The Trouble of ISRU Refueling NTR Spacecraft

[Spacescifi]

NTR spacecraft seem ideal for orbit to orbit and low gravity moon travel.

 

Refueling? 

 

Tricky and challenging.

Why?

According to scott manley to get the highest ISP by running your reactor hot as you can without damaging it you need LH.

Apparently higher atomic elements are more likely to MELT the reactor.

To get LH you must travel to a source, and extract and cool the hydrogen gained into LH.

If hydrogen is NOT available you run the chance of melting ordamaging your reactor from heat overload from using a denser atomic chemical...unless you go super slow....which has issues of it's own due to crew health.

 

Seems to me one easy solution is to keep spare LOX in storage and use regularLH/LOX chemical rocketry or anu other chemical with LOX when you do ISRU and hydrogen is not reasily available to mine.

 

So using known tech, any spacecraft exploring our home system will need BOTH nuclear and chemical rockets.

NTR for orbit to orbit and hydrogen ISRU when available, and stored LOX to use for chemical rockets if hydrogen is not available.

 

Best not to put all eggs in one basket I think.

 

What do you know on this? Did I understand this right?

 

Locations hydrogen is hard to come by:

1. The moon....we hope it has enough but it is limited.

Mercury: I dunno. I think it may have low if any ice at all.

Venus: Wouldbe easier to die trying to mine hydrogen here than to mine it.

 

Places Hydrogen IS available in other than Earth:

G

Jupiter, Neptune. Uranus, icy comets and asteroids. Likely several outlying moons farther from sun.

Edited May 10, 2021 by Spacescifi

[Xd the great]

Nuclear rocket engines work by heating up the propellant via a nuclear reactor, then expanding it out of a nozzle

Theoretically, you can use any fluid as a propellant. Of course, LH2 has highest ISP because of its low molecular weight.

To be honest, I suspect other fluids like liquid nitrogen or liquid oxygen may also work. 

[Spacescifi]

4 minutes ago, Xd the great said:

Nuclear rocket engines work by heating up the propellant via a nuclear reactor, then expanding it out of a nozzle

Theoretically, you can use any fluid as a propellant. Of course, LH2 has highest ISP because of its low molecular weight.

To be honest, I suspect other fluids like liquid nitrogen or liquid oxygen may also work. 

 

Yes they will, but only within thermal limts since those chemicals run hotter than cool hydrogen does.

 

And LOX will probably eat up a reactor like a big guy eats a pizza solo.

Some chemicals erode reactors bad...others not really.

Edited May 10, 2021 by Spacescifi

[kerbiloid]

The ions can be held by magnetic field.

Edited May 10, 2021 by kerbiloid

[Piscator]

When you're at the point of considering using liquid nitrogen or oxygen, you might as well consider water. It's easier to store and a lighter molecule.

[Spacescifi]

2 minutes ago, Piscator said:

When you're at the point of considering using liquid nitrogen or oxygen, you might as well consider water. It's easier to store and a lighter molecule.

 

Water is a good option....but remember just how complex this whole siituation is.

1. Big LH tank for NTR.

2. Multiple ISRU tanks for each different propellant you are likely to try and ISRU.

Cannot just go around shoving any propellant we want in any tank.

Ideally we could just use inflatable bladders as tanks to save on inertial mass resistance to enginet thrust.

[Piscator]

I'm not sure we're quite on the same page here. My comment was meant in reference to the suggestion of using liquid nitrogen/oxygen as reaction mass rather than hydrogen. My point was that water would probably be a better choice, since it's easier to store and has a lower molecular mass than both of those gasses, thus providing a better ISP. I was not suggesting to use it in any ISRU processes whatsoever.

The ISP of a NTR using water would probably be somewhat lower than that of a hydrolox engine (since both produce the same exhaust, but a reactor needs to run cooler to keep it from melting), but it might still be decent enough to outweigh the hassle of having to work with molecular hydrogen.

That said, I'm pretty sure you wouldn't want a chemical and a (separate) nuclear propulsion system on your spaceship, since the additional mass would likely negate any benefits the individual systems would have.

