History of the Delta Launch Vehicle

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The Delta II expendable launch vehicle is the product of a long evolution that dates back to the earliest days of American missile development. Use of proven components and gradual modification of those components has resulted in one of the most reliable launch vehicles in the world.

Over its fifty years of service, the Delta family of expendable launch vehicles has racked up the most successful flight record of any rocket currently in use. Of 343 flights, only 15 have been total failures, a success rate of 95.6 percent. The Delta II has had only one total failure (and one partial failure, Koreasat-1) since its first launch in February 1989—an incredible 99% success rate—and in September 2007 it set the all-time world record for consecutive successes, a tally that continues to grow with Delta 378 being the 99th success in a row.

Vehicle Development

The roots of Delta began in a 1954 USAF Request for Proposals for an Intermediate Range Ballistic Missile capable of carrying a thermonuclear bomb 1,500 miles—the distance from England to Moscow. The Douglas Aircraft Company (builder of the greatest airplane in history, the DC-3) was selected to build a design that utilized the warhead and guidance system already in development for the Atlas missile. For propulsion it used the engine from the Navaho cruise missile, which at the time was “the only one available.” Sixty-five feet long and eight feet in diameter, it could fit inside a Douglas C-124 Globemaster II for easy transportation to a launch site. The first Thor IRBM was ready to fly in August 1956, just seven months after Douglas was commissioned to build it. By September 1957 Thor had successfully flown to a range of 1,250 miles while heavily weighted down by instrumentation. The first operational Thors were deployed in England by the end of 1958 and remained there until August 1963.

(During 1962, several Thors were also used for high-altitude tests of nuclear weapons, and were launched from Johnston Island in the south Pacific to detonate above the atmosphere. But that’s a different story.)

The Thor was quickly modified for use in many roles, including military testing, scientific exploration, and strategic reconnaissance. The second stage of the ill-fated Vanguard rocket, the Aerojet AJ-10, was jury-rigged to form Thor-Able. Thor-Able tested a heat shield for use on reentry vehicles of the Atlas ICBM; launched the earliest American attempts to reach the Moon, known as Pioneer; and in 1960 orbited TIROS-1 (Television and Infrared Observation Satellite), the world’s first weather satellite. That same year, a solid third stage motor was added to make Thor-Able-Star, which flew the U.S. Navy’s Transit (navigation) and the U.S. Army’s Courier (communications) satellites.

Another Thor upper stage was the Lockheed-built Agena, which first launched in January 1959 as the booster for the Corona (a.k.a. Discoverer) program, the United States’ first spy satellite. The Corona reconnaissance spacecraft was launched into polar orbit to take photographic swaths as it passed over the Soviet Union. Corona was designed to collect its exposed film in a heat-resistant “bucket” at the nose. This bucket would then reenter over the Pacific Ocean to be recovered in the air by a passing aircraft. Strange as this sounds, the Corona program was very successful over the years, beginning with Discoverer XIV as it was snatched in midair by a C-119 cargo plane on 18 August 1960. It provided the earliest photos of the USSR’s Plesetsk rocket base. Thor-Agenas also boosted Echo 2 (passive communications), Nimbus 1 (weather), and Alouette 1 (Canada’s first satellite), among others.

In April 1959, NASA’s Goddard Space Flight Center signed the nascent agency’s first launch vehicle contract, commissioning Douglas to create a civilian launch vehicle based on Thor-Able and to produce and integrate 12 launch vehicles. As this would be the fourth modification of the Thor vehicle (after Able, Agena, and Able-Star), it would be called Delta, the radio code word for the fourth letter of the alphabet.* Thor-Delta used a Thor booster powered by a Rocketdyne MB-3 engine burning kerosene and liquid oxygen; and upper stages derived from Vanguard: the Aerojet AJ-10-118 (hydrazine/nitric acid) second stage previously used in Thor-Able, and the Allegheny Ballistics Laboratory X-248 solid motor as a third stage. The use of already available parts allowed Delta to be ready just 18 months after receiving the go-ahead.

