Propellant depot strategy & tactics pow-wow

[mmeijeri]

Here's a thread for those of us who can't wait for propellant depots and want them as soon as possible. Thanks to the Augustine commission prospects are better than they have been for years. We can expect a mountain of FUD from the SDLV people, and this thread is to discuss strategy and tactics for countering that. We don't have much time before the window of opportunity closes. Let's not screw this up people.

[mmeijeri]

Some context. The good news is that the subcommittee has stated quite bluntly that superheavy lift is not necessary. It has also said depots should be part of any option the commission considers. The bad news is that Jeff Greason has said he is no longer sure 25mT is enough. General Lyles has also said depot technology is still immature.

It sounds as if there may need to be a bigger launcher. What should we argue for? Obvious choices include EELV Phase 1, J-130 and NSC. EELV Phase 1 is very heavy from the point of view of a depot enthusiast, but the good thing is it might also increase the payload capacity of the more reasonably sized Delta Medium. An SDLV would be wasteful, and all EELV might be better, but if we aim too high we may end up with nothing. The commission may recommend depots, but I think we can expect tremendous opposition from the congressional delegations from Alabama and Florida. Resigning ourselves to an SDLV may be the right thing to do.

Another consideration is how to deal with depot development. If MSFC gets involved we would have to be worried they screw up again, especially since this time they'd have an incentive to screw up. Another aspect is the perceived immaturity of depot technology. Augustine himself has said it is pretty difficult to do liquid hydrogen transfer on the ground, let alone in space. He has also said it will be an important topic for discussion next week.

One less ambitious initial target would be to start with in-flight refueling as was proposed by Danny Deger.

As you will know I have been arguing in favour of hypergolic depots at L1 for a while now, in support of an all hypergolic lander. It may not be as sexy as cryogenic depots, but at least it doesn't have the perceived risks. After all, the Russians have been doing hypergolic propellant transfer ever since Salyut-6, way back in 1978. The technology has been in continuous use ever since and is used on ISS today. Hypergolic landers are also a proven technology and Orion uses hypergolic propulsion anyway.

I'm greatly relieved by what happened today and I think the committee will in all likelihood recommend development of cryogenic depots. This is the best news we have had in years. But I'm afraid the committee may hesitate to put cryogenic depots on the critical path and I expect enormous opposition from Florida and Alabama. It seems highly likely there will be funding for cryogenic depots, but the sooner we have operational depots and an exploration program, the bigger the boost to the commercial development of space.

One concern is that the Flexible Path Option would not immediately develop a lander, but a cheaper precursor of a lander could serve as a long duration transit hab and mini space station, which fits perfectly with the Flexible Path option. Hypergolics would also be a very natural fit for long duration missions. Hypergolics for the lander/transfer vehicle only would leave open the possibility of cryogenic depots refueling the EDS as soon as they became available.

J-130/NSC + in-flight refueling of the hypergolic transfer vehicle/lander only sounds like the least ambitious option and EELV Phase 1 and cryogenic depots like the most ambitious one the committee might accept, with a whole range of options in between. All of these options would allow for a commercial propellant market soon.

What should we aim for?

[rklaehn]

The realistic depot concepts I have seen so far are all based on existing upper stages. The easiest path to a depot would be building the wide body centaur or whatever the concept is currently called. A wide body centaur plus RS68a would get delta IV heavy to 35-40mt to LEO. That should be enough for even the biggest piece of exploration hardware.

If transferring LH2 proves too difficult initially, just limit the propellant transfer to the LOX, which is the majority of propellant mass anyway. LOX is also common in many different propellant combinations, and the only realistic candidate for lunar ISRU.

But ULA seemed relatively confident that they can make LH2 transfer work as well.

If a shuttle derived vehicle is required for political reasons, it should be DIRECT, since it is clear that they see the benefits of depots.   

[A_M_Swallow]

Some context. The good news is that the subcommittee has stated quite bluntly that superheavy lift is not necessary. It has also said depots should be part of any option the commission considers. The bad news is that Jeff Greason has said he is no longer sure 25mT is enough. General Lyles has also said depot technology is still immature.

Devise a plan to bring depot technology to TRL 9 within 3 years.  Launch the propellant on say an EELV.  Refuel the upper stage of a Falcon 1 so it can send a communications satellite to L2.  Then refuel a medium EELV's Centaur so it can send a satellite to GSO.

It sounds as if there may need to be a bigger launcher. What should we argue for? Obvious choices include EELV Phase 1, J-130 and NSC. EELV Phase 1 is very heavy from the point of view of a depot enthusiast, but the good thing is it might also increase the payload capacity of the more reasonably sized Delta Medium. An SDLV would be wasteful, and all EELV might be better, but if we aim too high we may end up with nothing. The commission may recommend depots, but I think we can expect tremendous opposition from the congressional delegations from Alabama and Florida. Resigning ourselves to an SDLV may be the right thing to do.

Which ever one you chose will make its rivals into enemies.  Since depots are compatible with all the LV types the answer is ALL.  For all the LV under consideration produce a page showing how big a cargo can be sent to L1 if they refuel in LEO.

[jongoff]

There are tools being worked on by industry and NASA for doing cryo fluid management technology maturation.  Centaur Test Bed has been mentioned before, but and industry team and NASA are working together on a new project called CRYOTE (CRYogenic Orbital TEstbed) that would be even more capable.  A ground-test version of it is actually funded and being built as we speak.  That's about all I think I'm safe with saying for now, but there should be more details at SPACE 2009.  I've also been doing some work at Masten to see if we can do a suborbital version of the same (CRYOSOTE?) that could fly on our suborbital vehicles, once they're available.

Testbeds like this can help with the rapid maturation of the technology.  It would also be nice if the two depot-related Centennial Challenges would actually get funded. 

NASA has some depot-related SBIR topics out on their solicitation, but adding more, or going with larger "Broad Area Announcement" style contracts would also be very helpful.

The technology is mostly there, and we have or will soon have the tools to retire the rest of the remaining risks quickly if depots end up being put on the critical path, like they ought to.

~Jon

[TOG]

Team-

Any thoughts on this alternative to LH2 - LOX storage: What if the fuel was stored as Stable Water?  Then when the time comes to transfer the fuel the water could be broken into H2 and O2 via energy gathered from solar panels. 

This could reduce the amount of loss due to the "boil off" effect, and would be more stable and less prone to "unfortunate incidents" on orbit.

Thoughts?

Drew Montgomery AKA TOG.

[jongoff]

Any thoughts on this alternative to LH2 - LOX storage: What if the fuel was stored as Stable Water?  Then when the time comes to transfer the fuel the water could be broken into H2 and O2 via energy gathered from solar panels. 

This could reduce the amount of loss due to the "boil off" effect, and would be more stable and less prone to "unfortunate incidents" on orbit.

The problem is that electrolyzing water (and then chilling it down to cryo temps) takes a nearly insane amount of energy.  You'd be better off using the much smaller amount of energy it takes to actively cool the LH2/LOX.

~Jon

[simon-th]

Team-

Any thoughts on this alternative to LH2 - LOX storage: What if the fuel was stored as Stable Water?  Then when the time comes to transfer the fuel the water could be broken into H2 and O2 via energy gathered from solar panels. 

This could reduce the amount of loss due to the "boil off" effect, and would be more stable and less prone to "unfortunate incidents" on orbit.

Thoughts?

Drew Montgomery AKA TOG.

Interesting idea, but not really viable.

4.4 kilowatt-hours of electricity converts 1 liter of water into 1.59 liters of liquid hydrogen and 0.79 liters of liquid oxygen. With efficiency losses we can think about 7-8 kilowatt-hours of electricity required.

For a metric ton of water converted into H2/O2 you would thus require about 8MWh. The peak output of the ISS' solar panels are 100KW. With these panels it would take 80 hours to convert one 1 metric ton. If you require say 50 metric tons of fuel for one mission, you end up having to wait 4000 hours or 160 days for your fuel depot to convert the water. And while it does so, you got the same boil-off problems you have if you bring up H2 and O2 separated in the first place.

I'd say fuel depots can realistically be a. for hypergolics only or b. for LOX only. Only in the very long run will we be able to build depots with LH2/LOX capability.

[yg1968]

Can someone explain or provide a link as to why propellant depots are such a great idea. Why are they better and cheaper than having a large rocket.  Thanks.

[mmeijeri]

I'd say fuel depots can realistically be a. for hypergolics only or b. for LOX only. Only in the very long run will we be able to build depots with LH2/LOX capability.

Heheh, usually I'm the one to argue hypergolic depots are the way to go for now, not cryogenic ones. Allow me to take the other side for a change.

What makes you say cryogenic depots are far in the future? I think the political risks far outweigh the technical ones, especially if development of the depots is left to LM / Boeing / ULA, not MSFC. Other than that the remaining argument would be that hypergolic depots could perhaps be operational sooner, which means the benefits to the launch sector would occur sooner.

Within the context of the Flexible Path / Deep Space option, hypergolics do start to make extra sense because of the long durations involved. They may even offer a greater "depot multiplication factor" than cryogenics, since their density is much greater. Payload fairings constrain the maximum volume for a dry-launched EDS. With hypergolics these constraints would be much less constraining. I think that if you make use of an Earth swingby the Oberth effect reduces the required delta-v's by so much the inefficiency of hypergolics is much reduced. This means you may actually be able to push larger masses towards Mars than with cryogenics. I'm not sure about this, I'm still working on the calculations.

[marsavian]

Propellant Depots - General Discussion

http://forum.nasaspaceflight.com/index.php?topic=12338.0

[mmeijeri]

In a nutshell:

1) they allow you to do exploration without HLVs
2) this can stimulate a thriving commercial launch market, which may drive down costs and eventually lead to RLVs

[simon-th]

Can someone explain or provide a link as to why propellant depots are such a great idea. Why are they better and cheaper than having a large rocket.  Thanks.

Just a couple of benefits:

1. Costs. You get your fuel up to the depot with a number of smaller launch vehicles. High flight rates (>20 flights per year) reduces cost per launch significantly. On the other hand large rockets do have high fixed costs and only make sense at large flight rates (that you don't get if you have a 120mt vehicle).

2. Flexibility. Your architecture basically involves your flight stack with an empty EDS going up to the depot and be fueled and then you go whereever you want to go. You can have an empty spacecraft (EDS and payload) in the 75mt range and after it's fueled you have a spacecraft with say 200mt ready to propel 60mt to a Mars trajectory.

3. Creating a market for commercial rockets. You get fuel up to your depot constantly. A commercial provider with e.g. a 15mt to LEO rocket may be able to sell 20 launches per year to NASA for the fuel depot. That lowers this providers cost per launch quite significantly. That also means that the DoD and NASA can use these launchers for other payloads for quite a lower price.

[TOG]

Jon & Simon,

Thank you both for your quick responses.  I can see now where this is not practical.  Forgot (briefly) that in this case the conversion of water to their base elements is only an energy transfer, and the amount of energy loss (as well as the time involved in the process) would make this a losing proposition.  I was just looking for a little different way to approach the problem.  The spin off of that solution would be "capturing" a comment and separating the elements for their fuel components. 

But as you both so succinctly pointed out, the amount of energy required to separate the elements is prohibitive.

I understand the attraction of Hypergolics (easier to store for longer periods of time), but was trying to look for alternatives that did not necessarily involve terrestrial sources.

Thank you again,
TOG.

[yg1968]

Can someone explain or provide a link as to why propellant depots are such a great idea. Why are they better and cheaper than having a large rocket.  Thanks.

Just a couple of benefits:

1. Costs. You get your fuel up to the depot with a number of smaller launch vehicles. High flight rates (>20 flights per year) reduces cost per launch significantly. On the other hand large rockets do have high fixed costs and only make sense at large flight rates (that you don't get if you have a 120mt vehicle).

2. Flexibility. Your architecture basically involves your flight stack with an empty EDS going up to the depot and be fueled and then you go whereever you want to go. You can have an empty spacecraft (EDS and payload) in the 75mt range and after it's fueled you have a spacecraft with say 200mt ready to propel 60mt to a Mars trajectory.

3. Creating a market for commercial rockets. You get fuel up to your depot constantly. A commercial provider with e.g. a 15mt to LEO rocket may be able to sell 20 launches per year to NASA for the fuel depot. That lowers this providers cost per launch quite significantly. That also means that the DoD and NASA can use these launchers for other payloads for quite a lower price.

Thanks for all of the answers.

[mmeijeri]

The problem is that electrolyzing water (and then chilling it down to cryo temps) takes a nearly insane amount of energy.  You'd be better off using the much smaller amount of energy it takes to actively cool the LH2/LOX.

