National Security Space Launch

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/National_Security_Space_Launch

 

Delta IV Heavy liftoff from SLC-6. Delta IV was one of the rockets developed under the initial EELV program.

 

National Security Space Launch (NSSL) is a program of the United States Air Force (USAF) intended to assure access to space for United States Department of Defense and other United States government payloads. 

Started in 1994 as the Evolved Expendable Launch Vehicle (EELV) launch system program, the initial program goal was to make government space launches more affordable and reliable, leading to the development of the Delta IV and Atlas V EELV families. As of 2019, these launch vehicles are the primary methods for launching U.S. military satellites, along with the Falcon 9 developed by SpaceX under NASA's CRS program.

On 1 March 2019, the program changed its name from EELV to National Security Space Launch (NSSL) to better reflect the changing nature of launch contracting, including the retirement of STS and the inclusion of reusable vehicles. The NSSL program launches the nation's most valuable military satellites; contracts to launch lower value payloads, such as those of the Space Test Program, are awarded using different methodologies.

History

Initial program goals

The USAF began the EELV program in 1994, following many years of government-funded studies into improved systems and architecture. The intent was to replace legacy vehicles, including Delta II, Atlas II, and Titan IV. EELVs were to reduce costs by being based on standardized fairings, liquid core vehicles, upper stages, and solid rocket boosters. A Standard Payload Interface bus was also proposed as a way to save money and improve efficiency.

Reducing the cost of launches and ensuring national access to space were the two main goals of the USAF space launch/EELV program. Some of the reasons why assured access to space is a priority for the United States are stated in National Presidential Directive Number 40, which reads:

Access to space through U.S. space transportation capabilities is essential to:

1. place critical United States Government assets and capabilities into space;
2. augment space-based capabilities in a timely manner in the event of increased operational needs or minimize disruptions due to on-orbit satellite failures, launch failures, or deliberate actions against U.S. space assets;
3. support government and commercial human space flight.

The United States, therefore, must maintain robust, responsive, and resilient U.S. space transportation capabilities to assure access to space.

Procurement of EELV boosters for military space launch was to evolve to more closely match commercial practice. The initial bids came from four major defense contractors: Lockheed Martin, Boeing, McDonnell Douglas, and Alliant Techsystems. Each of the bids included a variety of concepts. Boeing initially proposed utilizing the RS-25 Space Shuttle main engine (SSME). When McDonnell Douglas merged with Boeing in 1997, the latter put forth the Delta IV as their EELV proposal. Both the Delta IV and Lockheed Martin's Atlas V eventually entered service. 

1990s-2000s

In October 1998 two initial launch services contracts (known as Buy 1) were awarded. Along with the award of two development agreements, the total amount was more than $3 billion. Boeing was awarded a contract for 19 out of the 28 launches; Lockheed Martin was awarded a contract for the other 9. Boeing received $1.38 billion, and Lockheed Martin received $650 million for the launches. Boeing and Lockheed Martin were both collectively awarded US$100 million for the final phase of the bid. Boeing developed the Delta IV based around Common Booster Cores (CBC) and the Delta Cryogenic Second Stage, while Lockheed Martin developed the Atlas V based around Common Core Boosters (CCB) and the Centaur upper stage.

In 2003, Boeing was found to be in possession of proprietary documents from Lockheed Martin. The USAF moved 7 launches from Delta IV to Atlas V. To end litigation and competition for a limited market, both companies agreed to form the United Launch Alliance (ULA) joint venture. Each company has a 50% stake in ULA.

2010s

In December 2012, the DoD announced a re-opening of the EELV-class launch vehicle market to competition while authorizing the USAF to proceed with a block buy of "up to" 36 boosters from ULA. At the same time, another 14 boosters were to be procured competitively beginning in 2015, with the initial launches to be performed in 2017.

The USAF signed a contract at that time with SpaceX for two launches in 2014 and 2015 to serve as proving flights to support the certification process for the Falcon 9 v1.1 and Falcon Heavy. In April 2014, after the launches were contracted, SpaceX sued the United States Air Force, arguing that the RD-180 engines, produced in Russia by the government owned NPO Energomash and used by the Atlas V, violated sanctions against the Russian government. The USAF and SpaceX settled the lawsuit in Jan 2015 by opening up more launches to competitive bidding. The USAF certified the Falcon 9 in May 2015, and in 2016 SpaceX won a contract under the EELV program to launch a GPS Block III satellite payload to MEO.

