Main Engine Cut Off

In last week’s issue, and in the most recent episode of the podcast, I speculated how the slower fueling procedures SpaceX implemented for Falcon 9’s return to flight would affect overall performance, and specifically, first stage recoveries. Since then, we got some additional insight from Elon Musk, himself.

The next launch—EchoStar-23—is carrying a very heavy payload to GTO. With a payload mass of approximately 5,500 kilograms, the first stage will have to be expended. For context here, let’s compare to some past GTO flights.

SES-9—another heavy payload—is approximately 5,300 kilograms in mass and was launched to a slightly higher orbit than standard GTO. The first stage landing attempt ended with a hole in the deck of the droneship, but it was close.

JCSAT-14—while only a 4,600 kilogram payload—was the first GTO flight with a successful recovery of the first stage. The booster was brought home in one piece, but it was beat up. This became the booster that would lead SpaceX’s testing efforts in McGregor, Texas, and has been fired up 8 times since.

A few months later, JCSAT-16 was launched—a virtually identical mission. The landing on 16 was very different: it used a gentler, single-engine landing burn instead of a more stressful triple-engine landing burn as was used previously for GTO flights. The booster from 16 has not been retired or relegated to ground tests like the booster from 14. This shows that, as expected, SpaceX has been refining their flight profile and mechanics for softer entries and landings, and better reuse.

All of these details together paint a fairly full picture. A 5,300 kilogram payload headed to above standard GTO was on the upper end of recoverable, and then two nearly identical missions showed big progress in improving the flight and landing profiles. Of course, there could be some information we’re missing, but we can assume that the 10-11 months of refinements could have led to a recoverable first stage on EchoStar-23, if it weren’t for changes in fueling procedure.

It seems likely that the slower fueling we saw on Iridium-1 has affected Falcon 9’s performance enough to limit recovery on previously-recoverable (or close to recoverable) flights. When Musk stated that future flights in the EchoStar-23 class will fly on Falcon Heavy or Falcon 9, Block 5, I am led to read that as the version with the redesigned COPVs, among other changes. The redesigned COPVs will give SpaceX the ability to fly with fully-densified, quickly-loaded propellant again. The other upgrades included in Block 5 will improve booster lifespan, but propellant densification is the key to big improvements in performance.

Another important note: the EchoStar-23 launch will not—contrary to a few reports in large publications—be the last to expend a first stage. There are many missions that will need to fly with expendable boosters. Falcon Heavy flights to Mars will most likely expend the center core. It will be a rare occurrence to see a first stage plunge into the Atlantic—and rarer to see one plunge into the Pacific—but it will be required for some flights.

We’re still a week or two out from seeing EchoStar-23 launch. It’s been pushed back a few times because of ongoing work at Pad 39A. Once SpaceX completes work on the pad, they expect flights to pick up smoothly. They’re currently targeting a 15-day turnaround for 39A between EchoStar-23, CRS-10, and SES-10.

Thank you!

Thanks for reading the eleventh issue of Main Engine Cut Off Weekly. Each week, I bring you what I find interesting and important in spaceflight, and you can get it however you like best—blog, podcast, or this here column. If you like what I’m doing, I’d really appreciate your support. Head over to Patreon and become a patron for as little as $1 per month. Everything I do is supported entirely by readers and listeners like you, and every little bit of support helps. Big thanks to those of you out there supporting!

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Thanks for reading, and I’ll talk to you next week.

— Anthony