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Humans have place in space, machines not fail-safe

Returning from space, a space shuttle makes earthfall at better than 200 miles an hour. As it (literally) whistles down the runway, trucks bearing giant refrigeration units make chase.

The moment it rolls to a stop – even before the astronauts egress – workers attach huge hoses to the spacecraft to blow cold air under its skin. They’ve got roughly 15 minutes to cool the craft from the inside out.

Plunging into the atmosphere, belly-first, at better than 17,000 miles an hour, the shuttle compresses the air beneath it.



Much as a bicycle pump grows warm as the air within it is squeezed, the air compressed beneath the shuttle grows hot; it radiates this heat back to the shuttle, raising the spaceplane’s exterior to over 3000 degrees Fahrenheit – enough to melt its aluminum frame.

A camper in a sleeping bag is kept warm, not by down or fiber, but by the bubbles of air trapped by those materials; air is a poor conductor of heat. Similarly, the shuttle’s frame is protected by silica (quartz) tiles whose main constituent, besides silica, is empty space.




Tiles that experience the highest heat stress are covered with a black carbon composite material. The tiles are amazingly light … and fragile.

A machine that is “fail-safe” may still fail; it will do so, however, in a manner that does not endanger its mission … or its crew.

To be fail-safe, a system must be robust. One can make hardware robust by making it extremely strong.

Another way to make hardware robust is to make it redundant, with spares ready to take over if something goes wrong.

Unfortunately, increasing strength and redundancy both increase weight; were the space shuttle completely fail-safe, it would be too heavy to fly. A number of systems – thermal protection among them – simply cannot fail.

As I write this, NASA has yet to determine what damaged Columbia’s tiles sufficiently to lead to the craft’s disintegration at 200,000 feet, where velocity (12,000 miles an hour) and air density combined to surround the craft in an inferno. The accident has rekindled the debate of the future of humans in space. A light-year – the distance light travels in one year – measures roughly six trillion miles; the star nearest our solar system is four light-years away.

Stars can be more than a hundred light-years distant and still be within our galaxy; other galaxies are millions, even billions of light-years away.

The distance to the planets, however, is measured in light-minutes; to Pluto, the outermost planet (or Kuiper Belt object, if you prefer), is just a few light-hours. The planets of the solar system are truly within our neighborhood.

It was only a few centuries ago that humans first looked at the sky with a telescope, and realized that the planets were not the abodes of gods, but were worlds, like (and unlike) our own.

For some decades now, we’ve been exploring these worlds with robotic spacecraft. Each mission benefits from better hardware, better software … and much thought by scientists and engineers

Why not simply leave the exploration of the solar system to such “artificially intelligent” machines?

Two reasons (which will no doubt be countered by some computer scientists):

1. It will be a very long time – perhaps forever – before machines will match the human brain’s ability to confront the unexpected.

2. Never having experienced life, machines will never have common sense.

Our robots send back important, exciting data about the worlds in our neighborhood, but they can never completely replace the human who goes out to see for him – or herself.

Alan Stahler trained as a biologist and is an amateur astronomer. He teaches enrichment classes for children and adults at Sierra Friends Center. His science programs can be heard at noon on alternate Tuesdays on KVMR-FM (89.5).


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