Solar astronomy and space medicine were major experiment programs, and together with the so-called corollary experiments they were certainly adequate to fill the operational time available on the Skylab missions. They were also about as much as the program could comfortably accommodate and still launch on time, a point particularly stressed by program officials at Marshall Space Flight Center.
But when the Office of Manned Space Flight chose to develop the Shuttle as its next major program, Skylab was left as the only manned program that would be flying for an uncomfortably long time. For all of Headquarters' stipulations that only mandatory changes were to be made after the dry-workshop decision, there was a natural tendency to use this last set of missions to best advantage. Besides a number of changes in the workshop (pp. 123-24, 144-48), one major and one minor group of experiments were added between July 1969 and January 1973.
Cancellation of Apollo Applications mission 1A at the end of 1967 seemed to put an end to any possibility that Skylab would conduct studies of the earth (pp. 87- 88). Yet within two years the Skylab program office was preparing to add a set of complex and expensive instruments for that very purpose. Those two years had seen a tremendous upsurge of interest in remote sensing and its practical applications.i Increasingly in the late  1960s, users of aerial photography and other remote sensing techniques became aware of the potential and limitations of airborne surveys of the earth's surface. Advances in sensor technology had made remote sensing useful in agriculture, forestry, geology and mineral prospecting, oceanography, city planning, and land-use studies. The rise of the environmental movement in the late 1960s brought increased concern for air and water pollution and an appreciation that such problems existed on a scale that could hardly be assessed except through the synoptic eye of the satellite.
Not least important was the realization that the view of earth from an orbiting spacecraft was both wide in coverage and rich in detail. The color photographs taken on early Gemini missions surprised and delighted cartographers and geologists in several federal agencies.1 Besides having a wide view, a satellite could look at the same site frequently. For some applications, such as crop and snowpack surveys, this kind of realtime data collection exceeded anything aircraft could do.
NASA had launched a series of meteorological satellites (Tiros, Nimbus) starting in the mid-1960s, but in early 1968 was only beginning serious study of other earth-sensing vehicles. Activity in this field was a responsibility of the Manned Spacecraft Center, where remote-sensing instruments were tested on aircraft. By FY 1968 the program had a budget of $6 million and about 150 full-time NASA and contractor personnel assigned. The U.S. Geologic Survey, the Department of Agriculture, and the Naval Oceanographic Office helped to coordinate the program and evaluate its results.2
Since crops, minerals, and water supplies were among the features that could be monitored by remote-sensing instruments, the term earth resources came to be commonly applied to remote sensing. Toward the end of the 1960s, publicly expressed concern with dwindling natural resources drew much attention, and the notion gained currency that space technology could be exploited to help solve problems on earth. Speaking of this period, a Martin Marietta official later remarked, "Everybody had his own definition of what 'earth resources' meant, but all the definitions were good." Some who viewed the expensive manned spaceflight programs as pointlessly wasteful evidently felt that NASA could redeem itself by contributing to the solution of environmental problems, including resource shortages.3
Any such program was bound to have a wider appeal than some of the esoteric science projects. One Skylab program official, commenting on his own experience, said, "When I would [visit my home state] in those days, I could talk about that ATM all day and they'd be polite, but as soon as I started talking about taking a crop survey, my friends . . . knew what that meant." Many congressmen responded similarly. Those who were reluctant supporters of NASA's scientific programs found earth resources  a godsend: a space program with a payoff that could be easily appreciated by many of their constituents. The chairmen of both of NASA's House subcommittees became champions of earth-resource experiments. In early 1968, when John Naugle, associate administrator for space science and applications, outlined plans in that area for the Space Sciences Subcommittee, he found congressmen eager to support more than he proposed. At the end of that year the House Subcommittee on NASA Oversight published a staff report urging far more work in the earth-sensing field.4
At that time the Office of Space Science and Applications was still studying the objectives for an earth-resources technology satellite and conducting development work on sensors. Naugle told the Subcommittee on Space Science and Applications that he expected to ask for funds in fiscal 1970 to develop hardware for flight in late 1971 or early 1972. Meanwhile, the Office of Manned Space Flight had the only program- Skylab-that might be able to fly sensors any sooner (the official schedule listed an AAP flight in November 1970). Prospects were not good, however, in 1968; after the cancellation of AAP 1 A, about all OMSF could do was to establish the requirements for earth-sensing experiments to be carried on some future wet-workshop flight. In a year that saw the solar telescopes come to the verge of cancellation, any thought of adding another major set of experiments was visionary.5
Some, however, urged a different course. Jacob Smart, NASA's assistant administrator for DoD and interagency affairs, told George Mueller in May 1968 that an earth-resources project might be the salvation of the space program. "Whether or not justified," Smart said, "earth resource sensing from aircraft and space has been widely advertised as promoting great economic returns." Pointing out the unexpected riches that had been found in the Gemini and Apollo photographs, he suggested that Mueller ask OSSA for suggestions about instruments to fly on Apollo and Apollo Applications missions.6 Mueller had, in fact, listed earth-resource observations first among several possible objectives for AAP in 1965 (pp. 43-44).
