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Gentle Satellite Recovery Tubes

  [vote for,

It would be useful to be able to more easily recover satellites or their payloads from orbit.

Currently, there are two main ways of getting something back to Earth (or onto the surface of another rocky planet with an atmosphere) after it's been to space:

1) give it equipment to survive atmospheric entry and land on its own [1], or

2) give it equipment to survive atmospheric entry but not landing, including a parachute, and use an airplane to catch it as it's descending under the parachute [2].

Method 1 is mainly suitable for large objects such as crewed spacecraft and rovers, but has been used to return samples to Earth. I only knew of one time this was done deliberately, by Stardust [3]. However, it seems the Soviet Zenit spy satellites' camera-and-film capsules landed on their own [4], and the American Corona satellites' film capsules, which normally used method 2, were also capable of landing on their own [5].

Method 2 is only suitable for small things like sample capsules. This is cheaper than something that could land on its own to build and launch (because it has less mass), but recovery is more difficult because you have to intercept the descending payload with an aircraft. It's also unsuitable for landing on planets other than Earth, because we don't yet have suitable aircraft there.

Both of these methods have a big disadvantage: The vehicle must be designed for reentry from the start.

Sometimes, it would be nice to recover intact a spacecraft that was not designed for reentry. Perhaps some unexplained event (an unusual failure, growth of some form of life, etc.) occurred and we'd like to bring it into a lab to investigate. Perhaps it's at the end of its useful life, but it's carrying some incredibly valuable piece of equipment. Perhaps it's an enemy spy satellite that we'd like to reverse engineer. Sometimes it isn't even a spacecraft, and wasn't designed at all—wouldn't it be wonderful to be able to gently capture an asteroid or a would-be meteor(ite) for study?

This used to be possible using the Space Shuttle, but that is no longer in operation, and SpaceX hasn't developed a recovery system yet (though I have an idea on that that I should post).

Another thing that would be useful is cleaning up debris in orbit, which we don't yet have any practical solution for.

I have the solution!

Have a big tube. The diameter must be larger than the satellite or other object you want to capture, and the length is probably measured in kilometers. It doesn't have to be solid—it can be inflatable, or a tensegrity structure, or something like that. It doesn't have to be all that strong, but it does have to be stiff. The cross-section can have any shape, but I'll assume here that it's circular.

Along the side of it, there is a spline-like bulge all the way along. In operation, the tube has its axis horizontal, with this bulge downward. In the bulge (which is really a channel, from the point of view of the inside of the tube) there is a solution of soap and water. There are also lots of loops of string spaced along the inside of this soapy water channel, maybe one every 100 mm to 10 m or so. Each loop is attached to a winch at the bottom of the channel, so it can be constricted and pulled completely below the surface of the water. Each loop also has several cords attached to it at intervals, which go up to pulleys spaced around the circumference of the tube. Each of these cords, after passing over its pulley, comes back down inside the tube's wall, or on the outside of the tube, and ends up on the same winch, but wound the other way, and probably winding onto a part of the drum with a different circumference, to accommodate different distances they need to travel. In this way, one winch can be used both to pull in the loop and submerge it in the soapy water, and to pull the loop out of the soapy water and stretch it out to encompass most of the width of the tube.

The purpose of this is to slow satellites gently, by having them break through soap bubbles. Each loop of string creates a two-dimensional soap bubble when expanded. Each bubble popped by the satellite takes some energy from it, reducing its speed. This slows the satellite down very gently and saves it from colliding too hard with the atmosphere and burning up. Some of the bubbles won't form properly or will pop prematurely, but that's not a big problem, because there are all the others still.

The advantage of using soap bubbles over a tube full of air is that they're gentler. Air gets pressurized in front of the satellite, which causes it to heat up. Soap bubbles won't do that. Also, each soap bubble dissipates energy in popping, while air needs to flow out of the way after absorbing energy. (Popping releases the bubble's own potential energy, but it takes an activation energy to pop a bubble that's not ready to pop yet, and that energy comes from the satellite's kinetic energy.) Sheets of plastic film might also work, but they're not reusable without being remanufactured.

There are three ways to use such a machine to recover satellites.

First, you can launch it into orbit so that it's a satellite itself. It orbits at a specific altitude and can be used for recovery of many satellites at this altitude. It adjusts its orbit to intercept a given satellite (or piece of space junk). When it's nearly at the intercept, it submerges and then expands all of its loops, making many soap bubbles. The satellite passes through, is slowed, and is thereby deorbited. Due to conservation of momentum, the tube will be pushed in the direction of travel of the satellite it's deorbiting; with clever planning, this can probably be used to maintain its own orbit. It doesn't need to slow the being-deorbited satellite to a stop, just enough that its perigee is within the atmosphere. This role would be best served by a sealed tube (probably inflatable for launchability) with doors on the ends, to avoid excessive evaporation of the liquid. It will also need a liquid that can stay in place in the channel without gravity, or to rotate about its axis to keep the liquid in place centrifugally.

