Delta (rocket)

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Delta II, III and IV in comparison (Delta I is not in the picture)

The Delta is an American launcher . It was developed by the Douglas Aircraft Company and used the Thor rocket as a basic stage. Over the years the Delta has been continuously modified and expanded, so that today's Delta has little in common with the first models. So rose z. B. the take-off mass from around 50 t in 1960 to over 700 t in 2004, the payload capacity for the geotransfer orbit (GTO for short) rose from 130 kg to 13130 ​​kg in the same period. After Douglas Aircraft Company was bought by Boeing in 1997 , the Delta missiles are now produced and marketed by Boeing. The Delta has been started more than 300 times since 1960 and achieved a reliability of 95%. This makes it one of the most successful rocket models.

Since the Delta is no longer competitive today due to price competition from SpaceX , the last model still on offer - the Delta IV - is to be replaced by the new Vulcan .


A Thor Delta (No. 11) launches Telstar 1 (July 10, 1962, Cape Canaveral )
A Delta D with an INTELSAT-I satellite (April 6, 1965, Cape Canaveral)
Delta N6 with an ITOS satellite preparing for launch (October 1971, Vandenberg AFB )
A Delta 900 with the Nimbus E weather satellite from an unusual perspective (December 12, 1972, Vandenberg AFB)
The 112th Delta (Delta 1910) started with the OSO 8 solar observatory (June 21, 1975, Cape Canaveral)
Launch of a Delta 2914 with the ultraviolet satellite IUE (January 26, 1978, Cape Canaveral)
Delta 3910 with the SMM satellite (February 14, 1980, Cape Canaveral)
Delta 6920-10 started with ROSAT (June 1, 1990, Cape Canaveral)

In January 1959, NASA , which had just been established at the time, awarded the Douglas Aircraft Company an order for twelve rockets of the following types:

  • Stage I: Modified Thor-IRBM with a block I-MB-3 engine (676 kN thrust)
  • Stage II: Modified Able (called Delta) with an Aerojet AJ-10-118 engine (34 kN thrust).
  • Stage III: Altair with an ABL-X-248 solid fuel motor (12 kN thrust)

The rocket was supposed to have a payload capacity of 295 kg for a low orbit and 45 kg for a geotransfer orbit and was to serve as an interim solution in the years 1960-61 before other, more powerful missiles were operational. In addition, only scientific, meteorological and communication satellites should be launched with the rocket. The missile was named Thor Delta, later it was simply called Delta to underline the non-military character of the missile program. Of the first twelve missiles ordered, eleven were successful, so NASA decided to continue using the Delta and ordered another 14 missiles before 1962.

Many versions of the Delta rocket have emerged over the years, the most important of which are described below.

Delta I.

The first flight of a Thor-Delta on 13 May 1960 in which the satellite Echo 1 was to be launched into space, was a failure. But the second flight with the identical Echo 1A satellite on August 12, 1960 was successful. The rocket was soon named Delta and is now often called Delta I.

