Space is important to us and that’s why we’re working to bring you industry and top coverage of Florida launches. This type of journalism takes time and resources. Please support it by subscribing here,
Updates: NASA completed this test and met all of its test objectives on Wednesday afternoon. Engineers will be reviewing data and procedures going forward, so the next launch attempt is still tentatively scheduled for 11:37 a.m. EDT Tuesday, Sept. 27. Read our full post-Test story here.
Follow live as NASA targets Wednesday, Sept. 21 for the Space Launch System rocket fueling test at Kennedy Space Center in Florida.
The test, which will load liquid oxygen and hydrogen into the main stage of the 322-foot rocket, is necessary before proceeding with the next attempt to launch the Artemis I mission to the Moon. The last two attempts at the end of August and earlier this month were scrubbed due to hardware problems.
NASA expects this test to last until noon
If all goes according to plan, today’s test will fully load fuel and pave the way for a launch during a 70-minute window, which opens at 11:37 a.m. on Tuesday, Sept. 27.
Teams expect to have a full loading test by this afternoon.
Follow the live updates below (manual refresh required; for more frequent, real-time updates, follow this link,
SLS is now fully refueled
3:45 PM EDT: The SLS is now fully refueled. A hydrogen leak is still being detected, but it is a major milestone. Teams clearly have some more work to do to detect leaks.
This completes Wednesday’s fuel test. Although there were some rocky moments and hydrogen is still leaking out, engineers have probably obtained invaluable data.
3:35 PM EDT: The Artemis launch director has given a “go” to proceed with pre-flight pressurization of the propellant tanks at Pad 39B. This would simulate the level to which the rocket’s tanks need to reach just before liftoff – a critical milestone that was not reached during the previous two launch attempts.
Again, there will be no launch today. This is just a fuel test.
3:05 PM EDT: The refueling work in the second stage is almost complete. Liquid oxygen is loaded while hydrogen (LH2) is about half that. There’s about 30 minutes left for that LH2 load.
NASA, by the way, is almost done with today’s test. Just a few more milestones.
2:35 PM EDT: The second phase of filling is going on as per the plan and about 15 minutes are left in that process. Then the next milestone would involve depressurizing the SLS’s four propellant tanks – two for liquid oxygen, two for liquid hydrogen – to lift the pressure.
As it stands, it appears that NASA is behind the times. But since it’s not launch day, there isn’t necessarily a schedule as to the launch window – just what needs to be done to complete this test.
1:40 PM EDT: Now that both the liquid oxygen and hydrogen tanks are fully refueled, NASA is preparing to load the rocket’s second stage — known as the ICPS, or Interim Cryogenic Propulsion Stage — with both propellants.
1:10 PM EDT: NASA says the rocket’s two tanks are fully loaded with hydrogen while liquid oxygen is 100% full. But engineers are a little surprised by the data they’re seeing from today’s test.
At first, it formed a significant hydrogen leak, so the teams backed off and stopped loading. Then, they resumed slow and there was still a leak, but not nearly as significant (about 3.5%; the limit is 4%).
Now, however, engineers are seeing a leak rate of less than half a percent. This is a good problem, but it also begs the question: why is the performance of the propellant loading hardware fluctuating so much?
1 a.m. EDT: Liquid hydrogen has reached the 90% filled milestone. This is much further than what the teams were able to achieve during the final attempt in early September, so modifying the propellant pressure and loading procedures has clearly worked somewhat. We’ll see how it holds up.
12:45 PM EDT: The teams have proposed increasing the hydrogen pressure on pad 39B and the launch directors have agreed. The pressure was lowered to see at which point the already detected leak worsened; So far, refueling has mostly gone according to plan and the LH2 tank is about 70% full.
Teams saw the leak getting worse as the pressure increased, so staying in low pressure mode helped. But getting it up to the point of launch would require more pressure (which is not happening today as it’s just a fuel test). The severity of the leak is measured using an eight-inch quick-disconnect line, or sensor just outside the QD. As long as hydrogen is measured to be less than 4%, it is within limits. It appears to have affected about 3.4% during refueling to date.
12:35 PM EDT: Hydrogen loading in the core stage tanks of the SLS is looking good; Liquid oxygen remains stable. Newest:
- Liquid Oxygen: 100% Full
- Liquid Hydrogen: 60% Full
12:20 PM EDT: NASA says that the hydrogen leak detected during refueling increased as the pressure in the system increased, but went below the 4% threshold. This propellant loading is measured by sensors just outside the hardware.
Liquid oxygen is sitting at 100% filled while hydrogen is pushed to 50%.
