Algol (rocket stage)
![]() Scout D-1 rocket that used the Algol rocket stage at the Smithsonian Air and Space Museum, 2012. Algol stage and interstage are visible | |
Function | Rocket stage |
---|---|
Manufacturer | Aerojet Rocketdyne |
Size | |
Height | 9.4 metres (31 ft) |
Mass | 1,900 kilograms (4,200 lb) |

The Algol family of solid-fuel rocket stages and boosters is built by Aerojet (now Aerojet Rocketdyne) and used on a variety of launch vehicles. It was developed by Aerojet from the earlier Jupiter Senior and the Navy Polaris programs.[1][2] Upgrades to the Algol motor occurred from 1960 until the retirement of the Scout launch vehicle in 1994.
The Algol family use solid propellant fuel with a loaded mass of 10,705 kg, and produces 470.93 kN of thrust. The motor has a specific Impulse of 236 seconds in a vacuum environment. Variations Algol I, I-D, II, II-A, II-BA popular rating was 40KS-115,000 (52,000 kgf for 40 seconds), also known as Senior.
They were initially developed as the first-stage of propulsion for the Scout rocket, with the design being based on the UGM-27 Polaris, a submarine-launched ballistic missile developed for the United States Navy at the Jet Propulsion Laboratory.[3][4]
Algol 1 (XM-68)
[edit]Algol 1 (XM-68)
[edit]This rocket design started as the Polaris test motor, 31 feet in length with a 40 inches (1.0 m) diameter steel case,[5] and 86,000 lbf of thrust. The eventual UGM-27 Polaris A-1 was larger, 28.5 feet (8.7 m) in length and 54 inches (1.4 m) in diameter.[6]
The Algol 1 was first used for a successful suborbital launch of a Scout X-1 rocket on September 2, 1960.[7] The rocket started as a UGM-27 Polaris test motor with a 40-inch diameter, the largest solid motor ever tested at the time. It had a nominal performance rating of 40 seconds duration and 45,000 kgf thrust. It was 19.42 feet (5.92 m) long, 2.6 feet (0.79 m) in diameter.[8] Later versions for Scout D scaled to 1.14 m (45 in) in diameter.
Specifications
[edit]These are the basic specifications for the Algol 1 engine:[8]
- Gross mass: 10,705 kg (23,600 lb)
- Unfuelled mass: 1,900 kg (4,100 lb)
- Height: 9.12 m (29.92 ft)
- Diameter: 1.01 m (3.31 ft)
- Thrust: 470.90 kN (105,863 lbf)
- Specific impulse: 236 s
- Specific impulse sea level: 214 s
- Burn time: 40 s
Algol 1-A
[edit]Used on the Scout X (Cub Scout) test flight flown April 18, 1960.[9] served as prototype vehicle for eventual Scout rocket.
Algol 1-B
[edit]Used on Scout X-1, RM-89 Blue Scout I, and RM-90 Blue Scout II.[9]
Algol 1-C
[edit]Used on the Scout X-1A.[9] After this single flight, the Scout X-2 with Algol 1-D replaced this prototype.
Algol 1-D
[edit]It was first used on the Scout X-2 on March 29, 1962.[9] It continued to be used on Scout X-2 and Scout X-2M launches until 1963. The same year, it was also used on the Little Joe II Qualification Test Vehicle.

Specifications
[edit]These are the basic specifications for the Algol 1-D engine:[10]
- Gross mass: 10,700 kg (23,600 lb)
- Unfuelled mass: 1,200 kg (2,600 lb)
- Height: 9.40 m (30.8 ft)
- Diameter: 1.02 m (3.3 ft)
- Thrust: 440.00 kN (98,910 lbf)
- Burn time: 44 s
Algol II
[edit]
The Algol 2 (Algol II) series was first flown in 1962. It was used a first stage on Scout A, Scout B, Scout X-3 and Scout X-4.
Algol II was proposed as a strap-on motor for the 3BAS2 configuration of Titan 3B rocket proposed by Martin in the mid-1960s. It would have been used for deep space missions with a Centaur upper stage and strap-on for liftoff thrust augmentation. It was never flown. It was also proposed for the Athena RTX program in 1969, losing to Thiokol.
Algol II-A
[edit]The Algol II-A was introduced in 1963 using the Aerojet 40 KS motor. It first flew on Scout X-3 in 1963.[9]
Algol II-B
[edit]The Algol II-B was created after an Algol II-A flight failure, the nozzle was designed and designate the II-B model. It first flew on Scout X-4.[9]
Specifications
[edit]These are the basic specifications for the Algol II-B engine:[11]
- Gross mass: 10,700 kg (23,500 lb)
- Unfuelled mass: 1,170 kg (2,570 lb)
- Height: 9.10 m (29.80 ft)
- Diameter: 1.02 m (3.34 ft)
- Thrust: 400.00 kN (89,920 lbf)
- Burn time: 80 s
Algol II-C
[edit]The Algol II-C flew on Scout A-1 and B-1.[9] Scout A-2, B-2, C and 2 versions planned for Algol II-C were never used.
Specifications
[edit]These are the basic specifications for the Algol II-C engine:[12]
- Gross mass: 10,800 kg (23,800 lb)
- Unfuelled mass: 1,200 kg (2,600 lb
- Height: 9.10 m (29.80 ft)
- Diameter: 1.02 m (3.34 ft)
- Thrust: 436.00 kN (98,016 lbf)
- Burn time: 76 s
See also
[edit]References
[edit]- ^ Hammond, Walter (1999). Space Transportation: A Systems Approach to Analysis and Design. Reston, VA: American Institute of Aeronautics and Astronautics. doi:10.2514/4.862380. ISBN 978-1-56347-032-5.
- ^ "Scout Launch Vehicle Program". NASA.
- ^ "NASA'S SCOUT LAUNCH VEHICLE". NASA GSFC. Archived from the original on 2008-05-10.
- ^ "SERGEANT". Redstone Arsenal. Archived from the original on 2008-06-12.
- ^ "Algol". www.astronautix.com. Retrieved 2025-06-17.
- ^ "Polaris A1". Federation of American Scientists. May 30, 1997. Retrieved April 1, 2023.
- ^ "TSE – Scout". The Satellite Encyclopedia.
- ^ a b "Algol-1". astronautix.com. Retrieved April 1, 2023.
- ^ a b c d e f g "Scout (Algol-1, -2 based)". Gunter's Space Page. Retrieved 2025-06-17.
- ^ "Algol 1D". www.astronautix.com. Retrieved 2025-06-17.
- ^ "Algol 2B". www.astronautix.com. Retrieved 2025-06-17.
- ^ "Algol 2C". www.astronautix.com. Retrieved 2025-06-17.