NASA’s SLS (Space Launch System) program is preparing to serve its role in the agency’s first human spaceflight mission to the moon in nearly 50 years–Artemis 1. After completing a DCR (Design Certification Review) in late September, the program engineering groups are now organizing the data to certify SLS’s initial configuration for flight in a few months’ time.
Broken into multiple segments over more than a year’s time, the review certified that the SLS Block 1 Crew vehicle meets the design requirements for its first launch and that the complete program is ready for its rocket to fly.
Final Design Certification Review board
The final of five review boards was held on September 24. This was intended to go through the latest certification data and discuss the SLS Block 1 design and the review as a whole. “We split it up into five different data drops over a couple of years,” David Beaman, manager of the SLS Systems Engineering and Integration Office, said in an October 19 interview. “[We didn’t want to] wait until the end when you have all the data to try to find out if you have a problem, so we did it in bite-size pieces, and we did it based on the data we had available.”
“Over the last year, we did three of those pieces, and now we’re in a position where we’ve gone through the design certification process, we know the results of all of our tests and analysis up to this point on the design, and we’ve documented the results of those, and those documents are meant to serve as justification of why the design meets its requirements.”
“Ultimately when we got to the end, DCR drop number 5b, that’s when we tied everything together,” he noted. “It took all of the previous reviews, plus what was left, and tied it into a big package and said ‘We now have a complete certification of this design.’”
The pre-flight reviews ahead of Artemis 1 are going through different elements of readiness. “When you’re looking at certifying for a specific flight, there [are] four pieces,” Beaman said.
“[First] there’s the design certification, which is what we just went through, the DCR. So you certify the design to be able to meet a specific set of requirements that you specified. There’s a second piece of that, which is the operational readiness, and that focuses on looking across the ground operations, the flight operations, and your support groups in order to be able to say that you’re operational [and] ready to go execute a mission.”
“The third piece of that is the system acceptance, and that’s the hardware as designed and built,” he continued. “It has to be accepted, delivered to the Kennedy Space Center, and you have to make sure that you understand that it met all of its requirements in order to be accepted and ready to integrate into that operational process.”
“And then the fourth piece of that is the mission certification, and that’s really saying the design, the operational readiness, and the accepted hardware are coming together and we will be able to take this vehicle and execute a specific mission in time going to a specific location. So it’s looking at the actual hardware as designed, as ready to be flown, and are you going to be able to go do everything you said for that specific mission.”
(Photo Caption: A graphic highlighting the major elements of the SLS Block 1 Crew vehicle. Block 1 vehicles are planned for the first three SLS launches to send Orion spacecraft to the Moon.)
Beaman explained that the DCR examined the entire program. This ranged from the components of the SLS Block 1 Crew configuration for Artemis 1 to the integrated vehicle and overall organization. “It encompasses the entire program,” he said. “The elements are the hardware elements like the Core Stage or the Boosters, and so they have a design review within their organization that focuses specifically on their hardware.”
The elements within the program include the Booster, Liquid Engines, SPIE (Spacecraft/Payload Integration and Evolution), and Stages offices.
The Booster Office manages the Northrop Grumman five-segment SRB (Solid Rocket Boosters). These boosters evolved using existing hardware from the reusable four-segment Space Shuttle SRB design. The Liquid Engines Office manages the SLS application of two Aerojet Rocketdyne liquid hydrogen-oxygen engines–the RS-25 and the RL10. Four RS-25 engines are clustered in the Core Stage across all SLS designs. For the Block 1 vehicle, one RL10 engine flies on the ICPS (Interim Cryogenic Propulsion Stage) second stage.
The SLS Block 1 vehicle uses the ICPS as its in-space second stage. The ICPS is a variant of ULA’s (United Launch Alliance) DCSS (Delta Cryogenic Second Stage) with some customizations. The SPIE Office manages the application of the ICPS along with interstage and payload adapters for the Block 1 vehicle.
The Stages Office manages the all-new Core Stage produced by Boeing, which has been the pacing item throughout the program’s development. In parallel with beginning test flights of the initial Block 1 vehicle, the program and element offices are also developing their parts of the next-generation SLS vehicles, Block 1B and Block 2.
The Core Stage and Boosters are the base blocks of the SLS design. The Core Stage is a ground-started sustainer stage; it, along with the payload stacked on top, is lifted out of the low atmosphere and accelerated by two SRBs. The Core and Boosters in the initial SLS Block 1 Crew vehicle insert Orion and a fully-fueled ICPS on a high-velocity trajectory just shy of a stable orbit. This allows for a safe and targeted disposal of the Core Stage.
While the Core Stage re-enters from orbital velocity and rapidly breaks apart in the lower atmosphere before an ocean disposal, the ICPS will make a short burn with Orion on top to raise the perigee to a stable orbit. The ICPS will then make a long TLI (trans-lunar injection) burn to send Orion, itself, the connecting adapters, and ride-sharing CubeSats on a trajectory that will pass about 100 kilometers from the surface of the Moon.