2018 to 2020s

The USAF began the process of competitively selecting the next generation NSSL vehicles in 2018. Announced performance requirements include:

Orbit description	Apogee (km) x perigee (km)	Inclination (degrees)	Mass to orbit (kg)	Payload category
LEO	926 x 926	63.4	6,800	A, B
Polar 1	830 x 830	98.2	7,030	A, B
Polar 2	830 x 830	98.2	17,000	C
MEO Direct 1	18,200 x 18,200	50.0	5,330	A, B
MEO Transfer 1	20,400 x 1,000	55.0	4,080	A, B
GTO	35,786 x 190	27.0	8,165	A, B
Molniya	39,200 x 1,200	63.4	5,220	A, B
GEO 1	35,786 x 35,786	0.0	2,300	A, B
GEO 2	35,786 x 35,786	0.0	6,600	C

Category A payloads fit within a 4 m payload envelope, category B payloads fit within a 5 m payload envelope, and category C payloads require an extended 5 m envelope.

The USAF plans to use the next generation NSSL launch vehicles until at least 2030. At least one program was considering follow-on technologies before cancellation in 2012.

Launch vehicles

Currently, there are four vehicles certified to conduct NSSL launches: Atlas V, Delta IV Heavy, Falcon 9 and Falcon Heavy. Delta IV Medium was retired in August 2019. The USAF is currently in the process of soliciting bids for next-generation launch vehicles, with proposals due by 1 August 2019.

Active

Atlas V-certified

Atlas V liftoff from SLC-41

Each Atlas V launch vehicle is based on a Common Core Booster powered by one NPO Energomash RD-180 engine with two combustion chambers and a Centaur upper stage powered by one or two Pratt & Whitney Rocketdyne RL10A-4-2 engines. Up to five Aerojet Rocketdyne Graphite-Epoxy Motor solid rocket boosters can be added to increase vehicle performance, and two diameters of payload fairing are available.

A three-digit (XYZ) naming convention is used for the Atlas V configuration identification. An Atlas V XYZ will have a 4.2- or 5.4-meter diameter payload fairing (X= 4 or 5), Y solid rocket boosters (0-5), and Z RL-10's on the Centaur upper stage (1-2). As an example, an Atlas V 551 has a 5.4 m PLF, 5 SRBs, and 1 RL-10.

Delta IV Heavy-certified

Each Delta IV launch vehicle is based on a Common Booster Core (CBC) powered by a Pratt and Whitney Rocketdyne RS-68 engine and a Delta Cryogenic Second Stage (DCSS) powered by an RL10. Delta IV Heavy is distinguished by two additional CBCs and always flies with a 5 m DCSS and PLF, while Delta IV Medium flew with two or four SRBs on a single CBC.

The DCSS had 4 m diameter and 5 m diameter versions, with matching diameter payload fairings (PLFs). Delta IV CBCs and DCSSs are integrated horizontally before being transported to the launchpad. The 4 m diameter DCSS was retired with the Delta IV Medium after the 22 August 2019 launch of a GPS-IIIA satellite on a Delta IV M+(4,2) with one CBC, two SRBs, and a 4 m diameter DCSS and PLF.

Falcon 9-certified

Falcon 9 liftoff from SLC-4E

The main features of the Falcon 9 in its current Block 5 version include two stages, both powered by LOX and RP-1, with nine Merlin 1D engines on the first stage and one Merlin 1D Vacuum engine on the second stage.

GPS-IIIA USA-289 was the first NSSL-type B5 Falcon 9 launch. The launch occurred on December 23, 2018.

Falcon Heavy-certified

The Falcon Heavy is a heavy-lift rocket developed and produced by SpaceX. It has been certified for the NSSL program after the STP-2 launch completed on 25 June 2019, as confirmed by the commander of the Air Force Space and Missile Systems Center, Lt. Gen. Thompson. He clarified: "I certified them to compete last year" and "[o]ne of the requirements behind certification is to fly three missions." This requirement has been satisfied by the Falcon Heavy test flight in February 2018, Arabsat-6A in April 2019, and the STP-2 launch in June 2019. However, Falcon Heavy has been certified for two Phase 1A reference orbits only and "[i]t's not certified for all of our most stressing national security space orbits," Thompson said. Thus, the USAF is working with SpaceX to mature their Falcon Heavy's design. 

