As I recall, one shuttle (Challenger) blew up on assent because the solid rocket booster ruptured at the seams and the resulting blowtorch ignited the external fuel tank. The second shuttle (Columbia) was struck during ascent by a piece of foam debris that dislodged from the external fuel tank and blew a hole in the leading edge of one of the shuttle's wings. The ablative tiles on the shuttle never caused a catastrophe.

Musk tweeted:
"Looks like thrust was low on 1 of 3 landing engines. High g landings v sensitive to all engines operating at max."
"Upgrades underway to enable rocket to compensate for a thrust shortfall on one of the three landing engines. Probably get there end of year."

Landing video froze at the last moment but it looked like a bulls-eye landing. There was flame climbing up the side of the stage. Telemetry should be helpful in making improvements.

You might remember that the old Saturn 1 had eight engines on its first stage. It was designed by Wernher Von Braun who knew a thing or two about rocket design.

Seriously, with today's microelectronics and sensors, it's pretty practical to gang up a bunch of engines and be fairly sure that they will work. The Russian N1 engine had some kind of problem with its design, as Orbital recently found out when their Antares booster exploded.

"SpaceX is going to have to launch on the same *Lockheed* Atlas V initially as Boeing is"

Fat chance that will ever happen. Falcon 9 has triply-redundant avionics systems, and 2-engine out capability while still completing the mission. I'd be surprised if they have serious difficulty getting Falcon 9 man-rated. They had loss of an engine on a previous cargo flight and still made it to the space station.

After watching the Commercial Crew presser this afternoon, I was surprised at how lame the NASA people came off.

NASA director Charlie Bolden simply read verbatim from an email he sent earlier to NASA employees. He spent most of his time aggrandizing the Orion space capsule (Apollo-derived) and its launch vehicle SLS (space shuttle-derived) without devoting much time at all to the commercial crew effort.

Commercial Crew manager Kathy Leuders came off like an old Bob-and-Ray skit where she was armed with only three bits of information and that was all you're going to get out of her. Somebody asked her about the Boeing reliance on Russian rocket engines and her answer was not exactly convincing.

There was an astronaut there who waxed poetic about seeing the Milky Way from the space station. One other NASA guy had nothing significant to add.

Bottom line? Each company (Boeing and SpaceX) bid what they thought the job was worth; NASA awarded them what they asked for. Boeing got nearly twice the funding for a conservative, unimaginative Apollo capsule with a Russian-based launch vehicle. Most of the newsmen asking questions were suspicious about this, as am I.

The Russian Soyuz T-10A mission to the Salyut space station in September 1983 did have a launch pad explosion and the tractor escape system (emergency pull-away rockets on a tower above the Soyuz spacecraft) ignited 2 seconds before the explosion and pulled the spacecraft 2000 meters above the explosion and permitted a safe landing 4 kilometers away. Cosmonauts Titov and Strekalov were unhurt and required no medical attention (Wikipedia). So far, this type of thing has never been used while the rocket's first stage is actually flying. Boeing is offering a similar tractor rocket escape system on their commercial offering while SpaceX is planning to use the on board Super-Drako engines for this purpose. Good to know that our astronauts will have these systems available!