Feels like a conversation right out of the 1980s just prior to the
Challenger Disaster. Even a contributing factor to the Disaster. NASA
focusing on squeezing every last ounce of performance to make Sun
Synchronous Orbit with a useful payload for the Military. I did part of the
analysis of going to Sun Synchronous south out of KSC, dropping the SRBs
between the Bahamas and Florida and overflying Cuba. NASA when with
building a launch pad in Vandenberg and bendy Filament Wound Boosters with
a capture feature. Too busy squeezing every last bit of performance out of
the vehicle to incorporate the capture feature on the Aluminum SRBs.
On Sat, May 25, 2019 at 4:13 PM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Sat, 25 May 2019, William Claybaugh wrote:
I cannot rule out someone trying to build a dedicated TSTO for high
inclination launches only... More likely, in my view, is the use of
same technology strapon’s on the SSTO.
Or use a LEO-based high-Isp tug to do the plane change. If we're doing
this sort of thing much, investing in orbital transport infrastructure is
an alternative to investing in launcher variants.
Going to an inclination of 30-40deg will not hurt an SSTO's payload too
badly -- the gain from Earth's rotation is a cosine function of
inclination, so at 30deg you still get ~87% of the benefit. From there,
about a 60deg further plane change will get you to the worst-case orbit of
interest (sun-synch at about 97deg).
Doing 60deg the naive way requires delta-V equal to the orbital velocity,
about 8km/s, which sounds bad but is not that big a deal for ion thrusters
with an Isp of 5000s (not difficult for ion): only about 15% of the
initial mass is expended if you're patient. The tug then has to come
back, but that uses rather less because the heavy payload is gone.
Impatience incurs a delta-V penalty, but you can probably get some of that
back by using a less-naive maneuvering plan -- big plane changes are
cheaper at higher altitude, so almost any major plane change is best done
by boosting higher first, doing it, and then coming back down. (With high
thrust, a total delta-V of about 6km/s goes to *infinity* and back, so you
can do any plane change for that cost -- maybe rather less with lunar
gravity assist and aerobraking.
