STS Development Milestone Questions

Sorry to bother you guys I was wondering if anyone could shed some
light on the
topics below, Either causes, pictures or vids or anything. i found them
on the
astronautix site and was curious about each event


Thanks John John

1978 September 12 Shuttle SRB Drop Test An unloaded shuttle solid
rocket motor
is dropped from an NB-52 in a test of the parachute recovery system.

1979 July 2 Major Shuttle SSME failure Engine 2002 explodes violently
during a
test run due to a hydrogen leak. The MPTA test article sustains major
structural
damage due to overpressure of the heat shield support.

1981 February 20 Shuttle flight readiness firing The 20 second test on
the pad
at Cape Canaveral finally cleared the engines for the first shuttle
launch.