(Photo Caption: A September 2020 ground test of the five-segment SLS Solid Rocket Booster is captured by a drone at Northrop Grumman’s Promontory test and production facility in Utah. Two SRBs like this will provide most of the thrust during the first two minutes of ascent.)
Beaman heads the SE&I (Systems Engineering and Integration) Office, which oversees other work such as software development and how the vehicle’s hardware elements fit and work together. “What [the SE&I] Office is responsible for is the design review for the overall vehicle, so their data feeds into the overall review and the design certification at the vehicle level which I’m responsible for executing for the program,” he said.
“Flight software is in my organization, so [SE&I is also] responsible for the development and the integration of the software activity. [That] not only [includes software development for the] elements but [we also] integrate with the Orion program, as well as EGS [Exploration Ground Systems].”
“A lot of the test capability resides at Marshall Space Flight Center for flight software and for ground software, so we’re responsible for that within my office,” Beaman went on to say. “Then there’s other portions of [SE&I], the analytical portion of the vehicle, what we typically call systems analysis, that also falls with my organizational responsibility–so all of the loads and environments, the flight trajectories.”
“The actual execution of the flight mission to get the vehicle to where it’s supposed to be in space is the responsibility of my office [as well],” he added.
Remaining programmatic work
One of the things documented coming out of the Design Certification Review was the work remaining. “Based on the things that we identified, here’s the [work] that we have left to do before we can go fly,” Beaman said. “And you document those so that you make sure that you do [them].”
A couple of open items are in the final phases of work. One is a modification to a hydrogen bleed line in the Core Stage’s engine section that is a part of the MPS (Main Propulsion System).
During the Hot Fire tests that concluded the Green Run design verification campaign for the Core Stage, the pressures seen in the line were higher than predicted. “You design the system based on your analytical predictions,” Beaman noted. “You have models and drawings, and you design the system to perform a certain function, and one of the things was the bleed-off [of] excess hydrogen.”
Beaman said that the change increased the diameter of the line to lower the pressure. “It was safe to go ahead and do the [Hot Fire] test [with the original design], but we wanted to make that hydrogen line a little bit larger so we didn’t have those higher pressures,” he said. “So what we’ve done is we’ve gone through the redesign process.”
“That redesign has been successfully tested, so we know that it will meet the requirements that we have levied upon it, and now we’re in the process of implementing that design and putting it on the vehicle. It’s gone through its full certification test and meets the requirements.”
(Photo Caption: The flight article for Artemis 1, Core Stage-1, fires in the B-2 position of the B Test Stand at Stennis Space Center on March 18 during the second Green Run Hot Fire test. The second Hot Fire ran a full 500 seconds in duration, accomplishing all planned test objectives.)
Another open item has to do with the batteries that supply independent power to the part of the launcher’s flight safety system. “We have a range safety system that is to protect the public, and it has to have an active battery system that works all the time,” Beaman said.
“Last year during the qualification of our battery system, we had a couple of design issues that we had to deal with. What we did when we failed a particular qual test is we went in and instituted a redesign effort on that particular battery to be able to meet all the requirements, but at the same time we took a parallel path with another battery.
“That’s a battery that’s used on the Booster flight safety system. We wanted to make sure that if we had a problem with qualification in the future, we had a viable parallel path to fly either one of the batteries.”
“We have met with the range, the people with the [Space Launch Delta 45] for the Eastern Range, [and] they have accepted our dual-path approach,” Beaman added. “The [primary battery] that we planned on flying all the time has successfully passed its qualification, and should we have an issue in the future, we have a backup position with this secondary battery. So we’ve successfully completed the qualification activities on both of those batteries, and now it’s just a matter of closing out the paperwork.”
The safety system and batteries are independent of the Core Stage power system and the batteries it uses to operate the vehicle. “It is a dedicated battery, and you have to have that because the whole purpose of that is you want it to work in adverse conditions,” Beaman said. “It’s a flight safety system that’s designed to protect the public, and you do not want it tied to anything else other than its intended purpose.”
Following the DCR, Beaman’s office continues to prepare for the final reviews before launch. They are also supporting ongoing flight analysis and joint simulations across the EGS, Orion, and SLS Programs. “The mission certification that I talked about, my office is responsible for that, so we will review our data prior to having our [final reviews],” he said.
“We’ll look at the final mission analysis [and] the flight readiness analysis cycles, we’ll look at the individual [SLS hardware] elements [and] the work that they’ve done, so it’s a buildup of that. [Also] at the Kennedy Space Center, [they are] not only building up the hardware down there but [conducting] launch simulations.”
(Photo Caption: In early July, the Artemis 1 ICPS is moved under a lifting beam carried by one of the heavy-lift cranes in the Vehicle Assembly Building towards the partially integrated stack. Primarily used as the upper stage for ULA’s Delta IV launch vehicle, it will be used in the SLS Block 1 as an in-space lunar transfer stage.)
