Sounding Rockets Overhead — Arcas and Loki / Marquardt Dart

Each of these single-stage rockets could not get to space, but they were used in large numbers for scientific study and measurement of winds aloft. They are also a common design in the high-power model rocketry community (examples below), but these are the original rockets from the late 50’s.

• Arcas

A 1957 Stanford Research Institute study proposed a small single-stage sounding rocket to measure high-altitude winds to determine the spread of radioactive fallout. The U. S. Office of Naval Research and the Air Force Research Center awarded Atlantic Research Corporation (ARC) a contract to develop this sounding rocket, known as “Kitty” in January 1958. ARC designed the Arcas rocket which became operational in 1969. It is quite rare; I have only seen them at the Smithsonian and Air Force Museums.

The Arcas sounding rocket is an unguided vehicle with a diameter of 4.5 inches designed to carry payloads of 12 pounds or less to heights in excess of 200,000 feet when launched from sea level. Radar tracking provided altitude and wind information to correlate with instruments in the nosecone. Later payloads included falling spheres (tracked by radar to precisely measure drag), ozone measurements, and small biological experiments.

The Arcas was powered by a 29-second slow-burning SR45-AR-1 solid-propellant motor. This caused much less stress on the payload than, say, the very short high-acceleration burn of the contemporary Loki-Dart type sounding rockets (like the one seen here). Since the rocket diameter was larger than the nozzle diameter of the engine, the aft end of the rocket ended in a tapered “boat tail”, to decrease the subsonic drag.

During 1965 Goddard began using the Arcas sounding rocket, a vehicle first used back in 1958 by the Navy and in 1959 by Langley Research Center and Wallops. The Arcas was an inexpensive rocket, costing only about $2000 per round.

Many derivatives were built, until the basic meteorological profiling task was taken over by the even cheaper Super Loki in the late 1960’s which brings us to the:

• Loki Dart — Marquardt version

After WW II, the U.S. tried to develop an antiaircraft rocket using a dart that drag-separated from the main rocket body at engine burnout, freeing the dart to coast upward without the drag of the wider-diameter silver booster to reach higher altitudes. The black upper “stage” has no motor, it is just a heavy dead-weight mass that slides easily off the silver solid-rocket booster. Loki flew the first dart in 1951.

In order to obtain the necessary accuracy, it was necessary to fire thousands of rockets in order to prepare artillery-like ‘firing tables’. JPL eventually fired 3,544 Loki’s at White Sands during the testing program. These tests demonstrated that the launch of one rocket affected the flight path of the ones behind it, making the dispersion too large to be a useful weapon. Although this problem was studied in depth, it appeared there was no obvious solution. The Army eventually gave up on Loki in September 1955, in favor of the Nike Ajax missile, which had recently reached operational status.

In 1955, the U.S. Navy took many of the already-completed Loki’s and replaced the explosive warhead with a chaff dispenser (strips of radar-reflective foil). These WASP rockets were fired from ships from a helical launcher strapped to the five inch gun pointing directly upward, and the chaff deployed at apogee by an explosive charge. The USAF also used the Loki for this role, assigning it the name XRM-82.

Other companies developed additional versions, including this Marquardt Rocksonde. In 1956, the Cooper Development Corporation (CDC) received a contract for large scale production of sounding rockets of the Loki-Dart (PWN-1) type for use as weather research vehicles. Marquardt acquired Cooper in 1958. The U.S. Air Force assigned the designation XRM-88 to a Rocksonde 200 variant with chaff payload. And the RF signal was received by an AN/FMQ-6 ground-based radiosonde to obtain wind speed and direction data from high altitudes.

Like the Super Loki, the XRM-88 could reach an altitude of about 60 km / 37 miles / 200K ft. with a fast 1.9-second booster burn. This takes it to Mach 5, spin stabilized from the barrel launcher at 1000 RPM (which also allows for diminutive fins).