The first Thor-Delta flew on 13 May 1960 but failed due to a problem with attitude control in the second stage. Three months later, on 12 August, the Echo 1 reflight was a total success, as a 100-foot diameter aluminized mylar balloon [photo] inflated in orbit, providing a reflective surface so that two-way voice signals could be bounced from ground stations on the west and east coasts. Echo 1A constituted NASA’s first communications satellite, yet by the time it launched, its passive communications experiment was already made obsolete by active repeaters.

Nevertheless, many firsts came out of this initial batch of twelve Deltas. Among them, OSO-1 (Orbiting Solar Observatory, Delta 8) was the first satellite to have pointed instruments and onboard tape recorders for data storage, and using these was the first to observe solar gamma rays. Telstar, launched on Delta 12 and perhaps the most famous early satellite after Sputnik, was the first commercial communications satellite in orbit. Owned by AT&T and flown by NASA, it relayed the first transatlantic television transmissions between Andover, Maine, and stations in Goonhilly, England and Pleumeur-Bodou, France.

The original Delta could place a 100 pound payload in geostationary transfer orbit, though it was used for lower orbits only, and was initially regarded as an interim vehicle until more powerful rockets could be developed. However, in response perhaps to the successes of the first batch, in 1962 Douglas Aircraft began a series of upgrades and modifications which would increase Delta’s capacity tenfold over the next nine years. The Delta A used an improved MB-3 engine (Block II), and the B model was an A with a lengthened second stage using higher energy oxidizer. The C model added a bulbous fairing for greater payload space and used as its third stage the X-258 motor developed for the Scout rocket. The Delta D, also known as the Thrust Augmented Delta, took the C and added three Castor I strap-on solid boosters from the Thrust Augmented Thor-Agena D. These boosters gave the Delta the extra thrust necessary to propel the Syncom satellites into geosynchronous transfer orbits.

The Delta E, also known as DSV-3E or TAID (Thrust Augmented Improved Delta), incorporated several changes. The Rocketdyne MB-3 engine in the first stage was improved again (as Block III), and the Castor booster motors were replaced with more powerful Castor II motors. The second stage was made restartable and its propellant tanks were widened. The third stage was either the X-258 or the Air Force-developed FW-4 motor, and the payload space was enlarged again, using an Air Force Agena fairing.

Two satellites, BIOS-1 and -2, were launched using the unique designation Delta G. These were two-stage Delta E vehicles carrying a special re-entry vehicle, complete with built-in retrorocket for the deorbit burn, that would be caught in midair over the Pacific using the method the Corona project had perfected. The Biosatellite missions carried live specimens of frog eggs, fruit flies, wheat seedlings, and bacteria, to assess the effects of radiation and weightlessness. BIOS-1 was not recovered due to a failure in its retrorocket; but BIOS-2 successfully deorbited, was recovered in midair by the USAF, and provided the first scientific data about basic biological processes in space. A third BIOS flight, which orbited a macaque monkey aboard a Delta N, was terminated nine days into a 30-day mission due to the rapidly deteriorating metabolism of the test subject, which expired soon after landing, apparently from dehydration.

During the late ’60s and early ’70s, vehicle designations added several more letters: J, L, M, and N. The J model changed the third stage yet again, to the Star 37D motor (also known as TE-364-3). The L, M, and N models used the new Long Tank Thor first stage, which lengthened both propellant tanks and changed the tapered kerosene tank to a cylinder. These models had similar launch capabilities to each other but used different third stage configurations: the FW-4, the Star 37D, and none, respectively. An additional modification was to add three more Castor II boosters to some rockets, called the M-6 and N-6. This single modification increased the Delta’s performance by 27 percent, and M-6 rockets were capable of lofting 1000 pounds to geostationary transfer orbit (GTO). Around this time, McDonnell-Douglas and its subcontractors also began licensing with Japan to build that country’s first GTO-capable launch vehicle.