[jimmymcgoochie]

NTRs can run on many things besides hydrogen- water, ammonia, CO2, methane... Hydrogen is the obvious choice because it’s very light (so can be accelerated more = higher ISP), very cold (cools the very hot nuclear reactor) and is also a neutron moderator so it actually increases the rate of nuclear fission- the combination of increased reaction rate and increased cooling makes it (relatively!) simple to operate as the flow of hydrogen directly controls the reactor output in a linear and controlled manner, though it also means you’ll need to throttle up and down slowly to avoid damaging the reactor by cutting the fuel flow and overheating it.

Water, ammonia and methane are options as all are fairly light molecules containing hydrogen- methane is lighter and cryogenic so its ISP would be higher, and can be used for chemical rockets too, ammonia can manage a decent ISP and can be found in solid ices in some parts of the solar system, but water is more dense, more useful for humans and also more readily available without the need for ISRU systems as water ice exists all over the Solar system, whereas methane and ammonia would need to be found in the rare places they exist or made via ISRU.

All of this is ignoring the huge advantage hydrogen has over literally everything else as NTR propellant in terms of raw ISP, which can get over 900 with a conventional solid-core NTR; the hotter the reactor can run, the higher the ISP can go. Making that hydrogen by melting then splitting water ice is power intensive, yes, but if you have a multi-gigawatt nuclear reactor for propulsion then tapping just a few percent of that power to generate electricity will take care of that, plus waste heat can be used to melt more ice.

Back to the OP’s point about what to do with the oxygen if you’re running a hydrogen NTR- some of it can be injected into the engine as a kind of afterburner, increasing thrust but reducing ISP; see LANTR. If you’re talking about a ship with a crew aboard, they’ll need oxygen too so some can go to keeping them alive. Finally, any nuclear ship will have some kind of secondary propulsion system for when firing up the reactor wouldn’t be worth it- nuclear reactors can’t just be turned on and off on a whim, and they’ll likely have a limited number of start-ups as well as the inherent risks of starting up a nuclear reactor; in some cases it would be better to have a conventional chemical rocket burning e.g. hydrolox, so that excess liquid oxygen could be useful for that.

[kerbiloid]

51 minutes ago, jimmymcgoochie said:

very cold (cools the very hot nuclear reactor)

Not because it's cold, but because it has enormous heat capacity.
It's not much cooler than LO, LN, etc.

Edited May 10, 2021 by kerbiloid

[jimmymcgoochie]

30 minutes ago, kerbiloid said:

Not because it's cold, but because it has enormous heat capacity.
It's not much cooler than LO, LN, etc.

“Not much cooler”- in a very similar way that human body temperature is “not much cooler” than boiling water (373K-330K=63K difference, 90K-33K=57K difference for oxygen/hydrogen boiling points). Liquid hydrogen is the second coldest liquid around- only liquid helium is colder- which combined with all the other advantages makes it the best fuel for NTRs by a sizeable margin; only its poor density lets it down.

[kerbiloid]

3 minutes ago, jimmymcgoochie said:

“Not much cooler”- in a very similar way that human body temperature is “not much cooler” than boiling water (373K-330K=63K difference, 90K-33K=57K difference for oxygen/hydrogen boiling points). Liquid hydrogen is the second coldest liquid around- only liquid helium is colder- which combined with all the other advantages makes it the best fuel for NTRs by a sizeable margin; only its poor density lets it down.

The temperature of a substance has nothing to do about its cooling properties.

Its heat capacity decides.
 

And hydrogen has enormous value of it.

https://en.wikipedia.org/wiki/Table_of_specific_heat_capacities

Spoiler

Table of specific heat capacities at 25 °C (298 K) unless otherwise noted.^{[citation needed]}

