Last week, NASA's Artemis 2 moon mission was just a few weeks from launching four astronauts on a historic lunar flight. Today, it's facing a monthlong delay or more.

NASA on Sunday (Feb. 22) announced that the space agency will roll its massive Artemis 2 moon rocket, the second-ever Space Launch System, off its Launch Pad 39B at the Kennedy Space Center in Florida in order to fix a helium supply issue on the rocket's upper stage.

The decision was not a surprise. NASA chief Jared Isaacman telegraphed that the move might be necessary on Saturday after finding blockage in the flow of helium into the rocket's upper station.

"This will almost assuredly impact the March launch window," Isaacman said on X at the time.

Today, NASA confirmed a launch delay to April at the earliest as it prepares to roll the 322-foot-tall Artemis 2 rocket back into its hangar, the cavernous Vehicle Assembly Building, for repairs.

"Weather pending, NASA will roll the SLS (Space Launch System) rocket and Orion spacecraft for Artemis II off the launch pad at the agency’s Kennedy Space Center in Florida as soon as Tuesday, Feb. 24," NASA wrote in an update on Sunday.

NASA's launch window for March was relatively short. It ran from March 6 through March 9, with another opportunity on March 11. If Artemis 2 was unable to hit any of those dates, NASA would have to wait at least three additional weeks.

The next window features target launch dates of April 1, April 3-6 and April 30.

"A rollback would mean NASA will not launch Artemis 2 in the March launch window," NASA officials wrote in a blog post on Saturday. "However, the quick preparations enable NASA to potentially preserve the April launch window if a rollback is required, pending the outcome of data findings, repair efforts, and how the schedule comes to fruition in the coming days and weeks."

The news of a problem on the Artemis 2 rocket on Saturday was something of a surprise. It came just a day after NASA announced that it was targeting March 6 for the launch of Artemis 2, the first crewed mission beyond low Earth orbit since the end of the Apollo era. Artemis 2 will send three NASA astronauts and one Canadian on a roughly 10-day trip around the moon and back to Earth in a Orion capsule.

The agency made the March 6 call after reviewing data from Artemis 2's second wet dress rehearsal (WDR), a two-day-long practice run of the major operations leading up to launch.

The WDR wrapped up on Thursday (Feb. 19) with a successful fueling of both SLS stages. This was a big milestone for the Artemis 2 team, which had to terminate the mission's first WDR early on Feb. 2 due to a leak of liquid hydrogen (LH2) propellant.

LH2 leaks plagued Artemis 1, delaying the launch of that ultimately successful uncrewed moon mission multiple times back in 2022. But NASA seems to now have the issue under control.

During a press conference on Friday, Artemis 2 team members said there were just a couple of big boxes left to check before giving the mission a green light to launch.

One was the completion of the flight readiness review, which was expected to take place late this coming week. The other was the installation of two "contingency pad access" trusses on the SLS' mobile launch tower, which will allow teams to check Artemis 2's flight termination system on the pad.

Those trusses were installed on Friday, NASA officials wrote in Saturday's blog post. But they'll probably be removed soon.

"Teams are actively reviewing data, and taking steps to enable rollback positions for NASA to address the issue as soon as possible while engineers determine the best path forward," officials wrote in the update.

By Sunday, it was official. The "best path forward" would be a rollback of the Artemis 2 rocket for repairs and weeks of downtime. NASA officials said the early work to prepare for such a turn of events should help keep the Artemis 2 mission on track for April.

"The quick work to begin preparations for rolling the rocket and spacecraft back to the VAB potentially preserves the April launch window, pending the outcome of data findings, repair efforts, and how the schedule comes to fruition in the coming days and weeks," NASA wropte in the Sunday update.

Proper helium flow is vital to the proper functioning of the SLS upper stage; it pressurizes the LH2 and liquid oxygen propellant tanks and helps maintain "the proper environmental conditions" for engine operation, according to the blog post. The flow issue was not seen during the WDR.

Editor's note: This story, originally published on Saturday, Feb. 21, was updated at 3:16 p.m. ET on Feb. 22 with confirmation of the Artemis 2 rollback from NASA's new blog post.

The first crewed moon mission in more than 50 years will launch just two weeks from now, if all goes according to plan.

NASA announced today (Feb. 20) that it's targeting March 6 for the liftoff of Artemis 2, which will send four astronauts on a trip around the moon. No people have been beyond low Earth orbit since December 1972, when the Apollo 17 crew returned from lunar realms.

"The excitement for Artemis 2 is really starting to build," Lori Glaze, acting associate administrator for NASA's Exploration Systems Development Mission Directorate, said during a press conference today. "Every night, I look up at the moon and I see it, and I get real excited, because I can really feel she's calling us. And we're ready."

Today's announcement came a day after the successful completion of Artemis 2's wet dress rehearsal (WDR) — a two-day-long practice run of the major operations that precede launch — at Pad 39B at NASA's Kennedy Space Center (KSC) in Florida.

