2. Scale of things : Big and Small

3. Failure to convert units: Mars Climate Orbiter
Launched in December 1998.
Reached Mars in September 1999.
after a 122 million miles journey.
Mission:
It would be moved into a fixed orbit above
Mars, to carry out a one-Martian-year
observation program (approximately two
Earth years).
Goal:
Obtain valuable information about cycles of
water, carbon dioxide and dust on Mars.
Cost:
$125 million
NASA Photojournal
DISTASTER: On September 23rd, the Orbiter fired its main engine to commence
maneuvers into the target Martian orbit. All signals from the spacecraft
seemed normal, and it passed behind Mars five minutes later.
Unfortunately, the spacecraft never reemerged from behind Mars,
and was later concluded to have been lost.

4. Cause of the problem: Unit mix up
On September 30th, preliminary findings were released indicating that a simple mathematical error in translating units of measurement was the cause.
The Orbiter project involved a number of different development teams. It was discovered that in a critical piece of ground-based navigation software, one team had used English units, e.g. inches, feet and pounds, whereas the other team had used metric (or "SI") units.
The software hadn't been told to do any conversions,
so used English units as if they were metric and fed
them to the Orbiter. Not surprisingly, the Orbiter got
its flight trajectory wrong, and probably crashed.