This idea does make sense for propulsion systems for space stations. The quantities involved are much smaller. Plans for Space Station Freedom included LOX/LH2 propulsion with propellant stored as water. Bigelow is considering something similar for his planned stations.

EDIT: I think both plans were for gaseous H2 and O2, which makes sense for the small quantities and burns involved.

[agman25]

Team-

Any thoughts on this alternative to LH2 - LOX storage: What if the fuel was stored as Stable Water?  Then when the time comes to transfer the fuel the water could be broken into H2 and O2 via energy gathered from solar panels. 

This could reduce the amount of loss due to the "boil off" effect, and would be more stable and less prone to "unfortunate incidents" on orbit.

Thoughts?

Drew Montgomery AKA TOG.

Interesting idea, but not really viable.

4.4 kilowatt-hours of electricity converts 1 liter of water into 1.59 liters of liquid hydrogen and 0.79 liters of liquid oxygen. With efficiency losses we can think about 7-8 kilowatt-hours of electricity required.

For a metric ton of water converted into H2/O2 you would thus require about 8MWh. The peak output of the ISS' solar panels are 100KW. With these panels it would take 80 hours to convert one 1 metric ton. If you require say 50 metric tons of fuel for one mission, you end up having to wait 4000 hours or 160 days for your fuel depot to convert the water. And while it does so, you got the same boil-off problems you have if you bring up H2 and O2 separated in the first place.

I'd say fuel depots can realistically be a. for hypergolics only or b. for LOX only. Only in the very long run will we be able to build depots with LH2/LOX capability.

That is only if you use ecotrolysis. Other approaches such as Photocatalysis has zero power requirements. The work very well with UV light. Guess where UV is abundant.

[MZ]

Why is the choice of fuels at a depot between hypergolics and LH2?  I would think that there are fuels that are more easily stored and transferred than LH2, and that also has a better Isp than hypergolics.
Just curious why the other options have been discarded.

[neilh]

Why is the choice of fuels at a depot between hypergolics and LH2?  I would think that there are fuels that are more easily stored and transferred than LH2, and that also has a better Isp than hypergolics.
Just curious why the other options have been discarded.

Methane, for example, which I believe doesn't need cooling. Both Armadillo Aerospace and XCOR (Jeff Greason's company) have recently constructed LOX/Methane engines:

http://www.xcor.com/products/engines/5M15_LOX-Methane_rocket_engine.html
http://www.hobbyspace.com/nucleus/index.php?itemid=14018

The CEV was "originally" planned to use methane, but was switched to hypergolics in 2006:

http://www.space.com/spacenews/archive06/Methane_013006.html

Hypergols such as the nitrogen tetroxide and monomethyl hydrazine combination the space shuttle burns to maneuver on orbit are considered highly reliable and easier to store than other propellants. But they offer lower performance than methane and other so-called green propellants and are highly caustic, requiring painstakingly careful -- and therefore expensive -- handling by workers on the ground who have to be extremely careful to avoid potentially lethal exposure.

Scott Horowitz, NASA associate administrator for space exploration, said the decision to drop the methane-engine requirement from the CEV program came down to changing assumptions about the performance advantages and technical risk. There are no methane-fueled space propulsion systems in service today. Hypergolic systems, on the other hand, were used on board the Apollo command and service modules and the lunar landers.

This paper on scalable depot design (the first one which came up from some googling) lists the following propellant options: LOX, LH2, LCH4, kerosene, H2O2, liquid xenon.

http://www.ssdl.gatech.edu/Papers/Masters/Street_8900.pdf

On a related note, I'm not sure if anybody linked to this yet, but I came across a presentation by Boeing in 2007 on the "Potential Impact of a LEO Propellant on the NASA ESAS Architecture":

http://www.boeing.com/defense-space/space/constellation/references/presentations/Potential_Impact_of_LEO_Propellant_on_NASA_ESAS_Architecture.pdf

[fotoguzzi]

Can someone explain or provide a link as to why propellant depots are such a great idea. Why are they better and cheaper than having a large rocket.  Thanks.

I know this has been gone over before, but to simplify clongton's points,

Take the fuel up in the cheapest form possible.  It could be dozens of small, cheap rockets or one big giant cheap rocket--whatever works.  If a stable market can be developed, a candidate rocket will emerge.  There is less time pressure, and if it fails to reach orbit, you are only out one cheap rocket and some cheap propellant.

Then send as much precious crew and time-sensitive, expensive exploration gear, and a large propellant tank as you can afford to launch to the depot.

[MZ]

Thanks.  So it isn't that the other fuels perform badly it is just that they haven't been used for in space propulsion before...a new engine development would be needed.

Why is the choice of fuels at a depot between hypergolics and LH2?  I would think that there are fuels that are more easily stored and transferred than LH2, and that also has a better Isp than hypergolics.
Just curious why the other options have been discarded.

Methane, for example, which I believe doesn't need cooling. Both Armadillo Aerospace and XCOR (Jeff Greason's company) have recently constructed LOX/Methane engines:

http://www.xcor.com/products/engines/5M15_LOX-Methane_rocket_engine.html
http://www.hobbyspace.com/nucleus/index.php?itemid=14018

The CEV was "originally" planned to use methane, but was switched to hypergolics in 2006:

http://www.space.com/spacenews/archive06/Methane_013006.html

Hypergols such as the nitrogen tetroxide and monomethyl hydrazine combination the space shuttle burns to maneuver on orbit are considered highly reliable and easier to store than other propellants. But they offer lower performance than methane and other so-called green propellants and are highly caustic, requiring painstakingly careful -- and therefore expensive -- handling by workers on the ground who have to be extremely careful to avoid potentially lethal exposure.

Scott Horowitz, NASA associate administrator for space exploration, said the decision to drop the methane-engine requirement from the CEV program came down to changing assumptions about the performance advantages and technical risk. There are no methane-fueled space propulsion systems in service today. Hypergolic systems, on the other hand, were used on board the Apollo command and service modules and the lunar landers.

This paper on scalable depot design (the first one which came up from some googling) lists the following propellant options: LOX, LH2, LCH4, kerosene, H2O2, liquid xenon.

http://www.ssdl.gatech.edu/Papers/Masters/Street_8900.pdf

On a related note, I'm not sure if anybody linked to this yet, but I came across a presentation by Boeing in 2007 on the "Potential Impact of a LEO Propellant on the NASA ESAS Architecture":

http://www.boeing.com/defense-space/space/constellation/references/presentations/Potential_Impact_of_LEO_Propellant_on_NASA_ESAS_Architecture.pdf

[neilh]

Can someone explain or provide a link as to why propellant depots are such a great idea. Why are they better and cheaper than having a large rocket.  Thanks.

Just a couple of benefits:

1. Costs. You get your fuel up to the depot with a number of smaller launch vehicles. High flight rates (>20 flights per year) reduces cost per launch significantly. On the other hand large rockets do have high fixed costs and only make sense at large flight rates (that you don't get if you have a 120mt vehicle).

2. Flexibility. Your architecture basically involves your flight stack with an empty EDS going up to the depot and be fueled and then you go whereever you want to go. You can have an empty spacecraft (EDS and payload) in the 75mt range and after it's fueled you have a spacecraft with say 200mt ready to propel 60mt to a Mars trajectory.

3. Creating a market for commercial rockets. You get fuel up to your depot constantly. A commercial provider with e.g. a 15mt to LEO rocket may be able to sell 20 launches per year to NASA for the fuel depot. That lowers this providers cost per launch quite significantly. That also means that the DoD and NASA can use these launchers for other payloads for quite a lower price.

Thanks for all of the answers.

Just to add to what others have said, the white paper Jon Goff submitted to the Augustine Commission is an excellent explanation of the merits of propellant depots. I particularly like the chart which compares a depot-centric architecture with an HLV-centric one in terms of ability to meet the committee's objectives:

http://selenianboondocks.com/wp-content/uploads/2009/07/Depot-Centric_Human_Spaceflight.pdf
http://selenianboondocks.com/2009/07/depot-centric-human-spaceflight/

[Danny Dot]

Team-

Any thoughts on this alternative to LH2 - LOX storage: What if the fuel was stored as Stable Water?  Then when the time comes to transfer the fuel the water could be broken into H2 and O2 via energy gathered from solar panels. 

This could reduce the amount of loss due to the "boil off" effect, and would be more stable and less prone to "unfortunate incidents" on orbit.

Thoughts?

Drew Montgomery AKA TOG.

Someone crank the numbers on kw-hours to turn 30mT of water into rocket fuel?  I am too busy right now. 

My guess is a REALLY big number.  I looked a site on using electrolysis at gas stations to make hydrogen and the power requirements were HUGE.  They also stated the process is only 50% efficient and large quantities of waste heat is produced.  This means huge radiators. 

Danny Deger

[neilh]

On a related note, the wikipedia article on propellant depots could use a lot of improvement:

http://en.wikipedia.org/wiki/Propellant_depot

Just remember to cite your sources and maintain a NPOV!

[loomy]

Can someone explain or provide a link as to why propellant depots are such a great idea. Why are they better and cheaper than having a large rocket.  Thanks.

LOL!  The large rocket doesn't exist yet.  Is that a good place to start!

And how about this:  Orbital and SpaceX can use propellant depots.  They can't use Ares V.

Hat trick:  SpaceX says it'll take 2+ years and the $300,000,000 from COTS-D to develop a crew abort system.  Cargo doesn't need crew abort systems!

Bonus point:  In some places the competition NASA has with the private sector would be illegal or cause an international event, see: Softwood lumber dispute.  Depots are the first step in NASA transitioning from ridiculous socialism (NASA chose to build its own rockets over buying EELV when the mere existence of EELV should have ended NASA's medium lift business) to the american entrepreneur's capitalism you hear about on TV.

[butters]

Is there really any advantage to LCH4 over RP-1 for refillable upper stages?  The specific impulse is 3% higher, but the density is 20% lower.  This reduces the propellant mass ratio of each supply tanker, so it takes more IMLEO to deliver the same propellant mass.

LCH4 is promising for Mars ISRU, so it makes sense for a mars ascent stage, but I don't see any benefit for the rest of the trip, including return from low mars orbit (cheaper to send propellant from earth than to land a much bigger ascent stage and then haul it back out of the gravity well).

[Jorge]

Is there really any advantage to LCH4 over RP-1 for refillable upper stages?  The specific impulse is 3% higher, but the density is 20% lower.

Easier to keep the prop lines clean, I would think.

[mmeijeri]

Easier to keep the prop lines clean, I would think.

Do jet aircraft have similar problems, or is it something specific to rocket engines?

[mmeijeri]

One important consideration for hypergolic depots / propellant transfer: it really needs a depot or refueling at L1, not just in LEO. Hypergolics are too inefficient for use on an EDS, other than perhaps a one time transfer of a heavy fully reusable spacecraft, where the cost can be amortised. The spacecraft would have to be dry-launched to L1, either in one launch, or preferably in two launches with EOR with an EDS. Only at L1 would it be fueled.

In order to accommodate smaller launchers, especially small RLVs, but also including things like Falcon and potential new vehicles like Aquarius or Scorpius, you would want to have a LEO export depot as well. And since stimulating the launch industry and thereby reducing cost to orbit as soon as possible is the main point of doing all this, the LEO depot would be important. The LEO hypergolics depot could also refuel reusable tugs, which are crucial for making depots (including cryogenic ones) cost effective. These tugs would also make ISS resupply more efficient. Another initial application would be refueling unmanned Orions making trips into the inner van Allen belt and back to do radiation shielding tests.

The main argument in favour of hypergolics depots is that there are no technical obstacles that can be used as a pretext to put them off to the long run. Hypergolic propellant transfer is a mature technology that has seen continuous operational use ever since Salyut-6 in 1978. There are already spacecraft, either operational or in the pipeline (Orion, ATV, HTV, Cygnus, Dragon), that could use them. Based at L1, performance would not be an issue and hypergolics are perfectly suited for the long duration missions envisaged for the Flexible Path option.

The sales pitch is not helped if depot enthusiasts keep stressing cryogenic depots (even midly cryogenic ones like oxygen or methane) are better... They are, but hypergolic ones are good enough to avoid HLV and very useful in the short run anyway.

[agman25]

Anybody think of using solids. I think there was a late-70 MSR study that used two shuttle launch to launch 2 IUS's each and the spacecraft elements. Assembly on orbit.

[TOG]

Team-

This has probably come up elsewhere, but any thought of using one of the expandable modules that Bigelow is developing?

Or how about (if we HAVE to use cryogenic fuels) puling an ET up from a SSTS or SDHLV?