It was the second WDR for Artemis 2. The first was terminated early on Feb. 2, due to a leak of liquid hydrogen (LH2) spotted during the fueling of the mission's Space Launch System (SLS) rocket. The leak occurred at an interface with the tail service mast umbilical (TSMU), a line that delivers propellant to the SLS from its mobile launch tower.

An LH2 leak in that same spot plagued the prelaunch campaign for Artemis 1, contributing to significant delays. That mission was originally slated to launch in spring 2022 but didn't get off the ground until November of that year. Artemis 1 ended up being successful, however, sending an uncrewed Orion capsule to lunar orbit and back to Earth.

NASA officials have said that they learned a great deal from Artemis 1, and that experience apparently paid off during Artemis 2's second WDR. Mission teams replaced two seals at the TSMU interface after the first fueling run, then assessed that fix on Feb. 12 by partially filling the SLS' LH2 tanks.

The new seals worked during that "confidence test," and they held again on Thursday. The WDR team poured 730,000 gallons (2.76 million liters) of cryogenic LH2 and liquid oxygen into the tanks of SLS' core and upper stages, and both propellants stayed in their proper place.

There was "really no leakage to speak of," Artemis 2 Launch Director Charlie Blackwell-Thompson said during today's press conference. "It really performed well."

The team checked all the other major WDR boxes as well, putting Artemis 2's SLS, Orion capsule and ground equipment through their paces. The mission team ran the countdown clock all the way down to T-33 seconds, then recycled and did it again, getting to T-29 seconds — and they still had time left in the simulated launch window after that.

"Obviously, yesterday was really a really good day for us," John Honeycutt, chair of the Artemis 2 Mission Management Team, said during today's press conference. "I felt the test went extremely well."

There's still some work to do before Artemis 2 can be officially cleared for liftoff, however. For example, mission teams still need to install two "contingency pad access" trusses on SLS' mobile launch tower, which will allow them to test the mission's flight termination system (FTS) at Pad 39B.

This is a new capability: During Artemis 1, the SLS-Orion stack had to be rolled back to KSC's cavernous Vehicle Assembly Building for the required prelaunch FTS test.

That work should take a few days, Blackwell-Thompson said. And the Artemis 2 team still needs to conduct a comprehensive flight readiness review, which is expected to take place toward the end of next week.

Artemis 2 will send NASA astronauts Reid Wiseman, Victor Glover and Christina Koch and the Canadian Space Agency's Jeremy Hansen on a roughly 10-day trip around the moon and back to Earth.

The quartet did not participate in this week's WDR, but three of them were present for the proceedings.

"I was able to speak a little bit with with Reid Wiseman, with Christina Koch and Jeremy Hansen. They're all very, very excited," Glaze said. "They are really getting a lot of anticipation for a potential launch in March."

"I think a lot of folks up to this point have said, you know, we watched Artemis 1, and it went significantly beyond when we first started talking about it," she added. "But this is really getting real, and it's time to get serious and start getting excited."

All four Artemis 2 crewmates will go into quarantine — a common preflight safety measure — later today at NASA's Johnson Space Center in Houston, Glaze said. They'll return to KSC about five days before liftoff, staying in quarantine at the launch site.

Artemis 2's upcoming launch window runs from March 6 through March 9 and also includes March 10. If NASA can't hit those dates, we'll have a wait a few additional weeks: The next window features target dates of April 1, April 3-6 and April 30.

NASA's second attempt to fuel up its Artemis 2 moon rocket appeared to go well on Thursday (Feb. 19), potentially keeping the mission on track to launch as soon as early March.

The space agency wrapped up the Artemis 2 wet dress rehearsal (WDR) — a two-day-long practice run of the operations leading up to launch — on Thursday night (Feb. 19) at Kennedy Space Center (KSC) in Florida.

The Artemis 2 team notched a number of important milestones during the test, chief among them the successful fueling of the mission's Space Launch System (SLS) rocket.

The WDR is designed to put Artemis 2's SLS, Orion capsule, ground equipment and mission teams through their paces, ensuring that everything is ready for an actual liftoff.

That launch will send four astronauts — NASA's Reid Wiseman, Victor Glover and Christina Koch and the Canadian Space Agency's Jeremy Hansen — on a 10-day trip around the moon and back to Earth. Artemis 2 will be the first human spaceflight beyond low Earth orbit since the Apollo missions ended in 1972, as well as the first crewed mission of NASA's Artemis program.

The lone previous Artemis mission, Artemis 1, successfully sent an uncrewed Orion to lunar orbit and back in late 2022. That flight was delayed multiple times by leaks of liquid hydrogen (LH2) propellant during ground testing, and it looked like Artemis 2 might be heading down a similar path.

NASA cut short Artemis 2's first WDR on Feb. 2 after detecting an LH2 leak, which emanated from an interface with the tail service mast, a part of the SLS' mobile launch tower that supplies fuel and other resources to the rocket via lines known as umbilicals. The Artemis 1 leak came from this same trouble spot.