Interest in flying earth sensors on a manned mission remained alive in the Office of Space Science and Applications, though tempered by the experience with AAP 1A. When Floyd Thompson's Post-Apollo Advisory Group (pp. 97-98) suggested earth sensing as a promising activity for manned spaceflight, OSSA once again looked into the possibilities. If OMSF could orbit a substantial earth-sensing payload in 1969 or 1970, it could provide useful data for designing the earth-resources technology satellite, still in the planning stages. The Thompson committee's report, however, was not too promising, according to one OSSA official who looked into it. Coverage of the United States from the proposed wet  workshop was negligible on account of the low orbital inclinationii obtainable with a Saturn IB. The committee's estimate of the cost of such a mission was much too low. And finally, unless the experiments were defined as primary objectives of the flight, they would likely be dropped when schedules and budgets got tight-as they inevitably would (witness AAP 1A). It was simply not prudent for OSSA to rely on manned programs to provide information, though of course the possibility should not be excluded.7
One more influential voice was added to the chorus calling for earth-resource missions when the National Academy of Sciences published a report summarizing a two-year study of applications satellites conducted for NASA. That report urged a two- to three-fold increase in funding for applications satellites, more attention to communications and navigation vehicles, and a pilot program for an earth-resources satellite.8
In view of the ready market for earth-surveying experiments that existed in early 1969, it would have been surprising had the Office of Manned Space Flight not revived its earth-resource experiments-which it did. By the fall of that year, when the dust had settled somewhat after the dry-workshop decision, meetings were being held to determine whether the AAP 1A sensors, or upgraded versions of them, could be accommodated on the workshop. The Office of Space Science and Applications was defining a package of such experiments for study by its Space Science and Applications Steering Committee.9
When preliminary studies showed no insurmountable problems, MSC quickly presented a proposal to the Manned Space Flight Experiments Board on 8 December 1969. Leonard Jaffe, who as acting director of the Earth Observations Program Division represented OSSA, was concerned by the hasty preparation of the proposal. He noted several important unresolved questions-cost, particularly, but also the state of definition of the sensors themselves. Still, Jaffe strongly supported flying such a set of experiments and said that OSSA would present some definitive recommendations as soon as possible. Charles Mathews, chairing the meeting, conceded that funding and management needed more study; but he, too, strongly favored the project. The board accordingly gave final approval to only one of the proposed experiments, deferring consideration of the rest until better information was available.10
 Initially four instruments made up the new earth-resource experiments package. The only one that had been flown before was the multispectral photographic facility (experiment S190A; all experiments are listed in app. D). This was an improved version of an experiment flown with great success on Apollo 9 the previous spring. It consisted of six precision cameras with carefully matched lenses, each using a different film and filter combination to record a different spectral range of visible or infrared light. The other instruments, all experimental in the sense that their use in orbit had not been proved, were radiometric rather than photographic; they recorded the intensity of radiation emitted by or reflected from surface features. Two of these, a spectrometer (S191) and a 10-band multispectral scanner (S192), operated in the infrared. The spectrometer recorded the wavelength and intensity of infrared radiation from selected small areas (0.45-kilometer diameter) on the ground; the multispectral scanner simultaneously measured the intensity of infrared in 10 wavelength ranges, scanning a swath 74 kilometers wide centered on the spacecraft's ground track. The fourth instrument (S193) had two functions: it was a microwave radiometer, similar to the infrared instrument but sensing longer wavelengths, and a radar scatterometer, which measured the reflective properties of the surface toward radar waves. Somewhat later two more instruments were added: a passive L-band radiometer, S194, to map temperatures of terrestrial surfaces; and a higher-resolution camera, S190B, to aid in interpretation of data from the other sensors.11
