SpaceX and NASA could take a tentative step toward orbital refueling on the next test flight of Starship, but the US space agency says officials haven't made a final decision on when to begin demonstrating cryogenic propellant transfer capabilities that are necessary to return astronauts to the Moon.

SpaceX는 내년에 적어도 예비 추진체 이동 테스트를 위해 궤도에 오른 것으로 보입니다. SpaceX와 NASA는 Starship의 다음 테스트 비행에서 궤도 급유를 향한 잠정적인 조치를 취할 수 있지만 미국 우주국은 관계자들이 언제 최종 결정을 내리지 않았다고 말했습니다. 우주 비행사를 달로 돌려보내는 데 필요한 극저온 추진제 이송 능력을 시연하기 시작합니다.

NASA is keen on demonstrating orbital refueling technology, an advancement that could lead to propellant depots in space to feed rockets heading to distant destinations beyond Earth orbit. In 2020, NASA announced agreements with four companies—Lockheed Martin, United Launch Alliance, SpaceX, and a Florida-based startup named Eta Space—to prove capabilities in the area of refueling and propellant depots using cryogenic propellants.

These cryogenic fluids—liquid hydrogen, methane, and liquid oxygen—must be kept at temperatures of several hundred degrees below zero, or they turn into a gas and boil off. Russian supply freighters regularly refuel the International Space Station with hydrazine and nitrogen tetroxide, room-temperature rocket propellants that can be stored for years in orbit, but rockets using more efficient super-cold propellants have typically needed to complete their missions within hours.

이러한 극저온 유체(액체 수소, 메탄, 액체 산소)는 영하 수백 도의 온도로 유지되어야 합니다. 그렇지 않으면 가스로 변해 끓어오르게 됩니다. 러시아 공급 화물선은 궤도에서 수년간 보관할 수 있는 상온 로켓 추진제인 하이드라진과 사산화질소를 국제 우주 정거장에 정기적으로 연료를 공급하지만, 보다 효율적인 초저온 추진제를 사용하는 로켓은 일반적으로 몇 시간 내에 임무를 완료해야 했습니다.

NASA and industry engineers want to extend this lifetime to days, weeks, or months, but this requires new technologies to maintain the propellants at cryogenic temperature and, in some cases like Starship, to transfer the propellants from one vehicle to another.

NASA and several companies are funding efforts in this area, called cryogenic fluid management. NASA's agreements from 2020 committed more than $250 million in government funding for cryogenic fluid management tests in space. These funding agreements announced in October 2020, called "Tipping Point" awards, require substantial private funding from the companies participating in the demonstrations.

NASA와 몇몇 회사는 극저온 유체 관리라고 불리는 이 분야에 자금을 지원하고 있습니다. 2020년부터 NASA는 우주에서의 극저온 유체 관리 테스트를 위해 2억 5천만 달러 이상의 정부 자금을 지원하기로 합의했습니다. 2020년 10월에 발표된 "티핑 포인트(Tipping Point)" 상이라고 불리는 이러한 자금 지원 계약에는 시연에 참여하는 기업의 상당한 민간 자금이 필요합니다.

According to John Dankanich, who leads NASA's efforts in developing new capabilities for in-space transportation, there are "major technical obstacles" for cryogenic fluid management. The real challenge, he said, will be in validating things like automated couplers, flow meters, and advanced insulation all work together in microgravity. These, along with other technologies, are "highly interdependent" on one another to make cryogenic refueling a reality, he said.

Individual technologies necessary for in-orbit cryogenic refueling are at a stage of development where they are "ready now to go into flight systems," Dankanich said, either with a demonstration in space or on an operational spacecraft.

궤도 내 극저온 재급유에 필요한 개별 기술은 "이제 비행 시스템에 적용할 준비가 되어 있는" 개발 단계에 있다고 Dankanich는 말했습니다. 우주에서의 시연이나 우주선 운용을 통해 말이죠.

First, small steps

By the fourth anniversary of those awards, only SpaceX appears to have a chance to complete the tasks outlined in its "Tipping Point" award, valued at $53 million.

This test would involve transferring super-cold propellant from one tank to another inside a Starship spacecraft. It's a precursor to future, more complex demonstrations involving two giant Starships docked together in Earth orbit. Then SpaceX will be ready to send a Starship toward the Moon for a test landing without astronauts onboard. Once that is successful, NASA will clear Starship for a crew landing on the agency's Artemis III mission, marking the astronauts' return to the lunar surface for the first time since 1972.

That's easier said than done; all worthy projects require a first step. That could happen as soon as the next full-scale test flight of SpaceX's gigantic Super Heavy booster and Starship rocket, a stainless steel launcher that stands nearly 400 feet (121 meters) tall. SpaceX has flown the rocket twice, most recently on November 18, when the Starship upper stage reached space for the first time before self-destructing just short of orbital velocity. This test flight was largely successful, achieving several key milestones such as stage separation and demonstrating improved reliability of the rocket's methane-fueled Raptor engines.

