Science Web Corner I.S.S.N.: 1579-1149
El rincón de la Ciencia nº 2 (septiembre-1999)
The Spatial Probe Mars Climate smashes in Mars. Are units of measurement important? (RC-6)
M. A. Gómez
English Translation: J. Cantos
This is a English version of the La sonda espacial Mars Climate se estrella en Marte. ¿Son importantes las unidades de medida?
Last September 23rd, 1999 came to us the news about the fact spatial probe Mars Climate, sent by the NASA to be supported in Martian orbit and to study the climate of the planet, had smashed in Mars and remained completely destroyed. According to sources of the NASA, the disaster stemmed from an error in the conversion of the information that the computer had been given on board to the International System of units.
The spatial probe Mars Climate Observer was constructed in order to become a satellite of the planet Mars and like that to be able to study the atmosphere and the surface of the red planet. Besides, it had to provide information and serve as a station of communications to support the approach and " landing " of the Mars Polar Lander in Mars the following December. For all this, the probe Mars Climate was launched approximately 10 months ago, which was worth approximately 125 million dollars (over 20.000 millions of pesetas).
Why has the disaster happened? According to the information that the NASA has provided in the construction, programming of the navigation systems and launch of the spatial probe, several companies had taken part in the project. In particular, Lockheed Martin Astronautics from Denver was entrusted to design and to construct the spatial probe, whereas the Jet set Propulsion Laboratory from Pasadena was entrusted to programme the navigation systems of the probe. But it turned out that two laboratories did not work on the same way, the first one of them made its measurements and provided its information with the Anglo-Saxon system of units (feet, miles, pounds....) whereas the second one used the International System of units (metres, kilometres, kilograms...) . In such a way, that it seemed that the first one reckoned correctly using the Anglo-Saxon system and sent the calculations to the second one, but the information provided was transmitted without specifying the units of measurement used (serious error!), in such a way that the second laboratory used the numerical information that it received but interpreted them as if they should measure in units of the International System. The result was that the computers of the ship miscalculated the approach of the ship to Mars, making it stay in a wrong orbit, what provoked its fall on the planet and its destruction after having collided with the Martian atmosphere.
This is only a sample of the big importance that has the correct use of the units of measurement. It is not the same to use a system of units than another. This way the Anglo-Saxon system measures feet, yards or miles, whereas the International System measures them in metres or kilometres.
1 foot = 0,3048 m
1 mile = 1,61 km
With the mass units something similar happens, in the Anglo-Saxon system units as ounces or pounds are used, whereas in the International System grams or kilograms are utilized.
1 ounce = 28,35 g
1 pound = 0,453 kg
But the issue goes much further: will the same happen with other probes that the NASA has launched in the space? Will they manage to fulfill their mission or will they get lost in the infinite or covered with stars against any astral body? We do not know it, but the most pressing doubts arise with Mars Polar Lander, destined to deposit on Mars and to study the planet, and with the Starduts, destined to study a comet.
We will be attentive to what happens!
N. de la R.:
Later to the publication of this article, the NASA started having problems with another probe Mars Polar Lander.