The Evolution of the Delta Launch Vehicle

The Evolution of the Delta Launch Vehicle
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A Slight Reprieve for Vanguard

After Explorer, Vanguard tried again. A second attempt failed a few days after Explorer’s launch. On March 17, 1958, Vanguard finally orbited its grapefruit. But then four successive attempts failed. All told, only three of 11 attempts would achieve orbit. The program was cancelled as the Jupiter-C took its place as the reliable launch vehicle.

Another launch concept was resurrected as well.

Delta Development

Remember the Air Force’s moon shot concept that Charley Wilson tossed? It returned as the Thor Able launch vehicle. Three moon shot attempts were made but none were successful. However, a fourth Thor Able launched the first weather satellite—Tiros 1.

And the Thor booster went on to become the workhorse of the unmanned space program, getting ever more powerful upper stages including the Agena A and the Agena B. The Thor itself evolved, getting a more powerful motor. (The original was the H1 with 150,000 lbs thrust. Eventually its motor would have 207,000 lbs thrust.)

Delta LV

The launch vehicle itself finally morphed into a new design—the Delta—with three solid boosters. This increased its payload capacity. But the venerable old rocket was not done yet. In 1987, the Air Force awarded what was then McDonald-Douglas Aircraft (now Boeing) a contract to produce the Delta II. Gone was the distinctive tapered fuselage, giving the new booster more propellant capacity. The three solid boosters were replaced with nine.

Delta II

NASA liked the design as well. Delta II became a significant part of the space fleet. Boeing did not rest on Delta’s laurels, however. It introduced Delta III, a total redesign of the vehicle. Delta III was 13 feet in diameter, compared to eight feet for previous Deltas. The first stage motor was replaced with a new one generating almost 250,000 lbs of thrust. The strap-on solids were larger and more powerful.

And the second stage modernized Agena was replaced with an uprated Centaur LH2/LOX stage.

Unfortunately, III did not fare well. Only three were flown, with no successes.

So Boeing completely redesigned the package again. The basic fuselage structure was retained, but the propellant and motor were changed. The RP 1 and LOX were replaced with LOX and LH2. A new motor, the RS-68, designed by Pratt and Whitney, powered Delta IV, with an average 700,000 lbs of thrust.

Boeing developed a series of five launch vehicles (LVs) around this basic rocket, all with a modernized Centaur second stage. A medium launch vehicle used just the basic Delta IV. Three ‘medium plus’ LVs used the Delta IV with strap-on solid boosters.

A heavy LV uses two strap-on Delta-IVs to create an LV that can lift 50,000 lbs to LEO.

Delta IV family

Meanwhile, the Wall Falls

As the Delta went through its metamorphoses, the Soviet Union continued to uprate its basic rocket motors. Rather than design new ones, the Soviets simply kept improving what they had. The results were ever more powerful—and ever more reliable—motors.

When the Soviet Union fell, Russia inherited a stable of powerful, reliable launch vehicles that continue to perform almost flawlessly to this day including the Soyuz LV that ferries crews to the ISS and the Progress spacecraft that sends supplies there.

The RD-107 engine that formed the basis of most Soviet LVs had been continually improved. By the 21st century it was producing over 225,000 lbs of thrust per chamber, for a total of 900,000 lbs, and was re-designated the RD-108. It is so reliable, the French have contracted to launch Soyuz LVs from their equatorial launch site.

And the Russian RD-108 has another fan.

The Atlas of LVs

From the beginning of manned space flight, the venerable Atlas had been the U.S.’s mainstay for both manned and unmanned flights. Besides boosting the Mercury capsule into orbit seven times, the stage and ½ Atlas played a major role in the Gemini program, carrying Gemini’s target Agena vehicle to orbit. Beyond that, the Atlas/Agena combo sent many probes on their journeys to the

Atlas Agena


And the Atlas/Centaur, arguably the most elegant of all LVs, sent the Surveyor spacecraft to the moon to find landing spots for Apollo. Later, that combo would send ever more sophisticated craft to the outer planets.

Atlas Centaur

The Centaur became the standard second stage for all subsequent LVs, and is now available in two configurations—single chamber and dual chamber versions.

As an unmanned LV, the Atlas began like the Thor, with an Aerobee second stage as an Atlas/Able. But the power of the big rocket—360,000 lbs trust at the time—was too much to waste, so the other configurations were developed.

As this century began, both the Air Force and NASA saw the need for very heavy LV, much more powerful than even the Delta IV. Lockheed-Martin now was building the Atlas, and had made it more powerful and a much sturdier vehicle. Gone was the integral tankage that had been the LVs signature construction. Standard exterior fuselage and separate internal propellant tanks made a stronger vehicle. There was of course a weight penalty, but with the fuselage, solid boosters could be attached.

These changes took Lockheed-Martin through the Atlas III. To that version, the familiar stage and ½ configuration remained. But the aerospace giant wasn’t going to let Boeing have all the heavy lifting game. Its answer to Delta IV was the Atlas V.

Atlas V was a complete redesign of the venerable booster. No more half stage configuration. It has a single booster stage. But the surprise is its engine. It uses the reliable and powerful Russian RD-80 engine in a two chamber configuration. This develops 860,000 lbs of thrust. Additionally, three to five strap-on solid boosters can provide up to an extra 306,000 lbs of liftoff thrust.The ATLAS V that sent JUNO on its way to Jupiter used five strap-ons. Lockheed-Martin has a heavy ATLAS V with Shuttle type strap-ons in the wings.

Atlas V

But No Manned Rocket–Yet

Today, the Delta IV and Atlas V are the U.S.’s primary unmanned LVs. Because of President Obama’s decree that any manned LV be developed by private industry, there is no manrated LV. Both the Delta and Atlas have been proposed for man rating to launch the Orion spacecraft. Boeing is building NASA’s Multi Purpose Crew Vehicle (MPCV), but its DELTAs could be used only to get it to LEO. The ATLAS V could take it to a translunar injection orbit.

NASA has said it will make a decision on an LV soon.

Meanwhile, America hitchhikes to space on Russian LVs.

Sources and Credits

All Delta images: Boeing

Delta IV:

Atlas V:

All other photos: personal collection


This post is part of the series: All About Rockets

The design of modern rockets went through many variations in their brief history since 1926. Sounding rockets provided the basis for the technology that would eventually take us into space.

  1. The History and Design of Modern Rockets
  2. History of Rocket Development–From the Edge of Space to the Conquest of Space
  3. Rocket History and How Rockets Work: The Development of America’s Space Fleet