All the elements of the NASA flight test vehicle for the Orion program’s Ascent Abort-2 (AA-2) test in early July are now at Launch Complex 46. The test booster was stacked on the launch pad in April and overnight May 22 into May 23, the test article was rolled from a Kennedy Space Center (KSC) integration facility to the Cape Canaveral launch pad, where the Launch Abort System (LAS) test is set to begin.
AA-2 is a test of Orion’s LAS, and the production version used in the test is planned to fly with spaceflight hardware beginning on Exploration Mission-2 (EM-2), the first planned crewed mission now called Artemis 2.
Other versions of the LAS that have flown or will fly on launches of uncrewed Orion vehicles only have one of the three solid rocket motors active to allow the weight of the system to be jettisoned during ascent to improve launch vehicle performance.
This will be the second and final planned LAS test following the Pad Abort-1 (PA-1) development test conducted in 2010 as a part of the ccanceled Constellation Program and the abort system design changed from PA-1 to AA-2 both inside and outside.
Test article joins booster at launch complex
The flight test article (FTA) was slowly moved on a transporter from the Launch Abort System Facility (LASF) at KSC to Launch Complex 46 (LC-46) at Cape Canaveral Air Force Station (CCAFS), reaching the launch complex early in the morning of May 23 in preparation for a scheduled daybreak test on July 2. The FTA consists of an Orion Crew Module (CM) test article attached to a Separation Ring below, with the production LAS attached structurally to the top of the CM.
The LAS also includes an aerodynamic fairing that encloses the CM. To reduce overall costs, test-specific hardware was built rather than using or manufacturing a full, lunar Crew Module flight article. Lockheed Martin is the prime contractor for the LAS and for the overall Orion system.
Since the test is demonstrating the performance of the LAS, recovery of almost all the hardware is not a requirement; the output of the test is data. “We have DFI (Development Flight Instrumentation) sensors up and down the Launch Abort System stack, all kind of pressure sensors, sound sensors,” Mark Kirasich, NASA Orion Program Manager, said in an interview last week.
Data will be transmitted from the test article in real-time for ground stations to record, but will primarily be recorded onto a dozen storage devices that will be jettisoned from the Crew Module simulator in-flight following the conclusion of the test. The test is essentially over when the LAS separates from the Crew Module; the onboard data recorders will be ejected from the Crew Module simulator in pairs prior to impact after free fall into the Atlantic Ocean.
The FTA will now be attached to the top of the Abort Test Booster (ATB), which was assembled on the launch pad at LC-46 in April. “The motor was moved out there, the aeroshell moved out there and put on top, there’s closeouts you know to kind of seal it at the bottom and the top they’re all installed, so it is essentially ready and waiting for us,” Kirasich said.
“The SR-118 went to the pad first, it was stacked and then we brought the TRS (Thrust Reaction Structure) and the GCA (Guidance Control Assembly) as one assembly and it was stacked on top of the motor,” Joe Voor, NASA Operations Integration Lead for the Orion Flight Test Management Office, explained during the interview. “It actually rests on top of the motor, all the thrust reaction is done through the motor body itself and then the aeroshell was brought out and set over top of that whole assembly.”
“It sits on top of the Thrust Reaction Structure and so that force is reacted through the motor as well and all the ballast plates are stacked on top of the aeroshell.”
The SR-118 is a Northrop Grumman solid rocket motor that is the booster for the test. Its original purpose was as the first stage of the Peacekeeper Inter-Continental Ballistic Missile (ICBM). The Peacekeeper program was deactivated in 2002 and today the motors in the inventory are used for commercial purposes such as space launches.
The separation ring simulates the Crew Module Adapter that the Crew Module is attached to for flight articles; at 5.5 meters in diameter, it is significantly wider than the SR-118 and the TRS and aeroshells are adapters to connect and streamline the overall flight test vehicle.
(Photo Caption: Elements of the AA-2 Abort Test Booster (ATB) are lifted into place at Launch Complex-46 in April. From left to right, the SR-118 solid rocket motor is lifted onto the launch mount on April 12, the TRS/GCA assembly is lifted up into the mobile service tower to stack on the SR-118 on April 16, and finally, the aeroshell that fits over them is lifted for installation on April 18.)
The combined Crew Module Separation Ring (CSR) assembly was integrated at the Johnson Space Center in Houston last year and shipped to KSC in December. Overall test preparations were slowed down by a five-week long partial government shutdown, but following checkouts with the booster GCA, the assembly was moved into the LASF for integration with the LAS.
“We’re in the LASF and the Launch Abort System is mated to the Crew Module Sep Ring, all the ogives are installed,” Kirasich said in the interview on May 16. “We put over a hundred pounds of RTV — it’s white sealant — to seal up all the gaps, cover up all the fasteners to make sure no water gets in, and we finished the last part of that yesterday and today. Today and tomorrow we’re doing an interface checkout between the LAS and the Crew Module, and then we roll out next Wednesday, the 22nd.”
