SpaceX surpasses 4,000 Starlink satellites on-orbit with Starlink Group 5-6 launch

Lifting off from Space Launch Complex 40 (SLC-40) at the Cape Canaveral Space Force Station in Florida, SpaceX’s 30th launch of 2023 placed 56 Starlink satellites into a low Earth orbit. Liftoff of the Starlink Group 5-6 mission took place May 4, 2023, at 03:31 AM EDT (07:31 UTC).

This mission marked SpaceX’s 27th Falcon 9 flight of the year — alongside two Falcon Heavy flights and Starship’s maiden integrated flight test. The company has launched a rocket on average every ~4.2 days in 2023. Additionally, this launch was SpaceX’s 157th Falcon 9 flight with a flight-proven booster.

SLC-40 supported the O3b mPOWER 3 & 4 mission just 5.39 days before the planned T0, marking the second fastest turnaround in SLC-40’s history. SpaceX is expected to break the 5.15-day turnaround record this month.

On May 2, the Space Launch Delta 45 released a launch mission execution forecast, giving the weather a 95% chance of being go for launch. The only concern for Thursday’s launch attempt was the cumulus cloud rule, which states that a launch cannot happen within 18.5 km of cumulus clouds with tops that extend into freezing temperatures.

Following launch, SpaceX landed booster B1069-7 on its autonomous spaceport drone ship A Shortfall of Gravitas (ASOG), stationed 630 km downrange in the Atlantic Ocean. ASOG was tugged down range by Crosby Skipper. SpaceX’s multi-purpose recovery boat Bob will provide support for ASOG and recover the fairings from the water, just over 630 km downrange. This landing marked SpaceX’s 189th successful landing and 115th consecutive landing.

The booster supporting this flight, B1069-7, flew just 47 days ago and has supported CRS-24, Hotbird-13F, OneWeb Launch 15, SES-18 & 19, and two Starlink missions. Following B1052, B1053, and B1068 being expended on the ViaSat-3 Americas mission, B1069 is now one of 15 flight-proven boosters in SpaceX’s fleet. Upon successful landing, its designation changed to B1069-8.

Launching on Starlink Group 5-6 are 56 Starlink v1.5 satellites, lofted into an initial orbit of 298 by 340 km inclined at 43.00 degrees. Following deployment, the satellites will raise their orbits into a Starlink second-generation orbit: a 530 km circular orbit at 43 degrees. With these satellites in orbit, SpaceX surpasses 4,000 satellites in orbit and will have launched 4,340 total satellites. 

(Starlink information from Jonathan McDowell)

The now very-familiar Falcon 9 launch countdown sequence started at T-38 minutes where the launch director verified that all systems were go for propellant load. With the vehicle, ground service equipment, and teams happy with the data, both the first stage and second stage began to be fueled with rocket propellant-1 (RP-1) at T-35 minutes. Also at this time, the first stage began filling operations with liquid oxygen (LOX). 

The Falcon 9 launch vehicle uses super-chilled LOX, cooling it down to -205° C, which is significantly cooler than LOX’s -183° C boiling point. In fact, this temperature is not far below LOX’s freezing point of -219° C. Additionally, the RP-1 used on Falcon is also cooler than on other vehicles, with RP-1 being chilled to ~-10° C. By further chilling the propellants the density of each increases, thus increasing engine performance and mass of propellant on the vehicle.

At T-20 minutes, fueling on the second stage completed and the transporter erector began purging its lines, preparing for stage two LOX load, which started at T-16 minutes. This purging is what causes Falcon 9’s iconic T-20 minute vent (and Falcon Heavy’s T-22 minute vent). 

One minute before launch, the Falcon 9 entered start-up and began pressurizing its tanks for flight. This is when the vehicle takes command of the count; however manual aborts for technical reasons, weather, and range can still be called up until T-10 seconds. At this point, the vehicle is in full control of its countdown, and ground operators cannot abort the launch.

Falcon 9’s nine first stage engines right after liftoff. (Credit: SpaceX)

At T-3 seconds, the booster’s flight computer commanded all nine Merlin 1D engines on the first stage to ignite in pairs, reducing transients on the first stage. Once the flight computer verifies that all engines and the vehicle are nominal, it commands for the hydraulic launch clamps to be released, allowing Falcon 9 to lift off.

The first stage, B1069, burned for just under two and a half minutes before shutting down and separating from the second stage. Stage two burned for approximately six minutes, while the booster completed its reentry and landing burns, landing on ASOG. During this time, the two fairing halves deployed at T+2:46, which then utilize cold gas thrusters and parafoils to softly land in water for recovery.

Fairing reentry on the ViaSat-3 mission was the hottest and fastest we've ever attempted. The fairings re-entered the atmosphere greater than 15x the speed of sound, creating a large trail of plasma in its wake pic.twitter.com/VgdlH6r3yR

— SpaceX (@SpaceX) May 2, 2023

The second stage then coasted for approximately 45 minutes before igniting its single Merlin Vacuum engine for two seconds. The stage then coasted for about 10 minutes, during which the stage started to rotate end-over-end. The four tension rods then be deployed at T+1:04:51, allowing all 56 Starlink satellites to deploy at once. 

This launch was SpaceX’s second launch of the month; if all goes to SpaceX’s plan, this will be the company’s busiest launch month ever with up to 10 launches. In support of this, there are back-to-back Starlink missions on May 8 from both coasts, followed later in the month by Arabsat 7B, Iridium-9, and other Starlink launches.

(Lead image: B1076 sitting on SLC-40 ahead of the Intelsat 40e mission. Credit: Max Evans for NSF)

https://www.youtube.com/watch?v=r8tZkQrldu4