As of September 2019, it has two manifested classified national security flights for the USAF in 2020 and 2021.

Next generation vehicle competition

As of 2018, a competitive contract award to launch national security spacecraft is underway between ULA, Northrop Grumman Innovation Systems (NGIS), Blue Origin, and SpaceX. Two providers will be selected to launch spacecraft to a number of reference orbits. In October 2018, the USAF awarded funding to ULA, NGIS, and Blue Origin to develop their rockets.

On 12 August 2019, at least three of the four companies submitted their final bids for the launch services competition. SpaceX bid the existing Falcon rockets, while Blue Origin was expected to bid New Glenn, ULA bid Vulcan Centaur, and NGIS's bid status was not reported. Blue Origin also filed a pre-award protest of the request for proposal arguing that the requirements were ambiguous.

New Glenn

Blue Origin was awarded $500 million for development of New Glenn as a potential competitor in future contracts. As of 2019, New Glenn was expected to first launch in 2021. 

OmegA

OmegA is a rocket design by Northrop Grumman Innovation Systems with two main solid stages, a cryogenic upper stage, and the possibility of strap-on boosters. The first flight is expected in 2021.

Vulcan

ULA was awarded phase 1 funding for development of Vulcan as a potential competitor in future contracts. On 12 August 2019, ULA submitted Vulcan Centaur for phase 2 of the USAF's launch services competition. As of that time, Vulcan Centaur was on track for a 2021 launch.

Blue Engine 4

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/BE-4

 

Blue Engine 4

Country of origin	United States
Manufacturer	Blue Origin
Predecessor	BE-3
Liquid-fuel engine
Propellant	Liquid oxygen / Liquefied natural gas
Under development
Performance
Thrust (SL)	2,400 kN (550,000 lbf)
Chamber pressure	13,400 kPa (1,950 psi)
Gimbal range	±5°
Used in
Vulcan New Glenn

The Blue Engine 4 or BE-4 is an oxygen rich liquefied-natural-gas-fueled staged-combustion rocket engine under development by Blue Origin. The BE-4 is being developed with private and public funding. The engine has been designed to produce 2,400 kilonewtons (550,000 lbf) of thrust at sea level.

It was initially planned for the engine to be used exclusively on a Blue Origin proprietary launch vehicle, New Glenn, the company's first orbital rocket. However, it was announced in 2014 that the engine would also be used on the United Launch Alliance (ULA) Vulcan launch vehicle, the successor to the Atlas V launch vehicle. Final engine selection by ULA happened in September 2018.

First flight test of the new engine is expected no earlier than 2021.

History

Blue Origin began work on the BE-4 in 2011, although no public announcement was made until September 2014. This is their first engine to combust liquid oxygen and liquid methane propellants. In September 2014—in a choice labeled "a stunner" by SpaceNews—the large launch vehicle manufacturer and launch service provider United Launch Alliance selected the BE-4 as the main engine for a new primary launch vehicle.

As of April 2015, the engine development work was being carried out in two parallel programs. One program is testing full-scale versions of the BE-4 powerpack, which are the set of valves and turbopumps that provide the proper fuel/oxidizer mix to the injectors and combustion chamber. The second program is testing subscale versions of the engine's injectors. Also in early 2015, the company indicated it is planning to begin full-scale engine testing in late 2016, and that they expected to complete development of the engine in 2017.

As of September 2015, Blue Origin had completed more than 100 development tests of several elements of the BE-4, including the preburner and a "regeneratively-cooled thrust chamber using multiple full-scale injector elements". The tests were used to confirm the theoretical model predictions of "injector performance, heat transfer, and combustion stability", and data collected is being used to refine the engine design. There was an explosion on the test stand during 2015 during powerpack testing. Blue Origin built two larger and redundant test stands to follow, capable of testing the full thrust of the BE-4.

In January 2016, Blue Origin announced that they intended to begin testing full engines of the BE-4 on ground test stands prior to the end of 2016. Following a factory tour in March 2016, journalist Eric Berger noted that a large part of "Blue Origin’s factory has been given over to development of the Blue Engine-4".

