From Spaceflight Insider: “AA-2 – NASA’s JSC Getting Orion Simulator Ready for Key Test”

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Spaceflight Insider

April 30, 2018
Philip Sloss

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Crew module simulator for AA-2 test at JSC, April 26. The blue tape covers pressure sensors installed for the test. Credit: Philip Sloss for NSF/L2.

NASA is getting the hardware ready for an important test next year of the launch abort system (LAS) that Orion spacecraft will use during launch on missions to the Moon in the 2020s. At the Johnson Space Center (JSC) in Houston, Texas, a crew module simulator is being outfitted with equipment to turn it into a short-duration, high-speed flying laboratory by the end of the year, and then be connected to the rest of the test vehicle that is planned for launch in April, 2019.

The Orion 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 highly instrumented crew module simulator will be connected to a flight version of the Orion LAS and a Peacekeeper missile being modified to be the booster for the Ascent Abort-2 (AA-2) test.

The booster will take the vehicle up to a carefully chosen abort condition, where the LAS will fire to pull the top of the stack away. The LAS will then flip the crew module simulator around so it is in the right attitude for a real spacecraft to deploy parachutes for a soft landing before separating from the 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.

Crew Module Simulator Preparations

The structure of the crew module simulator was constructed at NASA’s Langley Research Center in Virginia before being transported to JSC in March. A little less than two months after arriving in Houston, JSC held a media day on April 26 to talk about work there to get ready for the test next year.

The AA-2 team at JSC is adding only the required test equipment inside and outside the simulator to command the dynamic parts of the test, while simultaneously collecting all of the desired test data and transmitting and recording it.

“There’s not a whole lot in there right now,” Jennifer Devolites, AA-2 crew module deputy manager for NASA, said. “We don’t have crew systems, we don’t have life support systems, but we have all the avionics and power, all the wiring and harnessing that has to be installed, all the instrumentation.”

“You can see some blue tape on the outside, those are protections where we have pressure sensors installed,” she added. “We’ve only done about half of the sensors that need to go on the vehicle, all that gets installed.”

To save money it was decided to use a crew module simulator for this test rather than launch a more flight-like crew module, such as the one that flew on Exploration Flight Test-1 (EFT-1). The LAS itself, which is fully active and fully exercised in the test, is a production unit. “The separation mechanisms, all of that is production [equipment],” Devolites also noted.

As with the simulator, the test avionics are not flight units. “Basically all the powered systems inside are different from the mainline Orion,” Devolites explained. “We were able to use a lot of commercial, off-the-shelf [systems since] we’re not going to space. And so we were able save a lot of money by using mostly off-the-shelf components for a lot of that equipment rather than going with spaceflight-qualified systems that are used on the mainline Orion.”

“The only piece of the software that’s the same is the guidance, navigation, and control (GNC) for the LAS,” she continued. “We wanted that to be the same, because that re-orientation is a critical part of the flight test. So we take that and then we’ve got it embedded in a different software environment.”

“The LAS has the computers to control the abort motor and the attitude control motor firings, but we send the commands, and so we actually send the steering commands to the LAS from our vehicle,” she noted.

After all the test equipment has been installed and connected, they’ll make it sure it’s working. “We do powered-on testing, and we’ll actually do closed-loop, hardware-in-the-loop testing out here,” Devolites said. “We have one of the LAS attitude control motor controllers here from Lockheed Martin that we use in our testing, so we can go all the way closed loop with it. So we’ll do testing here, we’ll do mission simulations.”

Lockheed Martin is the prime contractor for Orion.

After the instrumentation and avionics are installed and tested, Devolites said they will measure the mass properties of the simulator, such as weight and center of gravity (cg), again. “It’s our X-cg fixture,” she noted. “We…put the vehicle on it [and] rotate it over 90 degrees to get the X-cg, it’s going to be very exciting.” The simulator will mimic the production Orion’s mass and center of gravity.

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Crew module simulator in the X-cg fixture at Langley, February 2018. The simulator will be put in the fixture again after it is outfitted at JSC to re-measure its mass properties. Credit: NASA/David C. Bowman

The fully outfitted crew module simulator will then be transported from JSC to the Plum Brook Station facility near the Glenn Research Center in Cleveland, Ohio. “We’re doing acoustic characterization at Plum Brook, but it’s really from the model perspective, right?” Devolites said. “So they can characterize the acoustic environment before we fly — that way they can match it to the actual flight results and compare their models. That’s really for anchoring the models.”

