Delta Reborn:  Extra Extended Long Tank "Delta 2"
Twelveth in a Series Reviewing Thor Family History
by Ed Kyle, Updated 11/19/2009

Delta, Shutdown and Failure

Huntington Beach Delta Production Line in 1981

Space Shuttle finally began flying in 1981, bringing the planned shift of all U.S. expendable launch vehicle payloads to Shuttle nearer to reality.   With no new orders for Delta, the McDonnell Douglas Delta production line began grinding to a halt after 1982.  Only four Deltas flew in 1984, and none lifted off in 1985 - the first year without a Delta launch since the program began in 1960.  The company delivered its final Delta to NASA in December 1984.  At the time, McDonnell Douglas was said to have had enough parts on hand to build two more Deltas if needed, and enough engines for five more. 

Then, on January 28, 1986, everything changed, both for Delta and for all U.S. space programs in general.  On that date, Shuttle Challenger and crew climbed into a crystalline blue sky and were lost within sight of horrified spectators along Florida's "Space Coast".  In an instant, the fallacy of assigning all of the nation's space launches to a single launch system was made painfully evident.

Challenger's loss was straddled by a pair of costly Titan 34D failures, causing many to wonder if the soon-to-be-retired expendable programs had been starved of resources.  A previously planned Delta launch, it was hoped, would set things back on course.

Delta 178 Failure

The launch, the first by a Delta in 16 months, was performed by Delta 178, a Delta 3914 model with a TR-201 powered second stage and a Star 37E third stage.  It lifted off on a warm spring evening from Pad 17A on May 3, 1986, carrying GOES G, a weather satellite bound for geosynchronous transfer orbit.  Unfortunately, the launch failed 71 seconds after liftoff when a short circuit in first stage wiring caused the RS-27 main engine to suddenly shut down.  The rocket spun out of control into a fireball, once again within sight of thousands observing along the Cape's beaches. 

This, the fourth major U.S. launch failure within a few months, knocked down the most reliable U.S. launch vehicle on a day when NASA most needed a success, ending Delta's U.S.-record streak of 43 consecutive successes.  The failure led to instinctive finger pointing, followed by analysis and longer term strategic thinking.  Though it seemed impossible at the time, that dark day would mark a turning point for both Delta and U.S. orbital space launch capability in general.

MLV

It was the U.S. Air Force, not NASA, that revived the old Thor "Thunder God" workhorse.  Prior to Challenger's loss, up to 20 Air Force Global Positioning System (GPS) Block II satellites had been on the Shuttle manifest.  Two GPS satellites, stacked on enlarged PAM D2 upper stage motors, would be carried at a time.  With Shuttle out of service, The Air Force decided to shift the launches from Shuttle to expendables.    

On August 1, 1986, The Air Force awarded four six-month, $5 million research and development contracts to McDonnell Douglas, Martin Marietta, General Dynamics and Hughes Aircraft to develop plans for launching the GPS constellation.  The GPS requirement called for boosting 953 kg satellites into 20,200 km circular orbits at a variety of inclinations.  The effort was dubbed "Medium Launch Vehicle" (MLV). 

General Dynamics offered a variant of its existing Atlas G Centaur, as well as an alternative consisting of a stretched "Atlas K" first stage topped by an SGS-2A upper stage solid motor combination.   At the time, all first generation GPS "Navstar" satellites had been launched by refurbished Atlas E or F ICBMs topped by SGS ("Space Guidance System") upper stages.  The SGS stages consisted of a stacked pair of Star 37 (SGS-1) or Star 48 (SGS-2) spin stabilized solid motors.  An upgrade would be needed, however, since the new GPS satellites weighed about 200 kg more than the previous version.        

Martin Marietta offered a version of Titan 34D that would ultimately fly under the Titan III Commercial name.  Titan would presumably have lifted two GPS satellites on each flight.    

Hughes initially suggested its proposed "Jarvis" heavy lift rocket that would have been powered by a pair of Saturn V F-1 engines.  Boeing, which soon joined the Hughes proposal effort, quickly shifted the proposal toward a Shuttle-derived design also named "Jarvis" in honor of Hughes employee Gregory Jarvis who was lost on Challenger.  Boeing's Jarvis would have consisted of an External Tank powered by a single aft-mounted Space Shuttle Main Engine augmented by a pair of Solid Rocket Boosters.   Jarvis, able to lift 36 tonnes to LEO, would also have carried multiple GPS satellites on each launch. 

