SpaceX is gearing up to launch another batch of Starlink satellites to the fourth shell of the constellation. Teams are currently targeting January 6 at 21:49 UTC (16:49 EST) for the first global orbital launch attempt of the year.

Lifting off from historic Launch Complex 39A (LC-39A), the Starlink Group 4-5 mission will lift 49 Starlink v1.5 satellites southeastward from Kennedy into a 210 x 339 km low Earth orbit with an inclination of 53.22 degrees.

Following payload separation, the satellites will slowly raise their orbit until they are in their operational altitude of 540 km. This process takes several months due to the low-thrust but high-efficiency Krypton ion thrusters on the Starlink satellites.

This mission will defy decades of precedent, with SpaceX reaching the 53.22-degree orbit not via the northeast launch corridor up the eastern seaboard of the United States and Canada, but rather via a southeast corridor hugging the coast of the Bahamas as it performs a dogleg maneuver. 

This dogleg is the reason why SpaceX is launching fewer Starlink satellites on this mission from the East coast compared to other launches from Florida, such as Starlink Group 4-1 which launched 53 Starlink satellites.

Additionally, Starlink v1.5 satellites are approximately 10% more massive than the v1.0 Starlink satellites, which is why Starlink Group 4-1 already saw a decreased number of lofted satellites compared to the Starlink v1.0 missions.

Stationed approximately 637 km downrange from LC-39A is SpaceX’s Autonomous Spaceport Drone Ship (ASDS) A Shortfall of Gravitas (ASOG). ASOG was tugged to the landing zone by Zion M Falgout, a sister tug to the usual Finn Falgout, marking the first time this vessel was used to tow an ASDS. 

The multi-purpose vessel Doug will provide ASDS support for the Starlink Group 4-5 mission and will also recover the fairings from the water, a process known as wet recovery.

The 45th Weather Squadron’s launch mission execution forecast released on January 5 predicts a 20% chance of liftoff weather violating range launch constraints, with the Cumulus Cloud Rule being the primary concern. Weather officers additionally predict a low risk for upper-level wind shear, booster recovery weather, and solar activity.

A Shortfall of Gravitas droneship has arrived at the landing zone for the upcoming Starlink mission.

ASOG is ~637 km downrange on a new south east trajectory. pic.twitter.com/Ozp45VLdgk

— Gav Cornwell (@SpaceOffshore) January 4, 2022

In the event of a scrub, SpaceX has a backup opportunity just under 24 hours later on January 7; the weather on the seventh is marginally worse, with a 30% chance of violating launch weather constraints. Wind shear, booster recovery weather, and solar activity all remain low risk.

The Falcon 9 booster supporting this mission is B1062-4. The booster was first used on the GPS-III-SV04 mission in November 2020, followed by GPS-III-SV05 in June 2021. Most recently, the booster supported the all-private Inspiration4 crew launch in September 2021.

B1062’s missions
Launch Date (UTC)
Turnaround Time (Days)

GPS-III-SV04
November 5, 2020
N/A

GPS-III-SV05
June 17, 2021
224 days

Inspiration4
September 16, 2021
91 days

Starlink Group 4-5
January 6, 2022
112 days

Starlink

The Starlink constellation, when complete, will consist of five orbital shells; the first number in Starlink Group 4-5 signifies that the launch is headed to shell four. The second number signifies the mission number to that shell.

Mission numbers are not assigned chronologically and therefore do not launch in order. For example, Starlink Group 4-5 is launching before Starlink Group 4-2.

SpaceX’s main priority is currently to fill the fourth shell of Starlink, which will further increase capacity and reduce latency for customers between 52 degrees North and 52 degrees South latitude. 

SpaceX has also deemed it important to begin filling shell two, while shells three and five are currently the lowest priority, with the only launches to shell three being SpaceX’s Transporter smallsat rideshare missions.

Inclination (°)
Orbital Altitude (km)
Planes
Satellites per Plane
Number of Satellites
Currently Working Satellites

Shell 1
53.0
550
72
22
1,584
1,556

Shell 2
70.0
570
36
20
720
51

Shell 3
97.6
560
6
58
348
7

Shell 4
53.2
540
77
22
1,584
153

Shell 5
97.6
560
4
43
172
0

Ahead of the launch, B1062 did not perform a static fire. The rocket rolled out of the Horizontal Integration Facility (HIF) hours ahead of launch where it was then taken vertically by the Transporter-Erector (TE), also known as the strongback.

