By: James Oberg, Rt 2 Box 35O, Dickinson, Texas 77539
June 28, 1992

Subject: Actual explanation for the notorious STS-48 "UFOs" on videotape

After the HardCopy interview with Don Ecker (June 5), and my appearance with him on Larry King Live June 26, I've gotten an appreciation of where this UFO connection has come from. When I saw the original incoherent letters from [xxxxxxx], I dismissed it as complete looney-tunes, but subsequently I've found out what fundamental misunderstanding and ignorance has led to the fuss.

Lights on the shuttle TV cameras can be many things, and on these scenes in question they are stars, cities, lens spots, and nearby shuttle-generated debris (they are rarely if ever other satellites). Especially with the low-light cameras used for the nighttime mesoscale lightning surveys, the horizon is deceptive because the glowing line is the airglow and the actual edge of the earth is somewhat below it. With poor contrast; this means that stars can cross the glowing "horizon" and still be visible a bit further before actually setting.

There are more than 50 sources of ice on the shuttle, plus a steady source of debris such as insulation flakes from inside the payload bay. This includes 38 primary RCS jets and 6 vernier jets (which burn the hypergolic [self-igniting] propellants of nitrogen tetroxide and hydrazine), an air dump line, a waste water dump line, a supply water dump line, two fuel cell purge lines (the hydrogen one is always leaking water), two flash evaporators, a water spray boiler, and so forth. No surprise, then, that floating debris near the shuttle is a common sight. The particles usually (not always) spin, and depending on the axis of spin they may or may not flash, and depending on the speed of spin their flicker may or may not be picked up by the camera CCD scanner.

The RCS jets usually fire in 80-millisecond pulses to keep the shuttle pointed in a desired direction, under autopilot control (usually once every few minutes). These jets may flash when they ignite if the mixture ratio is not quite right. Propellant also tends to seep out the feed lines into the nozzle, where it accumulates, freezes through evaporative cooling, and flakes off during the next firing. The ejected burn byproducts travel at about 1000 ft/sec. One pulse usually emits about a quarter pound of propellant in a fan-shaped plume.

When small, drifting debris particles are hit by this RCS plume they are violently accelerated away from the jet. This is what is seen in the infamous "Case 2" sequence, where a flash (the jet firing) is immediately followed by all nearby particles being pushed away from the jet, followed shortly later by a fast moving object (evidently RCS fuel ice) departing from the direction of the jet (the streak is caused by the slow camera speed). If one plotted all the departure lines of the pushed debris and the expelled ice, they would converge at the jet's location.

These ice particles, in particular, form slowly inside the jets and elsewhere, as the fluid (water or propellant) seeps out and spreads over the surface, They take on the shape of the structure they form on. They can thus have just about any shape, usually flat. They have been seen and photographed for thirty years, about as long as UFOlogists have mistaken them for flying saucers.

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