In December 1998 NASA launched the 125-million dollar Mars climate orbiter,intended
as the red planet's first whether satellite. After a 416-million mi journey,the
spacecraft was supposed to go to Mars' orbit on September 23,1999. Instead entered
Mars' atmosphere about 100 km (62 mi) lower than planned and it was destroyed by heat.
The mission controllers said the loss of spacecraft was due to the failure to convert English
measurement units into metric units in the navigation software.
Engineers at Lockheed Martin Corporation who built the space craft specified
its thrust in pounds,which is an English unit. Scientists at NASA's Jet Propulsion Laboratory,
on the other hand,had assumed that thrust data they received were expressed in metric units,as newtons.
Normally,pound is the unit of mass.Expressed as a unit of force,however, 1 lb is
the force due to the gravitational attraction on an object of that mass.
To carry out the conversion between pound and newton,we start with,
1 lb = 0.4536 kg and from Newton's second law of motion,
force = mass * acceleration
= 0.4536 kg 9.81 m/s^-2
= 4.45 kg m/s^-2
= 4.45 N
because 1 newton(N)=1 kg m/s^-2.therefore,instead of converting one pound of force to
4.45N,the scientists treated it as 1N.
The considerably smaller engine thrust expressed in newtons resulted in a
lower orbit and the ultimate destruction of the spacecraft.Commenting on the failure
of the Mars mission,one scientist said : "This is going to be the cautionary tale that will be embedded into introduction to the metric system in elementary school high
school,and college science course till the end of time."
as the red planet's first whether satellite. After a 416-million mi journey,the
spacecraft was supposed to go to Mars' orbit on September 23,1999. Instead entered
Mars' atmosphere about 100 km (62 mi) lower than planned and it was destroyed by heat.
The mission controllers said the loss of spacecraft was due to the failure to convert English
measurement units into metric units in the navigation software.
Engineers at Lockheed Martin Corporation who built the space craft specified
its thrust in pounds,which is an English unit. Scientists at NASA's Jet Propulsion Laboratory,
on the other hand,had assumed that thrust data they received were expressed in metric units,as newtons.
Normally,pound is the unit of mass.Expressed as a unit of force,however, 1 lb is
the force due to the gravitational attraction on an object of that mass.
To carry out the conversion between pound and newton,we start with,
1 lb = 0.4536 kg and from Newton's second law of motion,
force = mass * acceleration
= 0.4536 kg 9.81 m/s^-2
= 4.45 kg m/s^-2
= 4.45 N
because 1 newton(N)=1 kg m/s^-2.therefore,instead of converting one pound of force to
4.45N,the scientists treated it as 1N.
The considerably smaller engine thrust expressed in newtons resulted in a
lower orbit and the ultimate destruction of the spacecraft.Commenting on the failure
of the Mars mission,one scientist said : "This is going to be the cautionary tale that will be embedded into introduction to the metric system in elementary school high
school,and college science course till the end of time."
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