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SpaceX restacked its nearly 400-foot-tall Starship rocket on Wednesday, June 5, 2024, in preparation for the fourth test flight of the program, scheduled for the following day.
Image: Michael Cain/Spaceflight Now |
For the fourth time in just over a year, SpaceX is gearing up to launch a test mission of its massive Starship rocket from its development facility in southern Texas, known as Starbase. This launch, dubbed Flight 4, aims to advance the vehicle towards its goal of becoming a mostly reusable rocket.
Similar to the previous three launches, Flight 4 will not carry a payload and will follow a suborbital trajectory. Liftoff is scheduled for 7:50 am CDT (8:50 am EDT, 1250 UTC), at the start of a 120-minute launch window.
Spaceflight Now, in collaboration with LabPadre, will provide live coverage starting at 7:00 am EDT (1100 UTC).
On Wednesday, SpaceX assembled the Starship rocket by stacking the Ship upper stage (Ship 29) on top of the Super Heavy Booster (Booster 11), creating a 121-meter (397-foot) tall vehicle. Both stages will be expanded during the flight, but the mission is designed to demonstrate their future reuse capabilities.
In a post on X (formerly Twitter) on June 1, SpaceX founder Elon Musk stated that “the main goal of this mission is to get much deeper into the atmosphere during reentry, ideally through max heating.”
During Flight 3, the upper stage began to roll uncontrollably, preventing the vehicle from relighting one of its six Raptor engines. However, thanks to its connection to the Starlink satellite internet network, another part of SpaceX's business, the rocket was able to stream high-definition camera views showing its reentry through a plasma blanket.
“The lack of attitude control resulted in an off-nominal entry, with the ship experiencing much larger than anticipated heating on both protected and unprotected areas,” SpaceX explained in a post-launch blog. “The most likely root cause of the unplanned roll was determined to be clogging of the valves responsible for roll control. SpaceX has since added additional roll control thrusters on upcoming Starships to improve attitude control redundancy and upgraded hardware for improved resilience to blockage.”
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| Onboard cameras on the Starship upper stage flown during Flight 3 (Starship IFT-3) show the vehicle surrounded by plasma as it reenters the atmosphere on March 14, 2024. Image: SpaceX |
Meanwhile, the Super Heavy Booster from the last flight also prematurely shut down six out of 13 Raptor engines used during the boostback burn, which remained offline when it attempted to perform a landing burn.
“The booster had lower than expected landing burn thrust when contact was lost at approximately 462 meters in altitude over the Gulf of Mexico and just under seven minutes into the mission,” SpaceX stated. “The most likely root cause for the early boostback burn shutdown was determined to be continued filter blockage where liquid oxygen is supplied to the engines, leading to a loss of inlet pressure in engine oxygen turbopumps.”
“Super Heavy boosters for Flight 4 and beyond will get additional hardware inside oxygen tanks to further improve propellant filtration capabilities.”
Eyes on the Moon
The upcoming Flight 4 is an important mission not only for SpaceX, but also for NASA. The rocket will take center stage when the agency embarks on the Artemis 3 mission, which is currently targeting September 2026.
Lisa Watson-Morgan, the manager of the Human Landing System program, and her team continues to work alongside SpaceX to understand the development of the rocket that will serve as the Moon lander for the yet-to-be-named astronauts of the Artemis 3 and Artemis 4 missions.
“It was great to see the lessons that came out of [flights] one and two and to see how that was employed either through manufacturing, production, through operations of how Flight 3 was conducted,” Watson-Morgan said. “There weren't any issues around Raptor. No fires and a lot of good consistency, frankly, around the engines. When you get all those engines to light up, for us, it was a significant win.”
She noted that while the Raptor relighted on the upper stage during Flight 3 wasn't able to be accomplished, there's still plenty of time to achieve that milestone. Watson-Morgan said they would need to see it demonstrated either in the back half of 2024 or in early 2025.
“As SpaceX continues to mature their Raptors, because they're working through their design and development, as they do that, they're making modifications and adjustments and changes,” Watson-Morgan said. “And all of that’s getting incorporated into an updated build sequence.”
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| Artist's illustration of the Starship landing system on the moon. Credit: SpaceX |
One notable success observed by Watson-Morgan and NASA was the propellant transfer, which involved shifting liquid oxygen (LOX) from the ship's header tank to the main upper stage LOX tank. This task was part of a $53.2 million Tipping Point contract with NASA's Space Technology Mission Directorate (STMD), requiring a demonstration of transferring 10 metric tons of propellant.
While the HLS office was not directly involved, STMD representatives agreed with SpaceX that it was a successful demonstration. This achievement marks the initial step towards enabling ship-to-ship propellant transfer, a crucial element for SpaceX's Artemis moon landing missions.
SpaceX's strategy involves launching a tanker version of the ship's upper stage into low Earth orbit, followed by a series of ships docking with the tanker to transfer propellant. This propellant would then be moved to the HLS version of Starship before it embarks on its journey to the Moon.