Early versions

  • Delta (Delta DM-19) - is the first version of the Thor-Delta, which was also often called Delta DM-19 because of its Thor-DM-19 first stage. It had a launch mass of 50 tons and could bring 130 kg into a low orbit or 45 kg into a geotransfer orbit. This version was launched a total of twelve times, with only one launch being a failure.
  • Delta A - differs from the Delta DM-19 by a modified first stage, which got an improved engine and was now called DM-21. The second stage of the rocket was also modified, giving it the option of re-ignition in orbit. The launch mass of the rocket remained practically the same, but the payload capacity increased to 181 kg for a low orbit and to 54 kg for the GTO. Delta A only started twice, both starts were successful. The first launch took place on October 2, 1962.
  • Delta B - differs from the Delta A only in a slightly longer second stage, which could take up more fuel. The payload capacity increased to 370 kg for a low orbit and to 68 kg for the GTO. The rocket launched nine times, only one launch was unsuccessful. The first launch took place on 13 December 1962 with the experimental communications satellites Relay I .
  • Delta C - received a new Altair 2 third stage, which replaced the old Altair 1. There was also a Delta C1 version that used an FW-4D third stage. The payload capacity of the Delta C was 410 kg for a low orbit and 82 kg for the GTO. Delta C (together with C1) was started a total of 16 times, with two false starts. The first launch took place on November 27, 1963.
  • Delta D - differs from Delta C in that it has three Castor I solid boosters attached to the first stage of the rocket. In addition, the first stage engine was slightly modified. The payload capacity was 450 kg for a low orbit and 104 kg for the GTO. Delta D was started twice, both missions were successful. The first launch took place on August 19, 1964.
  • Delta E - received a new third stage that was about twice as heavy as the old one. In addition, the diameter of the second stage was increased so that their tanks could hold more fuel. In addition, three Castor II boosters were used, which were a little stronger than the old Castor I. There was also a Delta-E1 version with a FW-4D third stage. The payload capacity of the Delta E has now increased to 750 kg for a low orbit and to 150 kg for the GTO. The rocket was launched 23 times, only one launch was unsuccessful. The first launch took place on November 6, 1965.
  • Delta G - this is a Delta E without the third stage, as it was only used to launch low-flying satellites, for which an additional third stage is not required. The payload capacity for a low orbit was 735 kg. Delta G had two missions, both were successful. The first launch took place on December 14, 1966.
  • Delta J - is a Delta E with a strong Burner 2 third stage that was about twice the size of the old Altair 2. Delta J was able to put 800 kg in low orbit or 263 kg in GTO. The rocket was only launched once, the launch was successful. The first launch took place on July 4, 1968.
  • Delta L - got a slightly longer first stage, which now weighs 20 t more than the old one. A FW-4D stage was used as the third stage. This increased the payload capacity of the Delta L to around 300 kg for the GTO. There was a successful and an unsuccessful start. The first launch took place on August 27, 1969.
  • Delta M - differs from the Delta L through the use of the Burner-2 upper stage, which was already used in the Delta J. There was also a Delta M6 version in which six Castor II solid fuel boosters were used for the first time. The payload capacity for a GTO was 356 kg (454 kg for the Delta M6). There were a total of 13 starts of the M versions, two of which failed. The first launch took place on September 19, 1968.
  • Delta N - differs from Delta M only in the absence of the third stage, which was not needed for takeoffs into low orbits, for which Delta N was designed. As with the Delta M, there was a Delta-N6 version that was equipped with six boosters. The payload capacity for a low orbit was 900 kg (1600 kg for the Delta N6). Of the nine launches of the N versions, one was unsuccessful. The first launch took place on August 16, 1968.

Later versions

Since naming the many versions of the Delta had become too complicated, it was decided to introduce a new naming system. Now each version has been assigned a four-digit number, whereby the individual digits have been assigned according to the following key:

