SpaceX sets new booster reuse record on Starlink mission

SpaceX launched the Starlink Group 4-12 mission with a Falcon 9 rocket with 53 satellites into Low Earth Orbit. Liftoff occurred at 12:42 AM EDT (04:42 UTC) on Saturday, March 19 from Space Launch Complex 40 (SLC-40) at the Cape Canaveral Space Force Station in Florida.

Saturday’s mission marked the first time a Falcon 9 booster flew for a 12th time and brought the total number of Starlink satellites launched to over 2,300.

The launch marked a return to the northeasterly trajectory that SpaceX used for the initial Starlink Shell 4 launches. Since Starlink Group 4-5 in January, SpaceX had instead been using a southeasterly trajectory with a dogleg around the Bahamas. This was implemented to avoid unfavorable recovery weather in the North Atlantic Ocean during the winter months. With spring coming, SpaceX is now returning to launching Starlink missions to the northeast.

Weather was 70% go on both the primary and backup launch opportunities, as published by the Space Launch Delta 45 Space Weather Squadron on their latest launch weather forecast. The main concern for both primary and backup days was cumulus clouds.

In preparation for Saturday’s launch, Falcon 9 was rolled out to SLC-40 in the early morning hours before being raised to the vertical position. With the rocket vertical, launch pad teams began the task of getting everything ready for countdown operations, with pad evacuation expected to occur as late as T-4 hours. The launch will be controlled from SpaceX’s Launch and Landing Control Center at CCSFS.

System checkouts, weather monitoring, and low-pressure helium loading proceeded until T-40 minutes when a telematic go/no-go poll is conducted to proceed with the fueling of the rocket. At T-35 minutes, the automated launch countdown sequence began and the loading of RP-1 highly refined kerosene propellant on both stages commenced. At the same time, the loading of supercooled liquid oxygen (LOX) began on the first stage of the rocket.

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At T-20 minutes, the second stage RP-1 load was completed and the umbilical lines connecting to the stage to the strongback – the white tower structure that moves the rocket to vertical position – were purged ahead of LOX load on the second stage which began at T-16 minutes.

Engine chill on the 9 Merlin-1D engines of the first stage came up at T-7 minutes with a small amount of liquid oxygen flowing into the pumps. This is done to avoid LOX being rapidly vaporized as it enters the pumps at engine ignition. At T-5 minutes, with the first stage RP-1 load complete, the tanks started pressurizing ahead of strongback retraction.

At T-1 minute, the rocket entered startup, when the onboard computers took over control of the countdown sequence. Seconds later, the launch director gave a final “Go” for launch and the rocket’s tanks were pressurized to flight levels.

Falcon 9 at SLC-40 on a previous Starlink mission (Credit: Stephen Marr for NSF)

The ignition sequence for Falcon’s nine Merlin-1D first-stage engines began at T-4 seconds, with the engines reaching full thrust just 2.5 seconds later. After a quick hold down on the pad for half a second to check engine health, the ground system hold-downs released the rocket and liftoff occurred.

Falcon 9 performs its usual pitch, yaw, and roll maneuver to align itself with the desired trajectory for Saturday’s north-easterly ascent. About 40 seconds into flight, the main engines throttled down in preparation for Max-Q, the point of maximum aerodynamic pressure. About one minute into, the flight the rocket reached Mach 1, the speed of sound, followed closely by Max-Q.

Once past the Max-Q point, the main engines throttled up and the rocket continued arching towards the northeast over the Atlantic Ocean. At around T+1 minute and 45 seconds, the second stage’s Merlin Vacuum (MVac) engine entered its chilldown procedure ahead of its own startup.

The first stage engines shut down at around 2 minutes and 35 seconds into the flight, with three pneumatic actuators on the perimeter of the interstage and a central pusher engaging to separate the two stages of the rocket. MVac ignition occurred at around 2 minutes and 45 seconds into the flight, and the payload fairing separated about 20 seconds later.

Falcon 9 booster 1051 on a previous mission (Credit: Thomas Burghardt for NSF)

Falcon 9’s payload fairing is reusable, and after separating, the two fairing halves from Saturday’s mission reentered and parachuted down to the Atlantic Ocean. They will be recovered by SpaceX multi-purpose recovery vessel Doug for reuse on a later mission.

After stage separation, the booster also executed its now-usual reentry and landing burns to land on SpaceX’s Autonomous Spaceport Drone Ship (ASDS) Just Read The Instructions which was located about 640 km northeast of the launch site in the Atlantic.

At eight minutes and 20 seconds mission elapsed time, the second stage shut down its engine and the mission entered a coast phase before the MVac engine reignition for a short, one-second burn to circularize the orbit. For Saturday’s mission, the target orbit was 304 by 317 kilometers with an inclination of at 53.22 degrees.

With the circularization burn complete, the second stage will initiate an end-over-end rotation maneuver ahead of deployment of the 53 Starlink satellites. That deployment will occur about 62 minutes after liftoff. The second stage will end its mission by executing a deorbit burn, placing it on track to burn up as it re-enters the atmosphere over the Indian Ocean.

Rendering of Starlink satellites deploying from the second stage. (Credit: Mack Crawford for NSF)

Following separation from the Falcon 9, the Starlink satellites will execute a series of orbit-raising maneuvers and checkouts before being raised into their operational orbit and entering service. SpaceX performs this screening process at lower altitudes to allow atmospheric drag to bring down any failed satellites within a few months.