In other words, any thoughts on WHAT would hold our fuels?

TOG

[NUAETIUS]

Team-

This has probably come up elsewhere, but any thought of using one of the expandable modules that Bigelow is developing?

Or how about (if we HAVE to use cryo genic fuels) puling an ET up from a SSTS or SDHLV?

In other words, any thoughts on WHAT would hold our fuels?

TOG

Search the forum, it has been talked about ad nausium.

[yg1968]

Can someone explain or provide a link as to why propellant depots are such a great idea. Why are they better and cheaper than having a large rocket.  Thanks.

LOL!  The large rocket doesn't exist yet.  Is that a good place to start!

That's a bad argument. Propellant depots don't exist either. But from the hearing on July 30th, probably the strongest proponent on the panel for propellant depots, Jeff Greason said that he was no longer convinced that there wasn't a need for a 75m ton rocket. He said that the next generation HLV should be capable of lifting between 25mt and 75mt. But even with a 75mt rocket, he felt that propellant depots were still a game changer and needed to be a priority but he also felt that a large enough rocket would not need to rely on propellant depots until the propellant depots are ready.

[neilh]

Can someone explain or provide a link as to why propellant depots are such a great idea. Why are they better and cheaper than having a large rocket.  Thanks.

LOL!  The large rocket doesn't exist yet.  Is that a good place to start!

That's a bad argument. Propellant depots don't exist either. But from the hearing on July 30th, probably the strongest proponent on the panel for propellant depots, Jeff Greason said that he was no longer convinced that there wasn't a need for a 75m ton rocket. He said that the next generation HLV should be capable of lifting between 25mt and 75mt. But even with a 75mt rocket, he felt that propellant depots were still a game changer and needed to be a priority but he also felt that a large enough rocket would not need to rely on propellant depots until the propellant depots are ready.

Here's the text from his actual slide:

http://www.nasa.gov/ppt/375965main_03%20-%20Integrated%20beyond%20LEO%20overview_2009july30_without%20backup%20slides.ppt (slide 86)
http://www.nasa.gov/offices/hsf/meetings/07_30_meeting.html#

Chemical in-space propulsion: Lunar return

* Revolves around some kind of Earth Departure Stage
** Considered three classes, which map to the three classes of launch vehicles (25mT, 75mT, 125mT)
* 25mT vehicles require propellant transfer and a depot for human Lunar exploration
** Still an open question whether mass/volume is sufficient for payloads
** Number of launches requires time to place propellant, vehicles, and mass on orbit; managing boil-off, orbit maintenance, keep-alive power drives need for a depot for missions beyond the first few
* 75mT vehicles can support some exploration missions with “top off” of one EDS by another, but can do significant exploration before depot is ready
** Cannot match Ares V capability without top-off transfer
* 125+ mT vehicles do not require propellant transfer for Lunar missions but would be greatly enhanced by them for Mars
* Point of departure EDSs for these classes provided to NASA for additional architecture analysis now underway

[JohnFornaro]

Water, Water, Water. 

Turns to ice, don't need to refrigerate, shade will do.  Stores forever with no boil-off.  Higher density for launching.  Triple use:  Fuel, Breathing, Drinking.  Requires electrolysis capability, either solar or nuclear. Cheaper to launch. Cheaper to purchase.  Less expensive to manufacture (electrolyze?) in space if the equipment is designed with sufficiently amortized life, and un-attended operation.  Does not rule our hypergolics, or other fuel combinations.  Depot should be multi-fuel capable, as well as able to store supplies, consumables, rescue craft, spare parts, ultimately habitat and micro-gravity & radiation experimentation.

Locate at Emily-1. Start small, build-out to 2400m diameter, rotating ring.

What's not to like?

[simon-th]

Water, Water, Water. 

Locate at Emily-1. Start small, build-out to 2400m diameter, rotating ring.

You want a large, rotating swimming pool at EML-1? 

Sorry, couldn't resist...

[JohnFornaro]

Uhh... actually ice rink.

[jongoff]

That's a bad argument. Propellant depots don't exist either. But from the hearing on July 30th, probably the strongest proponent on the panel for propellant depots, Jeff Greason said that he was no longer convinced that there wasn't a need for a 75m ton rocket. He said that the next generation HLV should be capable of lifting between 25mt and 75mt. But even with a 75mt rocket, he felt that propellant depots were still a game changer and needed to be a priority but he also felt that a large enough rocket would not need to rely on propellant depots until the propellant depots are ready.

I think you're misreading what Jeff said.  I thought he said that he was no longer 100% certain that 25mT would be enough.  That it might, but might be marginal.  That's completely different from saying we need a 75mT vehicle.  If 25mT is marginal for the "biggest smallest piece", but 30-35mT is ok, there are other options that don't involve building a big HLV.

~Jon

[loomy]

Can someone explain or provide a link as to why propellant depots are such a great idea. Why are they better and cheaper than having a large rocket.  Thanks.

LOL!  The large rocket doesn't exist yet.  Is that a good place to start!

That's a bad argument. Propellant depots don't exist either.

It is an awesome argument.  Depots could cost what, 5x less? 10x less to develop than Ares V?  (Remember that some of the Ares V cost is built into the cost of Ares I, and will be added back into the cost of Ares V when Ares I is gone)

And the resulting volume production of smaller rockets, the ones that would use the depots, would lower costs.

And the competition between suppliers of smaller rockets would lower costs. 

Oh, and those same rockets that use the depots will also launch the depots themselves.  Even more launches! 

And more frequent successful launches mean more safety guaranteed.

OH and entities other than NASA and its suppliers can use the depots.  Virgin Galactic hotel rockets can use depots for fuel and have nothing else to do with NASA.

Or you could do none of that and be socialist and build one big government rocket.  The soviet bear is alive and well in the united states.

[JohnFornaro]

Give up on the "Soviet bear" analogy.  The PTB like BFR's, perhaps even to the detriment of long term HSF. 

But Loomy's argument makes sense to a certain extent.  More smaller rockets are a good thing; it spreads the wealth, the saftety, the cost, the experience, the manufacturing capability.  It encourages private industry, minimizes investment capital, allows faster returns, spreads risk.

Just a few big 'uns.  Waterboys, if you will.

I think 25mt may be too low:  50?

[TOG]

Uhh... actually ice rink.

Sounds like you would add a Starbuck's there too.  Perhaps a nice strip mall for those tourists (where else to get a "My parents went to outer space and all I got was this lousy T-shirt" shirt?), a service station for refurbishing those reusable tugs, and perhaps a nice zero-g casino?

 

Completely agree with the water/ice concept, but as mentioned earlier, it could take a lot of energy to separate the water (yes the U-V idea looks pretty good).

Oh, and added benefit: water makes a nice shield against radiation.  FWIW.

TOG

[Bill White]

Water, Water, Water. 

Turns to ice, don't need to refrigerate, shade will do.  Stores forever with no boil-off.  Higher density for launching.  Triple use:  Fuel, Breathing, Drinking.  Requires electrolysis capability, either solar or nuclear. Cheaper to launch. Cheaper to purchase.  Less expensive to manufacture (electrolyze?) in space if the equipment is designed with sufficiently amortized life, and un-attended operation.  Does not rule our hypergolics, or other fuel combinations.  Depot should be multi-fuel capable, as well as able to store supplies, consumables, rescue craft, spare parts, ultimately habitat and micro-gravity & radiation experimentation.

Locate at Emily-1. Start small, build-out to 2400m diameter, rotating ring.

What's not to like?

Kerosene . . .

Turns to ice, don't need to refrigerate, shade will do.  Stores forever with no boil-off.  Higher density for launching.

No energy input needed to use as fuel, arrives at the depot with considerable potential chemical energy already contained within the material.

No compressors or giant tanks need for storage (as with the H that comes once the H2O is cracked).

[deltaV]

Kerosene . . .

You forgot to mention the LOX -- kerosene ain't much use without it! Fortunately LOX is apparently relatively easy to store with just a sun shield: http://forum.nasaspaceflight.com/index.php?topic=17962.msg453558#msg453558

[Bill White]

Kerosene . . .

You forgot to mention the LOX -- kerosene ain't much use without it! Fortunately LOX is apparently relatively easy to store with just a sun shield: http://forum.nasaspaceflight.com/index.php?topic=17962.msg453558#msg453558

Yep.

I thought everyone knew that already. 

[Jim Davis]

Depots could cost what, 5x less? 10x less to develop than Ares V? 

How do we know this?

[alexterrell]

As an alternative to pumping around fuels, would it be possible for, say Falcon 9H (EELV too expensive) to launch a standard 25 tons Earth Departure Stage, with a relatively low cost motor.

Rather than transferring propellant, these would be clipped together. Typically three would be clipped side by side (and possibly a fourth on top), and an Altair or Orion unit plugged on top. Two (or three) of these are expended for TLI, and the final one is used to enter Lunar orbit.

Crew missions could use LOR, or EOR, if six Departure Stages are clipped together.

Altair and Orion are only launched after the required number of EDS units are in orbit and report themselves well. It could even make sense to ensure an extra EDS unit is always in place.

If the EDS uses LOX / Kerosene, it can be stored for a long time and launched on a regular schedule, say twice per month (SpaceX might like that).

A Canadian shuttle arm on a truss could be used to assist assembly, or not. This "marshalling yard" could form a base.

So, no propellant transfer needed. Clip on architecture. Standard EDS with large production run and low launch costs.

 

[simon-th]

As an alternative to pumping around fuels, would it be possible for, say Falcon 9H (EELV too expensive) to launch a standard 25 tons Earth Departure Stage, with a relatively low cost motor.

Rather than transferring propellant, these would be clipped together. Typically three would be clipped side by side (and possibly a fourth on top), and an Altair or Orion unit plugged on top. Two (or three) of these are expended for TLI, and the final one is used to enter Lunar orbit.

Crew missions could use LOR, or EOR, if six Departure Stages are clipped together.

Altair and Orion are only launched after the required number of EDS units are in orbit and report themselves well. It could even make sense to ensure an extra EDS unit is always in place.

If the EDS uses LOX / Kerosene, it can be stored for a long time and launched on a regular schedule, say twice per month (SpaceX might like that).

A Canadian shuttle arm on a truss could be used to assist assembly, or not. This "marshalling yard" could form a base.

So, no propellant transfer needed. Clip on architecture. Standard EDS with large production run and low launch costs.

1. EDS hardware isn't cheap - if you require 4-5 stages for just the EDS, you end up paying a lot for all the engines and the structure etc.

2. Every EDS stage is a dry mass. The more you "clip on" the more dry mass you have vs. just one EDS stage.

3. For your "clip on" architecture, you need to have every EDS to have some loiter capability, passive RCS for docking etc. etc. That makes that EDS even heavy (dry).

4. LOX boils off as well. Hypergolics don't have boil-off issues. But the isp of both LOX/RP-1 and hypergolics is much lower than LH2/LOX, so you end up with a huge mass penalty for your "clip on" EDS architecture if you don't use LH2/LOX.

5. Overall, due to multiple dockings etc. your architecture gets rather complicated for one mission.

6. Falcon 9H is just a paper rocket right now. We don't know of its reliability, its costs or whether it will ever get built. On the other hand, fuel-transfer on orbit is real, we do it all the time on ISS.

[rklaehn]

As an alternative to pumping around fuels, would it be possible for, say Falcon 9H (EELV too expensive) to launch a standard 25 tons Earth Departure Stage, with a relatively low cost motor.

Sure, that could be done. I seem to remember some proposals from ULA doing just that: building trains of multiple centaur stages.

But I really don't see why everybody is so afraid of pumping cryogenic liquids around. Every time a centaur stage restarts in orbit, it is pumping cryogenic liquids around.

Insulating tanks in orbit to reduce boiloff to acceptable levels is proven, existing technology. See the planck and herschel telescopes.

ULA (not exactly a paper company or a reckless newspace company) has concrete plans on how to incrementally test and then build propellant depots.

The only reason NASA does not want propellant depots is that they want their own rocket. It does not matter how conservative your proposal is: if it does not require a heavy lifter, NASA will find a way to discredit it.

If they have the audacity to claim that "human rating" an existing launch vehicle will take almost a decade and will cost billions, they will have no problems discrediting even an extremely conservative proposal like a hypergolic depot.

[mmeijeri]

If they have the audacity to claim that "human rating" an existing launch vehicle will take almost a decade and will cost billions, they will have no problems discrediting even an extremely conservative proposal like a hypergolic depot.

