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- 8 - remains for future study.) Recoverable payloads and short-lived detection systems permit important observations not feasible with satellites and, because of flexibility in launching schedules, flights can be made under optimal conditions -- at lunar occultations or times of best seeing, for example. Sounding rockets also have the advantages of shorter lead times and much lower cost than satellites. The time between the conception of an experiment and the rocket flight may be about six months to a year, as compared with three or four years for satellites. Much of the high producti- vity of the rocket astronomy program can be attributed to the speed with which new rocket payloads can be designed and flown. The short time scale allows the investigator to adjust his program of study to continuing discovery, utilizing data from each previous experiment, and to make changes in instru- ments and experiments in the light of new data. It also permits the more rapid evolution of flight hardware. The lower cost of rockets makes them especially suited for experiments which are inherently brief, such as testing new instruments slated for eventual use in satellites or making chemical releases to study upper atmospheric processes. The lower cost in money and preparation time of rocket-based investigations means that more exploratory, less certain-of-success investigations can be tried. Calculated risks on less conventional equipment and experiments have brought substantial scien- tific rewards. Although individual rocket vehicles and payloads are far less expensive than satellites, it is sometimes more economical to employ satellites, as when a large number of rockets would be needed to gather the data obtainable by one satellite. Moreover, there is a tendency to design increasingly com- plex rocket payloads to perform a variety of measurements during a single flight. The cost of such payloads is naturally a good deal higher than that of simpler payloads, but the cost in terms of the data obtained may well represent a saving. The relative cost of rocket-based research as compared with that using satellite, airborne, or ground-based techniques is thus not always a straightforward computation. This stresses the need for careful weighing by the experimenter of the alternative techniques at his disposal. Sounding Rockets as an Educational Tool Sounding rockets are used extensively by university space science depart- ments for graduate education. There are very practical reasons for doing so. First there is the time element: a rocket experiment from inception through final data analysis requires about l8 months, a period that is sufficiently short to permit the student to have a significant role in the experiment from start to finish while at graduate school. The long time scale (24 to 72 months) of satellite experiments normally precludes student participation throughout the project. Second, the cost of rocket vehicles and instruments is generally not so severe that students must be excluded from meaningful participation in the experiments. Third, the reliability of standard rocket hardware minimizes systems failures and excessive delays in data acquisition.
