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 used to launch instruments from 48 to 145 km above the surface of the Earth, the altitude generally between weather balloons and satellites; the maximum altitude for balloons is about 40 km and the minimum for satellites is approximately 121 km. Certain sounding rockets have an apogee between 1,000 and 1,500 km, such as the Black Brant X and XII, which is the maximum apogee of their class. Sounding rockets often use military surplus rocket motors. NASA routinely flies the Terrier Mk 70 boosted Improved Orion, lifting 270–450-kg (600–1,000-pound) payloads into the exoatmospheric region between 97 and 201 km.
A Black Brant XII being launched from Wallops Flight Facility
Sample payloads for sounding rockets
A Loki-Dart (foreground) on display at the White Sands Missile Range rocket garden
A sub-orbital spaceflight is a spaceflight in which the spacecraft reaches outer space, but its trajectory intersects the surface of the gravitating body from which it was launched. Hence, it will not complete one orbital revolution, will not become an artificial satellite nor will it reach escape velocity.
Science and Mechanics cover of November 1931, showing a proposed sub-orbital spaceship that would reach an altitude 700 miles (1,100 km) on its one hour trip from Berlin to New York.
The X-15 (1958–1968) was launched to an altitude of 13.7 km by a B-52 mothership, lifted itself to approximately 100 km, and then glided to the ground.