OBSERVING U.S. MANNED ORBITING SPACECRAFT
by Paul D. Maley
The Space Shuttle has been one of the most outstanding items in the night sky during the past two decades. As an example, you can see the streak of STS41-G as it passes over the Castle of Chillon in Switzerland. This is a photo I shot on October 11, 1984 at 0439 UT.
In the image below I flew to Miami FL on July 4, 1982 and photographed Salyut 6 and STS-4 crossing each other’s orbit some 6.5 hours before STS-4 landing. The Shuttle was in ‘tail-to-sun’ attitude which meant its reflective surfaces relative to my position on the ground were in a really unfavorable attitude. The visual magnitude of STS-4 was +3 compared to +0 for the Salyut 6.
Even while working at the NASA Johnson Space Center we see Shuttle passes often. This photo shows a timed exposure of STS-32 as it passed behind the Mission Control Center Building 30. The orbiter COLUMBIA flew over at 1210 UT on Jan. 13, 1990 when this shot was taken.
We now turn our attention to what happens when an object reenters the earth’s atmosphere. My first experience with observing a reentering spacecraft was on October 24, 1967. From the campus of Pan American University, I watched as Cosmos 166 fragmented over the Gulf of Mexico. The fascinating display resulted in an observation of 2 pieces that appeared to skip back out into the atmosphere where they reentered later than the primary spacecraft mass. This example is where an earth satellite is destroyed upon reentry. It is not the same with the Space Shuttle. Though the Shuttle appears to be burning as it reenters the atmosphere, its protective tiles prevent its destruction.
Seeing a reentry is very unlikely. However, with the advent of email and the internet, it is more likely that sighting of a reentry may be reported soon after it occurs. The state of predicting decay from the atmosphere is probably no better than it was 20 years ago. The accuracy of decay predictions is usually within plus or minus one orbit within one day of actual reentry. The reentry is one of the most spectacular nighttime phenomena that one can witness. During daylight any reentry is likey to be too dim to view due to the bright background of the sky.
We have observed numerous reentries of the Space Shuttle since 1984. Prior to the building of the International Space Station, most reentry tracks took the Shuttle across Texas in order to reach the principal landing site in Florida. Since the orbital inclination of these flights was 28.5 degrees (the latitude of KSC), our location at latitude 29.5 allowed us to typically be very favorably positioned to witness reentry. Some passes took place during daylight but many occurred in the predawn hours. On one occasion I saw a reentry of the Shuttle while at Houston’s Hobby airport waiting for a bus to take me from the parking lot to the terminal while the sun was 3 degrees above the horizon and the reentering object was rising in the western sky moving west to east. This was the reentry of STS-70 on July 22, 1995.
The first image is that of the reentry of STS-11 taken in the midst of fog with the lights of Galveston, Texas in foreground on February 11, 1984. Prior to STS-11, I had found no written accounts to describe the reentry process of an orbiter. The most fortunate aspect of the landing plan was for a post-sunrise touchdown at KSC, which mandated a predawn flyover of northern Mexico and then, south central Texas. I prepared to set up a site near Galveston Island. I also dispatched a second observer team (R. and C. Peterson) to watch from Karnes City. On the morning of Februrary 11, a large cloud covered area swept over southern Texas causing rain and fog near the coastal plain. Where I was, the sky was overcast for hours prior to the pass. Just two minutes before the Shuttle was predicted to appear above the local horizon, the rain subsided and gaps appeared in a long narrow corridor of sky almost exactly along the expected reentry track.
An orange rocket-like plume immediately began to form above the southwest horizon and, with a stellar glow at its head, started a low angular climb toward the east. Instead of dissipating right away, the orange changed to yellow and persisted in place as the orbiter crossed the Texas coast like a rapidly moving comet. The head rivaled the planet Jupiter (magnitude -2). As the Shuttle sped through the open corridor, some slouds sporadically blocked portions of the luminous trail. The Shuttle velocity slowed to 9600 n.mi. per hour (16,000 fps) as it passed a maximum of 24.5 degrees above my horizon. I was located 92 n.mi. directly north of the flight path. The luminous trail left in the wake of the reentry was at one point estimated to span about 100 n. mi. before sections of it were seen to dissipate.
At Karnes City, observers reported a billowing effect in the reentry column as if vortices were present. I also noted this in the photographs taken at my site. Also apparent in the photos were series of equally spaced knots in the trail. The knots were spotted naked eye but were more distinct in the images. Persistence of the wake was most remarkable even after 30 or 40 seconds had elapsed.
