Elon got his rocket up ...

[kunkmiester]

Problem with a cloth sheet for a sweeper is it may become a trampoline. We want to remove the debris, not knock it flying somewhere else. There's probably other things that would work besides aerogel, but the idea would be the same--absorb the debris and remove it.

2. The blanket would probably work like a solar sail and even worse, it would probably interact with the atmosphere, so it would need a lot of boosting, or it will be very temporary.

Temporary was the idea I had in mind. This probably wouldn't even have a lot of thrust capability--it would go up, unfold to a hundred meters in diameter or more, cruise along until it's not soaking up much stuff, and then deorbit, taking the debris with it. This would probably be more of a streetsweeper than a total cleaning system.

If a more effective method exists for collecting it but keeping it in orbit, you could recycle it--satellites would ideally contain all the materials needed to make new satellites, all you need to lift is the factory and the small amount of reprocessing chemicals needed. Then you can get money out of space junk.

[kunkmiester]

I forgot to post my funny:

http://freefall.purrsia.com/ff1900/fc01888.htm

[zapkitty]

Problem with a cloth sheet for a sweeper is it may become a trampoline. We want to remove the debris, not knock it flying somewhere else.

With an impact velocity often measured in kilometers per second that's not going to be a primary design driver.

The design driver will be that the "sheet" sheds no debris whatsoever after impact... which would seem to mandate a multi-layered design of whatever materials are chosen.

If a more effective method exists for collecting it but keeping it in orbit, you could recycle it--satellites would ideally contain all the materials needed to make new satellites, all you need to lift is the factory and the small amount of reprocessing chemicals needed. Then you can get money out of space junk.

Now that would be cool!

... then all we would need to do is to figure out what kind of commercially viable sat one could build out of burned solid rocket propellant, corroded paint flakes and radioactive potassium coolant droplets from soviet-era spysat reactors...

[IntLibber]

My company did a launch at Wallops Island once. A boat failed to heed the Coast Guard notices on ours, too, and had to be pointed the way out of the range. You have no idea how slow a boat is until you watch one clear a range on radar, with your launch aircraft in the air and the clock running.

I'd like to know whose boat it was that was in the range to mess with SpaceX's window.

[IntLibber]

One source I read says they've sunk $400 M into the project so far.

500 including Dragon, according to Elon. That is extremely cheap!
I think that using so many engines is perfectly reasonable. The econmics of scale kick in earlier and they can use them for a wider range of vehicles. They also have a higher chance of mission success, even with one or more engines failing.

I liked a crack I read yesterday about the Ares test launch being essentially a fake.

That is exactly what it was!

Actually Elon said that they'd invested "less than $500 million" in order to dispute claims of multibillion dollar investments being made by some hyperbolic critics. He himself has invested only $100 million, with about $70 million from other investors, and to date they have only received a small fraction of the COTS-D crewed capsule funding, so IMHO its actually significantly less than $500 million. They haven't got a dime from the CRS cargo contract yet. Beyond investments, all they have are launch deposits from other customers and payments from those that have flown on previous F1 flights.

[Skipjack]

I saw Elons numbers somewhere and I thought they added up to a total of 530 or something like that. Anyway, it is splitting hairs. 500 million is EXTREMELY cheap for what they have achieved so far.

[Skipjack]

On the trampoline thingy. Maybe it is enough to just slow the junk down enough so it will deorbit all by itself within a rather short period of time.
Even if it takes months for it to deorbit, it is still better than having the thing float arround in orbit for years, if not decades.
Maybe one could also try deflecting it "downwards" instead of capturing it, so it will burn up...

[GIThruster]

Maybe one could also try deflecting it "downwards" instead of capturing it, so it will burn up...

Now that is a truly novel idea--launch something robust enough to survive collisions, that has perhaps a single, large, smooth surface, and play bumper-cars with it. Remotely steer it into the path of space junk, cause a collision, use the energy to alter the plow's orbit and at the same time deorbit the junk.

"Deflecting. . ." I haven't seen that idea before. Add an orbital mechanist and a programmer and you have enough for an alt-space start-up.

[IntLibber]

Maybe one could also try deflecting it "downwards" instead of capturing it, so it will burn up...

Now that is a truly novel idea--launch something robust enough to survive collisions, that has perhaps a single, large, smooth surface, and play bumper-cars with it. Remotely steer it into the path of space junk, cause a collision, use the energy to alter the plow's orbit and at the same time deorbit the junk.

"Deflecting. . ." I haven't seen that idea before. Add an orbital mechanist and a programmer and you have enough for an alt-space start-up.

Anything one does to make a sweeper big enough to catch a useful amount of space junk is also going to generate so much drag that it will deorbit itself long before it enough material to be useful.

There is currently a convention thats been agreed to all the major spacefaring powers that requires that all upper stages and satellites put in orbit must contain enough dV to deorbit themselves if in LEO, or generate enough drag to deorbit themselves within a few years, or move to a permanent parking orbit if in GSO at the end of their useful life. China recently agreed to the same convention.

As a result, the spacejunk problem should resolve itself over the next 5-10 years at least for LEO as objects lose altitude from drag and deorbit themselves.