“We just completed one last week [and] we have one in a couple of more weeks, so there’s quite a few launch simulations that exercise the infrastructure systems,” he added. “We have the Huntsville Operations Support Center, the (SLS Engineering Support Center), at Marshall where a lot of the data is looked at during launch countdown, so we’ll do launch simulations of that infrastructure as well as exercise our people.”
“We think it’s really important. A lot of times you’ll hear football coaches talk about [how] you need to practice like you play–we do the same thing in our business. We practice through launch simulations, and we make it look just like a launch, and we introduce problems so our team can practice solving those problems, so when we come to the actual launch day, we’re locked and ready to go.”
Multi-level Flight Readiness Review for launch and mission
Artemis 1 is the first integrated test flight of the government’s beyond-Earth ESD (Exploration Systems Development) division, which plans on the EGS launching an SLS Block 1 vehicle carrying an uncrewed Orion spacecraft from Launch Complex 39B. The SLS will then place Orion on a multi-day, trans-lunar trajectory that passes approximately 100 kilometers above the surface of the Moon.
All three programs in the ESD division under NASA’s human exploration directorates–EGS, Orion, and SLS–have reached the stage of pre-flight preparations where they are completing their final independent design reviews and are preparing for the final FRR (Flight Readiness Review). The FRR will certify that the organizations are individually ready and jointly ready as a team for Artemis 1.
“For this test flight we completed our design certification reviews, and what we’re in the process of doing now is finalizing some of the testing and the paperwork that’s required to commit to flight readiness,” Cathy Koerner, NASA’s Orion Program Manager, said in an October 22 media teleconference. “We will start that process here in the next few weeks, actually, [so] that we’re ready to support whenever the integrated stack is ready to support a launch.”
Artemis 1 will be the second in a series of three test flights for the Orion Program, which will see an initial crewed operating capability on the Artemis 2 mission. The EFT-1 (Exploration Test Flight-1) mission in December 2014 tested an uncrewed Orion Crew Module with a simulated Service Module on a short Earth orbit mission.
Artemis 1 combines an upgraded–but still uncrewed–Orion Crew Module with the first active Service Module, which allows the spacecraft to navigate into the mission’s cislunar Distant Retrograde Orbit. The Service Module will also power Orion’s return to Earth from the Moon. “This being a test flight, a lot of the mission activities and the data analysis and the things that we get out of this flight will feed into our design and certification readiness for the Artemis 2 mission when that happens,” Koerner added.
“So we’re anxious to see this mission be successful and get the test data back from this flight and fold that into our readiness for the next, crewed mission.” Artemis 2 will phase in all the Orion systems needed for a four-person crew from life support, to computer display-and-command stations, to radios for voice communications.
(Photo Caption: The Artemis 1 SLS vehicle is seen stacked in the VAB in mid-September prior to special umbilical and modal tests run prior to the upcoming first launch. A simulator of the Orion launch stack’s mass and center of gravity was fitted on top of the launch vehicle for the tests.)
“From a ground systems standpoint, we really kind of DCR [Design Certification Review] our ground systems, system by system,” Mike Bolger, NASA’s EGS Program Manager, said in the October 22 media teleconference. “We’ve completed 75 out of 76 [reviews], we’ve got one that’s coming up here in a few weeks related to [the] Pad ECS (Environmental Control System), so we’re in really good shape–everything’s on track for that.”
“We’ve accomplished all four of our operational readiness reviews, with the most recent one being our operational readiness review for integrated test and checkout, which is the sequence of tests that we’re getting ready to get into now. So we’re in a really good position to move forward with the testing that we’ve got in front of us.”
Similar to the design certification of Artemis 1’s launch vehicle, certification of flight readiness will be a multi-level series of meetings from the major flight and ground systems components. It will culminate in an agency-level FRR meeting–perhaps only a week before the first launch attempt.
“It’s a building block approach, so each one of the elements will have their flight readiness review, and then they will provide a certificate or an endorsement of flight readiness for their hardware,” Beaman said, referring to the SLS process. “So it’ll identify what they’ve done, and if anything is left to be done it documents that as a constraint, so you make sure that you do it [before launch].”
“Each one of the elements will go through [their own review], and that includes flight software. Then I will have a Systems Engineering and Integration review that ties the different analyses and processes that have happened up to that point together, and then after that, there will be [an SLS] program-level flight readiness review.”
After the EGS, Orion, and SLS Programs hold their program-level reviews, ESD will hold a division-level review. ESD is responsible for cross-program integration between the spacecraft, launch vehicle, and ground systems. This will be one of the aspects of the FRR at the ESD level.
The process will culminate in an agency-level flight readiness review to assess NASA’s overall readiness to support the launch, the mission, and recovery of the spacecraft at its conclusion. “We’re in essence presenting to the [NASA] Administrator and recognized technical authorities that we’re ready to fly,” Beaman noted.
If the agency gives the go-ahead to proceed at the FRR, they will conclude by endorsing an official launch date for Artemis 1.
Lead image: Two views of the completed Artemis I stack inside the Vehicle Assembly Building. Credit: NASA/Radislav Sinyak