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Archive for April, 1999

28-Apr-99 | Delta III aborted at T-minus 2 seconds

Last week’s Delta III on-pad abort at Cape Canaveral’s SLC-17B was caused by a ground-support software glitch. The main engine ignition command was never sent to the vehicle.

This marked the fourth scrub for this vehicle, which will carry the Orion F-3 comsat to geosynchronous orbit for Hughes and Loral. Boeing has replicated the error in ground tests and has completed a revision, and the next launch opportunity will be in less than 0 days, pending the successful launch of a Titan 4B on Friday. Available launch windows are:

The entire launch window on Thursday, 22 April, was a nail-biter, with three holds during the terminal count and a period of concern over wind shear data. At least two of the holds were caused by overly tight constraints during the vehicle’s transition from external to internal systems. For instance, a loss of merely two digits from a very long sequence of numbers for more than 400 milliseconds was enough to set off a momentary alarm and stop the count. All three alarms are considered by the launch team to be known and understood, and each time the count resumed at the 4 minute mark. The final countdown of the night was set for liftoff at 10:05 EDT, with about 4 minutes 30 seconds to spare in the 69-minute window. The weather report was green all the way.

Then came the main engine abort, somewhere in the last two seconds of the count. Main engine valves were not commanded to open, so contrary to Greg High’s inadvertent comment at T+2 seconds, it was not a “hangfire.” This sort of thing has occurred at least four times during the Delta II program, which uses the same RS-27A main engine package as the Delta III, and each of those vehicles went on to successful flights. Turnaround time depends of course on fixing the problem, but at a minimum it will take 48 hours: the Thrust Vector Control system requires that much time when its hydraulics have been activated, or “blown down.”

Exciting as the scrub was to watch, my nervousness was not aided by the shenanigans with Boeing‘s webcast. It began with the audio feed broadcasting solely in Korean, but as the count ran down someone figured out this was happening, and took to wandering around several blue menu screens on their satellite system to straighten it out. They found the Boeing audio feed after a while, but didn’t turn off the Korean audio until midway through one of the terminal counts, during which time they fed noise (and blue screen) for about 10-15 seconds before restoring the English only. Finally, the Boeing anchorwoman wins the irony award for talking over the main loop procedural patter during the last terminal count with “we’re going to remain silent….”

19-Apr-99 | NAVSTAR vehicle stacking

At Cape Canaveral, on Pad A, the vehicle for the first Navstar IIR Global Positioning System satellite since July 1997 is being prepared. The first two stages and all 9 solid boosters have been erected. The GPS spacecraft was scheduled to be mated to the Delta third stage, a Star 48B solid motor, spin balanced, and installed atop the vehicle by Monday, 12 April. Because of the busy range, this Delta II is now scheduled for launch on 4 May.

19-Apr-99 | MGS begins operations

Mars Global Surveyor (Delta 239) began full-time mapping operations on Tuesday, 9 March. The spacecraft is in a sun-synchronous, 1.97-hour orbit, and until the evening of 15 April was in excellent health. At that time the spacecraft went into contingency mode (which is apparently not as severe as “safe mode”) due to a stuck hinge on the high-gain antenna. Controllers are in the process of diagnosing the problem. (Latest info)

19-Apr-99 | Delta flight 268 – Landsat-7

Landsat-7 lifted off aboard its Delta 7920 at the very opening of its first launch window on Thursday, 15 April, at 18:32:00.288 UTC. The spacecraft was placed successfully into its proper orbit and is in excellent health. The next few weeks will be spent on systems checkout and calibration. The Landsat program, frequently referred to as “the central pillar of the national remote sensing capability,” has been continuously providing Earth images in visible and infrared wavelengths since 1972.



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