Not only did Gregg Easterbrook's article describe the dangers that would eventually lead to the demise of the Challenger and the Columbia, but he also mentions a third failure mode: the Space Shuttle Main Engines.

Could easily have failed catastrophically and taken out a third Shuttle. Instead, all the failures of the SSME turned out to be survivable. We just got really lucky.

From "Mr. Feynman Goes to Washington": http://calteches.library.caltech.edu/3570/

> NASA was claiming that the engines were in the regular range of engineering, but they're not; the engines had many difficulties that the guys at JPL told me about. (I found out later that the people who worked on the engines always had their fingers crossed on each flight, and the moment they saw the Shuttle explode, they were all sure it was the engines. But of course, the TV replay showed a flame coming out of one of the solid rocket boosters.)

Gregg Easterbrook wrote the following about simulated shuttle landings:

> They've never flounced like a twig on the crazy rapids of "bias"--the bland physics term for unexplained variations in the earth's gravitational and magnetic fields.

I can't make heads or tails out of it -- I can't find any reference to such a phenomenon called "bias" and I don't see how gravitational field variations (I assume he means the ones caused by uneven density) could have any effect at their minuscule amplitude. Is this a result of some misunderstanding or am I missing something?

Thanks. I didn't know that the differences change in space in such weird fashion. I guess what was meant were spatial differences, not temporal ones and it now the part about magnetic field makes some sense to me.

Interesting read, makes be wonder how Buran ever managed to fly.

I mean, Soviet space program of the time had neither financing nor time not priority outlined in the article.

Going to hit Wikipedia.

Buran was carried piggy-back on an expendable rocket (Energia), with no attempt at reusable main engines, less aggressive engineering on the expendable main engines than the SSMEs, and no SRBs. (The equivalent function was performed by liquid-fueled strap-ons.) The Buran orbiter looked a lot like the Shuttle, but the systems as a whole were engineered rather differently.

Also, the sole flight of the Buran was entirely unmanned - unlike the Space Shuttle, which had less sophisticated automation and required a pilot onboard to land the thing, Buran was capable of entirely automatic landing. The difference was probably mostly the result of political rather than technical reasons though.

The only reason Space Shuttle has required a pilot when landing from the point when the re-entry burn has started was to push a button that lowered the landing gear at a proper point in time. In fact, there was some equipment stored on the ISS that, if installed, would allow the Shuttle to land autonomously (the intended use for that was deorbiting a Shuttle with significant tile damage).

It is unclear whether Buran's autopilot is more or less complex than the Space Shuttle's fly-by-wire system. The pilot's inputs are the outer loop of a very complex feedback control system on the space shuttle; one need only look at how stable SS Columbia was on its last re-entry (despite heavy damage,) to appreciate the fly-by-wire system.

But it still had tiles, right?

Yes, the Buran had tiles.

However, it was not vulnerable to falling foam, because the Soviets put the insulation on the inside of the Energia: http://www.newscientist.com/article/dn20664-cosmonaut-soviet...

That having been said, it's still not safe enough. For example, what about a birdstrike or other debris? A small capsule on top of the stack would have a protective shroud while it is in the atmosphere, and the heatshield is at the bottom anyway. The Shuttle/Buran design was too big to protect in this way.

From my understanding a Bird Strike during launch would only occur very early in the flight, where the shuttle was still traveling at a relatively low speed.

> From my understanding a Bird Strike during launch would only occur very early in the flight, where the shuttle was still traveling at a relatively low speed.

There are a number of birds that can fly up to 10,000 feet. At 10,000 feet, the Shuttle is doing half the speed of sound. Hitting a bird at 10,000 feet would've been no picnic.

(In fact, the altitude record for birds is above 30,000 feet -- but these are unlikely to be found in Florida.)

Soyuz and Shenzhou both have a payload fairing that covers the entire spacecraft. Apollo had a partial shroud that covered the command module. These spacecraft do not even have an exposed heatshield during launch. Apollo didn't even need a fairing for aerodynamic reasons -- but it still had one anyway.