Talk:PFS-2

Lunar subsatellite PFS-2

Capturing descriptive text, and citation, for PFS-2, from another article (Apollo 16) where this REDIR currently points:

Lunar subsatellite PFS-2

[[Image:Apollo 15 Subsatellite.jpg|thumb|right|Artist's conception of subsatellite deployment]]

The Apollo 16 subsatellite (PFS-2) was a small satellite released into lunar orbit from the Service Module. Its principle objective was to measure charged particles and magnetic fields all around the Moon as the Moon orbited Earth, similar to its sister spacecraft, PFS-1, released eight months earlier by Apollo 15. "The low orbits of both subsatellites were to be similar ellipses, ranging from 55 to 76 miles (89 to 122 km) above the lunar surface."^[1]

"Instead, something bizarre happened. The orbit of PFS-2 rapidly changed shape and distance from the Moon. In 2-1/2 weeks the satellite was swooping to within a hair-raising 6 miles (10 km) of the lunar surface at closest approach. As the orbit kept changing, PFS-2 backed off again, until it seemed to be a safe 30 miles away. But not for long: inexorably, the subsatellite's orbit carried it back toward the Moon. And on May 29, 1972—only 35 days and 425 orbits after its release"—PFS-2 crashed into the Lunar surface.^[1]

In later years, through a study of many Lunar orbiting satellites, scientists came to discover that most Low Lunar orbits are unstable. Unfortunately, PFS-2 had been placed, unknown to mission planners at the time, squarely into one of the most unstable of orbits, at 11 degrees orbital inclination, far from the four frozen Lunar orbits discovered only later at 27º, 50º, 76º, and 86º inclination.^[1]

^ ^a ^b ^c "Bizarre Lunar Orbits". NASA Science: Science News. NASA. 2006-11-06. Retrieved 2012-12-09. Lunar mascons make most low lunar orbits unstable ... As a satellite passes 50 or 60 miles overhead, the mascons pull it forward, back, left, right, or down, the exact direction and magnitude of the tugging depends on the satellite's trajectory. Absent any periodic boosts from onboard rockets to correct the orbit, most satellites released into low lunar orbits (under about 60 miles or 100 km) will eventually crash into the Moon. ... [There are] a number of 'frozen orbits' where a spacecraft can stay in a low lunar orbit indefinitely. They occur at four inclinations: 27º, 50º, 76º, and 86º"—the last one being nearly over the lunar poles. The orbit of the relatively long-lived Apollo 15 subsatellite PFS-1 had an inclination of 28º, which turned out to be close to the inclination of one of the frozen orbits—but poor PFS-2 was cursed with an inclination of only 11º.

Cheers. N2e (talk) 22:36, 9 December 2012 (UTC)[reply]

[nasa20061106-1] "Bizarre Lunar Orbits". NASA Science: Science News. NASA. 2006-11-06. Retrieved 2012-12-09. Lunar mascons make most low lunar orbits unstable ... As a satellite passes 50 or 60 miles overhead, the mascons pull it forward, back, left, right, or down, the exact direction and magnitude of the tugging depends on the satellite's trajectory. Absent any periodic boosts from onboard rockets to correct the orbit, most satellites released into low lunar orbits (under about 60 miles or 100 km) will eventually crash into the Moon. ... [There are] a number of 'frozen orbits' where a spacecraft can stay in a low lunar orbit indefinitely. They occur at four inclinations: 27º, 50º, 76º, and 86º"—the last one being nearly over the lunar poles. The orbit of the relatively long-lived Apollo 15 subsatellite PFS-1 had an inclination of 28º, which turned out to be close to the inclination of one of the frozen orbits—but poor PFS-2 was cursed with an inclination of only 11º.

[1]