The elite of the electromagnetic spectrum, gamma rays are the most potent packets of energy produced by the interplay of atoms and atomic particles. They’re powerful enough to travel billions of light-years across the universe without flagging and to turn DNA into a mutated mess. But while this ferocious source of radiation regularly bathes our solar system, gamma rays are absorbed quite efficiently by Earth’s protective atmosphere. That may be fortunate for those who value the health of their chromosomes, but it’s frustrating for astrophysicists.
Frustrating because gamma rays bring news of the most sensational events in the history of the universe. They fly from star collisions and explosions, matter-antimatter annihilations, the frenzied burning of quasars, and the cataclysmic eating habits of black holes. Until recently, these violent cosmic events have simply teased gamma-ray researchers, who’ve been restricted to lofting short-term probes above the atmosphere on balloons, rockets, or brief orbiting missions.
All that changed in April 1991, however, when shuttle astronauts released NASA’s Compton Gamma Ray Observatory. The TRW-built satellite is now parked in a circular orbit 268 miles above the Earth, dutifully capturing evidence of gamma rays shooting from every corner of the cosmos. Already, Compton’s readings have thrown the high-energy astrophysics world into a delirious tizzy. In the words of Compton project scientist Neil Gehrels at NASA’s Goddard Space Flight Center, We’ve had a dream mission so far.
Yet without some speedy and innovative design work by TRW, the dream could easily have been a nightmare. Because gamma rays are scarce and only reveal themselves when they slam into matter, the detectors must be massive. The entire satellite weighs 17 tons, which makes it the heaviest unmanned spacecraft ever lofted by the space shuttle.
We had a much larger system than our people were used to dealing with, says TRW’s Jerry Gliksman, the program manager during the critical design years from 1985 to 1988. TRW’s bread-and-butter spacecraft are communications satellites that typically weigh two and a half tons. Although the Compton Gamma Ray Observatory was launched as a single platform, it’s actually four separate gamma-ray experiments. The detectors themselves were already being designed by 1983, when TRW won the contract. Some of them were originally planned for separate lofting on a series of small, rocket-launched platforms. Modifying the bulky instruments to suit a common carrier was not an option.
Two of the detectors, the Compton telescope and the Energetic Gamma-Ray Experiment, weighed more than 3,000 pounds each. Their sheer inertia threatened to twist and wrench a single platform to unacceptable stress levels during liftoff. We designed the structure to act as a shock absorber or a tuning bar, says Gliksman. This helped to separate the big instruments from the huge forces of shuttle liftoff. It was the first time we’d done that for this large a system. The computer-derived solution involved finding the perfect position for each of the elements so that the entire platform would be balanced.
But the design team wasn’t satisfied with simply modeling solutions on a computer. TRW’s engineers built a full-scale mock-up of the satellite, a normal step in building a new aircraft but unheard of in satellite design.
Made of metal and acrylic (and draped with J. C. Penney bed linen to simulate the gold thermal insulation used on the finished craft), the replica enabled engineers to package the instruments, electronic controllers, thrusters, and solar panels as intelligently as possible.
The mock-up also proved to be a boon to Compton’s ultimate handlers, the crew of the space shuttle Atlantis, who were charged with unloading the huge spacecraft from the orbiter’s payload bay. In early 1985, astronauts used the mock-up to practice yanking out Compton’s solar arrays and antennas by hand in case the components’ motor drives failed during deployment.
At the suggestion of the astronauts, TRW fitted extra handrails and foot-restraint sockets on the observatory’s frame. And as it turned out, the suggestion was prophetic: the crew put the hardware to use during an emergency space walk to finesse a balky high-gain antenna into its proper position. Fortunately, the antenna glitch was short-lived, and the observatory worked well.
More significantly, the observatory has revolutionized gamma-ray astronomy. Theorists are already struggling to explain why random gamma-ray flashes, known as bursts, pop from all parts of the sky. Astronomers had expected to detect such bursts only in the plane of our own Milky Way galaxy, where violent events are common. The wide distribution of these bursts may indicate that neutron stars and black holes are active in all regions of the sky. Compton has also spotted 14 so-called gamma-ray quasars at the very frontier of the universe. These mysterious galactic powerhouses seem to outshine the Milky Way 100-millionfold.
Amazing results like these will be likely to pressure NASA to extend Compton’s mission. Both TRW and NASA believe Compton has enough fuel to keep it in orbit for another six years. The life of the spacecraft can be extended even further by a refueling visit by the space shuttle. If budgets hold out, the Compton observatory should be bringing cosmic news to Earth for years to come.
Daryal Kuntman, manager of radar-product design at Allied-Signal Aerospace in Ft. Lauderdale, Florida, for the development of the Forward- Looking Wind Shear Detection/Avoidance Radar System. Wind shear was a contributing factor in at least 26 civil transport accidents, accounting for more than 500 fatalities, from 1965-1985 alone. Before this new system, wind shear was something pilots couldn’t see coming until its dangerous downdrafts were already jostling the plane. The Allied-Signal system senses and identifies hazardous wind shear conditions well ahead of an aircraft’s path by measuring the velocity of the tiny drops of moisture always present in the atmosphere. With this radar, flight crews have sufficient warning to avoid dangerous areas.
Ron Anders, project engineer at Logicon in San Diego, for the development of the T9000 air traffic controller training system. A revolutionary new way to train controllers, this computer-based system creates an eerily lifelike simulation of an airport’s traffic. Prior to the development of this system, air traffic controllers were trained by pushing model airplanes along a tabletop. The T9000 simulation is so detailed that it accurately portrays the paint schemes of different airlines. It also simulates the voice responses of the pilots a trainee is directing. Pilots and controllers alike are convinced that this system will lead to safer skies for us all.
Andrew Logan, vice president of engineering at McDonnell Douglas Helicopter in Mesa, Arizona, for the development of the NOTAR helicopter design. The NOTAR is the first conventional helicopter without a tail rotor. Traditionally, helicopters need a tail rotor to keep them from pinwheeling helplessly; but tail rotors are exceedingly noisy and create vibrations and instability in windy conditions. They are also the second- largest contributor to helicopter accidents. Instead of a tail rotor, the NOTAR uses powerful fans built into the tail boom that send out gusts of air to control torque. With this new, safer design, pilots can maneuver more easily and fly in more extreme weather conditions.
Ilan Kroo, associate professor of aeronautics and astronautics at Stanford University, for the development of the Swift sailplane, manufactured by Bright Star Hang Gliders in Santa Rosa, California. The Swift is a high-performance foot-launched sailplane that enables a pilot to take off from a hillside in the same way a hang-glider pilot lofts his craft. A conventional sailplane costs more than $40,000 and requires the use of another airplane to tow it into the air. The $9,500 Swift provides exceptional pilot control and soaring time, and it can be launched virtually anywhere. Because of its novel wing design and ease of use, the Swift deserves credit as an exciting--as well as ingenious--new form of aircraft.