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Using a direct elastic collision with a passing asteroid for propelling a spacecraft? 10

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KirbyWan

KirbyWan

Aerospace
Apr 18, 2008
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Howdy all,

So every time I see a news story about an asteroid that will pass close to the earth, I wonder if it would be possible to use an elastic collision with the passing asteroid to propel a spacecraft to deep space. I imagine either a long, multi-stage cylinder to compress a gas (I don't think this would work) or perhaps a pair of micro-satellites connected by a cable that would be in the path. (I think this has a chance of working.)

What would be the max G-loading a satellite could be designed to withstand while having useful systems for positioning, communication and of course science, survive?

If the elastic collision was efficient it could propel a spacecraft twice as fast as the asteroid was going.

Is this a reasonable idea? Or am I nuts? (for this specific idea since I know generally, yeah I'm a bit nuts.)

Thanks,

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.
 
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which is why this won't work … you cannot control the exit direction

another day in paradise, or is paradise one day closer ?
 
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I thought the point was to gain velocity for the "vehicle" ? I assumed the point to doing this was to go somewhere. The rebound trajectory from an asteroid impact is likely to be very variable.

another day in paradise, or is paradise one day closer ?
 
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For interstellar missions, one of the things I was thinking of for getting a big momentum transfer from a passing asteroid, the direction really isn't all that important. Pointed toward the heliopause within 30° would be good enough. Also with the idea of using a craft that has a toroidal magnet to "softly" transfer momentum the set up would tell us with a fair amount of accuracy where we would be headed and let us select the direction based on where we encounter the asteroid.

Maybe for any of these ideas we could use an ion thruster to reduce the delta-V between the asteroid and the vehicle to a survivable level. then use the ion thruster again to fine adjust the path after the encounter.

Let's be honest, this is a probably unworkable idea, but the back and forth has refined the idea and given us new ideas. It's the kind of impractical engineering that occasionally comes up with a workable, useful solution.

Kirby Wilkerson

Remember, first define the problem, then solve it.
 
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I was only thinking of targets in the plane of the Solar System being of interest, when I suggested a rail gun.
There are a LOT of different possible methods of electromagnetic acceleration, and deceleration hadn't even occurred to me at the time but I can see that as a possibility, too.
It's a common tool in Sci-Fi to move from one place to another, on the Moon for example, where air isn't an issue and you only need to clear the terrain. Usually works like the Japanese maglev trains.
Some attempts have been made to find a practical design. Superconductors are feasible in space. Look up the Star Tram for just one example.

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF
 
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I have ideas about workable space elevators. I never liked the idea of a tether that reaches down to the earth's surface and up to geosynchronous orbit. It would take a huge amount of material and the location it attaches to the planet would be a target. Here's my idea for a space elevator:

It uses an airplane as a first stage to get a payload as high and fast as possible. We could get the SR-71 to 80k feet and mach 3 in the 60's we could go higher and faster for a purpose build first stage air breathing launch vehicle.

This vehicle would rendezvous with a rotating space station with a long tether so that the tether would dip into the highest layers of the atmosphere when needed to receive a payload and then retract enough to minimize drag. If the tether rotated counter to the direction the space station traveled it would reduce the velocity at the end of the tether. The length of the tether, height of the space station, rate of rotation would all be adjusted to match the height/speed a launch vehicle could attain. When the tether is not being used to catch payloads, it could be used as an electro-dynamic tether for propulsion and station keeping. Rotation bonus: The station would have some artificial gravity since I expect the center of mass would be somewhere along the tether, though I expect much closer to the station end of the tether.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.
 
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That's called a skyhook by the tether guys. Workable, in theory, with current technology (material strengths), you just need to figure out how to build and deploy the tether. If down-going mass (really momentum change) (i.e. from asteroid/lunar mining?) equals up-going mass/momentum over time, you don't necessarily need to provide propulsion for the skyhook/tether, provided aero drag is minimized or avoided altogether. A skyhook combined with a surface railgun or ram accelerator launch system has been proposed as a low-cost to orbit tech.
 
