English/metric measurement error in the Mars Climate Orbiter

[Jon]

The Mars Climate Orbiter was a space probe launched by NASA in 1998. It was loaded with scientific measurement instruments, and it was supposed to enter orbit around Mars, gather data, and then communicate its findings back to Earth. Instead, it disintegrated.

Here's the Mars Climate Orbiter:



The orbiter completed a 286-day journey to Mars, and then fired its engine to push itself into orbit. However, something went wrong - on September 23, 1999, NASA lost contact with the orbiter.

What happened? NASA organized an investigation with a Mishap Investigation Board, which produced a detailed report. The suspected root cause? Failure to use the metric system. Here's a highlighted section from the NASA report:



All systems were supposed to use metric measurement, but a single software file was using English units instead. As a result, thruster measurements were miscalculated, and the orbiter was hundreds of kilometers off course, causing it to (most likely) disintegrate in the Martian atmosphere.

NASA handled the failure pretty well, at least externally. Rather than point the finger at Lockheed, whose engineers had programmed the software, they acknowledged that, while the software measurement error was the root problem, it was their responsibility to validate and verify the measurement systems to identify any such errors.



But when you read between the lines, the vague phrasing about communication structures and auditing processes seems to point at the age-old conflict between engineers and management. Some relevant industry magazines (like Aviation Week and Spectrum) published a good bit of anonymously sourced i-told-you-so's (this Spectrum article is especially notable). It looks like some of the involved engineers knew that the official story was being spun, and they leaked the dirty details to the industry press.

NASA's official claim was that nobody knew that the orbiter was off course until communication was lost. However, Spectrum's position was that some of the engineers voiced strong concerns, but were pushed aside by management.

This is the remaining inconsistency between NASA's official version of what happened and the one reconstructed by Spectrum. Our conclusion is that adequate doubts had been raised to require the TCM-5 burn, even in an emergency mode. Further, according to participants in this tragedy of errors, by the time the probe reached Mars, those most "in the know" were persuaded it was already doomed by its sick trajectory--but by then it was too late.

The incident is a fascinating combination of measurement errors, programming errors, management errors, and public relations errors. These mistakes collectively resulted in the loss of a $328 million spacecraft, and demonstrated that, unlike people, errors are great at working together.

Previously:

International Space Station tools
astronaut loses $100,000 tool bag during spacewalk

[mklotz]

Nothing ever gets fixed until a bunch of people die. It's going to require something like flying two fully-loaded A380 Airbuses into each other before we get rid of this nonsense of trying to use two measurement systems side-by-side.

The system is already cocked and loaded. The world standard for measuring and assigning flight level is feet, but China (and a few of its immediate neighbors) uses meters. Quick, is an assigned FL of 10000 m equal to 32000 or 33000 ft? And while you're worrying about that, when they refuel your plane in China for the trans-Pacific return do they measure fuel in pounds or kilograms?

On a completely unrelated idiocy, yesterday I was driving around in downtown Los Angeles. This is an active earthquake zone, near the San Andreas fault, and there are 50-60 story buildings across the street from each other! Oh, they're all certified "earthquake proof" construction. Yeah, sure. The tallest building is 83 stories. One good shake and it'll be toppling dominoes on a gargantuan scale. Even if a building doesn't fall, the tons of glass cladding falling to the street will do a slice and dice that I don't want to see.

[NortonDommi]

Above all else remember that every stuff-up starts in an office and the usual instigator is a University Educated Idiot that is too clever to make a mistake.

[elk-a-holic]

Already has been a major fuel mishap caused by mix up between units. Tragedgy was averted through luck and good piloting. For more look up "Gimli glider" which is a case of an out of fuel passenger plane making a dead stick landing on an abandoned WW2 training airstrip in Manitoba.

[SRQSid]

I recall a component in the Hubble Space Telescope camera had an English/Metric mix up that caused blurry images until a later mission applied corrective lenses (contacts?). The best-laid plans.....

[mklotz]

Above all else remember that every stuff-up starts in an office and the usual instigator is a University Educated Idiot that is too clever to make a mistake.

Well, speaking as a "University Educated Idiot that [sic] is too clever to make a mistake" I'd advise you that demeaning education is no way to solve the problem.

[mklotz]

I recall a component in the Hubble Space Telescope camera had an English/Metric mix up that caused blurry images until a later mission applied corrective lenses (contacts?). The best-laid plans.....

It wasn't "an English/Metric mix up". They neglected to make a simple test that would have revealed the error.

"Perkin-Elmer, which built Hubble at its Danbury plant in Connecticut, tested the primary and secondary mirrors separately, but no one tested the complete telescope before launch. An earlier check by NASA absolved the design itself of blame, leading the agency to narrow the inquiry to possible errors in the testing of the mirrors."

The complete story is here...

https://www.newscientist.com/article...mirror-fiasco/

[NortonDommi]

Regarding U.E.I'S,(University Educated Idiots), there are a lot of them out there, I know this as I personally have encountered a great many of them. That is not to say that everyone who graduates with a degree is an idiot, far from it but a piece of paper that [I]should[I]demonstrate a capacity for intelligent and rational thought is in today's world no guaranty and it is in the occupation of 'manager' that the unworthy usually surface.
I was not demeaning education more the questionable quality of some and the 'teaching' of subjects that are not and never will be of use to anyone also the adherence to wacky theories.
In the cases mentioned and a space shuttle disaster the fundamental problem was not an Imperial/metric problem it was system errors or more correctly people errors due to not following a system and there not being sufficient checks in place.
Everybody makes mistakes hopefully there is a system that is vigorously followed to catch them before they become catastrophic.

[12bolts]

As a commercial diver, I dealt with a fair number of engineers during my career. The difficulties they had were just grasping the basics of buoyant force mainly. Tertiary educated people that write things down and think that because it works in principle it must work in practice. A couple of examples that spring to mind are that of a civil job laying a railway track under water. The company freighted in a semi load of sleepers for the track to be laid on. We tried to tell them they wouldnt be able to position them. But the engineer responsible was adamant that because they were "so heavy" they would do the job. The crane lowered them into the water and we released the chains and watched as the waves washed them ashore again. On another job, a pipeline tie-in, the new section of pipe was manufactured, (about 100 metres long x 800mm dia) and capped at each end. This was then fitted with hundreds of 200 lt drums for buoyancy and floated into position. The drums were then selectively removed in a calculated manner to provide a controlled descent into position. After the last drums were cut loose this pipeline was still bobbing on the surface like a cork. Even setting moorings. Everybody thinks concrete is great for a mooring because its "so heavy" A m3 of dry concrete weighs almost 2.5 tonne. Problem is it displaces about 1 tonne of water, And it is massive for its weight so it also provides a huge resistance to water currents further undermining its properties as a mooring. A steel plate of maybe 3-400 kg flat on the bottom is far superior to a huge block of concrete.
I could list more that I have personally encountered, and there are dozens more I have heard about, but, its just comes back to people in offices unwilling to listen to experience on the ground.

[drum365]

Great writeup, Jon. Your article's last 8 words have gone into my "Great Quotations" file!