Whilst the details of the payload are classified, it is rumoured to be one of the NRO’s most expensive to date.
The Delta IV’s upper stage is expected to perform three burns, suggesting that the satellite will be placed into geosynchronous orbit. NRO satellites currently believed to be operating in geosynchronous orbits include SDS communications satellites, and two types of Signals Intelligence (SIGINT) spacecraft, known as “Mercury” and “Advanced Orion” or “Mentor”.
Because SDS satellites are typically launched on smaller rockets, tonight’s payload is expected to be the latter, a SIGINT satellite. It may be a continuation of one of the older series, or the first of a new generation of satellites – possibly the much delayed IOSA or “Intruder” satellite, designed to combine the roles of the two previous satellite classes, however it is unclear whether this programme is still active.
The Delta IV Heavy is the largest carrier rocket in the EELV fleet operated by ULA for the US military, and has been seen as a potential alternative to the Ares I as a Crew Launch Vehicle for Project Constellation.
The first stage, or Common Booster Core (CBC), is propelled by a cryogenically-fuelled RS-68 engine. In the Heavy configuration, two more CBCs are used as liquid rocket boosters, separating around four minutes after launch.
Less than two minutes later, the first stage will separate, and the RL-10B engine of the second stage will ignite for the first of what is expected to be three burns.
After the separation of the payload fairing, around twenty seconds later, coverage of the launch will cease, and no further information will be released until spacecraft separation.
It will lift off from Launch Complex 37B at Cape Canaveral. The pad was originally built as a backup launch complex for the Saturn I and IB rockets in the 1960s. After the launch of Apollo 5, it was mothballed and eventually demolished. In the late 1990s, it was rebuilt for the Delta IV, and has been used on six out of eight previous flights. The other two were launched from Space Launch Complex 6 at Vandenberg Air Force Base.
Rollback of the Mobile Service Structure this afternoon took about half an hour, with the tower, used to access the rocket on the pad, arriving in its parked position away from the rocket at about 14:00 GMT. The terminal phase of the countdown began five an a half hours before the scheduled launch, at 19:03.
This is expected to be the first orbital launch to be conducted in 2009, and the ninth flight of the Delta IV across all configurations.
Although the Delta IV has not suffered an outright failure, the first Delta IV Heavy, launched in December 2004, reached an incorrect orbit due to the premature shutdown of its boosters and first stage. It is the first of four Delta IV launches currently scheduled for 2009, the next of which will be a Medium+(4,2), with the GOES-O weather satellite.