They would undoubtedly try, but it would be a hard argument to make. After all, it is 30 year old technology which has seen continuous use ever since Salyut-6 in 1978 as I'm fond of pointing out. It's another gap, the Hypergolic Propellant Transfer Gap and it is high time it was closed. Note that mere in-flight refueling (one-way only) as opposed to a full depot would be even more conservative.

Still, if the Augustine commission doesn't recommend this as an option (and it looks as if they won't ), it's a moot point. If they really do want to put depots on the critical path without risk this would be a way to do it, especially if combined with EELV Phase 1 or J-130/NSC. There's a good chance cryogenic depots could be operational by the time you went beyond LEO, which means you could refuel upper stages in LEO, which means EDS launches would not be restricted to EELVs, which is good for competition.

[William Barton]

Regarding the "clip-on" architecture, I remember a proposal early on in STS development (meaning ca. 1971 or thereabouts). The idea was an EDS that was engine and thrust /support structure that was lofted by Shuttle. It was then fuelled by tanks brought up one at a time and transferred to the EDS entire. More or less the way you "refuel" a gas barbecue grill. That's sort of a half-step between a multi-stage EDS and pumping fluids in zero-gee.

[mmeijeri]

ESA has similar (unfunded) plans for multiple EDSs. You would still need boil-off mitigation, otherwise you would have to do many launches in rapid succession.

[TOG]

My apologies if this has been covered elsewhere-

What would be the desired launch rate/payload size for supplying a Propellant Depot, given, say, 4 flights annually to the moon.

How does this strategy change if the depot is maintained at L1 or L2?

Thanks in advance,
TOG

[adamsmith]

Team-

Any thoughts on this alternative to LH2 - LOX storage: What if the fuel was stored as Stable Water?  Then when the time comes to transfer the fuel the water could be broken into H2 and O2 via energy gathered from solar panels. 

This could reduce the amount of loss due to the "boil off" effect, and would be more stable and less prone to "unfortunate incidents" on orbit.

Thoughts?

Drew Montgomery AKA TOG.

Someone crank the numbers on kw-hours to turn 30mT of water into rocket fuel?  I am too busy right now. 

My guess is a REALLY big number.  I looked a site on using electrolysis at gas stations to make hydrogen and the power requirements were HUGE.  They also stated the process is only 50% efficient and large quantities of waste heat is produced.  This means huge radiators. 

Danny Deger

Make following assumptions:

1) Use slasr array as power source ( see www.slasr.com) 30% efficient conversion of solar light, 3kg/KW (stows at 80KW/m3)

2) In LEO cells 50% efficient due to "night"

3) Assume 8kwh/kg x 50% efficiency
4) Assume 3kg/KW radiators
5) Assume 4kg/KW for everything else

30MT of fuel need 16Kwh * 30,000 = 480MwH

Assume we want to make this in 1000 hours (5 weeks)

Take energy 480MwH divide by 1000 hours 480KW

Take 480KW multiply by 10kg/KW times 2 ( remember "Night") and you have 9.6 tons. A Falcon 9 can lift that.

Please tell me where I am wrong, because if I am not, H2O sounds too good to pass.  If there is water on phobos, it could supply both Mars Landers or even be returned to EML1 for moon landers.

Stanley

[A_M_Swallow]

1) Use slasr array as power source ( see www.slasr.com) 30% efficient conversion of solar light, 3kg/KW (stows at 80KW/m3)

The web site gives a completion date of last year, did it finish?  Or was the project cancelled?

30% efficiency of solar light to electricity conversion can also be achieved using using Stirling engines, which are naturally radiation proof.

A hydrogen based system will need power for cooling.

[adamsmith]

1) Use slasr array as power source ( see www.slasr.com) 30% efficient conversion of solar light, 3kg/KW (stows at 80KW/m3)

The web site gives a completion date of last year, did it finish?  Or was the project cancelled?

30% efficiency of solar light to electricity conversion can also be achieved using using Stirling engines, which are naturally radiation proof.

A hydrogen based system will need power for cooling.

The project did result in a full fledged prototype. And it appears that ATK is looking for customers.  Entech (www.entech.com) has taken the technology and applied to earthly pursuits and is now rolling out a product that provides Power and Heat.

I was looking for good kw/kg in a small package no maintenance package.  This beats a stirling engine in space.

I was examining the practicality of fuel production so I presumed that the Storage part was a separate problem.

I am reviewing the "model" and I think I am on the low side for the other category.  Apparently desktop model Hydrogen generators are about 10 times heavier, but a ratio between industrial and desktop of 10 to 1 is not unusual so I think the ballpark stands about right.

Stanley

[MP99]

Quick question about cryogenic depots - do they have to avoid boiling dry?

Alternate version of the same question - presuming a depot boils dry, it's temperature will then rise. Is there a practical process to restart loading cryogenic fuel and cool the structure back down to the required temperatures? If so, you'd presumably boiloff a lot of fuel from that first load?

cheers, Martin

[Danny Dot]

Team-

Any thoughts on this alternative to LH2 - LOX storage: What if the fuel was stored as Stable Water?  Then when the time comes to transfer the fuel the water could be broken into H2 and O2 via energy gathered from solar panels. 

This could reduce the amount of loss due to the "boil off" effect, and would be more stable and less prone to "unfortunate incidents" on orbit.

Thoughts?

Drew Montgomery AKA TOG.

Someone crank the numbers on kw-hours to turn 30mT of water into rocket fuel?  I am too busy right now. 

My guess is a REALLY big number.  I looked a site on using electrolysis at gas stations to make hydrogen and the power requirements were HUGE.  They also stated the process is only 50% efficient and large quantities of waste heat is produced.  This means huge radiators. 

Danny Deger

Make following assumptions:

1) Use slasr array as power source ( see www.slasr.com) 30% efficient conversion of solar light, 3kg/KW (stows at 80KW/m3)

2) In LEO cells 50% efficient due to "night"

3) Assume 8kwh/kg x 50% efficiency
4) Assume 3kg/KW radiators
5) Assume 4kg/KW for everything else

30MT of fuel need 16Kwh * 30,000 = 480MwH

Assume we want to make this in 1000 hours (5 weeks)

Take energy 480MwH divide by 1000 hours 480KW

Take 480KW multiply by 10kg/KW times 2 ( remember "Night") and you have 9.6 tons. A Falcon 9 can lift that.

Please tell me where I am wrong, because if I am not, H2O sounds too good to pass.  If there is water on phobos, it could supply both Mars Landers or even be returned to EML1 for moon landers.

Stanley

You would make a good conceptual design engineer   

Where did you get the 30,000 from?  Did you take into consideration the need for batteries, the efficiency of conversion, and energy to cool the cryo? 

Even with all this, it doesn't look as bad as I was thinking it might be.

Danny Deger

[adamsmith]

Team-

Any thoughts on this alternative to LH2 - LOX storage: What if the fuel was stored as Stable Water?  Then when the time comes to transfer the fuel the water could be broken into H2 and O2 via energy gathered from solar panels. 

This could reduce the amount of loss due to the "boil off" effect, and would be more stable and less prone to "unfortunate incidents" on orbit.

Thoughts?

Drew Montgomery AKA TOG.

Someone crank the numbers on kw-hours to turn 30mT of water into rocket fuel?  I am too busy right now. 

My guess is a REALLY big number.  I looked a site on using electrolysis at gas stations to make hydrogen and the power requirements were HUGE.  They also stated the process is only 50% efficient and large quantities of waste heat is produced.  This means huge radiators. 

Danny Deger

Make following assumptions:

1) Use slasr array as power source ( see www.slasr.com) 30% efficient conversion of solar light, 3kg/KW (stows at 80KW/m3)

2) In LEO cells 50% efficient due to "night"

3) Assume 8kwh/kg x 50% efficiency
4) Assume 3kg/KW radiators
5) Assume 4kg/KW for everything else

30MT of fuel need 16Kwh * 30,000 = 480MwH

Assume we want to make this in 1000 hours (5 weeks)

Take energy 480MwH divide by 1000 hours 480KW

Take 480KW multiply by 10kg/KW times 2 ( remember "Night") and you have 9.6 tons. A Falcon 9 can lift that.

Please tell me where I am wrong, because if I am not, H2O sounds too good to pass.  If there is water on phobos, it could supply both Mars Landers or even be returned to EML1 for moon landers.

Stanley

You would make a good conceptual design engineer   

Where did you get the 30,000 from?  Did you take into consideration the need for batteries, the efficiency of conversion, and energy to cool the cryo? 

Even with all this, it doesn't look as bad as I was thinking it might be.

Danny Deger

Ah Danny,

First, thanks for the complement.

I was breaking the problem down into two parts: the propellant production part and the depot part.  I "assumed" the existence of the depot part.  This is the incremental part associated with propellant production.  I saw somewhere on the Directlauncher site a reference to a "Large" (>100ton) depot in the 15ton range(?) so I cheated somewhat. But hey the idea was whether adding a good production capability would kill the deal.  I don't think it does.

Stanley

[jongoff]

Quick question about cryogenic depots - do they have to avoid boiling dry?

Alternate version of the same question - presuming a depot boils dry, it's temperature will then rise. Is there a practical process to restart loading cryogenic fuel and cool the structure back down to the required temperatures? If so, you'd presumably boiloff a lot of fuel from that first load?

Yes, there are chilldown techniques that have been developed.  Engines go "dry" on cryo upper stages and need to be conditioned before you can relight them.  If your depot is passively cooled, then you have to waste a bit of the propellant to chill everything down (but not a huge amount).  If your depot is actively cooled, you can rechill the chilldown fluid.

The amount of fuel (especially if it's LH2) doesn't have to be that much.  Remember, boiling anything sucks a lot of heat out, and then the heat capacity of hydrogen is really good.  If you keep the walls of your tank thin, to keep heat leaks down, you can keep the chilldown requirements low.  Plus, if you're using a sunshield, the equilibrium temperature it reaches, even if it is warmer than the normal boiling temperatuer of the fluid is still going to be pretty cold.

~Jon

[MP99]

Jon,

many thanks.

cheers, Martin

[Calphor]

Av-Week just put up an article on a ULA proposal for on-orbit propellant depots:

http://www.aviationweek.com/aw/generic/story.jsp?id=news/ULA08109.xml&headline=ULA%20Proposes%20On-Orbit%20Gas%20Stations%20for%20Space%20Exploration&channel=space

[agman25]

ULA Proposes On-Orbit Gas Stations for Space Exploration

http://www.aviationweek.com/aw/generic/story.jsp?id=news/ULA08109.xml&headline=ULA%20Proposes%20On-Orbit%20Gas%20Stations%20for%20Space%20Exploration&channel=space

Also Delta IV gets the centaur and The Air Force Research Laboratory is planning a hydrocarbon booster demonstration in 2018.

[simon-th]

Av-Week just put up an article on a ULA proposal for on-orbit propellant depots:

http://www.aviationweek.com/aw/generic/story.jsp?id=news/ULA08109.xml&headline=ULA%20Proposes%20On-Orbit%20Gas%20Stations%20for%20Space%20Exploration&channel=space

I think they are spot on. This IS the way forward.

I also like their near-term thinking:

Depots could be derived from the existing Centaur and planned advanced cryogenic upper stages for the EELV. The advanced stage would be designed to minimize heat transfer and propellant boil-off for extended operations in space. The depot additionally would be able to deploy a conical sunshield to fully encapsulate the tanks. “We can build a near-term depot without resorting to extreme, zero boil-off designs,” says Kutter.

I just am not sure going for a LEO depot is the way forward and they - at least according to the article - don't seem to think a L1/2 depot is what should be developed.

[adamsmith]

Av-Week just put up an article on a ULA proposal for on-orbit propellant depots:

http://www.aviationweek.com/aw/generic/story.jsp?id=news/ULA08109.xml&headline=ULA%20Proposes%20On-Orbit%20Gas%20Stations%20for%20Space%20Exploration&channel=space

I think they are spot on. This IS the way forward.

I also like their near-term thinking:

Depots could be derived from the existing Centaur and planned advanced cryogenic upper stages for the EELV. The advanced stage would be designed to minimize heat transfer and propellant boil-off for extended operations in space. The depot additionally would be able to deploy a conical sunshield to fully encapsulate the tanks. “We can build a near-term depot without resorting to extreme, zero boil-off designs,” says Kutter.

I just am not sure going for a LEO depot is the way forward and they - at least according to the article - don't seem to think a L1/2 depot is what should be developed.

Any depot is a good depot.  The concept to make self evident is that it is possible to separate the earth launch system from the space mission any type of depot will help that.