Initially, both first-stage and second-stage versions of the engine were planned. The second stage of the initial New Glenn design was to have shared the same stage diameter as the first stage and use a single vacuum-optimized BE-4, the BE-4U.

The first engine was fully assembled in March 2017. Also in March, United Launch Alliance indicated that the economic risk of the Blue Origin engine selection option had been retired, but that the technical risk on the project would remain until a series of engine firing tests were completed later in 2017. A test anomaly occurred on 13 May 2017 and Blue Origin reported that they lost a set of powerpack hardware.

In June 2017, Blue Origin announced that they would build a new facility in Huntsville, Alabama to manufacture the large BE-4 cryogenic rocket engine.

The BE-4 was first test fired, at 50% thrust for 3 seconds, in October 2017. By March 2018, the BE-4 engine had been tested at 65% of design thrust for 114 seconds with a goal expressed in May to achieve 70% of design thrust in the next several months. By September 2018, multiple hundreds of seconds of engine testing had been completed, including one test of over 200 seconds duration.

In October 2018, Blue Origin President Bob Smith announced that the first launch of the New Glenn had been moved back to 2021, which will be the first flight test of the BE-4. 

By February 2019, the BE-4 had acquired a total of 1800 seconds of hot fire testing on ground test stands, but had yet to be tested above 1.8 meganewtons (400,000 lbf) pounds of thrust, about 73 percent of the engine's rated thrust of 2.4 MN (550,000 lbf).

In August 2019, Blue Origin announced that BE-4 was undergoing full power engine tests.

Blue Origin BE-4 rocket engine powerhead and combustion chamber, April 2018—liquid methane inlet side view. This was the first BE-4 engine to be hotfire tested; test occurred on 18 October 2017.

Applications

As of 2017, the BE-4 was being considered for use on two launch vehicles currently in development. Prior to this, a modified derivative of the BE-4 was also being considered for the experimental XS-1 spaceplane for a US military project, but was not selected.

Atlas V successor - Vulcan

In late 2014, Blue Origin signed an agreement with United Launch Alliance to co-develop the BE-4 engine and to commit to use the new engine on the Vulcan launch vehicle, a successor to the Atlas V, which would replace the single Russian-made RD-180 engine. Vulcan will use two of the 2,400 kN (550,000 lbf) BE-4 engines on each first stage. The engine development program began in 2011.

The ULA partnership announcement came after months of uncertainty about the future of the Russian RD-180 engine that has been used in the ULA Atlas V rocket for over a decade. Geopolitical concerns had come about that created serious concerns about the reliability and consistency of the supply chain for the procurement of the Russian engine. ULA expects the first flight of the new launch vehicle no earlier than 2019.

Since early 2015, the BE-4 has been in competition with the AR1 engine for the Atlas V RD-180 replacement program. While the BE-4 is a methane engine, the AR1, like the RD-180, is kerosene-fueled. In February 2016, the US Air Force issued a contract that provides partial development funding of up to US$202 million to ULA in order to support use of the Blue BE-4 engine on the ULA Vulcan launch vehicle.

Initially, only US$40.8 million will be disbursed by the government with US$40.8 million additional to be spent by a ULA subsidiary on Vulcan BE-4 development. Although US$536 million was the original USAF contract amount to Aerojet Rocketdyne (AJR) to advance development of the AR1 engine, as an alternative for powering the Vulcan rocket, by June 2018, the USAF had renegotiated the agreement with AJR and decreased the Air Force contribution—5/6ths of the total cost—to US$294 million. AJR is putting no additional private funds into the engine development effort after early 2018.

Bezos noted in 2016 that the Vulcan launch vehicle is being designed around the BE-4 engine; ULA switching to the AR1 would require significant delays and money on the part of ULA. This point has also been made by ULA executives, who have also clarified that the BE-4 is likely to cost 40% less than the AR1, as well as benefit from Bezos capacity to "make split-second investment decisions on behalf of BE-4, and has already demonstrated his determination to see it through. [whereas the] AR1, in contrast, depends mainly on U.S. government backing, meaning Aerojet Rocketdyne has many phone numbers to dial to win support".