Another Falcon 9 from SLC-40 is expected to come right on the heels of Saturday’s mission, as SpaceX plans to launch the Transporter-4 mission on April 1st. SpaceX is also getting ready for their next Crew Dragon launch, currently targeted for launch on April 3rd with Crew Dragon Endeavour to carry four astronauts on a one-week mission to the ISS and back.

B1051 reaches twelfth flight milestone

Saturday’s mission marked the first time SpaceX uses the same Falcon 9 booster for a twelfth flight. Booster B1051 first flew on the Crew Dragon Demo-1 mission in March 2019, and since then it has performed another 10 missions including the Radarsat Constellation Mission (RCM), SXM-7, and eight Starlink missions.

The current fleet of operational Falcon 9 boosters has twelve active boosters, although B1049, B1053, B1069, and B1071 are being reserved for future flights and aren’t currently in the regular rotation of flights.

B1051 became SpaceX’s Falcon fleet life leader after passing B1049 with its eighth flight back in January 2021. Although newer boosters like B1058 and B1060 have since taken the lead in the fastest time to get to their tenth and eleventh flights, B1051 will be remembered as the first to push the envelope in reaching these milestones.

Graph showing the flight history of the current active Block 5 boosters

B1049 is expected to be expended on its next flight with recent sightings of the booster showing that all of its recovery equipment has been removed. This booster is expected to be used for the second O3b mPOWER mission, currently scheduled for launch in the summer. Expending the booster will allow Falcon 9 rocket to put the customer’s satellites closer to their final orbit, allowing them to enter operations faster and with the use of less of their own propellant.

B1053 is being refurbished for flight as a Falcon Heavy side booster and is slated to fly as the port-side booster on the Viasat-3 Americas mission, currently scheduled for launch in the late summer.

B1069 made its first flight in December but was damaged during its return to port after a successful landing aboard the drone ship. It is understood to be undergoing refurbishment that will allow it to be re-used on future missions beginning in the summer.

B1071 is currently at the SpaceX facility on the West Coast at Vandenberg Space Force Base, where it is being readied for launch with the NROL-85 mission for the National Reconnaissance Office, currently expected to lift off no earlier than April 15.

While Elon Musk had previously indicated that Falcon 9 boosters would need to undergo major refurbishment following ten flights, so far the turnarounds for boosters that have passed this milestone have not indicated that they have been taken out of service for this work. Instead, boosters with high numbers of flights have often faster turnaround times than newer boosters.

Graph showing days taken to turn around Block 5 boosters between launches

One of the many reasons why this is the case is because boosters with a higher number of flights fly on SpaceX’s own internal missions which have a higher cadence and can allow some extra risk to be involved. On the other hand, boosters on a lower number of flights are often reserved for customer missions which may result in more time waiting in the hangar while otherwise ready to fly.

Newer boosters are coming up for the fleet as SpaceX plans to launch up to five Falcon Heavy rockets this year while also introducing new Falcon 9 boosters to renew the fleet with fresh new hardware. SpaceX has already produced, tested, and shipped three Falcon Heavy center cores: B1066, B1068, and B1070; and has built and tested four new side boosters: B1064, B1065, B1072, and B1073. The latter is currently vertical at SpaceX’s McGregor testing facility undergoing the standard post-production testing before being transported to the launch site.

Starlink constellation adds 53 more satellites, passing 2,300 launched into orbit

The Starlink Group 4-12 launch will put 53 more Starlink satellites into orbit, bringing the total launched by SpaceX up to 2,335. Of these, 223 are no longer in service, having either failed after deployment, been deorbited before reaching their operational orbit, or disposed of some time after reaching operational status.

Of the 2,112 satellites remaining in orbit, only 1,579 Starlink spacecraft are currently in their operational orbits, most of them being in shell number 1 while the satellites being launched on Saturday’s mission are part of shell number 4.

The constellation will consist of five shells, with different orbital planes containing differing numbers of satellites.

(Active satellite data from Jonathan McDowell)

Satellites bound for the first shell were launched between May 2019 and June 2021 and, except for the very first one which was called “Starlink v0.9”, they were all named as “Starlink v1.0” with a launch number per official documentation by the US Space Force, Coast Guard, and the Federal Aviation Administration (FAA). These satellites relied only on ground stations to relay signals between spacecraft.

Beginning with Starlink Group 2-1 in September 2021, all Starlink launches have featured satellites with inter-satellite laser communication links. The laser links allow the satellites to transmit signals directly between each other through optical laser communications instead of having to rely on ground stations. These satellites have informally been referred to by Elon as “Starlink v1.5” satellites since they are more advanced than the original satellites launched to shell 1.

Beginning with this mission, SpaceX also changed the launch nomenclature to include the shell number and the number of the launch within that shell. Starlink 4-12 is the twelfth mission dedicated to deploying satellites into shell number 4.

SpaceX has plans for a second-generation Starlink constellation, Gen2, which will be launched on Starship and will have almost 30,000 satellites. The Federal Communications Commission (FCC) has not yet approved this plan. The company also has permission to launch and deploy over 7,000 satellites with V-band capability, however, no steps have yet been seen in this direction and it is likely that SpaceX has abandoned these plans altogether.

(Lead image: Falcon 9 booster B1051-12 soars into the cloudy skies over Florida. Credit: Stephen Marr for NSF)