|Mariner 1 launches atop an Atlas-Agena B rocket, a missile-based workhorse of the early Space Age. Image credit: NASA|
The Van Allen Belts are a feature of Earth's magnetosphere. Though fascinating in its own right, the magnetosphere became a source of frustration for scientists eager to study the Sun. This is because Earth's magnetic envelope blocks solar particles, preventing detailed study of flares and other solar phenomena.
|Physicist James Van Allen (center) holds aloft the backup Explorer 1 satellite and upper stage with Jet Propulsion Laboratory director William Pickering (left) and Wernher von Braun. Image credit: NASA|
Among them were Leo Steg, a General Electric scientist whose specialties were missile reentry vehicles and orbital mechanics, and Eugene Shoemaker, a U.S. Geological Survey geologist noted for his study of asteroid impacts, impact and explosion craters, and the cratered lunar surface. Their collaboration on a brief report on the uses of a libration (L) point satellite illustrates the interdisciplinary intent of the Iowa City study. It was also among the earliest proposals to treat the L points as destinations that could be explored and put to good use.
The Earth-moon system contains five L points. They are features as real as the moon and the Earth. In theory, an object parked at one of these "equilibrium" points will remain there indefinitely. In practice, the Sun's gravity perturbs objects parked at the Earth-moon L points, making station-keeping necessary. The propulsive energy (and thus propellants) needed to keep station is, however, quite modest.
Steg and Shoemaker examined the possibility of placing a satellite in orbit about the L4 or L5 point of the Earth-moon system. L4 is located 60° ahead of the moon along its orbit about the Earth; L5 is 60° behind the moon along its Earth-centered orbit.
Beyond Earth's magnetosphere and nearly always in view of the Sun, either L4 or L5 would, they wrote, "be an excellent location for a satellite whose objective is to perform solar-flare observations." Even if the magnetosphere did not interfere with its observations, a solar-observation satellite in low-Earth orbit would spend up to half its time in Earth's shadow, in the night portion of its orbit, so could not monitor the Sun continuously. The L4 or L5 satellite would be eclipsed by the Earth about as often as the moon is - that is, for a few hours each year.
|Schematic illustration of Earth-moon system with libration points indicated. Image credit: NASA|
Had it flown, Steg and Shoemaker's L point mission would have begun with an Atlas-Agena B rocket launch (image at top of post) from Cape Canaveral on 24 October 1963. After arrival in low-Earth parking orbit, the rocket's Agena upper stage would have restarted to boost a nearly 900-pound satellite toward the Earth-moon L4 point. The satellite would travel the 246,781-mile path to L4 in about 78 hours.
Steg and Shoemaker envisioned that their satellite would include a rocket engine and propellants with a total mass of 360 pounds for course corrections, injection into an elliptical orbit around the L4 point, and station-keeping. The satellite's 70-pound science payload would include a 30-pound micrometeorite collector/analyzer for study of Kordylewski cloud dust grains, thus permitting examination of possible lunar surface material without a moon landing. The remaining 40 pounds of instrumentation would be dedicated to solar-flare observations.
Fifty pounds of radio equipment would transmit the L4 satellite's findings to Earth. Steg and Shoemaker noted that their proposed satellite's unique position might enable it to serve as a useful "communication base" for future lunar missions. It might, for example, relay radio signals between Earth and part of the Farside, the lunar hemisphere that is turned always away from the Earth.
A Review of Space Research: The Report of the Summer Study conducted under the auspices of the Space Science Board of the National Academy of Sciences at the State University of Iowa, Iowa City, Iowa, 17 June-10 August 1962, Publication 1079, National Academy of Sciences – National Research Council, Washington, DC, 1962
"Dust-Cloud Moons of the Earth," J. Wesley Simpson, Physics Today, February 1967, p. 39
Earth-Approaching Asteroids as Targets for Exploration (1978)