Stanley

[jongoff]

Av-Week just put up an article on a ULA proposal for on-orbit propellant depots:

http://www.aviationweek.com/aw/generic/story.jsp?id=news/ULA08109.xml&headline=ULA%20Proposes%20On-Orbit%20Gas%20Stations%20for%20Space%20Exploration&channel=space

I think they are spot on. This IS the way forward.

I also like their near-term thinking:

Depots could be derived from the existing Centaur and planned advanced cryogenic upper stages for the EELV. The advanced stage would be designed to minimize heat transfer and propellant boil-off for extended operations in space. The depot additionally would be able to deploy a conical sunshield to fully encapsulate the tanks. “We can build a near-term depot without resorting to extreme, zero boil-off designs,” says Kutter.

I just am not sure going for a LEO depot is the way forward and they - at least according to the article - don't seem to think a L1/2 depot is what should be developed.

Actually, they're interested in both LEO and L1/2 depots.  With depots both in LEO and in L1/L2, you can do missions more capable than the ESAS architectures using commercially available launchers, with no need for heavy lift.  There should be several interesting papers out at the SPACE 2009 conference next month.  Patience grasshopper.  :-)

~Jon

[mmeijeri]

There's a new set of slides about propellant depots on the ULA website.

[simon-th]

There's a new set of slides about propellant depots on the ULA website.

Thanks for the link. Great pitch by ULA, of course the Committee will recommend an HLV with a minimum capacity of 75mt to LEO class, so the 2-launch lunar scenario with EELVs they outline with propellant depots is somewhat moot.

What really is interesting to analyze right now is a 1-launch lunar architecture involving LEO depots.

Let's assume a generic 75mt to LEO HLV with the following payload characteristics (assuming the current baseline scenario + assuming an Orion+Altair+EDS stack fits into a payload bay in length):
Orion:
- 10.5mt dry mass
- 9.5mt propellant (hypergolics)
Altair:
- ascent module dry mass 5.5mt
- ascent module propellant 5mt (hypergolics)
- descent module dry mass 9mt (including pot. cargo)
- descent module propellant 26mt (LH2: 4mt /LOX: 22mt)
EDS:
- 17mt dry mass
- 103mt propellant w/ 10% margin (LH2: 15mt / LOX: 88mt)

That would mean for a hypergolics depot a single launch would be out of the question.

However with a LOX depot, the launch mass can be around 75mt with no LOX in either the EDS or Altair. Problem would be - Orion would need to do the circularization burn and rendezvous maneuvers with the depot (functioning basically as a tug to carry the whole stack to the depot). At 80mt to LEO, some LOX in the EDS could be carried along to allow the EDS to the circularization burn.

The question here is, whether 1 LOX depot and probably 10 EELV or other commercial launches to bring about 110mt of LOX to the LEO depot are cheaper than another HLV launch.

[MP99]

Another question...

For H2/O2 in a passively cooled depot, is the boiloff rate affected by the propellant load? IE is the boiloff rate the same regardless of whether the depot is 1% full or 99% full? First principles suggest there is an incoming heat load, therefore a fixed rate of boiloff is required to keep the depot cold.

cheers, Martin

[jongoff]

Another question...

For H2/O2 in a passively cooled depot, is the boiloff rate affected by the propellant load? IE is the boiloff rate the same regardless of whether the depot is 1% full or 99% full? First principles suggest there is an incoming heat load, therefore a fixed rate of boiloff is required to keep the depot cold.

I remember getting an answer about this at one point, but I can't remember the details.  I'll have to get back with you later.  Send me an email to remind me.

~Jon

[Namechange User]

Another question...

For H2/O2 in a passively cooled depot, is the boiloff rate affected by the propellant load? IE is the boiloff rate the same regardless of whether the depot is 1% full or 99% full? First principles suggest there is an incoming heat load, therefore a fixed rate of boiloff is required to keep the depot cold.

cheers, Martin

First define passively cooled....

[MP99]

Another question...

For H2/O2 in a passively cooled depot, is the boiloff rate affected by the propellant load? IE is the boiloff rate the same regardless of whether the depot is 1% full or 99% full? First principles suggest there is an incoming heat load, therefore a fixed rate of boiloff is required to keep the depot cold.

cheers, Martin

First define passively cooled....

In Jongoff's response to my previous question he said "If your depot is passively cooled" - I just copied that phrase from his response!


I must admit, though, I thought this phrase meant it was cooled by evaporation and didn't realise it was complicated. (But that's why I asked the question).

So what are my options?

cheers, Martin

[Namechange User]

Another question...

For H2/O2 in a passively cooled depot, is the boiloff rate affected by the propellant load? IE is the boiloff rate the same regardless of whether the depot is 1% full or 99% full? First principles suggest there is an incoming heat load, therefore a fixed rate of boiloff is required to keep the depot cold.

cheers, Martin

First define passively cooled....

In Jongoff's response to my previous question he said "If your depot is passively cooled" - I just copied that phrase from his response!


I must admit, though, I thought this phrase meant it was cooled by evaporation and didn't realise it was complicated. (But that's why I asked the question).

So what are my options?

cheers, Martin

When it comes to cryo tanks there are multiple ways to passively cool it.  For example, using the boil-off you do have and using it in a vapor cooled shield to protect from thermal radiation.  I would consider that passive since it is putting to good use something that will happen anyway. 

Was just wanting to get everyone on the same page to best answer the question. 

[Norm Hartnett]

This is somewhat off topic but does anyone know why the ULA slides include the Scorpius Launch Vehicles? (center bottom page 3)

Seems a rather odd choice.

[grdja]

One question I haven't seen asked.

If propellant depots are actually developed. Could they have commercial role? I mean, could ULA and/or Energia and Krunichev finally build and launch tugs that stay in space and transfer comsats and weatherbirds to GEO and other non LEO orbits?

I suppose answer to that would be is (or can it be made that) keeping a tanked off propellant depot in space cheaper than using larger payload to LEO rocket and a 3rd stage for each non LEO launch.

[Namechange User]

One question I haven't seen asked.

If propellant depots are actually developed. Could they have commercial role? I mean, could ULA and/or Energia and Krunichev finally build and launch tugs that stay in space and transfer comsats and weatherbirds to GEO and other non LEO orbits?

Certainly.  And hopefully that will be/would be the goal.

[A_M_Swallow]

One question I haven't seen asked.

If propellant depots are actually developed. Could they have commercial role? I mean, could ULA and/or Energia and Krunichev finally build and launch tugs that stay in space and transfer comsats and weatherbirds to GEO and other non LEO orbits?

I suppose answer to that would be is (or can it be made that) keeping a tanked off propellant depot in space cheaper than using larger payload to LEO rocket and a 3rd stage for each non LEO launch.

The other advantage is that bigger satellites can be sent to GEO.

1) EELV (or rival) to LEO, refuel Centaur at depot, Centaur boosts satellite to GSO.

2) LV to LEO, solar electric tug collects satellite and say argon from depot,
    tug flies to GEO and releases satellite, then tug returns to LEO.

[grdja]

Doh as H. Simpson would say. I'm a space nut, I know its possible. I was asking:

In a realistic scenario where NASA goes Deep Space or Lunar Global and uses the LEO fuel depots, will there be real incentive for commercial operators to include depots in their operational plans (and by that I also mean that commercial operators share costs of developing and deploying and tanking the depots) or will business as usual be more economic option.

Edit. For example a amateur guesswork on commercial problems with depot. Electric/Ion is assumed not likely for close term. So for example a nice little .ppt spaceship, a Parom, has to fuel up, grab a sat in LEO, get it into GTO (depending on architecture sat has a engine to do circularization and plane transfer or tug has to go almost all the way to GEO with it), than our brave tug has to reverse all its orbital changes and return to LEO for another refueling.
So in such (amateurish and inefficient I know...) approach, is there a economic case for a fuel depot?

[Patchouli]

Another advantage of a propellant depot is it can conceivably turn a VTOL RLV like DCY into a lunar transportation system at least for time critical cargo such as crew.
Stuff that doesn't need a fast trip probably could be transported for lower cost with a SEP tug.
Refuel it in LEO then fly it to the moon.

Here's a good early example of what a fuel depot can do for an RLV.
http://www.astronautix.com/craft/proelena.htm

The vehicle doesn't have to be as big as rombus smaller actually might be better.

[TOG]

Another question...

For H2/O2 in a passively cooled depot, is the boiloff rate affected by the propellant load? IE is the boiloff rate the same regardless of whether the depot is 1% full or 99% full? First principles suggest there is an incoming heat load, therefore a fixed rate of boiloff is required to keep the depot cold.

cheers, Martin

First define passively cooled....

In Jongoff's response to my previous question he said "If your depot is passively cooled" - I just copied that phrase from his response!


I must admit, though, I thought this phrase meant it was cooled by evaporation and didn't realise it was complicated. (But that's why I asked the question).

So what are my options?

cheers, Martin

When it comes to cryo tanks there are multiple ways to passively cool it.  For example, using the boil-off you do have and using it in a vapor cooled shield to protect from thermal radiation.  I would consider that passive since it is putting to good use something that will happen anyway. 

Was just wanting to get everyone on the same page to best answer the question. 

IIRC - If  you keep the propellant in a closed system (where the vapor is contained instead of released, and you have an exterior shield to prevent tank wall heating, (based on standard chemistry) won't our propellant reach an equilibrium point where the act of evaporation will keep the remainder of the propellant cool?  And at the same time, with the increase in pressure due to the "vapor active" fluids, won't there be a degree of condensation internal to the tank?

The big IFs here is the method we are using to prevent additional heat from being applied to the system and whether we can contain the vaporous propellant (to keep a "closed" system) until we start to transfer the propellant to the active spacecraft.

TOG

[jimvela]

IIRC - If  you keep the propellant in a closed system (where the vapor is contained instead of released, and you have an exterior shield to prevent tank wall heating, (based on standard chemistry) won't our propellant reach an equilibrium point where the act of evaporation will keep the remainder of the propellant cool?  And at the same time, with the increase in pressure due to the "vapor active" fluids, won't there be a degree of condensation internal to the tank?

I don't see the need.  There are commercial providers with cryo experience (think instrument cooling- hint, hint) whom could build a closed loop system to return vapor to a tank in liquid form.  Once you get that, you get infinite loiter as long as your depot stays powered.

The big IFs here is the method we are using to prevent additional heat from being applied to the system and whether we can contain the vaporous propellant (to keep a "closed" system) until we start to transfer the propellant to the active spacecraft.

Again, no need. put the solar arrays on the sun side of the tankage, and the reprocessing facilities and radiators in the shadow.  The arrays (and possibly additional MLI or other insulation) help keep the tankage cool, and supply power for the system to cool propellant and  reprocess boiloff.

[TOG]

IIRC - If  you keep the propellant in a closed system (where the vapor is contained instead of released, and you have an exterior shield to prevent tank wall heating, (based on standard chemistry) won't our propellant reach an equilibrium point where the act of evaporation will keep the remainder of the propellant cool?  And at the same time, with the increase in pressure due to the "vapor active" fluids, won't there be a degree of condensation internal to the tank?

I don't see the need.  There are commercial providers with cryo experience (think instrument cooling- hint, hint) whom could build a closed loop system to return vapor to a tank in liquid form.  Once you get that, you get infinite loiter as long as your depot stays powered.

The big IFs here is the method we are using to prevent additional heat from being applied to the system and whether we can contain the vaporous propellant (to keep a "closed" system) until we start to transfer the propellant to the active spacecraft.

Again, no need. put the solar arrays on the sun side of the tankage, and the reprocessing facilities and radiators in the shadow.  The arrays (and possibly additional MLI or other insulation) help keep the tankage cool, and supply power for the system to cool propellant and  reprocess boiloff.

Jim- Not a bad direction, but to take it a step further, if, instead of standard solar panels you use heat exchange units (similar to a heat pump or more commonly called "air conditioner") to both power the unit and keep the propellant cool.  Two birds with existing technology - probably cheaper than sending the "normal" solar panels.

What do you think of that idea?

[gin455res]

I've seen  suggestions for a lox only depot, is there any rationale for an N2O4 only depot?

For example, what is the isp of N2O4/H2? if it is higher than hydrazine, then maybe it is possible to get the operational convenience of a storeable depot combined with a better isp, one that would make a storeable depot in leo worthwhile?

