United Launch Alliance to Launch First Direct Commercial Payload

The SES 20/21 Mission stands ready at SLC-41
Image Credit: Derek Newsome/Space Scout

United Launch Alliance is set to launch its first commercial satellite since 2016. The SES-20 and SES-21 satellites are scheduled to launch atop an Atlas V 531 on Tuesday, October 4th at 5:36 p.m. EDT. This is ULA’s seventh launch of 2022, and comes just days after their last launch, a Delta IV Heavy from Vandenberg Space Force Base. This mission also marks the companies first commercial mission to be run directly in house, with all previous commercial payloads being procured through Lockheed Martin Commercial Launch Services.

The SES-20 and 21 satellites stacked together.
Image Credit: SES

SES-20 and 21 are identical satellites, utilizing the Boeing 702SP satellite bus. This bus utilizes a fully electric station keeping/propulsion system, enabling it to be less than half the weight of its previous generation. The two SES satellites transmission systems will operate between 4 and 8 GHz, also known as the C-Band. SES-20 will be positioned at 103° West, while SES-21 will sit at 131° West.

The launch of SES-20 and 21 is scheduled to take place on October 4th, utilizing a United Launch Alliance Atlas V 531 rocket. This is the fifth, and final time the 531 configuration is slated to fly. The launch was originally scheduled to take place on September 30th, however Hurricane Ian led to ULA postponing the launch until after the storm.

Liftoff is scheduled for 5:36 PM EDT, where the RD-180 and three GEM-63 Solid Rocket Motors will ignite and power the Atlas V off the pad. The GEM-63’s will burn for 94 seconds, accelerating the vehicle over 3,600 kmh (2236 mph). 24 seconds after burnout the three solid rocket motors will be jettisoned and the main Atlas vehicle will continue to space.

Three minutes and 23 seconds into flight, the 5 meter diameter fairing will be jettisoned, exposing both the payload, and Centaur upper stage to the vacuum of space. One minute later, the RD-180 will shut down, and the Atlas Booster will separate from the upper stage. Centaur will then burn for seven minutes and 18 seconds, inserting the spacecraft into a low Earth parking orbit.

Twelve minutes after the first Centaur burn is completed, the RL-10C engine will ignite for a second time, raising the orbit’s apogee to near geosynchronous orbit. This second burn will last approximately four minutes and 52 seconds. Following this second burn, Centaur and the SES-20/21 mission will coast for more than 5 hours before igniting the RL-10C engine one final time. This final burn will utilize all of the remaining propellant in the Centaur, placing the spacecraft as close to Geosynchronous orbit as possible.

The two SES satellites will then be released, and the Centaur upper stage will safe itself, venting all excess commodities and depleting its batteries. The two satellites will then finalize their orbits over the coming months, slowly translating to their final operational locations over the western United States.

The SES-20/21 mission marks another shift in the ever changing US launch market, as it’s the first of many commercial payloads currently lined up for United Launch Alliance. Tune into ULA’s live webcast of the mission here for the liftoff of Atlas V.

Edited by David Diebold

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