Posts Tagged Space Shuttle

Whither NASA?

The demise of the Space Shuttle Columbia with seven astronauts onboard has raised important issues about NASA and space exploration. I once worked designing launch trajectories for Delta – I worked on the launches for IRAS, EXOSAT, and LANDSAT-D’ before moving on to smaller, more deadly aeronautical programs. I almost went to work at Rockwell in their Shuttle Ascent group.

Rand Simberg (among others) at Transterrestial Musings has made many important points about space exploration. The space shuttle has been an engineering failure – it hasn’t achieved, and will never achieve, it’s cost, turnaround, and safety goals. The problem is, the replacement programs, such as X-33 (VentureStar) have been even worse failures. The problems with the shuttle date back to decisions made from the dawn of the program, both in terms of engineering and cost. Columbia wasn’t destroyed by lack of near-term safety funding, of failure to pay heed to safety guru’s demanding more money, but by the inherently risky nature of space travel and design decisions made thirty years ago. 

And he’s right to say we need to go back to first principles when it comes to space exploration. The problem has been we’ve never really had any, and so as time has gone on, we’ve tended to let the programs drive the goals, rather than goals drive programs. So the proper response should be to figure out what we want to do, assign priorities, realistically figure up the cost, and go to it. Will that happen? I doubt it. But here are a few of my ideas anyway.

The space program should do the following:

(1) Provide a permanent human presence in space,

(2) Explore the cosmos, and

(3) Exploit the unique environments beyond earth.

We need humans in space. But that doesn’t mean we need to put humans in space when we don’t need them. Before Challenger blew up, NASA made Space Shuttle it’s only launch vehicle, eliminating expendable rockets, in an attempt to reach cost goals for the shuttle. So we were risking people to put up satellites, which we don’t need to do. And we were also putting all our launch eggs in one basket, which blew up in our face. I think there will always be a place for unmanned launch vehicles — they’ll be cheaper because the safety requirements will not have to be as stringent. 

Which brings us to safety and risk. One of the safety problems with the shuttle is that it represented a bunch of new technology. We now risk humans on the beta version of technology (sadly 30 years out of date now). Frankly, that’s not acceptable from a safety standpoint. People shouldn’t be risking their lives until we’ve tried out the technology on an unmanned vehicle, learned from the inevitable mistakes, and made improvements. While 100% safety is impossible, certainly we can use some common sense.

NASA has done a pretty good job when it comes to exploring the cosmos, but a lousy job when it comes to providing a permanent human presence and exploiting the unique environments beyond earth. There are many who seem to feel that NASA is standing in the way of these goals, and if they would just somehow get out of the way, private initiative would take care of them. I’m not so sure. The example of civil aviation is often cited, but while I think it provides a great notional roadmap, too many of the details don’t match. NASA should develop the technology that can be transitioned to private industry, just as it did for civil aviation, but is the technology mature? A lot of aviation pioneers died from accidents; society has become much more intolerant of fatal accidents. Capital costs are orders of magnitude greater as well, with uncertain payoffs. There is no denying that aviation technology received huge boosts from military investments in the world wars, but there hasn’t been any military interest in humans in space since MOL (Manned Orbiting Laboratory) was canceled in 1969. A couple modestly successful businessmen (AKA the Wright Brothers) could fund the development, design, construction, and test flights of the first aircraft. Can the same be said of launch vehicles, let alone space stations? That leaves tourism, so far the only money maker in manned space efforts. Is Disney ready to spend the billions required when the risks are large and the return uncertain? Is any company with the pockets deep enough ready to roll the dice on space? In short no. NASA needs to make the eventual privatization of space a goal (OK, make it number 4 up above) so that it’s programs support that goal, but I don’t think we’re there yet.

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Shuttle Aerodynamics

NASA now says that the drag on the left wing of Columbia is consistent with asymmetrical boundary layer transition, which it has seen on about a dozen prior occasions. The boundary layer is the part of the airflow where it changes from the freestream velocity somewhere above the surface to zero at the surface of vehicle. Boundary layers are either laminar or turbulent. In laminar boundary layers, the flow moves smoothly along lines which are essentially parallel with no mixing as you move away from the surface; in turbulent boundary layers, which are thicker and have more drag, there are eddy currents within the flow, so there is mixing and therefore increased heat transfer. 

The P-51 Mustang famously had a laminar flow airfoil. For airplanes, the flow over the wing and body is typically laminar initially and then transitions to turbulent – and one of the factors that determines where that transition occurs is surface roughness. One part of wind tunnel testing is to make sure that the boundary layer transitions on the subscale model in the same location as it would on the full scale, full Reynolds number vehicle. Transition strip, which is a strip of high surface roughness, is placed in the location where this occurs so that aerodynamics measured will correspond to the flight vehicle. Apparently the flow over the space shuttle wing starts outs totally laminar, and then later transitions to mostly turbulent. What happened with Columbia (and other flights) was that one wing was rougher than the other, and thus that wing transitioned from laminar to turbulent much sooner, leading to higher temperatures and higher drag on that wing. The drag meant that the control rockets had to be used more to correct for the induced yaw, and in the past NASA’s worry was that the control rockets would run out of fuel before the shuttle landed. So could the asymmetric transition itself have led to to the loss of Columbia? NASA doesn’t think so, and I have to believe the engineers who designed it wouldn’t have let a predictable occurrence like that have caused a vehicle failure. Of course, combined with another failure, it could have been a contributing factor.

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Columbia Ave Atque Vale

The space shuttle Columbia blew up today, killing the seven astronauts on board. It is a sad day for all of us, but especially for the friends and family of the astronauts. The space shuttle, and the space station for that matter, get very little news coverage anymore, unless something goes wrong. Space has become routine, so they say. It’s not routine for the brave souls who rocket into space on a pillar of fire and return riding a wave of white hot plasma. It’s not routine for all the people who work hard with the safety of those brave souls in mind. It’s not routine for all of us who understand the hard work, dedication, and yes, risk taking associated with scientific and engineering advancement. I’m sure NASA will figure out what happened, if they don’t already know, and it will be fixed, and we will return to routine. When I was a kid, I wanted to be a fighter pilot and an astronaut. Lousy eyesight and motion sickness ended those dreams. But I continue to dream about human exploration and advance into space – the final, unending, still beckoning frontier.

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