Starlink Group 4-26 slated for Tuesday launch from LC-39A


On August 9 at 6:57 PM EDT (22:57 UTC), SpaceX’s Falcon 9 rocket will lift off from pad 39A at the Kennedy Space Center, carrying 52 Starlink satellites to Low Earth Orbit (LEO). These satellites will contribute to filling up the fourth shell of the Starlink constellation, which is now available in 36 countries to provide internet access to people around the globe.

On August 3, 2022, SpaceX received special temporary permission to allow communications between Starlink satellites and U.S. ground stations at latitudes above 53 degrees using elevations down to 10 degrees, whereas the previous elevations were at or below 25 degrees. This is the first launch of Starlink satellites since the implementation of this special permission.

Starlink Group 4-26 will be launching using first stage B1073, which has flown on two previous missions, both of which were in the past three months. First, the stage launched Starlink Group 4-15 in May 2022 followed by SES-22 in June 2022, with this most recent flight occurring 41 days ago. It is unclear whether or not either of the fairing halves had flown previously.

This is SpaceX’s 178th mission and the company’s 35th in 2022. Once this batch of Starlink satellites is deployed, the total number of launched Starlinks will come up to 2,920.

The launch sequence will begin at T-38 minutes when the go/no-go poll is conducted, which takes into account the weather conditions, vehicle and payload health, and the status of the keep-out zones. For Starlink 4-26, the forecasted probability of acceptable weather for an on-time launch is 70%. An improved 90% chance is forecasted for a backup launch opportunity on August 10.

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At T-35 minutes, propellant begins being loaded into the vehicle, starting with sub-cooled RP-1 kerosene to both stages, which will be fully loaded by T-20 minutes, and super chilled liquid oxygen (LOX) to the first stage. At the T-20 minute point, a large vent can be seen from the Transport Erector (T/E) as it purges its lines to prepare for the next phase of fueling.

Four minutes later, at T-16 minutes, LOX begins being loaded into the second stage. This commodity is loaded second due to the differing temperatures to minimize boiloff. Both RP-1 and LOX are then topped off until T-90 seconds.

At T-7 minutes, engine chill on the first stage begins in order to minimize the thermal shock to the Merlin 1D engines as the super chilled LOX flows through them at ignition. Then, at T-60 seconds, the vehicle enters startup, meaning the flight computer takes over the countdown, and the fuel tanks are brought to flight pressure. Finally, at T-3 seconds, the flight computer sends the command for ignition of the nine Merlin 1D engines for liftoff at T-0.

The Merlin 1D engines remain lit for just over 150 seconds before Main Engine Cutoff (MECO) and stage separation occur. Following stage separation, a series of events will happen in quick succession. First, the second stage lights its single Merlin 1D Vacuum (MVac) engine to then perform a six-minute and four-second burn in order to insert the Starlink satellites into their initial parking orbit.

Departure! A Shortfall of Gravitas droneship is heading ~630 km downrange for the Starlink 4-26 mission.

— Gav Cornwell (@SpaceOffshore) August 5, 2022

At the same time, fairing separation occurs and the fairing halves both re-enter the atmosphere to splashdown downrange and be recovered by SpaceX recovery vessel Doug to hopefully be refurbished and reused.

Also following stage separation, the first stage booster deploys its grid fins and performs a series of thruster maneuvers in order to properly orient itself for re-entry. Once the vehicle’s clock reaches six minutes following launch, it will reignite one engine, followed by two more, then shut down two after a few seconds, then shut down the final engine about 20 seconds after its reignition, completing the entry burn.

Shortly after eight minutes following launch, the booster reignites its center engine for a gentle landing on SpaceX’s Autonomous Spaceport Drone Ship (ASDS) A Shortfall of Gravitas (ASOG), stationed off the coast of North Carolina.

Once the second stage reaches the correct parking orbit, Second Engine Cutoff 1 (SECO-1) occurs and the stage will enter a 45-minute and 14-second coast phase, after which the MVac will reignite for a one-second burn to ensure the satellites are positioned correctly before deployment. Finally, roughly one hour after launching, the four tension rods that hold the satellites in place are released, allowing the satellites to slowly drift away from the second stage and prepare to maneuver to their final positions over the next several months.

(Lead photo: Falcon 9 sits vertically at LC-39A before the launch of IXPE in December 2021. Credit: Julia Bergeron for NSF)

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