Substance	Phase	Isobaric mass heat capacity cP J⋅g−1⋅K−1	Isobaric molar heat capacity CP,m J⋅mol−1⋅K−1	Isochore molar heat capacity CV,m J⋅mol−1⋅K−1	Isobaric volumetric heat capacity CP,v J⋅cm−3⋅K−1	Isochore atom-molar heat capacity in units of R CV,am atom-mol−1
Substance	Phase	Isobaric mass heat capacity cP J⋅g−1⋅K−1	Isobaric molar heat capacity CP,m J⋅mol−1⋅K−1	Isochore molar heat capacity CV,m J⋅mol−1⋅K−1	Isobaric volumetric heat capacity CP,v J⋅cm−3⋅K−1	Isochore atom-molar heat capacity in units of R CV,am atom-mol−1
Hydrogen	gas	14.30	28.82			1.23 R
Helium	gas	5.1932	20.7862	12.4717		1.50 R
Ammonia	liquid	4.700	80.08		3.263	3.21 R
Lithium at 181 °C[6]	liquid	4.379	30.33		2.242	3.65 R
Water at 100 °C	liquid	4.1813	75.327	74.53	4.2160	3.02 R
Water at 25 °C	liquid	4.1813	75.327	74.53	4.1796	3.02 R
Lithium	solid	3.58	24.8		1.912	2.98 R
Animal tissue (incl. human)[2]	mixed	3.5			3.7*
Paraffin wax C25H52	solid	2.5 (ave)	900		2.325	1.41 R
Ethanol	liquid	2.44	112		1.925	1.50 R
Polyethylene (rotomolding grade)[9][10]	solid	2.3027
Gasoline (octane)	liquid	2.22	228		1.64	1.05 R
Methane at 2 °C	gas	2.191	35.69			0.85 R
Methanol[7]	liquid	2.14	68.62			1.38 R
Water at 100 °C (steam)	gas	2.080	37.47	28.03		1.12 R
Water at −10 °C (ice)[3]	solid	2.05	38.09		1.938	1.53 R
Beryllium	solid	1.82	16.4		3.367	1.97 R
Molten salt (142–540 °C)[8]	liquid	1.56			2.62
Sodium	solid	1.230	28.23			3.39 R
Nitrogen	gas	1.040	29.12	20.8		1.25 R
Neon	gas	1.0301	20.7862	12.4717		1.50 R
Magnesium	solid	1.02	24.9		1.773	2.99 R
Hydrogen sulfide H2S[4]	gas	1.015B	34.60			1.05 R
Air (typical room conditionsA)	gas	1.012	29.19	20.85	0.00121	~ 1.25 R
Air (Sea level, dry, 0 °C (273.15 K))	gas	1.0035	29.07	20.7643	0.001297	~ 1.25 R
Oxygen	gas	0.918	29.38	21.0		1.26 R
Aluminium	solid	0.897	24.2		2.422	2.91 R
Glass[3]	solid	0.84			2.1
Carbon dioxide CO2[4]	gas	0.839B	36.94	28.46		1.14 R
Granite[3]	solid	0.790			2.17
Graphite	solid	0.710	8.53		1.534	1.03 R
Silica (fused)	solid	0.703	42.2		1.547	1.69 R
Titanium	solid	0.523	26.060		2.6384	3.13 R
Argon	gas	0.5203	20.7862	12.4717		1.50 R
Diamond	solid	0.5091	6.115		1.782	0.74 R
Steel	solid	0.466			3.756
Chromium	solid	0.449	23.35			2.81 R
Iron	solid	0.412	25.09[5]		3.537	3.02 R
Zinc[3]	solid	0.387	25.2		2.76	3.03 R
Copper	solid	0.385	24.47		3.45	2.94 R
Arsenic	solid	0.328	24.6		1.878	2.96 R
Silver[3]	solid	0.233	24.9		2.44	2.99 R
Cadmium	solid	0.231	26.02			3.13 R
Tin	solid	0.227	27.112		1.659	3.26 R
Antimony	solid	0.207	25.2		1.386	3.03 R
Mercury	liquid	0.1395	27.98		1.888	3.36 R
Tungsten[3]	solid	0.134	24.8		2.58	2.98 R
Lead	solid	0.129	26.4		1.44	3.18 R
Gold	solid	0.129	25.42		2.492	3.05 R
Bismuth[3]	solid	0.123	25.7		1.20	3.09 R
Uranium	solid	0.116	27.7		2.216	3.33 R

 

[sevenperforce]

3 hours ago, jimmymcgoochie said:

“Not much cooler”- in a very similar way that human body temperature is “not much cooler” than boiling water (373K-330K=63K difference, 90K-33K=57K difference for oxygen/hydrogen boiling points). Liquid hydrogen is the second coldest liquid around- only liquid helium is colder- which combined with all the other advantages makes it the best fuel for NTRs by a sizeable margin; only its poor density lets it down.