New Glenn launch vehicle

The engine is to be used on the Blue Origin large orbital launch vehicle New Glenn, a 7.0-meter (23 ft)-diameter two-stage orbital launch vehicle with an optional third stage and a reusable first stage. The first flight and orbital test is planned for no earlier than 2021, although the company had earlier expected the BE-4 might be tested on a rocket flight as early as 2020.

The first stage will be powered by seven BE-4 engines and will be reusable, landing vertically. The second stage of New Glenn will share the same diameter and use two BE-3 vacuum-optimized hydrolox engines. The second stage will be expendable.

XS-1 engine

Boeing secured a contract to design and build the DARPA XS-1 reusable spaceplane in 2014. The XS-1 is to accelerate to hypersonic speed at the edge of the Earth's atmosphere to enable its payload to reach orbit. In 2015, it was believed a modified derivative of the BE-4 engine was to power the craft. In 2017, the contract award selected the RS-25-derived Aerojet Rocketdyne AR-22 engine instead.

Availability and use

Blue Origin has indicated that they intend to make the engine commercially available, once development is complete, to companies beyond ULA, and also plans to utilize the engine in Blue Origin's own new orbital launch vehicle. As of March 2016, Orbital ATK was also evaluating Blue engines for its launch vehicles.

The BE-4 uses liquid methane rather than more commonly used rocket fuels such as kerosene. This approach allows for autogenous pressurization, which is the use of gaseous fuel to pressurize remaining liquid fuel. This is beneficial because it eliminates the need for costly and complex pressurization systems which require storage of a pressurizing gas, such as helium.

Although all early BE-4 components and full engines to support the test program were built at Blue's headquarters location in Kent, Washington, production of the BE-4 will be in Huntsville, Alabama. Testing and support of the reusable BE-4s will occur at the company's orbital launch facility at Exploration Park in Florida, where Blue Origin is investing more than US$200 million in facilities and improvements.

Technical specifications

The BE-4 is a staged combustion engine, with a single oxygen rich preburner, and a single turbine driving both the fuel and oxygen pumps . The cycle is similar to the kerosene-fueled RD-180 currently used on the Atlas V, although it uses only a single combustion chamber and nozzle.

The BE-4 is designed for long life and high reliability, partially by aiming the engine to be a "medium-performing version of a high-performance architecture". Hydrostatic bearings are used in the turbopumps rather than the more typical ball and roller bearings specifically to increase reliability and service life.

• Thrust (sea level): 2,400 kN (550,000 lbf) at full power
• Chamber pressure: 13,400 kPa (1,950 psi), substantially lower than the 26,000 kPa (3,700 psi) of the RD-180 engine that ULA wants to replace
• Designed for reusability
• Design life: 100 launches and landings
• Restartable during flight, via head-pressure start of the turbine during coast
• Deep throttling capability to 65% power or lower

Centaur (rocket stage)

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Centaur_(rocket_stage) 

 

Centaur III

A single-engine Centaur III being raised for mating to an Atlas V rocket
Manufacturer	United Launch Alliance
Used on	Atlas V- Centaur III Vulcan- Centaur V
General characteristics
Height	12.68 m (499 in)
Diameter	3.05 m (120 in)
Gross mass	2,247 kg (4,954 lb) (single engine) 2,462 kg (5,428 lb) (dual engine)
Propellant mass	20,830 kg (45,920 lb)
Associated stages
Derivatives	Centaur V Advanced Common Evolved Stage
Launch history
Status	Active
Total launches	245 as of January 2018
First flight	May 9, 1962
Centaur III
Engines	1 or 2 RL10
Thrust	99.2 kN (22,300 lbf) (per engine)
Specific impulse	450.5 sec
Burn time	Variable
Fuel	Liquid oxygen and liquid hydrogen

The Centaur is a family of rocket propelled upper stages currently produced by U.S. launch service provider United Launch Alliance, with one main active version and one version under development. The 3.8 m diameter Common Centaur/Centaur III (as referenced in the infobox) flies as the upper stage of the Atlas V launch vehicle, while the 5.4 m diameter Centaur V is being developed as the upper stage of ULA's new Vulcan rocket.

Centaur was the first rocket stage to use liquid hydrogen (LH₂) and liquid oxygen (LOX) propellants, a high-energy combination that is ideal for upper stages but has significant handling difficulties.

