Aalice.128
net.columbia
utzoo!decvax!ucbvax!mhtsa!research!alice!wolit
Sat Oct 31 14:36:35 1981
COUNTDOWN

For those of you who want to follow along, here are the highlights of
the final countdown and early phase of STS Mission 2, set for 0730 - 1210
EST November 4.  The info is taken from Aviation Week & Space
Technology, October 26.

T-9min  Automatic ground launch sequencer starts.
-6:24   Stop liquid oxygen (LOX) replenishment and start drainback.
-5:00   Start Auxiliary Power Unit (APU).
-2:55   Prepressure LOX tank, close vent valve.
-1:57   Prepressure liquid hydrogen tank, close vent valve.
-0:31   Final hold point.  Holds after this require recycling to T-9:00.
-0:15   Start documentary cameras, sound suppression water system.
-0:10   Light hydrogen pyrotechnic igniters.  This is to burn off any excess
       hydrogen, which tends to puddle and cause a minor explosion at main
       engine ignition.

       A hold may be initiated at any time until solid rocket booster (SRB)
       ignition.  If one occurs after main engine ignition, 3 seconds earlier,
       turnaround time will be about two weeks, for main engine refurbishment.

       The following calls take place between Columbia and mission control's
       spacecraft communicator, Cdr. Daniel Bradenstein:

T+0:07  Maneuver initiate - (optional) Crew confirms that Columbia has started
       its 118-deg. roll from its 120-deg. heading on the pad to its 58-deg.
       initial flight heading.  (Orbital inclination will be 38-deg.)
0:30    Maneuver complete - (optional) Crew confirms that roll program has
       halted.
0:40    Go at 40 - Establishes formal communication with mission control.
       4 seconds later, main engines throttle back from 100% to 68% for
       passing through maximum dynamic pressure (Max-Q), which occurs at
       T+1:02 at 40,000 ft., and 452 kt.  4 seconds after that, at Mach 1.4,
       main engines throttle up to 100% again.
1:50    Negative seats - At 120,000 ft., the crew's ejection seats are no longer        usable.
2:00    PC less 50 - Crew reports thrust tailoff in the SRB's, which helps fix
       their splashdown point.
2:07    SRB sep - Crew confirms SRB separation.
3:00    Go at Three - Mission control reconfirms communication.  (There was
       some problem with data communication during Mission 1 due to inter-
       ference from the SRB exhaust plume.  A different tracking station,
       several miles north, will be used for Mission 2.)
4:18    Negative return - Insufficient energy exists for a return-to-launch-
       site abort.  3 seconds later, enough energy should exist for a forward
       abort.  In between, the Rota (Spain) Naval Air Station would have to
       be used for an abort.  This gap did not exist on Mission 1, due to the
       lighter weight of the spacecraft at that time.
4:20    Press to ATO - If they lose one engine, the crew must throttle the
       remaining two to 107% thrust to abort-to-orbit (ATO).  At this time
       Columbia will be approching its peak altitude during powered flight
       (70 mi.)  It then pitches down to gain speed, losing 10 mi. before
       main engine cutoff (MECO).  The 107% thrust option did not exist
       during Mission 1.
5:01    Normal throttles - A one-engine-out ATO can now be achieved with only
       100% thrust on the other two.
5:31    Press to MECO - ATO can now be achieved at normal MECO altitude and
       velocity targets, with 2 engines at 100% thrust.
6:05    Single engine Rota - At 12,500 fps., Columbia could reach Rota, Spain
       after crossing the Atlantic at Mach 20 and 310,000 ft. on one engine.
7:00    Single engine press to MECO - With 107% thrust on a single engine, the
       crew could achive ATO.  With another 1500 fps of forward velocity,
       this could be done at 100% thrust.

       MECO occurs at 25,688 fps and 60 nm. altitude, climbing at 220 - 230
       fps.  18 seconds later, the external tank is jettisoned.  The orbiter
       then pitches down away from the tank.  Unlike Mission 1, it will not
       have to yaw to get out of the way.  The crew now recieves a "go" for
       APU shutdown and the OMS 1 burn.

       2 min. after MECO, the first orbital maneuvering system burn (OMS 1),
       a 1 min., 23.3 sec. firing of the OMS, will place Columbia into a
       53 x 120 nm. orbit.

       At T+41:48, the 1 min., 48 sec. OMS 2 burn circularizes the orbit at
       120 nm.

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