Delta (rocket family)

Delta Family
Delta EELV family.svg
Delta II through Delta IV
RoleExpendable launch system with various applications
ManufacturerUnited Launch Alliance

Delta is an American versatile family of expendable launch systems that has provided space launch capability in the United States since 1960. There have been more than 300 Delta rockets launched, with a 95% success rate. Only the Delta IV remains in use as of 2018. Delta rockets are currently manufactured and launched by the United Launch Alliance.

Delta origins

Delta rocket on display at the Goddard Space Flight Center in Maryland

The original Delta rockets used a modified version of the PGM-17 Thor, the first ballistic missile deployed by the United States Air Force, as their first stage. The Thor had been designed in the mid-1950s to reach Moscow from bases in Britain or similar allied nations, and the first wholly successful Thor launch had occurred in September 1957. Subsequent satellite and space probe flights soon followed, using a Thor first stage with several different upper stages. The fourth upper stage used on the Thor was the Thor "Delta," delta being the fourth letter of the Greek alphabet. Eventually the entire Thor-Delta launch vehicle came to be called simply, "Delta."[1][2]

NASA intended Delta as "an interim general purpose vehicle" to be "used for communication, meteorological, and scientific satellites and lunar probes during '60 and '61". The plan was to replace Delta with other rocket designs when they came on-line. From this point onward, the launch vehicle family was split into civilian variants flown from Cape Canaveral which bore the Delta name and military variants flown from Vandenberg Air Force Base which used the more warlike Thor name. The Delta design emphasized reliability rather than performance by replacing components which had caused problems on earlier Thor flights; in particular the trouble-prone inertial guidance package made by AC Spark Plug was replaced by a radio ground guidance system, which was mounted to the second stage instead of the first. NASA made the original Delta contract to the Douglas Aircraft Company in April 1959 for 12 vehicles of this design:

  • Stage 1: Modified Thor IRBM with a Block I MB-3 engine producing 152,000 lbf (680 kN) thrust. (LOX/RP1 turbopump, gimbal mounted engine, two verniers for roll control)
  • Stage 2: Modified Able. Pressure fed UDMH/nitric acid powered Aerojet AJ-10-118 engine producing 7,700 lbf (34 kN). This reliable engine cost $4 million to build and is still flying in modified form today. Gas jet attitude control system.
  • Stage 3: Altair. A spin-stabilized (via a turntable on top of the Able) at 100 rpm by two solid rocket motors before separation. One ABL X-248 solid rocket motor provided 2,800 lbf (12 kN) of thrust for 28 seconds. The stage weighed 500 pounds (230 kg) and was largely constructed of wound fiberglass.

These vehicles would be able to place 650 pounds (290 kg) into a 150 to 230 miles (240 to 370 km) LEO or 100 pounds (45 kg) into GTO. Eleven of the twelve initial Delta flights were successful and until 1968, no failures occurred in the first two minutes of launch. The high degree of success achieved by Delta stood in contrast to the endless parade of failures that dogged West Coast Thor launches. The total project development and launch cost came to $43 million, $3 million over budget. An order for 14 more vehicles was made before 1962.

Thor-Delta flights

No. Date Payload Site Outcome Remarks
1 May 13, 1960 Echo 1 CCAFS LC 17A failure Launch at 9:16 p.m. GMT. Good first stage. Second-stage attitude control system failure. Vehicle destroyed.
2 August 12, 1960 Echo 1A success Payload placed into 1,035 miles (1,666 km), 47 degree inclination orbit.
3 November 23, 1960 TIROS-2 success
4 March 25, 1961 Explorer-10 success 78 pounds (35 kg) payload placed into elliptical 138,000 miles (222,000 km) orbit.
5 July 12, 1961 TIROS-3 success
6 August 16, 1961 Explorer-12 success Energetic Particle Explorers. EPE-A.[3] Highly elliptical orbit.
7 February 8, 1962 TIROS-4 success
8 March 7, 1962 OSO-1 success Orbiting Solar Observatory. 345 miles (555 km), 33 degree orbit.
9 April 26, 1962 Ariel 1 success Ariel 1 was later seriously damaged by the Starfish Prime nuclear test.
10 June 19, 1962 TIROS-5 success
11 July 10, 1962 Telstar 1 success Also later damaged by the Starfish Prime high altitude nuclear event.
12 September 18, 1962 TIROS-6 success
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