One of the spectacular effects that can sometimes be witnessed during a shuttle mission is that of a water dump. Throughout the flight electrical power on board the orbiter is provided by fuel cells. These combine hydrogen and oxygen in a reaction that yields electricity; one useful by-product is water (in fact the reaction is not unlike the electrolysis of water but in reverse). Of course, the water can then be consumed by the astronauts in the course of their daily activities. This spent water and any excess from the original reaction is disposed of by simply venting the liquid to the vacuum of space. In doing so the water rapidly cools condensing into a cloud of ice crystals. Under suitable lighting angles and conditions this has been seen as an almost cometary tail extending from the orbiter.
During the STS-73 mission of October 1995 daily water dumps coincided with passes over the southern US states and a number of observations were made including this one by Cal Deal at 0626 EDT, 26 October:
"I watched the Shuttle fly over Fort Lauderdale this morning. I noticed what I can only describe as a "headlight" effect a dim, gray glow that extended in front of the shuttle. I would say that it was not quite as long as the sun is wide, if that helps. It widened as it got farther away from the shuttle. It had sort of a rounded, elongated triangular shape that emanated from the shuttle."
The fact that this was a microgravity mission may have contributed to the spectacle - the persistence of the cloud and its proximity to the orbiter arising from the lack of maneuvers. He also described the following morning pass:
"Another unusual observation of STS-73: This morning at 6:34 EDT it passed over South Florida. Through binoculars I was easily able to discern a dim vaporous stream, or 'tail,' that seemed to arc forward of its direction of travel, then sweep backward, as though caught by a breeze. This was very different from the triangular cloud I observed with my naked eye yesterday. Today's vapor trail seemed much longer than what I saw yesterday, undoubtedly because of the binoculars. The length and shape of the trail were quite surprising; I've never seen anything like that before."
Gordon Garradd took the following photograph during the STS-85 mission in August 1997. Gordon is located in Loomberah, Australia at 151.0E/ 31.3S at 845 M (ASL).
Gordon writes [sic]; " I observed the 'beam' on two passes out of five that I saw from the STS-85 mission. These two photos were taken on Aug 15, 1997, at 08:44 UTC. The plume was about 10 degrees ahead of the shuttle. Discovery is to the lower right of the frame in each of the attached pictures. Another observation on the morning of Aug 10 was very spectacular in the dark morning sky with the plume about 30 degrees long and 1-2 degrees wide."
Craig Cholar, a subscriber of SeeSat-L, posted a notice dated Aug 15, 1997, informing the List of the next scheduled water dump for STS-85. He provided estimated times for the water dumps that periodically occur during a mission.
Jeff Poplin and others on SeeSat-L on Dec 25, 1999 posted reports of observation of a water dump during the STS-103 mission.
Paul Maley, who is an experienced satellite observer, has produced an excellent web site on satellite observing.
Paul took a video of STS-103 over the Houston, Texas area on December 25, 1999 on the shuttle's 2nd orbit since releasing Hubble just NE of Australia earlier. Below is a frame taken from that video with the shuttle and the ice crystal coma on the left and Hubble following closely behind (but at a slightly higher altitude). The other objects below are stars.
Search on "waste water dump" at NASA.
Links: to the VSO Home Page, observing guide, shuttle details, and satellite predictions.