The issue of space in geosynchronous orbit however continues to grow. The recent zombiesat issue helped to illustrate this.

[Skipjack]

Anything one does to make a sweeper big enough to catch a useful amount of space junk is also going to generate so much drag that it will deorbit itself long before it enough material to be useful.

I agree on the drag being a huge issue. This is what I said before as well.
This is why I think that going after the big stuff first, would be a good idea. Yes the small stuff is a problem, but the big stuff is a problem that can fixed much easier.

The issue of space in geosynchronous orbit however continues to grow.quote]
Well, the other problem that I see with GS orbit junk is that its orbit will eventually degrade as well. That will then, again threaten objects in lower orbits.

On a slightly related note, there was an article about orbital tugs on hobbyspace recently:
http://www.hobbyspace.com/nucleus/index ... id=21347#c

[zapkitty]

Anything one does to make a sweeper big enough to catch a useful amount of space junk is also going to generate so much drag that it will deorbit itself long before it enough material to be useful.

First, anything impacting the sweeper at orbital velocities is going to become plasma and fragments... it won't be bouncing. Thus my suggestion for a multilayered design.

A big ball of layered cloth and plastics stuffed with aerogel should do the trick

With a fusion powerplant pushing it around even a 100 meter fluffball should be able to reboost itself as needed... and avoid debris too large for it to "digest"...

There is currently a convention thats been agreed to all the major spacefaring powers that requires that all upper stages and satellites put in orbit must contain enough dV to deorbit themselves if in LEO, or generate enough drag to deorbit themselves within a few years, or move to a permanent parking orbit if in GSO at the end of their useful life. China recently agreed to the same convention.

As a result, the spacejunk problem should resolve itself over the next 5-10 years at least for LEO as objects lose altitude from drag and deorbit themselves.

But there are caveats to even that...

There are thousands of debris objects which went up (or were created on orbit) before the treaty.which are high enough and/or large enough to stay up for longer than ten years.

And speaking of debris created on orbit... there's nothing to prevent a modern "debris-free" sat and its tidy terminator tether from falling victim to a West Ford needle and becoming a debris spray in spite of the best efforts of its designers.

This problem will be with us for decades and could get exponentially worse at any given moment sans cleanup efforts... or even with cleanup efforts.

The issue of space in geosynchronous orbit however continues to grow. The recent zombiesat issue helped to illustrate this.

That's a flat-out growth market waiting to be tapped if someone had a tug that didn't need to be refueled after every pickup.

Wiser minds than ours have foreseen this in detail.

Everyone talks about using nets to wrap and snag larger debris and stray sats. A sensible solution given the the lack of unified grappling fixtures.. or any grappling fixtures for that matter... but isn't that net the very definition of a space baggie?

This is obviously a job for Commander Quark and his Polywell-Powered Sanitation Patrol Cruiser!

[Tom Ligon]

The problem is not with the lowest orbits where the ISS resides and lower, which do at least intermittently have enough atmospheric drag to drop stuff from orbit on a scale of decades. GEO is also not so bad as everything is in the same orbit, so even if there are collisions they are soft bumps.

But there is a very popular orbit around 900 miles above the surface that is heavily populated and crosses the poles. I believe it has a period of about 2 hours and tends to put a satellite over a given spot on Earth at the same time every day. An orbit like that tends to have a decay rate measured in tens of thousands of years, and a high probablility of collision, especially at the poles. That's likely where a cascade of collisions would start, and build.

One thing that might work is a satellite in such an orbit that deploys low-density aerogel of a temporary nature, possibly a gelatin, something that evaporates in a few orbits in full sunlight. Blow a ball of this stuff and send it into the path of whatever you want to bring down, as close to head-on as practical, and likely over one of the poles. If the piece of junk is fairly solid, it should slow and begin to orbit elliptically. At least would spend most of its time below the heavily-populated orbit, and might eventually decay.

What would a delta-V of a few tens of meters per second do?

If a whole satellite were hit this way I would expect pieces to come off, but I would expect the small stuff to be slowed down more than the main chunk.

I would not count on fusion for this, but it sure would help. Solar power and an ion or arc-jet propulsion system would probably provide enough delta-V to correct the orbit after deploying an aerogel ball.

[pfrit]

There are some very funky stable geostationary polar orbits possible (the satelite is in a solar orbit with a solar sail) but they are all well above 900 miles.

[Aero]

There are some very funky stable geostationary polar orbits possible (the satelite is in a solar orbit with a solar sail) but they are all well above 900 miles.

How does that work?
Geostationary - Of or having a geosynchronous orbit such that the position in such an orbit is fixed with respect to the earth.
Polar Orbits - an orbit in which a satellite passes above or nearly above both poles of the body (usually a planet such as the Earth, but possibly another body such as the Sun) being orbited on each revolution.
All Earth geosynchronous orbits have a semi-major axis of 42,164 km (26,199 mi).
http://en.wikipedia.org/wiki/Geosynchronous_orbit

[GIThruster]

The 26k miles includes inside it the diameter of the Earth. It is not 26k miles above the Earth or even 13k.

900 miles high sounds about right. 26k mile diameter is enough room of an awful lot of sats, so long as they're taught to share, play well with others, all the stuff we learn in kindergarden.