On the feasibility of putting fuel sources in LEO

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goodoltup

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I am a first time poster, and have a question.
Would there be any savings ( in dollars, time, or Delta-V ) in launching unmanned payloads of fuel into LEO, and then having the manned mission fuel up in space for a long distance trip? As an untrained observer, it appeared that that may be a way to give the mission a larger fuel budget without having to build a huge rocket simply to send that fuel into orbit. It could be done with existing technology like the Proton or Soyuz, etc., instead of putting engineering money and effort into building larger, more complicated rockets.
I appreciate everyone's time. I have very much enjoyed lurking on the forum so far.
 
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CalliArcale

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Well, to some extent, that is being done by the ISS, and was previously done by Mir. In those cases, though, the propellant delivered to orbit was just for stationkeeping, maneuvering around obstacles, and the occasional orbital reboost maneuver.

A more dramatic example closer to what you're suggesting is the Earth Orbit Rendezvous concept, which was explored early on in the Apollo program before finally settling on the Lunar Orbit Rendezvous concept. The Constellation program has been leaning towards EOR. The Ares V rocket would boost the propellant (and the large booster, comparable to S-IVB, to use the prop) and then a manned spacecraft launched by Ares I would dock with the booster and use it to go to the Moon. It's definitely more achievable than a "direct" mission profile (where you blast off from Earth, go to the Moon, land, blast off, and return home without rendezvousing with anything).

It doesn't save you delta-v; the total delta-v required is pretty much a constant. However, it does let you use smaller rockets, and there's something to be said for that. Granted, you're still gonna need a flipping huge rocket, but if you can break it up into components, launched separately, then an even larger vehicle becomes do-able.
 
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mr_magoo

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The Augustine Commission is looking at orbital depots and seems to view them favorably. Unfortunately it seems linked to a desire to use smaller launchers than Ares-V. We'll know by the end of the month what the revised space program is likely to look like.
 
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mental_avenger

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The only practical concept for putting fuel in LEO is if it is manufactured on the Moon and shipped from there to LEO, and we are a loooooong ways from that .
 
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StrandedonEarthsince1970

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Actually, having an orbital propellant depot isn't a bad idea, even if it is terrestrial-sourced. Propellant can be launched as water on BDBs (Big Dumb Boosters), and if a payload of water is lost, it's no big deal. In orbit, the water can be electrolyzed into H2 and O2 using cheap solar power, preserving our precious oil supplies. Then the multimillion dollar payloads can be launched with more expensive, more reliable boosters, without needing to factor propellant into the mass budget. Full tanks can be docked to payloads (or tugs!) and record masses can be lobbed to their destinations in record time.
 
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mr_magoo

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Yeah, it's a launch architecture issue. It seems that fans of EELV push it the most as it extends the capabilitiy of smaller launch vehicles. EELV fans tend to be people that are either concerned about space tourism, cost reduction through sharing rockets with commercial launches, and the cost savings of multiple small launches. There is a often a libertarian motive as well as they prefer private industry to government. Not judging, just noting it. I prefer large rockets because I'm a space telescope fan and Ares V could do that better but I have no argument with fuel depots.

Boeing has a pdf proposal floating around on the net for fuel depots. In their proposal they show how much even an Ares-v type mission could benefit from having its mission fuel seperated from the main launch.
 
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CalliArcale

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Ironically, I think the idea of floating fuel depots is less useful to private enterprise (at least currently) because although it does reduce the size of the launcher required, it increases the overall amount of infrastructure required. Nothing comes without a price. Long run, though, I think such things will be vital.
 
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MeteorWayne

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The real logistical fly in the ointment is...OK now that you've separated water into Hydrogen and Oxygen GAS[/b], what do you do with it? In gaseous form it is worthless as rocket fuel. It needs to be cooled enough to liquify it before it is compact enough to shove into fuel tanks. Once you've cooled it, how do you keep it cold? Remember, really cold it is....

All of a sudden the power and infrastructure requirements have gone waaaaayyyy up.

There may be solutions, but I know of noone that has calculated the energy budget for such an operation.
 