 Skylab Program Director Bill Schneider immediately ordered the centers to begin preliminary work: MSC to prepare the documentation, Marshall to study integration requirements and hardware modifications, and all three centers to continue basic compatibility studies. Every effort had to be made to keep costs down. The experiments board had been given an estimate of $10 million for developing the instruments and $11.125 million for support and data analysis, the latter to be funded by OSSA and user agencies.12
Early in February OSSA recommended that the first four instruments be flown; Dale Myers agreed on the 16th. The microwave instrument was only provisionally approved, however, since its compatibility with the spacecraft had not been conclusively established and it might cost an additional $2 million. Directing the centers to proceed with the earth-resource experiments, Schneider reminded them that "all possible effort must be made to deliver [the experiments] within present cost and schedule guidelines"-that is, $25 million for development, integration, and delivery by July 1971. Should development costs exceed the budget, it would be necessary to consider dropping the entire package. Requests for proposals were sent out, a source evaluation board appointed, and by the middle of 1970 contracts had been awarded for the instruments.13
Schneider's correspondence for the next six months documented a steady increase in projected costs, along with his repeated warnings that "we have no resource reserves to cover additional requirements." By mid-March the cost of the multispectral cameras was twice what had been estimated in December. By June, the cost of the entire package had soared to $36 million, and Schneider warned that reconsideration might be necessary. In June, although the Skylab office recommended deleting the microwave sensor, the Manned Space Flight Experiment Board, persuaded by OSSA's pleas to keep it, urged developing all the instruments for flight.14
Despite a cut in NASA's overall budget that summer, Myers had little choice but to go ahead with the earth-resource instruments. He informed Administrator James Fletcher of this intent in July, saying that he was limiting the cost of the project to $36.4 million. The extra $11.4 million would come from "further reduction in the planned Skylab uncosted obligation at the end of FY 1971"-in other words, out of funds already allotted for Skylab. Schneider passed the word to the center program managers, directing them to reallocate funds within current fiscal limitations. From Houston, where much of the burden of cost reduction would fall, Kenneth Kleinknecht told Headquarters that his back was to the wall, financially, and that the other projects in Skylab might suffer. He added that Washington ought to consider the centers' problems before adding expensive new experiments to a maturing program.15
Six months later costs had gone up still more, to an estimated $42  million, but seemed to be under better control. In mid-1971, reviewing the project's cost history for Myers, Schneider attributed much of the trouble to unrealistic initial estimates and to less-than-effective management at all levels. The fact that the sensors had been flown in the aircraft program-which was only approximately true-had thrown managers off their guard and led to poor assessment of development problems and costs. In the general eagerness to get the package ready for flight, neither OSSA nor OMSF had formulated requirements in sufficient detail before soliciting bids; changes in specifications during contract negotiation had increased costs. Nor had there been adequate coordination between MSC's Science and Applications Directorate (which directed instrument development) and program control officials in the Houston Skylab office. Changes had been made in the experiments without full assessment of the consequences. In sum, it had not been a good job of management, and in their haste to get the instruments into the program, managers at all levels had proceeded less carefully than they should have. The project was now under control, but any new major problems could wreck it. 16
Looking for a place to put the instruments and their control systems, planners quickly settled on the multiple docking adapter, where space was still available. An optical-quality window would have to be added for the multispectral cameras; the infrared spectrometer would have to be installed through the pressure hull; and brackets would have to be added to the outside to support the microwave and multispectral scanners, both of which used large antennas. Marshall went ahead at once with these changes, though they caused some interference with systems already installed on the module.