The Artemis 2 team replaced two seals in the area after the first WDR attempt, then partially filled the rocket's tanks on Feb. 12 to test the fix. The seals held then, and they held on Thursday: Team members successfully filled SLS' two stages with 730,000 gallons (2.76 million liters) of supercold LH2 and liquid oxygen "without exceeding the ground safety limit of the hydrogen leak concentration," according to a NASA update.

Launch teams checked off other important WDR boxes on Thursday as well — for example, closing the Orion crew module hatch and ensuring that the capsule's emergency-escape system was secure. They then ran through "terminal count" twice, taking the countdown clock to T-33 seconds and then to T-29 seconds.

"During terminal count, automated systems take control of countdown operations, final checks of flight computers, engine bleed systems, and ground support equipment occur, and the rocket transitions to internal power, and the countdown proceeds toward simulated engine start," NASA officials wrote in an another WDR update.

The WDR came to an end at 10:16 p.m. EST (0316 GMT on Feb. 20) with the completion of the second terminal count.

Not everything went perfectly on Thursday; for instance, the second terminal count was paused briefly due to a "booster avionics system voltage anomaly." But getting through the WDR may keep Artemis 2 on track to lift off in the next available window, which runs from March 6 to March 9 and also includes March 11. (A subsequent window opens in the beginning of April.)

We should learn more on Friday: NASA will hold a press conference at 11 a.m. EST (1600 GMT) to discuss the results of the WDR and the plan for Artemis 2 going forward. You can watch that live here at Space.com.

Editor's note: This story was updated at 11:15 p.m. ET on Feb. 19 to state that the WDR was completed.

NASA will take another crack at fueling up its huge Artemis 2 moon rocket this week.

The agency plans to load more than 700,000 gallons (2.65 million liters) of liquid hydrogen (LH2) and liquid oxygen (LOX) into Artemis 2's Space Launch System (SLS) rocket on Thursday (Feb. 19), wrapping up a crucial two-day-long test called a wet dress rehearsal.

This will be the second wet dress for Artemis 2, the first crewed moon mission since the Apollo era. The first rehearsal, which began on Jan. 31, ended prematurely due to an LH2 leak detected during propellant loading.

The LH2 leak occurred at an interface with the tail service mast umbilical (TSMU), a service line that connects the SLS with its mobile launch tower.

This was far from unprecedented. Artemis 1's test campaign was plagued by leaks in this area as well, which helped push the uncrewed mission's launch from spring 2022 to November of that year. All ended well, however: Artemis 1 successfully sent an Orion capsule to lunar orbit and back to Earth.

Artemis 2 teams replaced two seals in the aftermath of the first wet dress. Then, on Feb. 12, they partially filled SLS' tanks with LH2 in a "confidence test" designed to assess the efficacy of that fix. A problem with ground support equipment restricted the flow of LH2 during that test, but the team nonetheless was "able to gain confidence in several key objectives," NASA wrote in an update on Feb. 13.

Artemis 2 team members soon tied the ground-support issue to a filter, which they replaced over this past weekend. They now feel ready to conduct another wet dress rehearsal, which will run through the key operations leading up to launch.

The wet dress will officially begin today (Feb. 17) at 6:40 p.m. EST (2340 GMT), when team members arrive at their stations at the Launch Control Center at NASA's Kennedy Space Center (KSC) in Florida. They'll work toward a simulated launch time of 8:30 p.m. EST on Thursday (Feb. 17; 0130 GMT on Feb. 18).

"During the rehearsal, the team will execute a detailed countdown sequence. Operators will conduct two runs of the last 10 minutes of the countdown, known as terminal count. They will pause at T-1 minute and 30 seconds for up to three minutes, then resume until T-33 seconds before launch and pause again," NASA officials wrote in an update on Monday (Feb. 16).

"After that, they will recycle the clock back to T-10 minutes and conduct a second terminal countdown to just inside of T-30 seconds before ending the sequence," they added. "This process simulates real-world conditions, including scenarios where a launch might be scrubbed due to technical or weather issues."

If all goes well, Artemis 2 could launch from KSC as early as March 6. There are a few other dates available next month as well — March 7-9 and March 11. (The agency had also eyed March 3 as an option, but that's no longer in play, according to Monday's update.)

Artemis 2 will send four astronauts — NASA's Reid Wiseman, Victor Glover and Christina Koch and Jeremy Hansen of the Canadian Space Agency — on a 10-day trip around the moon and back to Earth.

The mission is designed to prove out the crew-carrying capabilities of SLS and Orion and pave the way for moon-landing missions, beginning with Artemis 3, which could launch as soon as 2028.

NASA is gearing up to launch Artemis 2, the first crewed mission to the moon in more than half a century.

There are five potential Artemis 2 launch dates next month (March 6-9 and March 11) and six in April (April 1, April 3-6 and April 30), according to the space agency. The liftoff window lasts 120 minutes on all of these dates except March 11, when it's 115 minutes long.

That works out to just 11 opportunities over a 61-day stretch — and some of them may be nixed by bad weather or the need to replenish commodities like rocket fuel. Why does Artemis 2 have so few chances to fly?

It's all about orbital mechanics and the specific requirements of the mission and its hardware.

