The artificial radiation belt and spacecraft

After a series of holds for weather and nagging problems with the Thor launch vehicle, Starfish Prime finally launched from Johnston Island late on July 8. Free from the constricting atmosphere, the blast took the shape of an ellipsoidal bubble, its major axis oriented along the Earth’s magnetic field lines. The bubble burst after just 16 seconds, replaced by the aurora as nuclear particles were injected into orbit around the Earth. This created an artificial radiation belt circling the globe near the detonation altitude of 250 miles. Due to Johnston Island’s low latitude, it also increased the radiation concentrated in the lower Van Allen belt that sits between 600 and 3,700 miles.
It didn’t take a leap of imagination for scientists to suspect that this increase in radiation would affect the nation’s space program. Spacecraft instrumentation would surely be compromised, as would solar cells, but exactly how badly was the question. Scientists didn’t have to wait long to find out. Less than 48 hours after the Starfish Prime event, NASA launched the Telstar satellite, and the nuclear explosion’s effects were immediately clear.

Telstar, a 171-pound nearly spherical satellite built by AT&T and operated by NASA, was history’s first communications satellite. Just hours after it reached orbit, Telstar broadcast a live picture of an American flag outside a receiving station in Maine to viewers in France. For many around the world, this satellite was more exciting than Sputnik. Telstar wasn’t just a shiny, beeping orb. It was an orb that could unite the eyes and ears of the world.
Telstar’s days were numbered as soon as it launched. It settled into an elliptical orbit—3,505 miles at its apogee and 903 miles at its perigee—that allowed it to regularly pass through both natural and human-made radiation belts. It was also covered in solar cells that couldn’t withstand the increased radiation. Telstar began experiencing transmission difficulties in November before failing entirely in February of 1963. And it wasn’t the only satellite casualty associated with the Starfish event. American satellites Ariel 1, Traac, Transit, Injun, and the Soviet Cosmos V all succumbed to the increased radiation.
But losing a robotic satellite wasn’t the same as losing a manned spacecraft. The question wasn’t one of how manned missions would deal with the Starfish radiation belt—it quickly became whether or not manned missions could continue at all.

Starfish Prime and manned spaceflight

NASA’s manned spaceflight program was still in its infancy in June of 1962, and it hadn’t yet crossed paths with Operation Dominic. The nuclear testing program wasn't underway when John Glenn became the first American in orbit on February 20, 1962. When Scott Carpenter followed in Glenn’s orbital footprints on May 24, the Fishbowl events had started, but none had successfully detonated. Starfish Prime had been a success, though, and the radiation that knocked out satellites was sure to have some effect on manned missions. The first to find out would be Wally Schirra. His Sigma 7 Mercury flight was scheduled for the fall.
Luckily for Schirra and for Gordon Cooper, who was the only other Mercury astronaut with a scheduled flight, NASA quickly determined the Starfish radiation belt wasn’t a threat to Mercury missions. These early manned missions orbited at 160 miles, well below the Starfish Prime radiation and Starfish-enhanced Van Allen belt.
Mercury might have been safe, but the Gemini and Apollo missions were a different matter. Gemini flights would see astronauts spending up to two weeks in orbit at much higher altitudes, and the Apollo crews would have no choice but to fly through both the Starfish radiation belt and the augmented lower Van Allen belt on their way to the Moon. The new concern became whether this increased radiation environment would last long enough to threaten Apollo.

The Bellcomm study

In March of 1962, NASA administrator Jim Webb asked Frederick R. Kappel, the president of American Telephone and Telegraph, if the agency could borrow some of AT&T’s talent. Kappel obliged and established Bellcomm Inc., a division of AT&T tasked with supporting the space agency by evaluating theoretical missions and running studies. It fell to Bellcomm to determine what effects Starfish Prime might have on Apollo missions.

The minimum radiation exposure for an Apollo crew would be 16.02 rads for a perfect LOR and 20 rads for a perfect EOR. At 15 rads, blood count starts to change. At 150 rads, death becomes inevitable without treatment.