The requirements of the earth-resource experiments caused major changes to mission plans. Primary among these was an increase in orbital inclination to 50°. Skylab would now go as far north as Vancouver, Winnipeg, Bastogne, Frankfurt am Main, Kharkov, Mongolia, and Sakhalin Island north of Japan. To the south, Skylab would pass over all of Australia and Africa and most of South America, except Tierra del....
 ...Fuego. Three-fourths of the earth's surface would lie under Skylab's path, the area where 90% of its population lives and 80% of its food is produced.17
Since NASA's network of tracking and communications stations was sited to cover a spacecraft in an orbit of lower inclination (or on its way to the moon), the 50° orbit meant that Skylab would be out of contact during a large fraction of each orbit. The increased inclination also changed the angular relation of the orbital plane to the sun line, requiring recalculation of heat loads in the workshop and power production by the solar arrays.18
Among the more significant changes was the new orbital attitude required by the earth-sensing experiments. While the solar telescopes had to be pointed directly at the sun, the earth sensors had to be aimed at that point on the earth's surface directly beneath the spacecraft (nadir). Except for minor perturbations, inertia would keep the cluster aligned with the sun, but would move it continually with respect to the nadir. When the earth-resource experiments were operating, the spacecraft would have to rotate at an angular rate equal to its angular velocity in orbit, about 4° per minute. This mode of operation (called the Z-local vertical because the Z axis of the orbital assembly pointed toward the center of the earth at each instant) made solar observations impossible, changed the cluster's heat balance, and reduced power production.
The new requirements, plus increasing weights and moments of inertia in the workshop cluster, touched off a series of design changes in the attitude-control system. Whereas the control moment gyros had been responsible for attitude control during solar observations and the thruster system was to be used for other maneuvers, Marshall engineers now transferred most of the maneuvering responsibilities to the gyros, with the thrusters held in reserve. New control programs were entered into the ATM's digital computer, which could, on command from the control and display console, maneuver the cluster between solar inertial and Z-local vertical attitudes and into any of several other attitudes required in special circumstances.19
The earth-resources package presented its largest challenge to flight planners. The photographic instruments required specific lighting conditions, which restricted the number of sitesiii that could be photographed from Skylab's orbit. Thermal and power problems in the Z-local-vertical attitude limited the number of successive earth-observing passes. Except for the microwave sensor, the earth-resource experiments were limited by weather conditions at the surface; observations planned for one pass  might have to be postponed if cloud cover was heavy. And always there was the fact that time for the earth-resource observations would have to be taken from medical or solar experiments or both.
