfere for propelants? - Just use ramjet to colect atmosfere..

Xenon is used because it is easy to ionize.  If you use gasses that are more difficult to ionize, the efficiency will be lower.

Rxke

Member

From: Belgium

Registered: 2003-11-03

Posts: 3,669

Re: Use LEO’s residual atmosfere for propelants? - Just use ramjet to colect atmosfere..

Excellent idea but not a new idea, Google for PROFAC (and it's somewhere on these boards too... So you could try to search here, i posted about it here some time ago, heh.)

Same idea, but with a nuclear motor... Turned out to be unfeasible but that was before ion thrusters, so maybe today it *IS* possible...
Solar power: big 'wings,' so lotsa drag... maybe if you orientate the wings for minimal drag... (EDIT: oops, already mentioned)

if you can't find any info on Google, try and find a copy in your local library of The illustrated Encyclopedia of Space Technology by Kenneth Gatland... it has pics of the thing, complete with drawings of a 'mission IIRC...

GCNRevenger

Member

From: Earth

Registered: 2003-10-14

Posts: 6,056

Re: Use LEO’s residual atmosfere for propelants? - Just use ramjet to colect atmosfere..

Euler is right, the drag produced will be more trouble than its worth, and you can't refuel an ion engine or hall-effect thruster or any other electric engine with atmospheric gasses. At the top of the atmosphere, most of the gasses are hydrogen and helium anyway due to fractioning... no oxygen for rocket fuel.

---

[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]

[i]The glass is at 50% of capacity[/i]

neviden

Banned

Registered: 2004-05-06

Posts: 99

Re: Use LEO’s residual atmosfere for propelants? - Just use ramjet to colect atmosfere..

Rxke: Yes, PROFAC is the same idea. Someone said that you can basicly capture only 2% of gasses. Is that that makes it unfeasible? (at that rate you would need Isp of 100K) Or was it because it was based on nuclear reactor (in LEO? that would be politicly unaceptable)?

GCNRevenger: High atmosfere is made of O, N2, O2. http://www.physics.usyd.edu.au/~cairns/ … node2.html

There are also great deal of thrusters that could use H and He:
- PMWAC - Propagating magnetic wave accelerator (any gass, 90% efficiency, 14000 Isp) http://niac.usra.edu/files/studies/fina … Slough.pdf
- MPD - Magnetoplasmadynamic thrusters (H, He, Li, 50% Efficiency, 2500 - 7000 Isp)
- Pulse-inductive thruster
- VASIMIR

Another option is to use theather, wich doesnt need any propelant, suply electricity and get reboost that way. All you need then is cryopump and empty tanks.

SBird

Banned

Registered: 2004-03-10

Posts: 490

Re: Use LEO’s residual atmosfere for propelants? - Just use ramjet to colect atmosfere..

EGADS, what is it with all this really cool spacecraft propulsion tech at my own university I was unwaware of?

First it's M2P2 and now this PMWAC drive that were right under my nose!

This PMWAC really has my interest piqued, do you have any direct comparisons between this tech and VASIMR?  They both seem to be high efficiency, variable Isp drives.  Is there any clear advantage of one over the other?

neviden

Banned

Registered: 2004-05-06

Posts: 99

Re: Use LEO’s residual atmosfere for propelants? - Just use ramjet to colect atmosfere..

You mean any clear advantage for PMWAC as in: "It is proposed here to solve not only (high thrust/ high Isp / high efficency), but to provide the breakthrough technology required to make fusion propulsion a realizable goal in the next decade." ? 

Forget about scooping gasses.. I WANT PMWAC 

SBird

Banned

Registered: 2004-03-10

Posts: 490

Re: Use LEO’s residual atmosfere for propelants? - Just use ramjet to colect atmosfere..

Having had a chance to read the PMWAC stuff in more detail, it's clear that the primary advantage is not in the high propulsive efficiency but in the fact that the plasma densitites in it are theoretically capable of achieveing fusion.  If that's the case, your Isp is going to be MUCH higher than 14000.

This is interesting work, it goes along with my assertion in  another thread that the fusion community's fixation on tokomak designs might not be a good one.  There do appear to be some plasma stability issues iwth PMWAC, though, from reading their latest progress report.  It might also be noted that this is actually 40 year old technology that predates tokomak designs.