Star Wars Spinoff : Cluster Probes Look for Lift on Space Guns

The question in many quarters of the American space program these days is how to do more with less, and it has led to some revolutionary concepts, such as borrowing electromagnetic rail guns now being developed for Star Wars to launch scores of tiny spacecraft to explore the solar system.

Scientists and engineers at NASA’s Jet Propulsion Laboratory in Pasadena also are coming up with a wide range of ideas involving space probes the size of coffee cans that could be launched cheaply on exceptionally fast trajectories.

The concept behind such proposals is to use a lot of smaller spacecraft, each equipped with only one instrument, instead of a large, complex vehicle that would be expensive to build and difficult to launch.

That could prevent the kind of disappointments that have plagued JPL’s Galileo spacecraft--a billion-dollar probe that was to have been launched to Jupiter two years ago, but now may not reach its target until after many of the scientists who built it have retired.

The grounding of the space shuttle after the Challenger tragedy stalled the Galileo program, and changes required in the craft’s propulsion system now mean that it will have to follow a bizarre course to reach Jupiter, delaying its arrival there until near the end of the century.

With that prospect in mind, the dreamers at JPL who plot the future of space exploration through the use of unmanned vehicles are thinking small again, just as they did in the early days when a 40-pound satellite was considered a big payload to deliver to space. Some of today’s satellites weigh more than 1,000 pounds.

Among the ideas now being considered is a proposal to send a large batch of tiny radio telescopes into space, and then link them together electronically so they would act as a single, huge telescope. That could be done for a few million dollars--a bargain-basement price tag in today’s space market. The individual satellites would be so cheap that a lot of them could be launched, thus reducing the risk of failure. If some of them do not work, there still will be enough left to do the job, according to developers of the proposal.

The fact that so many ideas for smaller vehicles are making the rounds at JPL is “primarily coincidental,” according to Ross M. Jones, a space systems engineer at the laboratory. There is no organized, structured program aimed specifically at miniaturization, he said, “but it is an obvious trend.”

Jones is to present the rail-gun concept today in a talk at the American Institute of Aeronautics and Astronautics’ Aerospace Sciences Conference in Reno.

His idea is to use the electromagnetic launchers, or rail guns, now being developed for the Strategic Defense Initiative, known popularly as “Star Wars,” to fire small probes into space.

Rail guns are similar to the nuclear accelerators that are used to hurl subatomic particles into violent head-on collisions, smashing them into even smaller pieces. But instead of using tiny particles, orbiting rail guns would fire projectiles into space by using powerful bursts of electrical pulses to produce strong magnetic forces that would accelerate the projectiles to extremely high velocities.

“Since they are developing these programs for space use, my idea is that NASA would piggyback on top of the SDI development,” Jones said.

He said microelectronics makes it possible to build space probes that would weigh only about three pounds, each designed to accomplish a single mission, such as studying cosmic rays from space. And if they could be launched by an orbiting rail gun, they would achieve extremely high velocities, reaching distant planets in less than half the time of even the fastest vehicles available today, he said.

After the rail guns are in orbit, where they would be serviced by the space shuttle, “You would just go up to the general and say, ‘would you please point your gun at Mars’ or something,’ ” Jones said.

Thus instead of struggling to launch a single billion-dollar spacecraft, NASA could fire off dozens of smaller probes each year, thus assuring the continuity of a wide range of scientific programs.

If necessary, NASA could even launch into orbit its own rail gun, which the Air Force calls hypervelocity guns. Such a device would probably cost less than a single major launch vehicle, and it could be used over and over for many years.

The rail guns being developed for “Star Wars” will be far more powerful than those needed by NASA.

“They want to fire these things a couple of times a second, so they need a big power supply, something like a nuclear reactor” orbiting with the gun, Jones said. A rail gun that would suit NASA’s needs would not have to fire so often, and thus would not require that much power.

“Just an ordinary sized solar array is all it would take” to generate enough electricity for a rail gun that would satisfy NASA’s objectives, he added.

Meanwhile, in another office at JPL, mathematician Edward A. Belbruno is working on a problem in the mind-numbing field of orbital mechanics. It is fine to have small spacecraft, Belbruno reasons, but if you want to put one in orbit around the moon, for example, it is going to have to be big enough to have powerful rockets to slow it down once it gets there or it will zip past the moon.

Unless, he reasons, you can use something he calls the “fuzzy boundary” to capture the probe in lunar orbit.

The “fuzzy boundary,” Belbruno said, “is a thick region about the moon, not well defined, where things just hang in the balance” between the gravitational fields of the moon and the Earth.

A tiny spacecraft entering that region “would feel both the Earth and the moon at the same time, so it’s captured,” he added. It would just take a tiny nudge with a small thruster rocket to send it into orbit about the moon. It might be possible to do that with other planets, but the formula is far more complex for more distant bodies, he said.

Size of Trash Can

Belbruno has even figured out how to get his tiny spacecraft--which he said would need to be about the size of a small trash can--to the moon without using the sophisticated rail gun.

Any probe that is to travel to other parts of the solar system must achieve “escape velocities” sufficient to overcome the gravitational pull of the Earth.

Normally, that requires a substantial propulsion system, and that means that the spacecraft has to be fairly large. But Belbruno argues that it could be done with a very small propulsion system, with enough patience.

A small probe released from the space shuttle in orbit about the Earth could use tiny thrusters to gradually build up its speed as it orbits the planet. Belbruno has calculated that after about 3,000 orbits, which would take two years, the craft would be traveling fast enough to leave the Earth.

It would take 14 days to reach the moon--much slower than the three days required for the massive Apollo rockets--partly because the probe would use the Earth’s gravity to slow it down as it speeds toward the moon. That way, Belbruno reasons, it should be traveling at just about the right speed to be “captured” inside the “fuzzy boundary.”

Think Small to Build Big

Meanwhile, other scientists at JPL are thinking small in hopes of building big. They would like to use a lot of small satellites to create a huge radio telescope in orbit about the Earth.

Radio telescopes use radio waves generated by distant objects to create images, just as an optical telescope uses visible light to make photographs. But the wavelength of radio waves is much greater than the wavelength of visible light, so to achieve similar results a radio telescope must be much larger than an optical telescope.

Radio astronomers solve that problem by linking different radio telescopes together, using the signals received by one to “interfere” with the signals received by the other in a process known as very long base line interferometry. The interference--or the difference between the two signals--produces the image.

Currently, radio telescopes on the far sides of the planet, in Australia and South Africa, for example, can be linked together to form a single unit the size of the distance between them. The same process could be done in space, thus building huge radio telescopes of immense power.

Last May, radio astronomers met at JPL to discuss the possibility of building such a telescope. They concluded, according to a report published recently by the lab, that not only is it possible, it should not be too expensive and it could do things that no radio telescope on Earth can do.

Can Build at Small Cost

The scientists concluded that half a dozen or so small satellites could be built at a cost of $1 million to $2 million each and could be put in orbit to create a giant telescope. One reason the cost could be held that low, the report concluded, is that there is no need to build the satellites to the pricey “flight certification requirements” that push the space program almost beyond reach. By keeping the price relatively low, spare satellites could be added so that if some fail, the system itself would not be jeopardized. That, in a sense, substitutes quantity for quality, but the savings could be enormous.

In addition, the system would study the universe through very long radio waves, something that is nearly impossible to do from Earth because of interference from man-made radiation in that wavelength.

That could give astronomers a valuable tool to study some of the most exotic objects in the universe, including the remnants of exploding stars such as the supernova that lit up the sky in the Southern Hemisphere last year.

Not a bad goal for a bunch of “trash cans” from a bargain basement.