The Castor 1 was first used for a successful suborbital launch of a Scout X-1 rocket on September 2, 1960.
It was 19.42 feet (5.92 m) long, 2.6 feet (0.79 m) in diameter, and had a burn time of 27 seconds. Castor 1 stages were also used as strap-on boosters for launch vehicles using Thor first stages, including the Delta-D. (A Delta-D was used in 1964 to launch Syncom-3, the first satellite placed in a geostationary orbit.) Castor 1 stages were used in 141 launch attempts of Scout and Delta rockets, only 2 of which were failures. They were also used on some thrust-assisted Thor-Agena launchers. The last launch using a Castor 1 was in 1971.
The Castor 2 was an upgraded version of the Castor 1. It was first used on a Scout in 1965, and continued to be used on Scouts until the last Scout launch, in 1994. Castor 2 stages were also used as the strap-on boosters for the Delta-E, and for the Japanese-built N-I, N-II and H-I rockets. It retained the same diameter as the Castor 1, and was from 5.96 m to 6.27 m in length.
The Castor 4, along with its A and B variants, were expanded to 1.02 m in diameter. They were used as strap-ons on some Delta, Delta II, Atlas IIAS, and Athena launch vehicles. They were also planned to serve as the first stage of the Spanish Capricornio booster, however, no such flights occurred before the project was cancelled.
Castor 4B is used in the European Maxus Programme, with launches from Esrange in Sweden.
The H-IIA rockets flown by JAXA use either two or four strap-on boosters developed and produced by Alliant Techsystems. These boosters use motors which are modified versions of the Castor IVA-XL motor design. These motors are 38 feet long and approximately 48 inches in diameter.
A Castor 120 that will be used as Stage 0 of a Taurus XL rocket
An unrelated development, the Castor 120 is a derivative of the first-stage motor of the MX ("Peacekeeper") missile. "120" refers to the planned weight, in thousands of pounds, of the booster at project inception. The actual product turned out lighter than this, however. It was first used as the first-stage motor of Lockheed Martin's Athena I, and later the first and second stages of Athena II. After a test launch in August 1995, the first launch of a customer payload took place on August 22, 1997, when an Athena was used to launch the NASA Lewis satellite. In 2006 Orbital Sciences Corporation agreed to pay $17.5 million for the Castor 120 motors used in the Taurus XL launch vehicles for the Orbiting Carbon Observatory and Glory satellites.
The CASTOR 30 motor is based on the CASTOR 120® motor, which has flown on the Taurus I, Athena I and Athena II launch vehicles. The inaugural flight of the new motor occurred in April 2013 as the second stage on the Orbital SciencesAntares medium-lift rocket for International Space Station resupply missions.
The CASTOR 30 upper stage measures 138 inches in length and 92 inches in diameter, and it weighs 30,000 pounds. The motor is nominally designed as an upper stage that can function as a second or third stage as well, depending on the vehicle configuration.
The CASTOR 30XL solid rocket motor measures 236 inches in length and 92 inches in diameter, and it weighs approximately 58,000 pounds. The nozzle is eight feet long with a submerged design with a high performance expansion ratio (56:1) and a dual density exit cone.