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The launch of a Thor-Ablestar 2 with a Transit satellite.
Function	Orbital carrier rocket
Manufacturer	Douglas / Aerojet
Country of origin	United States
Size
Height	29 metres (95 ft)
Diameter	2.44 metres (8 ft 0 in)
Mass	53,000 kilograms (117,000 lb)
Stages	2
Capacity
Payload to 1100km LEO
Mass	150 kilograms (330 lb)
Associated rockets
Family	Thor
Comparable	Delta
Launch history
Launch sites	LC-17, Canaveral LC-75-1, Arguello
Total launches	19
Success(es)	12
Failure(s)	5
Partial failure(s)	2
First flight	13 April 1960
Last flight	13 August 1965
First stage – Thor
Powered by	1 MB-3-1
Maximum thrust	760.64 kilonewtons (171,000 lbf)
Specific impulse	285 sec
Burn time	164 seconds
Propellant	RP-1/LOX
Second stage – Ablestar
Powered by	1 AJ-10
Maximum thrust	36.02 kilonewtons (8,100 lbf)
Specific impulse	280 sec
Burn time	296 seconds
Propellant	HNO3/UDMH
[edit on Wikidata]

The Thor-Ablestar, or Thor-Able-Star, also known as Thor-Epsilon was an early American expendable launch system consisting of a PGM-17 Thor missile, with an Ablestar upper stage. It was a member of the Thor family of rockets, and was derived from the Thor-Able.

The Ablestar second stage was an enlarged version of the Able, which gave the Thor-Ablestar a greater payload capacity compared to the Thor-Able. It also incorporated restart capabilities, allowing a multiple-burn trajectory to be flown, further increasing payload, or allowing the rocket to reach different orbits. It was the first rocket to be developed with such a capability and development of the stage took a mere eight months.

Two versions were built; the Thor-Ablestar 1, with a DM-21 Thor and an AJ-10-104 second stage engine, and the Thor-Ablestar 2, which had a DSV-2A Thor first stage, and an uprated AJ-10-104D engine on the second stage. Thor-Ablestar 1 launches occurred from LC-17 at Cape Canaveral, and Thor-Ablestar 2 rockets were launched from LC-75-1 at Vandenberg Space Force Base (now designated SLC-2).

Launches

Nineteen Thor-Ablestar were launched between 1960 and 1965, of which four failed, and a fifth resulted in a partial failure, as only one of two payloads separated from the upper stage.

The first failure was the launch of Courier 1A, an experimental communications satellite, on 19 August 1960 when the first stage shut down 30 seconds earlier than planned and was destroyed by the Range Safety Officer.

On 30 November, another launch involving a Transit satellite failed in practically identical fashion. This episode nearly created an international incident as parts of the Thor landed in Cuba. War was threatened. Cuban leader Fidel Castro subsequently sold off the Thor's engine to the Soviets and the Chinese received its thrust vectors, which ended up proving valuable to the latter's development of a ballistic missile capability. To prevent this from happening again, future Thor Ablestar launches had their flight paths modified to avoid passing over Cuba.

The launch of a Transit satellite on 22 February 1961 was successful, but its companion Lofti satellite failed to separate from the second stage.

On 29 June 1961, a Thor-Ablestar successfully inserted a Transit-4A into orbit, but two hours later the Ablestar exploded for unknown reasons into hundreds of pieces, which remained in orbit. This is the first known artificial object to break up unintentionally in space.

The third launch failure occurred on 24 January 1962 when the second stage produced insufficient thrust to achieve orbital velocity for several piggybacked satellites. The fourth and final failure was the launch of an Anna geodetic satellite on 10 May 1962 when the second stage completely failed to ignite.

See also

• List of Thor and Delta launches (1960–1969)

References

1. ^ Krebs, Gunter. "Thor Able-Star". Gunter's Space Page. Retrieved 30 November 2008.
2. ^ Wade, Mark. "Delta". Encyclopedia Astronautica. Archived from the original on 17 August 2013. Retrieved 30 November 2008.
3. Orbital Debris: A Chronology (PDF). NASA JSC. January 1999. p. 18. Archived from the original (PDF) on 1 September 2000. Retrieved 13 February 2016. Two hours after separating from the U.S. Transit 4-A satellite, its Able Star upper stage becomes the first known artificial object to break up unintentionally in space. The cause of the explosion is unknown. The event produces at least 294 trackable pieces, more than tripling the number of known satellites of Earth.
4. "A-Okay So Far: Glenn, Atlas Ready". The Gazette. Montreal, QC. Associated Press (AP). 25 January 1962. p. 1. Retrieved 29 December 2015.

v t e Thor and Delta rockets
PGM-17 Thor Thor family Delta family
Rockets	Thor Thor Thor-Able Thor-Ablestar Thor-Agena Thor-Burner Thor-Delta Thor DSV-2 Thor DSV-2U Thorad-Agena Delta Alphabetical Delta A Delta B Delta C Delta D Delta E Delta F Delta G Delta J Delta L Delta M Delta N Numerical Delta 0100 Delta 1000 Delta 2000 Delta 3000 Delta 4000 Delta 5000 Delta 6000 Delta 7000 Delta 8000 Delta 9000 Modern Delta II Delta III Delta IV Delta IV Heavy Export N-I N-II H-I
Launch sites	Canaveral (S)LC-17 LC-18B SLC-37B Johnston LE-1 LE-2 Tanegashima Osaki Vandenberg SLC-1 SLC-2 SLC-3 SLC-6 SLC-10 Bases Bardney Breighton Caistor Carnaby Catfoss Coleby Grange Driffield Feltwell Folkingham Full Sutton Harrington Hemswell Ludford Magna Melton Mowbray Mepal North Luffenham North Pickenham Polebrook Shepherds Grove Tuddenham
Components	Boosters Castor-1 Castor-1 Castor-4 Castor-4A CBC GEM-40 GEM-46 GEM-60 First stages Common Booster Core Upper Stages Delta Delta-A Delta-D Delta-E Delta-F Delta-K Delta-P DCSS Other Able Ablestar Agena Altair Burner FW-4D IABS PAM-D Star UM-129 Engines AJ10 B-8048 B-8081 B-8096 LE-5 LR-79 R-4D RL10 RS-27 RS-68 TR-201
Manufacturers	Rocket Douglas McDonnell Douglas Boeing United Launch Alliance Engines Aerojet Alliant Rocketdyne Thiokol TRW
Launches	1957–1959 1960–1969 1970–1979 1980–1989 1990–1999 2000–2009 2010–2019 2020–2024

• Thor (rocket family)
• Spacecraft that broke apart in space