EDITOR’S NOTE: Watch a replay of the Atlas 5 rocket’s rollout to the launch pad here.
United Launch Alliance hauled an Atlas 5 rocket to its launch pad Monday at Cape Canaveral on the eve of a planned blastoff with two commercial television broadcasting satellites for SES, owner of one of the largest fleets of geostationary communications spacecraft.
The Atlas 5 rocket rolled out from the Vertical Integration Facility around 10 a.m. EDT (1400 GMT) Tuesday to begin the journey to Space Launch Complex 41 at Cape Canaveral Space Force Station. The launcher rode a mobile platform pushed by trackmobile locomotives, covering about 1,800 feet (550 meters) before arriving over the flame trench at the launch pad.
The rollout briefly paused and then reversed course back toward the Vertical Integration Facility, but then resumed the move toward pad 41, where it arrived shortly after 11 a.m.
Once in position at pad 41, the Atlas 5 was expected to be connected to propellant loading lines and other ground systems. ULA’s launch team planned to load rocket-grade RP-1 kerosene fuel into the Atlas 5’s first stage Monday afternoon. The kerosene will feed the rocket’s Russian-made RD-180 main engine, in combination with super-cold liquid oxygen to be pumped into the Atlas 5 during the countdown Tuesday.
Liftoff Tuesday is set for 5:36 p.m. EDT (2136 GMT), the opening of a 45-minute launch window. There is a 70% chance of favorable weather for Tuesday’s launch window, according to the Space Force’s 45th Weather Squadron.
The rocket’s two payloads, named SES 20 and 21, are buttoned up for launch inside the Atlas 5’s payload shroud.
The Atlas 5 launch Tuesday will deliver the SES 20 and 21 satellites to an orbit near their operational altitude in geosynchronous orbit. The rocket’s Centaur upper stage will target a circular orbit roughly 21,750 miles (about 35,000 kilometers) nearly directly over the equator, just below geostationary altitude.
SES, based in Luxembourg, says the precise positioning enabled by the Atlas 5 rocket’s Centaur upper stage will expedite the entry into service for the new satellites. Built by Boeing, the SES 20 and 21 satellites are nearly identical, and are stacked one on top of the other in a dual payload launch configuration.
The Centaur upper stage will fire its RL10 engine three times to place the SES 20 and 21 satellites into the proper orbit for deployment. The flight profile will last more than six hours from liftoff until the final payload separates from the rocket, following a timeline more commonly used for U.S. military satellite missions than for commercial satellites.
After separating from the Atlas 5’s Centaur upper stage, SES 20 and 21 will unfurl their solar panels and run through post-launch checkouts. They will use electric thrusters to fine-tune their orbits and slide into their operating positions in geostationary orbit, where their velocities will match the rate of Earth’s rotation, giving the satellites fixed geographic coverage zones.
SES 20 will maneuver into a position along the equator at 103 degrees west longitude, while SES 21 will head for 131 degrees west longitude. Both satellites will provide C-band television and radio broadcast services over the United States. SES 20 and 21 are part of a program to redirect television communications services to a different part of the C-band spectrum, following the Federal Communications Commission’s decision in 2020 to clear 300 megahertz of spectrum for the roll-out of 5G mobile connectivity networks.
The FCC auctioned U.S. C-band spectrum — previously used for satellite-based video broadcast services to millions of customers — to 5G operators.
In compensation for losing the spectrum, Intelsat and SES — the two largest C-band satellite operators in the U.S. market — are set to receive $4.87 billion and $3.97 billion from 5G bidders, respectively, if they can accelerate the transition of C-band services to a smaller swath of spectrum by December 2023, two years before the FCC’s mandated deadline.
Intelsat and SES — along with operators with a smaller share of the U.S. C-band market — will also be reimbursed for their C-band relocation costs, including satellite manufacturing and launch expenses, by the winners of the FCC’s C-band auction.
As part of the agreement, the satellite operators were incentivized to buy new C-band broadcasting satellites from U.S. manufacturers to operate in the 4.0 to 4.2 GHz swath of the C-band spectrum. The lower portion of the band previously allocated to satellite operators — 3.7 to 4.0 GHz — is being transitioned to 5G services.
In 2020, SES ordered six new C-band satellites, including a spare, and Intelsat procured seven C-band satellites. SES says the new C-band satellites will enable the broadcast of digital TV services to nearly 120 million homes in the United States.
SES launched their first new C-band satellite as part of the program in June on a SpaceX Falcon 9 rocket. Later this week, following the Atlas 5 launch for SES, SpaceX is scheduled to launch another pair of similar C-band television broadcast satellites from Cape Canaveral for Intelsat.
The Atlas 5 rocket launching the SES 20 and 21 satellites will fly in the “531” vehicle configuration, with a 5.4-meter diameter (17.7-foot) payload fairing built by Beyond Gravity, formerly known as RUAG Space. The rocket’s first stage RD-180 engine will be augmented by three solid-fueled strap-on boosters provided by Northrop Grumman. And the Centaur upper stage will have a single RL10C-1-1 engine.
The launch Tuesday will mark the 96th flight of an Atlas 5 rocket overall, and the fifth Atlas 5 to use the 531 variant. There are 21 Atlas 5 rockets left in ULA’s inventory, including the mission set to take off Tuesday.
ULA is phasing out the Atlas 5 rocket and the Delta 4 rocket family. Both rockets will be replaced by the new Vulcan Centaur launcher, which ULA says is less expensive and more capable than the Atlas and Delta rocket fleets.
The Vulcan Centaur will also be powered by U.S.-made main engines produced by Blue Origin, replacing the Russian RD-180 on the Atlas 5. ULA say all of the RD-180 engines required for the remaining Atlas 5 flights have been delivered to the United States from Russia.
ULA personnel began stacking the Atlas 5 rocket Aug. 26 inside the Vertical Integration Facility at Cape Canaveral Space Force Station, with the raising of the launcher’s first stage onto the mobile platform that will carry it to the launch pad. The first stage was stacked on the mobile launch platform a few weeks after the previous Atlas 5 launch Aug. 4, which deployed a new missile warning satellites for the U.S. Space Force.
Teams added three Northrop Grumman-built solid rocket boosters, which will provide extra thrust in the first minute-and-a-half of the flight, firing in unison with the core stage’s Russian-made RD-180 engine. Then ULA installed the Centaur upper stage Sept. 6.
Stacking of the 96th Atlas 5 rocket was completed Sept. 20 with the hoisting of the payload module, the uppermost portion of the launch vehicle. The two SES communications satellites were encapsulated inside the payload fairing at the nearby Astrotech payload processing facility in Titusville, following their delivery to Florida from Boeing’s satellite factory in El Segundo, California.
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