EM-2 returns to Block 1
Throughout multiple iterations of its mission profile, EM-2 was intended as the first crewed flight of NASA’s Orion spacecraft. Whereas the major design, development, test, and evaluation (DDT&E) periods for EGS and SLS run through EM-1, Orion’s development was divided into three phases which run through EM-2.
The third and final phase following EM-1 adds the complement of crew systems, life support systems, and fully active launch abort elements to the Orion system on EM-2.
One of the first concepts for EM-2 was to put Orion and a four-person crew into a high lunar orbit for a few days. A subsequent iteration reduced the crew size to two for a month-long flight to rendezvous with a “redirected” asteroid on the crewed flight of the overall Asteroid Redirect Mission (ARM).
The latest mission profile more directly attempts to reduce some of the risks of a first crewed flight. Called a “hybrid triple” in early presentations, the profile has Orion flying in three orbits: a low Earth orbit still attached to the booster upper stage, a high Earth orbit (HEO) by itself that lasts for about one day, and a single solo lap around the Moon before returning to splashdown on Earth.
The profile was retained when the mission moved from ICPS to EUS, where it was dubbed “Multi Trans-Lunar Injection” (MTLI) after addition of the PPE secondary payload.
Using ICPS for the hybrid triple was again studied last year when the feasibility of flying crew on EM-1 was done; although the profile was still feasible, it was decided to keep EM-1 as-is and not put crew onboard.
Now back again to ICPS, the EM-2 mission doesn’t really change much from the point of view of Orion and her crew. “[It’s] pretty much the same thing,” Nujoud Merancy, Exploration Mission Analysis Lead at NASA’s Johnson Space Center, said in an interview with NASASpaceflight.com.
“The LEO orbit you use is different just the way it works out with SLS. The SLS lifting [EUS] goes to a circular orbit; [with ICPS], you transfer Core margin to ICPS so you go into an elliptical Earth orbit. So the LEO portion is going to be a little bit different; [but] Orion is kind of insensitive to that. Then the rest of the mission is kind of the same, regardless — you go to the High Earth Orbit for a day to check systems out and then do an Orion TLI to do a lunar flyby.”
After two orbits, the ICPS will fire to place the two in an even more elliptical High Earth Orbit (HEO), and then Orion will separate from the upper stage. Merancy said the proposed orbit would be 38,600 by 127 nautical miles, with a period of about 24 hours.
The purpose of the long orbit is observe the performance of new spacecraft systems close to home, especially the crew systems on their first flight. On a more typical lunar/cislunar mission, Orion and crew would be on their way to the Moon a few hours after launch.
“We’re only there [in LEO] for two revs, so you get three hours on the systems,” Merancy said. “So being the first time we fly the crew equipment and ECLSS systems that’s why we wanted the HEO because in the first three hours you really only see the swingbeds flip a couple of times, but it won’t have been stressed or anything.”
ECLSS stands for Environmental Control and Life Support System. The amine swingbeds are a part of Orion’s carbon dioxide removal system, which itself is a part of the ECLSS. “By having the 24-hour orbit, now the crew has to exercise, they go to sleep, they’ll use the potty — the WMS (Waste Management System),” Merancy explained.
“You can’t do exercise in the first three hours — they’re going to be a little busy. That’s why just being there a day, the crew will do all the normal things the crew does, but that will then go through all the cycles on the equipment that you would want to see.”
“To the crew, it’ll look like a nominal day essentially,” she added.
Assuming Orion and crew are healthy, the spacecraft will then use its main engine to perform a TLI burn that will set up a “free-return” lunar flyby at an altitude of about 4800 nautical miles above the far side of the Moon before returning to splashdown on Earth. The flyby distance was picked for its timing.
“[The trajectories] are all free-returns but the altitude that you target on your free return would adjust your mission duration,” Merancy explained. “We are picking 4800 nautical miles, because that makes it an even number of days so you fly by [the Moon] during the middle of the crew day — it would be really sucky to fly by in the middle of crew sleep.”