[gin455res]

Just tried to find isp  of n2O4/hydrogen using
http://rocketworkbench.sourceforge.net/equil.phtml
Used frozen flows,  chamber pressure 40bar. exit 0.1 bar
7 mols h2, 1 mol n2o4
- no idea if this is a sensible set-up but got output below
not sure if it is 363 or 378 that is the isp figure

Results

Propellant composition
Code  Name                                mol    Mass (g)  Composition
618   N2O4 (NTO NISC)                     1.0000 92.0111   2N  4O 
457   HYDROGEN (CRYOGENIC)                7.0000 14.1112   2H 
Density :  0.408 g/cm^3
3 different elements
N  O  H 
Total mass:  106.122241 g
Enthalpy  : -779.71 kJ/kg

29 possible gazeous species
2 possible condensed species

                       CHAMBER      THROAT        EXIT
Pressure (atm)   :      40.000      22.394       0.100
Temperature (K)  :    2941.315    2648.263     858.604
H (kJ/kg)        :    -779.714   -1804.553   -7386.048
U (kJ/kg)        :   -2640.413   -3479.865   -7929.208
G (kJ/kg)        :  -52013.330  -47933.613  -22341.737
S (kJ/(kg)(K)    :      17.419      17.419      17.419
M (g/mol)        :      13.143      13.143      13.143
(dLnV/dLnP)t     :    -1.00000    -1.00000    -1.00000
(dLnV/dLnT)p     :     1.00000     1.00000     1.00000
Cp (kJ/(kg)(K))  :     3.52882     3.46336     2.63710
Cv (kJ/(kg)(K))  :     2.89622     2.83076     2.00449
Cp/Cv            :     1.21843     1.22348     1.31560
Gamma            :     1.21843     1.22348     1.31560
Vson (m/s)       :  1483.35544  1431.67916   813.51089

Ae/At            :                 1.00000    28.59611
A/dotm (m/s/atm) :                52.25471  1494.28144
C* (m/s)         :              2090.18852  2090.18852
Cf               :                 0.68495     1.73904
Ivac (m/s)       :              2601.85206  3784.35164
Isp (m/s)        :              1431.67916  3634.92349
Isp/g (s)        :               145.99065   370.65904

Molar fractions

H                     1.2547e-02  1.2547e-02  1.2547e-02
HNO                   5.1643e-07  5.1643e-07  5.1643e-07
HNO2                  1.3835e-08  1.3835e-08  1.3835e-08
HO2                   4.5824e-07  4.5824e-07  4.5824e-07
H2                    3.6840e-01  3.6840e-01  3.6840e-01
H2O                   4.8960e-01  4.8960e-01  4.8960e-01
H2O2                  3.7989e-07  3.7989e-07  3.7989e-07
N                     5.2246e-07  5.2246e-07  5.2246e-07
NH                    1.0871e-06  1.0871e-06  1.0871e-06
NH2                   3.3825e-06  3.3825e-06  3.3825e-06
NH3                   2.2785e-05  2.2785e-05  2.2785e-05
NO                    2.9311e-04  2.9311e-04  2.9311e-04
NO2                   1.8924e-08  1.8924e-08  1.8924e-08
N2                    1.2369e-01  1.2369e-01  1.2369e-01
N2O                   4.1857e-08  4.1857e-08  4.1857e-08
O                     1.1054e-04  1.1054e-04  1.1054e-04
OH                    5.2720e-03  5.2720e-03  5.2720e-03
O2                    5.8312e-05  5.8312e-05  5.8312e-05

[jongoff]

One question I haven't seen asked.

If propellant depots are actually developed. Could they have commercial role? I mean, could ULA and/or Energia and Krunichev finally build and launch tugs that stay in space and transfer comsats and weatherbirds to GEO and other non LEO orbits?

Certainly.  And hopefully that will be/would be the goal.

I'd say it's a definitely maybe.  The technical capability of doing so would definitely be there.  It would more be a case of making the business numbers work.  I *think* there are some markets there, and possibly some big ones.  But only time will tell.

How was that for a complete non-answer?

~Jon

[lewis886]

I'm sorry if this is a stupid question, but i've been wondering this for a while.

When all of you are talking about propellant depots, how are you assuming that they operate?  Specifically,  do they have a large permanent tank(s) in which is stored the propellant that is brought up in smaller tanks and then transferred into the depot (as shown on the left part of my crude illustration below)

OR

Is a depot imagined as being only a central core with the plumbing/pumping/cooling features, into which the propellant delivery tanks are "plugged in", and then those tanks are discarded when empty? (as shown on the right side of my crude drawing)


I can see benefits and drawbacks to both ways.  First, the large tank takes much less plumbing/complexity inside the depot itself, plus the delivery tanks can be somewhat simpler. 

On the other hand, the plug-in tanks only have to last for a limited amount of time anyway, and you have to send the propellant up in something, so why transfer it until you need to transfer it into the EDS/spacecraft that needs it?  Just have a standard pump adapter on the top of all deliveries, plug them in to separate sockets, and transfer the propellant through the depot when a spacecraft docks at the specified fueling attachment.   Plus, you wouldn't have to worry about MMOD problems with the large permanent tank if you are always jettisoning and replacing these smaller tanks instead.

I'm really not sure.  As, I said, it could be a stupid question, but I'm still curious.

[mmeijeri]

I've seen  suggestions for a lox only depot, is there any rationale for an N2O4 only depot?

If that requires new engines then it makes the concept a lot less interesting. I think the main argument in favour of using a hypergolics depot for exploration is that you can do it safely and soon because it is a proven technology with a more than 30 years operational history.

A secondary argument is that it would be good for refueling reusable tugs. Those would be necessary for efficient resupply of both depots and space stations. An existing launch vehicle could drop off its cargo near the station or depot and the tug would pick it up and bring it to its destination. This saves you an expensive and heavy SM every time, which makes a lot of difference. There is a whole list of planned or existing vehicles that could serve as interim tugs (Orion, ATV, HTV, Cygnus, Dragon) and all use hypergolics. In the longer term you might see tugs with nontoxic RCS emerge.

Hypergolics would also be good for deep space missions because of reliable ignition, no need for turbopumps etc. Density would be good too if you're basing things on commercial launchers only, but methane also has good density and better Isp and better ISRU potential as well.

If you don't want hypergolics, you could also consider a kerosene depot with the EDS bringing its own LOX.

[mmeijeri]

On the shape of depots:

I'd be in favour of a universal jack of all trades vehicle. A fully reusable hypergolic lunar lander could contain 80-100mT of propellant and have a delta-v of 5-6 km/s. This is enough for a round trip L1-moon without refueling, a one way trip from LEO to L1 or back with sizeable cargo, a one way trip from EML1 to Mars L1 or back and Mars all propulsive landing or ascent.

This vehicle could be the basis of a depot, mini space station, cargo transfer stage for extremely valuable cargo from LEO to L1, a Mars transfer vehicle, a moon lander, an all propulsive Mars lander and makeshift surface hab. Propellant and uncrewed cargo could be prepositioned to L1 by cryogenic propulsion and efficient trajectories and from L1 to Mars by SEP tug, giving high effective Isp. It would be the Space Shuttle of the new exploration age and that would be a good thing.

Orion, this universal vehicle and EELV Phase 1 are all we need. The rest (cryogenic depots, SEP, aerobraking, ISRU etc maybe even HLV) would be valuable later additions but could be put on the technology development track, safely off the critical path. If you're willing to beef up future commercial crew capsules you could have them dock with your universal vehicle at L1 and such a smaller capsule would only require a modified Centaur, which can be launched fully fueled on existing EELVs. The Centaur would still need modifications, so you might as well go ahead with a new upper stage

[grdja]

I'd say it's a definitely maybe.  The technical capability of doing so would definitely be there.  It would more be a case of making the business numbers work.  I *think* there are some markets there, and possibly some big ones.  But only time will tell.

How was that for a complete non-answer?

~Jon

Thank you very much. "Definitely maybe" is much better than "wont ever work economically, only usable for big crewed spaceships", that I feared will hear.

[jongoff]

I'm sorry if this is a stupid question, but i've been wondering this for a while.

When all of you are talking about propellant depots, how are you assuming that they operate?  Specifically,  do they have a large permanent tank(s) in which is stored the propellant that is brought up in smaller tanks and then transferred into the depot (as shown on the left part of my crude illustration below)

OR

Is a depot imagined as being only a central core with the plumbing/pumping/cooling features, into which the propellant delivery tanks are "plugged in", and then those tanks are discarded when empty? (as shown on the right side of my crude drawing)


I can see benefits and drawbacks to both ways.  First, the large tank takes much less plumbing/complexity inside the depot itself, plus the delivery tanks can be somewhat simpler. 

On the other hand, the plug-in tanks only have to last for a limited amount of time anyway, and you have to send the propellant up in something, so why transfer it until you need to transfer it into the EDS/spacecraft that needs it?  Just have a standard pump adapter on the top of all deliveries, plug them in to separate sockets, and transfer the propellant through the depot when a spacecraft docks at the specified fueling attachment.   Plus, you wouldn't have to worry about MMOD problems with the large permanent tank if you are always jettisoning and replacing these smaller tanks instead.

I'm really not sure.  As, I said, it could be a stupid question, but I'm still curious.

Give me a month.  There's a slew of depot related papers that will be presented at Space 2009.  And several of them go into this question.

~Jon

[MP99]

Another question...

For H2/O2 in a passively cooled depot, is the boiloff rate affected by the propellant load? IE is the boiloff rate the same regardless of whether the depot is 1% full or 99% full? First principles suggest there is an incoming heat load, therefore a fixed rate of boiloff is required to keep the depot cold.

I remember getting an answer about this at one point, but I can't remember the details.  I'll have to get back with you later.  Send me an email to remind me.

~Jon

Jon,

did you manage to find up the previous answer to this question?

Cheers, Martin

[Xplor]

This is somewhat off topic but does anyone know why the ULA slides include the Scorpius Launch Vehicles? (center bottom page 3)

Seems a rather odd choice.

While Atlas and Delta are givens in a ULA slide it makes sense for the entire launch industry to participate in launching propellant.  Falcon is an obvious additional rocket.  So are the various foreign rockets.

Who else would you suggest?

[adamsmith]

On the shape of depots:

I'd be in favour of a universal jack of all trades vehicle. A fully reusable hypergolic lunar lander could contain 80-100mT of propellant and have a delta-v of 5-6 km/s. This is enough for a round trip L1-moon without refueling, a one way trip from LEO to L1 or back with sizeable cargo, a one way trip from EML1 to Mars L1 or back and Mars all propulsive landing or ascent.

This vehicle could be the basis of a depot, mini space station, cargo transfer stage for extremely valuable cargo from LEO to L1, a Mars transfer vehicle, a moon lander, an all propulsive Mars lander and makeshift surface hab. Propellant and uncrewed cargo could be prepositioned to L1 by cryogenic propulsion and efficient trajectories and from L1 to Mars by SEP tug, giving high effective Isp. It would be the Space Shuttle of the new exploration age and that would be a good thing.

Orion, this universal vehicle and EELV Phase 1 are all we need. The rest (cryogenic depots, SEP, aerobraking, ISRU etc maybe even HLV) would be valuable later additions but could be put on the technology development track, safely off the critical path. If you're willing to beef up future commercial crew capsules you could have them dock with your universal vehicle at L1 and such a smaller capsule would only require a modified Centaur, which can be launched fully fueled on existing EELVs. The Centaur would still need modifications, so you might as well go ahead with a new upper stage

Please see the following page as an advance Solar electric Mars system using Hypergolics that presumes a depot.


http://www.lpi.usra.edu/publications/reports/CB-1106/wash01.pdf

Stanley

[robertross]

Another question...

For H2/O2 in a passively cooled depot, is the boiloff rate affected by the propellant load? IE is the boiloff rate the same regardless of whether the depot is 1% full or 99% full? First principles suggest there is an incoming heat load, therefore a fixed rate of boiloff is required to keep the depot cold.

cheers, Martin

As an aside, something which was discussed well in the past was the use of Propane for engine fuel. In tandem with LOX, you would get a good balance of storage temperatures, not have to worry of Kerosene, and steer WAY clear of LH2.

I believe the Japanese are working on a propane-powered engine. This might be something to consider in the future. Of course Methane would be best for an ascent stage, but considering the volumes in play simply for ascent-only, long-term cryo storage has major benefits (especially for breathing oxygen/nitrogen).

[rklaehn]

The viability of propellant depots depends very much on how much propellant can be launched per supply flight. There have been extremely different assumptions on this topic.

On the one hand, there are people that assume that a significant part of a propellant depot flight will be lost for a spacecraft that is handling the approach and proximity operations close to the depot. For an example, see this recent space review article.

On the other hand we have optimists that assume that almost the entire payload of a propellant depot supply flight will be actual propellant and that the costs of propellant delivery will be dominated by the launch costs and not by the costs of the propellant delivery spacecraft.

