SpaceX to launch OneWeb 17 mission and return booster to LZ-1

SpaceX to launch OneWeb 17 mission and return booster to LZ-1

SpaceX is set to launch 40 high-speed internet communication satellites into a polar low Earth orbit on the OneWeb 17 mission on Thursday. Launching from Space Launch Complex 40 (SLC-40) at Cape Canaveral Space Force Station in Florida, Falcon 9 is scheduled to fly at 2:13 PM EST (19:13 UTC) and mark its 16th orbital SpaceX launch in 2023 – a launch every 4.25 days.

Following launch, less than 90% (578 of the planned 648) of operational satellites were launched. The satellites will be placed in a ~580 by 600 km orbit, inclined at 86.51 degrees. The satellites will spend the coming months raising their orbits to the operational 1,200 km circular polar orbit at 86.4 degrees.

On March 7, Space Launch Delta 45 issued a launch mission execution forecast giving the weather a 5% chance of breaching weather constraints. The only concern is the cumulus cloud rule. In the event of a delay, there will be a backup launch opportunity 24 hours later, with the probability of breaching time constraints rising to 15%.

The Falcon 9 booster supporting this mission is B1062-13; as the name suggests, the booster supported 12 previous missions: seven Starlink missions, two GPS missions, Inspiration4, Axiom-1, and Nilesat-301.

Following launch, the stage will perform a return to launch site (RTLS) landing, landing at SpaceX’s Landing Zone 1 (LZ-1). If successful, this will be SpaceX’s fifth RTLS landing this year, 177th booster landing, 103rd consecutive successful landing, and 27th landing at LZ-1.

Once removed from the second stage, the payload fairings gently splash into the ocean under a parachute. SpaceX’s multi-purpose recovery vessel Bob then they are recovered from the water.

OneWeb’s Constellation is a satellite internet constellation that aims to provide internet coverage around the world. When complete, the constellation will consist of 36 satellites in each of 18 orbital planes. 600 of these satellites are needed for global coverage, with an additional 48 on-orbit spares. Based on demand, the constellation can later be expanded to more than 900 satellites.

Each OneWeb satellite has a compact design and a mass of ~150 kg. They are equipped with a Ku-band antenna, which operates between 12 and 18 GHz, which allows for each satellite to have 8 gigabits per second of throughput. Initially, the satellites had Russian Fakel SPT-50 ion thrusters; however, due to the conflict in Ukraine, this was changed to Busek BHT-350 Hall effect thrusters on newer satellites.

The satellites have two solar panels for power and are built by Airbus Defense and Space; the first 10 were built in Toulouse, France, and the rest were made at OneWeb’s US-based factory.

Originally, the OneWeb satellites were launched by Arianespace and Roscosmos aboard the Soyuz-2.1b/Fregat-M. In 2022, also due to the conflict in Ukraine, OneWeb moved these launches to SpaceX’s Falcon 9 and ISRO’s GSLV Mk. III.

OneWeb satellites are being prepared for integration before the next launch of ISRO OneWeb. (Credit: OneWeb)

The current routine Falcon 9 launch sequence begins at T-38 minutes, where the launch director will certify that all systems go for propellant loading. First and second stage fueling begins at T-35 minutes, with the first stage liquid oxygen (LOX) loaded.

Falcon 9 uses super-chilled LOX and sub-cooled rocket propellant-1 (RP-1). This increases the density of the propellants, increasing the amount that can be stored in the vehicle and the performance of the Merlin engine.

At T-20 minutes, the fueling of the second stage is complete and the transporter erector begins to purge its lines, preparing the lines for the second stage LOX load, which begins at T-16 minutes. This purging creates the Falcon 9’s classic T-20-minute vent and is used to thermally condition and clean lines prior to LOX load.

At T-1 minutes, the Falcon 9 will enter start-up and the tanks will begin pressurizing to flight pressures. After 15 seconds, the launch director will verify that the vehicle will be launched.

At T-3 seconds, the engine controller will command the engine ignition of all nine Merlin 1D engines in the first stage. This is done by flowing trimethylaluminum and triethyl-borane (TEA-TEB) through machines. TEA-TEB is pyrophoric, meaning it ignites when in contact with oxygen.

The Falcon 9’s nine Merlin 1D engines shortly after liftoff. (Credit: SpaceX)

Before launch, the flight computer will verify that all nine engines and the vehicle are operating nominally and will command the launch clamps to release the vehicle.

The first stage will burn for 137 seconds before the stages close and separate. At this point, the second stage’s single Merlin vacuum engine will ignite, and the first stage will begin to flip and fire three engines for its boostback burn, which will last 48 seconds.

Three and a half minutes into the flight, the second stage will discard the fairings. The first stage would perform two more burns (the re-entry and landing burns), before gently touching down at LZ-1 less than eight minutes after launch. Upon successful landing, the booster designation will change to B1062-14.

Second stage engine cutoff 1 (SECO-1) will occur at T+8:34 before the stage enters a ~47 minute long coast section. The second phase will perform a three-second long burn, with SECO-2 occurring at T+55:20, before starting to deploy OneWeb satellites two at a time at T+58:50. This process will take a little under 37 minutes, with all satellites deployed by T+1:35:18.

This launch will mark SpaceX’s third launch in March, with the CRS-27, SES-18 and SES-19, and Starlink missions scheduled for next month.

(Lead image: B1062 on SLC-40 before the Nilesat-301 mission in June 2022. Credit: Stephen Marr for NSF)