Characteristics

Common Centaur is built around stainless steel pressure stabilized propellant tanks with 0.020 inch thick walls that can nevertheless lift payloads of up to 19,000 kg. The thin walls minimize the mass of the tanks, maximizing the stage's overall performance.

A common bulkhead consisting of two stainless steel skins separated by a fiberglass honeycomb is located between the LOX and LH₂ tanks, further reducing the tank mass. Heat transfer between the extremely cold LH₂ and relatively warm LOX is reduced by the fiberglass honeycomb insulating layer.

The main propulsion system consists of one or two Aerojet Rocketdyne RL-10 engines. The stage is capable of up to twelve restarts, limited by propellant, orbital lifetime, and mission requirements. Combined with the insulation of the propellant tanks, this allows Centaur to perform the multi-hour coasts and multiple engine burns required on complex orbital insertions.

The reaction control system (RCS) also provides ullage and consists of twenty hydrazine monopropellant engines located around the stage in two 2-thruster pods and four 4-thruster pods. Hydrazine (340 lb (150 kg)) is stored in a pair of bladder tanks and fed to the RCS engines with pressurized helium gas, which is also used to accomplish some main engine functions.

Current versions

As of 2019, all but two of the many Centaur variants had been retired: Common Centaur/Centaur III (active) and Centaur V (in development). In the future, United Launch Alliance (ULA) intends to replace Vulcan's Centaur V with the similar Advanced Common Evolved Stage, continuing Centaur's legacy.

Current engines

Version	Stage	Dry mass	Thrust	Isp (ve), vac.	Length	Diameter
RL10A-4-2	Centaur III (DEC)	168 kg	99.1 kN	451 s		1.17 m
RL10C-1	Centaur III (SEC), (DCSS)	190 kg	101.8 kN	449.7 s	2.12 m	1.45 m
RL10C-1-1	Centaur V	188 kg	106 kN	453.8 s	2.46 m	1.57 m

Centaur III/Common Centaur

Common Centaur is the upper stage of the Atlas V rocket. Most payloads launch on Single Engine Centaur (SEC) with one RL-10, but a Dual Engine Centaur (DEC) configuration will be used to launch the CST-100 Starliner crewed spacecraft and possibly the Dream Chaser ISS logistics spaceplane. The higher thrust of two engines allows a gentler ascent with more horizontal velocity and less vertical velocity, which reduces deceleration to survivable levels in the event of a launch abort and ballistic reentry occurring at any point in the flight.

Earlier Common Centaurs were propelled by the RL10-A-4-2 version of the RL-10. Since 2014, Common Centaur has flown with the RL10-C-1, an engine that is shared with the Delta Cryogenic Second Stage, to reduce costs. The Dual Engine Centaur (DEC) configuration will continue to use the smaller RL10-A-4-2 to accommodate two engines in the available space.

The Atlas V can fly in multiple configurations, but only one affects the way Centaur integrates with the booster and fairing: the 5.4 m diameter Atlas V payload fairing attaches to the booster and encapsulates the upper stage and payload, routing fairing-induced aerodynamic loads into the booster. If the 4 m diameter PLF is used, the attachment point is at the top (forward end) of Centaur, routing loads through the Centaur tank structure.

The latest Common Centaurs can accommodate secondary payloads using an Aft Bulkhead Carrier attached to the engine end of the stage.

Centaur V

Centaur V will be the upper stage of the new Vulcan launch vehicle currently being developed by the United Launch Alliance to meet the needs of the National Security Space Launch (NSSL) program. Vulcan was initially intended to enter service with an upgraded variant of the Common Centaur, with an upgrade to the Advanced Cryogenic Evolved Stage (ACES) planned after the first few years of flights.

In late 2017, ULA decided to bring elements of the ACES upper stage forward and begin work on Centaur V. Centaur V will have ACES' 5.4 m diameter and advanced insulation, but does not include the Integrated Vehicle Fluids (IVF) feature expected to allow the extension of upper stage on-orbit life from hours to weeks. Centaur V will utilise 2 different versions of the RL10-C engine with nozzle extensions to improve the fuel consumption for the heaviest payloads. This increased capability over Common Centaur will permit ULA to meet NSSL requirements and retire both the Atlas V and Delta IV rocket families earlier than initially planned. The new rocket publicly became the Vulcan Centaur in March 2018.