How did the STS-11 crew perceive the reentry? I talked with two crew members after the landing. Bruce McCandless commented that he noted swirls in the bright column left in the Shuttle wake and also was conscious of brightness variations in the sheath. R. Gibson viewed the wake as a dull pink color at entry interface with a steady glow being perceived at the cabin windows when the orbiter reached 350,000 feet. The color changed to a distinct orange pink at an altitude of 205,000 feet and as the Shuttle descended a further 10,000 feet a white flickering was seen on the center consoles of the cabin. As astronaut Gibson looked back into the tail, he could see a pulsating effect with a 1 to 3 second periodicity. He saw two sheets of flame interacting, moving back and forth before the orbiter reached an 11 ft/sec/sec deceleration level. As the Shuttle passed Mach 15.5, Gibson observed eddies outside the Shuttle within the recessed window spaces. These small scale turbulence effects were not in the overal flow stream but just adjacent to the orbiter skin. The pulsations noticed were also recorded in a 16mm film taken within the cabin as they reflected off the crew’s helmets. A similar experience was reported by STS-7 astronaut Dale Gardner as we recounted the reentry of that mission.
During STS-11 we heard a double sonic boom after the Shuttle passed by at an altitude of 206,000 feet. Up to now sonic booms had been measured from Shuttle reentries only up to Mach 6 (altitude of 130,000 feet). Many sonic booms detected at altitudes higher than this were sensed by microphones, pressure transducers and dynagages. So this discovery that booms could be audibly perceived at such high altitudes was quite interesting.
The more likely cause was isolated to chemiluminescence, a source of radiation caused by the meeting of O atoms and NO molecules. A spacecraft traveling faster than sound leaves NO in its wake. The O attaches to NO and becomes NO2. One out of 5 attachments leads to visible radiation. In the 1960’s a lot of attention was given to the study of high speed missile entries which was the prime reason for studying this type of radiation. Since then little work had been performed since missile trails were discovered to have very large cross sectional area and produce long trains. Meteor entries were given attention but these bodies produce radiation mainly in wavelengths of sodium, though occasionally some NO2 is present.
Work by C.Park at NASA Ames Research Center at the time suggested that O and NO combine in a way that is inversely proportional to atmospheric density. A typical meteor observed at 250,000 ft altitude might cause a persistent train of 3 to 5 seconds with a tail length of 6 to 12 miles. As the height decreased to 195,000 ft, the total persistence would only be a fraction of a second. The lifetime of any visible radiation produced is proportional to the speed at which the oxygen atoms disappear. The best candidate for a large persistence radiative effect is that involving NO and O3 (ozone). Although ozone is a stable molecule, it is also weaker by an order of magnitude than O2. NO2 produced in the laboratory produces a yellow color. NO constitutes 3-5% of the air encountered by the orbiter. The life of the chemical energy converted to radiation in this mode dictates the rate at which NO disappears. As the reentry wake grows with time it moves outward into ozone already present in the air. The wake forms a cylinder that spreads laterally into the flight path. As it grows, it envelopes ozone. NO reacts and disappears as the combinations occur. The entire radiation area will disappear if the amount of NO equals the number of ozone molecules.
Park determined that 6 tons of NO are produced from the time of Shuttle entry interface to landing. Another analysis showed that the “super reentry” in 1908 caused by the Tunguska meteorite generated 19 million tons of NO immediately, and the end result was that the evening sky was brightly lit for several nights in a row over much of eastern Europe. The massive interaction between ozone and NO is believed to have been the source of this luminosity beginning on the evening of the meteorite fall.
This experience with STS-11 marked our interest in tracking down Shuttle reentries. It was also the first time we witnessed the entire reentry process and recorded it on still images (as well as video) using ASA 400 print film. We discovered that the trail seen in the photo was double. (See the picture later in this text). Apparently there is a vortex created from the interaction of each wing of the Shuttle with the atmosphere. A picture below depicts a better indication of the duality of the trail where one is actually shadowed by the other.
The next shot is from the STS-51 reentry on September 22, 1993. This very impressive sight was recorded on Hi-8 video in color. It was flying just north of downtown Houston. Our observation site was located in a rather unsafe area near the Houston center.
