|9 July 1962: An artificial aurora lights the sky over the Pacific Ocean following the Starfish Prime space nuclear explosion. Image credit: U.S. Air Force.|
The Starfish Prime nuclear blast produced a flash of light visible over much of the Pacific basin. For seven minutes after the explosion, an artificial red aurora danced in the skies over island groups as widely separated as Hawaii, Tonga, and Samoa. The blast's electromagnetic pulse damaged electrical systems on the Hawaiian island of Oahu, 800 miles away from the explosion.
Starfish Prime, a follow-on to U.S. high-altitude nuclear tests conducted in 1958, was publicized in advance. Many widely scattered aircraft and naval vessels, as well as sounding rockets, were used to observe its effects.
Though it sought answers to scientific questions, it was intended also to test whether nuclear explosions in low-Earth orbit (LEO) could augment and expand the Earth-girdling Van Allen radiation belts to create a barrier that would incapacitate Soviet intercontinental missiles launched against the United States. The test series of which it was part, Operation Dominic, was partly a response to the Soviet Union's August 1961 decision to end a three-year nuclear testing moratorium.
No one knew how long the beefed-up radiation belts might persist. Some feared that the increased radiation might last until 1967-1968, when NASA hoped to carry out the first Apollo expedition to the Moon. The Apollo spacecraft, launched from Cape Canaveral on Florida's east coast, would have to traverse the augmented Van Allen Belts, and no one could say what effect their radiation would have on Apollo crews.
James and Schulte based their analysis of the LEO radiation environment during the first Apollo mission on a model of the post-Starfish Prime Van Allen belts developed by NASA Goddard Space Flight Center scientist Wilmot Hess. His model placed the lower limit of the expanded inner Van Allen belt at an altitude of about 600 miles.
Just two days after Starfish Prime, NASA announced that, after more than a year of sometimes heated discussion, it had selected the Lunar-Orbit Rendezvous (LOR) mission mode for accomplishing Apollo Moon landings. LOR would see lunar mission functions split between two manned spacecraft — a large command ship and a small Moon lander. The command ship would come no closer to the Moon than lunar orbit. The lander would operate independently only during descent to the Moon's surface, on the surface, and during ascent to lunar orbit.
Despite NASA's decision, James and Schulte examined the radiation environment for both LOR and EOR Apollo missions. This reflected lingering anxiety both inside and outside NASA concerning LOR.
Many worried that the LOR mission mode's namesake maneuver, the post-lunar landing rendezvous and docking between the command ship and the Moon lander in lunar orbit, might prove too challenging. They worried in particular that, with Earth's ground-based tracking stations too far away to be of use, the spacecraft in lunar orbit would have difficulty finding each other. If, during Apollo development, this were found to be so, then an EOR backup plan would become necessary.
In James and Schulte's EOR scenario, NASA would launch a single large piloted lunar spacecraft with mostly empty propellant tanks into LEO. There it would rendezvous and dock with a separately launched automated tanker containing its LEO departure propellants.
The Bellcomm planners determined that, based on the Hess model, the EOR Apollo astronauts would receive a radiation dose of four rad in LEO before setting out for the Moon. They would experience most of their LEO radiation exposure during orbits five and six, when they would begin to pass through a magnetic field anomaly that spans the Atlantic from Brazil to South Africa.
|NASA Goddard Space Flight Center illustration of the South Atlantic Anomaly.|
LOR Apollo would, by contrast, not linger in LEO. James and Schulte assumed that the LOR Apollo spacecraft/LEO-departure booster combination would circle Earth once in 252-mile-high LEO while controllers precisely tracked it to determine its orbit. It would then complete half an orbit more so that its orbital plane would align for departure to near-equatorial landing sites on the Moon.
The LOR Apollo crew would stay far from the South Atlantic Anomaly during their one and a half orbits of the Earth. Because of this, their radiation dose in LEO from the augmented Van Allen belts would amount to only 0.02 rad.
In both the LOR and EOR modes, the astronauts would receive a dose of 16 rad while crossing the Starfish Prime-augmented Van Allen belts en route to the Moon. Thus, the minimum dose the EOR astronauts would receive would be 20 rad, while LOR astronauts would receive 16.02 rad.
The Bellcomm planners noted that future nuclear explosions in LEO could dramatically boost the dose Moon-bound astronauts would receive during Van Allen belt passage. They added that a nuclear bomb packed with Uranium-238 could increase radiation in the belts "a hundredfold."
James and Schulte noted that the Van Allen belts are inclined relative to Earth's equator and do not cover its poles. If the belts became impassable, they wrote, NASA would have little choice but to launch Apollo astronauts through the Van Allen belt gaps over the poles.
Unfortunately, Cape Canaveral was poorly placed for polar launches because rockets launched due south or north would pass over populated areas. These included Cuba and Brazil to the south and the major cities of the U.S. eastern seaboard to the north.
James and Schulte wrote that a country with polar launch capability might explode nuclear weapons in space to bar a nation without such capability from launching men to the Moon. They did not mention the Soviet Union specifically, nor did they point out that the Soviet Union, with its extensive Arctic Ocean coastline, was well placed to carry out polar launches.
The Van Allen radiation belts returned to normal a few years after Starfish Prime. Nuclear explosions in space never menaced Apollo astronauts, in large part because on 5 August 1963, representatives of the U.S., Great Britain, and the Soviet Union met in Moscow to sign the Treaty Banning Nuclear Weapon Tests in the Atmosphere, Outer Space, and Under Water.
Conclusion of the treaty, which needed more than eight years to negotiate, very likely received some impetus from Starfish Prime. The treaty, which permitted only underground nuclear tests on Earth and sought to curtail spread of nuclear test fallout, entered into force on 10 October 1963, and has subsequently been signed by nearly all United Nations member countries.
Memorandum, D. James and H. Schulte, Bellcomm, to W. Lee, NASA Headquarters, "Radiation environment of EOR and LOR," Bellcomm, October 5, 1962.
"The Artificial Radiation Belt Made on July 9, 1962," W. Hess, Journal of Geophysical Research, Volume 68, Number 3, 1 February 1963, pp. 667-683.
Wikipedia - "Starfish Prime" (https://en.wikipedia.org/wiki/Starfish_Prime - accessed 9 January 2016).
Wikipedia - "Telstar" (https://en.wikipedia.org/wiki/Telstar - accessed 12 January 2016).
U.S. Department of State - "Treaty Banning Nuclear Weapon Tests in the Atmosphere, Outer Space, and Under Water" (http://www.state.gov/t/isn/4797.htm - accessed 12 January 2016)
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