SpaceX, NASA, ESA Launch Sentinel-6 Michael Freilich Mission

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Further reviews determined this issue could be present on multiple engines on newly built-boosters. Thus, all Merlin-1D engines on affected cores were inspected, including B1061 (the booster that launched the Crew-1 mission on 15 November) and B1063 (the Sentinel-6 Michael Freilich booster).

Upon further testing and inspections, it was decided that SpaceX would replace two engines on the first stage. As a result, the launch of Sentinel-6 Michael Freilich was delayed to Saturday, 21 November.

The spacecraft was fully encapsulated inside the Falcon 9 rocket’s 5-meter diameter payload fairing on 3 November in preparation for integration onto the launch vehicle. During this time, SpaceX began shipping the two replacement Merlin-1Ds to Vandenberg for installation and testing.

NASA, SpaceX, ESA, and other program managers held a Flight Readiness Review for the mission on 16 November and concluded the flight was ready to launch on 21 November at 09:17 Pacific Standard Time (17:17 UTC).

A day later, SpaceX conducted a static fire test of B1063’s nine Merlin first stage engines on pad SLC-4E and verified the engines had performed nominally. Following this test, the rocket was rolled back inside SpaceX’s Vandenberg Horizontal Integration Facility for integration and final checkouts.

The entire stack was then rolled back out to the pad and lifted vertical on the night of 20 November local time in preparation for launch.

The business end of the countdown began at T-38 minutes to liftoff, when the launch director will poll the mission teams to proceed into propellant loading operations. The auto-sequence began with rocket and pad systems commencing the flow of chilled RP-1 fuel into both stages of the Falcon 9 at T-35 minutes, along with liquid oxygen (LOX) loading into the first stage. LOX loading on Falcon 9’s second stage began at T-16 minutes.

At T-7 minutes, the LOX pre-valves on the nine Merlin-1D first stage engines opened, allowing LOX to flow through the engine plumbing and thermally condition the turbopumps for ignition. This process is known as “engine chilling” or “chilldown”, and is used to prevent thermal shock that could damage the motors upon startup.

At the T-1 minute mark, Falcon 9’s onboard flight computers ran through final checks of the vehicle’s systems and finalized tank pressurization before flight. The launch director gave a final “go” for launch at T-45 seconds.

The nine Merlin-1D engines ignited at T-3 seconds, with liftoff taking place at T0 following a quick final check by the onboard computers to verify that all systems are operating as expected.lifts off on the Sentinel 6A mission. (Credit: Michael Baylor for NSF/L2)

After lifting off from SLC-4E, Falcon 9 began to pitch downrange as it accelerated towards orbital velocity. At T+1 minute 1 second, the vehicle passed through the region of maximum aerodynamic pressure, or “Max-Q”. During this portion of flight, mechanical stresses on the rocket are at their highest.

The first stage burned until T+2 minutes 17 seconds, at which point the engines shut down simultaneously in an event known as MECO, or Main Engine Cutoff. Stage separation occurred shortly afterward, with second stage Merlin Vacuum engine ignition taking place at T+2 minutes 28 second. Upon engine startup, the second stage continued to carry the Sentinel-6 Michael Freilich to a 1,336 kilometer (830.2 mile) non-Sun-synchronous orbit, with an inclination of 66 degrees.

The 5-meter payload fairing housed the spacecraft during the initial phases of launch until it is deployed at T+2 minutes and 50 seconds. Both halves of the fairing will descend back to Earth to be recovered by support ship NRC Quest.

While Falcon 9’s second stage and Sentinel-6 Michael Freilich continued to press onward to a low parking orbit, the first stage performed a Return To Launch Site (RTLS) landing at SpaceX’s Landing Zone 4 (LZ-4) -1 a landing pad at Vandenberg Air Force Base, located 430 meters (1,410 feet) from launch pad SLC-4E.

Following stage separation, Falcon 9’s first stage flipped around and fired three of its nine Merlin-1D engines to perform a boostback burn, so as to divert its trajectory back towards Landing Zone 4. The entry burn at T+6 minutes 55 seconds refined the booster’s course and slowed its descent. Stage 1 touched down at T+8 minutes 19 seconds, with the final landing burn being performed by the center Merlin engine.

The Merlin Vacuum engine on Falcon 9’s second stage meanwhile shut down at T+8 minute 18 seconds, in an event known as Second Engine Cutoff-1 (SECO-1). This marked the completion of the first of two burns for this mission and inserted Sentinel-6 Michael Freilich into a low parking orbit of Earth.

Following a 45-minute-long coast phase, the Merlin Vacuum engine re-ignited for its second and final burn of the mission at T+53 minutes 18 seconds. The burn lasted for 10 seconds before Second Engine Cutoff-2 (SECO-2) occurs.

Separation of the Sentinel-6 Michael Freilich spacecraft followed a few minutes later.

The Sentinel-6 mission was one of many that SpaceX hopes to launch before the end of 2020, with others like Starlink V1 L15 (16th Starlink flight overall), NROL-108, CRS-21 (the first Cargo Dragon 2 resupply mission to the ISS), SXM-7, and Turksat-5A still waiting in the wings.

Starlink L15 should be next up after Sentinel-6, with launch targeted for no earlier than 22 November at 21:56 Eastern Standard Time (02:56 UTC on 23 November).

Following the launch of Sentinel-6, the next SpaceX launch set to take place from Vandenberg Air Force Base is the SARah-1 phased radar array satellite, currently scheduled for no earlier than February 2021. The spacecraft is expected to fly with smaller rideshare payloads.

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