Among America’s illustrious line up of powerful rockets, is their workhorse, the Delta IV
Like everything else for the Americans, the bigger it is, the better. The same hold true for their rockets as well. So, when time came for the successor to their Thor range of rockets, they settled on the powerful fourth upper stage on the Thor, which was called Thor-Delta. Eventually, the entire Thor-Delta launch vehicle came to be called simply, “Delta.”
Delta IV is an two stage, expendable launch system in the Delta rocket family and is the only launch vehicle from the Delta family that is still in use. The rocket’s main components are designed by Boeing’s Defense, Space & Security division and built in the United Launch Alliance (ULA), a joint venture between Lockheed Martin Space Systems and Boeing Defense, Space and Security Division. Final assembly is completed at the launch site by ULA. Although the Delta family of rockets have always been used for civilian purposes such as communication, meteorology, lunar probes etc rather than military purposes, the Delta IV was primarily designed to satisfy the needs of the U.S. military. The rocket was designed to launch payloads into orbit for the United States Air Force Evolved Expendable Launch Vehicle (EELV) program and also sporadically for the commercial satellite business. The rocket is launched from facilities in either Cape Canaveral or Vandenberg Air Force Base.
The Delta IV comes in five variants: Medium, Medium+ (4,2), Medium+ (5,2), Medium+ (5,4), and Heavy, depending on the payload size and weight. During the development phase, a Small variant was also also considered, but it was subsequently dropped in 1999.
The first stage of a Delta IV consists of one, or in the Heavy variety three, Common Booster Cores (CBC) powered by an Aerojet Rocketdyne RS-68 engine, which burns liquid hydrogen and liquid oxygen, while the second stage is powered by a cryogenic RL10B2 engine, which features an extendable carbon-carbon nozzle to improve specific impulse.
While the Delta-IV has the legacy of the Delta family of rockets, the vehicle is a new design, rather than an evolution of the older Delta boosters. A primary change in the design is that the first stage uses liquid hydrogen rather than the kerosene as fuel of earlier Delta boosters, and thus used a new engine, the Rocketdyne RS-68.
The Delta IV has always jangled the US government’s pockets as it is quite an expensive vehicle to launch, with a whopping 164+ million USD as its cost per launch. Moreover, it entered the market in 2002 when global capacity was already much higher than demand. It had a yet unproven design and competing launch vehicles were available much lesser costs. This sure was quite an expensive proposition for the US government. So much so that, in 2003, Boeing pulled the Delta IV from the commercial market, citing low demand and high costs. However in 2005, Boeing returned the Delta IV to commercial service.
To its credit, the Delta family of Rockets have a 95% success rate. The Delta IV in particular has never seen a failure, except for that one partial failure of the Delta IV Heavy in 2004. Perhaps, its success justifies its cost to the US government. Its next scheduled launch is that of the Delta Medium+(4,2) rocket in the spring of 2019.
Delta IV has had an illustrious history starting from 2002 and seems to have no plans of retiring soon with possible future upgrades that include adding extra strap-on solid motors, higher-thrust main engines, lighter materials, higher-thrust second stages, more (up to six) strap-on CBCs, and a cryogenic propellant cross feed from strap on boosters to the common core. However, its planned successor is the Vulcan which is set to replace the Atlas V and the Delta IV and has an expected first launch in April of 2021.
The Americans show their love for the Delta IV by calling it…the Big Sam!