Starlink Group 4-20 to be first Starlink rideshare mission in 2022 –


SpaceX will be launching another Falcon 9 Block 5 on Sunday, September 4 at 10:09 PM EDT (02:09 UTC on September 5). Lifting off from Space Launch Complex 40 (SLC-40) at the Cape Canaveral Space Force Station in Florida, this mission will carry 51 Starlink satellites, as well as the rideshare Varuna-TDM, to low-Earth orbit (LEO). It will mark the 40th Falcon 9 launch of 2022–a launch every 6.2 days.

Varuna-TDM, short for Varuna Technology Demonstration Mission, is a commercial program by Boeing, which intends to test V-band communications for a proposed constellation of 147 non-geostationary broadband satellites. Varuna is hosted on a Sherpa-LTC2 Orbital Transfer Vehicle (OTV) from Spaceflight Inc, which will raise the hosted customer payload to a 1,000-kilometer low-Earth orbit.

While in orbit, Varuna will attempt to confirm the assumptions of the propagation characteristics of the V-band spectrum, allowing the manufacturers of the terminal equipment, and other hardware compatible with Boeing’s V-band Non-Geostationary Fixed Satellite Service, to demonstrate the abilities of their design. Additionally, the satellite will provide prospective users of Boeing’s broadband communications services (both commercial and governmental users) an opportunity to evaluate the performance of V-band communications links for specific applications. 

The first stage booster supporting this mission, B1052-7, previously supported Arabsat-6A, STP-2, COSMO-SkyMed Second Generation FM2, KPLO, and two Starlink missions. This booster is being reflown after only 31 days following its previous mission, KPLO.

To begin the automated launch sequence, at T-38 minutes SpaceX’s Launch Director will give the go for propellant loading. Starting at T-35 minutes, sub-cooled RP-1 kerosene will be loaded into both stages, and the first stage will begin being loaded with liquid oxygen (LOX). 

At T-20 minutes, the RP-1 will be fully loaded on the second stage, and a large vent from the Transport Erector (T/E) will be seen. This is to purge its lines of RP-1 in preparation for the second stage’s next phase of fueling: at T-16 minutes, LOX will begin being loaded into the second stage. Following the completion of LOX loading, RP-1 on the first stage and LOX on both stages will be topped off until T-90 seconds. 

At T-7 minutes, the Falcon 9 first stage will begin engine chill—the booster will flow a small amount of LOX through the oxygen section of each M1D turbo pump, preventing propellant from flashing into a gas at engine ignition, which could severely damage the engine. Then, at T-1 minute, the flight computer will take over the countdown and begin final prelaunch checks. At the same time, the propellant tanks will pressurize to match the pressurization they will encounter during the flight, leading to the call out “tanks are pressed for flight.”

Next, the Launch Director will verify the final go for launch at T-45 seconds. Then at T-3 seconds, the engine controller will send the command for engine ignition. If by T-0.02 seconds the engines and vehicle are running nominally, the vehicle will command the hydraulic launch clamps to release at T0, allowing the vehicle to ascend.

Following liftoff, the vehicle will encounter Max-Q – the moment of maximum aerodynamic pressure – at T+ one minute and 12 seconds. The first stage Merlin 1D engines will remain lit until T+ two minutes and 29 seconds, at which a series of events will occur within seconds of each other. First, all nine M1D engines will shut down, followed shortly after by the separation of the stages. The second stage will then ignite its single M1D Vacuum engine.

The fairings, which protect the payloads from debris and atmospheric heating during ascent, will separate from the vehicle at T+3:13. Both halves will utilize RCS thrusters and parachutes to re-enter the atmosphere and softly splashdown in the Atlantic Ocean. The fairing halves will then be recovered by SpaceX’s fairing recovery ship, Doug.

B1069 being towed into port following the Starlink Group 4-23 mission. (Credit: Jack Beyer for NSF)

Also following stage separation, the first stage will deploy its four grid fins and perform a series of thruster maneuvers to orientate itself properly for re-entry. At T+6:05, the first stage’s re-entry burn will begin and continue for the next 31 seconds, at which point the engines will shut down. The first stage will then coast back toward Earth, continuing to use its grid fins to direct it toward its landing position. At T+8:05, the first stage will ignite for a third time to slow it down for a soft landing on SpaceX’s Autonomous Spaceport Drone Ship (ASDS) Just Read the Instructions (JRTI).

Once the second stage reaches the nominal parking orbit, Second Engine Cut Off 1 (SECO-1) will occur and the stage will enter a coast phase for just over 37 minutes. The MVac engine will then reignite for a two-second burn, raising the orbit for payload deployment. At T+ 49 minutes and 28 seconds, the Sherpa-LTC vehicle will be deployed from the top of the Starlink satellite stack. The second stage will then rotate over its x-axis, before deploying the two tension rods at T+ one hour, 12 minutes, and 23 seconds. Due to the stage’s rotation, the 51 Starlink satellites will have varying amounts of angular momentum, causing them to separate once the tension rods are deployed. 

The Starlink satellites will then spend the following months raising their orbit to Starlink Shell 4: a 540 km circular orbit at 53.2 degrees. SpaceX has at least four more missions in September, including at least three Starlink missions and the TTL mission.

(Lead image: Falcon 9 on the pad ahead of CSG-2. Credit: Stephen Marr for NSF)