Well, no one knows yet what the GTAT is. We'll find out. And if it's
used in addition for PtP, well...
On 10/3/21 18:09, Henry Spencer wrote:
On Sun, 3 Oct 2021, Rand Simberg wrote:
If you really want to get a LOT of mass to orbit cheaply, it's probably better to do it with a larger than a smaller rocket, just to reduce the total number of launches required...
There's no fundamental reason why per-launch overhead has to be large enough to be a major cost. The only *essential* per-launch activities that take significant time are to position the vehicle on the pad, put a cargo in it, and fill the tanks. The Zenit pads at Baikonur were built for a 90-minute launch cycle.
Ignoring complications like development cost and facilities limits, the ideal size is probably one where the reasonably-likely payload stream can keep a modest fleet -- say a dozen vehicles -- busy.
If the fleet is smaller than perhaps a dozen, then anything which takes a vehicle out of service -- permanently due to a crash, or temporarily due to repairs or maintenance -- becomes a substantial disruption. (Spacex has already had to scramble, at least once, because they lost a first stage that was already booked for later flights.) Such outages *will* happen; four or five vehicles is too few. And vehicles sitting around waiting for payloads are wasted investment. "The 747 is a good airliner, but if you don't keep it in the air at least 13 hours a day, it will eat your lunch."
I calculated the other day that we could deliver 300,000 tons to equatorial LEO with four flights per day of Starship/Superheavy.
If the turnaround time for a single vehicle is several days, that could make sense. If it's more like an advanced aircraft -- usually maybe a few hours of checkout and touchup -- then four launches a day is way too few, it wants to be more like 20-30. A short-turnaround SS/SH is grossly oversized for that payload flow.
Henry