There were at least three variants of the instrument payload, PWN-10, PWN-11, and PWN-12. The instruments consisted primarily of a thermistor to collect temperature, which was broadcast via a small radio operating in the 1680 MHz Meteorological Band. Altitude was tracked from the ground, by reflecting radar off the probe's "starute", a square mylar parachute and radar reflector, or with the PWN-10 by means of a ranging transponder. The SDC version was slightly heavier than the original Loki in order to improve stability during "cruise", which lowered maximum altitude by about 10,000 ft. Production of the Loki Datasonde started in 1966, and more than 20,000 were built until production ended in 1985. The Air Force requested a version that would not require radar tracking, and SDC responded by placing a transponder in the payload. This increased payload weight, and required the starute to be enlarged, further increasing launch weight. To reach the required altitudes, SDC developed a much larger booster, which also increased overall weight and further improved stability. The resulting Super Loki first flew in 1968, and since then 9,000 have been delivered. The Air Force Meteorologists and NASA's Observational Scientists desired higher apogees with the ROBINSphere payloads in the early 1970s. In 1972, Space Data completed the development of the Viper IIIA solid propellant rocket motor. This motor followed the design of the Super Loki nearly identically and provided apogees of ~120 km for the ROBINSphere. This higher apogee allowed for measuring the wind and atmospheric vertical profiles through the 110–95 km region that were unobtainable from the Super Loki boosted ROBINSphere. The ROBINSphere is a calibrated weight inflatable 1 meter diameter radar reflecting balloon, weighing in at about 150 grams. The weight is measured within one-half gram. A design change occurred in 1993 with a change in the elastomeric solid propellant with the more commonly available polymer, HTPB (hydroxyl terminated polybutadiene). This propellant design change occurred both in the Super Loki and the Viper IIIA. Orbital Sciences Corporation bought SDC in 1990. The production of the Super Loki and the Viper IIIA rocket boosted meteorological payloads continued until 2001 when the product line was abandoned. See also List of U.S. Army Rocket Launchers By Model Number 1.9KS2150 References External links https://web.archive.org/web/20070625000234/http://www.redstone.army.mil/history/pdf/loki/loki.pdf https://web.archive.org/web/20100102233831/http://astronautix.com/lvs/loki.htm Sounding rockets of the United States Space launch vehicles of the United States Anti-aircraft weapons