So which is closer to the truth?

I think that since most upper stages are basically complete spacecraft with RCS and all, there would be a significant benefit when delivering the same propellant as used from the upper stage.

In this case you would have to increase the size of the propellant tanks of the upper stage. For an atlas 552 propellant launch you would have to build a centaur with larger tanks and then use the centaur to fly close to the propellant depot. You would not need a payload fairing or payload adapter since the payload is the propellant remaining in the centaur tanks after reaching LEO. All proximity operations would be done by the depot itself, with the centaur acting as a passive target.

I realize that this is not easy to do. But is there anything fundamentally wrong with this approach?

[Downix]

A thought on a depot storage, we launch a perfect storage container every time we launch a shuttle... the fuel tank.  There is no reason why a shuttle launch using a specially modified tank could not carry the tank into an orbital location, or even a modified tank (using a Jupiter rocket-base w/ a single motor mounted) designed to move the tank into the proper orbit.  It's an incomplete idea, would need work and modification to the tank itself, but it seems doable.

**edit** Ok, random thought for a modification, if the tank could be placed into orbit, and a way to have the shuttle re-attach to it once in orbit, if the shuttle had the ability to have a full fuel tank waiting for it in orbit, how far up could it go?

[jongoff]

The viability of propellant depots depends very much on how much propellant can be launched per supply flight. There have been extremely different assumptions on this topic.

On the one hand, there are people that assume that a significant part of a propellant depot flight will be lost for a spacecraft that is handling the approach and proximity operations close to the depot. For an example, see this recent space review article.

On the other hand we have optimists that assume that almost the entire payload of a propellant depot supply flight will be actual propellant and that the costs of propellant delivery will be dominated by the launch costs and not by the costs of the propellant delivery spacecraft.

So which is closer to the truth?

I think that since most upper stages are basically complete spacecraft with RCS and all, there would be a significant benefit when delivering the same propellant as used from the upper stage.

In this case you would have to increase the size of the propellant tanks of the upper stage. For an atlas 552 propellant launch you would have to build a centaur with larger tanks and then use the centaur to fly close to the propellant depot. You would not need a payload fairing or payload adapter since the payload is the propellant remaining in the centaur tanks after reaching LEO. All proximity operations would be done by the depot itself, with the centaur acting as a passive target.

I realize that this is not easy to do. But is there anything fundamentally wrong with this approach?

This is fairly close to the approach ULA has suggested.  Stretching the Centaur tank axially is a fairly minor change (they've done it many times in the past), and adding an extra hydrazine bottle if necessary is also relatively easy (they've already got locations on the Centaur aft end that are sized right for attaching another tank).  Supposedly the Centaur avionics are capable of at least rendezvous.  If you combined the system with some sort of "boom rendezvous and docking" approach, it might make sense.

Me personally, I'd prefer using a tug system instead, since it makes it easier for different launch providers to compete (which should help keep costs lower).  But the idea of having the depot delivery tank be the same tank as the stage isn't bad.

~Jon

[A_M_Swallow]

Given a standard interface many ways of delivering and storing the fuel can be used.

[Arthur]

With all the discussion recently, let me take a moment to try to clarify the Depot architecture decisions which we have made for DIRECT.

There is much debate about using an all-EELV-class approach.   What this would require, is approximately 9 launches for each mission.   Assuming a combination of 20mT and 25mT vehicles the following approach is hypothetically possible (though only if you choose to completely ignore the volume/diameter issues entirely):

1 Orion (fueled) -- Heavy
2 Lander Ascent Stage (fueled) -- Intermediate
3 Lander Descent Stage (dry) -- Heavy
4 EDS (mostly dry) -- Intermediate
5 Fuel for Descent Stage -- Intermediate
6 Fuel for EDS -- Intermediate
7 Fuel for EDS -- Intermediate
8 Fuel for EDS -- Intermediate
9 Fuel for EDS -- Intermediate

This architecture certainly requires the use of Propellant Transfer technologies and would almost-certainly require a full Depot to be deployed as part of the baseline Critical Path to success.

Of these 9 launches, the first 4 in that list are all mission critical and the loss of any one would result in an LOM situation.   The latter 5 launches are somewhat "interchangable" so there is "Partial Redundancy" possible there.   It's not too bad, but the logistics and the necessity to coordinate the launch of 4 of those vehicles perfectly in support of each mission, plus the constant fuel deliveries as well, makes it a very demanding logistical nightmare.



Comparatively, DIRECT chooses a three-step approach to getting to the final arrangement.

Firstly we deploy Jupiter-130 in order to preserve jobs & experience to secure the political backing we need in Congress.   This provides an incredibly capable system all by itself, but still isn't quite enough for Lunar use (although with a Delta Upper Stage, the Flyby missions are quite possible).

Step 2 is the deployment of the Jupiter-24x and the Altair lander, which opens up the Lunar capabilities without requiring any Propellant Transfer technologies at all.   This is an interim step designed to begin our new exploration efforts and to allow NASA to start the Exploration efforts in earnest while other important technologies continue to be developed -- without those technologies every appearing on the "Critical Path".

Step 3 is the ultimate goal though.   Here, every Jupiter launch represents a complete mission, supported by a constant stream of fuel deliveries going to a (one or more) Depot.   The mission Hardware all launches upon a single launcher which then rendezvous with the Depot, fills up all the tanks it needs to with whatever fuel load is required for that mission and then departs upon its mission without ever requiring any other docking events.

The purpose of this approach is to maximize the number of units in production, not just for the costly launch vehicles, but also for the even more expensive spacecraft as well.

This architecture opens the door not to just 2 Lunar-class missions per year, but to a possible 8 (or more) every year.   More importantly, this approach also enables all of the NEO and Mars missions as well without further investment in the basic infrastructure.   This approach is quite capable of sending hundreds of tons of useful payload material towards Mars -- or even Jupiter if required.

I am including the costs for the launches below.

Ross.

I wanted to move this post and my question to a topic more "DEPOT" related. 

Does anyone know where similar data for an EELV can be found?

 I would like to compare the cost per kg to orbit for several different "market conditions" to generate a comparison of cost vs supply curves. Are DEPOTS cheaper for all annual demands? Is Jupiter cheaper for all annual demands? Is there a volume where the curves cross?

[rklaehn]

The viability of propellant depots depends very much on how much propellant can be launched per supply flight. There have been extremely different assumptions on this topic.

On the one hand, there are people that assume that a significant part of a propellant depot flight will be lost for a spacecraft that is handling the approach and proximity operations close to the depot. For an example, see this recent space review article.

On the other hand we have optimists that assume that almost the entire payload of a propellant depot supply flight will be actual propellant and that the costs of propellant delivery will be dominated by the launch costs and not by the costs of the propellant delivery spacecraft.

So which is closer to the truth?

I think that since most upper stages are basically complete spacecraft with RCS and all, there would be a significant benefit when delivering the same propellant as used from the upper stage.

In this case you would have to increase the size of the propellant tanks of the upper stage. For an atlas 552 propellant launch you would have to build a centaur with larger tanks and then use the centaur to fly close to the propellant depot. You would not need a payload fairing or payload adapter since the payload is the propellant remaining in the centaur tanks after reaching LEO. All proximity operations would be done by the depot itself, with the centaur acting as a passive target.

I realize that this is not easy to do. But is there anything fundamentally wrong with this approach?

This is fairly close to the approach ULA has suggested.  Stretching the Centaur tank axially is a fairly minor change (they've done it many times in the past), and adding an extra hydrazine bottle if necessary is also relatively easy (they've already got locations on the Centaur aft end that are sized right for attaching another tank).  Supposedly the Centaur avionics are capable of at least rendezvous.  If you combined the system with some sort of "boom rendezvous and docking" approach, it might make sense.

Carrying the payload in the upper stage would eliminate two failure modes from the launch: fairing separation (caused two launch failures this year!) and spacecraft separation. You would also save the expense for the fairing and spacecraft separation system.

Me personally, I'd prefer using a tug system instead, since it makes it easier for different launch providers to compete (which should help keep costs lower).  But the idea of having the depot delivery tank be the same tank as the stage isn't bad.

A tug would be the best solution for a large depot. But for a small depot you could just combine the functions of depot and tug.

By the way: One very nice thing about depots is that it decouples launcher capacity and payload mass:

If your GTO or TLI launch requires topping off at a depot, any performance improvement or large propellant margin of the launcher immediately translates to cost savings since you don't need as much propellant.

Likewise, if you have some weight growth of your spacecraft there is little risk of the spacecraft getting too heavy for the launcher. Instead you just have to buy a bit more propellant at the depot.

[TOG]

This could be a very different story, had a propellant depot been available at L1 or LLO:

http://www.space.com/missionlaunches/090826-lcross-anomaly.html

Tog

[StarGeezer]

Hmmm... Shoulda posted in this thread...

So if everyone is so enamoured with analogies, how about extending the petrol/gas meme to outer space? It looks like space isn't going to happen anytime soon till big business gets aboard(sic). How about letting, say, the big oil companies/OPEC or some energy conglomerates have an exclusive to provide the first and only - for a while - gas'n'go fuel depot in LEO? If there's anything these guys can do - its the big single mega projects - transcontinental gas lines, deep shore wells, etc. A space depot would be a natural for them. Probably at a small fraction(sic) of their advertising budget - the goodwill generated would be better than anything they are doing now - sort of reverse the trend of being seen  as the 'bad' guys.

[adamsmith]

Hmmm... Shoulda posted in this thread...

So if everyone is so enamoured with analogies, how about extending the petrol/gas meme to outer space? It looks like space isn't going to happen anytime soon till big business gets aboard(sic). How about letting, say, the big oil companies/OPEC or some energy conglomerates have an exclusive to provide the first and only - for a while - gas'n'go fuel depot in LEO? If there's anything these guys can do - its the big single mega projects - transcontinental gas lines, deep shore wells, etc. A space depot would be a natural for them. Probably at a small fraction(sic) of their advertising budget - the goodwill generated would be better than anything they are doing now - sort of reverse the trend of being seen  as the 'bad' guys.

I don't agree that the oil companies (or OPEC) have the technical ability to set up space propellant depots, but they do have the financial and management ability to handle very large engineering projects: the Alaska Pipeline.  In todays $, $30 BILLION in just 3 years, of their money, not the taxpayer's,  in some of the most inhospitable environments on Earth. Very cold, kinda like Mars.  These guys are real MEN with real guts.  To be honest, Bruce Willis types.  Gee, I wonder...

Stanley

[StarGeezer]

I don't agree that the oil companies (or OPEC) have the technical ability to set up space propellant depots, but they do have the financial and management ability to handle very large engineering projects: the Alaska Pipeline.  In todays $, $30 BILLION in just 3 years, of their money, not the taxpayer's,  in some of the most inhospitable environments on Earth. Very cold, kinda like Mars.  These guys are real MEN with real guts.  To be honest, Bruce Willis types.  Gee, I wonder...

So I doubt the oil company executives or decision makers can dig a hole for oil, weld a pipeline or operate a rig. But what they seem to be good at is organizing, paying for (arranging financing for - sorry) these mega-projects and gitin'r done. So imagine a converstation between Elox Muskoil of Exxoneration Corp and L-Bar Pickenavector of Conglomerated Space Agglomeration:

Elox: Howdy L-Bar I've been thinkin' about this new government contract they just put out for a space depot. I'm talking to our contractors to see if they can help out. Seems like we're gonna need some  heavy lifters to LEO for this thing. Can you help?

L-Bar: Sure can. Up to a hundred metric tons per rocket.

Elox: Probably need something a bit heavier. Ok L-Bar I'll get our people to talk to your people etc. etc. etc.

[Downix]

Hmmm... Shoulda posted in this thread...

So if everyone is so enamoured with analogies, how about extending the petrol/gas meme to outer space? It looks like space isn't going to happen anytime soon till big business gets aboard(sic). How about letting, say, the big oil companies/OPEC or some energy conglomerates have an exclusive to provide the first and only - for a while - gas'n'go fuel depot in LEO? If there's anything these guys can do - its the big single mega projects - transcontinental gas lines, deep shore wells, etc. A space depot would be a natural for them. Probably at a small fraction(sic) of their advertising budget - the goodwill generated would be better than anything they are doing now - sort of reverse the trend of being seen  as the 'bad' guys.

I don't agree that the oil companies (or OPEC) have the technical ability to set up space propellant depots, but they do have the financial and management ability to handle very large engineering projects: the Alaska Pipeline.  In todays $, $30 BILLION in just 3 years, of their money, not the taxpayer's,  in some of the most inhospitable environments on Earth. Very cold, kinda like Mars.  These guys are real MEN with real guts.  To be honest, Bruce Willis types.  Gee, I wonder...

