Braking spacecraft in a snow-filled tank?

In summary, a Russian MOD aerospace journal proposed a scheme for hard-landing payloads on the moon using a pipe filled with regolith or water to catch high-speed projectiles. However, this approach has several problems, such as high braking pressures and poor heat insulation. The idea of using loose snow as a braking medium may be more effective, but there are doubts about its feasibility. Further questions also arise regarding the need for guidance and how to prevent the braking medium from being ejected. The calculation for the stopping distance also raises concerns about accuracy. The use of a formula for projectile widths, rather than length, is also questioned. The conversation ends with the acknowledgment that there may not be better equations available for this scenario.
  • #1
trurle
508
206
Reading recently a Russian MOD aerospace journal, i stumbled upon (pretty unrealistic) scheme to hard-land payloads (metal ingots) on moon.
It involve catching 1.7 km/s slugs with the pipe filled by regolith or water, and even more hardcore option of digging up the payloads embedded in the Moon```'s natural regolith layers.
Well, the approach and materials have severe problems.
1) Braking pressures are too high (~0.3 GPa for water, and ~0.4 GPa for fine regolith) - therefore for most payloads soft-landing is more mass-effective option even assuming the payload is surviving.
2) Regolith is too good heat insulator, resulting in large cycle time and may be even regolith sintering/fusing to payload
3) Water is poorly compressible, producing a large pressure spike (water hammer effect)

After thinking a bit, seems "payload trap" filling with loose (40 kg/m3) snow may be much better.
a) The braking pressure is much lower at ~12 MPa
b) The over-pressure pulse is partially dissipated by breaking and melting snowflakes, transmitting less energy on "payload trap" walls.

Severe doubts are remaining. Could anybody help with the items below?
1) Penetration model is very far extrapolation (from the high density bullets striking sand bags to large low-density containers striking snow at double velocity). Is any relevant software/equation for estimating pressures in such impact scenario? I suspect 12 MPa braking pressure for 40 kg/m3 snow at 1.7km/s is not an accurate estimation.
2) Payload container veering off course and colliding with trap wall may be a problem. I can imagine fin-stabilized container self-guiding in core of denser snow supported by less dense snow envelope, but would it be sufficient? Any thoughts about path stabilization at such violent braking?
3) Is it plausible to make low-density snow similar to natural one? Typical snow-making machines which are designed for high throughput produce snow about 450 kg/m3, which is likely too dense for purpose. Ice block grinding method produce snow of ~250 kg/m3. Are any methods for lower-density snow?
4) Is the input shutter to prevent large loss of braking medium (snow?) necessary? Any design alternative to shutter? Need to prevent somehow braking medium from being ejected from input aperture each time a container is received.
5) Likely still need about 1-3% of container to be hydrazine for deorbit from storage orbit and fine guidance. Any chance to develop a fully inert container still hitting a small (few meters at most) aperture?
 

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  • #2
How did you calculate the stopping distance (or, closely linked, the acceleration)?
 
  • #3
mfb said:
How did you calculate the stopping distance (or, closely linked, the acceleration)?
Yes. It was not in the summary sheet because it was an array depending on transfer orbit.
Roughly 235 calibers (for 3 g/cm3 spherical containers) for low orbits.
 
  • #4
Where does that number come from?

Having an unguided bullet approach a base at orbital speeds with an error margin of a few centimeters doesn't sound very safe, by the way.
 
  • #5
mfb said:
Where does that number come from?

Having an unguided bullet approach a base at orbital speeds with an error margin of a few centimeters doesn't sound very safe, by the way.
I use for penetration estimation equation
PenetrationCalibers=2*(2800/DensityOfBrakeMedium)*(DensityOfContainer/9000)*(Speed/750)^2

Regarding guidance margin, i also think the container must be guided. Even in that case, with current technologies margins may be meters.
 
  • #6
That formula can't work well for high speeds. I would expect 1.7 km/s to be high in that context. It is also weird that it uses the width not the length of the projectile.
 
  • #7
mfb said:
That formula can't work well for high speeds. I would expect 1.7 km/s to be high in that context. It is also weird that it uses the width not the length of the projectile.
The measurement of penetration in projectile widths is common in ballistics. Anyway, for this particular calculation the projectile (container) is spherical therefore width and length are the same.
Apart from generic doubts on accuracy (which i also have) do you have better penetration equations?
 
  • #8
I don't have better equations. 1.7 km/s is too fast to use formulas for typical guns but too slow for high velocity approximations (e.g. what matters for most impacts on the ISS).
 

1. How do you brake a spacecraft in a snow-filled tank?

Braking a spacecraft in a snow-filled tank requires a combination of techniques. The first step is to use the thrusters to slow down the spacecraft's velocity. Then, the spacecraft can use its landing gear to make contact with the snow-filled tank, creating friction and further slowing down the spacecraft. Finally, the spacecraft can use parachutes or other aerodynamic devices to safely land on the surface of the tank.

2. Why is it necessary to brake a spacecraft in a snow-filled tank?

Braking a spacecraft in a snow-filled tank is necessary for a safe and controlled landing. Without proper braking, the spacecraft could crash or sustain damage upon impact with the tank's surface. Additionally, braking allows for a more precise landing, which is important for missions that require specific landing locations.

3. What challenges are involved in braking a spacecraft in a snow-filled tank?

One of the main challenges in braking a spacecraft in a snow-filled tank is the lack of friction on the tank's surface. Snow and ice can create a slippery surface, making it difficult for the spacecraft to slow down. Additionally, the extreme temperatures and harsh conditions in the tank can also pose challenges for the spacecraft's braking systems.

4. How do you account for the weight of the snow when braking a spacecraft in a snow-filled tank?

The weight of the snow in the tank must be taken into consideration when braking a spacecraft. This can be achieved by using the spacecraft's thrusters to adjust for the added weight and maintain control during the landing. Additionally, the spacecraft's braking systems are designed to handle the weight of the snow and slow down the spacecraft accordingly.

5. Are there any risks involved in braking a spacecraft in a snow-filled tank?

As with any space mission, there are always risks involved. However, proper planning, testing, and use of advanced technology can help mitigate these risks. The main risk in braking a spacecraft in a snow-filled tank is a loss of control during the landing, which could result in damage to the spacecraft or its payload. This is why extensive testing and simulations are conducted before any spacecraft is sent to land in a snow-filled tank.

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