AA-2: Orion’s in-flight abort test successfully completed

by Philip Sloss

NASA performed an in-flight test of the Launch Abort System (LAS) for its Orion crewed spacecraft Tuesday morning from Cape Canaveral Air Force Station (CCAFS) in Florida. A highly instrumented test article simulated the Orion Crew Module, connected to a flight version of the LAS and a Peacekeeper missile modified to be the booster for the Ascent Abort-2 (AA-2) test.

Lead Photo by Brady Kenniston for NSF/L2.

Lasting only three minutes from liftoff to ocean impact, the purpose of the atmospheric test was to demonstrate the production LAS and to collect detailed data on its performance. The LAS is designed to instantly pull the crew module away from its launch vehicle in extreme emergency situations that might occur before or during launch.

The key sequence in the short flight was an even shorter period of twenty seconds or so where the LAS pulled the Crew Module simulator away from a firing solid rocket motor.

The LAS is designed to quickly separate a crew in Orion in a launch emergency, get them as far away from the emergency as safely possible, and allow the Orion Crew Module to parachute into the ocean.

Ascent Abort-2 (AA-2) intentionally runs that emergency abort sequence. Three motors in the LAS fired in that short sequence of a few seconds and then the test was essentially over before the three minutes was up while the hardware was airborne.

NASA and its Orion contractor team recorded test data from real-time telemetry and in onboard data recorders, but the major hardware for the test fell into the ocean. A set of a dozen data recorders were ejected from the Crew Module test article for recovery before it hit the water and sunk.

Three-minute test within four-hour launch window

Liftoff occurred at 7 am Eastern time (1100 UTC) Tuesday at the opening of a four-hour launch window. The test vehicle launched from Launch Complex-46 at CCAFS.

AA-2 lifts off – via Jack Beyer for NSF

AA-2 was a test of the Orion LAS, the second and last planned for the program. The first, Pad Abort-1 (PA-1), was conducted in 2010. “[They are] the two, I’ll call them corners of the box that represent the most challenging conditions,” NASA Orion Program Manager Mark Kirasich said.

The PA-1 test represented an abort from standing still on the launch pad. “When you’re starting from a standstill, the most important thing is to get far away so that the wind doesn’t bring you back in,” he added. “So when you’re starting from a standstill it’s all about thrust times time, the area under the curve, to get away as far as you can.”

AA-2 tested the LAS under challenging atmospheric flight conditions. “It’s not exactly at the maximum dynamic pressure, because we want to get a couple of different objectives but you’re going really fast and you’re still in the atmosphere,” he said. “So there’s a tremendous air pressure which exerts a force as this abort system is trying to pull you away.”

“The aerodynamic factors are trying to keep you in place so that’s the key thing about the in-flight abort test, to make sure that we can not only overcome [the aerodynamics]. The harder part is to control, because the aerodynamics are pushing you all over the place under those circumstances.”

Credit: NASA/Ames/Timothy Sandstrom.

(Photo Caption: Image from a video of an Orion abort simulation produced by the NASA Advanced Supercomputing (NAS) Division at Ames Research Center. Colored plumes indicate high pressure (red) and low pressure (blue).)

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 and the program had to pick a single abort condition to test.

“In the Constellation program we did have more in-flight abort tests planned and what we did was we picked apart that in-flight profile more,” Kirasich said. “I’ll give you a ‘for example.’

“When you abort at a very high altitude there’s less atmosphere, so there’s not as much aerodynamic force on the vehicle. So you have to control your attitude differently, [in that example] it’s more of a reaction control system thruster test as opposed to where we’re right in the thick of the atmosphere it’s really the [LAS] attitude control motor that we’re testing, the dynamics in that.”

“So we spread the test points around and the point that we’re doing on AA-2 is the combination where we get kind of a smorgasbord of the most-challenging conditions,” Kirasich explained. “Perhaps not the hundredth-percentile of every one of the five or six key parameters but ninety-eight percent at most of them, and that’s why we picked the test conditions that we did.”

The data collected in the test will help to validate existing computer models, which will be used to simulate test cases throughout an envelope of possible abort conditions.

Final countdown

Jennifer Devolites, NASA’s Test Conductor for AA-2, outlined some of the final countdown milestones. “The tower rolls back at about four hours, 45 minutes,” she said. “ATB (Abort Test Booster) final arming starts around three hours, so we start clearing the pad at that point in time.”

“With our Flight Test Article we actually have to upload the wind tables for the day; we do that at about T-2 hours and we reboot our flight computers. As we press towards T-0 we do another couple of functional tests of our system and ATB does a functional test.”

“The ‘Go/No-Go’ call is at T-16 minutes and at T-12 the ATB programs the T-0 [time] into their flight computers,” she added. “We don’t have any holds, but if we have any weather issues or a boat in the box or anything like that we have lots of opportunities to hold and recycle.”

AA-2 on the pad – from Brady Kenniston for NSF

The test has the same set of standard launch weather criteria, but also includes customer-specific rules. “This one is a little bit trickier because there’s a lot of tests going on with this particular launch that they want to be able to film and so one of the user constraints that we have is cloud cover,” Will Ulrich, Launch Weather Officer with the U.S. Air Force 45th Weather Squadron, said.

“They don’t want any more cloud cover than 3/8ths of the sky because they have seven cameras that are going to be trained on this particular rocket that they need to ensure can film during the entire duration of the test, so that’s our primary concern tomorrow.”

“Tomorrow (July 2) we’ll still enough moisture that we think some scattered clouds, particularly in the mid and upper levels may hinder their ability to view the launch, but overall conditions do look favorable that’s why we’ve got right now a 30 percent probability of violation, mainly for that user constraint I just described,” Ulrich added.

