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NASA lays out how SpaceX will refuel Starships in low-Earth orbit​

"The fundamental flow mechanism is the pressure delta across the umbilical."


starships-docked-1-800x478.jpg


Some time next year, NASA believes SpaceX will be ready to link two Starships in orbit for an ambitious refueling demonstration, a technical feat that will put the Moon within reach.

SpaceX is under contract with NASA to supply two human-rated Starships for the first two astronaut landings on the Moon through the agency's Artemis program, which aims to return people to the lunar surface for the first time since 1972. The first of these landings, on NASA's Artemis III mission, is currently targeted for 2026, although this is widely viewed as an ambitious schedule.

Last year, NASA awarded a contract to Blue Origin to develop its own human-rated Blue Moon lunar lander, giving Artemis managers two options for follow-on missions.

Designers of both landers were future-minded. They designed Starship and Blue Moon for refueling in space. This means they can eventually be reused for multiple missions, and ultimately, could take advantage of propellants produced from resources on the Moon or Mars.

Amit Kshatriya, who leads the "Moon to Mars" program within NASA's exploration division, outlined SpaceX's plan to do this in a meeting with a committee of the NASA Advisory Council on Friday. He said the Starship test program is gaining momentum, with the next test flight from SpaceX's Starbase launch site in South Texas expected by the end of May.

"Production is not the issue," Kshatriya said. "They're rolling cores out. The engines are flowing into the factory. That is not the issue. The issue is it is a significant development challenge to do what they’re trying to do ... We have to get on top of this propellant transfer problem. It is the right problem to try and solve. We're trying to build a blueprint for deep space exploration."

Road map to refueling​

Before getting to the Moon, SpaceX and Blue Origin must master the technologies and techniques required for in-space refueling. Right now, SpaceX is scheduled to attempt the first demonstration of a large-scale propellant transfer between two Starships in orbit next year.
There will be at least several more Starship test flights before then. During the most recent Starship test flight in March, SpaceX conducted a cryogenic propellant transfer test between two tanks inside the vehicle. This tank-to-tank transfer of liquid oxygen was part of a demonstration supported with NASA funding. Agency officials said this demonstration would allow engineers to learn more about how the fluid behaves in a low-gravity environment.
Kshatriya said that while engineers are still analyzing the results of the cryogenic transfer demonstration, the test on the March Starship flight "was successful by all accounts."
"That milestone is behind them," he said Friday. Now, SpaceX will move out with more Starship test flights. The next launch will try to check off a few more capabilities SpaceX didn't demonstrate on the March test flight.
These will include a precise landing of Starship's Super Heavy booster in the Gulf of Mexico, which is necessary before SpaceX tries to land the booster back at its launch pad in Texas. Another objective will likely be the restart of a single Raptor engine on Starship in flight, which SpaceX didn't accomplish on the March flight due to unexpected roll rates on the vehicle as it coasted through space. Achieving an in-orbit engine restart—necessary to guide Starship toward a controlled reentry—is a prerequisite for future launches into a stable higher orbit, where the ship could loiter for hours, days, or weeks to deploy satellites and attempt refueling.
In the long run, SpaceX wants to ramp up the Starship launch cadence to many daily flights from multiple launch sites. To achieve that goal, SpaceX plans to recover and rapidly reuse Starships and Super Heavy boosters, building on expertise from the partially reusable Falcon 9 rocket. Elon Musk, SpaceX's founder and CEO, is keen on reusing ships and boosters as soon as possible. Earlier this month, Musk said he is optimistic SpaceX can recover a Super Heavy booster in Texas later this year and land a Starship back in Texas sometime next year.


