Java Reference
In-Depth Information
SOFTWARE FAILURE
What Happened?
As part of a series of missions exploring
Mars, NASA launched the Mars Climate
Orbiter in December, 1998, and the
Mars Polar Lander in January, 1999.
The two-spacecraft mission was designed
to observe the atmospheric conditions
on Mars through each of its seasons.
The orbiter and the lander would have
collected data about temperature, dust,
water vapor, clouds, and the amount
of carbon dioxide (CO2) added and
removed from the Martian pole regions.
After its nine-month journey, the orbiter
arrived at Mars in September, 1999,
and fired its main engines to establish
an orbit. The orbiter passed behind the
planet (from Earth's perspective) five minutes later as planned, but NASA could
not reestablish contact with it after expecting it to emerge. Review of the data
showed that the altitude of the orbiter when it was entering orbit was only 57
kilometers, whereas the planned altitude was 140 kilometers. The minimum sur-
vivable altitude was between 85 and 100 kilometers. NASA concluded that the
orbiter was destroyed by atmospheric friction.
The polar lander arrived at Mars in December, 1999, and all of the data indicated
it was on target to make a successful soft landing within 10 kilometers of the
target landing site on the Martian south pole. However, NASA lost contact with
the lander just after it entered the atmosphere. Multiple attempts to reestablish
contact with it over the following weeks and months were unsuccessful.
The total project cost for the orbiter and lander was $327.6 million.
■
Artist's concep-
tion of the Mars
Climate Orbiter
What Caused It?
The root cause of the orbiter's problem was an embarrassing communication
issue. The software that guided the navigation of the spacecraft used imperial
units of measure (pound-force), while the spacecraft itself expected the data in
metric units (newtons). Therefore the desired navigation changes and the actual
effects were off by a factor of 4.45. This mismatch resulted in part because one
team based in Colorado lead the efforts on the spacecraft, while a California-
based team managed issues of navigation.
111
Search WWH ::
Custom Search