[1] When the first Sputnik began beeping back scientific data from outer space in 1957, it seemed that the 12-year reign of the sounding rocket as the chief space research vehicle was over. Scientific satellites can stay above the atmosphere for months, even years. A satellite gives the Earth-confined experimenter data from its orbital track all the way around the world. The sounding rocket can offer the experimenter only a few minutes at high altitudes above the launch site.

Certainly satellites are superior in terms of staying power and geographical coverage - if that is what the experimenter wants. Often this is not what he wants; often he wishes to make measurements in regions of the atmosphere that are too thick and dense for satellites to orbit and yet too high for balloons to reach. Sometimes he does not wish to wait two or three years for the design, development, and launch of a scientific satellite. All three research vehicles - sounding rocket, balloon, and satellite - have their own roles to play and regimes to explore in space research. Far from being the "Model T's" of the Space Age, as they were once called, sounding rockets are more popular than ever with the scientists who use them.

The sounding rocket offers a scientist a vehicle that will carry his instruments (a few kilograms to a few hundred kilograms worth) to almost any altitude he desires between a few kilometers and a few thousand kilometers. Besides affording the opportunity of making measurements on the way up and back down through the atmosphere (a "vertical profile"), the sounding rocket can provide several minutes of observation time above the Earth's atmosphere, that layer of gas that insulates scientific instruments from much of the radiation, plasma, and micrometeoroid flux pervading outer space. Thus many sounding rockets are true spacecraft, albeit ephemeral ones. Just a few minutes above the atmosphere has been sufficient to make many fundamental discoveries about the nature of the Sun, the stars, and our celestial environment. And, of course, rockets remain our best....

....vehicles of all for exploring that region of the atmosphere above balloon altitudes (about 40 km, or 25 mi) and below satellite orbits (about 160 km, or 100 mi).

The payload and altitude capabilities are not the only features that attract experimenters to sounding rockets.

Some Advantages of Sounding Rockets

• Simplicity. Sounding rockets are usually much simpler than satellites, with far fewer interfaces to match. Launch facilities are also less elaborate.
• Informality: Most sounding rocket payloads consist of one experiment or one group of closely related experiments. The payload is the "property" of only one experimenter; and there need be no formal, time-consuming reviews to ensure compatibility with other experimenters.
• Low cost: Small sounding rockets can be bought for less than $10 000; the biggest for $150 000 to $200 000. Satellites, in contrast, are multimillion-dollar vehicles. Sounding rockets are cheap enough to try new ideas on. Indeed, many experiments [3] destined for satellites get their first rides on sounding rockets. By virtue of their low cost, hundreds of sounding rockets are launched worldwide each year for research purposes plus many more for weather studies.
• Recoverability: Payloads, such as film packs and even small animals, can often be recovered for study or reflight.
• Geographic flexibility: Sounding rockets can be launched almost anywhere, making them ideal for studying eclipses, solar flares, polar-cap absorption events, the equatorial electrojet, and other localized phenomena.
• Temporal flexibility. Experiments and rockets can be prepared in just a few weeks to take advantage of scientific targets of opportunity. Or they can be kept in readiness for firing during solar flares and, as has been done on occasion, during the passage of a scientific satellite to obtain vertical-profile and orbital data at the same time.

Some Disadvantages of Sounding Rockets

• Restricted time of observation. Sounding rockets are essentially "quick-look" vehicles.
• Localized coverage. Unlike satellites, sounding rockets do not see the geographical "big picture."
• Payload limitations: Some experiments, such as large telescopes, are just too big for sounding rockets.
• Lack of glamour. This used to be a factor right after Sputnik, but the advantages of sounding rocket research have overcome this subjective problem.

That the advantages of sounding rocket research greatly outweigh the disadvantages is obvious from the fact that NASA alone launches over 150 each year - launches by other U.S. agencies double this figure - with no slackening in demand as bigger satellites have become available.

Although sounding rockets perform much rather routine work of a synoptic nature in the upper atmosphere, they are also often first into space with new research tools. In this sense they are in the vanguard of space research and have marked up many "firsts." The discovery of cosmic X-ray sources by Herbert Friedman' and his group at the Naval Research Laboratory (NRL) is typical. Rockets were also the first to measure the [4] details of the extreme ultraviolet and X-ray spectrum of the Sun². The dust layers in the upper atmosphere were also first sampled by sounding rockets.³ These are just a few solid scientific accomplishments of the "lowly" and unglamorous sounding rocket; more will be introduced as the history of these remarkably versatile vehicles unfolds.

2. Homer E. Newell, Jr., "Rocket-Sonde," paper presented at the AIAA Sounding Rocket Vehicle Technology Specialist Conference, Williamsburg, Va., NASA N67-23480 (Feb. 28,1967), p. 9.

3. M. Dubin, "IGY Micrometeorite Measurements," in H. Kallmann-Bijl, ed., Space Research (New York, 1960), pp. 1042-1058.

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