Anthology of Interest - Engineering

Acceleware news

nospam@example.com (Matt Hughes) — Sat, 27 Jan 2007 04:32:24 -0500

My employer, Acceleware Corp., closed a $3MM dollar deal with nVidia this week. A further $5MM dollar investment deal was also closed.

Coinciding with this news is a little bit of a PR blitz. Acceleware was featured on ROBTV this morning, and CBC was in our office this morning filming a little piece. Tamara recorded it and I converted it to an Xvid avi, which you can see here: CBC News Business report on Acceleware. Heh, I can't play Xvid movies in my browser. If you can't play it, let me know. If no one can play it, I encode it as something else.

NEAR Shoemaker burn anomaly

nospam@example.com (Matt Hughes) — Tue, 28 Sep 2004 23:01:33 -0400

NEAR Shoemaker suffered a nearly fatal failure on December 22nd, 1998, at 22:00 UTC, as the spacecraft was executing rendezvous burn 1 (RND1). The failure caused mission control to lose contact with the craft for 27 hours, after which NEAR was found in it's lowest safe mode, Sun-safe-rotate. Controllers were able to figure out a way to get NEAR to it's target, the asteroid 443 Eros, but with a significant time penalty and a very narrow fuel margin. The only permanent damage suffered by the craft was a contamination of the multispectral imager's optics by propellant residues.

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Mars Pathfinder Reset Bug

nospam@example.com (Matt Hughes) — Tue, 28 Sep 2004 22:36:26 -0400

The Mars Pathfinder mission, while widely proclaimed to be flawless, actually had a small bug in the scheduling code which handled tasks while the craft was operating on the surface of Mars. This bug caused intermittent computer resets, each of which resulted in the loss of data.

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Mars Climate Orbiter falls victim to disorganized ground crew

nospam@example.com (Matt Hughes) — Tue, 28 Sep 2004 22:24:29 -0400

The Mars Climate Orbiter (MCO) fired its main engine at 09:01 UTC, September 23rd 1999, to begin orbital insertion into Mars orbit. Telemetry with the craft was lost five minutes later as it was occulted by Mars (went behind Mars as viewed from Earth), but communication was expected to be recovered twenty minutes later when it was supposed to reappear from behind Mars. No signal from Mars Climate Orbiter would ever be heard on Earth after 09:04:52 UTC, Thursday, September 23, 1999.

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Ariane 5, Flight 501

nospam@example.com (Matt Hughes) — Tue, 07 Sep 2004 18:21:57 -0400

The chain of events leading to the destruction of Ariane 5's maiden voyage, flight 501, began well before the launch. When the launch vehicle is sitting on its launch table, on-board computers use inertial measurements to make sure the vehicle knows its exact location on Earth. The rotation of the Earth and the sway of the vehicle in the wind must be taken into account so that the launcher can precisely place its payload in orbit. Instruments take measurements of the accelerations the vehicle is experiencing, and the Inertial Reference System (SRI) computer takes this information does a few operations on it, and then passes it to the on-board computer, which uses it to compute the position of the vehicle. Once the vehicle lifts off, it is no longer necessary to compute where the vehicle is on Earth, but the computers continue to analyse the data for about forty seconds after liftoff. This only occurs because it was required for Ariane 4, from which Ariane 5 inherited its tried and true SRI units. However, Ariane 5 operates on a different time line and flight path than did Ariane 4, and the software running the SRI units on Ariane 5 wasn't changed to take this into account. This was largely because the SRI units were believed to be the most reliable parts of Ariane 5 since they had already been extensively tested on Ariane 4.

After flight 501 lifted off, the vehicle experienced accelerations much greater than it did on the ground. Because the accelerations are much greater, the numbers used to represent accelerations in the SRI computers became very large. About 39 seconds after liftoff, the number related to horizontal acceleration became so large that when it was converted from a 64 bit floating point number to a 16 bit integer so that it could be passed to the on-board computer, an error occurred, which caused the SRI computers to shut down. Ariane 5 is equipped with two SRI units, so that one can take over if the other fails. In this case, both units failed in exactly the same way, so the data received by the on-board computer was not correct data, but instead a diagnostic pattern generated by the SRI computers after they had shutdown.

The on-board computer interpreted the diagnostic pattern as flight data, and that caused it to incorrectly command the engine nozzles on the solid rocket boosters and on the main engine to deflect as much as possible. For the rocket, this was like making a very sharp turn in a car that's moving very fast; the car will roll, or in Ariane 5's case, large aerodynamic forces caused the solid rocket boosters to separate from the main stage. At this point, Ariane 5 did what it was supposed to; it exploded.

An inquiry into the failure of flight 501 found the defect in the ADA code that performed the unprotected type cast, and the larger design defect that allowed that specific bit of code to run after Ariane 5 had lifted off. These defects were fixed, and haven't bothered Arianespace since.

References

Arianespace, Ariane 5 Failure - Full Report, 19 July 1996, http://www.esa.int/htdocs/tidc/Press/Press96/ariane5rep.html

Kunzig, Robert. "Europe's Dream." Discover, May 1997: ??.
(Try Discover.com, search the archives for Arianespace)

I wrote this a long time ago. I have lots of other engineering / space stuff that I wrote up for a web site a few years ago, so I thought I would post some of it here too.