Good weather expected for twilight Atlas 5 launch Tuesday

The NROL-101 mission patch pays tribute to the ‘Lord of the Rings’ stories, with a gold ring and Elvish script that translates to “Goodness Persists.” Credit: National Reconnaissance Office

Forecasters predict a 90% chance of good weather for liftoff of a United Launch Alliance Atlas 5 rocket from Cape Canaveral just after sunset Tuesday with a classified payload for the National Reconnaissance Office, the U.S. government’s spy satellite agency.

In an official forecast issued Sunday by the U.S. Space Force’s 45th Weather Squadron, meteorologists wrote they expect mostly clear skies and breezy winds from the northeast at 15 to 20 knots at launch time Tuesday. The main weather concern Tuesday is forecast with ground winds at the Cape Canaveral spaceport.

Liftoff is set for 5:58 p.m. EST (2258 GMT), around 23 minutes after sunset. Assuming clear skies, the Atlas 5 rocket and its plume of exhaust could put on a spectacular twilight sky show as the launcher climbs into sunlight on ascent from Florida’s Space Coast.

The mission is designated NROL-101. The National Reconnaissance Office has not disclosed details about the payload flying into orbit atop the 206-foot-tall (63-meter) Atlas 5 rocket, but the NRO said the mission will “carry a national security payload designed, built and operated by the agency.”

“NROL-101 supports NRO’s overall national security mission to provide intelligence data to the United States’ senior policy makers, the Intelligence Community and Department of Defense,” the NRO said in a press kit for the mission.

“ULA is proud to play a pivotal role in support of our mission partners and national security by keeping our country safe one launch at a time,” said Gary Wentz, ULA vice president of government and commercial programs, in a company statement. “We thank our mission partners for their continued trust and teamwork. The NROL-101 mission will be ULA’s 29th mission launched for the National Reconnaissance Office and the 17th NRO mission launched on an Atlas 5.”

Mission managers approved the continuation of launch preparations during a launch readiness review Saturday.

ULA ground teams will transfer the Atlas 5 rocket from its vertical hangar at Cape Canaveral Air Force Station to pad 41 beginning around 10 a.m. EST (1500 GMT) Monday. Pushed by trackmobiles, the rocket will ride its mobile launch platform on rail tracks for the third-of-a-mile trip to pad 41.

The National Reconnaissance Office’s top secret payload is lifted atop ULA’s Atlas 5 rocket Oct. 26 inside the Vertical Integration Facility at Cape Canaveral Air Force Station. Credit: United Launch Alliance

Once on the launch pad, the Atlas 5 will be connected to ground propellant supplies, telemetry interfaces, and other systems before the start of the countdown Tuesday morning.

After being powered up and going through a series of checkouts, the Atlas 5 will be loaded with cryogenic liquid hydrogen and liquid oxygen propellants beginning about two hours before launch.

The Atlas 5’s Centaur upper stage will be powered by an RL10C-1 engine consuming liquid hydrogen and liquid oxygen. The Russian-made RD-180 main engine on the first stage will burn kerosene mixed with liquid oxygen, and ULA’s launch team loaded the kerosene supply into the Atlas 5’s first stage during a practice countdown last month.

While the NRO has not revealed information about the payload flying on the NROL-101 mission, 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 spacecraft 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 Tuesday might be aiming for a similar Molniya-type orbit, or it could deliver a heavier payload to a lower-altitude orbit.

The launch campaign for the NROL-101 began with the raising of the rocket’s first stage — tail number AV-090 — on its mobile launch platform inside the Vertical Integration Facility near launch pad 41 on Sept. 11. In the following days, technicians installed the rocket’s three GEM 63 solid-fueled boosters on the bottom of the bronze first stage.

Workers then added the rocket’s Centaur upper stage, already integrated with the bottom part of the Atlas 5’s payload fairing, made by RUAG Space in Switzerland.

A GEM 63 solid rocket boosters is raised into position on the Atlas 5’s first stage inside the Vertical Integration Facility at Cape Canaveral Air Force Station. Credit: United Launch Alliance

On Oct. 26, ground crews raised the NRO spy satellite payload on top of the Atlas 5 rocket. The NRO payload was cocooned inside the Atlas 5’s Swiss-made nose cone.

The 5.4-meter-diameter (17.7-foot) 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 launch Tuesday evening will mark the 86th flight of an Atlas 5 rocket, and the fourth Atlas 5 to blast off in the “531” configuration with three solid rocket boosters and a 5.4-meter-diameter payload fairing.

It will be ULA’s fifth mission of 2020.

The new GEM 63 motors set to debut on the next Atlas 5 mission measure 66 feet (20 meters) long and 63 inches (1.6 meters) wide. They can produce 373,800 pounds of thrust at maximum power.

The GEM 63 boosters 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 Tuesday evening’s flight, depending on the final orbit targeted for deployment of the top secret NRO payload.

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