Artemis 2 will lift off from Kennedy Space Center in Florida, sending Canadian astronaut Jeremy Hansen and NASA's Reid Wiseman, Victor Glover and Christina Koch on a roughly 10-day trip around the moon aboard an Orion crew capsule.

But the astronauts won't head directly to lunar realms: Artemis 2's Space Launch System rocket will first deliver Orion to high Earth orbit, where the crew and ground teams will conduct a variety of checkouts to make sure the capsule is ready for its epic journey.

Therefore, "the launch day and time must allow SLS to be able to deliver Orion" to that orbit, NASA officials wrote in an Artemis 2 explainer last month.

"Orion also must be in the proper alignment with the Earth and moon at the time of the trans-lunar injection burn," they added. As its name suggests, that maneuver will put Orion on course for the moon, which it will fly by on a "free return" trajectory. The capsule will use lunar gravity to slingshot itself back toward Earth, without the need for another significant engine burn.

Orion's power requirements further constrain the mission's launch window.

"The trajectory for a given day must ensure Orion is not in darkness for more than 90 minutes at a time so that the solar array wings can receive and convert sunlight to electricity, and the spacecraft can maintain an optimal temperature range," NASA officials wrote. "Mission planners eliminate potential launch dates that would send Orion into extended eclipses during the flight."

Finally, viable launch windows also have to take into account Orion's return to Earth, which will feature a specific entry profile.

NASA is not officially targeting any of the March or April launch dates; that won't happen until Artemis 2 passes its wet dress rehearsal, a two-day-long practice run of the key operations that will occur in the leadup to liftoff.

The Artemis 2 team has already conducted one wet dress, which ended early on Feb. 2 due to a leak of liquid hydrogen propellant. That outcome took February out of consideration for the Artemis 2 launch. A second try is expected soon, perhaps as soon as this weekend.

And don't worry if it takes a while to get the hydrogen leak under control. The same happened on Artemis 1, a delayed but ultimately successful uncrewed mission to lunar orbit that flew in late 2022. There are potential Artemis 2 launch dates beyond April; NASA just hasn't published them yet.

"We've got opportunities in every month," Lori Glaze, acting associate administrator for NASA's Exploration Systems Development Mission Directorate, said during a press conference on Feb. 3. "So, you know, if necessary, we'll go beyond that."

Whenever Artemis 2 flies, the mission will be historic: No astronaut has been beyond low Earth orbit since December 1972, when the four Apollo 17 astronauts returned from the moon.

NASA was forced to end a critical fueling test of its giant Artemis 2 rocket early in the wee hours of Tuesday, delaying its mission to launch astronauts around the moon by at least a month. Now that a new day has dawned on the big orange launch vehicle, the space agency is attempting to shed some light on what exactly went wrong — and a lot of what it's saying sounds familiar.

The fueling testfor NASA's Artemis 2 Space Launch System (SLS) rocket began late Saturday (Jan. 31), and ran until Tuesday morning. Called a "wet dress rehearsal," it's a test to put the SLS launch vehicle and ground teams through a simulated countdown clock to fully power-on and fuel the rocket with the more than 700,000 gallons of liquid hydrogen and liquid oxygen it needs to get off the ground.

Tanking operations began smoothly yesterday (Feb. 2) after mission managers polled "go" to begin procedures, but hydrogen leaks detected at the SLS tail service mast umbilical quick disconnect on the launch platform put technicians into a troubleshooting mode most of the afternoon.

If that sounds familiar, it's because the Artemis 1 SLS experienced hydrogen leaks in the same location during its wet dress rehearsal three years ago. Those leaks resulted in three separate rollbacks to NASA's cavernous Vehicle Assembly Building (VAB) over the course of six months before Artemis 1 would finally launch.

Artemis 1 launched in November 2022 and flew an uncrewed Orion spacecraft on a month-long mission to lunar orbit and back.

With Artemis 2, NASA will test Orion's ability to sustain astronauts in deep space. NASA astronauts Reid Wiseman, Victor Glover and Christina Koch, and Canadian astronaut Jeremy Hansen, will ride aboard Orion on a 10-day mission around the far side of the moon. The flight will qualify the spacecraft's systems for Artemis 3, which NASA is planning as the mission to land astronauts back on the lunar surface.

"We really did learn a lot from the Artemis 1 mission, and we implemented a lot of the lessons learned yesterday through wet dress," Lori Glaze, NASA's Exploration Systems Development Mission Directorate acting associate administrator, said during a post-wet dress rehearsal press conference on Tuesday.

"Everyone's aware of some of the challenges with the hydrogen tanking from Artemis 1, and we've made some changes," Glaze said.

To NASA's credit, the Artemis 2 wet dress rehearsal went far smoother than Artemis 1's first fueling test.

Despite the hours of troubleshooting the persistent hydrogen leak — which NASA officials say was stabilized within acceptable limits (but never eliminated) —mission operators managed to fully fuel both SLS stages and carry the test down to the simulated clock's terminal count (the last 10 minutes before liftoff). But the team didn't quite get as close to T-0 as needed in order to earn NASA's gold stamp of approval to launch with a crew onboard.