The propellant entry temperature for an NTR is not really particularly important, actually. The NTR doesn't particularly care what temperature the propellant is before it enters; it merely cares what temperature it can reach before melting.

9 hours ago, Spacescifi said:

According to scott manley to get the highest ISP by running your reactor hot as you can without damaging it you need LH.

Apparently higher atomic elements are more likely to MELT the reactor.

No, that's not true. A solid-core NTR has the same operating temperature whether it's running on liquid hydrogen, liquid methane, liquid nitrogen, or liquid milk. Seriously. You can put anything you want into an NTR and it will still have the same core operating temperature.

Liquid hydrogen is best for NTRs not because it helps with cooling (although yes, you do need SOME regenerative cooling to keep your combustion chamber intact), but because it produces the maximum  specific impulse at any given operating temperature. If you're running an old-fashioned NERVA at ~2100 K, liquid hydrogen gives you the highest specific impulse of any propellant. If you're running a ceramic metal composite like Dumbo at ~2500 K, liquid hydrogen gives you the highest specific impulse of any propellant. If you're using a rotating pebble-bed engine like Timberwind at just under 3000 K, liquid hydrogen gives you the highest specific impulse of any propellant.

Any cryogen (or even water) will provide ample cooling for your engine; the engine operating temperature is limited by the engine design, not by the propellant choice. Liquid hydrogen is just the most efficient choice, primarily because of its low molecular weight. However, liquid hydrogen also sucks because it is so fluffy.

If you're writing a sci-fi where they are using ISRU to refill the propellant tanks of an NTR-powered spacecraft, keep in mind that your vehicle's propellant capacity is going to be volume-limited, not mass-limited. Depending on the size of your tanks, you may end up with more delta-v if you fill up with methane or ammonia or even plain old water.

[wumpus]

36 minutes ago, sevenperforce said:

Any cryogen (or even water) will provide ample cooling for your engine; the engine operating temperature is limited by the engine design, not by the propellant choice. Liquid hydrogen is just the most efficient choice, primarily because of its low molecular weight. However, liquid hydrogen also sucks because it is so fluffy.

I brought this up in the "using dirt for a NTR".  Using water in a NTR will give you *less* Isp than hyrdolox, because hydrolox is typically run fuel rich for higher efficiency.  Use anything heavier, and things get worse (CO₂ will give you much lower Isp than kerolox).

Also don't forget that turning off an NTR is non-trivial.  The reactor will keep reacting, and thus still require cooling.  So you have to keep pumping out propellant through your open loop cooling system at lower and lower temperature.  And this all happens when your wet mass is lowest and you are expecting maximum return for your Isp, but not getting it.  Simply ejecting the fuel rods (have several single use fuel rods) may be an option.

[Starman4308]

My understanding is similar to that of @sevenperforce: most of the factors discussed above are irrelevant. The exhaust velocity of a rocket engine largely depends on three factors:

1) Specifics of the combustion chamber and nozzle geometry, which I will largely ignore.

2) Molecular mass of the exhaust gases: lighter molecules travel faster at the same temperature.

3) Temperature of the exhaust gases at nozzle entry: higher temperatures mean higher particle velocities.

The lowest molecular mass exhaust gas you can find is hydrogen: H2, at 2 g/mol. The next best exhaust gases are all substantially heavier, e.g. methane at 16 g/mol, water at 18 g/mol.

The advantage of NTRs is that you can have a pure hydrogen exhaust: even though the temperature is often lower than a comparable hydrolox engine due to more sensitive machinery, the very lightweight exhaust gases mean much, much better specific impulse.

While you can still get acceptable specific impulses from methane and ammonia in a NTR, that's largely because those gases will often dissociate and produce some hydrogen in the exhaust. Water is a poor NTR propellant, as it's very stable and you get very little dissociation.

