Continuing its busy 2022 launch manifest, SpaceX has begun filling the next shell of the Starlink constellation. The Starlink 3-1 mission lifted off aboard a Falcon 9 rocket from Vandenberg Space Force Base at 6:39 PM PDT Sunday (01:39 UTC on Monday), tasked with delivering 46 Starlink satellites to low Earth orbit.
Starlink 3-1 is the first mission to begin filling up the third Starlink orbital shell. The shell is one of five planned for the constellation and consists of six orbital planes in a 560-kilometer circular orbit inclined at 97.6 degrees. Once completed, Shell #3 will contain 348 satellites.
This inclination and altitude mean the orbit is considered sun-synchronous. A sun-synchronous orbit (SSO) is a near-polar orbit around a planet, in which a satellite passes over any given point of the planet’s surface at the same local solar time every day. This type of orbit is commonly used for imaging satellites as it allows for similar lighting conditions through multiple observations; for Starlink, it will instead help to improve coverage in polar regions.
Shell #3 will be the first of two shells launching into a 97.6-degree inclination, with shell #5 to consist of 172 satellites across four planes at the same inclination and altitude. This high inclination orbit is needed for the constellation to provide service to the entire planet, as previous shells have launched into either 53 or 70-degree inclinations which are too low to service areas at extreme latitudes.
Sunday’s launch was the 50th dedicated Starlink launch, and the 17th so far this year as SpaceX continues the rapid deployment of its communications constellation. This also marks the 29th launch of 2022 for SpaceX, keeping the company on target to conduct at least 50 orbital missions before the year is out.
With 46 satellites aboard, Falcon 9 carried fewer spacecraft than have been carried on other recent Starlink missions: last Thursday’s launch having deployed 53 satellites into Shell #4. This is likely due to more fuel being needed to reach Shell #3’s more highly-inclined orbit.
The Starlink 3-1 launch comes just as SpaceX has begun to expand its internet service offerings with the recent additions of Starlink for Recreational Vehicles (RVs) and Starlink Maritime for seaborne users. These premium services allow users to purchase the Starlink hardware and install it on moving vehicles; previously coverage had been limited to specific service addresses, limiting users from being able to take the hardware with them in a mobile setting.
SpaceX has also begun expanding to offer Starlink to the airline industry, with Hawaiian Airlines announcing in late April that it planned to equip its Airbus A330 and A321neo aircraft with Starlink to allow passengers to access free, high-speed internet during transpacific flights.
Sunday’s launch made use of a flight-proven Falcon 9 rocket. The booster for the Starlink 3-1 mission was B1063-6, a veteran of five previous launches. B1063 first flew in the launch of the Sentinel-6A Michael Freilich mission in November 2020, and has since carried out the Starlink L28 mission in May 2021, the Double Asteroid Redirect Test (DART) launch for NASA in November 2021, and most recently a pair of Starlink missions: Starlink 4-11 in February, and Starlink 4-13 on May 13th. Falcon 9 flew from Space Launch Complex 4E (SLC-4E) at the Vandenberg Space Force Base in California.
The launch followed the normal Falcon 9 countdown sequence with the launch director giving the go for propellant loading at T-38 minutes and fueling of the vehicle beginning at T-35 minutes. During this time RP-1 kerosene and liquid oxygen (LOX) were loaded onto the vehicle. Due to the need to top off the LOX tanks throughout the countdown, fueling does not conclude until around one and a half minutes before liftoff.
One minute before launch, Falcon 9’s flight computer takes over control of the countdown and the propellant tanks begin to be brought up to flight pressure. At T-3 seconds, the vehicle sends a command to ignite the nine Merlin 1D engines that power the first stage, which then ignite, and the rocket lifts off from the pad at T-0.
After just under two-and-a-half minutes of powered flight, the first stage engines shut down and four pneumatic pushers on the booster extend to separate the first and second stages. Once separated, the second stage ignites its single Merlin 1D Vacuum (MVac) engine and performs a six-minute, four-second burn to insert the Starlink satellites into an initial parking orbit.
Shortly after second stage ignition, the two fairing halves separate from the vehicle, exposing the satellites to space for the first time. The fairings re-enter the atmosphere and splash down under parachutes about 654 km downrange, where they will be recovered by SpaceX’s recovery vessel NRC Quest. After recovery, the two fairing halves will be taken back to port for refurbishment ahead of their next flight.
Shortly after stage separation, the first stage deploys its four hypersonic grid fins and begins to orient itself for re-entry. Around six minutes after liftoff, the booster performs its normal entry burn sequence: first igniting one engine, then two more for a total of three, before dropping back down to one and then shutting down about 20 seconds after ignition.
Just over eight minutes after liftoff, the booster ignited its center Merlin 1D engine for the final time on Sunday’s mission, guiding it to a soft touchdown on SpaceX’s Autonomous Spaceport Drone Ship (ASDS), Of Course I Still Love You (OCISLY), which was located in the Pacific Ocean about 643 km southwest of the launch site.
While these events were occurring, the second stage was still making its first burn to reach the initial parking orbit. Second Stage Engine Cutoff 1 (SECO-1) marks the end of this burn, after which the stage entered a 45-minute, 14-second coast phase. At the end of this coast, the second stage fired its engine again for a brief one-second burn to place the satellites into their final deployment orbit of 308 x 320 km. Just over one hour after liftoff, the four tension rods that secured the satellite stack to the payload adapter separated, allowing the satellites to slowly drift away from the second stage.
Once deployed, each satellite will unfurl its single solar panel and undergo various health and system checks to ensure all systems are operating nominally. If all systems are performing as expected the satellites will ignite their single krypton-powered ion thruster and begin slowly raising their orbits to the operational altitude of 560 km over the next couple of months. During this orbit-raising period, the satellites will also begin to fan to fill up the orbital planes and slots for which they are destined.
Saturday’s launch brings the total number of Starlink satellites launched up to 2,805. Assuming all 46 satellites make it to their final orbit and enter service, this will bring the number of operational Starlinks up to 2,085.
(Lead image: Falcon 9 launches with the Starlink Group 3-1 mission. Credit: Pauline Acalin for NSF)