Ad Astra (to the stars)

Aug. 1, 1999
WASHINGTON — Is there anybody out there up to the task of developing an electronic component with a mean time between failure of at least 50 years? Yes, that`s years. If so, I have a killer application for you: interstellar space exploration.

by John Rhea

WASHINGTON — Is there anybody out there up to the task of developing an electronic component with a mean time between failure of at least 50 years? Yes, that`s years. If so, I have a killer application for you: interstellar space exploration.

The technological requirements are not as daunting as you might think these days, when many state-of-the-art components have product life cycles of 18 months. Based on electronics industry momentum since the dawn of the solid-state age 50 years ago, another three or four orders of magnitude in performance improvement at the chip level over the next 20 years is a reasonable expectation. Avionics need not be, to use the traditional Air Force expression, the long pole in that tent.

Any aerospace vehicle — from helicopters and fixed-wing aircraft to missiles and space vehicles — has only three principal ingredients: the aerodynamic structure, the propulsion system, and the avionics. Aerodynamics is a mature technology, and there is at least a substantial body of theoretical work available on propulsion systems capable of achieving respectable percentages of the speed of light.

In the case of avionics, those hoped-for three or four orders of magnitude improvement could contribute directly to the reliability of the four principal subsystems of guidance and control, sensors, onboard processing, and communications links. Availability of powerful chips would make multi-year space missions possible, just as solid-state electronics has made space flight possible ever since Sputnik in 1957. The basic system architectures, relying heavily on redundancy, would not have to be radically changed.

The longest pole in a tent full of long poles would be, of course, finding the money to pay for such an extravagant venture. Like the unmanned planetary programs of the past, however, the whole process could begin modestly with instrumented payloads to measure phenomena beyond our solar system (something NASA scientists are already working on) and then proceed incrementally toward the most ambitious mission of all: putting a spacecraft into orbit around another star to search for life.

Propulsion would be another long pole. Forget about the "warp drive" that science fiction writers so love and the sine qua non of the latest Star Wars movie playing to full houses. No responsible scientist is proposing any way to get around Einstein`s limitation. His famous equation E=MC2 means that any object exceeding the speed of light would have infinite mass, which is impossible. Sure, Einstein and his colleagues overthrew Newton and maybe they`ll get a taste of their own medicine in the next century, but I wouldn`t bet the egg money on it.

During the mid-1960s, when he was struggling to meet President Kennedy`s goal of putting a man on the moon in that decade, Wernher Von Braun was already looking for follow-on projects to keep the space program alive. He told me about one of those studies, a nuclear-electric rocket in which the reactor would heat a propellant fluid (in this case ions of cesium) to sufficient temperatures to achieve propulsion efficiencies one or two orders of magnitude beyond today`s conventional chemical rockets. Also unlike launch vehicles such as the Space Shuttle, which are placed in a ballistic trajectory at liftoff, Von Braun`s nuclear rocket would thrust continuously until it approached its destination.

This was how Von Braun proposed to achieve velocities of 10 to 20 percent of the speed of light. His primary intended application was rapid manned missions within the solar system at relatively low velocities, but the same system would be scaleable for interstellar missions. Nuclear rockets can`t be launched from the Earth`s surface, of course, but they could be assembled in orbit, perhaps at the International Space Station.

Assuming reasonable progress in avionics and successful resolution of the funding and propulsion issues, what would these hypothetical spacecraft actually do? To take an anthropocentric view of the matter, we`d naturally prefer to look for life around other stars like our own sun, which is known among astronomers as a G-class yellow dwarf.

Anybody who has ever studied astronomy will recall the mnemonic for remembering how stars are distributed along the Main Sequence, which is a handy way of classifying them by size and brightness: "Oh, be a fine girl, kiss me (O, B, A, F, G, K, M)." The blue giants at the O and B end are as much as a million times hotter than the sun, while down at the M end the red dwarfs generate as little as 1/10,000 as much energy. We can probably rule out both ends of the sequence as places to look for life, but that still leaves a dozen stars of interest within a radius of 20 light years.

Curiously, the closest star to us (after the sun) is another G. It`s Alpha Centauri, and it`s only — only? — 4.3 light-years away. If Von Braun`s rockets could achieve 20 percent of the speed of light we could get a spacecraft to Alpha Centauri in little more than 21 years. The problem is that we couldn`t stop it. To do that the spacecraft would have to be preprogrammed to turn itself completely around about halfway through the trajectory and use the rocket engines to brake it into an orbit around the star. This would be an extremely intricate maneuver hitting a moving target at interstellar distances and would need all the computing power the electronics industry could muster.

Total elapsed time for this, the easiest mission, would be about 43 years just to reach the target. The first sensor data wouldn`t begin arriving for another 4.3 years and it would certainly be desirable to keep up the transmissions for a few years, so mean time between failures is an overriding consideration.

There are even tougher missions, all of which would be a day at the beach for Luke Skywalker and Han Solo. The next closest G-class star, Tau Ceti, is 11.8 light- years away. After that you have to go to Sigma Draconis, 18.2 light-years away, before you reach another G-type star. Or you can go a little farther to Delta Pavonis, 19.2 light-years away.

If you`re willing to relax your requirements and consider the possibility of life on planets (if there are any) around the even cooler K-class stars, the list of potential neighbors increases somewhat. Epsilon Eridani, which is 90 percent the size of the sun and has about one-fourth of the luminosity, is a little closer than Tau Ceti at 10.8 light-years. There are seven other K stars within a radius of 20 light years.

Not a very encouraging picture, to be sure, but that`s the price we pay for living in the galactic suburbs. And you thought you had trouble achieving 50-hour mean times between failures?

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