The above image is from the STS-69 reentry, which passed over Houston on September 18, 1985. The building in the foreground is Building 30—the Mission Control Center facility at NASA Johnson Space Center.
In early video attempts we discovered that the reentry trail is actually two trails proven in the image below that emulates aircraft contrails.
Though the following image is rather faint, it and most others you see on this site were extracted from low light level video. Sometimes using the SNAPPY image capture tool, the frame grabber will not grab images with a high level of fidelity.
Water or waste dumps may sometimes be observed from the Shuttle. The earliest encounters reported by Shuttle crews were from STS-8 and STS-61A when particles contacted the Shuttle during subsequent orbits after water dumps. As a result, later dumps were planned more carefully to prevent recontact. I proposed a Detailed Test Objective (DTO) for application on STS-29 in order to investigate the shape of a water dump cloud. The proposal was accepted, and it was agreed that one main water dump would be planned around viewing opportunities from both the orbiter and ground cameras. DTO 334 occurred on orbit 49 on March 1, 1989. A typical potable water dump is performed at temperatures between 25 and 30 deg C and about 15-20 psia at the nozzle. The dump consists of pure water. Relative velocity of ejected particles (which froze upon ejection into space) was between 30-75ft/sec. The actual plume was found to be conical in form. STS-29 was placed in a 169 nautical mile circular orbit. Particle sizes were discovered to vary between .01 and 1.0 cm. It was found from this test that larger water particles spend a longer time in orbit. Release of water in posigrade trajectories (that is, in the direction in which the Shuttle is moving toward) was found to recontact the orbiter and could possibly cause problems for experiments operating in attached payload mode or even for certain cases of released payloads. Now, water dumps are made in a retrograde direction (behind the Shuttle’s motion) in order to preclude recontact. This prevents the orbiter from having to make a maneuver to dodge particles coming back toward it.
In the rare image below, the Shuttle is conducting such a dump as seen from Houston and the particulates are directed downward toward the earth. Because the particles are small and are forced into lower orbits, the comet-like tail curves forward as the particles below the Shuttle speed up. The object immediately to the lower right of the Shuttle and trailing it is the Hubble Space Telescope. This image was taken during the STS-103 mission. Other objects in the frame are stars.
In 1990, I was fortunate enough to be situated on the island of Hawaii and witnessed the reentry of the Shuttle’s External Tank (ET) from mission STS-31, the same flight that deployed that famous Hubble Space Telescope. The tank was intentionally dropped so that it would reenter the earth’s atmosphere and burn up over water but in such a way that sensors in the Hawaiian Islands would be able to observe and monitor the disintegration process. The first photo shows the tell-tale rotation of the tank is it is eclipsed by a volcanic cinder cone. Note the variation in the linear streak indicating that the ET is rotating end over end. This is a video image.
At the same time, the Mauna Loa volcano was in an eruptive phase. You can see a plume of smoke in both the image above and in the one below. The plume appears as an orange pall trailing off to the right (west). The clouds below the plume are actually the result of smoke started from fires as lava poured down the side of the mountain. As I was driving down Mauna Kea toward Mauna Loa, I made an amazing, though accidental discovery. I noticed the silvery white cloud you see in the center. Quickly I realized that this cloud was exactly in the place in the sky where the ET reentry had just occurred. The cloud was actually the disintegrated remnants. As the ET’s aluminum hull began to vaporize, the lower mass particles remained suspended at high altitude. As I drove down the mountain, twilight was rapidly approaching and the cloud of particles began to become illuminated by the sun. I stopped to make a series of photos, and this one is a good example.
Here is another reentry image I shot from Hawaii on a different External Tank entry. Unfortunately there was rain and cloud at Mauna Kea but some of the reentry was visible through the storm.
SPACE SHUTTLE CHALLENGER CREW TRAINING
Prior to the ill-fated Challenger mission, I coordinated crew training for the observation of Halley’s Comet. In the photo below, I and backup Teacher-In-Space Barbara Morgan are shown taping an instructional video.
AVIATION WEEK AND SPACE TECHNOLOGY PHOTOS
This is one of my AWST images showing Discovery on Mission 51-A reentering over Houston, Texas on Nov. 16, 1984. From AWST Nov.26, 1984, p.23.
This is a series of 3 of my video captured images showing STS-51A again revealing the chemiluminescent effect as the Shuttle streaks through the atmosphere. Note the double trail in the last image where each wing contributed to a trail. From AWST Jan. 21, 1985. p. 85.