"The fact that we got to full tanking yesterday on the first try was a tremendous success, and we gathered an enormous amount of data in the processes and how we want to go forward with that in the future," Glaze said.

At T-5 minutes 15 seconds, the SLS ground launch sequencer terminated the count due to a spike in the same quick disconnect hydrogen leak it had experienced all afternoon, which was cause to abort the test, NASA said.

"As we began that pressurization, we did see that the leak within the cavity came up pretty quick," Artemis Launch Director Charlie Blackwell-Thompson said during Tuesday's press briefing, referring to a cavity on the rocket's mast umbilical. The activity triggered safety procedures already in place for such contingencies, she added.

"We got into our safety steps. We saw the hydrogen concentration come down and then later in the evening, we got into our drain operation," she said.

While maintaining the wet dress rehearsal an overall success in terms of data gathered and the accolade of filling SLS's tanks on the first try, Blackwell-Thompson also assured that, unlike Artemis 1, the hydrogen hiccups can likely be addressed at the pad, and don't seem to warrant a rollback to the VAB for maintenance.

"During Artemis 1, we found out that we can do some work on these plates at the pad," Blackwell-Thompson said. "I had hoped that we would not have to demonstrate that again for Artemis 2, but we showed that we can go do this work at the pad and be ready for launch."

As for why SLS is still experiencing these same hydrogen leaks after three years between missions, NASA officials have some theories, but haven't quite nailed down a definitive cause. "These are very bespoke components," NASA Associate Administrator Amit Kshatriya said Tuesday, describing each SLS as its own unique vehicle to learn and understand.

The leaky seal could possibly be a result of vibrations incurred during the rocket's initial rollout to the pad,, Kshatriya said. It took the Artemis 2 SLS rocket nearly 12 hours to make the 4-mile trip to the pad from the VAB at a top speed of 1 mile an hour last month.

"That rollout environment is very complicated," he added, noting that the Artemis 1 SLS was put through different acceleration tests on its way between the VAB and the pad at Launch Complex-39B specifically to help determine the effect of such stresses on the rocket and launch platform. "We think that's a contributor. But again, we have to tear the seal apart and see what happened."

"This is the first time this particular machine has borne witness to cryogens. And how it breathes, and how it vents, and how it wants to leak is something we have to characterize," Kshatriya said, and testing before the launch pad can only go so far.

Even with an "aggressive approach" to dealing with hydrogen leaks during Artemis 1, "we're pretty limited as to how much realism we can put into the test," said John Honeycutt, the chair of NASA's Artemis Mission Management team. "We try to test like we fly, but this interface is a very complex interface, and when you're dealing with hydrogen, it's a small molecule, it's highly energetic," he said, admitting he and mission managers weren't expecting these issues to crop up again.

"This one caught us off guard," Honeycutt added. "The initial things that we were seeing in the technical team felt like we either had some sort of misalignment or some sort of deformation or debris on the seal."

NASA needs to evaluate the rocket and ground infrastructure at the pad before determining the next possible date to attempt another wet dress rehearsal, and has opted to forgo Artemis 2's February launch opportunity, which, had the test gone successfully, spanned from Feb. 8-11.

"With more than three years between SLS launches, we fully anticipated encountering challenges," NASA Administrator Jared Isaacman said in a post on X early Tuesday. "That is precisely why we conduct a wet dress rehearsal. These tests are designed to surface issues before flight and set up launch day with the highest probability of success."

Mission managers are now targeting next month's window, which is open March 6-9 and March 11, with about five days available around the first week of each month thereafter.

Humanity's return to the moon will have to wait at least another four weeks.

NASA had been targeting Feb. 8 for the launch of its Artemis 2 mission, which will send four astronauts on a 10-day trip around the moon and back to Earth. But the agency just moved the timeline back, after experiencing several issues during a key prelaunch exercise called a wet dress rehearsal. And some of those issues looked all too familiar to ones NASA saw on Artemis 1 in 2022.

"Engineers pushed through several challenges during the two-day test and met many of the planned objectives," NASA officials said in a statement early Tuesday morning (Feb. 3). "To allow teams to review data and conduct a second wet dress rehearsal, NASA now will target March as the earliest possible launch opportunity for the flight test."

There are five potential launch dates available in March for Artemis 2, which will lift off from NASA's Kennedy Space Center (KSC) in Florida: March 6-9 and March 11. If the mission can't make any of those dates, another window opens in April, with launch possible on April 1, April 3-6 and April 30.

A wet dress rehearsal is a practice run through the operations that will precede an actual launch. Artemis 2's 49-hour wet dress officially began Saturday (Jan. 31) at 8:13 p.m. EST (0113 GMT on Feb. 1), when launch team members arrived at their stations at KSC.

The team checked a lot of boxes over the next day and a half — powering up both stages of Artemis 2's Space Launch System (SLS) rocket, for example, and charging the flight batteries of the mission's Orion crew capsule.

