Quote from: TOG link=topic=18116.msg458099#msg458099 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.QuoteThe 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.
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.
Quote from: grdja on 08/12/2009 04:25 pmOne 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.
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've seen suggestions for a lox only depot, is there any rationale for an N2O4 only depot?
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
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)ORIs 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.
Quote from: MP99 on 08/11/2009 09:59 amAnother 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
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.
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.
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
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
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?
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) -- Heavy2 Lander Ascent Stage (fueled) -- Intermediate3 Lander Descent Stage (dry) -- Heavy4 EDS (mostly dry) -- Intermediate5 Fuel for Descent Stage -- Intermediate6 Fuel for EDS -- Intermediate7 Fuel for EDS -- Intermediate8 Fuel for EDS -- Intermediate9 Fuel for EDS -- IntermediateThis 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.
Quote from: rklaehn on 08/25/2009 07:35 pmThe 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.