By this time it was becoming obvious that the old letter designation system was inadequate to the task of describing a Delta’s ever-changing components. Therefore, in 1972 McDonnell-Douglas (the product of a 1967 merger) initiated a four-digit designator system. This system described the first stage tankage and engine, which continued to evolve; the number of booster motors, usually either 3 or 9; and a variety of upper stages. This numbering system is still in use today.

The early 1970s saw 8 different 1000-series models, each based on the Extended Long Tank Thor—another lengthening of the tankage. Also introduced in the 1000 series was an upgraded version of the Aerojet AJ-10 which had previously flown as the Titan Transtage. This new second stage was mounted to an 8-foot-diameter thrust structure which, along with a new 8-foot payload fairing, led to a nickname—the “Straight Eight”—that lasted until the Delta II with its bulbous fairing. Vehicles of the 1000 series launched several of NASA’s Explorer projects as well as the first Canadian commercial comsat, Anik 1.

The five models of the 2000 series, which primarily flew from 1974 to 1979, utilized a new first-stage engine design from Rocketdyne, the RS-27. This kerosene/liquid oxygen engine produced over 230,000 pounds of thrust at sea level. The second stage of the 2000 series was the Thompson-Ramo-Wooldridge TR-201, a modification of the engine used to power the Apollo Lunar Module’s descent stage. The TR-201, like the Aerojet AJ-10, burned nitrogen tetroxide and Aerozine-50 and was pressurized by helium.

In the late 1970s and early 1980s, the 3000 series upgraded the 2000 by using Castor IV boosters, motors which were considerably longer than their Castor II predecessors and thus more powerful. In 1979 McDonnell-Douglas realised the Space Shuttle would take longer to become operational than originally planned, and therefore the Delta would have to continue to evolve. The 3920 upgraded the second stage yet again, to another version of the AJ-10 with even larger tankage, the 118K. Many 3920s used the Payload Assist Module (PAM, also known as Star 48B), a 15,000-pound thrust solid kick motor developed for use on the Space Shuttle to push satellites from low orbit to their final destinations. The 3924 used the TE-364-4 as a third stage, which had about the same power as the PAM.

In 1982, as NASA prepared to commit to the Space Shuttle as the USA’s primary satellite delivery vehicle, the Delta production line was shut down.  It seemed that Delta’s days were numbered. However, the Challenger explosion of January 1986, along with an unprecedented string of launch failures during 1985–1987 (including a Delta 3914 which lost first stage power due to an electrical short), revealed the folly of this policy. The Air Force ran a competition to produce and launch 20 medium launch vehicles to loft the operational model of its new Global Positioning System (GPS) satellites. The contract was awarded to McDonnell-Douglas for their Delta II, a growth version of the 3920/PAM-D. This contract also provided the catalyst necessary for McDonnell-Douglas to begin marketing the Delta commercially.

The first model of the Delta II, the 6920-series, used the longest Thor tankage to date, called the Extra Extended Long Tank. This stage is 85.6 feet long and 8 feet in diameter and holds 211,000 pounds of propellant to fuel its RS-27 engine. Strapped onto the first stage were 9 Castor IVA motors, and atop the stack was a new two-piece bulbous fairing. The first nine GPS satellites were launched on 6925s.

In 1990 McDonnell-Douglas won a contract from NASA which included several west coast launches, and provided for refurbishment of Space Launch Complex 2-West at Vandenberg Air Force Base to reestablish west coast launch capability. In 1995 this resulted in the first west coast Delta launch in six years, a combined Canadian Space Agency and NASA satellite.

The current incarnation of the Delta II bears little resemblance to the original Thor-Delta. The Delta 7925 stands over 130 feet tall, 35 feet taller than its ancestor, and its first stage and interstage are painted in light blue primer rather than white. An improved RS-27A provides 237,000 pounds of thrust, and has an expanded nozzle for better efficiency at altitude. Augmenting this are nine solid motors with graphite epoxy casings, a composite material that is stronger and lighter than the steel used in Castor motors. GEM motors are six feet longer than Castor IVA motors and burn longer with more thrust. Six solid motors are started at liftoff, the remaining three at about 65 seconds into the flight. Three fairing sizes are available, from eight to ten feet in diameter. Total capacity to GTO is now approximately 4,120 pounds—more than forty times the capacity of Thor-Delta.

