SpaceX keeping up the pace with Starlink Group 4-9 launch

by Mihir Neal

SpaceX has launched another 47 Starlink satellites to low Earth orbit. The liftoff occurred at 9:25 AM EST (14:25 UTC) on Thursday, March 3, from the historic Launch Complex 39A at NASA’s Kennedy Space Center in Florida. This mission marked SpaceX’s ninth launch of 2022 and their first launch of the month.

The 45th Weather Squadron at Patrick Space Force Base forecasted a 90% chance of favorable weather for launch, with a low risk of violating weather criteria in the booster recovery area. Both the ascent and the first stage landing occurred nominally and on schedule.

The Starlink satellites were placed into an initial 53.2º inclination, 307 x 313-kilometer orbit. Over the coming months, they will make use of their onboard krypton-propellant ion engines to slowly reach their operational 540-kilometer circular orbits.

The slightly lower parking orbit — compared to 337 x 325 kilometers for the previous Starlink Group 4-8 mission — allows for a launch of 47 satellites instead of 46. These orbital altitude adjustments come in the wake of a geomagnetic storm that doomed 40 Starlink spacecraft last month while the satellites were maneuvering within their low insertion orbits.

As the Falcon 9 lifts off, the rocket headed southeast from Cape Canaveral, hugging the coast of the Bahamas as the upper stage performed a slight dogleg maneuver to avoid flying over populated areas.

Stationed 642 kilometers downrange from LC-39A is one of SpaceX’s Autonomous Spaceport Drone Ships, Just Read the Instructions (JRTI), tugged by Zion M Falgout in the Atlantic Ocean. Alongside JRTI is SpaceX’s multipurpose vessel, Bob. Named after one of the astronauts who flew on SpaceX’s Demonstration mission-2, Bob is providing ASDS support for this mission and will recover the fairings as they splash down on the Atlantic Ocean.

The Falcon 9 booster supporting this mission is B1060, having previously launched to space 10 times. It has supported the launch of the US Space Force’s GPS III-3 satellite, Turksat-5A, the Transporter-2 rideshare mission, and seven Starlink missions.

B1060’s missions Launch Date (UTC) Turnaround Time (Days)
GPS III-3 May 30, 2020 19:22 NA
Starlink V1 L11 July 20, 2020 21:30 66
Starlink V1 L14 October 6, 2020 11:29 42
Türksat 5A December 6, 2020 16:17 87
Starlink V1 L18 January 24, 2021 15:00 28
Starlink V1 L22 March 11, 2021 08:13 49
Starlink V1 L24 April 7, 2021 16:34 37
Transporter – 2 May 15, 2021 22:56 63
Starlink Group 4-3 & BlackSky November 13, 2021 12:19 156
Starlink 4-6 January 13, 2022 15:25 49

Starlink Satellite Constellation

Starlink is SpaceX’s constellation of internet satellites in low Earth orbit that aims to provide internet access to most of Earth, primarily serving areas devoid of a fiber connection. One of SpaceX’s two most capital-intensive projects, it has been under development for some time, with the first regulatory filings dating back to 2014.

Over the years, the plan underwent various changes, but in February 2018, SpaceX’s Tintin A and B satellites, experimental precursors to the operational Starlink satellites, were launched as secondary payloads from the then Vandenberg Air Force Base.

The constellation consists of five groups of satellites, or “shells,” which will operate at different altitudes and orbital planes. As denoted by the first number in the mission name — in this case, “4” for Starlink 4-9 — the mission targets the fourth shell of the Starlink Constellation.

Shells Inclination (°) Orbital Altitude (km) Planes Satellites per Plane Number of Satellites Active Satellites
Shell 1 53 550 72 22 1584 1538
Shell 2 70 570 36 20 720 51
Shell 3 97.6 560 6 58 348 3
Shell 4 53.2 540 72 22 1584 356
Shell 5 97.6 560 4 43 172 0

SpaceX is actively filling up the fourth shell of the mega-constellation, which when complete will increase the capacity and reduce the latency for customers located between 52 degrees North and 52 degrees South latitude.