말은 말처럼 쉽지 않습니다. 모든 가치 있는 프로젝트에는 첫 번째 단계가 필요합니다. 이는 SpaceX의 거대한 Super Heavy 부스터와 높이가 거의 400피트(121m)에 달하는 스테인레스 스틸 발사대인 Starship 로켓의 다음 번 본격적인 시험 비행이 완료되자마자 일어날 수 있습니다. SpaceX는 로켓을 두 번 비행했으며 가장 최근인 11월 18일에 스타십 상부 단계가 처음으로 우주에 도달한 후 궤도 속도에 미달하여 자폭했습니다. 이 테스트 비행은 대체로 성공적이었으며, 단계 분리와 같은 몇 가지 주요 이정표를 달성하고 로켓의 메탄 연료 랩터 엔진의 향상된 신뢰성을 입증했습니다.

SpaceX has a $2.9 billion contract with NASA to provide a commercial Human Landing System (HLS) derived from Starship for the Artemis III mission, the first human landing mission planned during NASA's Artemis program. The readiness of the Starship landing craft and new commercial spacesuits are widely seen as drivers of the schedule for Artemis III, which is at risk of a delay from late 2025.

Lakiesha Hawkins, deputy associate administrator for NASA's Moon to Mars program office, discussed the Artemis schedule Monday with a committee from the National Academies charged with reviewing the agency's workforce, infrastructure, and technology programs.

NASA의 달-화성 프로그램 사무국 부국장인 라키샤 호킨스(Lakiesha Hawkins)는 월요일 기관의 인력, 인프라 및 기술 프로그램 검토를 담당하는 국립 아카데미 위원회와 아르테미스 일정에 대해 논의했습니다.

Hawkins did not verbally address SpaceX's plans for the next Starship test flight, but one of her slides noted SpaceX is "moving quickly" toward the third Super Heavy/Starship launch, and that this flight "will include a propellant transfer demonstration."

However, Jimi Russell, a NASA spokesperson, suggested to Ars this is still only a possibility. When it does happen, the tank-to-tank propellant transfer within Starship will demonstrate moving 10 metric tons of liquid oxygen, according to the 2020 Tipping Point award terms. SpaceX is collaborating with NASA's Glenn Research Center and Marshall Space Flight Center on the demonstration.

"NASA and SpaceX are reviewing options for the demonstration to take place during an integrated flight test of Starship and the Super Heavy rocket," Russell said in a  statement. "However, no final decisions on timing have been made."

Elon Musk, the company's founder and CEO, said on November 19 that hardware for the next Super Heavy/Starship test should be ready in three to four weeks. That projection seems dubious because SpaceX hasn't moved any pieces of the rocket to the launch pad for pre-flight testing, but a test flight early next year appears realistic.

회사 창립자이자 CEO인 Elon Musk는 11월 19일에 다음 Super Heavy/Starship 테스트를 위한 하드웨어가 3~4주 안에 준비될 것이라고 말했습니다. SpaceX는 비행 전 테스트를 위해 로켓 조각을 발사대로 옮기지 않았기 때문에 이러한 예측은 모호해 보이지만 내년 초 테스트 비행은 현실적으로 보입니다.

Other factors that could play into the Starship launch schedule include tune-ups or fixes to resolve problems that occurred on the November 18 test flight and receiving a new launch license from the Federal Aviation Administration.

스타쉽 발사 일정에 영향을 미칠 수 있는 다른 요인으로는 11월 18일 시험 비행에서 발생한 문제를 해결하기 위한 조정 또는 수정과 연방 항공국으로부터 새로운 발사 라이센스를 받는 것 등이 있습니다.

When SpaceX tries transferring 10 metric tons of propellant from tank to tank inside Starship, it will be at a scale never before attempted in space. But it's a small fraction of the amount of fuel and oxidizer needed to fill a Starship spacecraft in orbit. The ship's total propellant capacity is some 1,200 metric tons. After the tank-to-tank demonstration, SpaceX will attempt a ship-to-ship propellant transfer between two Starships linked together in Earth orbit.

"That’s really when we start maturing the systems, and when it really gets exciting for HLS, because those are the building blocks that we need and, frankly, it’s never been done successfully in orbit," said Lisa Watson-Morgan, NASA's HLS program manager, in an interview with Ars last month.

NASA의 HLS 프로그램인 Lisa Watson-Morgan은 "이때가 바로 우리가 시스템을 성숙시키기 시작할 때이고 HLS에 대해 정말 흥미로울 때입니다. 왜냐하면 이것이 우리에게 필요한 구성 요소이고 솔직히 궤도에서 성공적으로 수행된 적이 없기 때문입니다"라고 말했습니다. 지난달 Ars와의 인터뷰에서 매니저.