Stanley

Not quite true, while a large portion of the construction was done by private firms, the government was heavily involved in arranging the land rights necessary for the pipeline.  It took cooperation between the two, gov't and business, to get the pipeline done.

[adamsmith]

Hmmm... Shoulda posted in this thread...

So if everyone is so enamoured with analogies, how about extending the petrol/gas meme to outer space? It looks like space isn't going to happen anytime soon till big business gets aboard(sic). How about letting, say, the big oil companies/OPEC or some energy conglomerates have an exclusive to provide the first and only - for a while - gas'n'go fuel depot in LEO? If there's anything these guys can do - its the big single mega projects - transcontinental gas lines, deep shore wells, etc. A space depot would be a natural for them. Probably at a small fraction(sic) of their advertising budget - the goodwill generated would be better than anything they are doing now - sort of reverse the trend of being seen  as the 'bad' guys.

I don't agree that the oil companies (or OPEC) have the technical ability to set up space propellant depots, but they do have the financial and management ability to handle very large engineering projects: the Alaska Pipeline.  In todays $, $30 BILLION in just 3 years, of their money, not the taxpayer's,  in some of the most inhospitable environments on Earth. Very cold, kinda like Mars.  These guys are real MEN with real guts.  To be honest, Bruce Willis types.  Gee, I wonder...

Stanley

Not quite true, while a large portion of the construction was done by private firms, the government was heavily involved in arranging the land rights necessary for the pipeline.  It took cooperation between the two, gov't and business, to get the pipeline done.

What the Federal goverment gave them was immunity from the @#@#! environmentalists lawsuits that were seeking to block the pipeline.  They paid for everything.  Read Atlas Shrugged.  Fact is stranger than fiction.

Stanley

[alexterrell]

http://www.lpi.usra.edu/publications/reports/CB-1106/wash01.pdf

Stanley

This uses the magsail. I first saw this described by Zubrin.

Has this (magasail for sailing around the solar system) been discussed in this forum and could someone provide a link?

[adamsmith]

http://www.lpi.usra.edu/publications/reports/CB-1106/wash01.pdf

Stanley

This uses the magsail. I first saw this described by Zubrin.

Has this (magasail for sailing around the solar system) been discussed in this forum and could someone provide a link?

This does not use the Magsail, it uses a completely different mechanism.  the article provides references.

[Xplor]

….
I am including the costs for the launches below.

Ross.

Is Ross trying to suggest that Direct can support 200mT/year for $959M ($4,796/Kg)?  Directs costs just to keep Michoud, ATK, PWR, KSC, MSFC, etc working will be >$2B not including any recurring launch costs.

I love the enthusiasm and thought of 8 or more annual missions, but over selling concepts will simply result in changing direction from the ESAS sales job to another fiasco in 4 years.

[jongoff]

In the Direct 3.0 thread, Ross wrote:

With all the discussion recently, let me take a moment to try to clarify the Depot architecture decisions which we have made for DIRECT.

There is much debate about using an all-EELV-class approach.   What this would require, is approximately 9 launches for each mission.   Assuming a combination of 20mT and 25mT vehicles the following approach is hypothetically possible (though only if you choose to completely ignore the volume/diameter issues entirely):

1 Orion (fueled) -- Heavy
2 Lander Ascent Stage (fueled) -- Intermediate
3 Lander Descent Stage (dry) -- Heavy
4 EDS (mostly dry) -- Intermediate
5 Fuel for Descent Stage -- Intermediate
6 Fuel for EDS -- Intermediate
7 Fuel for EDS -- Intermediate
8 Fuel for EDS -- Intermediate
9 Fuel for EDS -- Intermediate

This architecture certainly requires the use of Propellant Transfer technologies and would almost-certainly require a full Depot to be deployed as part of the baseline Critical Path to success.

Of these 9 launches, the first 4 in that list are all mission critical and the loss of any one would result in an LOM situation.   The latter 5 launches are somewhat "interchangable" so there is "Partial Redundancy" possible there.   It's not too bad, but the logistics and the necessity to coordinate the launch of 4 of those vehicles perfectly in support of each mission, plus the constant fuel deliveries as well, makes it a very demanding logistical nightmare.

While this is definitely one way to do things, it's far from the optimum for a depot-centric architecture.  If you're going to do an LEO depot, making a second copy and sending it to L1/L2 makes a lot of sense (since it allows both of them to be small single-EELV-launch depots that don't require any on-orbit assembly).  With such a system, you don't need a lander descent stage anymore.  It is possible to refuel a Centaur-sized EDS in L1/L2, and have it do the Lx-to LUNO burn and a large chunk of the descent burn.  The lander DV is now quite a bit less than was needed for ESAS, and you can have it be a single-stage system, which tends to be more mass efficient for landers. 

The "Orion" can also be a lot smaller with such an architecture, because you don't need anywhere near as much delta-V to return to LEO, especially if you stage out of L2.

Sure, the logistics gets more involved, and I'll have to run the numbers on how many launches you need to do an ESAS-equivalent mission, but my point here was just to mention that a depot-centric architecture will not look like an HLV-centric architecture with depots tacked onto the side.  That's black-aluminum thinking.

~Jon

[sdsds]

Thesis:  propellant depots will be successful to the extent that their advantages can be leveraged to market spaceflight products.

Exposition:
Imagine a future where NASA contracts with Lockheed-Martin for fully-fueled Earth-departure stages delivered on-orbit.  A good contract would specify penalties if LM could not provide a stage at the designated time, and bonuses if NASA requested a delivery delay (e.g. because the payload spacecraft would not be ready at the designated time).

Under contract terms like those, it might benefit LM to launch the stages early and operate a depot from which they could be replenished.  LM would choose to establish the depot because doing so would enable them to provide the product (fueled Earth-departure stages) with the high reliability and flexibility the customer wants.

[DonEsteban]

While this is definitely one way to do things, it's far from the optimum for a depot-centric architecture.  If you're going to do an LEO depot, making a second copy and sending it to L1/L2 makes a lot of sense (since it allows both of them to be small single-EELV-launch depots that don't require any on-orbit assembly).  With such a system, you don't need a lander descent stage anymore.  It is possible to refuel a Centaur-sized EDS in L1/L2, and have it do the Lx-to LUNO burn and a large chunk of the descent burn.  The lander DV is now quite a bit less than was needed for ESAS, and you can have it be a single-stage system, which tends to be more mass efficient for landers. 

The "Orion" can also be a lot smaller with such an architecture, because you don't need anywhere near as much delta-V to return to LEO, especially if you stage out of L2.

Sure, the logistics gets more involved, and I'll have to run the numbers on how many launches you need to do an ESAS-equivalent mission, but my point here was just to mention that a depot-centric architecture will not look like an HLV-centric architecture with depots tacked onto the side.  That's black-aluminum thinking.

~Jon

OK, do I understand this correctly?

You launch crew vehicle (let's call it Orion) on top of 2-stage launcher to LEO depot. At the depot, the same second stage refuels and goes to an L2 depot (3.44km/s dv). There, the Orion is detached and reusable lander is attached to this second stage, which is also refueled.

The second stage then does the Moon descent burn (almost all of it, i.e. 2.52km/s dv, which is not too far off 3.44km/s dv, so it could sort of work) and then crashes (possibly taking care not to crash into existing moon infrastructure - or possibly crashing into designated 'scrap metal recovery area' - after all, its terminal velocity will be low, and it is a free source of processed 'stuff' on Moon), leaving the lander to do just the final landing.

Eventually, the lander flies off to L2, where the astronauts switch back to Orion and return to Earth.

Of course, there are additional fueling flight fueling the depots...

[jongoff]

OK, do I understand this correctly?

That's pretty close.  My personal favorite nuance though is that if you top the Centaur back up all the way before doing the LX to LUNO burn, there's actually enough fuel leftover after staging for it to do a burn to return to LUNO and then to LX.  Reusing a stage that's only been used in-space, has not been contaminated by the lunar surface environment, and doesn't have to deal with the hellish reentry environment should be substantially easier.

Also you forgot to mention the step where you ship the actual lander out.  It would likely fly separately from the capsule, and depending on the dV split between the two, might even be capable of self ferrying.

Of course, there are additional fueling flight fueling the depots...

Quite a few.  But the hope is that these are run kind of like a logistics stream, instead of being ordered discretely, per mission.  The LX depot has fairly low boiloff, even passively cooled, so if you have a temporary dip in demand, you don't lose very much propellant from there.  So long as you treat the LEO depot as a "use it or lose it" waypoint that only exists to aggregate enough propellant for an outbound trip for L2, you can minimize your losses there too...

~Jon

[DonEsteban]

OK, do I understand this correctly?

That's pretty close.  My personal favorite nuance though is that if you top the Centaur back up all the way before doing the LX to LUNO burn, there's actually enough fuel leftover after staging for it to do a burn to return to LUNO and then to LX.  Reusing a stage that's only been used in-space, has not been contaminated by the lunar surface environment, and doesn't have to deal with the hellish reentry environment should be substantially easier.

Also you forgot to mention the step where you ship the actual lander out.  It would likely fly separately from the capsule, and depending on the dV split between the two, might even be capable of self ferrying.

...snip...

~Jon

Hm, I was thinking about reusable lunar lander with decent crew accommodation. That would be an expensive machine - but it will be reused. The return capsule with heat-shield would go just to LX, no need to bring its heatshield into the Moon gravity well. It needs dv just to return to Earth. The lander will be shipped once (ok, there will be more, and they will be slowly replaced). The dv of the lander will be a bit (few hundreds m/s, for landing) more then enough to return from Moon to Lx. You are right that over time it will be contaminated with dust and what not, though.

The LX station in my eyes has propellant depots, empty stages (Centaurs), crew Moon landers, cargo Moon landers, perhaps deep-space ships (more shielding, provision for more supplies for long autonomous missions, perhaps a good suite of instruments to examine NEOs/Phobos whatnot), and Earth return capsules attached. And a habitat for the station crew and whatnot. All of this built incrementally, starting with the depot and a basic hub.

The crew arrives in Earth return capsule delivered by a Centaur, has a rest/party/meeting with the station crew, then switched to a 
a crew Moon lander attached to a fueled Centaur and lands on the Moon. Eventually it returns, switches to Earth return capsule and goes home.

When a cargo for Moon arrives (possibly using slow solar/nuclear electric/thermal tug) , it is re-mated to a cargo lander (ideally no EVA needed, just some robotic arm work, which should be doable with proper design; EVA only if something does not work as planned - station crew can save the day in many cases where all-automatics fail and would have resulted in mission loss). Having ready hardware and lots of fuel might allow 'rescue' missions of all sorts (not only saving astronauts, but perhaps also costly satellites  ending in wrong orbit).

I think doing it this way minimizes the amount of fuel and hardware spent on serious and sustained exploration. The initial costs are quite high - but if we are really serious about sustained exploration, something like this will eventually emerge.

[veedriver22]

 Would it make any sense to have the Earth return vehicle ferried back to Earth by the centaur as well?

[Downix]

I got to thinking of the Tanker Truck analogy that's been floating around here a bit.  Saying, "you want to drive to Mexico, you drive a tanker truck to Dallas in order to wait for you".  Good Analogy, but not workable here.  For that to work, we'd have to basically be launching the equivelent of a Space Shuttle main fuel tank in one go.  A closer analogy for us would be us sending a dozen Motorcycles, each one with a fuel tank holding 2 gallons in it.

Now, if we could figure out how to launch a SSMT on top of a large booster, then I'd be impressed.

[JulesVerneATV]

bump for an old topic but maybe the idea of some US or International Orbital propellant depot United Launch Alliance propellant depot still applies

Even if ULA doesnt deliver Orbital Fuel Depot the USA still has Elon Musk's Spacxe-X Private Sector. After the Soviet tech political threat against NASA is a new political rival, the new 'China Threat'

US intel officials “concerned” China will soon master reusable launch
https://arstechnica.com/space/2025/09/us-intel-officials-cite-reusable-launch-as-difference-maker-with-china/
"They have to have on-orbit refueling because they don’t access space as frequently as we do."

[Striker58]

In terms of the depot itself, rather than using an existing would it be more effective to use an 'inflatable unit' such as Siera Space LIFE?  It would provide a larger volume for propelant than a fixed volume from an existing 2nd stage, and potential provide better thermal efficiency using multiple layes within the structure.

Orbital mobility could come from a tug such as Helios with extinible fueling umbilicals from a dedicted service module based of something like Haven.