The TE is used to fuel the second stage of the vehicle, provide structural support while horizontal and vertical, provide power and air conditioning to the payload, and take the Falcon 9 from its horizontal to a vertical position.

At T-38 minutes, the Launch Director will verify the vehicle is GO for propellant loading. Pending all teams being GO, at T-35 minutes, SpaceX will begin loading subcooled RP-1 onto both the first stage and the second stages as well as super-chilled Liquid Oxygen (LOX) onto the first stage.

Unlike every other operational rocket, the Falcon 9 uses RP-1 that is cooled to -7 degrees C, and LOX that is cooled to -205 degrees C. This further chilling increases the density of the propellants, enabling SpaceX to get more performance out of the Falcon 9 — something that is crucial for reuse.

This also comes with a trade-off: SpaceX is unable to hold the countdown once fuel loading has started — though there are post-fueling start recycle points to enable further attempts should a daily launch window permit.

Just before T-20 minutes, a large vent from the TE marks the end of second stage RP-1 load and the purging of the TE lines ahead of the start of LOX load to the second stage at T-16 minutes.

At T-7 minutes, the Falcon 9 enters chill down when a small amount of liquid oxygen is allowed to enter the nine Merlin 1D engines on the first stage. This process is done to cool down the engines slowly so they do not crack from thermal shock when super chilled LOX starts to flow through them at full volume at engine ignition.

Falcon 9 B1062 lifts off from LC-39A on the Inspiration4 mission in September 2021 – via Julia Bergeron for NSF/L2

At T-1 minute, the Falcon 9 will enter start-up and begin pressurizing its tanks for flight. At this point, Falcon 9 is fully in charge of its countdown, and all technical aborts from this point forward would be handled by the vehicle itself and not the ground operators. Launch controllers will only be able to abort the Falcon 9 in case of a weather or range violation.

At T-45 seconds, the Launch Director will verify all positions are go for launch.

The booster’s flight computer will command the ignition of the first stage’s Merlin 1D engines at T-3 seconds. The engines on the first stage ignite in pairs within milliseconds of each other to reduce startup transients and loads on the vehicle.

Once the computers have ensured all systems are nominal, the Falcon 9 will command the hydraulic clamps at the base of the vehicle to release, letting the Falcon 9 lift off from the pad.

B1062 will burn for approximately two and a half minutes before shutting down — once again in a staggered formation to reduce loads on the vehicle.

Four pneumatic pushers — three radially around the interstage and one in the center of the interstage — will then push the stages apart. The second stage’s single vacuum optimized Merlin will ignite seconds later.

After coasting up to its apogee and beginning its descent, B1062 will perform two burns to softly touch down on A Shortfall of Gravitas. The first burn — called the Entry Burn — will utilize three Merlin 1D engines (engines E1, E5, and E9), whereas the second burn — called the Landing Burn — utilizes only the center engine, E9.

A Shortfall of Gravitas — via Julia Bergeron for NSF/L2)

E1, E5, and E9 are the only engines capable of restarting in-flight as they have TEA-TEB canisters to hold ignition fluid.

The second stage, meanwhile, will continue burning toward orbit. At around three minutes after launch, the vehicle will command the latches connecting the fairing halves to release. Shortly after, the fairing halves will be pushed apart using the four pneumatic pushers stored in the active fairing half.

The fairing halves will then use RCS thrusters to reenter into the Earth’s atmosphere, before deploying a parafoil to softly land in the water. They will then be recovered by SpaceX’s fairing recovery vessel, Doug.

About nine minutes after launch, the second stage will shut down its Merlin Vacuum engine. From this point, the vehicle will use its RCS thrusters to start rotating around its X-axis.

At T+15 minutes 31 seconds, the vehicle will command deployment of the tension rods used to keep the stack of Starlink satellites together, and the satellites will slowly drift away from the second stage.

Shortly after, the second stage will perform a deorbit burn and a stage propulsive passivation.

SpaceX currently has four additional launches scheduled for January 2022: Transporter-3, which is launching from Space Launch Complex 40 on January 14; CSG-2 in late January; and up to two more Starlink missions.

(Lead image: A Falcon 9 vertical at LC-39A ahead of the Starlink v1.0 L12 mission in October 2020 – via Stephen Marr for NSF)

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