One slight clarification to what Jon just mentioned, there needs to be a slow venting of GH2 throughout the transfer in order to keep the propellants settled the whole time, not just to start the process.
I understand that 0.0004g is all that's required to ensure the propellant remains settled correctly. And a pressure differential in the order of just 4psi between the delivery and receiving tanks is all that is required to enable 100mT of transfer in about 1-2 hours.
This is exactly how Von Braun proposed to do cryo prop transfer for advanced Apollo missions. Also, everything needed to perform this has already been flown and fully tested in micro-gravity, with the sole exception being the coupling mechanisms.
Well, you don't actually have to vent continuously. You just have to provide enough propulsive force to overwhelm all the unsettling forces/disturbances on the vehicles. In some cases this would mean a continuous settling thrust, in other cases it can actually be intermittent. Centaur IIRC uses a pulsed vent to keep settled during coast phase.
Quote from: jongoff on 09/11/2009 09:55 pmWell, you don't actually have to vent continuously. You just have to provide enough propulsive force to overwhelm all the unsettling forces/disturbances on the vehicles. In some cases this would mean a continuous settling thrust, in other cases it can actually be intermittent. Centaur IIRC uses a pulsed vent to keep settled during coast phase.I believe D-IV US also uses timed pulses to keep the propellant settled and dissipate slosh energy after engine shutdown.
I am glad to finally see a solid EELV proposal. One only needs to look back about 2 to 3 years and we were all practically begging for ULA to put something, anything, on the table, the DIRECT team included. Of course only a few knew then how ULA and USA had been silenced. If this had been on the table back then the past 2-3 years would have been very different.
It's funny though on 2 scores:1. So many people pooh poohed the Propellant Depot idea when we made it part of our architecture over 2 years ago but now that ULA integrates it into theirs, suddenly everybody thinks it's a good idea. In spite of saying over and over again that we were getting all our data for the depot from industry, few people listened. Now the same industry makes it public and everybody loves it.2. Everybody now loves the ACES upper stage. This upper stage combines the best of the Atlas and Delta cryogenic upper stages. Once again, we went to industry to get help with the JUS and what we delivered is pretty much what the ACES is, only bigger diameter; 8.4 meter diameter to match the Shuttle ET manufacturing tooling and using 6 RL-10’s vs. 4 RL-10s. Again, the design data came directly from industry but few people listened and tons of people severely criticized it. Now that the same industry releases an architecture that uses that same data everybody loves it.
The people who pooh-poohed depots for DIRECT, and the JUS numbers for DIRECT will also probably pooh-pooh this.
In reality, no single industrial entity can entirely support this architecture."The production and launch rates are simply not sustainable by a single team. It must be a concerted effort of several launch providers, perhaps a consortium linking industry and NASA.”
Quote from: Robo-Nerd on 09/11/2009 08:46 pmDid anyone figure out why they proposed an L2 depot instead of an L1 depot? Is the delta-V significantly different? Thanks,Read Simon paper, very instructive :http://forum.nasaspaceflight.com/index.php?topic=17564.0
Did anyone figure out why they proposed an L2 depot instead of an L1 depot? Is the delta-V significantly different? Thanks,
Right. No heavy lift = zillions of small lifts = high cost and high complexity.
Just a quick post inbetween 128 fun to say thanks again for the nice words about the article. Seems a bit fluffy to post this, but it does mean a lot and it's really appreciated.
I guess in a lot of cases that the data doesn’t matter. It comes down to who says it. Go figure.
One might even say this approach is "Centaur on Steroids"
Notice many of these ULA documents also state that their components can be incorporated into a directly shuttle derived architecture.they are reading tea leaves.IE a mixed fleet.
a new company merging ATK, Boeing and Lockheed-Martin to develop and operate the Jupiter systems.
Can we have the 1.5 CxP ? Direct single launch cargo only to the moon base ?
Don't forget that this architecture is limited to 2 missions per year total, so 2 crew missions, 2 cargo missions, or 1 crew and 1 cargo mission per year.
Quote from: Marsman on 09/12/2009 12:26 amDon't forget that this architecture is limited to 2 missions per year total, so 2 crew missions, 2 cargo missions, or 1 crew and 1 cargo mission per year. I haven't had a chance to fully read the published version of Frank's paper, but wasn't someone mentioning earlier that they were talking about 4 missions per year, not 2?The nice thing about a depot-centric architecture like this is also that as more and improved launch services come online, you can continuously increase the affordability of lunar missions. It doesn't take much in the way of small commercial RLVs (which would finally have a market, BTW) to make it possible to do a lot more missions for the same overall cost. With an HLV-centric, non-depot architecture, you're pretty much locked in to a set of fixed costs that you can never really do much about.~Jon