For that satellite dish on your roof and the phone calls you make to Japan, you can thank Harold Rosen.
- By Guy Gugliotta
- Air & Space magazine, September 2009
(Page 2 of 4)
Then another colleague showed Rosen a journal paper written by two renowned Bell Laboratories engineers—Rudolf Kompfner and John Pierce—that described how to use space for transoceanic communications. The authors and Bell Labs were interested in low-altitude satellites. Rosen saw that low altitude had its virtues; from there, randomly spaced satellites could use omnidirectional antennas to receive and transmit signals. But he also found the approach sloppy, like surrounding Earth with a halo of whirling bowling balls. A geosynchronous system, by contrast, requiring only three satellites, was conservative and neat—“far more appealing to me,” he says now.
There were major challenges: how to transmit the signals; how to keep the satellite from wobbling or drifting out of orbit; whether the United States had enough rocket to lift a payload to 22,000 miles. But Rosen decided to go forward, and during the next four years, he, Hudspeth, and Williams built the world’s first high-altitude communications satellite. The Syncom program was the prototype for an industry that today has 275 satellites in geosynchronous orbit.
The team set to work at Hughes’ Lincoln Avenue campus in Culver City, a few miles from Los Angeles International Airport. They designed the system during normal work hours. No extra money was needed just yet. To get a payload into geosynchronous orbit, the rockets of 1959 would need two extra stages: one to lift the satellite from low altitude up to 22,000 miles, and another to make the resulting elliptical orbit circular. The rocketry was tricky, but Rosen, who had earlier worked on guided missiles at Raytheon, believed it could be done as long as the weight of the spacecraft was kept to a minimum.
The satellite would use a “traveling-wave tube” to amplify incoming radio waves for retransmission (see “How to Pump a Signal,” opposite). Developed by Kompfner and subsequently refined at Bell Labs by Kompfner and Pierce, the tube used a cathode to fire a beam of electrons through a coiled wire surrounded by a magnetic field. Incoming radio signals were transmitted through the coil and, as they interacted with the electrons, were amplified before being beamed back to Earth. Even in today’s satellite communications, traveling-wave tubes are a mainstay.
Hughes’ expert in traveling-wave tubes was John Mendel, a transplant from Bell Labs. He had developed a way to shrink the size of the tube’s magnets, thereby making the device a better fit for aircraft, and especially for spacecraft, where every ounce counted. Rosen told Mendel he needed a traveling-wave tube that was no more than a foot long and weighed no more than a pound. Mendel delivered it.
The most challenging task was to build the attitude- and orbit-control system. Satellites tend to drift away from a desired orbit and need small thrusters for station-keeping. To work properly, a geosynchronous satellite needed to be stabilized in orbit so the communications beam they shined on Earth would be consistent.
The most effective way to stabilize spacecraft in 1959 was with large, spinning reaction wheels, but they weighed a lot and tended to wear out. Rosen, however, had an inspiration. He remembered from his days at graduate school that rotational forces could exert a powerful stabilizing effect on a projectile, such as a bullet or a football. If a satellite were spinning on an axis parallel to Earth’s, station-keeping could be handled by a single thruster. First, however, the satellite, traveling like a tight spiral during launch, would have to be tipped over once it got into orbit so the spin axis would be parallel to Earth’s. Rosen figured he would need four additional thrusters on the satellite to accomplish this. He showed the idea to Williams.
“The basic concept was mine,” Rosen says. “But I didn’t do the math.” Williams did. He showed that by using fast-acting pneumatic valves and short bursts of compressed nitrogen, the satellite could be maneuvered into position with only one thruster. This made construction vastly simpler. Then Williams designed a sensor that could determine the angle between the satellite’s spin axis and the sun. By combining this measurement with information from the satellite’s signal, controllers could determine the spacecraft’s spin axis attitude. Carefully timed pulses from the thruster would then keep the satellite flying in the correct attitude. (This technology would lead to one of the longest patent lawsuits in U.S. history—the “Williams case”—which Hughes filed against the U.S. government in 1973. Hughes claimed the government had used the company’s patented technology on a number of space programs, including the Department of Defense’s Global Positioning System and NASA’s Galileo probe to Jupiter. The government argued that Hughes had exaggerated the importance of the technology and should not have been granted a patent in the first place. In 1999, a federal judge agreed with Hughes, ordering the government to pay $154 million for patent infringement.)