Reuse is fundamental to Starship's long-term goal of supporting a human settlement on Mars. However, SpaceX can move forward with orbital refueling demonstrations while engineers continue experimenting with booster and ship landings.
Before Starship's first landing on the Moon with astronauts, NASA's $2.9 billion Human Landing System (HLS) contract with SpaceX includes ship-to-ship propellant transfer testing and an unpiloted landing of a full-scale Starship on the lunar surface.
But each Starship test flight builds on the prior mission. This means pretty much every Starship test flight over the next couple of years will have goals that feed into the first Artemis lunar landing. During these upcoming Starship test flights, engineers will measure the slosh of propellants inside the ship, along with tank pressures, and observe how the fluids respond to impulses from small thrusters. In microgravity, these small rocket jets provide "settling thrust" to guide the ship's liquid toward the outflow needed for refueling.
Engineers will also monitor the boil-off rates of the methane and liquid oxygen in space. Over time, cryogenic liquids transition to a gaseous state without insulation or other measures to prevent boil-off. SpaceX and NASA officials want to know how much of the propellant will be lost from boil-off to know how many refueling tankers they need to launch for a Starship lunar landing mission.
"All of that needs to work properly," Kshatriya said. "We’re still in development, but at a high level, I think it’s important for folks to know that this sequence is underway, and they’re making good engineering progress."


hlsproptransferdemo2.jpg


For the first full-scale refueling demonstration, SpaceX must launch two Starships within about three or four weeks of one another. First, SpaceX will launch a Starship to serve as a target vehicle in low-Earth orbit. This ship will have an augmented power system and more battery capacity to sustain itself in space long enough for the launch of the chaser vehicle—a Starship that will play the role of a refueling tanker.

Both ships involved in the refueling demo will also have thermal insulation and vacuum jacketing around internal plumbing to limit boil-off. "Otherwise, the demo itself will not be achieved," Kshatriya said.

The current plan, according to Kshatriya, is for SpaceX to use a single launch pad for both flights. By the time NASA and SpaceX are ready for a lunar landing, multiple Starship tankers will take off from at least two launch pads to aggregate propellants at a depot to supply the Moon-bound Starship. SpaceX is planning to build an additional launch tower at Starbase in Texas, and at least two Starship pads on Florida's Space Coast.

This is hard, but it’s doable​

The two Starships will autonomously link belly to belly as they fly a couple hundred miles above the planet. On future Starship missions targeting destinations in deep space, like the Moon, this docking maneuver and refueling process will be repeated multiple times to give the vehicle enough gas to boost itself out of Earth orbit.
Computer models and flight data from numerous rockets show it is possible to gain control over cryogenic boil-off, tank pressures, and propellant settling in space. But no one has ever attempted to flow cryogenic propellants from one spacecraft to another in orbit.
"In my mind, all the technical issues associated with cryo transfer in space are solved," said George Sowers, former chief scientist at SpaceX rival United Launch Alliance and a longtime proponent of depoting propellants in space. "It’s just a matter of demonstrating it and fine-tuning the technology and the procedures. So, I think we’re on the cusp. I’m happy to see SpaceX taking the steps to make it work.


Docking two Starships together won't be easy. However, SpaceX can use its experience in flying Dragon capsules to the International Space Station, which requires many of the same types of laser navigation sensors and mechanical devices necessary for Starship dockings.
But there's a caveat. When Starship comes in for docking, its tanks will still be loaded with propellant, and the ship's maneuvers to approach its counterpart could induce sloshing inside the tanks. This could introduce unforeseen forces that the ship's navigation system must account for during the rendezvous.
Once the two Starships come together, they will connect using the same ports SpaceX uses to load propellants on the launch pad. Then, SpaceX will fine-tune tank pressures and fire propellant settling thrusters. "At that point, they'll open up and let the propellant flow."
The propellants will flow from one vehicle to the other using a pressure differential, or "delta," between the donor tank and the recipient tank. This is a simpler solution than relying on pumps.
"The fundamental flow mechanism is because of the pressure delta across the umbilical," Kshatriya said.
The "fine details" of this procedure work remain in work, he said. The slow boil-off of cryogenic propellant in the Starship refueler should raise pressures in the donor tank to help drive methane or liquid oxygen into the recipient vehicle. SpaceX can also adjust pressures using header tanks at the top of each ship.
“The trick is to get all that done, and all the transfer done, without boiling off all of your propellant in the process," Sowers said.

