Twice-Flown Falcon 9 Booster pulls into Port Canaveral for Well-Deserved Retirement
SpaceX’s twice-flown Falcon 9 booster pulled into Florida’s Port Canaveral at sunrise on Tuesday, rounding up its second trip to the edge of space and back to lift the company’s reuse ambitions to the next level via proving Falcon 9 first stages can be flown repeatedly.
Known by its serial number #1021, the booster supported the Dragon SpX-8 mission in April 2016 when it sent SpaceX’s cargo spacecraft on its way toward the International Space Station before becoming the first booster to stand the landing atop the SpaceX Drone Ship in the Atlantic. The Drone Ship ‘Of Course I Still Love You’ was in the Atlantic again on Thursday when #1021 embarked on its second mission, giving the SES-10 communications satellite a lift toward orbit.
In between flight assignments, the booster underwent four months of refurbishment work plus exhaustive inspections to ensure it was ready to withstand the rigors of spaceflight once again. Part of the refurbishment work was the partial disassembly of the booster, some components were replaced with upgraded subsystems but overall, the stage remained in its original configuration, meaning the air frame and nine Merlin 1D engines that flew in 2016 again launched & landed last Thursday.
The booster’s part in last week’s primary mission was a burn of 158 seconds, accelerating the 70-meter tall Falcon 9 rocket to a speed of 2.3 Kilometers per second before handing off to the MVac-powered second stage to finish the job of lifting the heavy SES-10 satellite into orbit. Unlike its first flight where plenty of fuel margin existed, the booster was looking at a much hotter re-entry as no propellant was available to slow the rocket down prior to re-entry.
The SpX-8 mission last year enjoyed the luxury of a much lower staging speed plus a partial boost back maneuver that created a benign re-entry environment.
#1021 lit three of its engines at the point of entry interface for 20 seconds, hitting the brakes and shielding the engine section. Onboard video from the booster clearly showed the extreme heating environment with the grid fins pictured on fire for several seconds before video from the first stage cut out. The actuated grid fins were in action for 80 seconds of atmospheric descent and maneuvered the booster toward the drone ship, holding position 550 Kilometers south east of Launch Complex 39A.
Touchdown of #1021 was marked eight and a half minutes after liftoff under the power of its center engine that lit up half a minute before to slow the 47-meter tall first stage down for a gentle landing on its four fold-out landing legs. Photos of the rocket’s landing clearly show the scars it incurred during the speedy re-entry – aside from the typical blackening of the RP-1 tank area, the booster also shows a toasty upper section with significant marks on the interstage – likely as the result of the grid fins starting to burn away and depositing aluminum onto the booster’s skin.
Following its successful return, the booster was remotely safed before crews re-boarded the drone ship to tie the first stage down onto the deck. SpaceX is developing a robotic ‘grabber’ that will see action in the coming months to secure a booster in position before personnel boards the ship, especially useful when seas are rough and workers can not safely access the drone ship while the booster is in a potentially unstable state.
F9/SES10: 1st reflown Falcon 9 booster now entering Port Canaveral atop SpaceX droneship pic.twitter.com/xED96ob39N
— William Harwood (@cbs_spacenews) April 4, 2017
Being towed back to Florida, the drone ship appeared on the horizon in the early hours on Tuesday and entered a holding pattern prior to advancing into port at sunrise, docking around 11:30 UTC to begin the process of offloading the booster. Previous returns allowed SpaceX to streamline the post-landing procedure that entails lifting the booster off the drone ship, draining remaining propellant and igniter fluid, removing the landing legs and rotating the stage to a horizontal position for transport.
#1021 was lifted off the ship within three hours of its arrival, being placed on a stand where it is likely to remain a few days to facilitate the necessary operations to fully safe the stage. Afterwards, the booster will be transported to one of SpaceX’s Cape Canaveral facilities for detailed post-flight inspections as engineers will be eager to see how the hardware fared after repeat exposure to the actual launch/landing environment.