While out at the pad, booster and the test article will be surrounded by a mobile service tower and hooked up to purge loops to keep their electronics dry. “We have a purge, big purges,” Kirasich said. “One that goes to the Abort Test Booster and then one that goes up to our Flight Test Article and it’s cool, dry air. There’s a big brown cooling cart and it’s got two big hoses, one each to those two vehicles. It’s out there in the damp Florida June summer and we get rained on every day. We don’t because we’ve got a roof over us but it’s still very humid so we keep everything nice and cool and dry.”
The last few weeks of work are to connect everything up, test it, and go through a few training simulations. “At a high level we do our initial stacking operations starting as soon as we get out to the pad, the very next morning,” Voor said, referring to the FTA and ATB.
“When we get out to the pad we’ll stack the FTA on top of the ATB and then we have some installations to do. [We will] do the mating operations between the ATB and the FTA, do the final mates and harness connections for the DFI that’s going to be connected, and then we install the outer mold line panels around the sep ring.”
(Photo Caption: The underside of the Separation Ring that connects the AA-2 Crew Module test article and LAS to the Abort Test Booster is visible as the FTA was lifted onto the transporter recently.)
“Then we’ll do some integrated testing to verify that we’ve got good functionality, that we can talk to the Range, all of our antennas are working,” he continued. “And then we actually have a couple of weeks of contingency built in because we have some potential range conflicts with [another] launch. They’re going to be required to use our control room so we have a couple of contingency weeks in there.”
An Atlas V is scheduled to launch the fifth Advanced Extremely High Frequency satellite (AEHF-5) for the U.S. Air Force in late June. “It’s not really contingency, it’s because we have potential range conflicts so it’s kind of to accommodate for that and for the potential that lightning and bad weather may keep us from getting some of the work done out at the pad,” Voor added.
“We have to clear personnel when there’s lightning out there and of course we’re hitting that time of the year when the lightning storms are coming in every afternoon. We do two launch rehearsals on the 3rd and 8th of June and then we have a Mission Dress Rehearsal on the 19th of June and then the final preps for launch start on about the 22nd of June,” Voor said.
Test focuses on the LAS
During the test the LAS will pull the Crew Module away from the separation ring, which will stay attached to the test booster. Following liftoff the booster will take the vehicle up to a carefully chosen abort condition, where the Crew Module will send the abort command to the LAS to fire the Abort Motor to rapidly get away from the booster and the Attitude Control Motor for steering. Northrop Grumman is the prime contractor for both motors.
“Inside the Crew Module there’s a computer that gets data from SIGIs that senses the accelerations and it’s the computer inside the Crew Module test article that then talks to an avionics box called the Attitude Control Motor Controller, the ACM controller,” Kirasich explained. “The computer in the Crew Module tells us which way to steer and then it’s the ACM controller which controls the pintles and the thrust of the pintles and steers it.”
(SIGI is an acronym of acronyms, Space Integrated GPS/INS or Space Integrated Global Positioning System/Inertial Navigation System.)
(Photo Caption: The elements of the flight test vehicle for the AA-2 test on the left. On the right, the elements of the Launch Abort System, which are currently being stacked in the LASF.)
“It’s a closed-loop control system, so it’s sensing rates and that’s what allows it to cover a wider range of survivable initial conditions because you can imagine depending on what happens to the rocket underneath you can have initial rates imparted so the LAS senses those rates, nulls the rates out, and steers away,” Kirasich explained. “Remember we’re going to be launching on a vehicle with solid rocket motors, so one of the scenarios is the rocket tries to chase us, so the LAS does essentially a pitch maneuver to steer it on the flight path and away from the launch vehicle.”
“It’s continuous throughout the duration of the abort firing and actually until it flips the Crew Module over. Actually flipping the Crew Module over it’s just doing a pitch maneuver itself, but it’s a closed-loop control.”
There are eight pintles in the Attitude Control Motor that steer the combined LAS/CM “Launch Abort Vehicle” during an abort. “It’s the valve that modulates the thrust out each one of the nozzles,” Kirasich explained.
“What the pintles do is the total thrust that comes out of all eight nozzles has to remain constant, but it modulates,” he said. “So while one is open on one side it closes the other so it modulates which direction you push.”
“It’s a solid rocket motor; you have to make sure the pressure is always constant so you’ve always got to have the sum total of the pintles open to allow the same total force.”
(Photo Caption: A frame from video of a March test of the Orion LAS Attitude Control Motor. The differential thrust is used to steer the combined LAS and Crew Module during an abort sequence.)
The LAS then separates itself from the simulator after the ACM reorients the Crew Module simulator. The simulator is not equipped with parachutes, but it will continue collecting and transmitting data until ocean impact less than three minutes after liftoff.
Evolution of LAS design
The AA-2 test is the second and last planned abort test for Orion. The first test was Pad Abort-1 (PA-1) in 2010, which tested an early version of the LAS in an abort starting at rest on the ground. At the time, Orion was still a part of a Constellation program that was being shut down ahead of the proposed cancellation.