The results of this refueling demonstration will allow SpaceX and NASA engineers to calculate how many refueling tankers they will need to fill up a Starship heading for the Moon. SpaceX's current estimate is approximately 10 refueling launches for one Artemis landing mission, but there are error bars on each side of this number.

In its current iteration, a fully fueled Starship contains roughly 1,200 metric tons (2.6 million pounds) of propellant. SpaceX is developing larger versions of Starship to haul heavier cargo and more fuel into orbit. These upgraded Starships should reduce the number of tankers needed to load a Starship heading for the Moon or Mars.

"We certainly have predictions, but we'll know how much fuel is it releasing, how long does this take, are we going to be as successful as the analysis says?" said Lisa Watson-Morgan, who manages NASA's lunar landing program, in January.

"We’re going to have to do this a few times," she said. "We’re going to have to do the prop transfer flights more than once or twice or three times in my opinion. We’ve never done this before.”

"I wish them well," said Sowers, now a professor at the Colorado School of Mines. "I’ve been away from ULA for almost seven years now. SpaceX used to be my competitor, and now I just want everybody to succeed. Especially, I want the whole refueling economy to get jump-started, and I’m really happy that both SpaceX and Blue Origin are going down that path, as is ULA. I think for the whole world, it’s finally clicked that the best way to beat the rocket equation is by refueling.”

Kshatriya said SpaceX's engineers are up to the task. "It's a phenomenal team, and they have exactly the right attitude in terms of how to kind of build-learn, build-learn, build-learn, and keep doing it. So I'm pleased with that. I'm pleased with the progress across the enterprise.

"A lot of folks have said it's ambitious to try this in this particular time frame. And absolutely it is."



@Nilgiri @Sanchez @Afif @Kartal1 @TR_123456 @Radonsider
 

Nilgiri

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Should we make this the dedicated US Space News thread (i.e not just SpaceX but also NASA et al.)?

Here is recent IG report on NASA findings (problems/issues) with the Artemis program, that gives larger indication of the challenges in general in this larger frontier of endeavour:


Summary brief:

May 1, 2024 IG-24-011 (A-23-07-00-HED)

WHY WE PERFORMED THIS AUDIT
With the Artemis campaign, NASA intends to return humans to the Moon and build a sustainable lunar presence as a foundation for human exploration of Mars. The uncrewed Artemis I test flight was completed in December 2022 and was a significant achievement for the Agency, providing important data and lessons learned from the testing of hardware, software, processes, and teams that will prepare NASA for future Artemis missions. The Artemis II crewed test flight aims to return humans to lunar orbit for the first time in more than 50 years and send its four crew members farther into space than any human has ever gone. Like Artemis I, the Artemis II mission will utilize the Space Launch System (SLS), a two-stage, heavy-lift rocket that will launch the Orion Multi-Purpose Crew Vehicle (Orion) capsule into space from the Mobile Launcher 1 (ML-1) at Kennedy Space Center. By September 2025, the planned launch date for Artemis II, NASA will have spent more than $55 billion on the SLS, Orion, and Exploration Ground Systems (EGS) programs.

Given the high stakes of the first crewed flight, the Agency is working to identify and mitigate any risks and challenges to ensure the safe return of the Artemis II crew and safeguard NASA’s significant investment in Artemis vehicles and systems. In particular, the Agency must address the risks identified in the Artemis I Post-Flight Assessment Review, execute planned modifications and upgrades required to support the Artemis II astronauts, and complete stacking and testing of the integrated SLS and Orion. In light of ongoing work to address issues with the Orion spacecraft, in January 2024, the Agency announced that it would push the Artemis II launch date from November 2024 to September 2025.

In this audit, we examined NASA’s readiness for the Artemis II crewed mission to lunar orbit. To complete this work, we conducted a site visit at Kennedy Space Center and interviewed officials with the Exploration Systems Development Mission Directorate; SLS, Orion, EGS, and Space Communications and Navigation programs; and other technical experts and stakeholders. To determine the extent to which Artemis I met its objectives, we reviewed key documents to evaluate mission performance as well as NASA’s mission coverage and preliminary flight reviews.
 