Similarly, in chemical engines, you often see non-stoichiometric fuel:oxidizer ratios to bring down the average molecular mass of exhaust gases. Hydrolox (hydrogen + oxygen) rockets generally run very fuel-rich, such that the exhaust has large amounts of unburned hydrogen in it.

[kerbiloid]

https://en.wikipedia.org/wiki/De_Laval_nozzle

[DDE]

10 hours ago, Xd the great said:

Of course, LH2 has highest ISP because of its low molecular weight.

Hilariously, a high-temperature dissociation effect means hydrogen deuteride has a marginally higher ISP.

[Spacescifi]

6 hours ago, sevenperforce said:

The propellant entry temperature for an NTR is not really particularly important, actually. The NTR doesn't particularly care what temperature the propellant is before it enters; it merely cares what temperature it can reach before melting.

No, that's not true. A solid-core NTR has the same operating temperature whether it's running on liquid hydrogen, liquid methane, liquid nitrogen, or liquid milk. Seriously. You can put anything you want into an NTR and it will still have the same core operating temperature.

 

 

Hahaha! You may regret saying that. Because we are about to boldly go where probably no scifi has gone before.

"Alright guys, I know you're sad about our two engineers dying from fixing the engine, but we owe our lives to them."

"Shall we store the bodies for burial when get back to Earth?"

"Do not throw away what you can still use. We are running low on propellant. We have already burned through half our orange juice and vodka reserves. I suggest we....boil them and use the liquid as extra propellant. That way we can save on our more precious LH propellant."

"You're a sick man Cap."

"Hey...I just want to go home and I know you do. Whatever it takes. It's either that or lower our chances and we all die anyway."

 

So how much ISP and what kind of thrust or disassociation can we get out of a half liquid ton of milk, a half ton of orange juice, and 3 gallons of blood plus whatever is left of the cadavers that was boiled into mush and burned as propellant LOL?

Edited May 10, 2021 by Spacescifi

[KSK]

6 hours ago, wumpus said:

I brought this up in the "using dirt for a NTR".  Using water in a NTR will give you *less* Isp than hyrdolox, because hydrolox is typically run fuel rich for higher efficiency.  Use anything heavier, and things get worse (CO₂ will give you much lower Isp than kerolox).

Also don't forget that turning off an NTR is non-trivial.  The reactor will keep reacting, and thus still require cooling.  So you have to keep pumping out propellant through your open loop cooling system at lower and lower temperature.  And this all happens when your wet mass is lowest and you are expecting maximum return for your Isp, but not getting it.  Simply ejecting the fuel rods (have several single use fuel rods) may be an option.

I’m not sure that the point about non-trivial turning off is correct. I imagine that NTR designs have progressed since the days of Project Rover, but (simplistically) the early designs used a combination of propellant flow and control drums to control the reactor. 
 

Hydrogen is a pretty good moderator so the more hydrogen going through the reactor, the greater the fission rate. The control drums were basically rods coated with a neutron reflector around a quarter of their circumference. Point the reflector into the reactor and the fission rate increases, turn the reflector away and the rate decreases because more neutrons are absorbed or can escape.

Net result, powering the reactor down is reasonably straightforward and multiple shutdowns and restarts of the same reactor were demonstrated during Rover.

There will be residual heat generated by fission product decay of course but I’m not sure if that would require active cooling. Even then, I’m speculating that it would be possible to fit the reactor with a closed loop cooling system (devote some of the channels through the reactor to coolant rather than propellant, lead coolant through a radiator or heat exchange it against a secondary coolant which then passes through the radiator.)

46 minutes ago, Spacescifi said:

 

Hahaha! You may regret saying that. Because we are about to boldly go where probably no scifi has gone before.

"Alright guys, I know you're sad about our two engineers dying from fixing the engine, but we owe our lives to them."

"Shall we store the bodies for burial when get back to Earth?"

"Do not throw away what you can still use. We are running low on propellant. We have already burned through half our orange juice and vodka reserves. I suggest we....boil them and use the liquid as extra propellant. That way we can save on our more precious LH propellant."

"You're a sick man Cap."

