Elon Emails

Why Monday's countdown aborted; go for Tuesday

From:
Elon Musk
Date:
March 20, 2007 (Posted Tuesday March 20, 2007 ('T-0 at 4pm California time today (Tues)'), the day after the March 19 terminal-count abort.)
To:
SpaceX update mailing list
Subject:
DemoFlight 2 launch update (abort explanation)
All systems are now go for launch with T-0 at 4pm California time today (Tues). The abort that occurred a few minutes before T-0 was triggered by our ground control software. It commanded a switchover of range telemetry from landline to radio, which took place correctly, however, because of the hardware involved, this transition takes a few hundred milliseconds. Before it had time to complete, our system verification software examined state and aborted. Our simulations done beforehand all passed, because the simulator did not account for a hardware driven delay in the transition. We considered putting the vehicle into a safe state yesterday and updating the ground control software to make the very minor fix needed, but the safer course of action was to stand down. Yesterday afternoon and evening (Kwaj time), our launch team updated the software to address the timing issue and verified that there were no similar problems elsewhere. We ran the software through several simulated countdowns and then once again with the rocket and range in the loop.

About this email

Musk explains that Monday's abort came from ground control software checking state before a telemetry switchover from landline to radio had finished, a delay the simulator had not modelled. The software was fixed and re-run overnight and all systems are go for a Tuesday launch.

Notes

Unsigned in the reprints; NASA Watch attributes it to SpaceX, Samizdata to Elon Musk. Three paragraphs as quoted by NASA Watch; it is possible the spacex.com posting had further lines. No title survives; subject is descriptive.

Where it came from

Published by Musk; attribution widely reported.

SpaceX, newsletter. Tags: spacex-update, falcon-1, demo-flight-2, launch-abort, software