1971-091
The 306 kg ITOS B was launched on 1971 Oct 21 by two-stage Delta N from Space Launch Complex 2 at Vandenberg. After Thor first stage burn, the Delta second stage ignited to enter transfer orbit. However one hour after launch prior to the Delta's second burn, the stage began to tumble. The second burn, intended to circularize the orbit, occurred on schedule but at the wrong orientation. The ITOS B satellite separated and reentered the atmosphere over the Arctic Circle. The second stage did remain in orbit and was tracked in a 102.5 min, 279 x 1474 km x 102.6 deg orbit from which it reentered on 1972 Jul 21. The failure was attributed to an oxidizer leak.
SECO-1 was at 1141 UTC. Restart should have been at about 1232 UTC.
In Aeronautics and Astronautics 1971 (NASA SP-4016) it says that during the post SECO-1 coast, pitch and yaw jets began firing to counteract an 'unknown force' until control gas was depleted and the vehicle tumbled. Delta restart (just south of equator crossing northbound) and spacecraft separation occurred at the planned times but `planned circular orbit was not achieved and spacecraft and Delta 2nd stage impacted above Arctic Circle'. This report was from quick-look information prior to the failure investigation.
On the other hand, NASA-GSFC TR-1022, Technical Summary of Unmanned Launch Operations, reports that the second burn failed when "the thrust chamber pressure decayed from 172 to 24 psi 7 seconds after ignition. Oxidizer depletion was the direct cause. Analysis of data indicated the oxidizer system developed a leak 42 seconds after liftoff that continued throughout the flight ... During the coast phase before the second burn started an external moment was acting on the vehicle, primarily in the yaw phase. The yaw right jet activated approximately once every second. The GN2 supply was depleted prior to the start of the second burn and the attitude control system failed.' So it looks as if the oxidizer leak caused the `unknown force' and was the main problem. Note that for NOAA 3, the second burn lasted 12 seconds.
- Is the spacecraft/Delta separation velocity really enough to allow the Delta stage to have a 300 km perigee but have the spacecraft perigee be in the atmosphere? I calculate this would have required a ~50 m/s (~160 fps) velocity difference. How did Delta reach orbit but ITOS didn't?
- I believe I am correct in understanding that in 1971 a Delta stage did not carry out a post-separation depletion burn - it was in 1972 that the first tests of a three-burn Delta were flown.
- In fact, to match an Arctic circle reentry, I calcuate ITOS-B must have been in an orbit between -82 x 1480 km and -835 x 1480 km, with impact between 1259 and 1310 UTC and a velocity change between 110 and 350 m/s. The inclination differences for the other debris objects are consistent with this magnitude of delta-V. This is more than just tumbling... some kind of explosive event?
- It's not clear what the transfer orbit perigee was. Was ITOS-B in orbit while attached to the Delta (albeit not making a complete orbit)? It would be nice to distinguish for the records whether it 'failed to orbit' or 'reached orbit and then was deorbited'.
- Does anyone have any other relevant documents or personal knowledge of the event?
| ITOS B | |||
| Date | Time | Event | Orbit |
|---|---|---|---|
| 1971 Oct 21 | 1132:00 | Launch by Delta N6 | V |
| SRM 1-3 burn | |||
| 1132:42 | St 2 oxidizer leak begins | ||
| SRM 4-6 burn | |||
| 1135:44 | T+3:44 MECO | ||
| 1135 | St 1 sep | ||
| 1135 | SES-1 6:14 | ||
| 1141 | SECO-1 | -100? x 1480? x 102.6 | |
| 1232? | SES-2 | ||
| 1232? | SECO-2 T+7s? | 102.5 279 x 1474 x 102.6 | |
| 1238? | St 2 sep | ||
| Explosion? | |||
| 1240? | ITOS-B orbit | -500? x 1479 x 102.6 | |
| 1303? | ITOS B reentered | ||
No comments:
Post a Comment