"Hey...I just want to go home and I know you do. Whatever it takes. It's either that or lower our chances and we all die anyway."

 

So how much ISP and what kind of thrust or disassociation can we get out of a half liquid ton of milk, a half ton of orange juice, and 3 gallons of blood plus whatever is left of the cadavers that was boiled into mush and burned as propellant LOL?

Slightly under what you’d get from a ton of water, plus three gallons of water plus however much water you can freeze dry out of two corpses.

I wouldn’t pour milk straight into the reactor if I could avoid it - too much residual solid to coke up the tubes. Flash distilling the water out first though should be possible given that access to high quality vacuum is really not a problem aboard a spaceship.

I think it would also be possible to ‘space cremate’ the corpses. Extract the water, keep the remains for respectful burial, keeping or scattering.

Edited May 10, 2021 by KSK

[FleshJeb]

57 minutes ago, Spacescifi said:

Because we are about to boldly go where probably no scifi has gone before.

Using a corpse for propellant is the ethical equivalent of "feeding the tree" in the Integral Trees, or reclaiming the "gift of your body's water" in Dune. It's not that dissimilar from Soylent Green, except there was no consent involved. While I've read a generation-ship's worth of science fiction and can't specifically recall corpses being used as propellant, I'm certain it's been done before, but perhaps I found it so non-shocking that I didn't note it.

Personally, if I believed in an afterlife, I'd be giggling my non-corporeal butt off as my component parts were blown out the engine. It's the most exquisite "burial at sea" I can think of. (Space travel will almost certainly be following naval traditions, because all lasting traditions are pragmatic, and are a product of the circumstances, rather than the other way around. You even could build a very fun religion around the spiritual/poetic aspects of being reaction mass.)

[insert_name]

2 hours ago, Spacescifi said:

 

Hahaha! You may regret saying that. Because we are about to boldly go where probably no scifi has gone before.

 

This is actually a relatively routine procedure on some 40k starships, assuming that they aren't fed back into the life support system, albeit with fusion heating instead of fission

[YNM]

20 hours ago, Spacescifi said:

To get LH you must travel to a source, and extract and cool the hydrogen gained into LH.

[...]

Seems to me one easy solution is to keep spare LOX in storage and use regular LH/LOX chemical rocketry or any other chemical with LOX when you do ISRU and hydrogen is not reasily available to mine.

Where do you get the oxygen again ?

Also, if you still have the LH2 to burn with LOX, why not just feed it into the NTR ?

Edited May 11, 2021 by YNM

[Spacescifi]

5 hours ago, KSK said:

I’m not sure that the point about non-trivial turning off is correct. I imagine that NTR designs have progressed since the days of Project Rover, but (simplistically) the early designs used a combination of propellant flow and control drums to control the reactor. 
 

Hydrogen is a pretty good moderator so the more hydrogen going through the reactor, the greater the fission rate. The control drums were basically rods coated with a neutron reflector around a quarter of their circumference. Point the reflector into the reactor and the fission rate increases, turn the reflector away and the rate decreases because more neutrons are absorbed or can escape.

Net result, powering the reactor down is reasonably straightforward and multiple shutdowns and restarts of the same reactor were demonstrated during Rover.

There will be residual heat generated by fission product decay of course but I’m not sure if that would require active cooling. Even then, I’m speculating that it would be possible to fit the reactor with a closed loop cooling system (devote some of the channels through the reactor to coolant rather than propellant, lead coolant through a radiator or heat exchange it against a secondary coolant which then passes through the radiator.)

Slightly under what you’d get from a ton of water, plus three gallons of water plus however much water you can freeze dry out of two corpses.

I wouldn’t pour milk straight into the reactor if I could avoid it - too much residual solid to coke up the tubes. Flash distilling the water out first though should be possible given that access to high quality vacuum is really not a problem aboard a spaceship.

I think it would also be possible to ‘space cremate’ the corpses. Extract the water, keep the remains for respectful burial, keeping or scattering.

