A 206-foot-tall Atlas 5 rocket returned to pad 41 at Cape Canaveral on Tuesday evening after an unplanned rollback to a nearby integration hangar for repairs. Credit: United Launch Alliance
Ready for blastoff just after sunset Wednesday with a classified payload for the U.S. government’s spy satellite agency, a United Launch Alliance Atlas 5 rocket rolled out to its launch pad at Cape Canaveral late Tuesday afternoon after an unplanned trip back inside its integration building for repairs.
The 206-foot-tall (63-meter) Atlas 5 rocket arrived on pad 41 at Cape Canaveral Air Force Station around 5:30 p.m. EST (2230 GMT) Tuesday following an 1,800-foot journey from ULA’s Vertical Integration Facility. Pushed by locomotives, the Atlas 5 and its mobile launch platform followed rail tracks leading to the launch mount at pad 41.
The rollout followed the same path the rocket traveled Monday, when ULA transferred the Atlas 5 to the launch pad ahead of a planned liftoff Tuesday evening. But officials ordered the Atlas 5 back inside the VIF to resolve a concern with an environmental control system line feeding conditioned air to the National Reconnaissance Office payload on top of the rocket.
After returning the rocket to the VIF on Monday night, technicians swapped out the problematic environmental control system duct, which may have been damaged from high winds during the Atlas 5’s first trek to the pad. Tory Bruno, ULA’s president and CEO, tweeted that the company installed a reinforced duct in its place.
The return of the Atlas 5 to the VIF allowed workers to use platforms to access the location of the environmental control system line, which ULA said is inaccessible at the launch pad.
After finishing the repair work, ground crews retracted the work platform and rolled the Atlas 5 back to pad 41. Once on the pad, teams planned to connect the Atlas 5 to ground systems at pad 41, and ULA’s ground crew will complete inspections, checkouts and other activities.
Liquid oxygen will be loaded in the first stage during the countdown Wednesday afternoon, along with liquid hydrogen and liquid hydrogen for the Atlas 5’s Centaur upper stage. RP-1 fuel for the first stage was loaded last month during a countdown dress rehearsal.
The latest forecast issued this morning indicates an 70% chance of favorable weather conditions for launch at 5:54 p.m. EST (2258 GMT). The primary weather concern is with ground winds at Cape Canaveral.
Forecasters predict east-northeast surface winds of around 20 to 26 knots at launch time, with broken clouds at 3,000 feet. The temperature at launch time should be around 75 degrees Fahrenheit.
Liftoff is scheduled around 19 minutes after sunset. Assuming clear skies, the Atlas 5 and its exhaust trail could put on a spectacular show in the twilight sky over Florida’s Space Coast.
The launch Wednesday — designated NROL-101 — will mark the 86th flight of an Atlas 5 rocket since 2002, and the fifth Atlas 5 mission this year. It will be ULA’s 30th mission for the NRO, which owns a fleet of spy satellites supplying optical and radar imagery, signals and communications intercepted from adversaries, and other data to the U.S. government’s intelligence agencies.
The NRO has not revealed information about the payload flying on the NROL-101 mission, but warning notices released to pilots and mariners suggest the Atlas 5 rocket will head on a northeasterly track from Cape Canaveral, following a path parallel to the U.S. East Coast before flying near the Canadian maritime provinces.
The trajectory indicates the Atlas 5 will release the NRO payload into a high-inclination orbit.
The NRO owns data relay satellites and several spacecraft designed to intercept communications signals in elliptical Molniya-type orbits that stretch nearly 25,000 miles (40,000 kilometers) above Earth at their highest points. Those orbits are tilted around 63 degrees to the equator, giving satellites regular views of Russia and other parts of the northern hemisphere.
The Atlas 5 scheduled for launch Wednesday might be aiming for a similar Molniya-type orbit, according to multiple independent experts who track spy satellite activity.
The launch vehicle for the NROL-101 mission will fly in the Atlas 5’s “531” configuration with three solid rocket boosters and a 5.4-meter-diameter (17.7-foot) payload fairing.
The payload fairing for the NROL-101 mission will fly in its medium-length variant, offering more volume for the classified spacecraft on-board than the standard shorter-length 5.4-meter-diameter shroud. The medium-length 5.4-meter fairing has flown on seven prior Atlas 5 missions.
The launch Wednesday will be the fourth time an Atlas 5 rocket has flown in the 531 variant, but it will be the first to launch with new GEM 63 strap-on boosters produced by Northrop Grumman. They are the same form, fit and function as the AJ-60A solid rocket boosters made by Aerojet Rocketdyne that have flown on all prior Atlas 5 missions that required strap-on motors.
The GEM 63 motors measure 66 feet (20 meters) long and 63 inches (1.6 meters) wide. They can produce 373,800 pounds of thrust at maximum power.
ULA says the GEM 63 motors are less expensive and easier to handle during launch preparations. The company’s next-generation Vulcan Centaur rocket will fly with a larger Northrop Grumman solid booster named the GEM 63XL, and the introduction of the new rocket motors on the Atlas 5 will help retire risk before the first Vulcan Centaur launch, according to ULA.
The three GEM 63 boosters on the NROL-101 mission will ignite on the launch pad and burn for 94 seconds, consuming 97,500 pounds (44.2 metric tons) of pre-packed solid propellant before jettisoning at T+plus 1 minute, 53 seconds, to fall into the sea.
The RD-180 main engine on the Atlas 5’s first stage will continue firing, then the rocket will jettison its payload fairing at T+plus 3 minutes, 19 seconds, after soaring above the denser, lower layers of the atmosphere.
United Launch Alliance will end its live broadcast of the launch after separation of the payload fairing, and the rest of the mission will play out in a government-ordered news blackout. The NRO typically requires its launch contractors to end live coverage in the first few minutes of flight.
Assuming the rest of the mission follows a standard Atlas 5 launch profile, the RD-180 engine will shut down around four-and-a-half minutes into the flight, followed a few seconds later by first stage separation and ignition of the Centaur upper stage’s RL10 engine.
The RL10 engine might fire one or more times on Wednesday evening’s flight, depending on the final orbit targeted for deployment of the top secret NRO payload.