The Missing History of the Explorer 1 Satellite

When a curator is approached by an object’s original designer, he discovers there’s a missing piece that helps tell the story of the United States’ first successful launch into orbit.

Sometimes, seeing isn't believing until you take something apart. On the 60th anniversary of the first successful satellite launch by the United States, I'm prompted to recall the most valuable lesson I ever learned about what it means to be a curator. The object in question is what we always thought was our "fully instrumented flight spare of Explorer 1." We received it from NASA's Jet Propulsion Laboratory (JPL), inventoried it in 1962, and displayed and toured it prominently before the National Air and Space Museum  opened in 1976. We then placed it center stage in our Milestones of Flight gallery. We always thought it was complete. We were wrong. To appreciate just how we found out, I want to take you on a little tour through history that will illuminate the poignancy of the discovery.

Explorer 1 was launched by a Jupiter-C missile on January 31, 1958, from the Army Ballistic Missile Agency's (ABMA) Cape Canaveral Missile Annex in Florida. A few miles from the launch pad, crowded into one corner of a Quonset hut, engineers, technicians, and scientists intensely examined radio and radar telemetry data and plotted the trajectory of the missile. The launch looked good, and messages from Explorer continued until the satellite dipped below the horizon. Unfortunately, there were no tracking stations down-range able to communicate its progress for some time and all the team could do was estimate probabilities. This was the dawn of the Space Age.

About a half hour after launch, Albert Hibbs, Explorer's systems designer from JPL responsible for orbit calculations, walked to the next room to report that they were 95 percent certain that Explorer was in orbit. In response, ABMA Maj. Gen.  John B. Medaris snapped: “Don’t give me any of this probability crap, Hibbs. Is the thing up there or not?”

The stakes were impossibly high and so were tensions. The United States Navy had failed to launch the Vanguard satellite just two months prior in early December, and the Soviet Union by now had launched two Sputniks (the second one with a dog, Laika). Everyone keenly knew that up in Washington DC, very important people at the Pentagon and at the National Academy were waiting for word, as were plenty of reporters.

It had been something of a mad dash getting Explorer 1 ready. Army Ordnance had lost out to the Navy in 1955 to launch the United States' first satellite, but as ABMA continued to develop reentry vehicles for ballistic missiles, it also kept its hopes of getting into orbit alive. Three principal players stayed in close touch and remained ready to act: geophysicist James Van Allen of the University of Iowa, who would provide the primary scientific instrument for the payload; JPL director William H. Pickering, who would provide the satellite itself; and Wernher von Braun of the ABMA, who would provide the launch system. Just after the launch of Sputnik-1 on October 4, 1957, and the Navy’s first Vanguard failure in December, the JPL-ABMA group was permitted to adapt their Jupiter-C reentry test vehicle into an instrumented satellite.

The bullet-shaped satellite payload, about 6.5 inches in diameter and 3 feet long, carried three micrometeorite detectors (a microphone, a wire grid, and metallic film), temperature sensors, and a special cosmic-ray chamber developed by Van Allen's graduate students at Iowa State University to determine the intensity of high-energy charged particles surrounding the Earth. The Iowa team cannily designed the cosmic-ray detection system—complete with its Geiger counter, electronics, and batteries—to fit inside either the 20-inch Project Vanguard sphere or the bullet-shaped Explorer payload, which JPL staff originally dubbed “Deal 1.” Therefore, once authorization was given, most of the work on the payload was done by Iowa State graduate student George Ludwig and JPL engineers. The cosmic ray payload was in every respect Ludwig's baby. When he got word that it would fly in the Explorer configuration, Ludwig packed up his family and payload components and set off for JPL to make the needed alterations.

At launch, George Ludwig was also at the Cape, in the Navy's Vanguard Microlock receiving station trailer near the Quonset hut, eagerly listening and watching the telemetry that reported on the health of his cosmic-ray package. He experienced the acoustic shock of the launch: "I felt as though it was trying to pound me into the floor." As the thunder abated, he could hear the ticking of his instrument over a loudspeaker. The first 300 seconds of data were very hopeful: the quick rise in the counting rate followed by a drop to a constant rate between 10 and 20 counts per second was what he was expecting. But then only silence as the payload went over the horizon. Was it still alive? Was it in orbit? The waiting was expected, but excruciating. Ludwig keenly recalls that after about 30 minutes, Al Hibbs visited the trailer to report on the high probability that all was well. Ludwig and his co-trackers were thankful for the encouraging words. Spirits remained high until the expected signal from tracking stations in California didn't happen on time. Following that came 12 minutes of pure, silent, palpable hell, but jubilation soon after when Explorer 1 finally reported home.

