Delta II is an expendable launch system, originally designed and built by McDonnell Douglas. Delta II is part of the Delta rocket family and entered service in 1989. Delta II vehicles included the retired Delta 6000, and the two currently-used Delta 7000 variants ("Light" and "Heavy"). In 2018, the rocket is scheduled to fly its final mission, ICESat-2, which will earn the launch vehicle a streak of 100 successful missions in a row if successful.
|Manufacturer||United Launch Alliance (Boeing IDS)|
|Country of origin||United States|
|Cost per launch||US$51 million in 1987 (7920-10 mod.)|
|Height||38.2–39 m (125–128 ft)|
|Diameter||2.44 m (8 ft 0 in)|
|Mass||151,700–231,870 kg (334,440–511,190 lb)|
|Stages||2 or 3|
|Payload to LEO||2,700–6,100 kg (6,000–13,400 lb)|
|Payload to GTO||900–2,170 kg (1,980–4,780 lb)|
|Payload to HCO||1,000 kg (2,200 lb)|
Cape Canaveral SLC-17|
Vandenberg AFB SLC-2W
Delta 6000: 17
Delta 7000: 131
Delta 7000H: 6
Delta 6000: 17
Delta 7000: 129
Delta 7000H: 6
|Failures||1 (Delta 7000)|
|Partial failures||1 (Delta 7000)|
|Boosters (6000 Series) – Castor 4A|
|Thrust||478 kN (107,000 lbf)|
|Specific impulse||266 s|
|Burn time||56 s|
|Boosters (7000 Series) – GEM 40|
|No. boosters||3, 4, or 9|
|Thrust||492.9 kN (110,800 lbf)|
|Specific impulse||274 s|
|Burn time||64 s|
|Boosters (7000 Heavy) – GEM 46|
|Thrust||628.3 kN (141,200 lbf)|
|Specific impulse||278 s|
|Burn time||75 s|
|First stage – Thor/Delta XLT(-C)|
|Engines||1 RS-27 (6000 series) or RS-27A (7000 series)|
|Thrust||1,054 kN (237,000 lbf)|
|Specific impulse||302 s|
|Burn time||265 s|
|Second stage – Delta K|
|Thrust||43.6 kN (9,800 lbf)|
|Specific impulse||319 s|
|Burn time||431 s|
|Third stage – PAM-D (optional)|
|Thrust||66 kN (15,000 lbf)|
|Specific impulse||286 s|
|Burn time||87 s|
In the early 1980s, all United States expendable launch vehicles were planned to be phased out in favor of the Space Shuttle, which would be responsible for all government and commercial launches. Production of Delta, Atlas-Centaur, and Titan 34D had ended. The Challenger disaster of 1986 and the subsequent halt of Shuttle operations changed this policy, and President Ronald Reagan announced in December of that year that the Space Shuttle would no longer launch commercial payloads, and NASA would seek to purchase launches on expendable vehicles for missions that did not require crew or Shuttle support. McDonnell Douglas, at that time the manufacturer of the Delta family, signed a contract with the U.S. Air Force in 1987 to provide seven Delta IIs. These were intended to launch a series of GPS Block II satellites, which had previously been manifested for the Space Shuttle. The Air Force exercised additional contract options in 1988, expanding this order to 20 vehicles, and NASA purchased its first Delta IIs in 1990 for the launch of three Earth-observing satellites. The first Delta II launch occurred in 1989, with a Delta 6925 boosting the first GPS Block II satellite into a 20,000 km high orbit.
The first Delta II 7000-series flew in 1990, replacing the RS-27 engine of the 6000-series with the more powerful RS-27A. Additionally, the steel-cased Castor 4A solid boosters of the 6000 series were replaced with the composite-cased GEM 40. All further Delta II launches except three were of this upgraded configuration, and the 6000-series was retired in 1992.
McDonnell Douglas began Delta III development in the mid-90s as increasing satellite mass required more powerful launch vehicles. Delta III, with its liquid hydrogen second stage and more powerful GEM 46 boosters, could bring twice as much mass as Delta II to geostationary transfer orbit (GTO), but a string of two failures and one partial failure, along with the development of the much more powerful Delta IV, led to the cancellation of Delta III program. The upgraded boosters would still find use on the Delta II, leading to the Delta II Heavy.
On March 28, 2003, the Air Force Space Command began the process for deactivating the Delta II launch facilities and infrastructure at Cape Canaveral once the last of the second-generation GPS satellites were launched. However, in 2008, it instead announced that it wouild transfer all the Delta II facilities and infrastructure to NASA to support the launch of GRAIL in 2011.