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mr_magoo

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The boeing proposal is for sending up liquid oxygen/liquid hydrogen to a couple of depots. Just a gas station, not a refinery. The technical issues are apparently storage related. The pdf is out there somewhere but heres an article: http://www.popularmechanics.com/science ... tml?page=2

If the moon missions die next month I really think youll see these depots heavily studied as part of the "flexible" path.
 
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docm

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And let's also not forget what a nuclear driven VASIMR could mean to deep space missions, manned or otherwise, originating in LEO. Spiral out, transfer and spiral in.

Someone needs to get cracking on a reactor design for that.

OOPS....forgot about Hyperion's uranium hydride modular reactor, and they have proposed one for use on the moon or in space. Core about the size of a hot tub and the containment & internals would fit on a flat bed. 20+ MWe, and Chang-Diaz has said 12 MWe would do. Designed to be built on production lines and used in unattended situations (self regulating) even if buried.

They already have 70 international orders @ $25-$30 million each.

Capitalizaton: over $100 million US.
 
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CalliArcale

Guest
mr_magoo":1n8wyja7 said:
The boeing proposal is for sending up liquid oxygen/liquid hydrogen to a couple of depots. Just a gas station, not a refinery. The technical issues are apparently storage related.
The storage issues are not at all minor. No spacecraft uses LH2/LOX for a propellant after the initial boost phase; it boils off way too quickly to be practical. Right now, the kinds of spacecraft that would benefit from an orbital depot would be those using hypergolic propellants, which are very storable and actually have a better energy density than LH2/LOX (despite having a lower specific impulse, which is a measure of efficiency -- how many pounds of propellant are required to accelerate a specific amount). This usually means some form of hydrazine (MMH, or UDMH, or another) and nitrogen tetroxide. There are also monopropellant forms. These are really the ideal propellants for this application.
 
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ScottCarpenter

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My question is, is it going to be a jobs program like they run in Oregon, where you're not allowed to pump your own gas.
 
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Jazman1985

Guest
Going off docm's point about the nuclear reactors, if they are actually mass produced at that size and utilized correctly then orbital depots with H2 fuel would be all that is needed for a VASIMR type engine. Storage of that would be far easier as I don't believe it needs to be kept liquid. Also, if a couple of those reactors got up there, that could make the cold storage facility much more feasible for chemical rockets too. Does anyone know the total mass of these proposed nuclear reactors? With that kind of power-output in space I think the current space-race will advance quite a bit faster. Development of high thrust electric propulsion could be made feasible for research and use.
 
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MeteorWayne

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ScottCarpenter":o9q8jy5v said:
My question is, is it going to be a jobs program like they run in Oregon, where you're not allowed to pump your own gas.
This is your first post. Making a poor joke, unrelated to the topic of the discussion is not a good way to make a good first impression. Welcome to Space.com We take science seriously here.
 
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mikecrane

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Are we still going to be using chemical rockets by the time we start building fuel depots? I think they'll more likely be supply depots.
 
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Jazman1985

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I think so, there's lots of things chemical rockets are good for. Any high thrust application, such as planetary landing or quick delta-v changes.
 
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aremisasling

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I'm asking this as a question for those of us who may understand orbital dynamics more than myself. Is there a benefit for a multi-purpose depot in space that could supply not just the craft going to other orbits, but those in LEO like the ISS, Bigelow Modules, capsules, or shuttle-like craft?

I guess what I'm envisioning is a sort of LEO ferry that would bounce between the depot and the various LEO assets taking water, supplies, fuel, even electrical power, were we to equip the depot with solar arrays and batteries. I'm always a fan of standardized, single point or multi-point nodes like the big box store-style distribution centers, but I'm well aware of the fuel expenditures required to change orbital characteristics so I'm not sure if such a design would be workable. The idea being you could send a craft up with just hypergolics, just water, or just compressed gasses for life support and avoid the complex internal structures and potential wasted space in multipurpose capsule structures. Futhermore, you could send up scheduled deliveries to the depot without interfering with crew or construction deliveries like we have with the ISS. And if you had all the stndardized payloads coming on regular flights to a depot with a ferry-system tranferring them, you could reduce parts and supplies-type payloads to just that and avoid trying to cram in all the necessities of life onto one spacecraft that absolutely needs to get there by a certain time or they'll run out of fuel, breathable air, food, water, etc.

