Monday, February 25, 2013

Remembrance: Columbia (Part 1)

by Stephanie Osborn

You may remember that I started my career as a payload flight controller for first Shuttle, and then Station. And that I had a friend aboard Columbia during her final flight. For those who have read my all-too-painfully prescient book, Burnout: The mystery of Space Shuttle STS-281, you know I dedicated that book to my friend Kalpana Chawla, her crewmates, and all those who have died in pursuit of space. "Ad astra, per ardua." ("To the stars, through struggle/adversity.")

We've just passed through a period of time of which most people are unaware. You see, all of the major space disasters that America has experienced all occurred within a 2-3 week span on the calendar. And interestingly, they occurred in chronological order on the calendar.

Apollo 1 Fire - January 27

Space Shuttle Challenger disaster - January 28

Space Shuttle Columbia disaster - February 1


Columbia - What happened?

On February 1, 2003, space shuttle Columbia experienced a catastrophic malfunction during re-entry. This was a result of damage sustained during lift-off 17 days earlier, on 16 January. Debris – specifically, a briefcase-sized piece of insulating foam from the external tank (ET) penetrated the leading edge of the port wing, and gouged a groove the length of the wing, possibly dislodging and at least damaging the flashing surrounding the port landing gear, and driving part of the carbon-carbon composite heat shielding on the leading edge into the wing’s interior.

The combination resulted in softening the wing struts, shearing off the wing when hydraulic pressure failed, resulting in a loss of control.

The resulting total loss of aerodynamic stability as well as wing loss caused a failure of structural integrity of the vessel, which broke apart around the crew at ~Mach17 or higher.

Kalpana Chawla, my friend, was a crew member.

But why did all this happen? Why did the foam turn loose? How could FOAM damage the wing?

First of all, remember when we talked about the Challenger disaster, how the SRBs (solid rocket boosters) had to be cast in segments like concrete? It's sorta like that for the external tank, too. Oh, it doesn't have to be done in segments, but it's next to impossible not to, because the thing is so durn big. So you spray your container for as far as it'll go, then you get another and pick up where you left off. That still results in a kind of segmentation, because there's a slight discontinuity in the uniformity of the foam at the point where you stopped and switched to a fresh container. At that discontinuity, you can get tiny cracks, you can get bubbling, you can get ice crystal formation, especially given the ET's function of holding cryogenic fuels. Unfortunately there's just no other way to do it with current technology. And while it had been noticed in several previous Shuttle missions that bits of foam would spall, nothing serious had ever come of it.

Until Columbia's last voyage, of course.

So how the blazes (pardon the rather dark pun) did a hunk of foam do this?


The foam is largely composed of a variety of dichlorofluoroethane. That stuff has a density of 1.25g/cc at 20°C. For a suitcase-sized piece, we'll assume dimensions of roughly 3in x 12in x 15in – this just happens to be the size of one of my laptop cases, and a reasonable approximation. That translates to 7.62cm x 30.48cm x 38.10cm. This yields a volume of 8849cc. This gives a mass for that little chunk of foam of just a smidge over 11kg (24lb and change)! At the time it detached, the Shuttle was moving at a little under Mach 2.5, about 840m/s or 1,870mph. Engineers estimated the impact occurred with a closing speed of ~530mph (~883km/hr or 245m/s) Therefore the kinetic energy of the impact was ½mv2, which is 0.5 x 11kg x (245m/s)2, which comes to roughly 330,000J. Put a simpler way, over a falling distance of about one meter, that is the equivalent of about 37 tons of force.

Not exactly a light tap.

So, at T + 82s, a chunk of foam fell off the left bipod foam ramp, hit the leading edge of the wing – one of the most crucial areas, as the only thing to take more friction heat during re-entry is the nose – and punched a hole in it, and according to the information I had, may also have gouged a scratch down the bottom of the wing.

During the mission, something was observed floating away from Columbia's underside on orbit. It is still not known for certain if this was a piece of the reinforced carbon-carbon heat shielding, or if it was a piece of flashing from the landing gear bay door, or something else. Also during the mission, the ground reviewed footage of the launch, specifically that from the camera which had become routine only 2 launches prior, to look for evidence of possible damage due to foam spalling. Concern was raised, but NASA management refused despite multiple requests for DOD viewing assistane from the engineers and scientists who worked on the heat management system. In this respect, the Columbia Accident Investigation Board (CAIB) reached the same conclusions that the Rogers Commission reached after Challenger – a difference in the views of management and the working engineers and scientists. To quote Richard Feynman from the Rogers Commission, "It appears that there are enormous differences of opinion as to the probability of a failure with loss of vehicle and of human life. The estimates range from roughly 1 in 100 to 1 in 100,000. The higher figures come from the working engineers, and the very low figures from management. What are the causes and consequences of this lack of agreement? … we could properly ask, 'What is the cause of management's fantastic faith in the machinery?'"

But that is precisely what happened. Per the blog of Wayne Hale, one of the Flight Directors on that mission, JSC's Director of Mission Operations, John Harpold, told him, “You know, there is nothing we can do about damage to the TPS. If it has been damaged it’s probably better not to know. I think the crew would rather not know. Don’t you think it would be better for them to have a happy successful flight and die unexpectedly during entry than to stay on orbit, knowing that there was nothing to be done, until the air ran out?” []

Unfortunately, according to Hale, the Astronaut Office agreed. Everyone in charge agreed. And so nothing was done, no attempt was even made to find out if there was anything seriously wrong.

At the point in time when management decided to let the crew fly blind, the end game was set.

Next week we'll chronicle Columbia's final moments.

-Stephanie Osborn