SpaceX launches Starlink 4-15 mission, expands booster fleet – NASASpaceFlight.com

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SpaceX is launched its twentieth Falcon 9 rocket of the year with a batch of Starlink satellites to Low Earth Orbit (LEO) on the Starlink Group 4-15 mission. Liftoff occurred on Saturday, May 14 at 4:40:50pm EDT (20:40:50 UTC) from Space Launch Complex 40 (SLC-40) at Cape Canaveral Space Force Station (CCSFS) in Florida.

The Falcon 9 for this mission was of special interest as it uses a new booster, B1073-1, something not seen until now on a Starlink mission.

The Falcon 9 rocket performed its traditional 35-minute-long automated launch countdown sequence prior to liftoff. Main Engine Cut-Off – or MECO – occurred about two and a half minutes into flight with stage separation and MVac ignition occurring shortly after. The fairing halves separated approximately 5 seconds after MVac ignition.

The first stage for this mission then performed its usual trip back to Earth via a set of entry and landing burns. It soft landed on SpaceX’s Autonomous Spaceport Drone Ship (ASDS) “Just Read The Instructions” stationed approximately 626km downrange in the north Atlantic Ocean.

The fairing halves also came back to Earth via a set of thrusters that orient them for reentry and a parachute that slows them down to a soft splashdown in the ocean. Recovery from the ocean will be performed by SpaceX’s multi-purpose recovery vessel Bob.

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The second stage’s first burn, the orbital insertion burn, lasted approximately 6 minutes after which the second stage and the Starlink satellites were in an elliptical Low Earth Orbit (LEO). About 30 minutes later, the second stage made a second burn to inject the satellites into the 305 by 318-kilometer 53.2° inclination target orbit. The satellites will then separate about an hour after launch.

The second stage will perform a third and final burn for deorbit and disposal over the Indian Ocean west of Australia. The Starlink satellites will then raise their orbit to an approximate 350km circular orbit for checkouts and phasing. Those that pass the checks will then raise their orbit to the 540km operational altitude.

This mission was the 46th dedicated Starlink mission by SpaceX and it is launching 53 Starlink satellites into shell four of Starlink’s first generation constellation. This will make up a total of 2600 satellites launched into LEO by SpaceX. Of these, 248 of them have reentered and 1749 are in their operational orbit.

Shell #1Shell #2Shell #3Shell #4Shell #5
Orbit550km circular at 53º570km circular at 70º560km circular at 97.6º540km circular at 53.2º560km circular at 97.6º
# of orbital planes72366724
Satellites per plane (target)2220582243
Satellites launched16655107560
Satellites in operational orbit14591802720
Total satellites (target)15847203481584172

(Status of Starlink constellation information from Jonathan McDowell as of May 13th)

Booster fleet expands, SpaceX upgrades launchpads and improves rocket performance.

Saturday’s mission featured a new Falcon 9 booster, something never seen before for a Starlink mission. The only other Starlink mission that has seen a booster this early in its flight history was Starlink v1.0-28 launched in May of 2021 when booster B1063-2 lifted off from SLC-40 with 60 Starlink satellites headed to shell one of the constellation.

It is understood that this new booster, B1073-1, debuted on this mission in order to expand SpaceX’s fleet of Falcon 9 boosters. The company aims to launch up to 60 times this year and plans to expend or temporarily retire some of the oldest boosters in the fleet which means they’ll need to have new boosters at hand to meet the increased demand for flights both internally and from customers.

(Graph of active Block 5 boosters per flight number and year)

For example, booster B1049 is now set to be expended on the Nilesat 301 mission, with the O3b mPOWER missions having been re-planned in such a way that the first stage won’t have to be expended to meet customer requirements.

On the other hand, booster B1060 is set to be temporarily retired once it reaches 15 flights later this year; this is understood to be for a deep-dive examination of its systems and components to better understand how to refurbish and reuse boosters up to 20 flights.

Apparently, this is not meant to be a complete overhaul but rather just a study into what it takes to efficiently and cheaply refurbish and keep using Falcon 9 boosters beyond the 15-flight mark. After this, the booster will return to the fleet with aims to fly it up to the 20-flight mark by next year.

With boosters going out of commission and demand at all-time high at SpaceX for launching their own Starlink satellites and new customers coming in like One Web, it was necessary to introduce another booster in the fleet to meet schedules. Although this could have been done on a customer mission, apparently SpaceX had already assigned boosters to customer missions well into the year, so the only possibility was to introduce the booster in one of their own missions.

Another particular rarity of this booster is the lack of the usual F9 logo, and the SpaceX logo is only on one side of its fuselage, which led observers to initially think it was destined to be a Falcon Heavy side booster. While its first flight is going to be as a Falcon 9 booster, it is indeed true that currently this booster is being targeted for flight as a Falcon Heavy side booster on its seventh flight.

SpaceX’s drive to meet schedules not only includes expanding the fleet or, as previously reported, experimenting with faster turnaround times, but it also includes upgrading ground systems. It is understood that both of SpaceX’s launchpads in Florida are seeing gradual upgrades between launches to reduce the work needed between flights, in the way making it cheaper and faster to ready the ground systems for the next launch.

However, problems with ground systems still occur to this day. Sources indicate that SpaceX had to repair SLC-40’s launch mount after the previous launch with reports of cracks and fatigue shown in the reaction frame of the Transporter/Erector. Although this could be seen as a deal-breaker, ground teams were capable of rapidly repairing and bringing the launch mount to full functionality in record time with it supporting another flight just two weeks after the previous one.

Part of the increased internal demand on Starlink missions stems from SpaceX’s desire to deploy the constellation as soon as possible. The company not only plans to do this by increasing cadence but also performance of the rocket. We’ve seen them recently launching 53 satellites to trajectories and orbits where in previous occasions, the rocket could only launch 46 or 47 satellites.

William Gerstenmaier, SpaceX’s Vice President of Build and Flight Reliability, already claimed during the post-Flight Readiness Review conference for Axiom-1 that thrust profile optimizations for Starlink flights had been implemented to improve performance of the rocket.

It is understood that SpaceX is also improving the performance of the rocket by changing certain timings during flight like igniting the MVac engine a few seconds earlier than on other missions or separating the fairing closer to stage separation to shed dead weight earlier in the flight.

Additionally, SpaceX is loading propellants on the rocket at slightly lower temperatures than usual in order to pack more of them into the tanks and increase the amount of Starlink satellites the Falcon 9 can put into orbit.

All of these improvements to Falcon 9’s performance have been made possible thanks to the storied flight history of the rocket and the huge amounts of data the company can gather with each Starlink flight and the confidence in the reliability of it.

Two more SpaceX missions are set to launch this month with another Starlink mission and a Transporter mission both set for the second half of May.

(Lead photo: A Falcon 9 sits at SLC-40 before launching the GPS-III-SV05 mission in June 2021. Credit: Julia Bergeron for NSF)

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