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.
>Of course, LEO+ missions would only be an adjunct for an SSTO launch
>services business. Given an operations model that has the boat coming
>home every day, doing what is in effect a recovery from a contingency
>abort remote landing would be something of a headache. (The marketing
>guy, of course, will say, "We need to practice that anyway. Let's
>make money at it.")
Actually, that's what the engineering guy says... :). The
marketing guy sold this mission without inquiring to deeply into the whys
and wherefores.
-p
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