By Cliff Lethbridge

Delta 4000 Series Launch, Photo Courtesy U.S. Air Force

Delta 4000 Series Launch, Photo Courtesy U.S. Air Force

Classification: Space Launch Vehicle

Length: 128 feet

Diameter: 8 feet

Date of First Cape Canaveral Launch: August 27, 1989

Date of Final Cape Canaveral Launch: June 12, 1990

Number of Cape Canaveral Launches: 2

The Delta 4000 Series was to have been the last generation of the Delta family at a time when virtually all commercial, civilian and military satellite delivery duties were being transferred to the multi-purpose Space Shuttle. However, in the early 1980’s McDonnell Douglas proposed improvements to the Delta 3000 Series with the goal of being able to carry a 3,000-pound payload to geostationary transfer orbit. Although the Delta program was waning at the time, this goal was indeed met by increasing the first stage burn time and incorporating other technical innovations. The same nine Castor solid rocket boosters used in the Delta 3000 Series were used in the Delta 4000 Series, but in the Delta 4000 Series configuration six of the solid rocket boosters were typically ignited at launch, with the remaining three solid rocket boosters ignited following burnout and jettison of the first six.

The Delta 3000 Series first stage RP-1 (kerosene) liquid fuel tank was extended by 4 feet, 3 inches and the liquid oxygen fuel tank was extended by 7 feet, 3 inches for incorporation in the Delta 4000 Series. Extending the fuel tanks allowed the Delta 4000 Series rockets to carry more fuel, thus extending the burn time of the first stage and improving performance. In the first departure from the “straight-eight” Delta configuration introduced over a decade earlier, the Delta 4000 Series introduced a payload fairing adapted from the Titan III-C program. This payload fairing had a maximum diameter of ten feet, allowing added room for larger payloads. The Delta 4000 Series also introduced improvements to the rocket to make it stronger and more durable, such as increasing the skin thickness of a number of component parts. The increased length of the Delta 4000 Series rockets over previous Delta variants required expensive modifications to support structures at Cape Canaveral and Vandenberg Air Force Base. While these expenses may have seemed risky, the McDonnell Douglas investment on the Delta 4000 Series would prove to be very fruitful. Although Delta production officially ceased in 1984 following 24 years of service as a workhorse of the civilian, commercial and military satellite launch industry, the Delta retirement would be short-lived.