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12:24 AM

TildalWave has added an event to this room's schedule.

Stu

2:09 PM

quick question: the Orion test will send the module at speeds of 8.9 km/s on reentry. What would full speed be when returning from the moon? 13 km/s?

TildalWave

@Stu Apollo 13 reentered at 11 km/s so I doubt it would be much more than that, tho there was one instance of an even faster reentry (IIRC Stardust at about 12.5 km/s?)

history.nasa.gov/SP-4029/Apollo_13a_Summary.htm

says 36,210.6 ft/sec = 11.037 km/s

actually Apollo 10 was a tad faster even at 36,397 ft/s

history.nasa.gov/SP-4029/…

And Apollo 16 experienced max deceleration at 7.19 g

briligg

2:29 PM

@TildalWave - re: lunar fuel - isn't magnesium difficult to handle because of its high reactivity? Maybe in a vacuum environment that could be avoided but i remember that high school demonstration.

btw, i now have literally a score of papers to read related to this, largely thanks to you.

TildalWave

@briligg Well you need oxygen to sustain exothermic reaction 2 Mg + O2 → 2 MgO ... in a near-zero atmosphere environment that's not a problem, you could easily use magnesium rods for light and heat (or other uses) if you can control oxygen supply to it.

Actually it's not that difficult to control it even in Earth-like atmosphere, it might just be a whole lot simpler by not using pure magnesium

might be the next best thing to (calcium) carbides that seem to be missing from lunar regolith ;)

briligg

Because there is like 6% Mg overall in the soil, so it is certainly interesting, but i don't know that anyone has really examined that option. Again it is a whole other line of thought. If the whole calutron based idea for separation is viable i suppose it can be used with any ore, which is nice.

TildalWave

magnesium is potentially useful as nanopowder fuel for bipropellants but aluminum is even better if it makes economic sense (it's more difficult to extract)

briligg

Why do you mention above that organics would be needed for such fuels, other than ALICE?

TildalWave

because the Moon is poor in organics (carbon compounds)

briligg

2:41 PM

But i guess the thing is i'm going with the calutron design, and it needs no organics, as far as i can tell. Where in the process do the organics come in?

This whole question has become very sticky because i am not in a position to assess extraction processes.

TildalWave

and because you would likely need some binder for solid mixtures ... you can't simply use metallic nanopowders as they are in a zero atmosphere environment because you have to account for "cold-welding"

and if you use them in oxygen-rich environment then you have to account for monolayer oxidation reducing burn rate ... depends on grain size a lot where is the optimum

briligg

The moon miner manifesto paper posited the powder could be fed using a small amount of hydrogen.

Don't know if that means they were thinking of that in the storage too.

TildalWave

They tried using nano-aluminum in many ways to reduce its viscosity and make it work as a liquid, including some toothpaste-like gels ... that didn't work as expected, was still too viscous. I'm not sure how to mix it with (liquid?) hydrogen and maintain constant mixture density

briligg

There is an unfortunate lack of english-speaking aeronautical engineers in my vicinity i can go pester about this. Or any engineers, really.

TildalWave

it's a conundrum :shrug:

Stu

2:48 PM

@TildalWave thanks pal. 7.19g huh?? that's some serious deceleration.

briligg

I almost bought the Brower paper from the AIAA a while ago, and am still toying with the idea. Because this idea sounds enchanting because of all you mention - "Another technique is a hybrid rocket engine using solid aluminum and liquid oxygen. A conceptual
design for such an engine was proposed by Brower et al. [1]. Their design calls for a hexagonal array of
aluminum bars the length of the combustion chamber. Liquid oxygen would be fed down the bars for
regenerative cooling before reaching the flame at the bar tips. The engine could use oxygen and

And as you pointed out the same can be done with Mg bars, which also sounds great.

briligg

3:14 PM

Eep! Just found this - ads.harvard.edu/books/lbsa 800 pages. And this - archive.org/details/nasa_techdoc_19930004784 400 pages.

Stuff to read on the beach :)

TildalWave

3:24 PM

@briligg I'd instead of solid rods suggest rather porous rods made via vapor deposition since you'd be already extracting aluminum by mass separation ... a sort of "additive manufacturing" where you use aluminum gas and some rotating membrane to create an "aluminum sponge" solid grain with oxidizer path already "built-in"

briligg

oooo...

TildalWave

maybe I should attach ®©™ to the "aluminum sponge" part :)

briligg

methinks i am going to have to try to sort out enough about the calutron model to go to SE's Electrical Engineering site and ask them what they think.

in a while, once i've read enough and have the time...

TildalWave

dunno if that's the site for that ...

for the power / cooling it could actually be one with the other, just place photovoltaics around the inner rim of some crater and cooling pipes with heatsinks in their shadow, then radially switch to the parts that give you one or the other or both at some period of time

you'll even have your own mini-moon phases on the moon :)

briligg

huh. that sounds nice.

what kind of coolant would make sense? is there anything that can be at least partly sourced locally?

TildalWave

3:38 PM

if you can make it work then ionic liquids (liquid salts)?

briligg

sounds good...

TildalWave

Average daytime temperature on the lunar surface is what ... about 107°C? Should work at around 100°C and you don't need it when it's night

briligg

ah, you are thinking of hybridizing the system with the dump-it-on-the-ground idea?

TildalWave

at least not some giant loops, plus you need to conserve stored power during that time

@briligg no I'm thinking what could be achieved with lunar regolith ISRU ... i.e. what's there

any word on mercury on the moon?

metal that's liquid at room temperatures would be of course even better than ionic liquids :)

briligg

what info i have cuts off at chromium, at something under 0.5%

also i guess you get into a chicken and egg problem i guess, you need the equipment to refine the ores to get the coolant to run the equipment...

TildalWave

3:51 PM

You expand gradually, it should be doable without running into the chicken and egg problem (on the Moon no less! LOL)

briligg

i just thought if you were going with the idea that you don't need the coolant at night, you are okay with the idea of trailing the separated stuff out to let it cool?

do the photovoltaics themselves need cooling?

(lightbulb appears)

TildalWave

Yes but it'd be a painstakingly slow process ... but you can just focus on oxygen extraction at first and later upgrade the whole thing. It's essentially same thing you just need more power and better cooling and you're good to go. Eventually, you have industrial scale operation going on there

@briligg thermal expansion will limit their total generating power and there might be upper and lower limits, depends on design ... but if it works in LEO there's no reason it wouldn't on the Moon either

briligg

a coolant system would surely be useful for a number of things, that kind of crater rim design could be integrated with different systems...

making aluminum sponge rods probably needs it...

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