This discussion of propellant transfer leaves out critical work on Starship's life support system needed to accommodate crews on the lunar surface. SpaceX also needs to move forward with more Raptor engine testing, but the company recently completed a ground test to confirm it can reignite a Raptor engine in the extreme cold conditions resulting from extended time in space. SpaceX has also completed Raptor test-firings at different throttle settings to simulate how the engines must perform during a descent burn to reach the lunar surface.

Others in the running

다른 사람들은 실행 중

The other companies working with NASA on cryogenic fluid management are still at least a couple of years away from any meaningful flight demonstrations.

극저온 유체 관리에 관해 NASA와 협력하는 다른 회사들은 의미 있는 비행 시연을 하려면 아직 최소 2년 이상 남았습니다.

Lockheed Martin's demo, expected to use liquid hydrogen, is scheduled for 2025 and will test 15 key cryo fluid management technologies. Eta Space is developing a small-scale fuel depot to demonstrate long-duration cryogenic storage of liquid oxygen for nine months. This mission, known as LOXSAT, is scheduled to launch with Rocket Lab in 2025, according to Dankanich.

Liquid hydrogen is the smallest molecule and needs to be stored at colder temperatures than methane or liquid oxygen. It is the most efficient rocket fuel in common use, but is prone to leaks.

United Launch Alliance is working on a liquid hydrogen/liquid oxygen "smart propulsion cryogenic system" on a Vulcan Centaur upper stage, testing precise tank pressure control, tank-to-tank transfer, and multi-week propellant storage, according to NASA. Dankanich said Monday ULA's flight demonstration is scheduled for 2026.

Like Starship, Blue Origin's human-rated lunar lander for Artemis will rely on orbital refueling but with liquid hydrogen. Blue Origin's approach to cryogenic fluid management involves actively controlling the temperature of liquid hydrogen using cryocoolers, while SpaceX is using passive thermal control on Starship.

Starship과 마찬가지로 Blue Origin의 인간 평가 Artemis 달 착륙선은 궤도 급유에 의존하지만 액체 수소를 사용합니다. 극저온 유체 관리에 대한 Blue Origin의 접근 방식에는 극저온 냉각기를 사용하여 액체 수소의 온도를 능동적으로 제어하는 ​​것이 포함되는 반면 SpaceX는 Starship에서 수동적 열 제어를 사용합니다.

Dankanich said Blue Origin plans "multiple interim demonstrations" with its cryogenic systems before its lander is certified to carry astronauts to the Moon's surface, but he didn't offer a schedule for those flight tests leading up to Blue Origin's first human landing mission, slated for no sooner than 2029.

Dankanich는 Blue Origin이 착륙선이 우주 비행사를 달 표면에 태울 수 있도록 인증되기 전에 극저온 시스템으로 "다중 임시 시연"을 계획하고 있다고 밝혔지만 Blue Origin의 첫 번째 인간 착륙 임무로 이어지는 비행 테스트 일정은 제공하지 않았습니다. 빠르면 2029년까지.

Aside from technical hurdles, Dankanich said there's another potential barrier to widespread advancements in cryogenic refueling and propellant depots. For most of the tech demos, NASA is partnering with companies on a cost-sharing basis, reducing the cost to taxpayers. NASA would like to use data from the demonstrations to provide "ground truth" for models to predict the behavior of cryogenic fluids in space. Because NASA is a government agency, these models would be available to a broad cross-section of researchers and engineers.

Under the terms of these public-private partnerships, industry retains ownership, and these companies may consider details about their technology proprietary, limiting NASA's ability to share lessons learned with academic institutions or other outside groups.

“In some cases, we can't force them to even instrument the systems in the way that we need them instrumented in order to get the data that we would need to validate," Dankanich said. "If they're willing to provide the telemetry that we need, then we may, on the NASA side, be able to get some of that information. But we can't disclose the design details or the specifics to the community, which is necessary for model validation.

Dankanich는 "어떤 경우에는 우리가 검증해야 하는 데이터를 얻기 위해 필요한 방식으로 시스템을 계측하도록 강요할 수 없습니다."라고 Dankanich는 말했습니다. 필요한 원격 측정법을 사용하면 NASA 측에서 해당 정보 중 일부를 얻을 수 있습니다. 하지만 모델 검증에 필요한 설계 세부 사항이나 세부 사항을 커뮤니티에 공개할 수는 없습니다.

"Data right restrictions are a big challenge with the way that we're procuring all of our cryogenic fluid management systems," Dankanich said. "At the same time, the outlook is pretty good, right? We do have the SpaceX large-scale cryo settling propellant transfer planned for next year."

Dankanich는 "데이터 권한 제한은 우리가 모든 극저온 유체 관리 시스템을 조달하는 방식에 있어 큰 과제입니다."라고 말했습니다. "동시에 전망은 꽤 좋습니다. 그렇죠? 내년에는 SpaceX의 대규모 극저온 침전 추진제 이송이 계획되어 있습니다."