The then-existing Delta 3920/PAM D could not meet the GPS requirements, so McDonnell Douglas and its subcontractors began looking at Delta-upgrade options.  One possibility - adopting Japan's H-1 liquid hydrogen upper stage engine - was deemed too costly and time-intensive.  This was bypassed in favor of upgrading the first stage and its strap on motors to create an upgraded Delta that was soon named "Delta 2".  

Shortly after the MLV competition began, President Reagan ordered NASA to get out of the commercial launch business.  His August 1986 directive opened the U.S. commercial launch market.   It was apparent that the MLV contract winner would have a competitive advantage in that market.

Delta 2

Delta 201, the First Delta 2-7925 with Hercules GEM-40 strap on solid motors.

McDonnell Douglas won the MLV contract on January 21, 1987.  The $316.5 million contract covered seven Delta 2 launches.  An option for 13 more flights would bring the contract total to $669 million.  Soon, Delta 2 also began to win commercial launch orders.              

Delta 2 was built around a longer first stage, stretched one final time to 26.1 meters, that was named Extra Extended Long Tank Thor (XELT).  The stage carried 96 tonnes of propellant, 16 tonnes more than the previous Extended Long Tank Thor. 

There were two early "Delta 2" models.  The first, interim versions, identified as the Delta 6000 series, were powered by RS-27 engines created from the final remaining H-1 inventory and by upgraded Thiokol Castor 4A strap on motors that produced 43.46 tonnes of sea level thrust and burned for 56 seconds.  Castor 4A produced 22% more thrust than Castor 4, carried about 9.2% more propellant, and had slightly better specific impulse.   

The final, Delta 7000 series rockets were powered by new RS-27A engines fitted with a bigger nozzle.  RS-27A produced slightly less liftoff thrust than RS-27, but more thrust at high altitude and with higher specific impulse.  The 7000-series was boosted by new GEM-40 Graphite Epoxy Motors developed by Hercules.  GEM-40s were longer (12.96 meters) and wider (1 meter) than Castor 4A and developed more thrust (50.9 tonnes sea level). 

Delta 2 used the existing Aerojet AJ10-118K ITIP engine-powered second stage.  Star 48B, similar to PAM, served as the third stage for GPS missions.  A new 8.5 meter long, 2.9 meter diameter payload fairing housed the satellites.

Delta 2 initially used the previous DRIMS guidance and control system, but on December 30, 1995 Delta 230 became the first to be controlled by a new Redundant Inertial Flight Control Assembly (RIFCA).  RIFCA, built around six ring laser gyroscopes and six accelerometers, provided triple redundant guidance, flight control and mission sequencing functions.

A fully fueled Delta 7925 with nine SRMs and a Star 48B third stage weighed nearly 232 tonnes at liftoff and could boost 1,840 kg to GTO.  By comparison, the first Delta flown in 1960 weighed only 54 tonnes and could carry only 45 kg to GTO.

McDonnell Douglas restarted Delta production at a new final assembly site in Pueblo, Colorado.  Substantial part fabrication for Delta continued at Huntington Beach, California.

ELT Flyout and Transition

Delta 183, the Final Delta 3000-series Vehicle

As the company spooled up Delta 2 production, it also flew out the final Extended Long Tank (ELT) Deltas.  

Delta 180, a 3920, flew successfully from the Cape's LC 17B on September 5, 1986, carrying the Strategic Defense Initiative's (SDIO) "Delta 180" Vector Sum Experiment mission into LEO.  The mission orbited a  modified "Payload Assist System" that was equipped with a suite of target seekers and powered by a TR-201 engine.  This unit separated from the Delta second stage and, several orbits later, targeted and intercepted the Delta second stage at a closing speed of about 2,900 m/sec. 

Delta 182 (a 3920 PAM-D) and Delta 179 (a 3914) orbited Palapa B2P and GOES 7, respectively, in 1987.  Delta 181 (a 3910) carried the SDIO Thrusted Vector Experiment into LEO on February 8, 1988 from 17B.  During this mission, more than one dozen objects were released from the second stage-mounted payload.   These objects were observed by sensors on the primary payload. Delta 181 was the final flight of a TR-201 powered second stage. 

