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by Jean-Jacques Serra

Castor 1 & 2

The Thiokol Castor booster, used since 1960 as second stage for Scout were derived from the tactical Sergeant missile. This missile, built by Sperry, was 10.6 m long for 79 cm diameter and weighed 4.5 tons. Its range was: 45 to 140 km.
The Castor 1 was used by all the Scout-X version and was replaced my Castor 2 (TX354-3) when Scout-A1 was introduced in 1965.


Designation Length (m) Diameter (m) Mass (t) Main engine Thrust (kN) Main engine SI (sec.)
Castor 1 (TX33) 5.92 0.79 3.85 286 27.4
Castor 2 (TX354) 5.96-6.27 0.79 4.32-4.42 259-275 37
Castor 4 (TX526) 9.07 1.02 10.53 428 53.9
Castor 4A (TX780) 8.09-920 1.02 11.58 436-476 53.1
Castor 4B (TX859) 8.98 1.02 11.48 429 60.9

From 1963 on, the Thor first-stage-based launchers were equipped with Castor solid boosters to get the TAT (Thrust Augmented Thor). The TAT Agena was launched in 1963, the TAT Delta (or TAD) in 1964. Those Castor-1 & Castor-2 boosters were then used by groups of 3, 6 (Delta M6) and finally 9 (Delta 900). The last models were used from 1975 on by the Japanese N1, N2 and H1 rockets.

The boosters of Sergeant missiles are still used by OSC for Starbird (targets for the ERINT program), LCLV (Low Cost Launch Vehicle) and Storm (targets for the THAAD program).

Castor 4 & 4A

After 1975, when the only Thor first stage-based was the Delta (3900 series) the Castor-2 were replaced by Castor-4 (TX526) of 1.02 m diameter that we herited from the Athena-H sounding rocket. In 1989 an enhanced version was introduced on the Delta 2 (6900 series): Castor-4A (TX780) weighing 11.6 tons. Two pairs of Castor-4A boosters also equip the Atlas 2 (2AS version) since 1993.

The light launcher Conestoga was designed from associated Castor-4. The most powerful version, Conestoga 1620, is made of 6 Castor-4 (4 Castor-4B with deployable nozzle and 2 Castor-4A with fixed nozzle) surrounding a Castor-4B. Four Castors are fired at launch time (1st stage), 2 are ignited then (2nd stage) and the central Castor-4 acts as the third stage. The top stage is a Star-48, also built by Thiokol.

The Castor-4A boosters are also used by OSC for Prospector sounding rockets since 1991. The Maxus rocket (German & Swedish) is the largest sounding rocket fired from Europe (Kiruna). It is also made of a Castor-4B; with 12.3 tons and 500 kg payload.

Castor 120 GT

The Castor-120 is a large solid fuel booster derived from the MX Peacekeeper (TU 903) missile. This booster is 8.89 m long and 2.34 m diameter. It weighs about 54 tons. Castor-120 was modified to provide a smaller acceleration than the TU 903: 1546 kN (in vacuum) during 86 seconds.

Two light launchers are based on it: Taurus from OSC (with the 3 Hercules stages of Pegasus) and Athena from LM (with an Orbus 21 UTC/CSD).

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