Delta II

Delta II was an expendable launch system, originally designed and built by McDonnell Douglas.

Quick Facts About the Delta 2000.

- Type: Expendable launch system.

- Origin : United states.

- In service : Delta 6000: 14 February 1989 - 24 July 1992. Delta 7000: 26 November 1990 - Delta 7000: 15 September 2018. Delta 7000H: 8 July 2003 - Delta 7000H: 10 September 2011.

- Mass : 152,000–286,000 kg (335,000–631,000 lb).

- Length/Height : 38.9 m (128 ft).

- Diameter : 2.44 m (8 ft).

- Payload to LEO : 2,800–6,140 kg (6,170–13,540 lb).

- Payload to GTO : 1,140–2,190 kg (2,510–4,830 lb).

- Payload to HCO : 806–1,519 kg (1,777–3,349 lb).

- Propellant: Boosters: Solid. First stage: RP-1 / LOX. Second stage: N2O4 / Aerozine 50.

- Engines: Boosters:(6000 series) 9 x Castor 4A with thrust of 478 kN (107,000 lbf), (7000 series) 3, 4, or 9 GEM 40 with a thrust of 492.9 kN (110,800 lbf), (7000 Heavy) 9 GEM 46 with a thrust of 628.3 kN (141,200 lbf), First stage: 1 RS-27 (6000 series) or RS-27A (7000 series) with thrust of 1,054 kN (237,000 lbf), Second stage: 1 AJ10-118K with thrust of 43.6 kN (9,800 lbf), Third stage(optional): 1 x Star 48B with thrust of 66 kN (15,000 lbf).

Delta II was part of the Delta rocket family and entered service in 1989. Delta II vehicles included the Delta 6000, and the two later Delta 7000 variants ("Light" and "Heavy"). The rocket flew its final mission ICESat-2 on 15 September 2018, earning the launch vehicle a streak of 100 successful missions in a row, with the last failure being GPS IIR-1 in 1997.

The first stage of the Delta II was propelled by a Rocketdyne RS-27 main engine burning RP-1 and liquid oxygen. This stage was technically referred to as the "Extra-Extended Long Tank Thor", a derivative of the Thor ballistic missile as were all Delta rockets until the Delta IV. The RS-27 used on the 6000-series Delta II produced 915 kN, while the upgraded RS-27A used by the 7000-series produced 1,054 kN.The stage was 26 meters long and 2.4 meters wide, weighted over 100 t when fueled, and burned for 260 seconds. In addition, two LR101-NA-11 vernier engines provided guidance for the first stage.

For additional thrust during launch, the Delta II used solid boosters. For the 6000-series, Delta II used Castor 4A boosters, while the 7000-series used Graphite-Epoxy Motors manufactured by ATK. The vehicle could be flown with three, four, or, most commonly, nine boosters. When three or four boosters were used, all ignited on the ground at launch, while models that used nine boosters would ignite six on the ground, then the remaining three in flight after the burnout and jettison of the first six.

The second stage of Delta II was the Delta-K, powered by a restartable Aerojet AJ10-118K engine burning hypergolic Aerozine-50 and N2O4. These propellants are highly toxic and corrosive, and once loaded the launch had to occur within approximately 37 days or the stage would have to be refurbished or replaced. This stage also contained a combined inertial platform and guidance system that controlled all flight events. The Delta-K stage was 6 meters long and 2.4 meters wide, containing up to 6 t of propellant, and burned for up to 430 seconds.

For low Earth orbit, Delta II was not equipped with a third stage. Payloads bound for higher energy orbits such as GTO or to reach Earth escape velocity for trans-Mars injection or other destinations beyond Earth used a solid propellant third stage. This stage was spin-stabilized and depended on the second stage for proper orientation prior to stage separation, but was sometimes equipped with a nutation control system to maintain proper spin axis. It also included a yo-weight system to induce tumbling in the third stage after payload separation to prevent recontact, or a yo-yo de-spin mechanism to slow the rotation before payload release.

Credit/References and for further info please see:

Delta II image
NASA launches its second Mars Exploration Rover, Opportunity,. Photo Credit : NASA Kennedy Space Center (NASA-KSC), Public domain, via Wikimedia Commons.

Delta II image
Schematic drawing rocket Delta II 7425 Launch Vehicle. Photo Credit : NASA Kennedy Space Center (NASA-KSC), Public domain, via Wikimedia Commons.