Modern Software Problems - The Technical and Social History of Software Engineering - page 363

1998: Mars Climate Orbiter Crash
After successfully journeying for 286 days from Earth to Mars, the climate orbiter
fired its rockets in order to shift within an orbit around Mars. The algorithms for
these adjustments had been based on imperial units in pounds rather than in met-
ric units in Newtons, as specified in the NASA requirements. This error caused
the orbiter to drop about 100 kilometers lower than planned, so it encountered at-
mospheric problems that caused overheating and system shutdowns that led to the
ship crashing onto the surface.
Lessons learned: The key lesson here is that requirements need to be checked and
understood to be sure they find their way into the code.
Problem avoidance: If inspections were used, they would have found the problem
almost instantly. Both requirements modeling and static analysis might also have
found this problem. Pair programming might have, but if the error occurred up-
stream in design, then pair programming might not have found it.
The reason why this problem was not found by testing may be nothing more
than carelessness. Attempting to transmit data from a subroutine using imperial
units to another subroutine using metric units is about as obvious a problem as is
likely to occur.
1999: Failure of the British Passport System
In 1999, the United Kingdom attempted to deploy a new automated passport sys-
tem that had not been fully tested when it went operational. The staff using the
new system had not been fully trained. Adding to the confusion was a new law
that required all travelers under age 16 to have passports. This law caused a huge
bubble in new passport applications at the same time that the new system was de-
ployed.
Roughly half a million passports were delayed, sometimes for weeks. This
threw off travel plans for many families. In addition, the U.K. passport agency
faced millions of pounds of extra costs in the form of overtime and additional per-
sonnel, plus some liability payments to travelers whose passports were late.
Lessons learned: The obvious lesson from this problem is never, ever, attempt to
go online with a major new system without fully training the staff and fully testing
the system jointly with the older system to be sure the new system works. Also,
when a new law is passed that adds a huge bubble of new clients, be sure you have
the staffing and equipment to handle the situation.