SXM-7: SpaceX launches 25th Falcon 9 launch of the year

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Two days after a last-second scrub, SpaceX launched a Falcon 9 rocket with the SiriusXM-7 (SXM-7) high power broadcasting satellite. The Falcon 9 lofted SXM-7 to a geostationary transfer orbit (GTO).

The SXM-7 mission will continue to break records SpaceX set in 2018. With 21 launches in 2018, SpaceX broke that record with the Sentinel-6A Michael Freilich mission in November 2020. The SXM-7 mission will mark the 25th flight of the year for SpaceX’s Falcon 9 rocket.

Payload and mission prep:

SXM-7 is one of two satellites to replace the aging XM-3 and XM-4 crafts that were launched in 2005 and 2006, respectively. Both satellites used the Boeing 702HP satellite bus and were launched on the Zenit 3(SL) rocket from the Sea Launch Ocean Platform in the Pacific Ocean. 

SXM-7, and its twin SXM-8, are owned by SiriusXM as a part of their high power broadcasting satellite constellation. SiriusXM ordered the satellites in July 2016; built by Space System/Loral (SSL), now MAXAR Technologies, the satellites are based on the SSL-1300 satellite bus. 

The two satellites will operate in the S-band spectrum, and both satellites will have a massive unfurlable antenna reflector. This antenna will enable broadcast to radios without the need for a sizable dish-type antenna on the ground. The two satellites will be equipped with two large solar panels that will generate more than 20-kilowatts of power to support the satellite’s operations. Both satellites have an expected lifetime of 15-years.

SXM-7 has a mass of 7,000 kg (15,432 Ib), making it one of the heaviest geostationary (GEO) satellites ever launched. It will fly on a flight-proven Falcon 9 on Booster B1051.7.

The “.7” signifies it will be flying for the seventh time. B1051 first supported the SpaceX Uncrewed Demo-1 mission in March 2019 before going to Vandenberg to support the RADARSAT Constellation mission in June 2019. 

Following RADARSAT, B1051 flew several Starlink launches, supporting the Starlink V1.0 L3 mission in January 2020, the Starlink L6 mission in April 2020, and after a long delay caused by hardware issues with the second stage, the Starlink L9 mission in August 2020. B1051 most recently supported the Starlink L13 flight in October 2020. 

Once B1051 flew on the SXM-7 mission, marking its fifth flight alone this year. The most flights a booster has flown in a year. 

B1051.7 is the second oldest booster in the fleet, behind B1049, which first flew in September 2018 on the Telstar 18 Vantage mission. B1049 was the first booster to fly for a seventh time on the Starlink L15 mission in November 2020.

Despite being the booster’s seventh flight, this mission marked B1051’s fastest turnaround at 54 days, the third-fastest turnaround in the booster fleet. B1058 and B1060 are the only two boosters with quicker turnaround times at 51 days. 

Normally, B1051 has usually — and coincidentally — launched from the historic Launch Complex (LC)-39A and landed on the droneship Of Course I Still Love You (OCISLY), having launched five times from LC-39A and landed on OCISLY six times. This mission will see the booster launch from SLC-40 and land on Just Read The Instruction (JRTI).  

JRTI left Port Canaveral on 6 December to head 643 km (400 miles) downrange to support the SXM-7 mission. 

The Falcon 9 is SpaceX’s workhorse rocket, which to date has flown 102 times. The Falcon 9 is a 70 meter (230 feet) tall two-stage rocket that is 3.66 meters (12 feet) in diameter. The Falcon 9 was designed to be partially reusable and carry crew to orbit on SpaceX’s Crew Dragon spacecraft. Since Falcon 9’s first flight in 2010, it has launched two crew missions to the International Space Station and flown 47 times using reused boosters.

For this mission, Maxar delivered SXM-7 to the Cape Canaveral Air Force Station — as it was called at the time — in October 2020. The facility was renamed on Wednesday, 9 December to the Cape Canaveral Space Force Station. This will mark Falcon 9’s and SpaceX’s first flight from the newly renamed spaceport, with the location’s debut launch under the new name coming one day later when United Launch Alliance used their Delta IV Heavy to launch the classified NROL-44 mission.

Soon after delivery at the center, SXM-7 was taken to the payload integration facility and loaded with propellant before technicians integrated it onto the Falcon 9’s payload adaptor. Soon after, the satellite was encapsulated by the Falcon 9’s 5.2 meter (17 feet) diameter payload fairing. Both of the payload fairings have already been used on the ANASIS-II mission back in July 2020. This will be the first time payload fairings are reused on a non-Starlink mission. 

Before the satellite was attached to the Falcon 9, a final test needed to be completed. The fully stacked Falcon 9, without the payload, was rolled out to SLC-40 on 6 December and raised vertical. 

SLC-40 is one of three launch sites SpaceX uses for its Falcon 9 rocket and was built alongside SLC-41 for the Titan IIIC rocket. It was used for the Titan rocket family from 1965 to 2005. The Cassini-Huygens and Mars Observer missions were launched on Titan rockets from SLC-40. When the Titan IV was retired in 2005, SLC-40 was mothballed. In 2007, SpaceX took over the site. Since the first Falcon 9 launch in 2010, SLC-40 has been the primary launch site for the Falcon 9 rocket.

