Earlier installments traced the history of the Thor-Delta series from the original Thor intermediate range ballistic missile to a workhorse satellite launcher for NASA and the U.S. Air Force:
- Thor—From Cold War Stopgap Weapon to Workhorse Satellite Launcher
- Evolution of the Delta Rocket Family, Part 1
This video describes the further evolution of the Delta family as satellites gained weight and girth over time, its expected demise with the advent of the Space Shuttle, its comeback when it became clear the Shuttle could deliver on none of its promises of safety, low cost, frequent, and responsive access to space, and the final step to the Delta IV, which is, with different structure, engines, and propellants, a “Delta in Name Only” (DINO) but adapted to the requirements of its time.
Interestingly, the Delta IV in its original configuration and the Delta IV Heavy variant are the only rockets to ever have launched to orbit using only liquid hydrogen and liquid oxygen propellants. The base Delta IV is, in fact, similar in configuration to the launcher I proposed in my 1993 paper “A Rocket a Day” but super-sized: my rocket had a payload to low Earth orbit (LEO) of 2000 kg, while Delta IV with no strap-on solid boosters can launch 11,470 kg to LEO.
With the Delta IV Medium now retired and the Delta IV Heavy expected to make its last flight in 2024, the Thor-Delta series will have a history stretching 68 years from project start in 1956 through retirement.