Future U.S. military satellites will be matched to Atlas and Delta launch vehicles as late as six months before launch, a new strategy the Air Force hopes will limit cascading delays stemming from late payload deliveries.

File photo of a Delta 4-Heavy rocket. Credit: Pat Corkery/United Launch Alliance

The new slot manifest concept will begin in early 2011, when three Air Force payloads are candidates to launch on two Atlas 5 rocket flight opportunities.

"It is a philosophical change in the approach to launch scheduling from a project-centric approach frequently limited by delays in hardware readiness to an opportunity-based approach enabled through synchronizing multiple satellite payloads to a launch vehicle," a Space and Missile Systems Center launch and range systems wing spokesperson said.

Instead of pairing a payload with a launch slot up to two years in advance, rocket assignments will remain fluid until a point between six and 12 months before liftoff.

At that time, Air Force officials will select a primary and backup payload for a single launch slot. The decision will be based on spacecraft readiness and mission priority, according to the Air Force.

"Essentially, the satellite would compete for the next available slot for which they are ready," the Air Force said in a written statement to Spaceflight Now. "The competition for that slot is based on national priority or, in some cases, missions that have unique launch requirements."

Another decision point at least six months before launch will select the primary or alternate payload for the flight opportunity.

"This allows more flexibility and higher confidence that the spacecraft is ready," the Air Force said.

The Air Force is instituting a new mission prioritization process to determine what payloads should launch first. The strategy will also give military commanders the option of switching satellites closer to launch based on changing conditions.

But the military runs the risk of losing a launch opportunity if a satellite encounters a problem less than six months before liftoff, the Air Force spokesperson told Spaceflight Now.

United Launch Alliance, the operator of Atlas and Delta rockets, plans five launches for U.S. government customers in early 2011.

A Delta 4-Heavy rocket will loft a classified payload for the National Reconnaissance Office spy agency around Jan. 15 from Vandenberg Air Force Base, Calif.

An Atlas 5 rocket is scheduled to blast off in February from Cape Canaveral, Fla. The leading candidate satellite for that launch opportunity is the second Advanced Extremely High Frequency communications satellite for the Air Force. The Pentagon's second X-37B spaceplane is slotted in the standby role for that launch.

In March, two more NRO payloads are due for launch on a Delta 4 rocket from Florida and an Atlas 5 vehicle from California.

Cape Canaveral will host another Atlas 5 mission in May with either the X-37B spaceplane or the first SBIRS early warning satellite to geosynchronous orbit. The Air Force has not identified which payload is primary or backup.

Atlas 5 rockets can theoretically blast off from Cape Canaveral every 45 days, and Delta 4 boosters have a turnaround time of about 60 days. The Air Force provided additional funding for ULA to add a second shift in vehicle processing and flight analysis.

The extra work shift permits ULA to accommodate launch surges for constrained NASA planetary probes and high-priority national security missions.

ULA provides customers with a launch slot, a period of time in which a flight can occur.

NASA has two planetary missions scheduled for launch in late 2011. The Juno probe to orbit Jupiter will blast off in early August, followed in late November by the Mars Science Laboratory rover bound for Mars.

Both payloads only have a few weeks to lift off in tight windows when the alignment of the planets permits a trajectory to reach each mission's target.

"NASA planetary missions with rigid launch timeframes will be manifested to meet their mission need," the Air Force spokesperson said. "The other missions that competed for that slot, and were not deemed primary, slip to the next slot for consideration."

A launch schedule review board of the 14th Air Force, which oversees the military branch's space operations, implemented the slot manifest concept at its last meeting. Development of the new strategy began in February, according to the launch and range systems wing spokesperson.

The spokesperson said the change has become "standard operating procedure," but officials are still working out details before it is officially adopted.