Challenger at liftoff on mission STS-51L. The smoke seen at bottom right was the first visible sign that an SRB joint may have been breached.
THE CHALLENGER DISASTER
On January 28, 1986, the Space Shuttle Challenger, designated mission number STS-51L, blasted off from Cape Kennedy. For those watching, it appeared initially to be another exhilarating, yet almost routine, liftoff. Among the spacecraft’s mission tasks was the deployment of the second in a series of tracking and data relay satellites. Also on board Challenger was a teacher, Christa McAuliffe, who was there as part of the Teacher in Space Project. But just over a minute into the Shuttle’s flight, the unthinkable occurred.
In January 1986 Mike Mullane was in training for a secret military Shuttle mission to be launched from its alternative launch site at Vandenberg Air Force Base in California. He recalls:
I was with the rest of the STS-62, we were in training at Los Alamos Labs. One of our payloads was being developed at Los Alamos Labs, so we were up there at Los Alamos. We were in a facility that didn’t have easy access to a TV. We knew they were launching, and we wanted to watch it, and somebody finally got a television or we finally got to a room and they were able to finagle a way to get the television to work, and we watched the launch, and they dropped it away within probably 30 seconds of the launch, and we then started to turn back to our training. Somebody said: “Well, let’s see if they’re covering it further on one of the other channels,” and started flipping channels, and then flipped it to a channel and there was the explosion, and we knew right then that the crew was lost and that something terrible had happened.
In the two years before the Challenger accident there had been 15 missions, 12 in the previous year alone. The Shuttle was beginning to do what it was meant to do—or rather what the PR said it should do—that is, become a regular “space truck,” routinely plying between the ground and low-Earth orbit. In April 1985 the Shuttles Discovery and Challenger were launched just 17 days apart. There were spacewalks, some nontethered satellite deployments for the Department of Defense and the commercial satellite retrievals and in-orbit repairs. The robot arm worked impressively. There were also myriad experiments performed on the mid-deck and in the payload bay. But the high flight rate was straining the system in terms of engineering manpower and spare parts. There were specific warning signs for those who knew how to recognize their significance.
Between Challenger’s fourth flight—the STS-41B mission in February 1984—and its final flight (its tenth) in January 1986, there were 15 successful Shuttle missions. In only three of those missions was there no visible damage to the SRB O-rings; in nine of the missions the burn-through was serious. One mission, 51C, was launched after a bitterly cold January night at Cape Kennedy. When the recovered SRBs were inspected, the O-rings were found to be severely damaged. The Shuttle fleet should have been grounded. Sooner or later its luck would run out.
On the next flight, STS-51D, Discovery blew a tire and the brakes seized on landing due to a strong crosswind. For the time being landings at Cape Kennedy were halted. Three months and three Shuttle missions later, Challenger’s central SSME failed during ascent. Fortunately it was straightforward to “abort to orbit,” reaching a safe but slightly lower orbit than intended.
The mission prior to Challenger-61C (Columbia’s seventh voyage)—could also have been a disaster. A valve malfunction meant that one of the SSMEs could have exploded at main engine cut-off when the Shuttle reached orbit. The shower of debris from the explosion would have crippled the Shuttle, making it impossible to survive reentry. Fortunately, the launch was scrubbed for another reason and the fault found. But even that was not the only potentially fatal flaw. A faulty drain back valve from the external tank that could have killed the crew was also discovered.
Challenger at liftoff on mission STS-51L. The smoke seen at bottom right was the first visible sign that an SRB joint may have been breached.
As well as the crew of specialist astronauts, Challenger’s final flight also had a passenger: the schoolteacher Sharon Christa McAuliffe. (She was not the first passenger aboard a Shuttle, however: STS-41C also had a passenger on board—Congressman William Nelson, who was ostensibly a “payload specialist” but in reality was hitching a ride because of his influential political position. He was the second politician to fly on the Shuttle following Senator Jake Garn the previous April.)
Seventy-three seconds after liftoff Challenger exploded in a heartbeat just after Commander Dick Scobee gave the order: “Go at throttle up.” Shortly afterward pilot Mike Smith was heard to say: “Uh oh.” An O-ring in the right-hand SRB had failed, and flame was visible through the SRB wall. The damaged SRB then pulled away from the external tank, causing it to fragment. There were more than a million pounds of propellant in it when it detonated. Challenger disintegrated at 14,630 meters (48,000 ft.) but continued to climb to 18,288 meters (60,000 ft.). In fact, there was no explosion in the true sense. Although the dramatic and massive release of oxidizer and fuel gave that impression, the liquids were actually vaporizing and burning. Challenger disintegrated, but it seems the crew were not killed instantly.
Six weeks later NASA found the crew cockpit. Many had hoped that it would never be discovered, but since it was in relatively shallow water, sooner or later it would have been encountered by a diver or snagged on a fishing net. The cockpit section of Challenger was well built and survived the accident intact. It can be seen in still-frames training cables. For a few seconds the G-forces on the crew would have been intense—12 to 20 G—but then they would have swiftly fallen to about 4 G and then a few seconds after that down to zero G as the cabin would have been in free fall. There is evidence that some of the crew were conscious after break-up because three of the four personal egress air packs on the flight deck were turned on, and air consumed was consistent with breathing until impact with the sea. We do not know if the crew were conscious all the way to the impact. The air supply was unpressurized, so if the cabin had been breached they would, mercifully, have passed out within a few seconds. The cabin fell 19,812 meters (65,000 ft.) in 285 seconds before striking the ocean. It was this impact, at 210 miles per hour (338 km per hour), which killed the crew.
On the evening of the disaster President Reagan canceled the State of the Union speech for a week and gave a national address from the Oval Office. Written by speechwriter Peggy Noonan, it closed with a quote from the poem “High Flight” by John Gillespie Magee Jr.:
We will never forget them, nor the last time we saw them, as they prepared for their journey and waved goodbye and “slipped the surly bonds of Earth” to “touch the face of God.”
The subsequent Rogers Commission that looked into the cause of the accident discovered that engineers’ worries about the O-rings were not passed on to NASA managers at HQ in Washington, the astronauts in Houston or the launch director at Cape Canaveral on that fateful day. Afterward one astronaut said that every new NASA administrator should be taken on the Shuttle. Then they would know what it was all about after they had been scared “witless.” In the aftermath of the Challenger disaster there was a hiatus in Shuttle flights for 33 months.