Goddard’s First Homegrown Satellite, Explorer 10, Was Launched 50 Years Ago Today: We Talk to the Father of Explorer 10, James Heppner, About the ‘Opportunity Years’ at the Dawn of NASA
This photo from the early 1960s shows Goddard employees Earl Angulo (at left) and Ron Browning examining an Explorer 10 model attached to a test fixture. They were responsible for the mechanical engineering and testing of the satellite.
Fifty years ago today, Goddard’s first homegrown scientific satellite roared off the pad at Cape Canaveral on a Thor-Delta rocket. Although key components came from outside the gates, Explorer 10 was the first satellite to be designed, assembled, tested, and flown from Goddard Space Flight Center.
James Heppner, a young space physicist (barely 30 then) and one of NASA’s early employees, conceived of the mission that came to be called Explorer 10. Heppner functioned as a sort of one-man band — Project Manager, Project Scientist, and Principal Investigator for the magnetometer instruments on the satellite.
Before NASA was founded, Heppner worked for the Naval Research Laboratory (NRL) on the Potomac River in Washington, D.C. It was there he developed methods to measure Earth’s magnetic field. At NRL he used sounding rockets to study charged particles and magnetic fields high in Earth’s atmosphere. His earlier research in Alaska focused on the aurora and its effects on radio wave propagation, and was the basis for his Caltech PhD thesis.
Heppner calls these times the “opportunity years,” a period when methods and technology for measuring magnetic fields and space plasma — the bread and butter of space physics — were being invented. He was at the right place at precisely the right time.
In late 1958, as Heppner and many of his colleagues were being “handed over” to the nation’s new aerospace agency, he had already helped create a magnetometer for the Vanguard program. Vanguard, an NRL project, was created to loft the first civilian scientific payloads into space for the International Geophysical year of 1957-58. Heppner’s proton magnetometer went into space aboard Vanguard 3 on September 18, 1959.
At the time of the transition to NASA, Heppner today recalls, he conceived of a satellite to measure the magnetic field of the moon. The mission, then called P-14, would accomplish its goal by extreme measures:
“I originally proposed Explorer 10 when NASA was formed,” explains Heppner, 83, who spoke with me recently from his home in New Market, Maryland. “And the intent was to try to hit the moon and measure the moon’s magnetic field on the way in.”
The original plan was deferred. The truth is, hitting the moon — even intentionally — was no simple trick in those days. It wasn’t clear the Thor-Delta launch system would accomplish the task, and even tracking a spacecraft to the moon was straining the technical capabilities of the time.
“With time we realized that the odds of hitting the moon would be extremely low, from the vehicle performance and ability to track, things like that,” Heppner explains. “I was told that with the odds of hitting the moon being so low, it would be embarrassing to even try. So I was essentially directed by NASA headquarters to make sure that the trajectory was such that it couldn’t be interpreted as an attempt to hit the moon.”
The new mission goal was to measure magnetism and plasma particles in space from outside of Earth’s protective magnetic bubble, or magnetosphere. This had been attempted previously, but not with great success. To do it required launching P-14/Explorer 10 into a highly elliptical orbit that would take it a great distance from Earth, dozens of time the planet’s radius.
The satellite weighed approximately the same as a space physicist: 79 kilograms, or 178 pounds. “It was very light,” Heppner says. “We were trying to get distance.” An engineering model hangs in the Smithsonian if you care to look at the real thing..
For the records, here is the complete entry in the NASA/National Space Science Data Center mission database:
“Explorer 10 was a cylindrical, battery-powered spacecraft instrumented with two fluxgate magnetometers and one rubidium vapor magnetometer extending from the main spacecraft body, and a Faraday cup plasma probe. The mission objective was to investigate the magnetic fields and plasma as the spacecraft passed through the earth’s magnetosphere and into cislunar space. The satellite was launched into a highly elliptical orbit. It was spin stabilized with a spin period of 0.548 s. The direction of its spin vector was 71 deg right ascension and minus 15 deg declination. Because of the limited lifetime of the spacecraft batteries, the only useful data were transmitted in real time for 52 h on the ascending portion of the first orbit. The distance from the earth when the last bit of useful information was transmitted was 42.3 earth radii, and the local time at this point was 2200 h. All transmission ceased several hours later. “
Rubidium vapor magnetometers could measure extremely weak magnetic fields, and were a totally new technology, Heppner says. They were invented at a company called Varian Associates in Palo Alto, California. The Faraday cup plasma instrument, which measured particles streaming off the sun’s “solar wind,” came courtesy of a team of scientists at MIT led by the pioneering X-ray astronomer and plasma physicist Bruno Rossi.
Finally the big day came on March 25, 1961. The launch managers for the Thor-Delta rocket worked in “the block house” at the Cape, while Heppner and his colleagues were encamped in a machine shop, peering at oscilloscopes to assess the health of their satellite and staying in contact with the blockhouse, and the other scientists and engineers, by telephone.
Explorer 10, as was typical in those days, was powered by a expendable battery. The craft radioed back data for 52 hours as it swooped through and outside of the magnetosphere, travelling for 42.3 Earth radii — about 167,466 miles — before the battery dimmed and the craft shut down. (For comparison, consider that the average distance form Earth to the moon is 238,857 miles.)
After launch, tracking stations record data on tapes and send them to the scientists. Heppner published a number of scientific papers from the data. He headed the Goddard Magnetic Fields Group, and worked on many major missions over the succeeding years.
The next big missions for Heppner after Explorer 10 were the Orbiting Geophysical Observatories, which grew substantially in mass and capability. He retired from the civil service in 1989, but continued to work as a contractor until 1996.
How were those days different from the later, larger, more complex place NASA has become? What was it like in the opportunity years?
“It was a very busy period in the sense that the technology was developing,” Heppner explains. “The early satellites weren’t very sophisticated because everything was new.”
But things moved fast. Heppner summed it up best in a chapter he wrote for a 1997 book, Discovery of the Magnetosphere.
“Opportunities for new endeavors were plentiful and the time between conception and results was unbelievably short when viewed in the light of today’s space programs.”
OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.