After the Falcon 9 went vertical, it was loaded with its propellant of super-chilled Liquid Oxygen (LOX) and chilled Rocket Propellant (RP)-1 and then fired its 9 Merlin-1D engines for around seven seconds for a static fire test. A static fire is a routine part of Falcon 9 operations and was conducted to find any possible issues with the rocket and ground systems at the launch pad before liftoff. After the test was complete, the Falcon 9 had its fuel unloaded before it was brought back into the horizontal position and taken back to the HIF.  

The encapsulated SXM-7 satellite was attached to the top of Falcon 9’s second stage, and Falcon 9 was then rolled back out on 10 December for launch.

The launch:

At T-38 minutes the launch director verified that the Falcon 9 was GO for propellant loading. Following the launch director’s approval, Falcon 9 began liquid oxygen fueling in the first stage, and RP-1 kerosene fueling in the first and second stages at T-35 minutes. 

At T-17 minutes, RP-1 kerosene loading into the second stage entered stable replenish — where only enough to top off the tank is added. One minute later, SpaceX began liquid oxygen loading on the second stage.

Due to the significantly smaller nature of the second stage, it can fuel in significantly less time than the first and also receives its propellant load separately. In contrast, the first stage is loaded with liquid oxygen and RP-1 kerosene simultaneously.

At T-7 minutes, the Falcon 9 first stage engines began chill down, when a small amount of liquid oxygen flows through the engines to begin cooling them down to operational temperatures. This is important. If the engine was not cooled before launch, the drastic temperature change could lead to thermal cracking and cause the liquid oxygen to vaporize into a gas, which would cause significant damage to the engine.

At T-1 minute, the Falcon 9 began pressurizing its tanks to flight pressure: around 3 bar in the RP-1 tanks and just under 4 bar in the liquid oxygen tanks. (A “bar” is just slightly less, but nearly equal to, 1 atmosphere of pressure or the normal pressure you feel by the air every day).

At the same time, Falcon 9 entered start-up and took over the control of the countdown from the ground computers. At this point, Falcon 9 commanded every part of the countdown, with the only human interaction being in case of a weather or range related abort. At T-10 seconds, the launch control team is unable to abort the launch, and only the rocket can issue that command.

At T-3 seconds, the engine controller aboard Falcon 9 commanded all 9 Merlin 1D engines to start on the first stage. The engines ignite in pairs of two, with 100 milliseconds between each pair of ignitions. This is done to reduce the start-up transients and vibrations and keep acoustics within limits for the rocket. The engines’ staggered start is a common practice used on multi-engine first stages as they are lit for flight.

Once all nine engines have reached full thrust, the rocket is held down for about a second to ensure all systems are healthy. If all data is nominal, the Falcon 9’s hydraulic hold-down clamps release the rocket for flight at T-0 seconds.

Once Falcon 9 has lifted off, it conducted a pitch maneuver to follow the planned flight path. The Falcon reached Max Q, at T+1:12. Max Q stands for maximum aerodynamic pressure, which is when the aerodynamic forces are highest on the vehicle. 

At T+2:33, Falcon 9 shut down its nine Merlin engines on the first stage. Similar to engine start-up, Falcon 9 shuts down pairs of engines 200 ms apart. Four seconds later, the two stages separate. At T+2:44, the singular Merlin 1D Vacuum engine ignited on the second stage for the first of two planned burns.

After stage separation, B1051 deployed its four titanium grid fins and started a flip maneuver to prepare for reentry. 

At T+3:37, the payload fairing separated from the second stage, exposing the SXM-7 satellite to the vacuum of space. 

After fairing separation, the fairings reentered and either softly touch down in the ocean and be fished out of the water by SpaceX’s fairing recovery boat Ms. Tree. Another boat, GO Searcher, left Port Canaveral on 6 December to also fish out a fairing. GO Searcher is one of two identical boats to recover the Dragon 2 spacecraft from the ocean. 

The second fairing catching vessel, Ms. Chief, is still in port at Cape Canaveral.

Once the fairings are recovered, they will be taken to Port Canaveral to begin refurbishments for a possible reflight.

At T+6:17, the first stage began its entry burn. The first stage ignited its E9 (Engine 9) center Merlin 1D engine first, followed quickly by ignition of the E3 and E5 Merlins. This entry burn lasted about 20 seconds, slowed the first stage down, and protected it from aerodynamic heating. 

Then, at T+8:14 into the flight, the second stage engine shut down, and 15 seconds later the first stage landed on SpaceX’s autonomous spaceport drone ship JRTI. This landing marked the 19th consecutive successful landing and the 69th successful overall landing.

After B1051 landed, the booster was safed and will be brought back to Port Canaveral to begin inspections and refurbishment, preparing it for another flight. 

The second stage coasted for roughly 16 minutes before conducting another burn to raise its perigee to the geostationary transfer target orbit for this mission. The second stage coasted for another five minutes before releasing SXM-7. 

Once the Falcon 9 released the satellite into geostationary transfer orbit, the twin solar panels opened. Then the onboard thrusters will then slowly start to maneuver the satellite to GEO, or geostationary orbit. Once it reaches GEO, it will deploy its onboard antennas and begin on-orbit testing. Once those tests are complete, the satellite will then become operational.  

Remarkably, this was the 25th flight of Falcon 9 this year and the 24th to launch from Florida; yet SpaceX is still not done for the year. Less than a week from now, on 17 December, the agency will launch the classified NROL-108 mission from historic LC-39A using Booster B1059.5.

And after that, they’re still not done. Before the end of the year, SpaceX also aiming to launch an NROL mission. 

(Lead image: Falcon 9 on the launch pad for SXM-7. Credit: SpaceX)