In view of these limitations, a preliminary study showed that about 45 of Skylab's trips across the United States during the three missions would be useful for earth-resource sensing. That figure was used for planning purposes for about a year, until proposals from potential users demanded more. It would take a great deal of juggling to optimize all the factors that had to be taken into account.20
For two years, no one knew exactly what the earth-resource instruments were going to do. Not only was NASA evaluating a set of sensors; it was also evaluating a new concept of experiment management. The earth-resource instruments were to be a scientific "facility," whose specifications were determined by NASA; users would be asked to propose specific uses for the data those instruments could gather. (Previously experimenters had proposed both the instrument and the experiment, with NASA providing support for its development and the spacecraft on which to fly it.) The principal investigators' responsibilities for earth resources were not the same as those of the principal investigators for the solar telescopes. Users would have no control over sensor design, but they could (within operational limits) specify when and where they wanted data taken.21
Until those users were chosen, a number of important activities could not proceed. Particularly frustrated by this situation was Eugene Kranz, chief of Houston's Flight Control Division. Having to define its role in Skylab by the end of 1970, Kranz's division could not get a grip on the earth-resources package. Whereas normally the office would have sponsored meetings with experimenters to find out what they needed from the instruments, there were-only two years before flight-no investigators to talk to. Nor could requirements be compared effectively with the design constraints of the cluster during critical design reviews. In mid-1970, Flight Control had been given responsibility for collecting Skylab's data requirements, including data processing and distribution, and once more the earth-resource experiments raised unanswerable questions. Was the purpose of the experiments to evaluate the sensors or to collect data? The distinction markedly affected the way experiments would be handled. Pending receipt of specific instructions, Kranz decided to treat the earth resources as data-collecting science experiments. He was aware that this conflicted with other opinion at MSC, but by taking that approach he hoped to get some clarification of center policy.22
Kranz's difficulty undoubtedly stemmed from the same source as Schneider's cost problems: the haste with which NASA was attempting to  organize and carry out a major addition to an existing program. With OSSA in charge of some aspects of earth resources, MSC responsible for others,iv and Headquarters coordinating the activity under severe budgetary restraints, it is probably not surprising that communication sometimes broke down.
Even as Kranz was complaining, however, selection of experimenters was about to begin. On 22 December 1970,6000 announcements of flight opportunity were sent out to potential users of earth-resource data. Universities, state and local government agencies, private concerns, and foreign governments were solicited for proposals. By mid-1971 approximately 230 proposals had been received and screening had begun. After the Office of Space Science and Applications had examined them for scientific merit, the proposals were evaluated by the manned spaceflight centers (primarily MSC) for compatibility with the planned missions. Not until that process was complete could definitive flight planning begin.23
Although many proposals needed to be better defined, there were more good proposals than 45 earth-resource passes allowed for. Schneider therefore directed Houston and Huntsville to determine how much more Z-local-vertical time they could provide. Marshall found that within certain limitations, another 40 passes could be made; the main problems were encroachment on ATM observing time and providing space to store film. The extra 40 passes included some in the solar inertial attitude; for some investigators an oblique view of the earth was acceptable, and this allowed the earth sensors and the solar telescopes to operate simultaneously. With these extra passes available, 160 of the more than 230 proposals were placed on a candidate list for further negotiation.24
Consultation with the investigators during the first half of 1972 produced changes to many of the proposals and brought them within Skylab's capability. As MSC got a clearer picture of the cost of supporting these investigations, however, officials urged cutting the total to a far smaller number-a proposal vigorously opposed by both OSSA and OMSF. When Headquarters suggested that management of some of the investigations could be moved elsewhere to relieve the strain on MSC, the center agreed to negotiate with all 160. In August 1972, nine months before the scheduled flight of the first mission, Headquarters announced that 106 investigators, 83 from the U.S. and 23 from other countries, had been selected for the earth-resource experiments.25
While project officials were negotiating the final details of earth-resource experiments with investigators, mission planners were refining  their plans for taking data. An important change was made early in 1972, when Houston proposed to launch the workshop into a controlled repeating orbit, in which the spacecraft passed over the same point at regular intervals, to increase the probability of successful coverage of the earth-resource sites. With Marshall's concurrence, this feature was incorporated into mission plans in June. The workshop was to be inserted into a 372.5-kilometer orbit that would repeat its first ground track on the 72d revolution, five days (less two hours) later. Minor adjustments would be made periodically during the mission to correct for normal perturbations.26
Flight planning for earth-resource passes was at least as complex as any other experiment activity in Skylab, including the solar observations. There were 570 combinations of ground sites and experimental tasks to be accomplished in 60 earth-oriented passes during the three missions; frequently ground observations or aircraft flights had to be coordinated with orbital passes, to calibrate the instruments. Weather conditions could always interfere. And after completing an observing pass, experimenters could never be sure that they had secured the data they wanted, since results were not available until the film was processed on earth after the mission.
