A sounding rocket or rocketsonde, sometimes called a research rocket or a suborbital rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments during its sub-orbital flight. The rockets are often used to launch instruments from 50 to 150 km (30 to 90 mi) above the surface of the Earth, the altitude generally between weather balloons and satellites; the maximum altitude for balloons is about 40 km (25 mi), and the minimum for satellites is approximately 120 km (75 mi). Due to their suborbital flight profile, sounding rockets are often much simpler than their counterparts built for orbital flight. Certain sounding rockets have an apogee between 1,000 and 1,500 km (600 and 900 mi), such as the Black Brant X and XII. Sounding rockets may be flown to altitudes as high as 3,000 km (2,000 mi) to allow observing times of around 40 minutes to provide geophysical observations of the magnetosphere, ionosphere, thermosphere, and mesosphere.
Etymology The origin of the term comes from nautical vocabulary to sound, which is to throw a weighted line from a ship into the water to measure the water's depth. The term itself has its etymological roots in the Romance languages word for probe, of which there are nouns like sonda and sonde and verbs like sondar, which means "to do a survey or a poll." Sounding in the rocket context is equivalent to "taking a measurement."
Design
The basic elements of a modern sounding rocket are a solid-fuel rocket motor and a science payload. In certain sounding rockets, the payload may be nothing more than a smoke trail as in the Nike Smoke, which is used to determine wind directions and strengths more accurately than may be determined by weather balloons. A sounding rocket, such as the Nike-Apache, may deposit sodium clouds to observe very high altitude winds. Larger, higher altitude rockets have multiple stages to increase altitude and payload capability. A flight of a sounding rocket has several parts. During the boost phase, the rocket burns its fuel to accelerate upwards, nearly vertically. Once the motor burns all of its fuel, the rocket may fall away to allow the payload to coast along a ballistic trajectory. The path of the rocket is then nearly parabolic, being influenced only by gravity and small wind resistance at high altitudes. The speed decreases near the highest point of the flight, the apogee, allowing the payload to linger around this point for a few minutes. Lastly, the rocket descends, sometimes deploying a drag source such as a small balloon or a parachute. The average flight time is less than 30 minutes; usually between 5 and 20 minutes. Sounding rockets have used balloons, aeroplanes, and artillery as first stages. Project Farside used a rockoon composed of a 106,188-cubic-metre (3,750,000 ft3) balloon, lifting a four-stage rocket. Sparoair was launched in the air from Navy F4D and F-4 fighters. Sounding rockets can also be launched from artillery guns, such as Project HARP's 5-, 7- and 15-inch (130, 180 and 380 mm) guns, sometimes having additional rocket stages.
Development history The earliest sounding rockets used liquid propellant, such as the WAC Corporal, Aerobee, and Viking. The German-built V-2 was used in both the US and the USSR immediately after World War II. Starting in the 1950s, inexpensive surplus military boosters such as those used by the Nike, Talos, Terrier, and Sparrow were used. Since the 1960s, most sounding rockets have been specifically designed for the purpose, such as the Canadian solid-fuel Black Brant (first flown in 1959). By the early 1960s, the sounding rocket was considered established technology.
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