12:10 PM EDT: NASA is now moving on to the next phase of fuel testing at Kennedy Space Center, which will divert some of the cooled propellant to the RS-25 main engines. This engine chilldown procedure is designed to cool the hardware prior to liftoff, which will help avoid thermal shock as the propellants are rapidly pumped.
- Liquid Oxygen: 99% Full
- Liquid Hydrogen: 39% Full
11:55am EDT: The hydrogen fast-fill process is looking better now, especially when compared to the previous launch attempt earlier this month. The LH2 was only able to hit about 11% during the window, but has so far seen a further climb of 27% in today’s testing.
- Liquid Oxygen: 93% Full
- Liquid Hydrogen: 27% Full
11:45am EDT: Engineers continue to see hydrogen leaking into the system, but it’s not as important as before. SLS Chief Engineer John Blevins has requested a contingency plan in case the leak continues – or increases as the pressure in the system increases.
Then, that’s exactly when the scrub was called out during the last attempt earlier this month.
Latest Fill Number:
- Liquid Oxygen: 89% Full
- Liquid Hydrogen: 17% Full
11:35am EDT: The Hydrogen team again begins rapidly filling the SLS rocket with propellant, getting us to the point that caused the scrub last time. It’s moment of truth to see if the seal was re-seated and the system can pump out LH2 without any kind of leakage.
11:10am EDT: Mission managers have agreed to start loading liquid hydrogen, or LH2, again. The LH2 team will begin fueling the rocket with an even lower pressure in an attempt to slowly start the system. Hopefully this will prevent any leaks from forming and allow the seal to stay in place.
Hydrogen, by the way, is a historically finicky propellant to work with. More on that here.
10:40am EDT: NASA is still investigating the hydrogen leak at Pad 39B, which was detected at the same time as the system switched from slow-fill to fast-fill. This is very similar to what we saw during the last launch attempt earlier this month.
As of now, the troubleshooting plan is to allow the line going to the rocket to overheat, then they will attempt to load fuel again. Hopefully this re-establishes the seals and closes any gaps that may have formed. For what it’s worth, it’s the same recovery plan as last time.
Meanwhile, the preloaded hydrogen in the tank is “boiling out” and losing it to a low temperature of minus 423 degrees Fahrenheit. To keep it up, NASA will have to keep pumping cold hydrogen into the tank, but it apparently continues until the problem is resolved.
10:10 a.m. EDT: NASA has stopped loading liquid hydrogen into the Space Launch System rocket at Kennedy Space Center due to another leak in the system. Teams are attempting to isolate the source of the leak, which appears to be somewhere in the tail service mast navel—a historically problematic piece of hardware.
NASA says Launch Director Charlie Blackwell-Thompson has signed off on a plan that will “heat the line to try and reset the connection point.”
9:09am EDT: NASA has confirmed that hydrogen is being loaded into the tank of the 322-foot SLS rocket at a slow filling rate. This means that the rocket’s two primary propellants – liquid oxygen and hydrogen – are now being pumped without issue. This slow phase will be followed by the next rapid one, assuming there is no further leakage in the hydrogen system.
8:45 a.m. EDT: Now in slow-fill for Liquid Oxygen, a good sign. This process slowly loads the LOX through the propellant system and into the tanks, giving the hardware the opportunity to thermally adjust and avoid damage.
NASA has just given permission to do the same for liquid hydrogen, so teams are preparing for that as well.
Once the slow-filling process is complete for both propellants, the entire loading process begins. This is known as “fast-fill”.
8:30 a.m. EDT: It’s official: The countdown clock at Kennedy Space Center has been ticking by just over 6 hours and 30 minutes. Teams should soon begin filling the main stage with liquid oxygen and hydrogen.
If all goes according to plan, the test should be completed sometime after 3 p.m. EDT.
8:20 a.m. EDT: NASA says chilldown of liquid oxygen loading lines is complete; Now focusing on cooling the main propulsion system. Then, it will help prevent thermal shock when it comes time to fully pump the propellants into the 322-foot rocket.
7:55am EDT: As planned, teams are preparing ground support equipment on pad 39B for today’s full-on fueling test. By letting some of the cooled propellant flow through the lines, engineers hope to reduce thermal shock to the instrument as the supercooled oxygen and hydrogen move through.
It is those thermal shocks, as well as the high pressure required to pump fuels such as hydrogen, that are causing problems and exposing even the tiniest of leaks.
7:30 a.m. EDT: NASA’s launch director has given a “go” to begin loading liquid oxygen and hydrogen propellants at Kennedy Space Center. Teams are a little off on time, but the delay should be minimal.
Security had to remove anyone who was very close to the explosion danger zone – the area affected when the rocket exploded – so that’s at least part of the reason for this morning’s delay.
Teams are eyeing some storms to the east, but they don’t pose enough danger at this time to stop the process. Electricity is the biggest danger there.