The latest modification to the Delta II is a 10-foot-diameter composite fairing which offers several improvements over the aluminum skin-and-stringer construction of the old 10-foot diameter fairing that was used to protect such observation satellites as POLAR and WIND. The new composite fairing is built in two sections, rather than three, reducing the number of pyrotechnic separation devices needed; it has 500 parts, versus 5,000 in the metal version; and it is lighter, stronger, and more aerodynamic. These improvements allow Delta II to carry an additional 80 to 100 pounds to low earth orbit. Boeing, which acquired McDonnell-Douglas in 1997, has also developed a lengthened version of this fairing for an increase of nearly 200 cubic feet of payload space.

Thirty-eight years of continual development increased the Delta’s payload capacity slowly and gradually, but in 1998 this progress took a significant leap. The Delta III is an "upgrade" of the Delta II that is in a different payload class entirely. The Delta III, known to Boeing planners as Delta 8930, can lift 8,400 pounds to GTO, over twice the capacity of the Delta II. It accomplishes this by means of a number of major changes. Most significant is the Delta III’s new second stage, powered by a Pratt & Whitney RL10B-2 engine derived from the RL10 engine that has been the basis of the Centaur stage for over 30 years. Burning liquid hydrogen and oxygen, the RL10B has a world-record specific impulse rating of 462 seconds and is the first use of a high-energy cryogenic engine in a Delta. In addition, new booster motors provide 25% more thrust, and 3 of the 9 motors are equipped with thrust vector control for improved manoeuvrability. As in the first stage of the Delta II, a Rocketdyne RS-27A provides main engine thrust and is fed by the same oxygen tank, while the fuel tank has been shortened and increased in diameter to improve control margins. The RIFCA (Redundant Inertial Flight Control Assembly) avionics systems and launch operations infrastructure are also identical to the Delta II. A new 4-metre-diameter payload fairing tops the assembly. The first Delta III was launched in August 1998. Like the very first Delta, Delta flight 259 carried a real payload, the Hughes HS-601 communications satellite Galaxy-X, rather than a test article. Unfortunately, it also suffered the same fate, as an attitude control problem doomed the flight. The second Delta III flight, in May 1999, demonstrated that Boeing’s control software redesign was successful, but later failed due to a rupture in the thrust chamber of the RL10 engine, stranding the Orion F3 satellite in a useless orbit. The third flight attempt, on 23 August 2000, vindicated the new launch vehicle in an almost Pyrrhic victory. Delta 280 orbited a mass simulator that accurately duplicated the properties of an HS-601—the first and only test payload in Delta history. Delta III has not flown since, and with Delta IV having entered service no launches are planned.

Workhorse of the Revolution

As the steam engine and railroads were the machines which brought the Industrial Revolution to the world, so Delta brought the Telecommunications Revolution. Due to its reliability and the fact that its capacity closely matched the relatively small size of early satellites, the Delta vehicle quickly became the workhorse of satellite communications and weather observation.

Echo and Telstar were rudimentary experimental communications satellites, flown to low orbit and with minimal or no transmitting ability. Low-orbit comsats required expensive and complicated ground stations—the antenna at Andover weighed 370 tons and was fully steerable in order to track Telstar as it crossed the sky. Geostationary orbit, theorized by Sir Arthur C. Clarke in 1945, promised to simplify ground stations by placing a satellite 22,300 miles up, where its orbital period closely matches the rotation of the earth and the satellite appears to stay in one place relative to the ground. After a nitrogen tank explosion crippled Syncom-1 during its apogee burn, Syncom-2 was launched in 1963 and was the first comsat to reach geosynchronous orbit successfully. It weighed just 71 pounds, carried only one two-way telephone channel, and (due to its 33° orbital inclination) described a lazy figure-eight path north and south of the equator, but it demonstrated the viability of synchronous communications. Syncom-3, the first geostationary satellite, took up station above the equator near the International Date Line and relayed short daily TV broadcasts from the 1964 Olympics in Japan.