SpaceX CEO Elon Musk said the booster is unlikely to fly again and will be offered to the Kennedy Space Center’s Visitor Complex to go on display as the first re-flown orbital-class rocket. Re-flying this particular booster makes little sense given its prior exposure and the fact that many of its components are from a previous generation that is not fully optimized for easy re-use.
SpaceX’s future iteration of Falcon 9, commonly referred to as the Block 5, will implement a number of changes based on lessons learned from previously recovered cores to make re-use more efficient. Block 5 will also be the launch vehicle for future crewed Dragon missions and SpaceX plans to fly at least seven Block 5 missions with a frozen design to prove its reliability to NASA. Previously, no SpaceX rockets were alike with frequent hardware changes between successive flights to improve the performance of the vehicle or increase the odds of successful landings.
The Block 5 version will debut the final performance increase on the Merlin 1D engines, stepping up from a sea level thrust of 756 Kilonewtons to around 845kN. This will further lift Falcon’s payload capacity and increase fuel margins for recovery missions.
Additionally, Block 5 will host a number of reinforced components to decrease the wear and tear suffered by returning boosters. Modifications are being made on the rocket’s four grid fins seen burning last Thursday when the rocket went through the peak heating environment of its descent into the atmosphere. Forged titanium grid fins will enable SpaceX to fly them for many missions and improvements to the heat shield at the base of the rocket will help protect internal hardware such as the engines and associated plumbing. Currently, SpaceX has to replace the shield between each mission of the same booster.
Block 5 will further enhance Falcon’s payload performance by making its return more efficient through greater controllability during descent, flying the booster at a higher angle of attack using a better pitch control system. All in all, around 100 changes are being made on the rocket and Block 5 vehicles are envisioned to fly ten times without any refurbishment between missions and several dozen times with some maintenance carried out between flights.
Elon Musk said up to six cores will be re-flown this year, including the two side boosters of the Falcon Heavy debut mission this summer. Next year could see a dozen re-use missions and SpaceX aims to cut refurbishment times to a single day in the long run to achieve the goal of rapidly reflying first stages and drastically cutting the costs of launching payloads into space.
SpaceX is also pursuing the re-use of Falcon’s large payload fairing and carried out the first experimental return on last Thursday’s mission, successfully recovering one of the 13-meter long fairing halves. Following separation, three minutes and 49 seconds into the flight, the fairing halves were to use small thrusters to stabilize prior to re-entry into the atmosphere. Auto-steering chutes were then to deploy and maneuver the halves to a precise location for a soft splashdown in the Ocean.
One of the fairing halves managed to survive the trip and returned to Cape Canaveral on Monday.
Eventually, SpaceX will likely upgrade to a mid-air recovery of the fairing halves for operational re-use. Fairing re-use was identified as an area of interest some time ago as the large composite structures represent around 10% of Falcon 9’s manufacturing cost and require a lengthy production process.
Musk also said the company was looking into options for recovering the second stage of the Falcon Heavy rocket on its debut mission this summer. This one-off experiment would take advantage of surplus performance on the demonstration mission to deliver valuable data to SpaceX for an evaluation of the feasibility of second stage re-use, however, Musk said the experiment would only have low odds of success.
For the near term, SpaceX’s focus will be on keeping its current pace of launches with missions out of Cape Canaveral roughly every two weeks with occasional launches from California to fly out a manifest of 20 missions prior to the end of 2017. The company hopes to return Space Launch Complex 40 to service by summer, repairing damage from last September’s explosion of a Falcon 9 and giving the pad a new Transporter-Erector-Launcher. After SLC-40 is readied, Cape missions will shift there to allow LC-39A to undergo around two months of outfitting work for Falcon Heavy as well as the installation of the crew access arm in anticipation of the debut mission of the crewed Dragon later this year ahead of a crewed test flight as early as May 2018.