MIflyer
1st Lieutenant
On 19 Dec 1981 the 6595th Aerospace Test Group prepared to launch the Navstar 7 Global Positioning System mission from Space Launch Complex 3 East at Vandenberg AFB,CA. The booster was Atlas 76E, originally built as a CGM-16E ICBM in the late 1950's and then converted into a space booster. All the first eleven GPS developmental spacecraft were launched on converted Atlas ICBMs, as well as the two proceeding Navigation Technology Satellites that proved the GPS concept would work.
The previous launch attempts for Navstar 7 had presented unusual challenges. The heavy upper stage plus the GPS payload made the vehicle sensitive to winds both on the ground and aloft, resulting in launch scrubs. A General Electric Radio Tracking System (GERTS) failure during the countdown resulted in another scrub. But finally, on the evening of 19 Dec 1981 everything came together, the countdown proceeded, and the vehicle lifted off.
But it was only 6 seconds after liftoff that the General Dynamics telemetry monitor, Gary Vick, saw the telltale signs on the strip charts that led him to announce that the booster's B-2 engine was shutting down. The loss of thrust from the B-2 engine combined with the loss of hydraulic pressure from the flight control system caused the vehicle to pitch over sharply and then begin rotating rapidly. It hit the ground 19.8 seconds after liftoff, only about 500 ft from the launch pad. Fortunately the impact occurred just over the slope of a large ravine and the blast did virtually no damage to any ground facilities.
The formal USAF mishap investigation revealed that an error had been made during the reassembly of the B-2 engine gas generator (GG). Inspection had revealed an excessive gap between the lower and upper sections of the GG. As had been done 23 times before, the GG had been opened, a seal that was out of its groove removed and replaced, and then the GG was reassembled.
As it turned out, the new GG seal had been coated with a sealant, Plastiseal, before it was placed in its groove, per the manual. But the manual did not caution that the seal should have a thin coating of Plastiseal but simply that large gobs of it should not be dripping off the seal. The result was that a portion of Plastiseal covered the film coolant holes for the GG. The GG featured holes that flowed fuel along the inner wall, resulting in cooling of the stainless steel casting as well as ensuring that the local mixture ratio was very much on the rich side to further ensure that the temperatures did not exceed a safe level.
The film coolant holes were covered in an area that was especially critical, next to the GG igniter. The result was that within a few seconds after ignition a hole had been burned in the wall of the GG. That was bad enough, but the hole's location essentially directed a kerosene-oxygen torch at the LOX line that fed the GG. The engine's performance dropped by about 4% when the burn through occurred before the puncture of the LOX line shut it down entirely.
The Atlas 76E failure followed failures of Atlas 19F and Atlas 68E in the previous year. But the Atlas team recommitted itself to success and by the time the nation faced the failures of two Titan 34D booster, a Delta booster, an Atlas Centaur booster at Cape Canaveral, and the loss of the Space Shuttle Challenger in 1985-1987, the old 1950's vintage Atlas converted ICBM's had proved to be the most reliable space boosters the US had on hand, as well as by far the cheapest.
Unfortunately the decision had been made to replace all expandable launch vehicles with the Space Shuttle in the early 1970's, and 26 Atlas missiles in storage had been scrapped, most by running them over with a bulldozer. A billion dollars worth of viable, reliable, and low cost space launch hardware was destroyed to avoid about a million dollars worth of storage costs.
And we have not lost another Atlas mission from Vandenberg AFB since that fateful night, forty years ago.
And I was there.
The previous launch attempts for Navstar 7 had presented unusual challenges. The heavy upper stage plus the GPS payload made the vehicle sensitive to winds both on the ground and aloft, resulting in launch scrubs. A General Electric Radio Tracking System (GERTS) failure during the countdown resulted in another scrub. But finally, on the evening of 19 Dec 1981 everything came together, the countdown proceeded, and the vehicle lifted off.
But it was only 6 seconds after liftoff that the General Dynamics telemetry monitor, Gary Vick, saw the telltale signs on the strip charts that led him to announce that the booster's B-2 engine was shutting down. The loss of thrust from the B-2 engine combined with the loss of hydraulic pressure from the flight control system caused the vehicle to pitch over sharply and then begin rotating rapidly. It hit the ground 19.8 seconds after liftoff, only about 500 ft from the launch pad. Fortunately the impact occurred just over the slope of a large ravine and the blast did virtually no damage to any ground facilities.
The formal USAF mishap investigation revealed that an error had been made during the reassembly of the B-2 engine gas generator (GG). Inspection had revealed an excessive gap between the lower and upper sections of the GG. As had been done 23 times before, the GG had been opened, a seal that was out of its groove removed and replaced, and then the GG was reassembled.
As it turned out, the new GG seal had been coated with a sealant, Plastiseal, before it was placed in its groove, per the manual. But the manual did not caution that the seal should have a thin coating of Plastiseal but simply that large gobs of it should not be dripping off the seal. The result was that a portion of Plastiseal covered the film coolant holes for the GG. The GG featured holes that flowed fuel along the inner wall, resulting in cooling of the stainless steel casting as well as ensuring that the local mixture ratio was very much on the rich side to further ensure that the temperatures did not exceed a safe level.
The film coolant holes were covered in an area that was especially critical, next to the GG igniter. The result was that within a few seconds after ignition a hole had been burned in the wall of the GG. That was bad enough, but the hole's location essentially directed a kerosene-oxygen torch at the LOX line that fed the GG. The engine's performance dropped by about 4% when the burn through occurred before the puncture of the LOX line shut it down entirely.
The Atlas 76E failure followed failures of Atlas 19F and Atlas 68E in the previous year. But the Atlas team recommitted itself to success and by the time the nation faced the failures of two Titan 34D booster, a Delta booster, an Atlas Centaur booster at Cape Canaveral, and the loss of the Space Shuttle Challenger in 1985-1987, the old 1950's vintage Atlas converted ICBM's had proved to be the most reliable space boosters the US had on hand, as well as by far the cheapest.
Unfortunately the decision had been made to replace all expandable launch vehicles with the Space Shuttle in the early 1970's, and 26 Atlas missiles in storage had been scrapped, most by running them over with a bulldozer. A billion dollars worth of viable, reliable, and low cost space launch hardware was destroyed to avoid about a million dollars worth of storage costs.
And we have not lost another Atlas mission from Vandenberg AFB since that fateful night, forty years ago.
And I was there.