The first operational geosynchronous satellite was Early Bird (aka Intelsat-1 after its managing organization, the International Telecommunications Satellite Corporation), a modified Syncom spacecraft. It flew on a Delta D in 1965 and provided 240 telephone channels from its station over the Atlantic at a time when transatlantic cables only provided 412 channels. This was soon followed by the Intelsat II series, which had similar capacity to Early Bird and provided coverage of about two-thirds of the earth’s surface. Intelsat III upgraded the spacecraft to 1,500 voice channels, and was the first operational satellite system to use a despun antenna structure; a despun antenna allows a satellite to spin for stability while keeping its antenna pointed at earth, thus avoiding the waste of transmitter power that an omnidirectional broadcast incurs. (Intelsat IV and later versions outgrew Delta and were launched on Atlas-Centaur rockets, among others.)

A 1972 policy change by the Federal Communications Commission allowing domestic satellite service prompted RCA in 1975 to launch Satcom 1 aboard a Delta 3914. It was immediately used by a group of entrepreneurs to transmit a new type of pay TV, Home Box Office, to cable providers throughout the United States. HBO was extremely popular and spurred the rapid development of cable television as a new industry.

A number of developing countries, particularly those with large areas and diffuse populations, saw the benefits of satellite communications in terms of the expensive microwave and coaxial networks they would no longer have to build. Indonesia led the way, as Deltas launched Palapa 1 in 1976 and Palapa 2 in 1977. These provided telecommunications service to the Philippines, Malaysia, Thailand, and Singapore, as well as Indonesia.

Satellite weather observation as it is today owes much of its heritage to Delta rockets. Though the first weather satellite, TIROS 1, flew aboard a Thor-Able, all subsequent TIROS satellites and their follow-ons (TIROS Operational System and Improved TOS) flew to low polar orbits on Deltas. The first TIROS series was experimental, but the results were so immediately successful that the fleet was put into “operational” service. For example, TIROS 3 was the first weather satellite to discover a hurricane, spotting Esther two days before conventional means would have revealed it. TIROS 9 flew a sun-synchronous polar orbit and was the first to provide complete global coverage—on 13 February 1965 it took 480 photos in a single day, forming a mosaic [photo] which covered the whole world (except the Arctic, which was dark at that time of year). The TIROS Operational System, or TOS, included a system called Automatic Picture Transmission which allowed simple ground stations to receive up-to-date photos on demand; within a few years, more than 400 such stations were in use in over forty countries.

The next step was to place weather satellites in geosynchronous orbit, where a stationary camera could provide images which could be strung together to form animations of weather patterns. This would allow meteorologists to follow the development and dissipation of storm systems. Ford Aerospace Corporation built two prototypes for NASA, the Synchronous Meteorological Satellites, which flew in 1974 and 1975. These were followed by the Geostationary Operational Environmental Satellites (GOES), which took pictures every thirty minutes of entire hemispheres of the earth in both visible light and infrared. Such pictures are now commonplace in daily newspapers and television weather reports.

The use of infrared imagery in GOES showed more than just cloud patterns at night. Investigators found that by using the right infrared wavelengths, forests, farms, and other vegetation could be easily mapped. This led to a series of polar-orbiting earth observation satellites known as Landsat, the first five of which flew on Deltas. Landsat images provided new fault line detail for geological maps, gave early hints of global warming, and showed clearly the ravages of Amazon deforestation. Landsat’s infrared cameras could even discern whether or not trees and crops were healthy. At first an experimental series, NASA now considers Landsat "the central pillar of the national remote sensing capability."* Landsat 5 continued to send images more than 25 years after its launch, and Landsat 7 was successfully launched aboard a Delta 7920-10 on 15 April 1999.