But the wet dress' main event came on Monday (Feb. 2) — the tanking test, which involved loading more than 700,000 gallons (2.65 million liters) of super-cold liquid hydrogen (LH2) and liquid oxygen (LOX) propellant into the SLS.

Artemis 1 experienced multiple LH2 leaks during its prelaunch campaign, which contributed to extensive delays for the mission. Originally slated to fly in spring 2022, Artemis 1 didn't get off the ground until that November. (The mission was successful, however, sending an uncrewed Orion to lunar orbit and back to Earth.)

So leaks were on the minds of many space fans during the Artemis 2 wet dress — and they popped up on the pad Monday as well.

"During tanking, engineers spent several hours troubleshooting a liquid hydrogen leak in an interface used to route the cryogenic propellant into the rocket’s core stage, putting them behind in the countdown," NASA officials wrote in the Tuesday update. "Attempts to resolve the issue involved stopping the flow of liquid hydrogen into the core stage, allowing the interface to warm up for the seals to reseat, and adjusting the flow of the propellant. "

The leaks observed on Monday appear similar to those that plagued Artemis 1's prelaunch campaign; they all involved LH2 and occurred at an interface with the tail service mast umbilical, a line that runs propellant to the SLS from the mobile launch tower.

The launch team dealt with the Artemis 2 leak effectively, managing to fill the SLS' LOX and LH2 tanks and keep them topped up. However, the leak rate spiked again late in the wet dress' simulated countdown, causing NASA to end the exercise with about five minutes left on the clock.

The launch team encountered a few other issues during the wet dress as well. For example, there were several dropouts of audio communications during the test, something that had also happened in the past few weeks leading up to the exercise.

In addition, "a valve associated with Orion crew module hatch pressurization, which recently was replaced, required retorquing, and closeout operations took longer than planned," NASA officials said in the update. ("Closeout operations" are those that ensure Orion is secure and ready for crew ingress. But astronaut boarding itself is not a wet dress milestone; the Artemis 2 crew did not participate in the test.)

Speaking of the crew: The Artemis 2 quartet — NASA's Reid Wiseman, Victor Glover and Christina Koch, and Canadian astronaut Jeremy Hansen — have been in quarantine in Houston since Jan. 21 and were scheduled to travel to KSC on Tuesday to gear up for launch. They won't make that trip now, and they can exit quarantine; they'll have to go back into quarantine two weeks prior to the new target launch date.

We'll learn more about the wet dress on Tuesday at 1 p.m. EST (1800 GMT), when the agency holds a press conference to discuss the results. You can watch it here at Space.com.

Whenever the Artemis 2 astronauts fly, they'll make history: No human has been beyond low Earth orbit since December 1972, when the Apollo 17 astronauts returned from the moon.

Editor's note: The issues encountered during the fueling tests have led NASA to delay the Artemis 2 mission to March.

NASA's big moon rocket leaks a little bit, but it just might be ready to carry astronauts beyond Earth.

The space agency conducted a crucial fueling test today (Feb. 2) with the Artemis 2 mission's Space Launch System (SLS) rocket, loading more than 700,000 gallons (2.65 million liters) of cryogenic liquid hydrogen (LH2) and liquid oxygen (LOX) into the two-stage vehicle on Pad 39B at Kennedy Space Center (KSC) in Florida.

Teams had to stop loading LH2 into the SLS core stage twice to deal with leaks, but they managed to troubleshoot the issue in relatively short order and top up the rocket's enormous tanks.

Today's tanking was the trickiest part of the Artemis 2 wet dress rehearsal, a two-day-long practice run through the operations that will precede an actual launch.

Currently, NASA is targeting Feb. 8 for the liftoff of Artemis 2, which will send NASA astronauts Reid Wiseman, Victor Glover and Christina Koch and Canada's Jeremy Hansen on a 10-day trip around the moon. But that's contingent upon a successful wet dress, as well as a number of other factors — good weather conditions, for example.

It's too soon to tell whether or not NASA considers the wet dress a complete success; the exercise is still going on, after all, and may not conclude until 1 a.m. EST (0600 GMT) on Tuesday (Feb. 3).

But we may get an answer on Tuesday at 12 p.m. EST (1700 GMT), when the agency holds a press conference about the wet dress. You can watch that briefing live here at Space.com when the time comes.

It wasn't surprising that leaks sprang up during LH2 loading today, given how small that molecule is; it can slip through the tiniest of cracks. And history is a guide here as well: The Artemis 1 launch campaign was delayed repeatedly by LH2 leaks and other issues.

That mission, the first of NASA's Artemis program of moon exploration, was originally scheduled to launch in the spring of 2022, but it didn't get off the ground until Nov. 16 of that year.

Things went well after liftoff, however: Artemis 1 successfully sent an uncrewed Orion capsule to lunar orbit and back to Earth, showing that Artemis hardware can handle a crewed mission to deep space.

NASA is taking many lessons learned from Artemis 1 to Artemis 2 and beyond — and some of those lessons apparently helped out today.

