Observers from South Africa to Europe witnessed a unique space event last Sunday evening. What appeared to be 1 or 2 “comet”-like objects surrounded by expanding “smoke” rings was in fact a fuel dump from a recently launched weather satellite.
Fuel and water dumps from spacecraft and rockets happen quite often. These types of events have been seen throughout the world. Sometimes the dumps appear as slowly expanding clouds. On one occasion the dump took on an almost “angelic” appearance.
At 16:12 GMT on October 18 an Atlas-5(401) rocket was launched from Vandenberg Air Force base in California. The rocket carried the American DMSP F18 military weather satellite into a near-polar (sun synchronous) orbit. Though this satellite is operated by the US military, there is nothing secret about it and it is very similar to civilian weather satellites. A Centaur upper stage was used to place the satellite in its operational orbit. It is this upper stage that produced the light show seen by African and European observers.
After their mission is over, most upper stages dump any remaining fuel overboard, a procedure known as a fuel dump. This is done to prevent the remaining fuel from eventually causing an explosion which would litter space with hazardous (for other satellites and astronauts) debris. The DMSP F18 launch was a little different. The Atlas-5(401) rocket and Centaur upper stage combination was more than capable of lifting the DMSP F18 to orbit. As a result, more fuel than usual remained in the upper stage. The excess fuel allowed the operators of the Centaur to conduct a number of tests, including what is known as a “pulsed chilldown mode”. These tests resulted in the periodic release of fuel resulting in the observed series of quickly expanding concentric rings. The tests started as the upper stage was traveling over southern Africa. By the time it was over Europe the tests were over though the ring(s) were still faintly visible. European observers did witness the Centaur conducting a burn which eventually placed the upper stage on a heliocentric orbit around the Sun.
The South African Astronomical Observatory published a description of the event.
Absolutely amazing images of the event over South Africa can be found here.
A collection of images, mostly from Europe, can be found at Spaceweather.com