The impetus for McDonnell-Douglas’ development of the Delta II was the Air Force’s GPS contract. The Global Positioning System consists of a constellation of 24 satellites (21 plus 3 spares) in 6 planes, each orbiting the earth every 12 hours. All operational GPS satellites were launched by Delta II vehicles. Each satellite broadcasts two L-band radio signals containing ranging codes, ephemeris parameters, and Coordinated Universal Time (UTC) synchronization information. Both military and civilian users can use GPS receivers to receive, decode and process the signals to gain 3-D position, velocity, and time information. Military users achieve accuracies of 16 metres spherical error probable (SEP) for position, 0.1 metres per second root mean square along any axis for velocity, and 100 nanoseconds one-sigma for time transfer, which allow a military-issue receiver to pinpoint its location. Receivers have been placed in spacecraft and launch vehicles for accurate guidance control, and the latest generation of weaponry uses GPS to reach its targets, eliminating the risk of sending human operators into heavily-defended areas. Civilian GPS receivers are somewhat less accurate, owing to their inability to read the coded portions of the satellite transmissions, but work very well in nautical and aviation applications. Simple hand-held GPS receivers are now available for less than $100.

The Delta II also launched the inaugural flights of two competing constellations of communications satellites. Iridium and Globalstar are multinational corporations created to provide wireless personal communications networks designed to permit any type of telephone transmission—voice, data, fax, or paging—to reach its destination anywhere on earth. Transmissions via satellite will be routed through ground stations and from there to local ground-based telecommunications systems, or back to a satellite to reach another user on the same system. Though it seems likely that the global coverage of this type of system will someday make the common land-based cell tower obsolete, the present drawbacks (including unwieldy user hardware, expensive air time, connection difficulties, and marketing miscalculations) have already taken their toll, as Iridium declared bankruptcy and terminated service in March 2000. Their 88 satellites (55 of which flew on 11 Deltas) have been saved from deorbiting by New Iridium LLC, which has purchased the entire system and is attempting to resurrect service. Meanwhile, a Zenit launch failure in 1998 spurred Globalstar to re-manifest many of its flights (5 in 1999 alone) to the Delta II, and future flights to maintain the health of that constellation are planned for Deltas as well.

Deltas have orbited several firsts, among them the first passive communications satellite (Echo), the first commercial comsat (Telstar), the first European satellite (Ariel 1), the first comsat to reach geosynchronous orbit (Syncom 2). A constellation of GPS satellites provides precise location data to military and civilian users. Mars Pathfinder successfully landed on the Red Planet July 4, 1997, carrying the Sojourner rover vehicle for robotic exploration. Mars Global Surveyor, an orbital mapping satellite equipped with a laser altimeter and wide-angle camera, used a series of aerobraking manoeuvres to circularise its orbit and has returned an unprecedented amount of data regarding Mars’ surface features, atmosphere, and magnetic properties. The next generation of Mars probes, Mars Climate Orbiter and Mars Polar Lander, were launched on Delta II Med-Lite rockets in December 1998 and January 1999 (sadly, both missions were lost upon arrival at Mars). NEAR (Near-Earth Asteroid Rendezvous) became the first satellite to orbit an asteroid on 14 February 2000, and a year later survived a landing on the asteroid. Deep Impact intercepted a comet on 4 July 2005, collecting data as its precision-targeted, 800-pound impactor slammed into the hapless interloper. Stardust returned the first sample of cometary debris to Earth in 2006. And Pioneer 6, launched 16 December 1965 aboard Delta 35, when last contacted in December 2000 was still sending data about solar wind and cosmic rays to scientists on Earth after travelling more than 18 billion miles on 35 orbits around the sun.

Version 2.25, last update 27 November 2017. Written by Kevin S. Forsyth, who welcomes any questions, comments, or corrections.

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History of the Delta Launch Vehicle by Kevin S. Forsyth