In May 2018, the Aerojet Rocketdyne RL-10 was announced as Centaur V's engine following a competitive procurement process against the Blue Origin BE-3. Each stage will mount two engines.

History

The Centaur concept originated in 1956 when Convair began studying a liquid hydrogen fueled upper stage. The ensuing project began in 1958 as a joint venture among Convair, the Advanced Research Projects Agency (ARPA), and the U.S. Air Force. In 1959, NASA assumed ARPA's role. Centaur initially flew as the upper stage of the Atlas-Centaur launch vehicle, encountering a number of early developmental issues due to the pioneering nature of the effort and the use of liquid hydrogen. In 1994 General Dynamics sold their Convair division to Lockheed-Martin.

Centaur A to D (Atlas)

An Atlas-Centaur rocket launches Surveyor 1

The Centaur was originally developed for use with the Atlas launch vehicle family. Known in early planning as the 'high-energy upper stage', the choice of the mythological Centaur as a namesake was intended to represent the combination of the brute force of the Atlas booster and finesse of the upper stage.

Initial Atlas-Centaur launches used developmental versions, labeled Centaur-A through -C. The only Centaur-A launch on 8 May 1962 ended in an explosion 54 seconds after liftoff when insulation panels on the Centaur separated early, causing the LH₂ tank to overheat and rupture. After extensive redesigns, the only Centaur-B flight on 26 November 1963 was successful. After three Centaur-C failures, Centaur-D was the first version to enter operational service, with fifty-six launches.

On 30 May 1966, an Atlas-Centaur boosted the first Surveyor lander towards the Moon. This was followed by six more Surveyor launches over the next two years, with the Atlas-Centaur performing as expected. The Surveyor program demonstrated the feasibility of reigniting a hydrogen engine in space and provided information on the behavior of LH₂ in space.

By the 1970s, Centaur was fully mature and had become the standard rocket stage for launching larger civilian payloads into high Earth orbit, also replacing the Atlas-Agena vehicle for NASA planetary probes.

By the end of 1989, Centaur-D and -G had been used as the upper stage for 63 Atlas rocket launches, 55 of which were successful.

Centaur D-1T (Titan III)

A Titan IIIE-Centaur rocket launches Voyager 2

 

The Centaur D was improved for use on the far more powerful Titan III booster in the 1970s, with the first launch of the resulting Titan IIIE in 1974. The Titan IIIE more than tripled the payload capacity of Atlas-Centaur, and incorporated improved thermal insulation, allowing an orbital lifespan of up to five hours, an increase over the 30 minutes of the Atlas-Centaur.

The first launch of Titan IIIE in February 1974 was unsuccessful, with the loss of the Space Plasma High Voltage Experiment (SPHINX) and a mockup of the Viking probe. It was eventually determined that Centaur's engines had ingested an incorrectly installed clip from the oxygen tank.

The next Titan-Centaurs launched Helios 1, Viking 1, Viking 2, Helios 2, Voyager 1, and Voyager 2. The Titan booster used to launch Voyager 1 had a hardware problem that caused a premature shutdown, which the Centaur stage detected and successfully compensated for. Centaur ended its burn with less than 4 seconds of fuel remaining.

Centaur-G (Atlas)

An upgraded Centaur-D, Centaur-G was introduced on the Atlas G and was carried over to the very similar Atlas I.

Shuttle-Centaur

Illustration of Shuttle-Centaur with Ulysses

 

Centaur-G was a proposed Space Shuttle upper stage. Both Challenger and Discovery were modified to carry the stage. To enable its installation in shuttle payload bays, the diameter of the Centaur-G's hydrogen tank was increased to 14 feet (4.3 m), with the LOX tank diameter remaining at 10 feet (3.0 m). Centaur-G was planned to launch the Galileo and Ulysses robotic probes, with a shortened version planned for U.S. DoD payloads and the Magellan probe to Venus.

After the Space Shuttle Challenger accident, and just months before the Shuttle-Centaur was scheduled to fly, NASA concluded that it was far too risky to fly the Centaur on the Shuttle. The probes were launched with the much less powerful solid-fueled IUS, with Galileo needing multiple gravitational assists from Venus and Earth to reach Jupiter.