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so instead of geo-synchronous we'd go for an orbit with a low ground speed, something we could match with the plane. Maybe flying to the end of this tether isn't much different to inflight refueling (except much faster) ?

another day in paradise, or is paradise one day closer ?
 
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rb1957,

Yeah, The expensive part of getting to space is getting out of the atmosphere. Since the tether is rotating backwards, it's ground speed is much lower than the station. The ISS is at an altitude of 400 km, and we probably don't need to be that high, above a 100 km absolute minimum, say 150 km and subtract off the 30 km or so for the first stage and we're working with a 120 km tether, much more workable from an engineering perspective than 23,000 km to geostationary orbit. Once you can obtain a low earth orbit, high efficiency ion thrusters (or again electro-dynamic tethers, why has this propulsion tech never taken off?) could get you to the orbit you want, just not quickly.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.
 
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Dang, that's 23k miles for geostationary orbit, or 35,000 km. -Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.
 
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KirbyWan (Aerospace) (OP) 7 May 19 15:42 "I have ideas about workable space elevators. ..."

Re: Space Elevators

Reportedly, one of the most difficult aspects (*) of a vehicle climbing a tether to reach space is the energy needed by the vehicle. Dreamers imagine beaming microwave or laser energy up the vehicle, as it climbs higher and higher.

[sub](* A loony claim, but let's go with it for now.)[/sub]

The solution is obvious and perfectly trivial.

Install a pulley at the top.

Make the cable twice as long, and form it into a loop.

Then use an electric motor at the bottom to turn the cable. The electric motor can obviously be wired to the grid.

Easy.

Acknowledge that the cable will be twice as long, twice as heavy, under twice the tension, and that's before making it thicker to deal with the added tension. But these are mere details, since "the most difficult aspect" was carrying the necessary energy.

 
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and another thread successfully hi-jacked.

you're welcome !

we're talking more today about returning to the moon. I wonder if a lunar space elevator makes sense ? it'd be easier to accomplish but I think it'd be a very long term investment … but it makes for good wondering.

another day in paradise, or is paradise one day closer ?
 
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(or again electro-dynamic tethers, why has this propulsion tech never taken off?)

I have a colleague, who's probably still in the biz, who did some research work while we were interns at Nasa-Lewis, mostly regarding tethers.

ED tethers work against a magnetic field, like that of Earth's. Far enough away from those fields and you get no propulsion. But, even for satellites, the concept is tricky, because having a long tether means increased chances for collisions with space debris. A lot of trials have failed due to deployment issues, not sure what is up with that. In the comsat biz, they are looking for spacecraft with 10-yr and by now closer to 15 or 20 years lifetimes. At GEO orbits a longer tether is required to get propulsion (and the main component for delta-V is N-S stationkeeping, which I don't think tethers can do, cuz the magnetic field lines are running N-S? Not sure). But anyway, longer tether means bigger odds of collisions and shorter tether life expectancy.

Past that, there have not been any really successful deployments and verification of propulsive tethers. Lots of trials and experiments, lots of failures, a few notable successes - see

and more generally
 
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Torque rods on LEO spacecraft are a thing, I know that all of the Iridium s/c since the first ones had them. But they don't work as well at higher orbits, and most GEO comsats don't use them.

from :

A broader disadvantage is the dependence on Earth's magnetic field strength, making this approach unsuitable for deep space missions, and also more suitable for low Earth orbits as opposed to higher ones like the geosynchronous. The dependence on the highly variable intensity of Earth's magnetic field is also problematic because then the attitude control problem becomes highly nonlinear. It is also impossible to control attitude in all three axes even if the full three coils are used, because the torque can be generated only perpendicular to the Earth's magnetic field vector.[2][3]

Magnetorquers or torque rods are fairly small, compact devices, not tethers.
 
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