It just seems to me that using a depot as a stopping point for GEO, GTO, trans-lunar, etc missions is a good starting point, but there could be gains in safety and reliability of LEO assets from payload standardization and dividing up our ciritical payloads so a wrench they can get in 2012 isn't riding on the same ship as the water they absolutely need by next month.

But it all depends on if such a fuel/supply ferry would spend too much fuel getting there for it to be worthwhile.

Any thoughts from the peanut gallery?

Aremis

EDIT: Nevermind, I answered my own question. http://en.wikipedia.org/wiki/VASIMR I hope VASIMR does what is hoped of it.
 
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aremisasling

Guest
mikecrane":3q61iqcv said:
Are we still going to be using chemical rockets by the time we start building fuel depots? I think they'll more likely be supply depots.
Given the limitations of radioactive fuel and ion-stlye fuel systems, I think chemical engines will be a necessity for a very long time to come. There's some serious skittishness in the international community for firing anything radioactive over their citizens' heads on tin can powered by a controlled explosion, let alone a full-blown nuke reactor. Many nations won't even let a nuclear submarine dock at their ports. As for ion propulsion, it's nice for low-deltaV applications like Dawn where we're not too concerned with the idea that it takes months to get up to speed or change course. But for anything short of interplanetary operations or station-keeping, it's not really practical. The only other options we really have are experimental at best, or not physically possible at worst.
 
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Jazman1985

Guest
As long as we're assuming the use of chemical rockets the actual benefit as far as energy consumption or energy saved is nil. As far as economics there's probably a fantastic benefit for exactly the reasons you mentioned, specific refueling missions can be devoted to just that, which means that more vital missions can be given more importance and launch schedules can be made accordingly. A refueling depot is also a logical step to take before departing for a lunar mission and when returning from one.
 
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TreasureHuntFan

Guest
About that idea launching H2O and converting to H2/O2... On earth we normally use boiling to keep the liquids liquid (naturally). But in space it seems that we could reduce heat exchange to the point that boil-off would not be necessary. In a vacuum, insulation is just a really good radiant barrier right? And no compressor would be needed because you could simply radiate away the excess heat, cooling the H2/O2 into a liquid state.

I am sure there is something I am missing about doing this?
 
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MeteorWayne

Guest
From what I understand, it would be converting the gases to liquid in the first place.

Anything in sunlight is going to be ~ 500K? The non sunlight side would be cold enough to condense the liquids. Is it manageable? Maybe, but the logistics need to be examined.
 
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ZenMasterSauce

Guest
mr_magoo":38jao5fb said:
Yeah, it's a launch architecture issue. It seems that fans of EELV push it the most as it extends the capabilitiy of smaller launch vehicles. EELV fans tend to be people that are either concerned about space tourism, cost reduction through sharing rockets with commercial launches, and the cost savings of multiple small launches. There is a often a libertarian motive as well as they prefer private industry to government. Not judging, just noting it. I prefer large rockets because I'm a space telescope fan and Ares V could do that better but I have no argument with fuel depots.

Boeing has a pdf proposal floating around on the net for fuel depots. In their proposal they show how much even an Ares-v type mission could benefit from having its mission fuel seperated from the main launch.

So right. It is seriously an infrastructure issue. What can be used to store the fuel? How long can it stay there in space? Will it be manned or unmanned stations? These are simple questions bound only by what we decide to do. The space shuttle external tank can be used for such things in a cluster formation. The benefits are truly endless.
 
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ZenMasterSauce

Guest
mikecrane":ppugvq11 said:
Are we still going to be using chemical rockets by the time we start building fuel depots? I think they'll more likely be supply depots.

Of course we will. Although a completely new style propulsion system is yet to be in full position to overtake chemical rockets in the near future, all of those companies both private and government based will probably use chemical rockets to still get to LEO, which is going to be a massive draw for interest in the future. Even if space agencies of countries are actually moving past to something better, rockets will still be of interest for quite a bit.
 