The LH2 leaks that plagued Artemis 1 centered on an interface with the tail service mast umbilical (TSMU), a line that carries propellant from the mobile launch tower to the rocket. The two leaks observed during today's wet dress also occurred at a TSMU interface, according to a NASA update. But the mission team quickly troubleshot the issue and moved on.

The astronauts of NASA's Artemis 2 moon mission want to become a mere footnote in the annals of space history.

Artemis 2 will send NASA's Reid Wiseman, Victor Glover and Christina Koch and Canada's Jeremy Hansen on a 10-day flight around the moon. As the first crewed trip to lunar realms since Apollo 17 in 1972, this mission will be momentous — but the Artemis 2 astronauts hope future generations have reason to gloss over their contributions.

"I hope they forget all about Artemis 2," Koch told Bill Whitaker of CBS' "60 Minutes," which aired a piece about the mission on Sunday night (Feb. 1). "I think that's a little bit extreme, but we talk about our legacy being enabling the future missions, all the way from Artemis 3 to Artemis 100 to missions to Mars."

"I completely agree," Wiseman said.

"But you're the first step," Whitaker pointed out.

"Yeah, but watch what's coming next," Hansen responded. "It gets pretty extraordinary from here."

NASA is targeting Feb. 8 for the launch of Artemis 2, which will take place atop a Space Launch System (SLS) rocket from Kennedy Space Center (KSC) in Florida.

Hitting that date, however, is contingent upon the successful completion of numerous prelaunch checks, including a crucial SLS fueling test that's happening at KSC's Pad 39B today (Feb. 2). Artemis 2 has backup launch opportunities on Feb. 10 and Feb. 11. After that, there are windows available in March and April.

Artemis 2 is the first crewed mission of NASA's Artemis program, which aims to establish a permanent human presence on and around the moon by 2030 or so and, as Koch mentioned, help pave the way for crewed trips to Mars. If all goes to plan, Artemis 3 will put astronauts down on the lunar surface in 2028, and future missions will help establish and operate a base in the area.

You can watch the 13-minute "60 Minutes" Artemis 2 piece on YouTube. The discussion of the mission's legacy quoted in this article came from a separate, seven-minute "'60 Minutes' Overtime" segment, which you can find here.

NASA will fuel up its huge Artemis 2 moon rocket today (Feb. 2), and you can watch the crucial prelaunch test live.

On Saturday night (Jan. 31), the agency officially began Artemis 2's "wet dress rehearsal," a two-day-long exercise that runs through the key procedures and operations that will precede an actual liftoff. Perhaps the most important of these operations is fueling — loading up Artemis 2's Space Launch System (SLS) rocket with more than 700,000 gallons (2.65 million liters) of super-cold liquid oxygen and liquid hydrogen propellant.

The Artemis 2 wet dress is targeting a simulated launch time tonight of 9 p.m. EST (0200 GMT on Feb. 3). Tanking operations are scheduled to begin about 10 hours before that — so, around 11 a.m. EST (1600 GMT). You can watch live here at Space.com, courtesy of NASA; the agency is livestreaming the wet dress 24/7.

You shouldn't necessarily expect everything to go smoothly today. Fueling up a giant rocket is a tricky operation, after all — especially when one of the propellants is liquid hydrogen, whose constituent molecules are tiny. Liquid hydrogen can escape through the smallest of fissures, as we saw during the wet dress rehearsals for Artemis 1.

Artemis 1 was originally targeted to launch in early 2022, but hydrogen leaks discovered during multiple wet dresses pushed things back considerably. In the end, everything worked out: Artemis 1 launched in November 2022, successfully sending an uncrewed Orion capsule to lunar orbit and back to Earth.

A lot more is riding on Artemis 2. It will carry four astronauts — NASA's Reid Wiseman, Victor Glover and Christina Koch, and the Canadian Space Agency's Jeremy Hansen — on a roughly 10-day trip around the moon and back to Earth. It will be the first crewed mission to lunar realms since Apollo 17 in December 1972.

NASA is currently targeting Feb. 8 for Artemis 2's liftoff, which will take place from Launch Complex-39B at Kennedy Space Center (KSC) in Florida. The SLS-Orion stack rolled out to Pad 39B from KSC's cavernous Vehicle Assembly Building on Jan. 17.

There are backup launch days on Feb. 10 and Feb. 11. If Artemis 2 can't fly during that stretch, additional windows are available in March and April.

SpaceX's latest Starship prototype just passed another big preflight test.

The company conducted a "wet dress rehearsal" at its Starbase site in South Texas on Tuesday (Oct. 24), filling the Starship vehicle with cryogenic fuel to check for leaks and other potential issues.

"Starship and Super Heavy were loaded with more than 10 million pounds of propellant today in a flight-like rehearsal ahead of launch," SpaceX said Tuesday night in a post on X (formerly Twitter) that featured video of the test. (Super Heavy is the vehicle's first-stage booster, whereas Starship is its upper-stage spacecraft. Both elements are powered by SpaceX's new Raptor engines, which burn liquid methane and liquid oxygen.)

"Vehicle is ready for the second test flight of a fully integrated Starship, pending regulatory approval," SpaceX wrote in another Tuesday night X post.