The company is hoping to launch 40 Starlink missions this year to complete this shell, after which they are expected to start filling the second shell.

Launch Timeline

At T-38 minutes, the Launch Director gave a go for propellant loading. At T-35 minutes, SpaceX began loading sub-cooled RP-1 kerosene onto both the first stage and the second stage as well as super-chilled LOX (liquid oxygen) onto the first stage.

SpaceX, unlike other launch providers, uses RP-1 which is cooled to -7 degrees Celsius along with LOX that is cooled to -205 degrees Celsius. Using supercooled propellants increases the performance of Falcon 9 by densifying the fluids, packing more energy into a smaller space. This is beneficial for reuse, since the first stage must reserve some energy for landing.

Just before T-20 minutes, the second stage RP-1 load was completed, which was marked by a large vent from the T/E (Transporter Erector). This vent indicates the purging of the T/E lines ahead of the start of LOX load onto the second stage at T-16 minutes.

At T-7 minutes, the Falcon 9 allowed a small amount of liquid oxygen to enter the nine Merlin 1D engines on the first stage. This process cools the engines slowly so they do not get damaged from thermal shock when super chilled LOX starts to flow through them at full volume during engine start.

The signature “T-20 minute vent” is seen during a scrubbed launch attempt for the Starlink v1.0 L12 mission in October 2020. (Credit: Thomas Burghardt for NSF)

At T-1 minute, the Falcon 9 entered start up and began pressurizing its tanks for flight. At this point, Falcon 9’s onboard computers assume full control of the countdown, and any technical aborts from this point forward would have been handled autonomously and not by the ground operators.

At T-45 seconds, the Launch Director verified that all positions were go for launch. At T-3 seconds, the F9’s flight computer commanded the ignition of the nine Merlin 1D engines on the first stage. The ignition happens in pairs, within milliseconds of each other to reduce startup transients and loads on the vehicle.

Once the computers ensure all systems are working nominally, they command the hydraulic clamps at the base of the vehicle to release, letting the Falcon 9 lift off from the pad.

B1060 fired its engines for approximately two and a half minutes before shutting down, once again in a staggered formation to reduce loads on the vehicle.

The first stage separated from the second stage using pneumatic pushers, followed by ignition of the second stage’s single vacuum optimized Merlin engine seconds later. Meanwhile, after coasting up to its apogee and then beginning its descent, B1060 performed two burns to softly touch down on Just Read the Instructions.

The second stage, meanwhile, continued to burn toward orbit. At around two minutes and 47 seconds after launch, the vehicle commanded the latches connecting the fairing halves to release. The fairing halves will then use their onboard RCS thrusters to reenter into the Earth’s atmosphere before softly splashing down in the Atlantic. They were planned to be recovered by Bob, although the vessel did make a detour to Nassau in the Bahamas which means recovery may be delayed or scrubbed for this mission.

About eight minutes and 46 seconds after launch, the second stage shut down its Merlin Vacuum engine, beginning an approximately 48-minute coast phase. At T+56 minutes, the second stage re-ignited for just a second to circularize its orbit. From this point, the vehicle used its RCS thrusters to start rotating around its x-axis.

At T+65 minutes 47 seconds, the vehicle commanded the deployment of the tension rods used to keep the stack of Starlink satellites together, and the satellites slowly drifted away from the second stage.

Shortly after, the second stage performs a deorbit burn and destructively reenters Earth’s atmosphere, leaving only the tension rods as debris objects which will naturally decay. The Starlink satellites will, meanwhile, begin maneuvering toward their operational orbits.

(Falcon 9 lifts off from LC-39A on the Starlink Group 4-9 mission. Credit: Stephen Marr for NSF)

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