Pierce Nichols wrote: > > At 12:10 PM 8/1/02 -0700, Randall Clague wrote: > >On Thu, 01 Aug 2002 11:02:21 -0700, Pierce Nichols > ><[EMAIL PROTECTED]> wrote: > > > > > It's not really possible to say a priori whether the staging event > > >should be orbital or suborbital. That's a determination that must be made > > >as part of the trajectory optimization, and it depends heavily on the > > >desired trajectory and the specific designs of the proposed vehicles. > > > >It is possible to say a priori whether the staging event should even > >occur, though. SSTO offers so many operational advantages that if > >it's possible, it should be done. > > I was speaking specifically about the asteroid flyby mission under > discussion. That's at least a 13 km/s delta-V, which will require at least > two stages with current tech and a realistic budget. You know well enough > that I'm a fairly dedicated heretic when it comes to the whole staging > question, however :). > > > Payload capacity need not be high, either, to support an expendable > > upper stage for a mission beyond LEO. The SSTO doesn't have to make > > it to orbit before staging for the mission to work, and with the > > delta-v requirement relaxed, the payload capacity goes way up. > > OTOH, the delta-V requirement for the upper stage goes up. The > balancing point is intensely dependent on mission and vehicle specific > parameters. I suspect it's some kind of suborbital, because they eliminate > the need for a circularization burn or orbital maneuvering fuel aboard the > lower stage.
It seems that once you've got the altitude and delta-V to release the upper stage, trying to take the booster orbital from there increases, rather than decreases, the operational complexity... the total impulse to orbit for the booster may be less than if it took the upper stage all the way, but it's still more than would be required to soft-land the nearly-empty booster after a suborbital boost (not to mention the increased thermal load on the booster re-entering from orbital velocity) - there's also the difficulty of staging off the asteroid probe from the booster partway through an ascent to orbit (separating an upper stage seems to loom large enough as a "difficult maneuver" when executed after booster cutoff; taking the booster to orbit after separation would require doing a separation during the booster burn, or doing a shutdown and restart of the booster). -dave w _______________________________________________ ERPS-list mailing list [EMAIL PROTECTED] http://lists.erps.org/mailman/listinfo/erps-list
