For Questions That Don't Merit Their Own Thread

[Aghanim]

5 hours ago, sevenperforce said:

Eh, I don't like it. It's not really realistic to mine aluminum to refuel a solid rocket; you can't refuel a solid. Better to have a hybrid rocket full of solid reducer that uses oxidizer from attached tanks as a resource. You can mine for more oxidizer if you want.

That rocket looks like it is a hybrid rocket, as:

• It uses both aluminium and oxidizer as its resources
• It literally says hybrid rocket in the name and in the description

It seems to be inspired from real life research on lunar ISRU: https://forum.nasaspaceflight.com/index.php?topic=14380.0

[shynung]

14 hours ago, sevenperforce said:

It's not really realistic to mine aluminum to refuel a solid rocket; you can't refuel a solid.

You can, if you store the aluminium in powdered form or as pellets. Of course, this means the equipment to refine aluminium for use in a refueable hybrid rocket needs to form powder or pellets, which would make them heavy and complicated.

[sevenperforce]

14 hours ago, Aghanim said:

That rocket looks like it is a hybrid rocket, as:

• It uses both aluminium and oxidizer as its resources
• It literally says hybrid rocket in the name and in the description

It seems to be inspired from real life research on lunar ISRU: https://forum.nasaspaceflight.com/index.php?topic=14380.0

 

5 hours ago, shynung said:

You can, if you store the aluminium in powdered form or as pellets. Of course, this means the equipment to refine aluminium for use in a refueable hybrid rocket needs to form powder or pellets, which would make them heavy and complicated.

The difficulty, I think, is in the whole "packing aluminum into your cylinder" aspect.

[shynung]

47 minutes ago, sevenperforce said:

The difficulty, I think, is in the whole "packing aluminum into your cylinder" aspect.

Think of it as a sugar-KNO3 rocket. The aluminium powder/pellets could be mixed with a setting binder, then poured/cast into the cylinder, which is set afterwards. The tricky part is designing the binder material - it needs to flow while still in the ISRU/refueling equipment, then solidify/set after it's in the cylinder in an acceptable period and manner, kind of like cement.

To be sure, this is kind of a complicated procedure, better suited to a workshop or garage. However, assuming you can set up such a workspace and there's alumina to be mined, this is one way to refuel a Al/LOX hybrid rocket.

[sevenperforce]

20 minutes ago, shynung said:

Think of it as a sugar-KNO3 rocket. The aluminium powder/pellets could be mixed with a setting binder, then poured/cast into the cylinder, which is set afterwards. The tricky part is designing the binder material - it needs to flow while still in the ISRU/refueling equipment, then solidify/set after it's in the cylinder in an acceptable period and manner, kind of like cement.

To be sure, this is kind of a complicated procedure, better suited to a workshop or garage. However, assuming you can set up such a workspace and there's alumina to be mined, this is one way to refuel a Al/LOX hybrid rocket.

Fine for a lunar base but not feasible for a mobile ISRU unit. That was my gripe with the one linked above.

[shynung]

1 minute ago, sevenperforce said:

Fine for a lunar base but not feasible for a mobile ISRU unit. That was my gripe with the one linked above.

I agree, that system is not really suitable for a mobile onboard ISRU. Much better for a lunar base.

The silver lining on that system is that the process requires lunar regolith instead of water(LH2/LOX), of which the former is much more abundant than the other. I can see an Al/LOX hybrid-rocket-powered lunar SSTO shuttle being feasible with that setup.

[cubinator]

When Apophis flies past Earth in 2029, it will be closer than the geostationary belt. What are the odds of it knocking out some satellites as it passes by?

[DerekL1963]

3 hours ago, cubinator said:

When Apophis flies past Earth in 2029, it will be closer than the geostationary belt. What are the odds of it knocking out some satellites as it passes by?

Essentially zero.  Not impossible, but improbable as all [curse word].

[_Augustus_]

23 hours ago, cubinator said:

When Apophis flies past Earth in 2029, it will be closer than the geostationary belt. What are the odds of it knocking out some satellites as it passes by?

Very low, but if we have 10000 sats by that time, who knows?

[wumpus]

On 6/6/2017 at 4:27 PM, cubinator said:

When Apophis flies past Earth in 2029, it will be closer than the geostationary belt. What are the odds of it knocking out some satellites as it passes by?

Less likely than any individual satellite getting taken out by the combined crush of all other satellites orbiting the planet during any specific hour.  Way less, considering the ones that crash are almost certainly in LEO and the GSO birds are vastly further apart (sure, there's always the difference in the size of Apophis vs. most satellites, but  I suspect the ratio of Apophis vs. a regular satellite isn't quite as big as the ratio of LEO satellite spacing vs. GSO spacing).

Don't worry about it.

[StupidAndy]

what would happen if you pull all the protons out of all the atoms of somebody?

[StrandedonEarth]

1 hour ago, StupidAndy said:

what would happen if you pull all the protons out of all the atoms of somebody?

All the electrons would repel themselves out and you'd be left with a blob of neutronium?

[StupidAndy]

2 minutes ago, StrandedonEarth said:

All the electrons would repel themselves out and you'd be left with a blob of neutronium?

what a wonderful sight that would be...

but would you just instantly disappear, or would something else happen?

[K^2]

2 hours ago, StupidAndy said:

but would you just instantly disappear, or would something else happen?

Neutrons would rapidly decay, lacking sufficient gravity to stabilize neutron matter, and you'd disappear into a rapidly expanding, superheated cloud of hydrogen plasma.