 

4 hours ago, FleshJeb said:

Using a corpse for propellant is the ethical equivalent of "feeding the tree" in the Integral Trees, or reclaiming the "gift of your body's water" in Dune. It's not that dissimilar from Soylent Green, except there was no consent involved. While I've read a generation-ship's worth of science fiction and can't specifically recall corpses being used as propellant, I'm certain it's been done before, but perhaps I found it so non-shocking that I didn't note it.

Personally, if I believed in an afterlife, I'd be giggling my non-corporeal butt off as my component parts were blown out the engine. It's the most exquisite "burial at sea" I can think of. (Space travel will almost certainly be following naval traditions, because all lasting traditions are pragmatic, and are a product of the circumstances, rather than the other way around. You even could build a very fun religion around the spiritual/poetic aspects of being reaction mass.)

 

Oh...this could be still be untrodden territory for scifi.

Consider....are they prepped for boiling cadavers and using them as propellant?

No.

Which means....the boiler they do have is too small for a cadaver, let alone two. Which means some poor guy or gal is going to have to 'disassemble'  them...piece by piece. IN ZERO G! Messy and gross is an understatement.

Do they have medical saws aboard? Hope so. Otherwise we are talking cutlery.

Don't envy this person...at all. Probably will suffer from PTSD after. Even worse if they lack medical training and or the cadaver is opposite gender and they had a romantic relationship with them in the past or were developing one. Even if they were not, how do you explain to your significant other back home on Earth what you did to survive.? You don't....not easily probably.

Also somehow the people responsible must transport the hot boiled soup of the deceased, likely by unbolting and transporting the boiler itself to a place to pour the contents into a spare propellant tank for miscellaneous propellants.

 

1 hour ago, YNM said:

Where do you get the oxygen again ?

Also, if you still have the LH2 to burn with LOX, why not just feed it into the NTR ?

 

Exactly.

If stored you can do that. But when you run out?

ISRU is your only option. The problem is how many different spare empty tanks do you need? There are more options than you can really put tankage space form

If you are relying on LOX and LH then those are the only resources you hunt for. Since an LH tank as far as I know is not something you want to mix up with other propellants, and definitely not an LOX tank...because of possible combustion/explosive reactions.

So there is a limit to tge variety and number of spare ISRU tanks you can realistically carry on any spaceship.

One design I think could work well is an oblong vessel with an inflatable bladder at it's center of mass.

Ideally it would find an icy comet or icy asteroid, extract as much water as possible and fill up the bladder balloon.

So that you have an oblong vessel with a massive balloon in the center connecting both halves of the vessel, since it has more volume to hold propellant than the actual vessel's interior hull.

Fat and ugly? Sure.

Effective? Very if designed properly with the best materials for the job.

Edited May 11, 2021 by Spacescifi

[YNM]

1 minute ago, Spacescifi said:

If stored you can do that. But when you run out?

You know that we only refuel nuclear reactors after years and years in use already, right ? Meanwhile we spent a stage full of chemical propellants just a few minutes after leaving the ground (sometimes enough to make sure they can land back and be reused but after that that's about it).

Try to read again what exactly I was asking.

[Spacescifi]

2 minutes ago, YNM said:

You know that we only refuel nuclear reactors after years and years in use already, right ? Meanwhile we spent a stage full of chemical propellants just a few minutes after leaving the ground (sometimes enough to make sure they can land back and be reused but after that that's about it).

Try to read again what exactly I was asking.

 

I did.

If you have LOX you can use it. If you do not....ISRU. Which is mission difficult because you need the mission to pay off more propellant than it costs the crew in propellant...or at least break even.

[YNM]

47 minutes ago, Spacescifi said:

If you do not....ISRU. Which is mission difficult because you need the mission to pay off more propellant than it costs the crew in propellant...or at least break even.

55 minutes ago, Spacescifi said:

Ideally it would find an icy comet or icy asteroid, extract as much water as possible and fill up the bladder balloon.

Excerpt of the first paragraph of Wikipedia's page about ISRU :

Quote

In space exploration, in situ resource utilization (ISRU) is the practice of collection, processing, storing and use of materials found or manufactured on other astronomical objects (the Moon, Mars, asteroids, etc.) that replace materials that would otherwise be brought from Earth.

Taking water from asteroids is ISRU.