Atlas 5 rocket completes high-altitude tandem satellite delivery for SES

United Launch Alliance’s Atlas 5 rocket climbs off pad 41 Tuesday at Cape Canaveral Space Force Station with the SES 20 and SES 21 television broadcasting satellites. Credit: Michael Cain / Spaceflight Now / Coldlife Photography

Running a few days late after a delay caused by Hurricane Ian, an Atlas 5 rocket built by United Launch Alliance thundered off a launch pad at Cape Canaveral Tuesday and soared to an altitude of nearly 22,000 miles to deploy two commercial television broadcasting satellites for the commercial operator SES.

The Atlas 5 launcher lit its Russian-built RD-180 main engine in the final seconds of a smooth countdown Tuesday. As the countdown clock struck zero, three strap-on solid rocket boosters supplied by Northrop Grumman ignited to propel the 196-foot-tall (59.7-meter) rocket off the pad at Cape Canaveral Space Force Station, Florida.

The main engine and boosters combined to generate nearly 2 million pounds of thrust as the Atlas 5 darted through scattered clouds and arced downrange toward the east from Florida’s Space Coast. The Atlas 5 powered through the speed of sound in 40 seconds, and jettisoned its three solid rocket booster casings nearly two minutes into the flight. About 90 seconds later, the rocket released its nose cone to shed weight on the climb into space.

The kerosene-fueled RD-180 main engine shut off more than four minutes into the flight, and the Atlas 5’s first stage separated to fall into the Atlantic Ocean. Then the rocket’s hydrogen-fueled Centaur upper stage got to work with a series of three burns by its Aerojet Rocketdyne RL10 engine.

The Centaur upper stage’s first burn placed the mission’s two commercial communications payloads — SES 20 and SES 21 — into a parking orbit a few hundred miles above Earth. A second RL10 engine firing propelled the the rocket and the tandem satellites into an oval-shaped transfer orbit with its highest point, or apogee, stretching to an altitude of nearly 22,000 miles (35,000 kilometers).

After the second Centaur burn, the rocket coasted through space for five hours before reigniting for a final maneuver to reshape the orbit to a more circular path around Earth, and nudge the satellites closer to the final operating position over the equator.

Then the Centaur upper stage sent commands to release the satellites one at a time. The SES 20 satellite deployed first from the upper position on the dual-payload stack, followed by separation of SES 21 at 11:54 p.m. EDT (0354 GMT), more than six hours after departure from Cape Canaveral.

The satellites were injected directly into an orbit just below geosynchronous altitude, where their motion around Earth will match the rate of the planet’s rotation, completing one lap around the equator every 24 hours.

The launch Tuesday was the first commercial Atlas 5 mission to head directly to a near-geosynchronous orbit. The trajectory requires a lengthy coast phase, and additional battery capacity and other upgrades to the Centaur upper stage. Atlas 5 rockets have deployed payloads directly into similar orbits near geosynchronous altitude on four previous missions for the U.S. military.

Three strap-on solid-fueled boosters and a core stage RD-180 main engine combined to generate nearly 2 million pounds of thrust at liftoff. Credit: Alex Polimeni / Spaceflight Now

The SES 20 and 21 satellites are nearly identical, and were manufactured by Boeing in El Segundo, California. Each satellite uses all-electric propulsion for in-orbit maneuvers, and were built on Boeing’s 702SP satellite platform.

The Atlas 5’s guidance computer aimed to release the two spacecraft in a circular orbit roughly 21,750 miles (about 35,000 kilometers), just below geostationary altitude, at an inclination angle of 1.9 degrees to the equator. ULA said the Atlas 5 rocket’s Centaur upper stage delivered the satellites to an on-target orbit, and SES confirmed both spacecraft were alive and healthy following launch.

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 plasma thrusters to fine-tune their orbits and slide into their operating positions in geostationary orbit.

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, which are paying satellite operators like SES through multibillion-dollar compensation agreements. SES and Intelsat, another large geostationary satellite operator, purchased new C-band broadcasting satellites to function in the narrower swath of spectrum.