Second, you can launch it suborbitally to deorbit a single satellite. You would have to launch it very precisely to make the intercept, but if you time it right, you could get two potential intercepts with one launch (on the way up and on the way down, with the satellite making one more orbit between the opportunities). This role needs an expandable version, so that it fits into the fairing of the launch vehicle.

Third, you can use it within the upper atmosphere, possibly carried by balloons, to more gently slow a satellite that has been deorbited by one of the previous methods or by its own propulsion, and therefore is going to fall in a known location. In this role, it would be on an angle, so it would need a pump to pump the liquid from the bottom of the channel to the top, to keep a roughly uniform depth along the length, or, more practically, each loop of string could have its own reservoir. At the end of the tube, there could be a detachable soft bag with a parachute attached, which will carry the satellite softly to the ground or to midair retrieval.

N/A [2018-04-24]

notexactly, Apr 24 2018

[1] Atmospheric entry https://en.wikipedi...i/Atmospheric_entry
[notexactly, Apr 24 2018]

[2] Mid-air retrieval https://en.wikipedi...i/Mid-air_retrieval
[notexactly, Apr 24 2018]

[3] Stardust sample return https://en.wikipedi...raft)#Sample_return
[notexactly, Apr 24 2018]

[4] Soviet Zenit spy satellites https://en.wikipedi...i/Zenit_(satellite)
Dropped capsules from orbit containing both cameras and film. No mention of aerial recovery, so it looks like they descended to the ground on their own. [notexactly, Apr 24 2018]

[5] American Corona spy satellites https://en.wikipedi.../Corona_(satellite)
Dropped capsules from orbit containing film only, which were supposed to be caught by a plane as they parachuted down, but could also land on their own. [notexactly, Apr 24 2018]

[Vernon], we can provide the materials for your orbital remanufacturing Near_20Earth_20Orbi...ation_20Corporation
[normzone, Apr 29 2018]


       I'm pretty sure I don't understand why hitting soap bubbles containing presumably some kind of low-density air behind each one is less violent than hitting low-density air at high speed.
RayfordSteele, Apr 24 2018

       I'm pretty sure that in the long run we should put remanufacturing facilities in orbit. Then we would never want any satellites to come back to Earth; we would want to recycle their mass in space, and save the cost it took to get that mass up there in the first place (by not needing to replace an old satellite with a newly-launched satellite).
Vernon, Apr 24 2018

       ^ [+]
FlyingToaster, Apr 24 2018

       This bit here:   

       // In the bulge (which is really a channel, from the point of view of the inside of the tube) there is a solution of soap and water.//   

       ...is where the bubble bursts.   

       You're gonna need a lot of soap.
mitxela, Apr 24 2018

       Outside the atmosphere, there's no air between the bubbles. Inside the atmosphere, the bubbles interrupt and cool the shockwave, as well as absorbing some of the kinetic energy so less goes into heating the air. Alternatively, the tube inside the atmosphere can be evacuated. It doesn't need to be collapsible, because it doesn't get launched by a rocket, so it can be evacuated on the ground prior to launch.
notexactly, Apr 24 2018

       How do you prevent this liquid from almost instantly boiling off into the vacuum?   

       What 2fries said.
RayfordSteele, Apr 25 2018

       How about a stack of engineered expanded foams? then there is a gradient of bubbles with varying hardness. I am intrigued with the idea of shooting a hole saw, though.
wjt, Apr 26 2018

       Yes, but what about the rubber ducks and a loofah?   

       But seriously, only last night I was pondering rockoons to get stuff up there, then have the 'oon bit loiter in the high atmosphere to catch the rock(et) bit on the way down.
not_morrison_rm, Apr 26 2018

       // How do you prevent this liquid from almost instantly boiling off into the vacuum? //   

       That's what the //sealed tube (probably inflatable for launchability) with doors on the ends, to avoid excessive evaporation of the liquid// is for.   

       // How about a stack of engineered expanded foams? then there is a gradient of bubbles with varying hardness. //   

       That might work well. It's similar to the engineered foam crash barriers used on race tracks and such. But how do you make it reusable? One way to make reusable foam would be to make a foam of soap bubbles by blowing a gas through the liquid, but then you have some gas in there, heating up the satellite as it passes through. Maybe helium at a really low pressure would do it.   

       // rockoons to get stuff up there, then have the 'oon bit loiter in the high atmosphere to catch the rock(et) bit on the way down. //   

       I like that idea. How would you get them to maneuver to meet up? Would the rocket have to go around once before coming down?
notexactly, Apr 29 2018

       Err dunno....but I would guess the oon bit might have to come apart before the rocket part blasts off, or the hydrogen filled balloons just catch fire, or maybe it doesn't matter? Hydrogen and balloon material are cheap.   

       Then just release the second oon to catch the rocket on the way down.
not_morrison_rm, Apr 29 2018


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