Several years passed between the last U.S. manned mission (ASTP) and the first launches in 1981 of the Space Shuttle (an informal term for the Space Transportation System [STS]). Film-based remote sensing in general advanced greatly as astronaut photography from the Shuttle became a far more extensive activity, evolving into the permanent and formal Space Shuttle Earth Observations Project (SSEOP). This plot shows the significant increase in photographs returned for just the earlier missions (current total return exceeds 250,000):
A useful summary of the SSEOP by Helfert and Wood, emphasizing photo scheduling, equipment, crew training, and the enormous problem of cataloging and inventorying, appears in the March 1989 (Vol. 4, No. 1) special issue of Geocarta International *. The recent 1996 publication * by astronauts Jay Apt, Michael Helfert, and Justin Wilkinson presents a stunning collection of the SSEOP pictures, with technical data for each.
Before summarizing the hand-held photography, we should describe the Large Format Camera (LFC). The LFC was by far the most capable camera ever flown on a U.S. manned mission. Hard-mounted in the Shuttle payload bay, this 405 kg camera, with a 305 mm focal length and a 23 cm by 46 cm format (see Mollberg and Schardt, 1988 *) was the central element of photographic experiments on the few missions in which they used it. It is probably the only space payload in which cast iron was a major constituent. From a typical altitude of 300 km (186 mi), a frame covers ground dimensions of about 225 x 450 km (140 x 280 mi). Although quite successful, the LFC doesn't always fly, primarily because it requires dedicated payload-bay space, attitude-control fuel, and scheduled time, in contrast to the hand-held photography. This view of the Mojave Desert in California taken with the LFC during the 41-G mission in 1984, is typical of the quality achieved with this instrument:
Astronauts photographed the Himalaya Mountains (looking west) during STS-17, in which the oblique view extends from the Ganges Plains in India, across the Siwalik Hills, into the great peaks of Nepal, and beyond. Also visible is the vast Tibetan Plateau, the highest broad land mass in the world, which receives very little snow during most of the year, because precipitation falls on the mountains to the south, when monsoonal winds blow northward.
As evident from the above photo, a large percentage of astronaut photos from the Shuttle are slanted, i.e., look obliquely at an angle to the surface rather than straight down. This is evident in this next photo which shows the southwestern U.S. pointed in that direction:
In addition to the Shuttle photography being more advanced and varied than prior missions, the flights are more frequent, last longer, and cover more territory because of the higher orbital inclinations (up to 57°). Other major improvements:
1. Pre-flight Preparation: Shuttle crews receive extensive training in photography and in subjects such as geology, meteorology, oceanography, and ecology. Their training stresses global change, especially since we now have four decades of space photography covering some areas. Specialists prepare extensive lists of observation sites for each mission, embracing, so far, more than 1,800 significant areas.
2. Equipment: Space cameras have improved over the years, although the Hasselblad 70 mm is still the workhorse. With the wider variety of cameras and lenses, the crews can now match optimal equipment with the subject.
They still commonly use Ektachrome 64 film, which the Johnson Space Center processes. This film permits valid comparisons of Shuttle pictures with pre-Shuttle pictures of similar subjects. Also, astronauts have used an Electronic (digital) Still Camera successfully on recent flights.
3. Post-mission Processing and Archiving: The SSEOP has systematically catalogued Shuttle photographs. Archivers listed early Shuttle mission photos in printed catalogs but they stopped this practice in favor of Internet retrieval that favors easy scene selection and rapid downloading. Addition of digital data extracted from exposed film aids in this process. The digital data help the processers reproduce better colors and detail than with the multi-generation transparencies needed to preserve the flight film.