NASA’s Space Launch System Is Headed Back To The VAB
The Space Launch System is one of the biggest and most powerful rockets in the world. Right now after many years of preparation, we are watching it progress on some of the final steps before a launch expected to happen this summer. Unfortunately, the launch vehicle has not had the smoothest wet dress rehearsal over the past few weeks.
Specifically, the rocket destined for the Moon left Launch Pad 39B last night and was rolled back into the Vehicle Assembly Building. Here, teams will work on replacing a faulty upper stage check valve and a small leak within the tail service mast umbilical ground plate housing on the mobile launcher. Both of which joins a list of other complications that have delayed the wet dress rehearsal.
What was intended to be a multiple-day test is about to reach the month long mark. This will end up delaying upcoming missions such as Artemis 1 which is intended to happen in only a few months this summer. However, it’s very important that NASA fixes any issues during the testing phase prior to any uncrewed or crewed launch attempts. Here I will go more in-depth into the recent roll back into the VAB, SLS progress, and what to expect in the near future.
Leaving Pad 39B
Around 3 a.m. on Saturday, April 2nd, at approximately L-35 hours and 20 minutes, the Artemis I launch control team powered up the Space Launch System rocket’s core stage, and worked to attempt to load it with more than 700,000 gallons of propellants during the tanking phase of the countdown. During the day, teams then charged Orion flight batteries, conducted final preparations on umbilical arms, and conduct a final pre-launch walkdown. Over the next few weeks, the wet dress rehearsal was delayed for a large number of reasons. This included lightning strikes, valve issues, vent complications, and more. Now in late April, NASA has just moved the Space Launch System off the pad and back into the Vehicle Assembly Building. Unfortunately, this is not because the tests are done but instead because repairs are needed. Specifically, teams need to work on replacing a faulty upper stage check valve and a small leak within the tail service mast umbilical ground plate housing on the mobile launcher. Yesterday, on April 25th, NASA tweeted saying, “At approximately 5:30pm ET today, @NASA’s #Artemis I Moon rocket atop the crawler-transporter is scheduled to leave Launch Complex 39B and begin the four-mile trek to the Vehicle Assembly Building.” Not long after, they provided another update mentioning, “The @NASA_SLS rocket and @NASA_Orion spacecraft for the #Artemis I mission have begun the four-mile journey back to the Vehicle Assembly Building.
The move is expected to take between eight to 12 hours.” Only a few days earlier teams at NASA’s Kennedy Space Center in Florida prepared the Space Launch System and Orion spacecraft for their return to the Vehicle Assembly Building. As work continues at the launch pad throughout the weekend, the agency will also continue working closely with its commercial crew partners to confirm a date and time. The transition was then underway to move from the testing configuration to the roll back formation needed to return to the VAB. This process includes offloading hydrazine from the twin solid rocket boosters and disconnecting the rocket and spacecraft from the ground systems infrastructure at the launch pad. The core stage propellant was drained shortly after completing the last test attempt. The rocket and spacecraft were in a safe configuration prior to being rolled back inside. Inside the VAB, engineers will repair a faulty helium check valve and a hydrogen leak on the mobile launcher while the supplier for the gaseous nitrogen makes upgrades to their pipeline configuration to support Artemis I testing and launch. Specifically, on a previous test, engineers identified a helium check valve that is not functioning as expected, requiring these changes to ensure the safety of the flight hardware. Helium is used for several different operations, including purging the engine, or clearing the lines, prior to loading propellants during tanking, as well as draining propellant. A check valve is a type of valve that allows liquid or gas to flow in a particular direction and prevents backflow. The helium check valve is about three inches long and prevents the helium from flowing back out of the rocket. Finally, only hours ago, NASA tweeted saying, “At 6am ET, the @NASA_SLS rocket & @NASA_Orion spacecraft arrived inside of the Vehicle Assembly Building after a 10-hour journey from Launch Complex 39B. Over the next several days, the team will extend the work platforms to allow access to SLS and Orion.”
What Objectives Have Been Met?
NASA pointed out that most objectives associated with the wet dress rehearsal were met during recent testing, and that teams plan to return to the launch pad when repairs and checkouts in the VAB are complete for the next full wet dress test attempt. Following completion of the test, SLS and Orion will return to the VAB for the remaining checkouts before rolling back out to the pad for launch. The wet dress rehearsal is intended for the Space Launch System, Orion spacecraft, and Exploration Ground Systems before the Artemis I launch at Launch Pad 39B at NASA’s Kennedy Space Center in Florida. The rehearsal is intended to run the Artemis I launch team through operations to load propellant into the rocket’s tanks, conduct a full launch countdown, demonstrate the ability to recycle the countdown clock, and also drain the tanks to give them an opportunity to practice the timelines and procedures they will use for launch. In addition, NASA describes the timeline by saying, “During the approximately two-day test”. This obviously has not been the case however the agency is determined to finish the test. The process begins with teams activating the facilities needed for launch and formally beginning the countdown sequence. NASA will staff the Launch Control Center at Kennedy and connect with staff in the Mission Control Center at NASA’s Johnson Space Center in Houston, the Space Force Eastern Range, and the SLS Engineering Support Center at the agency’s Marshall Space Flight Center in Huntsville, Alabama. Launch controllers will power on different rocket and spacecraft systems, along with ground support equipment.
From here teams will then load more than 700,000 gallons of cryogenic, or super cold, propellants including liquid hydrogen and liquid oxygen into the rocket at the launch pad on the mobile launcher according to the detailed timeline they will use on the actual launch day. They will practice every phase of the countdown, including weather briefings, pre-planned holds in the countdown, conditioning and replenishing the propellants as needed, and validation checks. During the wet dress rehearsal, once launch controllers reach the point just before the rocket’s RS-25 engines will ignite on launch day, they will recycle back to the T-10 minute point, and then resume the countdown once more after a hold. The team will then deliberately halt the countdown at about 10 seconds before the simulated liftoff to demonstrate stopping a launch and draining the propellants from the rocket. Sometimes called a “scrub,” launch controllers may decide not to proceed with launch if a technical or weather issue arises during or prior to the countdown, so demonstrating the ability to remove propellants will ensure teams are prepared for various launch day scenarios. Several days after the wet dress rehearsal, the integrated rocket and spacecraft will be rolled back to the Vehicle Assembly Building. In the VAB, technicians will extend platforms to reestablish access to several parts of the rocket and spacecraft. They will remove sensors specifically used for monitoring during the wet dress rehearsal, charge Orion and other system batteries, stow late-load cargo into Orion, and run final checkouts on several elements, among other tasks. Orion and SLS will roll to the launch pad for a final time about a week before launch.
Not long after, NASA will review data from the rehearsal before setting a specific target launch date for the Artemis I launch. The first in a series of increasingly complex missions, Artemis I will provide a foundation for human deep space exploration and demonstrate our commitment and capability to extend human existence to the Moon and beyond prior to the first flight with crew on Artemis II. While this test has not gone to plan, the agency has still completed many of the necessary objectives over the past few months. We can expect repairs to finish not long from now before SLS is rolled out again to finish the wet dress rehearsal.
Conclusion
Right now we are closer than ever to returning humans to the Moon. A key aspect of these future Artemis missions involves the Space Launch System, Orion, and the ground systems. All of which need to be perfect in order for the future missions to be a success. Over the past month, NASA has been working on the wet dress rehearsal of these various systems. Unfortunately, it has presented a number of problems that have delayed it. As of right now, it has recently arrived back in the VAB for repairs. We will have to wait and see how it progresses and the impact it has on the space industry.