Related: Relive SpaceX's explosive 1st Starship test in incredible launch photos

That pending approval is a launch license, which the U.S. Federal Aviation Administration (FAA) has not yet granted for the upcoming flight. 

Six weeks ago, the agency closed its investigation into Starship's first-ever fully stacked flight, which lifted off from Starbase on April 20. That test mission aimed to send the upper stage partway around Earth, ending with a Pacific Ocean splashdown near Hawaii. That didn't happen, however; Starship suffered several problems shortly after launch, and the flight ended with a controlled detonation high above the Gulf of Mexico.

"The closure of the mishap investigation does not signal an immediate resumption of Starship launches at Boca Chica," FAA officials said in an emailed statement on Sept. 8, referring to the Starbase site. "SpaceX must implement all corrective actions that impact public safety and apply for and receive a license modification from the FAA that addresses all safety, environmental and other applicable regulatory requirements prior to the next Starship launch."

Elon Musk said recently that SpaceX has implemented all of the corrective actions required ahead of flight number two, and it's clear that the company wants to fly again soon. 

"It's a shame when our hardware is ready to fly and we're not able to go fly because of regulations or re-review," Bill Gerstenmaier, the vice president of build and flight reliability at SpaceX, said last week during a hearing of the U.S. Senate's Subcommittee on Space and Science called "Promoting Safety, Innovation and Competitiveness in U.S. Commercial Human Space Activities."

"We need to be safe, we need to protect the environment; we don't dismiss those. But we need to fly at the fastest pace that we can do hardware development to do this active development process and this test flight experience that we've described," Gerstenmaier added, referring to SpaceX's development strategy of flying prototypes frequently, and iterating frequently based on the results.

Starship is the biggest and most powerful rocket ever built, and both of its stages are designed to be fully and rapidly reusable. 

SpaceX believes that the vehicle will revolutionize spaceflight, making a variety of bold exploration feats — including the human settlement of Mars, a long-held dream of Musk's — economically feasible.

NASA shuttlemanagers decided Thursday not to test fuel the external tank that will feed theDiscovery orbiter during a plannedlaunch this July, space agency officials said.

Shuttlemanagers have debated the fuel-loading test sincelast month, when engineers openedup the aft end of Discovery's Lockheed Martin-built external tank to replacefour enginecut-off sensors inside its liquid hydrogen compartment.

Known as atanking test, the fuel-loading check operation involves pumping Discovery's 15-storyfuel tank with the 526,000 gallons (about two million liters) of super-chilledliquid oxygen and liquid hydrogen into the orange vessel while it sits atop thelaunch pad. The test would verify the performance of the new ECO sensors and allowengineers a chance to see the changes made to ET-119's foam insulation covering- the most noticeable of which is the removalof a 38-foot (11-meter) ramp - under fully fueled conditions.

"There's acost to it in a lot of places and that's what they were looking at, the prosand the cons," James Hartsfield, a NASA spokesperson with the agency's JohnsonSpace Center in Houston, told SPACE.com, adding that the test couldreduce the contingency time at the pad for the planned space shot.

Discovery'slaunch will mark NASA's second shuttle mission - STS-121 commanded by veteran astronautStevenLindsey - since the 2003Columbia accident. The spaceflight is currently slated to launch on July 1,but has a flightwindow that stretches through July 19.

NASAdecided to swapout Discovery's fuel tank ECO sensors with new ones in March afteridentifying a wiring defect in similar units. The sensors are designed to shutdown a shuttle's three main engines before its fuel tank runs dry. They can bechecked during tanking tests or actual pre-launch fueling to verify that theyare working properly.

Last week,shuttle managers also said that they would notmake additional changes to Discovery's external tank aside from the alreadycompleted removal of a protuberance air-load (PAL) ramp that shielded a cabletray and pressure lines.

DuringDiscovery's last launch - NASA's firstreturn to flight mission STS-114 - a one-pound (0.4-kilogram) piece of foampoppedfree from the ramp during the orbiter's ascent. While the foam debris didnot strike the orbiter, it was reminiscent the foam shedding problem that doomedthe Columbia orbiter and its seven-astronaut crew in 2003.

NASA's spaceshuttle chief Wayne Hale said Friday that the PAL ramp removal marked "thelargest aerodynamic change" to the shuttle launch system since its first flight25 years ago.

At NASA'sKennedy Space Center (KSC) spaceport in Florida, preparations are underway tomove Discovery from its hangar-like Orbiter Processing Facility to the 52-storyVehicle Assembly Building, where the shuttle's external tank has alreadybeen mated to the two solid rocket boosters that will launch the spacecraftinto orbit, on May 12.

Thecomplete launch stack is also on track to roll out to the launch pad on May 19,KSC spokesperson George Diller said.

• NASA Mulls Fuel Tank Test for Next Shuttle Flight
• NASA's Next Shuttle to Fly Without Ice Frost Ramp Fix
• NASA Plans Partial Fix for Discovery Orbiter to Reduce ISS Risk
• Return to Flight Special Report: NASA's Road to STS-121