Discussion Orbital Propellant Tanker

T.Neo

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This is an LH2 tanker. LH2 provides the best exhaust velocity for both nuclear thermal rockets and certain kinds of fusion drives, due to the low particle mass of the exhaust. Hydrolox rockets also have the highest exhaust velocity of any practical chemical rocket.

In addition, hydrogen is quite common in the solar system which makes it an ideal common fuel/propellant.

If I want to ship oxygen, I'll do it on a seperate vehicle. It's much easier to ship than LH2, because it is more dense. For a chemical rocket,most of the propellant mass is LOX. For an NTR, all of the propellant mass is LH2 (if you use LH2, that is).

Since I want to ship primarily LH2, and water is mostly Oxygen (in terms of mass), shipping water to LEO for the hydrogen content would likely be waste of mass.

So unfortunately it looks like I'll have to deal with LH2's boiloff patterns.

I am not a materials expert, but I keep wondering if there's a way to add an outer layer of foam over the MLI, and shed it off in the exoatmospheric flight, with some light pyro contraption (a detonation cord?). Re - mega cooling. What is the timeframe that the tanker should stay in orbit? As a consequence, what should be the primary power supply? What is the figure of merit for this design? The FOM should drive your choices.

I'm not sure about the shed-able foam; such pyrotechnics could add mass, not be entirely effective, and also damage the MLI.

I assumed an on-orbit stay of 5 days maximum; it's all dependant on the time it takes to rendezvous with the client ship/orbital tug. Of course time from docking with the tug to docking with the client ship/propellant depot must also be considered, but it may be possible to devise some sort of closed-cycle cooling system using infrastructure on the tug.

Assuming 1% per day propellant loss per day, even after 5 days there would still be something like 48-49 tons of payload in the tank; that is less than 50 tons, but it isn't that bad. Of course then you would be talking about something like 3.5-7 million dollars worth of payload mass lost over that time period with that loss rate...
 

Wishbone

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The 1% per day figure seems too harsh. BTW, have you got any links to papers which discuss the boiloff formulae and state the real coefficients? Would dearly like to grab them (the only stuff I have seen somewhere was in pounds per square meter per day at LEO).

Also suppose that realistic LEO figures should include contribution from earthshine heating the tanker.

There's one thing I have learnt for sure: there should be a paper or a book with all the engineering type formulae for a particular field I dive into as an amateur, and it is much better to find that book than to re-invent the bike.
 

Capt_hensley

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RE T-Neo, OK That's resonable. even at 1% loss, the compromise seems to be your low mass initiative. What about those ultra low weight insulation materials I read about in the NASA spin-off programs? Surely by now we have something that parallels the carbon-nanotube tech that has come about in recent years.

I can understand your desire to minimize your dollar loss, but with multiple 5 day missions, maybe the $3.5-7 million loss is an acceptable number for a year.
 

T.Neo

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There's one thing I have learnt for sure: there should be a paper or a book with all the engineering type formulae for a particular field I dive into as an amateur, and it is much better to find that book than to re-invent the bike.

Yeah, the lack of easily accessable knowledge in this sort of field is really annoying; reinventing something advanced as an amateur is often hopeless. :dry:

The 1% per day figure seems too harsh. BTW, have you got any links to papers which discuss the boiloff formulae and state the real coefficients? Would dearly like to grab them (the only stuff I have seen somewhere was in pounds per square meter per day at LEO).

Well, there is this, it doesn't go into depth about formulae and coefficients but it points toward a NASA-related technical report.

Also suppose that realistic LEO figures should include contribution from earthshine heating the tanker.

Yes, but I also wonder how much difference this would make...

RE T-Neo, OK That's resonable. even at 1% loss, the compromise seems to be your low mass initiative. What about those ultra low weight insulation materials I read about in the NASA spin-off programs? Surely by now we have something that parallels the carbon-nanotube tech that has come about in recent years.

Carbon nanotube tech? Is there some exciting new structural application of nanotubes I don't know about somewhere?

I'm trying to (mostly) stay away from highly experimental technologies (though ultralightweight insulators sound pretty good, provided they're practically cheap and durable).

One idea I had, was a relatively thin layer of foam (similar to the SOFI on the ET) covering the tank, then the MLI, and then a second layer of higher density, stronger foam, (coated with an ablative in crucial areas, or perhaps even somehow an ablative itself), painted/impregnated with compounds to give it a high albedo (titanium dioxide, etc). This layer could be precast, and have a ribbed texture, so as to fit on the rest of the tank without conducting that much heat to it.

I can understand your desire to minimize your dollar loss, but with multiple 5 day missions, maybe the $3.5-7 million loss is an acceptable number for a year.

