SpaceX staying busy with Starlink Group 4-6 launch

At 7:04 PM EST on January 18 (00:04 UTC on January 19), SpaceX will launch another batch of 49 Starlink satellites to orbit aboard a flight-proven Falcon 9 rocket from Launch Complex 39A at NASA’s Kennedy Space Center (KSC).

This will be the third mission for SpaceX in 2022, as the company has already launched the Starlink Group 4-5 and Transporter-3 missions this month. In addition, this mission will mark a quick turnaround for LC-39A, as Starlink Group 4-5 also launched from the same pad on January 6.

This launch is also following a similar trajectory to the last Starlink launch, flying southeast from Cape Canaveral.

Starlink is SpaceX’s broadband internet constellation in low Earth orbit, with an operational altitude of around 550 km. Each satellite features a single solar panel and uses Hall thrusters for propulsion.

In preparation for the mission, SpaceX’s newest autonomous spaceport drone ship, named “A Shortfall of Gravitas,” departed Port Canaveral on January 13, right as the Transporter-3 mission was lifting off from SLC-40.

A Shortfall of Gravitas arrives at Port Canaveral for the first time in July 2021. (Credit: Julia Bergeron for NSF/L2)

The former barge was converted to a drone ship in Port Fourchon, LA, and work was completed in mid-2021. It is also known as MARMAC 302. Both “A Shortfall of Gravitas” and “Just Read The Instructions” are based out of Port Canaveral, while ”Of Course I Still Love You” is based in California.

The drone ship “A Shortfall of Gravitas” was last deployed on the Starlink Group 4-5 mission.

On January 15, the SpaceX recovery ship named Doug departed Port Canaveral for the recovery zone. The ship is named after Demo-2 Astronaut Doug Hurley and will recover the fairings from the ocean.

The Group 4-6 mission was originally targeted for January 17 local time, but was delayed 24 hours in order to take advantage of more favorable weather conditions.

This Starlink mission, like the last, will take a southeastern trajectory which will aid first stage recovery efforts. This is believed to be an effort to avoid the rough weather in the Atlantic Ocean towards the northeast in the winter months.

Past Starlink missions had their recovery zone off the coast of the Carolinas. For the Group 4-6 mission, the drone ship will be stationed near the Abacos Islands in the Bahamas.

The booster supporting this mission is B1060-10, which is making its tenth flight and is the fourth booster to reach this milestone. The booster first launched in June 2020 for the GPS III SV03 mission and subsequently flew on Starlink missions, Turksat-5A, and Transporter-2.

This Falcon 9 last launched on December 2, 2021 on the Starlink Group 4-3 mission, making this a turnaround of a little more than a month for this specific booster.

Falcon 9 B1060 launches the Starlink Group 4-3 mission in December 2021. (Credit: Stephen Marr for NSF)

The Falcon 9 was rolled out from the Horizontal Integration Facility (HIF) to the launch pad at LC-39A on January 16.

Launch

The launch sequence begins when the launch auto sequence is initiated on the Falcon 9 at T-35 minutes prior to launch. At the same time, fuel loading starts on the launch vehicle with RP-1 Kerosene loading on both the first and second stages. Loading of Liquid Oxygen (LOX) is also started on the first stage.

At T-20 minutes, the Transporter Erector (TE) will conduct a large vent to purge propellant lines as the loading of RP-1 is completed. Four minutes later, LOX loading on the second stage begins.

At the seven minute mark before liftoff, the nine Merlin 1D engines on the first stage of the Falcon 9 rocket will begin to be chilled down in preparation for launch. This prevents thermal shock on the nine engines from the Falcon 9’s super-chilled propellants.

Around four minutes and 25 seconds prior to launch, the TE will start to retract from the launch vehicle.

Each of the tanks on both stages on the launch vehicle will continue to be topped off with liquid propellants up until the T-two minutes mark. This will be followed by the Falcon 9 entering “startup,” which is when the control of the vehicle is handed off to the rocket’s onboard computers.

Ignition of the nine Merlin 1D engines will occur at the T-3 seconds mark. At T-0, the hold-down clamps on the pad will release, and the Falcon 9 will be underway. Also, at launch, the TE will retract further, further protecting it from the launch.

As it ascends, the Falcon 9 will pitch downrange and roll to the proper launch azimuth to align the vehicle on an inclination of 53.2 degrees. Around one minute and 15 seconds after launch, the rocket will experience Maximum Aerodynamic Pressure, or Max-Q, when the vehicle experiences the maximum aerodynamic loads.

A Falcon 9 rocket ascends towards space during the Starlink Group 4-5 mission. (Credit: Stephen Marr for NSF/L2)

Around two minutes and 40 seconds into flight, the nine Merlin 1D engines will shut down in an event known as Main Engine Cut Off or MECO. This will be followed by stage separation.

The single Merlin vacuum engine, or MVac, on the second stage will ignite around T+ two minutes and 50 seconds into flight.

Next, the fairings will separate, which protect the Starlink satellites from the aerodynamic forces in the dense parts of the atmosphere. At around the same time, the four titanium grid fins on the first stage will deploy.

At around T+ six minutes and 55 seconds into flight, the entry burn will occur on the first stage of the Falcon 9. For this burn, three Merlin 1D engines will be used. After this burn is completed, the grid fins will help steer the first stage as it descends.

The first stage of Falcon 9 will then land on “A Shortfall of Gravitas” around T+ nine minutes after launch. Simultaneously, the single MVac engine will shut down.

After landing, a robot called Octagrabber will exit a shelter on the drone ship and will secure and safe the successfully landed Falcon 9 booster.

Around 15 minutes after launch, the 49 Starlink satellites will separate from the second stage into their initial orbit. Each satellite will then individually maneuver to their operational orbits over the coming weeks.

(Lead image: Falcon 9 B1060 vertical at LC-39A prior to the Starlink v1.0 L11 mission in September 2020. Credit: Stephen Marr for NSF)

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