[v] In addition to the large, and to some extent better known, instrument groups onboard Skylab, there were also a sizable number of relatively small instruments serving a variety of scientific disciplines. These instruments were small, not in terms of their scientific importance, but in terms of their individual demands on the resources of Skylab. Some of them explored various areas of space science and astronomy, and the results are summarized in this volume.
In the area of far-ultraviolet astronomy, data obtained by one instrument on Skylab increased by a factor of 10 the number of stars with well-resolved spectra between 1400 and 2000 Å, and indicated the need for some revision in the classification of hot stars. The search for "superheavy" cosmic rays was once again unsuccessful, no elements with atomic number greater than 110 having been found. Evidence was found of a "soft auroral zone" at an altitude of 100 km, between the aurora at 120 km and the airglow at 80 km. Comet Kohoutek provided a particular flurry of activity during the last Skylab mission-the astronauts participated in the large coordinated effort to observe it. In the ultraviolet region of Kohoutek's spectrum, the known OH and CN emission lines at 3100 and 3900 Å, respectively, were again observed, but no other lines were seen. Photographs from one of the 35-mm Skylab cameras provided a tie between ground-based observations and the Apollo Telescope Mount coronagraph observations of the comet. Kohoutek results, however, were not spectacular because it turned out that Kohoutek was only a modest comet.
As in many areas of science, most of the specific results will be of particular interest to the principal investigators and their colleagues, but the total Skylab science program should have far-reaching significance for a much larger audience. One of the special characteristics of Skylab was its ability to provide a platform for a large number of physically small and relatively simple experiments that could never have obtained a solo ride on a satellite. Its multidisciplinary character allowed the Skylab mission to serve a very broad science constituency-ranging from observations of cosmic rays to the growth of semiconductor crystals. The multidisciplinary science payload also permitted very full utilization of the space laboratory. A satellite devoted solely to solar astronomy can observe the Sun during only roughly two-thirds of each orbit. The same is true of a satellite devoted solely to Earth observations, etc.
[vi] On the other hand, the multidisciplinary nature of Skylab greatly increased its complexity and required frequent compromises between totally nonequivalent science goals. The issue of whether to obtain a medical run or to make an Earth observation pass during a given time period is never resolved in a truly satisfactory manner.
The length of the Skylab missions and, most importantly, the presence of man onboard allowed us unprecedented flexibility in modifying both observing plans and procedures. Ironically, our flexibility in replanning was probably helped by the problem experienced during Skylab's launch, which immediately necessitated a large replanning effort and very quickly accustomed us to the idea of short-term replanning. During the missions, the scheduling of the major blocks of time for each day was accomplished 24 to 36 hours ahead of time. For Earth observation passes, the lead time for some details was occasionally reduced to approximately 6 hours, and, in cases of solar activity, observing programs were modified in real time. Because of the "revisit" capability, we were able to respond to the arrival of Comet Kohoutek by sending up the electrographic camera after the Skylab itself had been launched. Although an electrographic camera of very similar design had previously flown on Apollo 16, it is still worth noting that the total time for preparing and planning the Skylab electrographic camera experiment, including camera modifications, was less than 6 months. Because of its flexibility, Skylab functioned very much like an "ordinary" laboratory here on Earth.
It is to be hoped that, having learned how to provide a laboratory with responsive accommodations and a flexible operating climate, we will be able to build successfully on the Skylab experience and achieve an even more flexible and productive environment for research as we enter the Space Shuttle era.