Centaur T (Titan IV)

The capability gap left by the termination of the Shuttle-Centaur program was filled by a new launch vehicle, the Titan IV. The 401A/B versions used a Centaur-T upper stage with a 14 feet (4.3 m) diameter hydrogen tank. In the Titan 401A version, a Centaur-T was launched nine times between 1994 and 1998. The 1997 Cassini-Huygens Saturn probe was the first flight of the Titan 401B, with an additional six launches wrapping up in 2003 including one SRB failure.

Centaur II (Atlas II/III)

Centaur II was initially developed for use on the Atlas II series of rockets. Centaur II also flew on the initial Atlas IIIA launches.

Centaur III/Common Centaur (Atlas III/V)

Atlas IIIB introduced the Common Centaur, a longer and initially dual engine Centaur II.

Atlas V cryogenic fluid management experiments

Most Common Centaurs launched on Atlas V have hundreds to thousands of kilograms of propellants remaining on payload separation. In 2006 these propellants were identified as a possible experimental resource for testing in-space cryogenic fluid management techniques.

In October 2009, the Air Force and United Launch Alliance (ULA) performed an experimental demonstration on the modified Centaur upper stage of DMSP-18 launch to improve "understanding of propellant settling and slosh, pressure control, RL10 chilldown and RL10 two-phase shutdown operations. DMSP-18 was a low mass payload, with approximately 28% (5400 kg) of LH₂/LOX propellant remaining after separation. Several on-orbit demonstrations were conducted over 2.4 hours, concluding with a deorbit burn. The initial demonstration was intended to prepare for more-advanced cryogenic fluid management experiments planned under the Centaur-based CRYOTE technology development program in 2012–2014, and will increase the TRL of the Advanced Cryogenic Evolved Stage Centaur successor.

Mishaps

Although Centaur has a long and successful flight history, it has experienced a number of mishaps:

• April 7, 1966: Centaur did not restart after coast — ullage motors ran out of fuel.
• May 9, 1971; Centaur guidance failed, destroying itself and the Mariner 8 spacecraft bound for Mars orbit.
• April 18, 1991: Centaur failed due to particles from the scouring pads used to clean the propellent ducts getting stuck in the turbopump, preventing start-up.
• August 22, 1992: Centaur failed to restart (icing problem).
• April 30, 1999: Launch of the USA-143 (Milstar DFS-3m) communications satellite failed when a Centaur database error resulted in uncontrolled roll rate and loss of attitude control, placing the satellite in a useless orbit.
• June 15, 2007: the engine in the Centaur upper stage of an Atlas V shut down early, leaving its payload — a pair of National Reconnaissance Office ocean surveillance satellites — in a lower than intended orbit. The failure was called "A major disappointment," though later statements claim the spacecraft will still be able to complete their mission. The cause was traced to a stuck-open valve that depleted some of the hydrogen fuel, resulting in the second burn terminating four seconds early. The problem was fixed, and the next flight was nominal.
• August 30, 2018: Atlas V Centaur passivated second stage launched on September 17, 2014 broke up, creating space debris.
• March 23–25, 2018: Atlas V Centaur passivated second stage launched on September 8, 2009 broke up.
• April 6, 2019: Atlas V Centaur passivated second stage launched on October 17, 2018 broke up.

Centaur III Specifications

Source: Atlas V551 specifications, as of 2015.

• Diameter: 3.05 m (10 ft)
• Length: 12.68 m (42 ft)
• Inert mass: 2,247 kg (4,954 lb)
• Fuel: Liquid hydrogen
• Oxidizer: Liquid oxygen
• Fuel & oxidizer mass: 20,830 kg (45,922 lb)
• Guidance: Inertial
• Thrust: 99.2 kN (22,300 lbf)
• Burn time: Variable - eg. 842 seconds on Atlas V
• Engine: RL10-C-1
• Engine length: 2.32 m (7.6 ft)
• Engine diameter: 1.53 m (5 ft)
• Engine dry weight: 168 kg (370 lb)
• Engine start: Restartable
• Attitude control: 4 27-N thrusters, 8 40-N thrusters
  • AC Propellant: Hydrazine