When it comes to innovation and milestones, SpaceX has no shortage of firsts. This past weekend marked not only the first time the company launched payloads from both their East and West coast facilities, but one of the rockets also featured a set of considerably enhanced titanium grid fins. The first of the weekend’s back-to-back launches occurred Friday, June 23rd from Kennedy Space Station’s Launch Complex 39A with the successful delivery of the 8,000-pound BulgariaSat-1, the first geostationary communications satellite in Bulgaria’s history.
The first stage for this mission had been used earlier this year to ferry the Iridium-1 satellites to orbit from Vandenberg Air Force Base, making this booster the first to launch payloads from both coasts.
SpaceX founder, Elon Musk, wasn’t confident that the booster would be recovered. He tweeted, “Falcon 9 will experience its highest ever reentry force and heat in today’s launch. Good chance rocket booster doesn’t make it back.”
Despite the rocket being “extra toasty” having used almost all of its aluminum honeycomb crush core as it hit the deck hard, the stage arrived vertically on drone ship, Of Course, I Still Love You.
“Rocket was suddenly slammed sideways right before landing,” Musk stated. “Heavy gust or something malfunctioned onboard. Reviewing telemetry.”
Two days later, all eyes turned to Vandenberg AFB for the second launch of the weekend doubleheader featuring the slightly heavier and more robust grid fins. Launch Complex 4-East (SLC-4E) became enshrouded in fog during the 1:25 p.m. (PST) instantaneous launch window, which didn’t interfere with the otherwise 100% go-for-launch forecast.
Falcon 9 successfully carried a second set of 10 Iridium NEXT satellites to low-Earth orbit. Of the company’s 81-satellite constellation, 75 are set to be launched by SpaceX by mid-2018.
Iridium is the only mobile voice and data communications network that spans the entire globe. The replacement of individual satellites by Iridium NEXT in a constellation of this size will mark one of the largest “tech upgrades” in history.
Good weather may have granted liftoff, but the drone ship, Just Read the Instructions, had to be repositioned downrange due to extreme weather as it awaited the return of the first stage and its latest “no-maintenance” feature.
“Flying with larger & significantly upgraded hypersonic grid fins.” Musk tweeted the day before launch. “Single-piece cast & cut titanium. Can take reentry heat with no shielding.”
The unfavorable landing weather seemed practical in testing the fancy new grid fins, which were designed to have “more aero effectiveness for steering in high winds.” The edges resemble a bear trap with steep spires on the windward side, significantly improving control and stabilization as the booster falls back to Earth.
Musk discussed issues with the current aluminum grid fins during a post-launch press conference back in April, stating that the new design would be capable of withstanding high-velocity reentry temperatures without burning up. Eliminating the need to refurbish the grid fins is in line with SpaceX’s next goal of being able to re-fly a booster within 24 hours, as the new fins would require no maintenance, only inspection.
Six minutes into the flight, after delivering Iridium-2 into orbit, three of the nine Merlin engines fired up for 20 seconds to slow the booster as it reentered the atmosphere. At seven minutes, 24 seconds the landing burn began, followed by a successful touchdown 20 seconds later on drone ship, Just Read the Instructions.
Another durability feature can now be checked off the list of achievements toward attaining rapid reusability. When asked about other upgrades in durability during an interview last week, Gwynne Shotwell, President and COO of SpaceX, stated that the company’s desire is to fly pre-flown boosters far more quickly than new vehicles.
“We’ve worked a lot on this particular vehicle, a lot of the active components. The valves have been qualified, redesigned and re-qualified for much higher levels and much longer durations,” she said.
Shotwell’s list continued with mention of work being done on the octaweb (the thrust structure for Falcon 9), and the COPVs (composite overwrapped pressure vessel), which will now be able to withstand many cycles. “The Merlin engine, as well, has a number of improvements on it that should give us more life.”
Regarding rapid reusability, Shotwell added, ‘Block 5’ Falcon 9s will contain the final upgrades necessary to be able to re-fly with only inspection required before the booster would be ready for re-launch. We expect to be able to re-fly those boosters at least a dozen or so times, as opposed to the 2-3 times for the current ‘Block 3’ boosters. ‘Block 4’ starts flying shortly and then ‘Block 5’ at the end of this year.”
When asked if there was a certain number of first stages SpaceX wants to have in inventory she replied, “No set plan, largely depends on market demand. I think I predicted at the beginning of the year that we might fly six boosters that have flown before. So we got SES flown, we’re getting ready to fly Bulgaria-Sat tomorrow, and then the Falcon Heavy demo will fly a couple and then we’ve got 3-4 more this year that want to fly on pre-flown, so the market has responded. I knew they would respond well, but it has responded even more favorably towards it.”
SpaceX has clearly been meeting their launch schedules, and according to Shotwell, the main reason has been the ramp in production. “Three years ago or so we were producing six rockets a year and this year we’re going to produce more than 20,” she said, and then added that the increase in production was harder than she anticipated due to the pad failure on Sept 1 of 2016 which broke the company’s stride, halting launches for five months.
As far as further reusability, Musk stated they are, “Getting closer to fairing recovery and reuse. Had some problems with the steerable parachute. Should have it sorted out by end of year.”
“We’re gonna try to bring back the second stages,” Shotwell said in a recent interview. “That’s much harder, obviously, they’re moving faster than the first stage. It’s very typical for SpaceX to want to try to recover every piece of hardware. We’ve got the booster part working pretty well right now, we’re working on the fairing next, and then after that would be the second stage. I don’t want to guess on a timeframe for that, but it’s definitely something that we want to try. Knowing that it’s hard. Really hard.”