Final design refinements
The flight test data from the AA-2 test is also showing that the existing design has better margins for the extremes of an abort case. “The abort motor acoustics are one of the biggest factors that we have to deal with, with respect to the ogives which was a huge concern going into the test,” Decoursey explained.
“Thanks to the AA-2 data we have been able to show increased structural margins in many areas. Some of our predictions were higher than they needed to be and so what we’re finding now is that some of those low margins that we went into the test with are actually much better.”
The ogives are the main aerodynamic fairing that encapsulates the Orion Crew Module during the early part of ascent. Named for its shape, the ogive is assembled from four pieces that connect to two fillet panels that provide additional streamlining from the LAS abort motor and truss adapter to the ogive shroud.
(Photo Caption: The hatch in the LAS ogive fairing is open to allow access to the Crew Module test article for AA-2 in early May. The four ogive panels and the two fillet panels above them provide most of the aerodynamic fairing for the Orion Crew Module.)
An emergency abort would be a stressing case above and beyond normal flight, and the system has to have the margins to handle the range of emergency abort case. “The AA-2 loads that we saw completely envelope all nominal trajectories,” Decoursey said.
Decoursey also noted that the ogive panels flown on AA-2 had extra reinforcements to account for the lower margins predicted by the models. With the test data showing better margins than expected pre-test, those additional, complicating reinforcements shouldn’t be needed.
“For AA-2 we actually ended up putting in some metallics, some bolts through the ogives to raise the margins,” he said. “Well that sort of hardware is not going to be necessary any more and with that hardware comes engineering requirements to do all the analysis to show where to make those changes.”
“So that’s not necessary any more [and] the ogive becomes a much easier element to build. The engineering team believes that with the design changes that we will not only meet schedule, but the cost eventually will come down below where they are today.”
“For Launch Abort System that was really the biggest concern we had going into the test, at least as far as the margins we were seeing,” Decoursey said. “One of the big things we also have to deal with or show is that we don’t recontact anything when we separate.”
“When we pull off the booster when the abort motor fires and we come away from the booster we have to show no recontact and we do that with accelerometers and strain pods and all that data looked good, we did not recontact the ATB. And then when we separate from the Crew Module we fire the jettison motor and once again we use strain pods and accelerometers to prove that we don’t recontact and we did not.”
“And so the attitude control motor and the controller that drive the ACM all functioned perfectly. We don’t anticipate any changes to that for Artemis 2.”
“Right now the only part that we are foreseeing mods (modifications) is like I said to those fairing panels and those changes are well underway already and like I said not only are we expecting to be well ahead of schedule, but also we expect our cost to come down as well.”
For Artemis 2, Decoursey noted that the Jettison and the Abort Motors are already delivered and the Attitude Control Motor is scheduled for delivery in February, adding that all of the LAS Artemis 2 hardware is on schedule to arrive at the launch site in Florida by next summer.
(Photo Caption: The three separated elements of the AA-2 test vehicle now more or less in free fall following the dynamic portion of the test. The burned-out Abort Test Booster with the still-attached Separation Ring of the Flight Test Article is lower left. Top middle, the Launch Abort System motor tower and aerodynamic fairing. The Crew Module test article (middle right) is still busy retransmitting data recorded during the dynamic phase of the test. The twelve EDRs were ejected from the top of the Crew Module simulator in pairs using a military chaff deployment as it fell to the water.)
The acoustic data collected in the test was also an interest for some Crew Module qualification work. “We did see acoustics lower around the heatshield which is one of the areas we had concerns with because that’s where a lot of the Crew Module avionics are located,” Decoursey said.
“There were two things called out specifically,” Corpening added. “One was the heatshield loads and that in turn looks like it’ll result in a reduced loads in an upcoming heatshield risk mitigation test. And then also the windows, it looks like the loads on the windows would be reduced in an upcoming qual test.”
Collecting acoustic data was similar to a 2017 ground qualification test firing of the Northrop Grumman abort motor, which used a test fixture to measure acoustic levels in the relative location of the heatshield. In the AA-2 test, the LAS provided shielding for the Crew Module test article; however, the boilerplate was not a perfect analog for the spacecraft structure.