“So we picked the altitude for the shortest time that was an even number of days,” she continued, “so four days out, four days in, which puts fly by right in the middle of the crew day, the same time they did TLI. That was the rationale for the altitude we’ve picked right now. If you wanted to do a longer mission, you just pick a further altitude but that does mean you’re flying farther from the Moon when you go by. There’s no real reason to do that right now.”
When work in the SLS Program on the ICPS was formally suspended in 2016, the ICPS still needed to be outfitted with additional systems and hardware to meet NASA’s human rating standards. Now that it will fly crewed missions, one of the primary additions needed is emergency/fault detection avionics.
“The fault detection system, it’s really just an avionics box that detects the faults and if the crew had been put on EM-1, they would have put that on ICPS,” Merancy explained. “The big thing that it does is it shuts down the engine if it detects a fault during dynamic flight. And you need that because if you detect a fault during dynamic flight you need to shutdown the liquid engine so that Orion can separate and abort.”
“On EM-1, we don’t have that — we can’t abort the EM-1 vehicle during TLI,” she continued. “You would have to wait until TLI finished or cutoff if it had a failure and then you could get the vehicle off. With people, you don’t take that risk, you can’t wait — you have to just detect it, shut it down, and get off.”
“That was the avionics difference on ICPS if we did put crew on EM-1. And the same would be true whether we have crew on EM-2 (with) ICPS or EUS, we have to have that dynamic shutdown, so you can abort Orion.”
Although it was decided not to fly crew on EM-1, it was realized in the technical feasibility assessment that United Launch Alliance (ULA) was certifying an emergency detection system (EDS) that will fly on the Atlas V booster being used by Boeing’s CST-100 Starliner Commercial Crew vehicle.
“A long time ago when crew was supposed to be on ICPS, it was a whole new avionics system they we were going to put on,” Merancy noted. “And then when we went to not human-rate ICPS, they stopped work on that and now, because the Commercial Crew stuff happened in parallel and it’s a simple box, you’d use that now that wasn’t available way back when.”
“It would be much easier to put crew on ICPS now then it was before when we thought we were going to have to make a whole new avionics system for it in order to human-rate it,” she added.
One of the long-term efforts that ULA has been working on is integrating “Common Avionics” across its Atlas and Delta launch services, standardizing computers and software that fly the vehicles from liftoff to spacecraft separation to end-of-mission.
Common Avionics debuted on the Delta 4 with the launch of the National Reconnaissance Office-47 (NROL-47) payload in January after first flying on Atlas V launches.
ICPS is also using ULA Common Avionics. “ULA’s Common Avionics suite does afford the ICPS with EDS interface compatibility,” Janet Anderson, Public Affairs Officer at NASA’s Marshall Spaceflight Center, said in an email.
Kathryn Hambleton also noted in her email that “NASA would look to use the Emergency Detection System avionics and software in human rating the ICPS for a flight with crew, as well as additional hardware modifications, such as selective placement of micro-meteoroid protection.”
During the ASAP’s May 17 meeting, Dr. McErlean noted that the crew on EM-1 study conducted last year also had additional benefits. “We learned that the ICPS was in fact more tolerant to MMOD (Micro-Meteoroid and Orbital Debris) damage, which was its primary weakness in terms of human-rating, than was anticipated,” he said.
“So we are now moving forward to make changes to the ICPS between EM-1 and EM-2 to make it safe, human-safe if you will, and those changes have turned out to be much more modest than we originally anticipated, and hence much more feasible to get done.”
“That includes providing the emergency detection system into the vehicle, changing some of the electrical bus connections, to making some electrical changes including the flight termination system and so forth,” he added. “And they are providing some extra Kevlar blankets in a couple of places in ICPS that were still below our tolerance limit for MMOD but it turns out those make the system relatively robust.”
Now that the scheduling iron-bar has been removed, a new launch readiness date still remains to be re-evaluated for EM-2. At a recent media event in Houston, NASA Orion Program Manager Mark Kirasich said the Delta CDR for the Orion EM-2 vehicle is scheduled for the early Fall, perhaps in the October time-frame.