10 January 2016

Starfish and Apollo (1962)

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
Since I first posted a less detailed version of this post on my old Romance to Reality website (1996-2006), the Starfish Prime nuclear test has become a popular topic on the Internet. On 9 July 1962, the U.S. Air Force launched a 2200-pound W-49 nuclear warhead into space on a Thor rocket from Johnston Atoll in the Pacific Ocean. The warhead exploded with a yield of 1.44 megatons of TNT at an altitude of 248 miles above the Pacific.

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.

Schematic cross-section of the inner and outer Van Allen Belts based on James Van Allen's 1958 model. In February 2013, NASA announced that data from the two Van Allen Probes indicated that a third radiation belt can sometimes form beyond the outer belt. Image credit: Wikipedia
High-energy particles Starfish Prime pumped into the belts probably contributed to the failure of Telstar 1 just four months after its 10 July 1962 launch. Telstar 1 was the first active communications satellite, meaning that it received and re-transmitted incoming radio signals. The satellite was reacquired in January 1963, but failed permanently on 21 February. Six other satellite failures have been traced to Starfish Prime.

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.

A Bell Labs technician puts the finishing touches on the experimental multi-national Telstar 1, the world's first privately sponsored satellite. A Thor-Delta rocket boosted the 170-pound satellite into a 592-by-3687-mile Earth orbit the day after the Starfish Prime nuclear explosion. Image credit: Bell Laboratories 
D. James and H. Schulte, researchers with NASA's newly created advance planning contractor, Bellcomm, analyzed the effects of Starfish Prime on NASA moon plans in a memorandum they sent to NASA Headquarters on 5 October 1962. It was among the first of many memos and reports Bellcomm would supply to NASA over the decade that followed.

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.

LOR mission plan. Please click to enlarge. Step 10 shows the lunar lander separating from the command ship; 11 and 12 show the lander descending and on the surface; 13 and 14 show the lander ascent stage climbing to lunar orbit and docking with the command ship; and 15 shows the ascent stage being cast off and the command ship firing its engine to leave lunar orbit and fall back to Earth. Image credit: NASA
LOR had won out over Earth-Orbit Rendezvous (EOR) because it promised to reduce the mass of the lunar spacecraft, enabling launch on a single Saturn C-5 rocket (as the Saturn V was known in 1962), and because it would make the moon lander small compared to the EOR lander and thus safer to land. EOR needed multiple Earth launches and landed the entire piloted lunar spacecraft on the moon.

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.

James and Schulte assumed that, before an EOR Apollo spacecraft could set out for the moon, it would need to orbit the Earth at least six times in a 252-mile-high parking orbit inclined 28.5° to Earth's equator (28.5° is the latitude of launch facilities at Cape Canaveral). During its first orbit after launch, controllers on the ground would track the piloted EOR spacecraft to determine its precise path.

Rendezvous and docking with the tanker would need up to 2.5 orbits, then propellant transfer and final orbit determination/spacecraft checkout would require two more. After a final half-orbit, the EOR Apollo spacecraft's orbital motion would have caused its orbital plane to become aligned for launch to near-equatorial landing sites on the moon. It would then ignite its engines to depart LEO.

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.
Within the South Atlantic Anomaly, as it is known today, the Van Allen belts dip to within 100 miles of Earth's surface. If the EOR Apollo astronauts could not depart LEO on schedule, then they would pass through the widest part of the South Atlantic Anomaly during orbits seven, eight, nine, and 10, and would receive up to six rads per orbit.

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 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 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 the 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 Earth's 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 curtailed spread of nuclear test fallout, entered into force on 10 October 1963, and has subsequently been signed by nearly all United Nations member countries.

Sources

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)

More Information

What If Apollo Astronauts Became Marooned in Lunar Orbit? (1968)

What If Apollo Astronauts Could Not Ride the Saturn V Rocket? (1965)

Space Race: The Notorious 1962 Plan to Launch an Astronaut on a One-Way Trip to the Moon

Solar Flares and Moondust: The 1962 Proposal for an Interdisciplinary Science Satellite at Earth-Moon L4

He Who Controls the Moon Controls the Earth (1958)

No comments:

Post a Comment

I like hearing from my readers. No rules except the obvious ones - please keep it civil and on topic.