XR Flight Operations Manual Version 3.0
Copyright 2006-2018 Douglas Beachy. All Rights Reserved.
33
XR2 Ravenstar on SCRAM Ascent
14.
If you fly your ascent correctly (and assuming no payload), at about 60 km
you should reach Mach 20+ before the SCRAM engines approach their
thermal limit or run out of fuel, with ~60% main fuel remaining (with the
default fuel ISP settings). You may want to keep a few percent of your
SCRAM fuel in reserve in case you need it later during reentry if you are short
of the base by a few hundred kilometers. If that occurs, remember to engage
the SCRAM engines at velocities greater than Mach 4, and preferably about
Mach 7-9; below Mach 4 the TSFC is much higher because the engines make
much less thrust for a given amount of fuel. The engines operate at peak
efficiency around Mach 7-9.
15.
Once you shut down the SCRAM engines,
close the scram doors!
(
CTRL-G
,
or use the switch on the upper panel.) If you don't do this and you engage
the main engines, the SCRAM engines will begin to overheat because the
temperature of the diffuser (which compresses the incoming air) is directly
proportional on the velocity of the freestream. Overheating the SCRAM
engines may damage them or even destroy the ship if you overheat them too
much!
16.
After you close the SCRAM doors, push the main engines to full power and
pitch up about 10 degrees initially. Then adjust pitch to enter your desired
orbit as you ascend smoothly. Once your apoapsis altitude (ApA on the
Orbiter MFD) reaches 200 km, shut down the main engines. Note that you
are not in orbit yet, but you have to wait until you reach apoapsis
(the “high
point” of your orbit)
before burning your main engines again to raise your
periapsis (the
“low point”
of your orbit).