“The launch as I understand it only goes up to about 44-45,000 feet so any clouds in between the surface and that point we’re going to be evaluating.”

Test sequence Overview – Pre-test:

The abort was triggered when the vehicle was traveling at approximately Mach 1.3 at an altitude of around 31,000 feet. After liftoff, the booster took the vehicle up to the abort condition and then signals the crew module.

“We’re actually steering to a very precise test point and so we’ve got functions in our algorithms that are predicting where we’re going to be based on the performance of the motor, which will vary, and so we’re predicting when we’re going to be exactly in the box and we’ll send the signals when we hit the optimal point,” Phil Joyce, Vice President of Small Space Launch for Northrop Grumman Innovation Systems, said. He added that the booster should reach the test point in about fifty-five seconds from liftoff.

“The booster is responsible for getting us to the abort condition and then based on the signal to us to say ‘we’re here,’ we execute the abort and perform the rest of the flight after that,” Devolites explained. “It’s over Mach 1, and it’s a high dynamic pressure, and it’s a combination of angle of attack and a couple of other parameters.”

The LAS has three different motors that fire at different points in the test, the abort motor, the attitude control motor (ACM), and the jettison motor.

When the abort is initiated, the abort motor instantly generates about 400,000 pounds of thrust at ignition, putting loads on the abort vehicle of twelve to thirteen g’s to get away from the booster, while the ACM also fires to control the flight of the vehicle.

LAS fires during the AA-2 abort – via Jack Beyer for NSF

The abort motor fires for about five seconds with the thrust tailing off while the ACM puts the vehicle in a safe attitude. The ACM then reorients the vehicle for the separation events, followed by firing of the jettison motor to separate the LAS from the crew module.

Devolites said it’s about twenty-seven seconds from the abort command to jettison of the LAS from the Crew Module simulator.

The SR-118 motor burn time is just short of a minute, so the abort is expected to occur a few seconds before it burns out. “The booster is close to burnout, it will continue to burn and then fall into the ocean in one piece,” Robert Douglass, Launch Operations Branch Chief of the Small Launch and Targets Division at Kirtland AFB, said in an email.

“We’ll still be trying to fly but now we’ve lost our front section, so we’re just this giant beer can, so we expect it to tumble,” Joyce noted. “The Air Force has validated a bunch of recontact analysis to make sure a tumbling booster won’t come back and contact the Flight Test Article. We’re tailing off as they pull away at 7-gs, so they’re pulling away pretty quick.”

LAS pulling Orion away from the booster – photo from Mike Deep for NSF

The Crew Module test article is qualified as a short-duration, low-atmosphere, flying test device rather than a long-duration, cislunar spacecraft. It resembles an Orion Crew Module on the outside in size and shape, but inside is equipped just to pull off this uncrewed abort test.

The computers on-board will carry out the abort and transmit and collect as much data as possible in that time. Once it is in free fall, it will eject a dozen data recorders before water impact.

Orion hits the water – photo: Mike Deep for NSF

To manage costs, the single-purpose test article has no requirements to fly into orbit, navigate from the Earth to the Moon and back, or re-enter Earth atmosphere and parachute to a low-speed splashdown. Lacking all of that equipment allowed NASA to avoid certifying any of that for any of those phases of spaceflight or for emergencies in any of those phases of flight.

The Crew Module test article, along with the expended LAS and booster, will all break up on water impact and are not intended to be recovered.

Data from nine-hundred sensors measuring temperatures, pressures, accelerations, and acoustics will be collected during the test. The test article will transmit the data collected during the test to the ground and also record it to onboard, ejectable recorders. The AA-2 team is using another off-the-shelf system in order to recover the recorders.

Credit: NASA/Kim Shiflett.

(Photo Caption: Practicing recovery of one of the orange-colored ejectable data recorders last August. The twelve recorders will be ejected from the Crew Module while it is falling into the ocean after the test.)

“The deployment system we’re using is ALE-47, which is a military, Air Force chaff deployment system,” Devolites explained. “It’s an ejection system for fighter aircraft for the chaff or the flares and so we said that’s perfect, we just need an ejection capability to get the data recorders out. We’re using that system and [the recorders] are just built very robust, so they can just eject and drop in the water and then survive.”

There are twelve recorders grouped in two sets of six located at the top of the crew module simulator on opposite sides under the simulated forward bay cover. After the jettison motor fires to pull the LAS away from the crew module, the simulator will free fall to the water.

“The recorders start getting ejected about twenty seconds after LAS has jettisoned,” she noted. “We wanted to continue collecting data during free fall and not just immediately start ejecting. They eject in pairs and we eject every ten seconds so that way we get more and more data as we get down.”

The recorders are designed to float and have beacons to expedite locating them for recovery.  “We only need one to give us everything up through twenty seconds after LAS jettison, but we keep ejecting basically as long as we can,” she added.  “Those are redundant as well so you get a pair — one from each side on each ejection.”

The LAS can be used for Orion Mode I aborts while the spacecraft is still on the pad and during launch up to altitudes of 300,000 feet. During a nominal SLS crew launch, the jettison motor will fire to separate the LAS from the CM and the rest of the launch vehicle about three and a half minutes after liftoff.

Once the LAS is jettisoned, Orion still has Mode II and Mode IV abort capabilities where the spacecraft separates from the SLS. If the spacecraft has enough altitude and forward velocity, it could Abort To Orbit (ATO, Mode IV); if not, it would configure itself for a long, downrange water landing in the Atlantic.

A diagram of Orion launch abort modes using the LAS. Credit: NASA.

The test had been placed on the schedule in December, 2019, between the EM-1 and EM-2 (now Artemis 1 and Artemis 2) cislunar test flights, but was moved up to April, 2019, following the feasibility study of placing crew on the EM-1 mission that was conducted in early 2017.

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