After the Orion program was re-scoped following its cancellation along with all of Constellation, the AA-2 test was the only in-flight “ascent abort” test brought forward. Data from PA-1 was used as a part of a wide set of modifications to internal and external LAS components.
“PA-1 was a development version of the LAS and after that all the lessons learned from the structure, the three motors, and the controller, there were tweaks made to every one of them to the flight version, which is going to fly on AA-2 and EM-2,” Kirasich said. “The only difference from those to the other missions were the inert motors.”
(Photo Caption: A side-by-side overview of the production LAS configuration (left) and the PA-1 test configuration (right), as briefed at the time of the May 2010, PA-1 test. An early development test of the LAS abort motor in 2008 identified higher than expected acoustic loads which in part led to the move to the current design that included an ogive-shaped fairing that fully covers the Crew Module.)
Both the other missions, Exploration Flight Test-1 (EFT-1) in 2014 and Exploration Mission-1 (EM-1, now called Artemis 1) forecast for 2021 are uncrewed, so the abort motor and the ACM are inert and can’t be fired. Only the jettison motor is live for those two flights, which allows the LAS and its mass to be jettisoned during those and other nominal launches to improve overall launch vehicle performance to orbit insertion.
In an abort case, the jettison motor separates the LAS from the Crew Module at the end of the LAS firing sequence. Aerojet Rocketdyne is the prime contractor for the jettison motor.
The outer mold line changed after PA-1, with more aerodynamic fairings added around the abort motor and the Crew Module. “There is a very fond name for what we flew on PA-1,” Kirasich noted. “It was called the ‘party hat’ and if you looked at it, it kind of looked like a party hat.”
“There was always a cover at the bottom of the LAS that covers the Crew Module so when you fire the abort engines you don’t put char on the windows and all that,” he explained. “There were several iterations of the party hat but when we built PA-1 that was the version of the cover if you will.”
“And then [with] natural design maturity in the 2010-ish, [2009-2010]-ish time frame we developed this ogive which is a much smoother aerodynamic surface with the fillets,” he added. “We changed from the party hat to the ogives to provide a more aerodynamically sound vehicle, so it transitions through the atmosphere cleaner and the abort loads when the abort motor fires, these ogives provide better damping of the sound waves through to the Crew Module structure, so it had several benefits.”
The ogive fairing is made up of four panels, which have to account for access inside the Crew Module and other external protuberances around its circumference. A hatch on one of the panels will be linked to the hatch on flight articles.
“This is the first time we’re flying this config in the LAS,” Kirasich said. “[This] is a production LAS and that is for all practical purposes the first production version of our LAS hatch.”
(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 side hatch to Orion flight article Crew Modules will be linked to the LAS hatch to allow flight crews to more quickly exit in the contingency case of an emergency launch pad evacuation. The AA-2 Crew Module test article has a bolt-on hatch.)
“On EM-1 and EM-2 there’s an interconnection between the Crew Module and the LAS hatch such that you open the Crew Module it pushes the LAS hatch open.” Each of the ogive panels is unique.
“They’re very similar but they’re not identical,” Kirasich added. “Another one has got a cutout for where the umbilical comes in, there’s an umbilical between the Service Module and the Crew Module and not only does it have to go into the Crew Module but it has to go through a cutout in the LAS ogives.”
“There’s other things like there’s vent lines and all that, so everyone is a little bit different.”
“There’s little what they call tangential fittings that control how the tangential forces are put on the [fairing] so they all have their little cutouts,” Voor added. “They’re definitely unique and they are not interchangeable.”
Outer mold line changes are only part of the differences between the PA-1 and AA-2 designs. “After PA-1 we made small changes to just about everything,” Kirasich said.
“There were small changes to each one of the motors. The abort motor that flew on PA-1 had a maximum thrust of five-hundred thousand pounds and after PA-1 we shrunk it slightly and our flight version for the rest of Orion it’ll have a thrust of four-hundred thousand pounds.”
“Once the system was fully designed and we knew what the Crew Module weighed, we did not need quite as much maximum thrust and by going from five-hundred to four-hundred thousand pounds we were able once again to reduce the acoustic loads on the spacecraft, so that was the big change for the abort motor.”
“Moving up the stack on the jettison motor, we actually changed the design of the insulation inside the motor to make it more reliable,” he continued. “The jettison motor is the motor that has to fire every single flight and we learned something about the way the insulation protected the rest of the structure from the hot gases inside the motor, so on that one there were some very small insulation tweaks.”
“Continuing up the stack all the way to the ACM, that worked on PA-1 but you can imagine these are really hot, super hot, very high pressure gases, imagine being a solid structure inside of a burning solid rocket motor. When we did the development test prior to PA-1, we didn’t have the factors of safety.”
“So through development testing we verified and improved the structural factor of safety with these pintles in the ACM since the last one,” he added. “And by the way we redesigned the controller to eliminate a few quirks of the initial design.”
Lead image credit: NASA/Frank Michaux.