Quote from: Jim on 01/14/2009 12:35 amIncorrect, it is needed. LH2 will not become stable in the tank without itDoes that mean it will be at a full rolling boil without it? Would that cause foam or what (besides losses)?
Incorrect, it is needed. LH2 will not become stable in the tank without it
Lack of fuel destroys engines, which is why they run fuel rich.
Quote from: Lobo on 01/13/2009 10:52 pmMy guy tells me the latter should be true...but are these things that have all been absolutely accounted for? Can we even know until a buildable blueprint for the new ET has been done?*shrug*Yes and yes. Look at the NLS document Ross posted
My guy tells me the latter should be true...but are these things that have all been absolutely accounted for? Can we even know until a buildable blueprint for the new ET has been done?*shrug*
Another reason not to scale down Direct is that everything smaller than the 120 could easily be replicated with the Delta IV. I remember the suggestion of a "Baby-Jupiter" with 1 RS-68, but it was found that at that point, the Delta IV Heavy would be much better.
Quote from: gladiator1332 on 01/14/2009 12:07 amAnother reason not to scale down Direct is that everything smaller than the 120 could easily be replicated with the Delta IV. I remember the suggestion of a "Baby-Jupiter" with 1 RS-68, but it was found that at that point, the Delta IV Heavy would be much better. It's kind of interesting that a Jupiter 110 would be *very* similar to the Ariane 5, both in look and payload capability. (I'm not sure about the external dimensions, though)But I certainly understand why you don't want to scale down the 120 further... and it would be nice to have a launcher that wouldn't have such tight mass margins.
It would make a nice "What If?" scenario, where NASA is able to develop a launch vehicle that can be used commercially. I would like to see how a Jupiter-110 would have fared against the EELVs and Ariane V.
For the Jupiter 232 design to close, the ultralightweight upper stage has to meet the ambitious goals set by the Direct team and their anonymous engineers.
Quote from: gladiator1332 on 01/14/2009 02:49 amIt would make a nice "What If?" scenario, where NASA is able to develop a launch vehicle that can be used commercially. I would like to see how a Jupiter-110 would have fared against the EELVs and Ariane V. NASA is forbidden by law to compete in the commercial area. Shuttle pretty much wiped out the US commercial launch industry, no reason to do so again.
Quote from: Lobo on 01/13/2009 10:52 pmI understand the ET won't leave LEO, but it was never designed to carry a load that would like it will be used for now.Like I said, maybe it's not a major obsticle. Just pointing out some other consideration that people might not be thinking about, especially when they all get excited about their own ideas.So you think people, which are working on DIRECT project for 2 years now, somehow "might not be thinking about" whether it is feasible of making ET-derived tank to support this weight.Surprise! They did think about it, and found out that it is possible, and not even hard.
I understand the ET won't leave LEO, but it was never designed to carry a load that would like it will be used for now.Like I said, maybe it's not a major obsticle. Just pointing out some other consideration that people might not be thinking about, especially when they all get excited about their own ideas.
Quote from: robertross on 01/14/2009 01:09 amLack of fuel destroys engines, which is why they run fuel rich.I thought they also ran fuel rich to reduce the average molecular weight of the exhaust, which increases ISP.
That's the Achilles' heel of the Direct proposal. Ares now has a three year head start,
Quote from: Lee Jay on 01/14/2009 01:14 amQuote from: robertross on 01/14/2009 01:09 amLack of fuel destroys engines, which is why they run fuel rich.I thought they also ran fuel rich to reduce the average molecular weight of the exhaust, which increases ISP.Yes and no. Running stoichiometric (burn everything equally) means maximum energy is extracted from the chemical reaction. Running fuel or oxidiser rich means you are chucking more mass overboard for less chemical energy per unit mass... hence a lower collective exhaust velocity. However, it also means that the thermal energy is more efficiently distributed amongst molecules. It's easier to plunk thermal energy into H2 because it has one bond. H2O has 3 bonds so it gets squished out in the interactions. (Real rocket engineers please feel free to correct me wherever I foul up).
Quote from: Will on 01/14/2009 01:20 amFor the Jupiter 232 design to close, the ultralightweight upper stage has to meet the ambitious goals set by the Direct team and their anonymous engineers.I may not be reading these numbers right, but what's so ambitious about it? According to the baseball cards it weighs 47,367 pounds, and carries under 800,000 pounds of propellant, while the ET weighs 58,500 pounds (23% more) and carries over 1,600,000 pounds (over 100% more) of propellant. It sound's as if the current ET is much more ambitious from those numbers, and it has to side-mount the orbiter, support the beam from the SRBs, and it's not a common-bulkhead design.What am I missing?
Quote from: Will on 01/14/2009 01:20 amFor the Jupiter 232 design to close, the ultralightweight upper stage has to meet the ambitious goals set by the Direct team and their anonymous engineers.It doesn't get any more anonymous than Bernard Kutter, Manager of Advanced Programs at ULA - Lockheed-Martin publicly saying the JUS is verging on conservative, does it?I suppose that once you make up your mind about something, no amount of authority in the field will convince you otherwise. You wouldn't be forgetting this point that was brought up to you earlier otherwise. Sure, believe Steve Cook, he's an expert on cryo upper stages.