Evolved Expendable Launch Vehicle

Delta IV liftoff from SLC-37. Delta IV is one of the rockets in the EELV program.

Evolved Expendable Launch Vehicle (EELV) is an expendable launch system program of the United States Air Force (USAF), intended to assure access to space for Department of Defense and other United States government payloads. The program, which began in the 1990s with the goal of making government space launches more affordable and reliable, resulted in the development of two launch systems, Delta IV and Atlas V. These were later joined by the Falcon 9.^[1] These launch systems are the primary methods for launching U.S. military satellites.^[2] The USAF plans to use the EELV family of launch vehicles until at least 2030. Follow-on technologies are being considered, one of which was originally the Reusable Booster System^[3] until its discontinuation.

History

United States' liquid rocket propulsion technology has evolved over the past five decades to meet the changing needs of the commercial community, agree with Department of Defense (DoD) diminishing budgets, and ensure national access to space.^[4] The importance of the United States having assured access to space is best laid out by the National Presidential Directive Number 40 which states:

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.^[5]

The United States’ current solution to assure space access for operational space assets is to maintain two families of launch vehicles under the EELV program. The EELV program was initiated in 1995 as the Air Force’s premium space lift modernization program. The purpose of this program was to reduce the cost of operational space launch by 25–50% and to improve reliability over the heritage launch systems (Atlas II, Delta II, and Titan IV). Procurement of EELV boosters for military space launch was to evolve into a "commercial like" nature.^[6] The EELV program eventually produced two families of launch vehicles as the solution to US space lift needs. These two families are the Delta IV launch system, developed by McDonnell Douglas (now The Boeing Company), and the Atlas V launch system, developed by Lockheed Martin.

The Atlas V and Delta IV space launch boosters initially made up the EELV program, with the United States Air Force (USAF) overseeing the development of the two launch systems in just five years.^[6] Boeing’s Delta IV and Lockheed Martin’s Atlas V programs eventually merged to form the United Launch Alliance (ULA). ULA then held a monoply on United States military launches until SpaceX gained approval for its Falcon 9 launch vehicle.^[7]

Current booster systems

The Atlas V and Delta IV systems evolved through different paths. Major differences include launch processing, launch pad operational concept, and some major components. Falcon 9 was developed privately by SpaceX.

Atlas V

Atlas V liftoff from SLC-41.

The Atlas V space launch system has a lineage which began in 1954 under the Intercontinental Ballistic Missile (ICBM) program.^[8] The first US Intercontinental Ballistic Missile (ICBM) was the SM-65 Atlas. Although the Atlas started as ICBM technology, emergence as a space launch vehicle (SLV) followed soon thereafter.^[8]

Main features include the Common Core Booster powered by a NPO Energomash RD-180 engine, Aerojet strap-on solid boosters (up to five), Centaur (rocket stage), powered by a single or dual Pratt & Whitney Rocketdyne RL10A-4-2 engine(s), and an option of a 4.2 or 5.4 meter payload fairing (PLF). A three-digit (XYZ) naming convention is used for the Atlas V configuration identification. The first digit represents the payload fairing size (either 4 or 5), the second digit represents the number of solid rocket boosters used (0 through 5), and the third digit represents the number of engines used on the Centaur (1 or 2)

Delta IV

The Delta SLV is a direct descendant of the Thor missile, PGM-17 Thor. Originating as a launch vehicle in the 1950s, the Delta program was initiated by NASA.

Main features include the Common Booster Core (CBC) powered by a Pratt and Whitney Rocketdyne RS-68 engine, a Delta Cryogenic Second Stage (DCSS), and off pad horizontal vehicle integration. The Delta IV M configuration consists of a CBC first stage and a 4-m diameter DCSS.^[9] There are three variants of Delta IV M+ configuration. The Delta IV M+(4,2) uses two strap-on solid rocket motors (SRMs) solid rocket booster to augment the first-stage CBC and a 4-m diameter DCSS and PLF. The Delta IV M+(5,2) and Delta IV M+(5,4) have two and four SRMs, respectively and 5-m diameter DCSS and PLF. The Heavy Lift Vehicle (HLV) variant has two strap-on CBC cores with a 5-m DCSS and PLF. The Delta IV-Heavy utilizes the same configuration as the Delta IV-M (no strap on Aerojet boosters) but with two additional Common Booster Cores.

Falcon 9

Falcon 9 liftoff from SLC-4E.

The Falcon 9 is a clean-sheet rocket designed by SpaceX. Announced in 2005, the Falcon 9 had its first flight in 2010. As of January 2016, it has gone through three major revisions.

All Falcon 9 versions are two-stage, LOX/RP-1-powered launch vehicles.