Well, it depends on how fast you can do a rendezvous. I think I've docked with space stations in orbit after about 16 hours before, and on other occasions even less, though in all instances I was using vehicles with impressive dV* and in the latter I skipped the normal alignment procedures and intercepted the other vehicle on a hohmann (I launched to a lower altitude parking orbit, I think the whole rendezvous manouver cost at the most 650 m/s).

*Ok, so I didn't fly a brachistochrone to the target, but I wasn't limited to the Shuttle's realistically small ~300 m/s dV. I suppose we can always increase the dV on these vessels; what kind of orbital tug would it be if it only had the dV budget of the Shuttle's OMS?
 
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Capt_hensley

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*Ok, so I didn't fly a brachistochrone to the target, but I wasn't limited to the Shuttle's realistically small ~300 m/s dV. I suppose we can always increase the dV on these vessels; what kind of orbital tug would it be if it only had the dV budget of the Shuttle's OMS?

I'm guessing not much more than an ATV or HTV, although I think ATV has a higher rate. Just guessing. I looked into a using the ATV prop section as a Prop module for Gateway, and it works, but I'm also in GEO where there is less drag, and less dV needed. Plus I'm just maintaining orbit, not achieving it. And I use 4 of these Prop modules at once. Your tanker would be equipped with only one. I also use the same variant for a tug, but I already have fuel in long term storage aboard Gateway. I like your tanker because it represents future possibilities for getting the fuel up to Gateway. One tug one job, then refuel after re-dock. I'm toying around with an enhanced version, but it's hard to mate it with the proper launch vehicle that's not an Ariane 5.

I'm pretty sure OMS is a bit out of date, and most items it's size are 20-30% more efficient. This requires allot more research, and far better expertise than I have.

---------- Post added at 12:46 AM ---------- Previous post was at 12:42 AM ----------

Carbon Nano-tubes are a very interesting subject, DARPA has invested in a panel of a certain size made from tubes, and it's strength is very impressive, but they aren't talking about it much, so I'm not sure where we are in the practical use sense.

Enhanced insulation like "solid smoke" and "glass foam" are probably closer to application than we know.
 

T.Neo

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Well, aerogel is promising... but as far as I know it is pretty fragile and relatively expensive to manufacture.
 

T.Neo

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Yes but so is your tanker, .

I know, and I'm trying to avert it as much as possible. ;) :p
 

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fsci123

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OrbitalPropellantTanker.jpg


The only real downside, is that it ended up looking like a feminine hygiene product. :facepalm:

Have you considered the flower config...
 

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T.Neo

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Interesting but I hardly see how it would be a good shape for a launch vehicle that has to contend with mass and aerodynamic issues. :shifty:
 

fsci123

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Interesting but I hardly see how it would be a good shape for a launch vehicle that has to contend with mass and aerodynamic issues. :shifty:


Those are pods with a central core the pods could easily fit into an ariane 5... Possibly even several of them...
 

T.Neo

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This isn't a ~20 ton payload designed to fit into an Ariane 5. It's a launch vehicle intended to ship ~50 tons of propellant-payload into LEO. ;)
 

Cras

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I was under the impression this was a payload tank as well and required a launch vehicle, but if you intend to make the thing be able to launch itself into orbit, that is just more awesomeness included I say!
 

fsci123

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Well the pod design could solve the problem of moving propellant from one part of a tank to the the craft you are trying to refill... In micro-G the liquids could be anywhere in the tank it could be in center or the lower edge or in the worst case outside the craft... A pod design could spin slightly to provide 0.025g in order to settle most of the liquid at the "bottom"...
 

garyw

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Why would you do that though? Why not pressurise the tank with helium or use a tank design that wicks the fuel to the pumps?
 

T.Neo

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I can spin the tank to try and 'settle' the propellant. Likely it would rely on some combination of slow spinning on the long axis, and a 'wick' structure inside the tank, to ensure that most of the payload as possible was transferred to the client ship/propellant depot.
 

fsci123

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Why would you do that though? Why not pressurise the tank with helium or use a tank design that wicks the fuel to the pumps?

Well I am thinking about something that engineers could build with current tech, something that can be built with readily available parts, and something that isn't so complex that Stephen hawking has a siezure just thinking about it... Thus making the minutely rotating flower config the most logical... It will feature a central hub with a noble gas(most likely helium) tank that pumps the gas into the to the pods... The pressure difference will cause the fuel to flow into a central tube and into a vessel...
 

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i did some calculation: with the same basic structure, but with only four RS-68 engines and with five Aerojet SRB (the same of the Atlas V rocket), the payload raise to about 75.000 kg... + 50%!
 

T.Neo

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OPT has severe problems, including but not limited to paper propellant tanks and neglect for the requirement of extra fuel to run gas generators.
 
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