The last GPS launch aboard a Delta II, and the final launch from SLC-17A at Cape Canaveral AFB was in 2009. The GRAIL Launch in 2011 marked the last Delta II Heavy launch and the last from Florida. The final five launches would all be from Vandenberg.
On July 16, 2012 NASA selected the Delta II to support the Orbiting Carbon Observatory (2014), Soil Moisture Active Passive/SMAP (2016), Joint Polar Satellite System/JPSS (2017), and ICESat-2 (2018) missions. This marked the final purchase of Delta IIs. OCO-2 was launched on July 2, 2014, SMAP was launched on January 31, 2015 and JPSS was launched on November 18, 2017. All of these launches were, or will be, placed into orbit from Complex 2 at Vandenberg Air Force Base in California.
The Delta II family has launched 155 times. Its only unsuccessful launches have been Koreasat 1 in 1995, and GPS IIR-1 in 1997. The Koreasat 1 launch was a partial failure caused by one booster not separating from the first stage, which resulted in the satellite being placed in a lower than intended orbit. By using reserve fuel, it was able to achieve its proper orbit and operated for 10 years. The GPS IIR-1 was a total loss as the Delta II exploded 13 seconds after launch. The explosion occurred when a damaged SRB casing ruptured and triggered the vehicle's flight termination system. No one was injured, and the launch pad itself was not seriously impacted, though several cars were destroyed and a few buildings were damaged.
In 2007, Delta II completed its 75th consecutive successful launch, surpassing the 74 consecutive successful launches of the Ariane 4. With the launch of JPSS-1 in 2017, the Delta II has enjoyed 99 consecutive successful launches, with one more scheduled in September 2018. Should this launch be successful, the Delta II would achieve an unprecedented 100 consecutive launch successes.
The first stage of the Delta II is propelled by a Rocketdyne RS-27 main engine burning RP-1 and liquid oxygen. This stage is 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 produces 1,054 kN. The stage is 26 meters long and 2.4 meters wide, weighs over 100 t when fueled, and burns for 260 seconds. In addition, two LR101-NA-11 vernier engines provide guidance for the first stage.
For additional thrust during launch, the Delta II uses solid boosters. For the 6000-series, Delta II used Castor 4A boosters, while the 7000-series uses Graphite-Epoxy Motors manufactured by ATK. The vehicle can be flown with three, four, or, most commonly, nine boosters. When three or four boosters are used, all ignite on the ground at launch, while models using 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 is 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 must occur within approximately 37 days or the stage will have to be refurbished or replaced. This stage also contains a combined inertial platform and guidance system that controls all flight events. The Delta-K stage is 6 meters long and 2.4 meters wide, contains up to 6 t of propellant, and burns for up to 430 seconds.
For low Earth orbit, Delta II is 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.
The Delta II family uses a four-digit system to generate its technical names:
For example, a Delta 7925H used an RS-27A, nine GEM-46 boosters, and a PAM third stage. A Delta 7320 is a two-stage vehicle with three GEM-40 boosters and no third stage.
At T-45 minutes, fueling completion is confirmed. At T-20 minutes, the FTS pyros are armed. At T-20 minutes and T-4 minutes, there are built in holds. During these holds, final checkouts are performed. At T-11 seconds SRB igniters are armed. Ignition is at T-0.4 seconds. The ascent profile varies between missions.
In 2008 ULA indicated that it had "around half a dozen" unsold Delta II rockets on hand, but ULA CEO Tory Bruno stated in October 2017 that there are no complete, unbooked Delta II rockets left in the ULA inventory; and though there are leftover Delta II parts, there are not enough to build another vehicle. It is possible that the remaining pieces will be used to create a museum piece for the Smithsonian.
The only person on record ever hit by space debris was hit by a piece of a Delta II rocket. Lottie Williams was exercising in a park in Tulsa on January 22, 1997 when she was hit in the shoulder by a six-inch piece of blackened metallic material. U.S, Space Command confirmed that a used Delta II rocket from the April 1996 launch of the Midcourse Space Experiment had crashed into the atmosphere 30 minutes earlier. The object tapped her on the shoulder and fell off harmlessly onto the ground. Williams collected the item and NASA tests later showed that the fragment was consistent with the materials of the rocket, and Nicholas Johnson, the agency's chief scientist for orbital debris, believes that she was indeed hit by a piece of the rocket.
Media related to Delta II at Wikimedia Commons