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Larry_1

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On the feasibility of putting fuel sources in LEO


Several companies are building and testing lunar lander engines that use LOX/Liquid methane implying that lunar landers can be launched from Earth with empty tanks and fueled onorbit or stored fully fueled or refueled many times.

http://www.aviationweek.com/search/arti ... 13,%202009

If they can be fueled up in orbit, then they can be refueled and potentially reused anywhere and anytime. This opens up a lot of new and potentially better ways to get to and from the Moon in case something bad happens along the way. If you don’t look at what happens when something fails before you write requirements and design an engine, you paint yourself in the corner when an engine fails like it did on Apollo 13. Fortunately, they had a backup engine system completely separate from the stage that failed.

There also is no such thing as a requirement that an engine cannot fail for any reason. Instead, we use the phrase “increase reliability” as a replacement for such a requirement. Reliability is simply a statistic that can only be calculated based on the number of previously successful engine burns and not measured. The more the engine is reliable, the more the company can charge the customer for it since customers demand the most reliable engine.

Refueling and reusing a lunar lander lowers cost and improves safety when engines fail. It also makes it safer for the outpost crew’s personal well-being, especially during their return trip during the ascent phase from the lunar surface. They don’t have to worry all of the time about their precious fuel, especially if they are going to be there for 6 months in a very inhospitable environment. It also opens up lunar surface access to competition for others with engines that burn or supply the same fuel.

If you could refuel a spent descent engine on the lunar surface and use it again, then the descent engine transforms into the ascent engine. You could also use it to hop around on the Moon like divers do in a similar fashion exploring caves that are several miles long.

If you lift off of the lunar surface with a fully refueled descent engine, you now have a backup engine stage in the form of the part of the lunar lander configuration which houses the crew and the return cargo. You have 2 systems capable of getting into lunar orbit instead of 1. So, if the primary refueled stage fails, you ignite the backup stage and proceed to lunar orbit. Without two stages with two sets of separate tanks and engines, you crash on the lunar surface if your engines fail. This risk was present during the Apollo program. If their ascent engine failed, they were doomed. It took some very brave and courageous heroes to accomplish Kennedy’s goal. Two stages are always better than one, especially in this instance. If you don’t believe an Astronaut, just ask any Navy pilot.

So onorbit fuel depots make good sense no matter if they are in low Earth orbit or low Lunar orbit. The other advantage of having a refueling station in low Lunar orbit is the ability to provide this type of engine failure redundancy by landing an unmanned lander with cargo and fuel needed during the stay and return trip. You land the unmanned cargo and fuel before you send the crew to the surface. Their job would be to get and use the cargo and fuel during their trip. You delay sending the crew in case the unmanned lander fails to land intact.

Sending crew, cargo, and fuel into low Earth orbit and onto the Moon and back in one shot is how we did it in the Apollo program. Notice, we have altered this approach to one that assembles transfer vehicles together before embarking on the trip to the Moon and now, we are now considering having fuel in space somewhere ready for the crews when they get into space. Sounds like a natural progression of things are happening where one shot deals that are extremely risky are a thing of the past. :)
 
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Gravity_Ray

Guest
The short answer is no.

The Earth is a massive gravity well. Sending anything up is expensive and should be done with thought. Right now it costs from $3,000/lb to $10,000/lb to get things to orbit (depending on type of orbit). Fuel is very heavy and you can imagine filling your space ship up is going to cost and arm and a leg and several internal organs as well.

Most of the fuel a ship needs is gobbled up in getting into orbit. You really dont need that much fuel to do deep space exploration. What you really need for deep space human exploration is an RTG (Radioisotope thermoelectric generator) in your space ship. This will produce all the heat your ship will need to stay warm and you can use some of the heat to generate electricity and use that to propel yourself in space. You dont need massive fuel tanks.

Big fuel depot's in space is a bit sci-fi to me. I think that will only happen in sci-fi movies (usually followed by massive explosions).
 
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