Mission planners worked out basic earth-resource procedures in the first half of 1972. Planning for a given day's observations would start five days before (a consideration based on the five-day repeating ground track), with all of the activities preplanned for the mission but not yet accomplished put on a "shopping list." Many of these would be eliminated because of the spacecraft's ground track or the crew's work-rest cycle. Those remaining would be compared against the expected sun angle, the day's flight plan (other experiments might have higher priority), and the condition of the workshop's attitude-control system. Weather forecasts and the readiness of ground support and aircraft were then considered, perhaps eliminating a few more possible activities. Two days before execution, planners chose the observations with the highest probability of success, and summary flight planning began, with updated weather forecasts being continually monitored. On the day before, detailed flight planning was completed-coordinates of each site, instruments to be operated, time of spacecraft maneuvers-and, after checking the latest available weather reports, flight planners committed Skylab to an activity not later than three hours (two orbits) before it was executed.27
The short time available for development of the instruments presented problems. While the S190A cameras were similar to others that had been flown before, the infrared and microwave sensors were less well developed and encountered a number of delays. Martin Marietta, whose responsibility included both integrating the experiments into the multiple docking adapter and building the controls and displays for them, often had to cope with changes in the instruments that affected the company's  own hardware. To make sure that everyone concerned was aware of the implications of such changes, Martin set up a working group of representatives of the five other contractors and the astronaut office, which met monthly to make decisions on proposed changes. It was probably the only way that the tradeoffs between the various factions could be accomplished in the time available.28
By November 1971, Program Director Bill Schneider could report to the Office of Space Science and Applications that flight hardware had been completed and delivered for integration into the multiple docking adapter. In spite of that, each sensor had one or more problems that would require hardware changes before launch; and after integration checks the instruments were pulled off the module for additional work. Some subsequent qualification tests required juggling the schedules to work around the missing experiments.29
Late in 1971 Schneider again recommended cancellation of two experiments. The multispectral scanner was experiencing difficulties that could delay launch, and the microwave sensor had so few investigators interested in its data that it seemed an unjustifiable expense. Neither experiment was in fact dropped, but OSSA conceded that the multispectral scanner was expendable if the workshop launch had to be postponed on its account. Any lengthy delay would disrupt the seasonal variations that other investigators wanted to observe, and the multispectral scanner was not worth that.30
On 6 October 1972 the multiple docking adapter and airlock were delivered to the Cape. The S193 microwave experiment arrived nine days later. During the next few months a number of equipment failures occurred; both the multispectral scanner and the microwave sensor had to be returned to the manufacturers for correction of defects, as did the control and display panel and one of the tape recorders. Late in March 1973 the last earth-resources simulation test was completed satisfactorily, and the experiments were pronounced ready to go.31
While the earth-resource experiments were publicized as offering benefits to the public as a whole-in contrast to the medical and solar astronomy experiments-some in the Skylab program felt that public interest and support should be broadened. In the spring of 1971 Ken Timmons, a Martin Marietta official whose office had responsibility for the multiple docking adapter, conceived the idea of allowing high-school students to propose some simple experiments for the workshop. Preliminary discussions with Colorado education officials indicated a strong interest, so Timmons passed the idea on to Marshall Space Flight Center. Skylab manager Leland Belew also liked the idea, and he in turn  mentioned it to William Schneider in a telephone conversation. Headquarters then negotiated a contract with the National Science Teachers Association to organize and manage a nationwide competition for student proposals.32
In October 1971 NSTA mailed out some 100 000 announcements, specifying a 4 February 1972 deadline for receipt of proposals. More than 55 000 teachers requested entry materials and 3409 proposals were finally submitted, involving over 4000 students from all 50 states in grades 9 through 12. By 1 March, 12 regional screening committees had selected 300 proposals for the final winnowing, which would produce 25 winners. Proposals were judged by NSTA on scientific merit, but throughout the selection process NASA engineers were called on for quick judgments as to feasibility. By 15 March, 25 national winners and 22 "special mention" entries had been chosen.33