As Van Allen, Von Braun, and Pickering were being whisked from the Pentagon to the National Academy  for a press conference, Ludwig's senior associates from ABMA and JPL were racing to their own press conference. That left Ludwig and his graduate school cohorts to hitch rides back to their hotels. Once in his room, Ludwig, all of a sudden feeling isolated from friends and family, fell asleep. The next day, he packed up all his equipment and hopped a train back to Iowa.

Once in orbit, Explorer 1 instruments transmitted scientific data for 105 days.  Because of the great rush, Explorer 1 carried no means to store observations on board, though later Explorers carried tiny wire recorders devised by Ludwig.  So, only a small fraction of Explorer 1 data could be received when the satellite was in sight of a ground station, and there was not yet continuous coverage around the globe.  This was the source of Medaris’ frustration at not knowing quickly if the satellite had achieved orbit, and indeed, the intermittency caused the data interpretation to be tentative at best. Although Explorer 1 was reported as fully successful in the first month of operation, it was recording less meteoric dust than expected and varying amounts of cosmic radiation, and was sometimes puzzlingly silent when the satellite was above 600 miles.

Back in Iowa with his family, Ludwig was anxious to check in with Van Allen and the others to start analyzing data and making plans for future flights. Van Allen, of course, became a media star, and Ludwig too got warm attention, from the local newspapers and from his father, who hosted a daily radio program in Iowa City.

The second Explorer launch on March 5 carried a tiny wire tape recorder built by Ludwig, but the launch was a failure because the fourth stage failed to fire. Only after the successful launch of Explorer 3 on March 26 and its insertion into a highly elliptical orbit, and after several weeks of data collection, did Van Allen’s team figure out why the Geiger counter was silent only at certain altitudes above 600 miles: counter saturation. In fact, there were high-energy belts of particle radiation enveloping the Earth, what we today call the Van Allen radiation belts. At the time, one reporter called the belts a “hot band of peril” and wrote that, indeed, “Death [was] lurking in a belt of unexpectedly heavy radiation about 70 miles above the earth.” Ironically, we now know that the belts deflect damaging high-energy particulate radiation from the Sun, and indeed are one of the reasons why sustained life is possible on Earth.

Ludwig graduated from Iowa State University in 1960 after working on Explorers 1-7. He then moved to NASA's Goddard Space Flight Center, soon becoming project scientist for NASA's Orbiting Geophysical Observatory. In 1972 he joined the new National Oceanographic and Atmospheric Administration (NOAA) to construct earth observing systems which included the Television Infrared Observation Satellite (TIROS) polar orbiting satellite system. He eventually returned to NASA and retired in 1984.  

All this time, Ludwig was a note taker and collector. He kept diaries and equipment journals, and many, many tools and instrument parts. In the early 2000s, while preparing to write his memoirs and take stock of his life, he looked for all the surviving cosmic-ray counters his records identified had existed in Van Allen's Iowa laboratory during the early Explorer era. He then set out to find the ones that were missing and to verify that the ones he had collected and carried with him for some 40 years were properly inventoried. He wondered if one of his cosmic ray detectors had come from the flight backup we display at the Museum. So he wrote us asking what was in our Explorer. Was it indeed fully instrumented?

We all thought this was not only an excellent opportunity to inspect the satellite, but also to make sure it was still in good condition. So, collections staff rode a scissor lift into the Milestones of Flight gallery to retrieve our Explorer 1. The satellite was carried to our Paul E. Garber Restoration Facility in Suitland, Maryland, where we opened it up to find, lo and behold, it was empty!

Not completely, though. The framework that held the detector was in place, and in fact it was marked "Payload II," which, to everyone's joy, George Ludwig had at his home in Winchester, Virginia.

Within the year, George donated the detector to the Museum, along with a wonderfully broad array of cosmic ray detector elements that document the history of his project. But was this indeed the very detector in the flight spare? It was definitely the Vanguard payload Ludwig had taken to JPL in 1958, but just as Al Hibbs could only give Medaris a probability that Explorer was indeed in orbit, George could only say he was not absolutely positive that his cosmic-ray package had been inside our Explorer satellite, because the two were identical. Regardless, the discovery helped add to our knowledge of the Explorer 1, and the harrowing events that brought it to orbit.

Additional Resources

Albert Hibbs "On the Edge of Space" Caltech Engineering & Science, Volume LXVI Number 2, 2003.
Walter Trohan, “Radiation Belt Dims Hope of Space Travel,” Chicago Daily Tribune, May 2 1958, 4.