[StupidAndy]

2 minutes ago, K^2 said:

Neutrons would rapidly decay, lacking sufficient gravity to stabilize neutron matter, and you'd disappear into a rapidly expanding, superheated cloud of hydrogen plasma.

an even BETTER sight!

[peadar1987]

Is the flammability of materials in oxygen determined solely by the partial pressure of the oxygen, or will a buffer gas change things? i.e. are things more or less flammable in a 20kPa oxygen atmosphere than in normal air at the same temperature?

[K^2]

5 minutes ago, peadar1987 said:

Is the flammability of materials in oxygen determined solely by the partial pressure of the oxygen, or will a buffer gas change things? i.e. are things more or less flammable in a 20kPa oxygen atmosphere than in normal air at the same temperature?

Buffer gas will take away some of the heat from the flame, so yeah, things will definitely be more flammable in pure oxygen even at the same partial pressure of the later.

[Green Baron]

A question i always had since i first heard that: why did they fill the first american capsules with oxygen ? What's the benefit over all the down sides (corrodes, reacts happily, ...)

[Steel]

13 minutes ago, Green Baron said:

A question i always had since i first heard that: why did they fill the first american capsules with oxygen ? What's the benefit over all the down sides (corrodes, reacts happily, ...)

I believe it was partly a weight-saving measure. To have a mixed-gas atmosphere you'd need an additional set of tanks and plumbing for nitrogen as well as oxygen, along with an additional control system to maintain the correct mixtures and pressures.

Edited June 12, 2017 by Steel

[Green Baron]

Hm.... one could use pure air from a single tank. or nitrogen if the "inhabitants" had an independent oxygen supply ...

 

[peadar1987]

I think it also had to do with the risk of the Bends in the event of depressurisation.

[Steel]

9 hours ago, Green Baron said:

Hm.... one could use pure air from a single tank. or nitrogen if the "inhabitants" had an independent oxygen supply ...

 

But since the spacecraft already had onboard oxygen tanks for the fuel cells and such, that's still an additional tank. Also personal oxygen tanks are not a great idea, there's more chance of something going wrong (assuming you have more than one astronaut), plus you have to carry an oxygen tank with you at all times which gets a little unwieldy (also as I said before, the spacecraft tend to carry oxygen anyway)

7 hours ago, peadar1987 said:

I think it also had to do with the risk of the Bends in the event of depressurisation.

It is partly, but Soyuz has used a mixed gas atmosphere the whole time and been fine. In general if you have a cabin decompression and you're not properly suited up you're pretty much dead anyway, so the bends isn't so much of a problem.

 

EDIT: To be honest, there's no real reason why American spacecraft couldn't be have been designed to have mixed gas atmosphere (see Soyuz), it's just that the Americans didn't really see having a pure oxygen atmosphere as a big problem until the Apollo 1 fire. By that point adding the extra mass and putting the program on hold to re-engineer plumbing e.t.c in order to convert Apollo to mixed gas was a big enough deal to stop them doing it (they wanted to reach the moon within 3 years at that point after all!)

Edited June 12, 2017 by Steel

[K^2]

It was, indeed, about saving weight. Primarily, that of the structure, as there is a lot less mechanical stress at 1/5th the pressure. That means many walls and windows can be made thinner. Also, while you can recycle most of the nitrogen, you need some to restore any losses of pressure. Especially, if space walks are planned. So you do indeed bring a nitrogen tank along, not just oxygen.

Edit: I don't think bends are a factor. Not enough usefull consciousness time in event of pressure loss to matter.

Edited June 13, 2017 by K^2

[Green Baron]

1 hour ago, K^2 said:

It was, indeed, about saving weight. Primarily, that of the structure, as there is a lot less mechanical stress at 1/5th the pressure. That means many walls and windows can be made thinner. Also, while you can recycle most of the nitrogen, you need some to restore any losses of pressure. Especially, if space walks are planned. So you do indeed bring a nitrogen tank along, not just oxygen.

Edit: I don't think bends are a factor. Not enough usefull consciousness time in event of pressure loss to matter.

Yep, in case of complete pressure loss one only has a few seconds before falling unconscious. It's not like holding your breath.

I just didn't expect a small capsule, designed for a rocket powered ascent and an atmosphere reentry from the mun, to have structural problems with an internal pressure of let's say 0.7 or 0.8 atmospheres.

[K^2]

2 hours ago, Green Baron said:

I just didn't expect a small capsule, designed for a rocket powered ascent and an atmosphere reentry from the mun, to have structural problems with an internal pressure of let's say 0.7 or 0.8 atmospheres.

Re-entry deceleration is typically well under 10g. Apollo CM has diameter of 3.9m and mass of 5557 kg. Pressure of just 0.5 atm against this cross-section applied to the full mass of the module already gives you well over 10g. So the net stress due to internal pressure is actually greater than peak re-entry stress.

Granted, structure has to withstand brief surges in stress that greatly exceed this value, but much of the re-entry stress can be absorbed by the frame. And while the frame can also pick up some of the stress from the internal pressure, much of it is up to the skin to maintain. That will have all kinds of places where stress can accumulate, significantly exceeding average across the structure. Nuances upon nuances.

Point is, stress due to internal pressure is by no means insignificant in terms of requirements for structural integrity. Lowering internal pressure to one fifth would definitely allow for a lighter module. And even a few kilograms you save on the CM is literal metric tons of savings on the first stage.