The selection process had taken into account such limitations as weight, volume, power consumption, and crew time needed. But once the winning experiments had been chosen it was necessary to run them through NASA's normal sequence of reviews. To avoid overwhelming the students with paperwork, however, certain documentation requirements were relaxed; a streamlined system of record-keeping summarized the results of the reviews. And in light of the short time available for developing the experiments, project officials insisted that each NASA office designate a single person to participate in reviews. This ensured that action could be taken on the student experiments when necessary.34
The 25 winning students participated in a preliminary design review at Huntsville during the week of 8 May 1972. The experiments were put into three categories: those that required fabrication of separate pieces of hardware, those that could be affiliated with existing Skylab experiments, and those whose general objectives could be attained by cooperation with related research already in the program. Six experiments were put in this latter category when it developed that they could not be carried out on account of technical problems. These students were allowed to work with principal investigators whose research programs closely approximated their own interests, so that they could at least participate in some part of Skylab's science program. Of the rest, 8 would use data already planned for collection and 11 required development of new hardware. These students spent the next three months working with NASA advisers, designing the equipment for their investigations and preparing for a critical design review in August. By early 1973 the student experiments had been completed. The flight acceptance review was held at Marshall 2324 January and flight units were delivered to the Cape two days later.35
The experiments devised by these students ranged in quality from fair to extremely good, according to Marshall's program manager and others who participated in the judging. One proposal called for measuring  the intensity of neutron radiation at orbital altitudes, something that professional scientists had never done. Another proposed to study x-radiation from Jupiter, using one of the ATM instruments. One of the most widely publicized student experiments was designed to study adaptation to zero g by determining whether a spider could spin a normal web and, if not, whether the arachnid could adapt to weightlessness during a mission. Others dealt with questions in astronomy, biology, and space physics (all 19 are listed in app. D).
Both NASA and NSTA participants were agreeably surprised by the overall sophistication of the student proposals. Some of the students, on the other hand, felt that NASA's expectations had been too low. One significant secondary finding was that many students had serious misconceptions of scientific principles and the scientific method, leading some of the evaluators to examine their own college-level teaching. The contest judges were also distressed to find that quite a number of the students could not express themselves clearly in writing.36
The student experiments were the last addition to Skylab. On the whole, it was probably a worthwhile exercise. Both students and science teachers were grateful for NASA's interest in science at a preprofessional level. The student winners, though few in number, learned a great deal-not only about science, but about the day-to-day conduct of a complex project like Skylab, where nonscientific considerations often determine the course of a scientific project.
i Remote sensing designates a variety of activities, from photography to radiometry, conducted from high-flying vehicles and usually measuring electromagnetic radiation reflected or emitted from features on the earth's surface. Mapping by means of aerial photography is a common example, but nonphotographic measurements (photometry) including infrared (heat) and microwave radiation have applications in other areas. Even more useful for some purposes is multispectral sensing, the simultaneous measurement of several different bands in the visible and infrared spectra. A major drawback to surveys by aircraft is the difficulty of covering large areas in a short time. Peter C. Badgley, Leo F. Childs, and William L. Vest, "The Application of Remote Sensing Instruments in Earth Resource Surveys," paper G-23, 35th Annual Meeting of the Society of Exploration Geophysicists, Houston, 6-10 Nov. 1966.
ii The angle Of the orbital plane with the equator, e.g.30°, gives the latitudes that mark the northern and southern-most travel Of the spacecraft. At an inclination Of 30O, about as high as the wet workshop could go, the spacecraft flies no farther north than New Orleans.
iii Since much of Skylab's flight path was over foreign countries, some of them sensitive to the possibility of surveillance from orbit, the use of the word target to refer to ground sites was forbidden. The word was not used even in training, lest an astronaut inadvertently use it in flight. Leonard Jaffe to Skylab prog. dir., "Nomenclature for EREP Observations," 31 Aug. 1972.
iv In 1970 as in 1967, MSC was wrestling with Apollo problems-not a catastrophe this time, but a near miss the aborted night of Apollo 13 in April 1970 and the subsequent investigation.