Sunday, February 3, 2013

A long fall to Earth and a short tumble downhill

In the history of manned spaceflight, there have been only two high-altitude rocket accidents. In 1986, an o-ring seal failed at launch, allowing pressurized gas to escape one of Challengers's solid rocket boosters. The leak compromised the integrity of the solid rocket booster and the external fuel tank. Challenger, its rockets, and the fuel tank broke apart just 73 second after launch. All seven astronauts aboard died.

Challenger's last flight, moments after lift-off.
Source: Universe Today.

The crew of Soyuz 18a, Cosmonauts Oleg Markov and Vasili Lazarev, experienced the other high-altitude rocket accident in April 1975. Less than five minutes into their flight to Salyut 4 (one of the Soviet Union's early space stations) the second stage of the craft's rocket failed to fully separate from the third stage. The third stage fired with the second still attached, straining the booster and causing the Soyuz to fly off course. This triggered an automatic abort, detaching the launch/re-entry capsule from the service module, orbital module, and rocket, and sending the capsule straight back down to Earth.

Markov and Lazarev.

An abort early in Soyuz flight is a rough ride under ideal conditions. Typically cosmonauts would experience 15Gs on their ride back to Earth. But Soyuz 18a's capsule was pointed straight down at Earth when the abort was triggered, making the descent even more severe. During the worst of it, the two cosmonauts experienced 21.3 Gs (which I wouldn't have thought survivable...). Amazingly, both men lived through the G-forces, the parachute worked, and the capsule landed in one piece. The G-forces were enough to break their ribs, though, and Lazarev in particular was pretty badly hurt. Markov went on to fly in space again several more times after Soyuz 18a, but Lazarev never did.

A Soyuz being transported to the launch pad.
Source: Wikipedia.

If its flight to Salyut 4 had gone as planned, Soyuz 18a's crew would have spent 60 days in space and then landed on the empty plains of central Kazakhstan. The aborted mission ended up landing hundreds miles further west than this intended target, though. The capsule impacted on a snowy mountainside in the Altai Range. It had fallen 90 miles in about 15 minutes, and Sir Isaac Newton wasn't quite done yet.

Upon landing, the barrel-shaped spacecraft began to roll down the mountainside! Luckily, its parachutes got snagged on surrounding trees; otherwise Soyuz 18a it would have rolled right off a 500 foot cliff that was just downhill from the spacecraft's impact site!

Markov and Lazarev.

Even though the spacecraft came to a stop, the danger wasn't quite over yet. The wildly off-course flight could have landed Soyuz 18a in Western China instead of Eastern Kazakhstan. That would mean trouble for Markov and Lazarev. In 1975, Sino-Soviet relations were icy. The cosmonauts would most likely have been imprisoned by the Chinese government.

Markov later recalled that the injured crew was joined after landing by curious folks from a nearby village who'd seen the capsule parachuting down. He knew they were finally safe when he heard the approaching crowd shouting at them in Russian, not Chinese. Soyuz 18a stop short of plummeting down a cliff, and stopped short of crossing the Chinese border.

A view of the Alati Mountain Range.
Source: Wikipedia.

A few months ago I wrote about another Soyuz mission that encountered high drama after landing. But I don't want to give the impression that Soyuz spacecraft are particularly dangerous- they've flown over a hundred times, and haven't experienced a fatal accident in over 40 years! Launching and falling to Earth in a capsule has proven safer than flying in a shuttle. A serious rocket accident during a Soyuz launch may well be survivable, since each Soyuz has a launch abort system. A rocket accident during a space shuttle launch would not be survivable. Even with the escape system added to shuttles after Challenger, astronauts could only survive bailing out of the shuttle during a controlled glide below 50,000 feet and travelling slower than 230 miles per hour.

Good thing NASA's replacement for the space shuttle is a capsule, featuring a launch abort system!

Orion on parade, during the 2013 inaugural festivities!
Source: NASA.

Sources: Christ Jones, Too Far From Home; The Once and Future Moon; Wikipedia; CollectSpace.

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