NASA to Launch Craft Powered by Trekkie-Style Propulsion

NASA is about to launch a spacecraft worthy of “Star Trek”--Deep Space 1, a small but smart self-navigating probe that will be propelled all the way to an asteroid by an ion engine.

It’s the opening act in NASA’s New Millennium program.

“This is the first Star Trek-y thing that NASA has done,” says Curt Cleven, deputy spacecraft systems manager for Deep Space 1. “It’s the first time we’re really trying something out of the ordinary.”

The goal is to test technologies too new and risky to fly on science missions, but which could lead to smaller, faster and cheaper spacecraft in the future.

Twelve such technologies will soar with Deep Space 1; launch is targeted for today. Perhaps the most intriguing, and futuristic, are the ion-propulsion engine and autonomous navigation system.

“These two technologies are like having your car find its own way from Washington, D.C., to Los Angeles, arrive at a designated parking space and do it all while getting 300 miles per gallon,” says Marc Rayman, chief engineer and deputy mission manager at the Jet Propulsion Laboratory in Pasadena.

Rayman first heard about ion propulsion in a 1968 episode of “Star Trek.” An alien spacecraft uses advanced ion propulsion, impressing the crew of the faster-than-the-speed-of-light starship Enterprise.

In the much slower real world, solar-powered ion engines are 10 times more efficient than traditional chemical engines. In other words, they require only one-tenth the amount of fuel, which allows for lighter spacecraft and therefore smaller (i.e., cheaper) launchers.

A small Delta rocket costing a modest $43 million, for instance, will launch the 1,080-pound Deep Space 1 on its one- to three-year mission. The Delta’s third stage will boot the spacecraft out of Earth orbit and put it on a perpetual sun-orbiting course.

The ion engine, once it’s running, will provide the extra kick needed for Deep Space 1 to meet up with asteroid 1992 KD next July.

That extra kick will be light but long.

The thrust of an ion engine is 10,000 times weaker than that generated by typical interplanetary spacecraft. Hold a piece of paper, Rayman says, and that’s how light the thrust of an ion engine would feel.

The farther Deep Space 1 gets from the sun--which provides the power that drives the engine--the lower the thrust. Because of the constant acceleration, however, the spacecraft can zoom along at incredibly high speeds after months and even years.

“It’s what I like to call acceleration with patience,” says Rayman.

Deep Space 1’s ion engine will run on 180 pounds of xenon gas. Here’s how it will work:

The colorless, inert gas is bombarded by electrons that knock away one of the 54 electrons orbiting the nucleus of each atom of xenon. This leaves each atom one electron short, resulting in positively charged ions.

The xenon ions are drawn toward high-voltage grids at the open end of the engine and expelled into space at a speed of more than 62,000 mph. They’re mixed with electrons again to neutralize their electrical charge and protect the spacecraft from shorting out or the engine from shutting down.

This glowing blue stream of xenon ions, traveling fantastically fast, is what provides the push.

To provide enough solar power for the ion engine, Deep Space 1 is outfitted with a pair of newfangled solar wings. Some 720 silicone lenses on the exterior of the wings will focus sunlight onto the 3,600 solar cells below, vastly improving efficiency.

“Ion propulsion, if it works--and we think it will-- . . . it’s a whole new way to get someplace a lot faster,” Cleven says.

The estimated 10-year trip to unexplored Pluto, for instance, could be reduced by at least a couple of years with ion propulsion.

Although ion engines have flown before--they’re helping, for example, to maintain the position of some high-orbiting communication satellites--this will be the first use of such an engine as the primary propulsion for a deep-space mission.

Cautious ground controllers will wait a week or two before firing up Deep Space 1’s ion engine. They’ll try a variety of throttle settings, then suspend operations for a few weeks to evaluate the data. If all goes well, the engine will begin thrusting again six weeks after launch.

After this initial shakedown phase, Deep Space 1’s motto will be: Don’t call me. I’ll call you.

In the first such test, the spacecraft will find its own way to asteroid 1992 KD and attempt to pass within six miles of the two- to three-mile-diameter rock.

Deep Space 1 will determine its place in the solar system by taking pictures of known asteroids and comparing their positions to background stars. The orbits of 250 asteroids and the positions of 250,000 stars will be stored in its computer memory.

What’s more, Deep Space 1 will take charge of some of its own commanding thanks to artificial intelligence in the autonomous navigation system, reminding itself when to turn, take pictures and change the throttle settings, among other things.

And in another experiment, the spacecraft will keep Earth posted about its health and whereabouts, periodically radioing back one of four tones.

No. 1, the so-called green tone, means, “All is well, leave me alone.” No. 2 means, “I’ve got some data, how about scheduling a hookup via NASA’s Deep Space Network sometime soon.” No. 3 means, “I’ve had a problem, better take a look.” No. 4 is the emergency red alert: SOS.

Such a straightforward monitoring system requires a relatively small antenna on Earth and thereby frees up the congested Deep Space Network of giant antennas for other uses, says Rayman. It also reduces the number of ground controllers needed to run a mission, further cutting costs.

Rayman estimates fewer than 40 controllers will be needed during the early part of the Deep Space 1 mission, primarily to validate the experimental technologies. That compares to a cast of hundreds on some deep-space missions.

Deep Space 1 was developed in three years, practically no time at all by NASA standards. What’s more, the entire mission--spacecraft, rocket and nearly a year of flight operations--is budgeted at $152 million, a bargain compared to the behemoth projects of yesteryear.

The cost will jump another $15 million if NASA extends the mission beyond September 1999, enabling Deep Space 1 to fly past one and maybe two comets in 2001.

Any scientific observations of the asteroid or comets will be “pure bonus,” says Rayman. Only a few million dollars, as a matter of fact, is targeted for science.

“The real science return from Deep Space 1 is in the future missions that are enabled by the technologies that we’re carrying,” Rayman says. “We’re taking the risks so that the future missions don’t have to.”