SpaceX keeping up cadence with Starlink Group 5-5 mission

by Alejandro Alcantarilla Romera

SpaceX’s 20th mission of the year launched on Friday, March 24, sending another batch of Starlink satellites into low Earth orbit (LEO). The mission, named Starlink Group 5-5, lifted off at 11:43 AM EDT (15:43 UTC) from Space Launch Complex 40 (SLC-40) at Cape Canaveral Space Force Station, in Florida.

The weather forecast released by the Space Launch Delta 45’s Weather Squadron called for a greater than 95% chance of favorable weather during the primary launch window. 24 hours later, during the backup launch window, the weather forecast was slightly worse with the chances of favorable weather dropping to 85%.

Coming right on the heels of the debut flight of Starlink v2 Mini satellites, this mission was also launching into Starlink’s second-generation constellation (Starlink Gen 2). However, the satellites on this mission were the older version 1.5 satellites that have also been launched on the four previous Group 5 missions. 

As part of the launch preparations, SpaceX conducted a static fire test of the rocket on Thursday, March 23–a rarity these days. These pre-launch static fire tests are becoming less common as Falcon flies more and gains experience and reliability. The booster for this mission, B1067, flew for a tenth time on Friday, marking the seventh booster to fly ten times. 

The reason for the static fire before launch is not known, but SpaceX officials have claimed in the past that these tests are usually performed only when refurbishment of the booster has shown the need for the extra data before launch. This may come as a result of engine swaps or fixes that need to be corroborated.

The countdown sequence for this mission followed the usual 35-minute-long propellant load sequence. This began with RP-1, a refined form of kerosene, being loaded onto both stages and liquid oxygen (LOX) being loaded onto the first stage.

Loading of RP-1 on the second stage wrapped up 15 minutes later and chill down of the LOX umbilicals for the second stage began, creating the now-famous “T-20 minute vent.” This vent lasted approximately four minutes, after which liquid oxygen load on the second stage began.

Nine minutes later, the chill down on the nine first stage Merlin 1D (M1D) engines began. In this process, a small amount of liquid oxygen is let to flow through the oxygen turbopump to lower its temperature ahead of engine ignition. This avoids the formation of bubbles of gaseous oxygen during engine startup and initial operation when the highest flow of liquid oxygen is present in the oxygen turbopump. About a minute later, RP-1 load was completed on the booster.

At T-3 minutes and T-2 minutes, LOX load wrapped up on the first and second stages respectively. From that point, the ground systems initiated the purge of all the propellant lines ahead of liftoff. 

One minute before liftoff, the ground computers handed off command to Falcon 9’s onboard computers. These began a number of system checks on the vehicle and initiated the pressurization of the tanks for flight. 

Three seconds before liftoff, the engine controller initiated the engine start sequence on all nine M1D engines on the first stage. These ignited in a staggered manner, taking about two seconds to reach full power. During the last second of the count, vehicle computers performed health checks on all engines before commanding the ground clamps to release the rocket for liftoff. 

Friday’s launch followed a southeasterly trajectory with Falcon 9 grazing the northern parts of the Bahamas as it went into orbit. The nine first stage engines burned for approximately two minutes and 27 seconds. Four seconds later, the two stages separated via four pneumatic pushers on the interstage, three on the perimeter and another in the center. 

Six seconds after that, the Merlin 1D Vacuum (MVacD) engine on the second stage ignited and initiated the approximate six-minute long burn to put itself and the satellites into an elliptical parking orbit.

While the second stage powered itself to orbit, the first stage returned itself down to a powered landing on SpaceX’s autonomous spaceport drone ship A Shortfall Of Gravitas, which was stationed 660 kilometers downrange. 

Eight seconds after MVacD ignition, the fairing halves separated and performed a parachute-assisted splashdown in the Atlantic Ocean. SpaceX’s multi-purpose recovery vessel Doug was waiting downrange for the retrieval of both halves. 

Once in the initial elliptical parking orbit, the second stage coasted for about 45 minutes to arrive at its apogee. Then, it briefly relit its engine for orbit circularization. 

Ten minutes after MVacD’s second burn of the mission, the Starlink satellites separated, allowing SpaceX teams to begin checkouts and on-orbit testing processes. The satellites will later raise their orbits to their operational altitude, which for this shell is a circular 530 km orbit. 

After satellite separation, the second stage will perform a third and final burn for deorbit and disposal over the western Indian Ocean.

Friday’s launch carried 56 Starlink v1.5 satellites into Starlink Gen 2’s 43-degree inclination shell. This brings the total of Starlink satellites launched into orbit to 4,161, of which 302 no longer remain in orbit.

Starlink Gen 1

Starlink Gen 2



Group 2

Group 3

Group 4

Group 5

Group 6


550 km at 53º

570 km at 70º

560 km at 97.6º

540 km at 53.2º

530 km at 43º

Satellites launched







Satellites reentered







Satellites in operational orbit







(Status of Starlink constellation from Jonathan McDowell as of March 23)

This Starlink Gen 2 mission comes a few weeks after the debut of Starlink v2 Mini: a downsized version of the Starlink v2 satellite bus sized for Falcon 9’s fairing envelope. Orbital tracking data has shown that the first batch of v2 Mini satellites has had issues during their checkout phase and they’ve experienced orbital decay as a result of this.

In response to these observations, SpaceX’s CEO Elon Musk confirmed on Wednesday that these satellites are experiencing issues and some of them will be deorbited as a consequence. Sources indicate these issues are not affecting all satellites in the same manner and are of varying natures. Some of these issues are related to power or communications dropouts, and some may be experiencing sporadic attitude control issues as well. 

These issues are currently being identified and fixes are underway for future satellites. As a consequence, an upcoming launch of Starlink v2 Mini satellites, Starlink Group 6-2, has been delayed from March 29 into April. 

To occupy the leftover gap in the schedule, the company has brought forward the Starlink Group 5-10 mission, which is now scheduled to launch on that date. That launch, just like Friday’s mission and prior Group 5 missions, will send Starlink v1.5 satellites into orbit instead of Starlink v2 Mini satellites.

(Lead image: Falcon 9 lifts off from SLC-40 on the Starlink Group 5-5 mission. Credit: NASASpaceflight)

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