# Thor-Ablestar

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.
| Date/Time (UTC) | S/N | Launch Site | Payload | Function | Outcome |
| 1960-04-13 12:02:36 | Thor 257 Ablestar 002 | CCAFS LC-17B | Transit 1B | Navigation | Success, maiden flight of Thor-Ablestar |
| 1960-06-22 05:54 | Thor 281 Ablestar 003 | CCAFS LC-17B | Transit 2A, GRAB-1 (Solrad 1) | Navigation, ELINT | Success |
| 1960-08-18 19:58 | Thor 262 Ablestar 004 | CCAFS LC-17B | Courier 1A | Communications | Failure (Premature first stage cutoff. RSO T+150 seconds.) |
| 1960-10-04 17:50 | Thor 293 Ablestar 005 | CCAFS LC-17B | Courier 1B | Communications | Success |
| 1960-11-30 19:50 | Thor 283 Ablestar 006 | CCAFS LC-17B | Transit 3A, GRAB-2 (Solrad-2) | Navigation, ELINT | Failure (Premature Thor cutoff. RSO. Debris fell in Cuba.) |
| 1961-02-22 03:45 | Thor 313 Ablestar 007 | CCAFS LC-17B | Transit 3B, LOFTI-1 | Navigation, Technology | Success |
| 1961-06-29 04:22 | Thor 315 Ablestar 008 | CCAFS LC-17B | Transit 4A, Injun 1, GRAB-3 (Solrad 3) | Navigation, Ionospheric, ELINT | Success |
| 1961-11-15 22:26 | Thor 305 Ablestar 009 | CCAFS LC-17B | Transit 4B, TRAAC | Navigation | Success, Transit Research and Attitude Control |
| 1962-01-24 09:30 | Thor 311 Ablestar 010 | CCAFS LC-17B | LOFTI-2, SECOR, GRAB-4 (Solrad 4), Injun 2, SURCAL 1 | Technology, Geodesy, ELINT, Ionospheric, Calibration | Failure (second stage insufficient thrust) |
| 1962-05-10 12:06 | Thor 314 Ablestar 011 | CCAFS LC-17B | ANNA 1A | Geodesy | Failure (second stage failed to ignite) |
| 1962-10-31 08:08 | Thor 319 Ablestar 012 | CCAFS LC-17A | ANNA 1B | Geodesy | Success, final flight of Thor DM-21 Ablestar |
| 1964-04-21 18:50 | Thor 379 Ablestar 014 | VAFB LC-75-1-1 | Transit 5BN-3, Transit 5E-4 | Navigation | Failure |
| 1964-10-06 17:04:21 | Thor 423 Ablestar 016 | VAFB LC-75-1-2 | OPS 5796 (Transit O-1), Dragsphere 1, Dragsphere 2 | Navigation | Success |
| 1964-12-13 00:08:10 | Thor 427 Ablestar 017 | VAFB LC-75-1-2 | OPS 6582 (Transit O-2), Transit 5E-5 | Navigation | Success |
| 1965-03-11 13:39 | Thor 440 Ablestar 018 | VAFB LC-75-1-1 | OPS 7087 (Transit O-3), SECOR 2 | Navigation, Geodesy | Success |
| 1965-06-24 22:35 | Thor 447 Ablestar 019 | VAFB LC-75-1-1 | OPS 8480 (Transit O-4) | Navigation | Success |
| 1965-08-13 22:11 | Thor 455 Ablestar 020 | VAFB LC-75-1-1 | OPS 8464 (Transit O-5), Dodecapole 2, Tempsat 1, Surcal 5, Long Rod 1, Calsphere 2 | Navigation, Calibration | Success, final flight of Thor-Ablestar |