While the crew module simulator is at Plum Brook, Devolites noted that the JSC team will receive the separation ring from Langley and outfit that for the test before the crew module simulator returns to Houston to be mated to the ring. “So we’ll do that here, integrate them together, and ship it all to the Cape, hopefully by December,” she said. The separation ring sits between the crew module and booster to quickly disconnect them when the abort is initiated.

Once at the launch site, the vehicle elements will be connected for integrated systems testing. “We’ll do testing with the LAS before it gets stacked,” Devolites explained. “We do what’s called soft-mate testing. We’ll electrically connect it [and] check out all the interfaces between the systems. We also do soft-mate testing with the booster — electrically make sure everything works.”

“We just keep doing incremental, integrated tests up until launch,” she added. The test is scheduled for April, 2019.

AA-2 Overview

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 proposed cancellation; the plans in Constellation included a longer test series.

After the Orion program was rescoped 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,” NASA Orion Program Manager Mark 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.”

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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). Credit: NASA/Ames/Timothy Sandstrom.

“So we spread the test points around and…right now the point that we’re doing on AA-2 is the combination where we get…kind of a smorgasbord of the most-challenging conditions,” he explained. “Perhaps not the hundredth-percentile of every one of the five or six key parameters but 98 percent at most of them. And that’s why we picked the test conditions that we did.”

Kirasich noted that the abort condition for this test will stress the ability of the LAS to maintain control of the aborting vehicle more than the ability of the LAS to get away from the booster. “The harder part is to control, because the aerodynamics are pushing you all over the place under those circumstances,” he explained.

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.

The test will launch from Launch Complex 46 (LC-46) at the Cape Canaveral Air Force Station (CCAFS) in Florida. An Orbital ATK SR 118 rocket motor 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 abort will be triggered when the vehicle is traveling at approximately Mach 1.3 at an altitude of around 31,000 feet. After liftoff, the booster takes the vehicle up to the abort condition and then signals the crew module.

“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 and the attitude control motor (ACM) are built by Orbital ATK and would only be used in an abort case, and the jettison motor. Aerojet Rocketdyne makes the jettison motor, which is used on every mission to separate the LAS from Orion.

The Orion crew module and the LAS elements make up the launch abort vehicle (LAV) that separates from the test booster in flight. The three motors make up the launch abort tower; other elements of the LAS include a fairing assembly that covers the crew module and a Motor Adaptor Truss Assembly (MATA) that structurally connects the LAS with the CM.

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Diagram of AA-2 test vehicle, left. Diagram of Orion LAS, right. Credit: NASA

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 steer the vehicle away and put it in a good attitude. The abort motor fires for about five seconds with the thrust tailing off quickly while the ACM maintains control of the vehicle.

The ACM then reorients the vehicle for separation events and for the crew module parachute deployment sequence. The LAS is then separated from the crew module with the jettison motor.

The LAS can be used for 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.

During the AA-2 test, the crew module is collecting all of the data from the sensors inside and outside. “Primarily it’s a lot of pressure sensors, a lot of accelerometers, a lot of thermocouples to measure that whole aerothermal environment,” Devolites noted. “There’s of course all the on-board flight instrumentation for the systems — we get all of that data telemetered down.”

The data is being transmitted from the crew module for local ground stations to receive and record. “We have no uplink or command capability,” she said. “We would like to watch the whole thing as it happens during flight but we really just need to get all the data down.”

Devolites said they are looking at using four ground stations for the test: “A couple of them will be able to give us real-time data and a couple of them are going to be just recording the data that we can retrieve later.”

For redundancy, the crew module is also recording all the data on-board. “We think we’ll have comm all the way down and get the telemetry, but just in case we’ve got the backup data recorders,” she added.

“At the point at which the LAS jettisons, you’ve got a plume and even during abort you’ve got a plume,” she said. “We think that’s not going to be a problem [for telemetry]. You also have an orientation at various points in time away from the ground tracking stations, and so for full coverage, that’s why we’ve also got ejectable data recorders.”

The crew module will impact the water without being slowed down and is expected to sink, so the AA-2 team is using another off-the-shelf system in order to recover the recorders.

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Image from NASA animation of the AA-2 test. Credit: NASA.

“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 they 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.”

From liftoff to water impact, the test is expected to last less than three minutes.

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