The Falcon 9 tank walls and domes are made from aluminum lithium alloy. SpaceX uses an all friction-stir welded tank, the highest strength and most reliable welding technique available.^[10] The second stage tank of a Falcon 9 is simply a shorter version of the first stage tank and uses most of the same tooling, material and manufacturing techniques, reducing production costs.^[10]

SpaceX uses multiple redundant flight computers in a fault-tolerant design. Each Merlin rocket engine is controlled by three voting computers, each of which has two physical processors that constantly check each other. The software runs on Linux and is written in C++.^[11] For flexibility, commercial off-the-shelf parts and system-wide radiation-tolerant design are used instead of rad-hardened parts.^[11] Each stage has stage-level flight computers, in addition to the Merlin-specific engine controllers, of the same fault-tolerant triad design to handle stage control functions.

Development

The U.S. Air Force assembled its initial blue print for the EELV in 1994, following many years of government funded studies into an improved system and architecture, which was intended to replace most if not all existing "legacy" spacelifters (e.g. Delta II, Atlas II/Centaur, Titan IV, etc.). The architecture called for the spacelifter to be based on standardized fairings, liquid core vehicles, upper stages, and solid rockets. The Standard Payload Interface bus was also proposed as another way to save money and improve efficiency.

The initial bids came from four major defense contractors: Lockheed Martin, Boeing, McDonnell Douglas, and Alliant Techsystems. Each of the bids had a variety of different concepts. One of the contractors, Boeing, initially proposed utilizing the Space Shuttle Main Engines (SSME).^[12] McDonnell Douglas merged with Boeing in 1997 and used its Delta IV spacelifter for their EELV proposal.

Design

Boeing and Lockheed Martin were both collectively awarded US$100 million for the final phase of the bid. Both companies built their designs around modularization, standardization and minimizing the amount of equipment and using proven, reliable and simplified systems. Boeing developed the Common Booster Core (CBC) that would be the center of the Delta IV. For the Atlas V Lockheed Martin did something similar, calling it a Common Core Booster (CCB).^[13]

Industrial espionage

Boeing was found to be in possession of proprietary documents from Lockheed Martin.^[14] To end litigation, both companies agreed to join forces and formed the United Launch Alliance joint venture.^[15] Each company has a 50% stake in ULA.^[16]

Launch services contracts

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.^[13] 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.^[17] In 2003 the USAF moved 7 launches from Delta IV to Atlas V.^[18]

Competition

In December 2012, the DoD announced a re-opening of the EELV-class launch vehicle market to competition beginning in 2015. "Under the new plan, the Air Force is authorized to proceed with a block buy of "up to" 36 launch cores from current monopoly vendor United Launch Alliance, while at the same time opening up another 14 cores to be purchased competitively. The new era will begin in 2015 with initial launches to be performed in 2017."^[19]

The Air Force 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.^[20] Following these, in April 2014, SpaceX sued the United States Air Force in order to gain access to the EELV program.^[21][22] SpaceX argued the RD-180 engines used by the Atlas V violated sanctions against the Russian government.^[23] The Air Force and SpaceX settled the lawsuit in 2015 by opening up more launches to competitive bidding.^[24][25] The Air Force certified the Falcon 9 in May 2015,^[26] and SpaceX won a contract under the EELV program to launch a GPS III payload to MEO.^[27]

Human-rating

For the launch vehicle for the Orion spacecraft, the Aerospace Corporation was asked by NASA three times, in 2005, 2008 and 2009, to assess technical feasibility and cost of modifying an EELV to be human-rated for use in NASA human spaceflight missions.^[28] Two later assessments also addressed the possibility of replacing the Ares I with a Delta IV Heavy. The reports indicate that the Delta IV Heavy meets ISS and lunar target performance requirements.^[29] Unlike other modifications of the Delta IV, the Heavy variant does not use solid rocket boosters.

In a presentation to the Review of U.S. Human Space Flight Plans Committee, an Aerospace Corporation representative presented a summary of the study. The summary asserts that even without a newly developed upper stage, it would be feasible for a human-rated Delta IV Heavy to launch a crewed Orion spacecraft to the International Space Station.^[30] ULA has since published a paper^[31] detailing the changes needed for man-rating EELVs. On February 2, 2010 NASA awarded^[32] ULA $6.7 million in stimulus funds under the Commercial Crew Development (CCDev) program. A Space Act Agreement was set up to develop an Emergency Detection System (EDS) that could be used on both EELVs. An EDS monitors critical launch vehicle and spacecraft systems and issues status, warning and abort commands to the crew during their mission to low Earth orbit.

See also

• Reusable Booster System the program that was intended to follow EELV after 2025

References

External links

• United Launch Alliance
  • Atlas website by Lockheed Martin
  • Delta website by Boeing
• SpaceX