Satgen 411  Why Satellites Crash  by GM4IHJ   (BID SGEN411)   8 Feb 97

Recent events involving , the European Ariane 5, the American Delta
rocket and , the Russian Mars probe, have highlighted the rather
alarming and expensive casualty rate still apparent 40 years after
Sputnik 1 successfully inaugurated the Space Age.

As a natural consequence of this , Amateur satellite users are often
brought hard up against a deeply ingrained public perception that 
Space travel is a. Too expensive , and b. In the hands of people who
do not know what they are doing. 

It is difficult for the ordinary public to understand, the far from
simple problem of overcoming the earths gravity , and, the very small
margins by which even the best of launch systems achieve a safe orbit.
Perhaps if it were possible to demonstrate this by sending " John Doe
" commuter to the office with his cars gas tank containing just one
small spoonful of gasoline more, than that needed to get him there in
normal circumstances , at economic speed - the lesson might start to
sink in. But even that is unlikely, noting that his car would simply
come to a slow safe stop, if the gas ran out before he reached his
destination. If only we could drop his motionless car from a height of
several miles, Mr Doe might really get the point. However this is
impractical, as would be similar rapid descents if his engine ,
ignition, brakes or steering failed. All these things have occured
with GM4IHJ. In 40 years of motoring the IHJ transport has slowed to a
halt in 5 or 6 highly inaccessible places, but with no more harm than
a long walk being required for assistance. When these things occur to
a rocket the ending is far more painful.

Sometimes the rocket motors themselves fail ,as with the Shuttle
Challenger tragedy, the recent Delta explosion, or our ill fated
original Phase 3A. Ariane 5 however appears to have failed for a quite
different reason. Something caused the rocket to vere off course as it
launched. One theory being that Inertial guidance normally used in the
start up and ignition phase in all previous smaller Ariane 4 launches,
was left on as Ariane 5 began to rise. Previously this made no
difference to Ariane 4, but Ariane 5 is much more powerful with far
more upward thrust. So the inertial system was subject to G forces it
could not take, and it hit the stops. Thereby interfering with all
attempts of the control system gyros to keep the rocket on course.

Ariane like other rockets is made of very fragile thin metal, to save
weight. This is fine if it goes straight up, but if it starts to
twist, it tears itself to pieces. Causing the accident which has meant
, an expensive delay in launch plans for Amsats Phase 3D,( now
rescheduled for the next Ariane 5 launch in July 97), and a very big
headache for Ariane designers and operators.
PS The Iridium satellite mobile phone launch has still not taken place
(7th Feb). Early reports blamed a rocket lagging material defect but 
this long delay suggests something more serious.