Rodeo

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Should we make this the dedicated US Space News thread (i.e not just SpaceX but also NASA et al.)?

Here is recent IG report on NASA findings (problems/issues) with the Artemis program, that gives larger indication of the challenges in general in this larger frontier of endeavour:


Summary brief:

May 1, 2024 IG-24-011 (A-23-07-00-HED)

WHY WE PERFORMED THIS AUDIT
With the Artemis campaign, NASA intends to return humans to the Moon and build a sustainable lunar presence as a foundation for human exploration of Mars. The uncrewed Artemis I test flight was completed in December 2022 and was a significant achievement for the Agency, providing important data and lessons learned from the testing of hardware, software, processes, and teams that will prepare NASA for future Artemis missions. The Artemis II crewed test flight aims to return humans to lunar orbit for the first time in more than 50 years and send its four crew members farther into space than any human has ever gone. Like Artemis I, the Artemis II mission will utilize the Space Launch System (SLS), a two-stage, heavy-lift rocket that will launch the Orion Multi-Purpose Crew Vehicle (Orion) capsule into space from the Mobile Launcher 1 (ML-1) at Kennedy Space Center. By September 2025, the planned launch date for Artemis II, NASA will have spent more than $55 billion on the SLS, Orion, and Exploration Ground Systems (EGS) programs.

Given the high stakes of the first crewed flight, the Agency is working to identify and mitigate any risks and challenges to ensure the safe return of the Artemis II crew and safeguard NASA’s significant investment in Artemis vehicles and systems. In particular, the Agency must address the risks identified in the Artemis I Post-Flight Assessment Review, execute planned modifications and upgrades required to support the Artemis II astronauts, and complete stacking and testing of the integrated SLS and Orion. In light of ongoing work to address issues with the Orion spacecraft, in January 2024, the Agency announced that it would push the Artemis II launch date from November 2024 to September 2025.

In this audit, we examined NASA’s readiness for the Artemis II crewed mission to lunar orbit. To complete this work, we conducted a site visit at Kennedy Space Center and interviewed officials with the Exploration Systems Development Mission Directorate; SLS, Orion, EGS, and Space Communications and Navigation programs; and other technical experts and stakeholders. To determine the extent to which Artemis I met its objectives, we reviewed key documents to evaluate mission performance as well as NASA’s mission coverage and preliminary flight reviews.
SLS flew only once and they want to put astronauts on it its second flight, whereas Musk says Starship must have 100 consecutive successful flights before he can put any human on it.

IMO, SLS will be abandoned in two or three years. One launch of SLS costs $4billion dollars. Artemis has no chance of becoming sustainable with those exorbitant costs. They can't land on the moon without Starship anyway. And if Starship can land on the moon then SpaceX will have solved on-orbit refueling and reusability and will cost a fraction of SLS, moreover will be able to launch many times a year(on demand). NASA will have no case to defend SLS and will drop it.
 

Nilgiri

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SLS flew only once and they want to put astronauts on it its second flight, whereas Musk says Starship must have 100 consecutive successful flights before he can put any human on it.

IMO, SLS will be abandoned in two or three years. One launch of SLS costs $4billion dollars. Artemis has no chance of becoming sustainable with those exorbitant costs. They can't land on the moon without Starship anyway. And if Starship can land on the moon then SpaceX will have solved on-orbit refueling and reusability and will cost a fraction of SLS, moreover will be able to launch many times a year(on demand). NASA will have no case to defend SLS and will drop it.

We will have to see, NASA has a huge RnD budget and massive capital (both physical and human) that is frontloaded on it (so it brings the costs up).

But this pays dividends strategically for the US to create spaceX et al commercial ecosystem downroad as well to begin with.

Govt agency vs private company , what are the contexts, feedback loops and so on or next chunk of years is still ongoing thing.
 

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