Shuttle entry profiles
Richard Clark (rclark@LPL.Arizona.EDU)
Tue, 27 May 97 08:00:30 MST
bkrosney@mbnet.mb.ca was wondering:
>I am trying to understand the details of the Shuttle re-entry to help
>explain the marginal observing conditions presented for observing the
>rentry from my location: Winnipeg, Canada. (Hey...I'm not complaining,
>even marginal is better than not!)
So am I, but from Tucson Az (110.95w, 32.25n :-)
[snip] ... orbital pass at Winnipeg would have been nearly zenith but
landing pass that orbit was at 12 deg.
>Is it due strictly to the difference in the Shuttle's height above the
>surface of the Earth?
...
>Or...has the satellite by this time maneuvered out of its original
>orbital plane?
Both. At your range from KSC the shuttle's height during entry has
decreased to about 70-80km.
During entry the shuttle can maneuver substantially out of plane, over
2000km if necessary although the largest crossrange actually required for
any landing so far is probably STS53 with about 1500km. The first roll
typically begins at a range of about 4500-5000 km from the landing site.
I don't have details of crossrange deviation vs range/speed/height. When a
large crossrange is required the first roll reversal will be delayed. A
large part of the entry is flown with a pronounced roll atitude because it
is part of thermal control as well as crossrange maneuvering and
deceleration. (comming in nose up but no roll causes greater heat buildup)
OBservability:
Here in Tucson 3.8 degrees (420km) north of 28.45 deg the crossrange
displacement is quite noticeable.
Assuming the orbital apex is at 110w (usually very close to the case with
entry opportunities) a normal orbital pass with a height of 280km is 30-35
deg.
During entry (70km height) with no corssrange the altitude would be 7.6
deg. This is very marginal with my south horizon although I have managed
to see one such pass.
With a crossrange departure 160 km north of the orbital path the altitude
is 15 deg. I have seen 3 passes at 15-20 deg. So crossrange departures of
up to 200 km are clearly possible at Tucson's range from KSC, which is
probably similar to Winnipeg's.
For an entry 160km south of the orbital path the altitude is down to 4 deg.
I have noticed that the brightness of the orbiter fireball is greater when
the underside is facing me (the plasma trail is unaffected) so the most
impressive view is when the initial roll maneuver takes it north of the
orbital path and the first roll reversal occurs just west of here. Now if
I could just explain that to the flight dynamics guys in Houston:-)
I have also noticed that my efforts to predict the extent and direction
of crossrange maneuvers based on the longitude of equator crossing on the
entry orbit have been quite unsuccessful.
Richard Clark
rclark@lpl.arizona.edu