Investigating the potential of including a crew on the maiden flight of SLS
With NASA’s management officially informing the workforce that evaluations are taking place into installing a crew on to the first flight of the Space Launch System (SLS), the challenge of ensuring crew safety will gain additional focus. Without an uncrewed test flight, a modification to the Exploration Mission -1 (EM-1) profile is likely, ranging from documented options such as a hybrid profile through to an ISS crew run.
The previous – and currently installed – plan is to launch a Block 1 SLS rocket on a 2018 mission that will send an Orion spacecraft around the Moon, prior to a splashdown in the Pacific ocean.
A gap of around three years would follow before a near-repeat of the mission, this time including a crew.
It is also expected that the current EM-1 mission will slip into mid-2019 at the upcoming Mission Integration Review (MIR) in March, due to ongoing schedule issues with the Core Stage’s path to its Green Run and the troublesome Orion spacecraft – specifically the European Space Agency’s role with the Service Module.
This, along with the need to sell SLS to the new political regime, has played a part in Acting Administrator Robert Lightfoot’s wish to renew the role for SLS’ debut, in conjunction with the transition team that is laying the path for the next NASA boss.
Mr. Lightfoot, a former director of NASA’s Marshall Space Flight Center (MSFC) that is deeply involved with SLS, informed the NASA workforce on Wednesday morning with the effort to realign the SLS early life in space, after speaking to Space Launch System/Orion Suppliers Conference.
“I have asked Bill Gerstenmaier (NASA’s Associate Administrator for Human Exploration and Operations) to initiate a study to assess the feasibility of adding a crew to Exploration Mission-1, the first integrated flight of SLS and Orion.
“I know the challenges associated with such a proposition, like reviewing the technical feasibility, additional resources needed, and clearly the extra work would require a different launch date. That said, I also want to hear about the opportunities it could present to accelerate the effort of the first crewed flight and what it would take to accomplish that first step of pushing humans farther into space.”
Those challenges are numerous. However, there has already been some work on the options that would find a middle ground between the technical requirements of testing SLS and Orion and the safety regime for the astronauts flying on a maiden launch – which would also be the first time since John Young and Bob Crippen rode with Columbia on her STS-1 mission.
Sources point to two potential mission Design Reference Mission (DRM) options from SLS’ CONOPS (Concept Of Operations) documentation that would help fulfill a test flight and while keeping the risk to astronauts to a “minimum” when compared to simply transitioning EM-2 into the role of the maiden flight.
The first option has been touted in numerous iterations of the CONOPS as a hangover from the defunct Constellation Program (CxP).
Known as “LEO_Util_1A_C11A1: International Space Station (ISS) Back-Up Crew Delivery“, this mission would involve SLS and Orion conducting a crew rotation mission for the ISS, as was the initial plan for Orion during the CxP era.
However, the CxP plan involved Ares I, a far less powerful rocket when compared to SLS.
The power difference becomes almost comical when the official NASA documentation cites tons of “ballast” would need to be added to the upper stage to pull back on the reins of SLS.
Sources note the benefit of changing the maiden flight into a LEO mission to the ISS would allow for several safety elements that were installed for the Space Shuttle during ISS missions, such as a speedy return to Earth in the event of a serious problem with – for example – the untested lift support systems, and the “Safe Haven” option of the Station should Orion’s Thermal Protection System (TPS) suffer a critical problem.
The potential benefit of a crew rotation would soon be lost if lawmakers used this DRM as another excuse to penny pitch the Commercial Crew Program (CCP) budget line to help SLS’ schedule.
Based on EM-2 crew safety evaluations, a version of the EM-2 flight profile may become the new EM-1 option. Known as EM-2 Hybrid, the “Orion Mission Design” report notes that “the Orion Program and NASA may choose to fly a mission that is less risky in some aspects.”
This profile conserves propellant for contingency abort cases and flies a trajectory that avoids High Lunar Orbit (HLO) and allows the crew to return to Earth faster than an HLO flight path would permit.
This kind of mission would see the crew launch into three different Earth elliptical orbits, albeit using the Exploration Upper Stage (EUS) as the example, while the first flight of SLS is currently manifested with the Delta Cryogenic Second Stage (DCSS).
The first orbit would be close-range, with a first-orbit-complete-perigee engine firing from the EUS to raise the craft’s orbit to 391 x 71,333 km (242.9 x 44,324.3 miles).
After this burn, Orion and its SM would separate from the upper stage.
This second orbit of Earth would carry a total orbital period of 24 hours and would allow the crew to fully vet and check their spacecraft and its systems before committing to the swing around the moon.
During this 24 hour orbit, if a system does not check out, Orion can remain in this orbit until the situation is resolved.
Conversely, if a serious issue develops while in this 24 hour orbit, Orion can return the crew to Earth within 12 hours.
However, if all systems check out, Orion’s SM engine would, at a perigee of 391 km, fire for the TLI burn and propel Orion toward the moon.
This TLI would put Orion and the crew on a “near-free return trajectory,” notes the “Orion Mission Design” report, and would result in a swing through the lunar L2 point.
Concretely, it would result in Orion performing a lunar flyby at the L2 point at a distance of 61,548 km (38,244.15 miles) from the lunar surface.
At this point, Orion’s SM engine would perform the Return Trajectory Adjust (RTA) burn with a deltaV of 77 m/s (253 f/s) to aim the craft for the location Earth will be at for Entry Interface and landing.
This Hybrid mission would last approximately 15-16 days. Per safety requirements, this profile would carry an added risk of radiation and MMOD strikes as Orion would make multiple passes through the Van Allen Radiation Belts and Earth proximity space.
However, the “Orion Mission Design” report notes that the “radiation dosage to the crew for two revolutions in the intermediate orbit is roughly equivalent to a six-month stay on the ISS.”
Any options that come from the evaluations will receive a rigorous evaluation from oversight bodies, not least NASA’s Aerospace Safety Advisory Panel (ASAP) – which has previously been overly concerned about crew safety on the early Orion missions.
This body had previously noted they wish to see a 30 hour checkout period for Orion in LEO before venturing out into deep space.
How such bodies will react to a crew riding on the maiden launch of SLS and Orion is unknown. However, there are some positive factors, thanks to Orion having already flown on the Exploration Flight Test -1 (EFT-1) and SLS’ use of proven hardware, such as the RS-25 engines and Solid Rocket Boosters.
It is also likely Mr. Lightfoot has conducted preliminary conversations with relevant departments, such as the Astronaut Office, before making his statement of intent to the workforce.
How this will all play out on the schedule and budget line for SLS and Orion remains to be seen.
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