Delta 183, the final 3000-series (a 3920) Delta, performed the "Delta Star" SDIO mission from 17B on March 24, 1989.  The Delta second stage performed two burns to insert Delta Star into a 500 km x 47.7 deg orbit.   Sensors on the spacecraft then observed the second stage deorbit burn and its reentry into the atmosphere.  The mission continued for several more months while Delta Star observed a series of launches, including launches  from Wallops Island, Cape Canaveral and Baikonur.

Delta 187, a Delta 4925 Powered by an MB-3-3 Engine, Stands at LC 17B

Three additional transitional Delta launches took place during 1989-1990 using unique "hybrid" Delta rockets cobbled together from a combination of old surplus and new parts.  One, Delta 189, was a Delta 5920, which was a 2.5 stage  ELT Delta fitted with the new Castor 4A motors.  It orbited NASA's Cosmic Background Explorer (COBE) from Vandenberg AFB SLC 2W on November 18, 1989 - the first Delta to fly from Vandenberg in nearly six years.  Six more years would pass before the next Vandenberg Delta launch.  

The other two transitional Deltas were 4925 vehicles, consisting of ELT first stages powered by surplus, lower-thrust MB-3-3 engines, but augmented by the new higher-thrust Castor 4A solid motors.  The rockets were topped by AJ10-118K powered second stages and Star 48B third stages.  Both flew from Canaveral's Pad 17B.   Delta 187 boosted Marco Polo 1 to GTO on August 27, 1989.  Delta 196, the 93rd and final ELT Delta, launched Insat 1D to the same type of orbit on June 12, 1990.

Back in Business

Delta 184, the First Delta 2, a Model 6925, Launched on 2/14/1989

The first Delta 2, a 6925 identified as Delta 184, orbited Navstar (GPS) 2-1 from LC 17A on February 14, 1989, slightly more than two years after the MLV contract was awarded.  It was the first of nine GPS launches on 6925 rockets from the Cape during 1989-90.  A total of 17 6000-series Deltas would fly, the final being Delta 212 in 1992.  Delta 212 was the final flight of a Saturn H-1 derived RS-27 engine. 

Delta 201, the first 7925 model with potent GEM-40 strap on motors, orbited the first of the heavier Navstar 2A series GPS satellites on November 26, 1990.  Delta orbited fourteen GPS-2A satellites by the end of 1993. 

Delta was back in business, performing 49 consecutive successful launches from late 1986 through the end of 1994, including 11 flights in both 1990 and 1992.  Delta 2 augmented its primary GPS business with missions for NASA, SDIO, European and Japanese space agencies, and commercial satellite operators. 

The pads were busy, but Delta's busiest years still lay ahead.

Delta Model Numbering System         

Table 1 lists the Delta model number designations used prior to and during the Extra Extended Long Tank era.

Table 1:  Delta Model Numbers

First Digit:  First Stage and Strap on Motor Types

0:  Long Tank, MB-3-3 engine, Castor 2 motors (1968)
1:  Extended Long Tank, MB-3-3 engine, Castor 2 motors (1972)
2:  Extended Long Tank, RS-27 engine, Castor 2 motors (1974)
3:  Extended Long Tank, RS-27 engine, Castor 4 motors (1975)
4:  Extended Long Tank, MB-3-3 engine, Castor 4A motors (1989)
5:  Extended Long Tank, RS-27 engine, Castor 4A motors (1989)
6:  Extra Extended Long Tank, RS-27 engine, Castor 4A motors (1989)
7:  Extra Extended Long Tank, RS-27A engine, GEM-40 motors (1990)

Second Digit:  Number of Strap on Motors

Third Digit:  Second Stage Type

0:  AJ10-118F (Aerojet Transtage derivative, 1972)
1:  TR-201 (TRW LM Descent Engine derivative, 1972)
2:  AJ10-118K (Aerojet ITIP engine, 1982)

Fourth Digit:  Third Stage Type

0:  No third stage
3:  Star 37D (TE-364-3, 1968)
4:  Star 37E (TE-364-4, 1972)
5:  Star 48B (TE-M-799, 1989)
6:  Star 37FM (1998)

Photos by NASA, USAF, McDonnell Douglas