“Part of the challenge the subject matter experts have is because we had a boilerplate Crew Module, the structural responses are somewhat different than they would see for Artemis 2 with the abort system on board,” Corpening explained. “So it takes them a while to look at the data for the boilerplate and then transfer those lessons learned to an updated model for the actual Crew Module hardware and that’s some of the activities in work as we speak.”
The AA-2 test was a critical milestone towards qualifying and certifying that the LAS is ready for the first crewed Orion mission on Artemis 2. While the review and analysis of data from the test continues, other work continues to support interim milestones and flights.
(Photo Caption: The third and final jettison motor qualification unit is test-fired on October 16 at the Redstone Arsenal in Alabama. The propellant in this “ambient” test was not conditioned; previous tests fired qualification units conditioned to “hot” and “cold” temperatures.)
Qualification of the three LAS motors is nearing completion, with one additional ground test scheduled for the attitude control motor and the abort motor. The third and final Aerojet Rocketdyne jettison motor qualification article was fired at the Redstone Test Center on Redstone Arsenal in Huntsville, Alabama, on October 16.
“The way the process works is that we qualify everything on the ground,” Decoursey explained. “So for instance the jettison motors, we fire three of those, a hot, cold, and an ambient and we just fired the last one last week down at Redstone, so our jettison motor except for the final report is fully qualified for Artemis 2.”
“Our last ACM qual motor is next month, that’ll finish up the atttitude control motor as far as qual is concerned, and then we have an actual structures test next year. AA-2 is a demonstration that the system operates as intended under very severe conditions, Max-Q and transonic.”
Structural test articles for all the main Orion elements are undergoing testing both individually and integrated together by Orion Prime Contractor Lockheed Martin in the Structural Test Lab at their Space Systems Waterton facility in Littleton, Colorado.
“AA-2 informs everything, basically the noise shakes everything and so you’re looking at how that shaking induces loads in the ogives and the rest of the hardware and so all of that certainly informs our structural test,” Decoursey noted. “Our final structures test is right now scheduled for next August I think.”
All of the qualification testing and certification work leads up to the Artemis 2 mission forecast for launch no earlier than late 2022, where a fully-outfitted Orion will take a crew of four on a test flight first in a high Earth orbit, and then on a Lunar flyby to demonstrate that the spacecraft is ready to begin supporting lunar landing missions. “All the hardware goes through hardware acceptance reviews and we have engineers that go to these reviews at the vendors and everywhere else,” Decoursey said.
“There’s a long certification process so all of the subsystems go through a cert review process with both Lockheed and NASA in attendance. That all culminates with a system acceptance review and a DD250 (a form signifying government acceptance of contractor deliverables), so for us all that for Artemis 2 happens next summer and next fall.”
(Photo Caption: Artemis 1 LAS integration in the Launch Abort System Facility (LASF) at Kennedy Space Center in mid/late August. As with the first Orion test on Exploration Flight Test-1 (EFT-1), Artemis 1 will fly with no flight crew and this LAS unit will similarly fly with only a live jettison motor. The abort and attitude control motors for Artemis 1 are inert. Elements of the Artemis 1 LAS unit were fabricated prior to the AA-2 hardware using earlier designs. The black, composite cone of the Motor Adapter Truss Assembly (MATA) for Artemis 1 seen here is the last of its kind. The cone was updated for AA-2, Artemis 2, and beyond to a metal alloy design. When fully integrated, two fillet panels cover the MATA cone providing part of Orion’s aerodynamic launch fairing.)
The LAS will not be active for the Artemis 1 launch that is forecast for 2021, but it still serves as the aerodynamic launch fairing for Orion and will be heavily instrumented like the rest of the vehicle for the first integrated Orion/Space Launch System (SLS) launch. Although the abort motor and the attitude control motors are inert, as on Exploration Flight Test-1 (EFT-1) and all nominal launches the live jettison motor will pull the assembly off the Crew Module after the spacecraft and launch vehicle climb through the lower atmosphere.
Decoursey noted that the LAS for the launch is already assembled at the Kennedy Space Center launch site. “Artemis 1 for us is fully stacked down at the LAS Facility, so our Artemis 1 Launch Abort System is finished and sitting in storage.”
Lead image credit: Mike Deep for NSF.