“Propellant transfer is really the key to accessing the rest of the universe. It's essential for Mars, the South Pole, and beyond. We're doing everything we can to prepare for this and to support SpaceX,” said Watson-Morgan. “Additionally, we're assisting Blue Origin with their similar concept.”
The exact number of fueling flights to the tanker is still undetermined, as it depends on several factors, including the size of the tanks, the amount of propellant to be transferred, and other mission objectives.
“It depends on the size of the tanks, the amount we want to transfer, and what other objectives we aim to achieve during the flight test demonstration,” Watson-Morgan explained. “It could be just a few flights or more, depending on our goals.”
“One thing I appreciate about SpaceX is their openness and flexibility with objectives, and their willingness to add more if NASA deems it necessary based on the timing,” she added.
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| Two Starships linked together in space for in-orbit refilling. Credit: SpaceX |
While she was limited on what she could say about it, Watson-Morgan also mentioned that SpaceX is developing a smaller thruster-style engine to help with the prop transfer demonstration. She said a development milestone on that is coming up later this year.
“Our team has been very impressed. They've developed this engine within less than half a year and it's, so far, been performing well,” she said.
Starship expansion
Part of the timing for the propellant transfer will hinge on being able to launch multiple Starship missions from more than the one launch tower SpaceX currently has. The company is in the process of building a second tower down at Starbase.
To that end, they manufactured additional segments and components at their facilities at NASA's Kennedy Space Center in Florida and have barged them down to Texas. A collection of four tower segments shipped earlier this year and this week, they loaded two more segments onto the barge, along with the tower's so-called “chopsticks” and their elevator system supports.
Watson-Morgan said the propellant transfer mission could be conducted from two towers at Starbase, but NASA is very interested in making sure that Starship launch capabilities come online at KSC as well. Next week, the Federal Aviation Administration (FAA) will host public scoping meetings to gather input on allowing around 44 Starship launches per year from historic Launch Complex 39A.
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| A Starship tower segment along with the chopstick elevator system rolls to the turn basin near the Press Site at NASA's Kennedy Space Center on Saturday, June 1, 2024. The components were some of the cargo bound for Starbase in southern Texas to erect a second launch tower. Image: Will Robinson-Smith/Spaceflight Now |
Simultaneously, the Department of the Air Force is also doing a similar assessment for Starship launches from either Space Launch Complex 37, which is the former launch site of United Launch Alliance's (ULA) Delta 4 Heavy rocket, or from a proposed new launch pad called SLC-50.
“We definitely want to see that. We have to see it by the uncrewed demo for sure and clearly, we'd like to see that before to make sure that everything checks out,” Watson-Morgan said. “We will go ahead and have pad checkouts and all that and operational readiness reviews in advance of it.”
Part of SpaceX's HLS agreement with NASA is that it will perform an uncrewed landing of Starship on the Moon prior to the Artemis 3 mission.
Humans in loop
As they're developing the human-rated version of Starship, they're also gathering input from Astronaut Office, which is located at NASA's Johnson Space Center. Watson-Morgan, referring to them as “the crew” for shorthand, said the office offers insight and opinions on the functionality of certain parts of the vehicle, like interface, control system and location of handles.
She said the HLS office mainly works with astronauts Raja Chari and Randy Bresnik, the latter of whom has been a part of the process “since the very beginning.” Watson-Morgan said that they also have members of the astronaut office on their control board.
“We have a Human Landing System control board, where any requirements changes or updates or how things are implemented get to go through their formal board actions and the crew's a voting member,” she said.
On April 30, at the SpaceX headquarters in Hawthorne, California, NASA astronaut Doug “Wheels” Wheelock and Axiom Space astronaut Peggy Whitson performed the first integrated test of Axiom's pressurized spacesuits alongside mockups of a Starship elevator and the airlock.
“Overall, I was pleased with the astronauts' operation of the control panel and with their ability to perform the difficult tasks they will have to do before stepping onto the Moon,” said Logan Kennedy, lead for surface activities in NASA's HLS Program, in a statement. “The test also confirmed that the amount of space available in the airlock, on the deck, and in the elevator, are sufficient for the work our astronauts plan to do.”
Shorter turnaround?
Through the Starship test campaign, SpaceX achieve shorter and shorter turnaround times between launches. That's partly due to accomplishing more each time in a less destructive way, but also thanks to work being done by the FAA.
Flight 2 came just 212 days after Flight 1, Flight 3 was 117 days after Flight 2 and Flight 4 comes just 84 days after Flight 3. Watson-Morgan said her understanding is that SpaceX would like to reach a monthly launch cadence at Starbase, but knows that they'll want to infuse the learning of previous flights into successive ones, which may take more time.
“Even if it's every two to three months, that's still quite an achievement for a test campaign and each one of these tests will buy down different risks,” Watson-Morgan said. “For a NASA perspective, seeing each one of those launches, we'll get a little deeper insight into how all the engines act, how they're performing, with respect to the ISP (specific impulse) and so, we will have that .”
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