Text File

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.

----------------------------------------------------------------- gopher://quux.org/ conversion by John Goerzen <jgoerzen@complete.org> of http://communication.ucsd.edu/A-News/

This Usenet Oldnews Archive article may be copied and distributed freely, provided:

1. There is no money collected for the text(s) of the articles.

2. The following notice remains appended to each copy:

The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996 Bruce Jones, Henry Spencer, David Wiseman.