    • the first digit corresponded to a significant change to the first stage of the rocket or to the solid fuel boosters. The Thor-LLT stage that is currently in use (since Delta L) with the Castor II boosters was given the number 0 .
    • the second number meant the number of solid fuel boosters, with 0 standing for a rocket without a booster.
    • the third digit corresponded to the second level. The level currently in use received a 0 .
    • the fourth digit corresponded to the third level. A Star 37D level received a 3 and a Star 37E a 4
  • x00 series - differs from the Delta N through a slightly modified second stage and in that up to nine boosters can now be attached to the rocket. From this series only the 0300 and 0900 versions started, whereby the first digit was often left out, and these versions were only named 300 or 900 . There were a total of five starts, one of which was a false start. The first launch took place on July 23, 1972.
  • 1000 series - received a modified Thor ELT first stage that was 14 t heavier than the old one. This changed the first digit in the name to a 1 . There was also a modified, second stage of the rocket in this series, which corresponded to a 1 in the third position of the designation. For all missiles with the modified second stage, the diameter up to the conical missile tip has been increased to that of the Thor first stage from 8 feet (2.44 m). This was achieved with a new step adapter and a payload fairing with a diameter of 2.44 m each, which enclosed everything above the first step. The second step, the diameter of which was smaller than the surrounding cladding, was fastened from the inside in its center. In addition, the older second stage was used without the new cladding. ( 0 in the third position). The following versions were launched: 1604 , 1410 , 1900 , 1910 , 1913 and 1914 . There were eight starts in this series, all of which were successful. The first launch took place on September 23, 1972.
  • 2000 series - in this series, the first stage received a new RS-27 engine. In addition, the Delta was only built with a diameter of 8 feet , so from the 2000 series it always had the appearance of the modern Delta II rocket. This series launched many commercial payloads and was therefore built in large numbers. A total of 44 starts were carried out, with only one start being a partial success. The following versions were used: 2310 , 2313 , 2910 , 2913 and 2914 . The first launch took place on January 19, 1974.
  • 3000 series - the first digit was changed due to the switch from Castor II to Castor IV boosters, which were considerably larger and heavier than the old boosters. In addition to the previous one, a new AJ-10-118K-ITIP second stage was also used in this series, which was marked with a 2 in the third position. In addition, there has been a new PAM-D third stage since this series . In contrast to other upper levels, PAM-D was not marked by a number, but was written after the rocket designation. Of this series, 38 missiles were launched, three of which failed. The following versions were used: 3910 , 3913 , 3914 , 3910 PAM-D , 3920 , 3924 and 3920 PAM-D . The first launch was on December 13, 1975.
  • 4000 series - in this series, new solid matter boosters were introduced again, this time in the Castor IV-A and IV-B versions. The two booster versions were used in parallel, with IV-A being ignited when the rocket was launched and IV-B only later in flight. The Castor IV-B had - compared to the otherwise identical Castor IV-A - larger thrusters to adapt to the lower air pressure at high altitude. These were used to improve the relaxation ratio and increase the thrust. In addition, the 4000 series used the old MB-3-III engine for the first stage, which was last used in the 1000 series. This was because there were still some old engines left and they didn't want to be scrapped. The PAM-D upper level now also received an identification number, namely a 5 in the fourth position. There were two launches of this series, both rockets flew in the 4925 version , and successfully launched their payload into space . The payload capacity of a Delta 4925 was 1312 kg for the GTO. The first launch was on August 27, 1989.
  • 5000 series - differs from the 4000 series only in the use of the RS-27 engine in the first stage of the rocket, which has been used since the 2000 series. There was only one start of this series and that was the 5920 version . The launch took place on November 18, 1989 and was successful.
  • 6000 series - this series was developed as a replacement for the space shuttle , which was no longer available for launching commercial and military satellites after the Challenger disaster since 1986. To increase the Delta's payload capacity, the first stage was significantly lengthened so that it could hold more fuel. In addition, there have been three different payload fairings since this version, the old with 2.4 meters (eight feet) in diameter and the new with 2.85 and 3 meters (9.5 and 10 feet) in diameter, which is achieved by attaching a - 8 or -10 was marked on the missile type (9.5 feet was now the standard fairing and was not specially marked). The rockets in this series took off a total of 17 times, and all launches were successful. The following versions were used: 6920-8 , 6920-10 , 6925 and 6925-8 . The first launch was on February 14, 1989.

Delta II

A Delta 7920-10C will launch on April 20, 2004 with the Gravity Probe B satellite .
Delta II 7925 (2925) with Deep Impact

The only difference between the Delta II and the 6000 series was a modified first stage engine and a new solid fuel booster. The first stage got an RS-27A engine, which provided a little more thrust than the RS-27. The Castor IV boosters have been replaced by the slightly larger GEM 40 boosters. The numerical identification system was also used for the Delta II, with a 7 in the first position. In addition, there has been a Delta II with more powerful GEM-46 boosters since 2003, which were also used in the Delta III and were adopted by it. This Delta rockets are by adding the letter H marked. The payload capacity of a Delta II 7920 is approximately 5000 kg for a low orbit and a Delta II 7925 is approximately 1800 kg for the GTO.

The first launch of a Delta II took place on November 26, 1990 with a GPS satellite on board. Since then she has flown more than 100 times, with only two false starts so far, the last on January 16, 1997 (as of early 2005). Since the Delta II has become too weak for commercial communication satellites since the beginning of the 90s , it is now mainly used for launching smaller military satellites, such as. B. used the GPS satellites up to the end of the GPS IIR-M series and to launch NASA research satellites . In addition, many NASA interplanetary spacecraft were launched with the Delta II, such as B. all Mars missions from 1996 to 2003, Stardust , MESSENGER , Deep Impact and many others.

For low earth orbits and planetary missions, versions with just three or four boosters are also available. The Delta II is also used with a smaller third stage when launching some very light spacecraft. This has a Star 37FM drive and weighs only 1063 kg, instead of 2141 kg as the PAM-D upper level. However, the new upper stage massively reduces the payload capacity, which is why it is only used very rarely. This upper level received a 6 as the final digit . So far it has only been used for the missions IMAGE , Stardust, Genesis and Deep Space 1 .

