Thor DSV-2U

Thor DSV-2U

Launch of the last Thor DSV-2U carrying DMSP-5D1 F5
Function	Expendable launch system
Country of origin	United States
Launch history
Status	Retired
Launch sites	Vandenberg SLC-10W
Total launches	5
Successes	4
Failures	1
First flight	1976-09-11
Last flight	1980-07-15

The Thor DSV-2U or Thor LV-2F Star-37XE Star-37S-ISS was an American expendable launch system used to launch five DMSP weather satellites between 1976 and 1980. It was a member of the Thor family of rockets, and a derivative of the Thor DSV-2.

The first stage was a Thor missile in the DM-19 configuration. A Star-37XE was used as the second stage, and the third stage was a Star-37S-ISS. All five launches were conducted from Space Launch Complex 10W at the Vandenberg Air Force Base. The final launch on July 14, 1980 of a DMSP 5D satellite failed.

Thor boosters launched from SLC-10W used an erector system to hoist them up to the pad. While common on Soviet launch vehicles, this method was unusual in the US space program. Thor 304 had been erected on the pad a few weeks before launch, and during this step, a connecting pin in the erector broke and sent the rocket falling back down to ground level. Launch crews examined the Thor for damage, but could not find any outward indication of it. The booster passed routine preflight systems checks and liftoff took place at 6:22 PM PST on July 14. Shortly after liftoff, the Thor's telemetry system failed, but weather conditions and visibility were excellent, and the booster could be tracked visually for over two minutes. Telemetry from the DMSP satellite indicated that it was operating properly. SECO took place on time, as did the second stage burn. Third stage burn began, and then after about four seconds, all telemetry abruptly ceased. The initial assumption was that the third stage exploded, and initial Air Force press releases about the launch stated such. However, radar tracking showed that the third stage motor continued operating as it drove the DMSP into the Pacific Ocean. The investigation board concluded that connectors in the electrical interface between the second and third stage had been jolted loose by the erector mishap several weeks earlier. After second stage burnout, staging failed to take place due to the misaligned connectors, and the third stage motor thus fired with the spent second stage still attached to it. The force from the third stage motor burning managed to tear the second stage free, but in doing so, it ripped out wiring in the base of the third stage, which shorted out the guidance computer and caused it to direct the stage and spacecraft down into the ocean. Much like the DMSP failure in 1976, the incident was attributed to poor program management.