On June 6 at 04:25 UTC, SpaceX’s Falcon 9 booster 1061 launched the SXM-8 satellite into geostationary transfer orbit for satellite radio provider SiriusXM.

The fairings were brand new and successfully recovered from the water by SpaceX’s GO Navigator. Booster 1061 successfully landed on the drone ship Just Read The Instructions.

SXM-8 follows on the heels of SXM-7, which failed shortly after its launch in December 2020. SXM-8 was delayed several months to make sure it wouldn’t share its twin’s fate. Both satellites use the proven L-1300 bus that had previously worked over one hundred times. This mission was sorely needed as SiriusXM’s current satellites are aging, with XM-3 and XM-4 turning 16 this year.

Blasting our radios requires a massive satellite. SXM-8 uses a nine-meter diameter dish, which is taller than an average house, and solar panels that are longer than a 737 passenger plane’s wingspan. Weighing in at almost seven metric tons, SXM-8 is one of the heaviest commercial satellites ever launched.

After a fifteen-minute coast phase, the second stage restarted for a one-minute burn to deliver the satellite into its geostationary transfer orbit. 

We throw around the phrase Geostationary Orbit a lot without really talking about this super useful orbit. First discussed in fiction by Arther C. Clark, this particular orbit is big enough that satellites orbit the planet at the same rate the planet rotates. If an orbit is exactly over the equator, and not inclined, that spacecraft will stay over the same point on Earth pretty much until the average length of a day changes. 

The thing is, these orbits can be inclined, and when that happens, the spacecraft will slowly pace north and south along a single line of longitude. That’s not entirely useful if you’re a satellite TV provider where your customers have stationary dishes. Inclined, however, is the default for spacecraft launching from anywhere in the U.S. 

The Falcon 9 has a pretty cool way to flatten out orbits. While they could achieve an orbit with the needed 35,789 kilometer highest point, or apogee, in one engine firing, that would put the satellite in a tilted and elliptical orbit, where the orbit’s closest point to the Earth would be somewhere off the coast of Florida, and the far point is on the opposite side of the world and south of the equator. 

Fixing both the shape of the orbit to make it a circle and changing the tilt to align with the equator in different maneuvers would take a lot of fuel, so SpaceX doesn’t go straight out. Instead, the Falcon 9 coasts in a low orbit and restarts its engine at the equator so the spacecraft is left in an orbit where it arrives at 35,789 km altitude just as it passes over the equator. This alignment allows them to circularize their orbit and orient themselves over the equator in a single, fuel-saving maneuver. That fuel savings on reaching orbit translates into more fuel for keeping the music flowing. SXM-8 should be able to keep Sirius Radio broadcasting for at least 15 years.

More Information

Launch discussion thread (Reddit)

Sirius XM Form 8-K (SEC)

XM-3 and XM-4 info page (Gunter’s Space Page)

Preparing for Launch: SXM-8 Arrives at Launch Base (Maxar)

SXM 7 and 8 info page (Gunter’s Space Page)

Launch video