One of the key decisions of the Apollo program was called the mission mode decision—the determination of how NASA would actually go to the Moon. The agency publicly announced its choice two days after the Starfish Prime event. It picked Lunar Orbit Rendezvous (LOR), a mission architecture that would have one Saturn-class rocket send a modular spacecraft to the Moon, part of which would descend to the surface while the other stayed in orbit. It was a risky method since reconnecting those two halves of a spacecraft in lunar orbit was a big unknown. In case it turned out that this mission would be impossible, NASA settled on Earth orbit rendezvous—where one lunar landing spacecraft was assembled in Earth orbit after multiple launches—as a backup method. For Bellcomm researchers D. B. James and H. J. Schulte, this meant studying the radiation effects of both mission modes on a theoretical crew.
From a radiation standpoint, Earth Orbit Rendezvous (EOR) was a bad option since assembling a spacecraft in orbit was a lengthy affair. It would take at least six 252-mile-high orbits inclined 28.5° to Earth’s equator, to be exact, or about nine hours. This would give mission control enough time to plot the spacecraft’s orbit and give the crew time to complete the rendezvous and docking procedures, transfer propellant from an orbiting tank into the Moon-bound vehicle, and check that all systems were working.
The advantage of this method was that it gave the mission plenty of opportunities for holds. If anything went wrong—if a docking failed or the spacecraft’s orbit was off—the crew could just stay in Earth orbit longer to solve the problem. The disadvantage was that the longer the crew stayed in orbit, the longer it sat in a high radiation environment.
James and Schulte determined that astronauts on an EOR-model Apollo mission would receive four rads of radiation during their entire Earth orbital phase. Most of that would come during the last two orbits, which would take them through the so-called South Atlantic Anomaly, a point where the Van Allen belts dip to within 100 miles of Earth’s surface. But if they had to stay in orbit longer, they risked passing through the SAA multiple times, which would expose them to an additional six rads per orbit.
LOR offered a safer environment as far as radiation exposure was concerned. With this mission mode, James and Schulte assumed an Apollo crew would only circle the Earth once. One orbit is all ground controllers would need to plot the crew’s trajectory and ensure they were lined up for the burn that would take them to the Moon. On this mission, the crew would only be exposed to 0.02 rad.
But these figures—four rads for EOR and 0.02 rads for LOR—didn’t take into account the crew passing through the Starfish Prime-augmented Van Allen belt. This inevitable maneuver would expose the crew to 16 rads. All told, the minimum radiation exposure for an Apollo crew would be 16.02 rads for a perfect LOR and 20 rads for a perfect EOR. At 15 rads, blood count starts to change. At 150 rads, death becomes inevitable without treatment. The Bellcomm researchers added that it was likely an astronaut would fly multiple missions, an Earth orbital Gemini flight before an Apollo flight to the Moon. Multiple missions in the Earth’s artificially enhanced radiation environment could be fatal.

Radiation from bad to worse

James’ and Schulte’s predictions got worse. Their estimated radiation levels assumed there would be no additional atmospheric test that would increase the radiation environment surrounding the Earth. But this wasn’t the case. There were still scheduled Fishbowl events within Operation Dominic, at least one of which involved a large weapon detonating at high altitude.
The Bellcomm researchers warned of the effects continued testing would have on manned spaceflight. A second nuclear explosion in low Earth orbit akin to Starfish Prime could dramatically increase the already augmented Van Allen belt. And if the government decided to test a bomb packed with Uranium-238, it risked increasing the Earth’s radiation a hundredfold.
But there was a loophole. Literally. James and Schulte noted that the Van Allen belts don’t envelop the Earth like a bubble. They are belts, and they’re inclined relative to Earth’s equator. The poles are uncovered. If the radiation levels didn’t go down or further testing made the belts impossible for humans safely to pass through, NASA could launch crews on trajectories that would take them through the polar radiation gaps.
It would be a very fuel-inefficient way to go to the Moon and a dangerous option for NASA. Launching north or south from Cape Canaveral would mean launching over highly populated areas. If a launch vehicle failed, which wasn’t unheard of at the time, falling debris could kill thousands on the ground.
And there were ways for another country to sabotage an American Moonshot that took advantage of the polar radiation gaps. A country with favorable polar launch sites could deliberately detonate nuclear weapons in this space to prevent Apollo from flying to the Moon. James and Schulte didn’t vilify the Soviet Union directly, but they did point out that the nation has extensive Arctic Ocean coastline and an excellent polar launch capability.

Apollo and a lasting ban

NASA acknowledged what James and Schulte laid out in their report: Starfish Prime posed a risk to Apollo. But for the space agency, it was a case of weighing the risks of radiation exposure against the benefits of completing the Apollo mission. The need to reach the Moon weighed heaviest. As a precautionary measure, plans for the missions reduced the crews’ exposure to radiation by having missions orbit the Earth below the Van Allen belts, then pass through them quickly on the way to the Moon. Protection, both in the spacecraft and in the spacesuits, was designed to shield the crew from the natural radiation of space.
It transpired that NASA’s decision not to take extra precautions against the Starfish Prime radiation was the right one. By 1969, the radiation in the environment around the Earth dropped to just one-twelfth of the 1962 post-Starfish Prime levels. The dire predictions the Bellcomm report made for Apollo missions were never realized. The maximum operation dose-limit for Apollo astronauts was 400 rads on skin, which is equivalent to an x-ray. The average Apollo astronaut received less than one rad.
There were other Fishbowl events—Bluegill, Checkmate, and Kingfish—and while NASA recognized the dangers these could have posed, they proved to be irrelevant to spaceflight. None involved weapons as large, or explosions as high, as Starfish Prime. The Soviet Union also launched nuclear atmospheric tests, but none matched Starfish Prime either. In August of 1963, the United States and the Soviet Union finally agreed to a test ban. The Treaty Banning Nuclear Weapon Tests in the Atmosphere, Outer Space, and Under Water took effect on October 10.