Based on the newer nomenclature of the Delta IV, NASA also speaks of the Delta 2xxx . There is a risk of confusion with the 2000 series of the Delta I. The manufacturer Boeing has kept the old spelling 7xxx .

The Delta II had its last launch on September 15, 2018 with the ICESat-2 .

Delta III

Second stage of a Delta III

Since Delta II has become too small to launch commercial payloads due to the increasing satellite mass, it was decided in the mid-1990s to develop the much more powerful Delta III.

At the first stage of the Delta III hardly anything was changed compared to Delta II: The tanks were shortened so as not to increase the total length of the rocket significantly, and the old GEM-40 solid fuel boosters were replaced by the slightly longer and wider GEM-46, also called GEM LDXL (Large Diameter Extended Length). Delta III received a new, high-energy second stage powered by a Pratt & Whitney RL-10 B2 engine. RL-10B2 used liquid hydrogen and oxygen as fuel and delivered a thrust of 110 kN. The engine is a variant of the RL-10 engine of the Centaur upper stage, which also has a thrust nozzle with extendable parts. This makes it easier to integrate the stage into the rocket, but still offers increased efficiency after the stage separation and subsequent extension of the nozzle to the full length. The exhaust nozzle, which is made of carbon fiber composite materials, is manufactured by SEP in France . The stage also differs from the Centaur in that its tanks maintain stability even without pressurization, which is not the case with the Centaur. The diameter of the hydrogen tank of the second stage is 4 m, that of the oxygen tank below is 2.4 m, which corresponds to the diameter of the Delta II. In addition, the rocket received a new, more spacious payload fairing with a diameter of 4 m. As a result of all these measures, the payload capacity of the Delta III increased to 3810 kg for the geotransfer orbit, more than double that of a Delta II. The numerical designation system also applies to the Delta III, with an 8 in the first position and an 8 in the third 3 for the new second stage. NASA, on the other hand, would use a 3 in the first place according to their new nomenclature .

The first launch of a Delta III took place on August 27, 1998 and ended shortly after take-off with the rocket exploding. The next start on May 5, 1999 was also a failure. It was not until the third launch on August 23, 2000 that the payload reached an orbit, which, however, was lower than expected, so that this launch was only to be assessed as a partial success. All three missiles flew in the 8930 version .

After these failures, production of the Delta III was discontinued and it was eventually replaced by the new Delta IV in 2002. All payloads of the Delta III were transferred to the Delta IV. Some of the technologies developed for Delta III are used in Delta IV, such as: B. The second stage of Delta III was taken over almost unchanged. The GEM-46 solid boosters, on the other hand, were taken over from the Delta III for the new Delta II Heavy versions.

Delta IV

Launch of a Delta IV Medium with a DSCS satellite

On November 20, 2002, the first Delta IV took off from Cape Canaveral . Delta IV was created as part of the US Air Force's Evolved Expendable Launch Vehicles program to replace the older missile types. A completely new first stage was designed for the Delta IV, which is powered by a newly developed Rocketdyne - RS-68 - rocket engine. The engine burns liquid hydrogen with liquid oxygen (LH2 / LOX). The first stage was named CBC (Common Booster Core) and formed the basis for all versions of the Delta IV. The second stage of the Delta IV was largely taken over from the Delta III.

Boeing currently offers five different versions of the Delta IV series:

  • Delta IV Medium - has a payload fairing four meters in diameter and no solid fuel boosters.
  • Delta IV Medium + (4.2) - differs from the medium basic version in that it has two additional GEM-60 boosters.
  • Delta IV Medium + (5.2) - differs from the Medium + (4.2) version in that it has a payload fairing five meters in diameter and a slightly higher fuel capacity of the second stage.
  • Delta IV Medium + (5.4) - is the most powerful version of the Medium series and differs from the Medium + (5.2) by two additional GEM-60 boosters, which increases the number of boosters to a total of four.
  • Delta IV Heavy - consists of three bundled CBCs as the first stage, and is about twice as strong as the strongest medium version.

Web links

Commons : Delta  album with pictures, videos and audio files


  1. ^ Norbert Bruges: Delta I.
  2. See photos: Delta 1410 and Delta 1910
This version was added to the list of articles worth reading on September 22, 2005 .