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The first nighttime launch of SpaceX’s Falcon Heavy rocket, and the first Falcon Heavy flight for the U.S. military, is set for no earlier than June 24 from pad 39A at NASA’s Kennedy Space Center in Florida, Air Force officials said Friday.

The four-hour launch window opens at 11:30 p.m. EDT on June 24 (0330 GMT on June 25). The new target launch date is two days later than previously planned.

The Falcon Heavy will launch 24 satellites into three distinct orbits around Earth, using up most of the heavy-lift rocket’s lift capacity with a series of four upper stage engine burns, the most ever by a SpaceX launch vehicle.

“We are now looking at no earlier than June 24 while we finish up integrating these satellites and finish our launch operation preparations,” said Lt. Col. Ryan Rose, chief of the small launch and targets division at the Air Force’s Space and Missile Systems Center, or SMC.

The 24 satellites come from the U.S. military, NOAA, NASA, and academic institutions, pursuing missions ranging from weather observation to technology demonstration. The mission is designated Space Test Program-2, or STP-2, and is managed by the U.S. Air Force.

The Falcon Heavy rocket set to fly on the STP-2 mission will use two side boosters recovered after the most recent Falcon Heavy flight April 11, which delivered the commercial Arabsat 6A communications satellite to orbit. The center core booster for the STP-2 mission is fresh from SpaceX’s factory in Hawthorne, California.

Each booster is powered by nine Merlin 1D engines, burning a mix of kerosene and liquid oxygen propellants.

The Air Force agreed to use the side boosters from the Arabsat 6A mission to familiarize military officials with SpaceX’s process of recovering and refurbishing rocket hardware. It is the first time the Air Force has used previously-flown hardware on a military satellite launch.

“STP-2 is the government’s first launch on a SpaceX Falcon Heavy vehicle, and is one of the most challenging missions the Space and Missile Systems Center has ever launched,” said Col. Robert Bongiovi, director of SMC’s launch enterprise systems directorate. “We’re putting 24 research and development satellites into three separate orbits, with a first-ever four engine start and burn of the second stage.”

The Air Force contracted with SpaceX for the STP-2 mission in 2012, targeting a launch in 2015. Delays in the development of the Falcon Heavy pushed the mission’s schedule back to 2019.

Military officials originally intended for the STP-2 mission to be a test flight for the Falcon Heavy, and an opportunity to place a batch of experimental — and relatively low-cost and low-priority — payloads into orbit on a new rocket. But now the mission has evolved to become a critical test to move the Air Force closer to allowing more expensive national security satellites to launch on the Falcon Heavy, and potentially with reused booster stages.

SpaceX has launched 21 missions with previously-flown booster stages — all successfully — with payloads for NASA and commercial customers.

“The use of the previously-flown hardware is providing critical insight into reusability and quality assurance that will allow us to provide space access to the warfighter in a more cost-effective and expedient manner, and I really appreciate the efforts of our industry partner SpaceX to make this happen,” Bongiovi said Friday in a briefing with reporters.

The first two Falcon Heavy missions lifted off from the Kennedy Space Center in daylight, but the STP-2 mission will launch at night. Like the previous two Falcon Heavy flights, the two side boosters will return to SpaceX’s onshore landing site at Cape Canaveral Air Force Station for nearly simultaneous propulsive landings, according to Walter Lauderdale, STP-2 mission director from the Falcon systems and operations division at SMC.

“The plan is to recover all three cores, two coming back to land and one out on the drone ship,” Lauderdale said Friday. “SpaceX is looking for this opportunity to demonstrate this capability (for) continued reuse. We’re excited to be part of that journey.”

A regulatory filing associated with the STP-2 mission submitted by SpaceX to the Federal Communications Commission in March suggested the company’s drone ship, used for offshore rocket landings, will be stationed near Florida’s Space Coast for the recovery of the Falcon Heavy’s center core.

The drone ship is typically positioned hundreds of miles offshore from Florida. The regulatory filing, which requested authority to operate radio transmitters during the booster’s descent, indicated the vessel will be parked roughly 24 miles (40 kilometers) east-southeast of pad 39A for the center core landing on the STP-2 mission.

Assuming favorable viewing conditions, the nighttime launch of the world’s most powerful rocket — producing 5.1 million pounds of thrust at full throttle — followed minutes later by the return of the three Falcon Heavy boosters to Earth could be a dazzling spectacle.

“As long as there are no clouds, having been down there for a couple, the recoveries back on land, they do end up being a spectacular sight coming back to the landing zone,” Lauderdale said.

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