lower sabot was considerably slower, with
one piece falling away at about 1.3 seconds
after motor ignition, and the other piece
hanging on until about 1.6 seconds. The
grid fins deployed as intended, and the SS-
25 demonstrated stable flight.
Based on the onboard computers, the
SS-25 flew to about 2,700 feet, well below
the expected 4,200 feet. This difference
was probably due to the slow separation
of the lower sabot components. A Rock-
Sim simulation in which the lower sabot
never separates predicts apogee at only
1,900 feet. The observed apogee is there-
fore plausible for sabot separation partway
into flight.
At apogee, the piston ejection system
fired and successfully deployed both para-
chutes. Then, disaster struck. As the para-
chutes opened, it quickly became evident
that the body was falling much faster than
the parachute that was meant to control its
descent. Post-recovery inspection revealed
that the 2" wide nylon piston strap, rated
at 6000 lbs, sheared at a point about one
foot from the base of the parachute bay.
Most likely, the strap had been weakened
during the course of a thorough series of
ejection system ground testing. To my en-
during frustration, a simple Nomex shock
cord protector probably would have pre-
46 JANUARY/FEBRUARY 2020 SPORT ROCKETRY
Figure 14. SS-25 first flight showing
the sabots falling away.
Photo credit: Craig Klimczak.