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.

“We’re excited to support our commercial partner SES in their C-band transition efforts to meet the FCC’s objective to deploy 5G service across the U.S. Their mission aligns with our mission to connect the world and these capabilities will enable uninterrupted commercial services to many Americans,” said Gary Wentz, ULA vice president of government and commercial programs, in a statement.

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.

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, which will raise their altitude a few hundred miles and maneuver directly over the equator using their own thrusters. The satellite will also extend power-generating polar panels and complete in-orbit checkouts before entering commercial service.

“Our unique dual-launch configuration was again successful on this mission,” said Ryan Reid, president of Boeing Satellite Systems International. “That coupled with the ULA Atlas 5’s ability to achieve an advantageous orbit enables SES to get these satellites into service in a matter of weeks. We appreciate the faith SES has put in our industry team to make that happen.”

Reid said the two SES communications satellites had a combined weight of about 3.3 metric tons, or about 7,300 pounds, fully fueled for launch.

The low-thrust plasma engines on the SES 20 and SES 21 satellites come with high fuel efficiency, but they would take months to propel the spacecraft into their operational orbit from a conventional transfer orbit reachable by other commercial rockets. Using the Atlas 5, which is more expensive than its competitors, enables SES 20 and SES 21 to enter service sooner.

“The reason SES selected this particular Atlas was because of the critical nature of this mission, and the desire to get it on orbit and operational as fast as possible,” said Vern Thorpe, ULA’s director of commercial programs. “So they selected a vehicle that had the performance capability and the long coast mission capability, so that we could take them right up and put them right on the doorstep of geosynchronous orbit, and that basically saves the spacecraft at least five months of orbit raising time.”

Steve Collar, CEO of SES, said Tuesday that the satellites will begin commercial television broadcast operations in November.

“The successful launch of SES-20 and SES-21 will allow us to support our customers in delivering high-quality sports and entertainment to tens of millions of U.S. households while delivering on our promise to repurpose spectrum to enable U.S. leadership in 5G,” Collar said.

“These satellites are going to be operational within just a few weeks of launch, which is fantastic,” Collar said. “And they’re part of a much broader plan, five satellites that we will launch in order to continue … to deliver on the plan that we have on the clearing of spectrum, but also most critically to support the ongoing services of our customers.”

After the launch of SES 22 on a SpaceX Falcon 9 rocket in June, and the Atlas 5 launch Tuesday, SES plans to launch another pair of C-band communications satellites on a future Falcon 9 flight late this year or early next year.

The launch Tuesday was the 96th flight of an Atlas 5 rocket overall, and the fifth Atlas 5 to use the “531” variant with a 5.4-meter diameter payload fairing and three solid rocket boosters. There are 20 Atlas 5 rockets left in ULA’s inventory.

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 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.

The SES 20 and 21 satellites (top and bottom) stacked together in launch configuration before encapsulation inside the payload fairing of an Atlas 5 rocket. Credit: Boeing

ULA’s next Atlas 5 launch is scheduled Nov. 1 from Vandenberg Space Force Base in California with NOAA’s JPSS 2 polar-orbiting weather satellite.

The Atlas 5 launch from Cape Canaveral on Tuesday was the first of three rockets set to blast off from Florida’s Space Coast this week. SpaceX is preparing two Falcon 9 rockets for takeoffs from nearby launch pads.

Next up will be a Falcon 9 launch from pad 39A at NASA’s Kennedy Space Center with a four-person crew heading to the International Space Station. That launch is scheduled for 12 p.m. EDT (1600 GMT) Wednesday.

That will be followed by another Falcon 9 rocket launch as soon as Thursday evening from pad 40 at Cape Canaveral Space Force Station with Intelsat’s Galaxy 33 and Galaxy 34 C-band TV broadcasting satellites, continuing the next phase of the C-band spectrum clearing mandated by the FCC.

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