NASA’s new spaceship, the Orion crew capsule, will be able to actively host a crew for 21 days, a requirement designed to cover all exploration missions, but mainly those outlined in the Lunar sorties Design Reference Missions (DRM) – missions that will see the crew spend more time in Orion, compared to long duration missions involving the crew taking residency in an in-space habitable module.
Although the Orion capsule is far smaller than the Space Shuttle on appearance, the orbiters were surprising short on habitable space for their crews of up to seven astronauts. Their flight deck and middeck were still luxurious compared to the Apollo era. but the crew decks were based on the orbiter’s missions of less than a month in their domain of Low Earth Orbit (LEO).
Orion, larger than the Apollo capsule, will be used for Beyond Earth Orbit (BEO) operations, providing a “bridge” for the crew during the key launch, rendezvous, and re-entry phases of the mission – resulting in the total time a crew will be expected to occupy Orion to be in the region of just days in total.
This total is know as the Orion – or MPCV (Multi-Purpose Crew Vehicle) – “active mission duration”, a Mission Directorate controlled requirement that has been outlined in a new ESD (Exploration Systems Development (ESD) document – (available on L2 – LINK).
“MPCV Active Mission Duration: The MPCV shall provide a habitable environment for a crew of four for a minimum duration of 21 days.”
More interesting is how the ESD came to this number, which is explained as a requirement per lunar sortie missions and for the contingency of crew return in the event of an emergencey.
“The 21 day performance value was originally derived from analysis of Lunar Sortie DRM concepts for Constellation. Initial assessment of the Lunar Surface Sortie DRM (post CxP) indicates that this performance is still sufficient. Forward work will validate it,” noted the document.
“The Lunar Surface Mission DRM, including loitering in LEO until the Trans-Lunar Injection window and emergency return from cis-Lunar space in the event of a main propulsion failure, is (also a) bounding case for MPCV active mission days.”
At present, the proposed Lunar Sortie DRM is not baselined into NASA’s under development plans, with a return to the Moon’s surface effectively cancelled via the end of the Constellation Program (CxP). However, during the seemingly unending exploration roadmap evaluations, options to include lunar surface missions have been discussed, supported and documented into the DRM outlines.
The main reference can be found in the ESD Con Ops (Concept of Operations) document (available on L2 – LINK), listing it alongside the main NEA (Near Earth Asteroid) missions under the Architectural Timeframe DRMs.
“Lunar Surface Sortie (LSS): Lands four crew members on the surface of the Moon in the equatorial or Polar Regions and returns them to Earth,” noted the Con Ops presentation.
“Expected drivers include: MPCV operations in LLO (Low Lunar Orbit) environment, MPCV uncrewed ops phase, MPCV delta V requirements, RPOD (Rendezvous, Proximity Operations and Docking), MPCV number of habitable days.”
Notably, the debut mission of Orion on the Space Launch System (SLS) in 2017 – known as EM-1 (Exploration Mission – 1) – should satisfy a number of these key drivers, based on its mission profile. The ESD also now have the 21 day total for Orion’s habitable days capability, to aid any further lunar sortie mission evaluations.
With other Orion-based missions based around the crew living in a habitable module for the long journey to an asteroid or Mars, the 21 day active mission duration is more than enough for a nominal long duration flight. However, 21 days does enable some contingency margin.
“For NEA DRMs, which include seven or 12 active MPCV days in the nominal mission, capability for up to 21 total active days provides limited early return capability,” added the ESD document.
“The architecture shall support a crew of two, three or four with a demonstrable evolution path of up to six. Rationale: The various elements of the architecture will be designed so that four crewmembers can be supported on a mission,” added the ESD document,
Interestingly, the ESD document intimates that a four member crew would only be an actual requirement if the mission involved EVAs – such as those involved with NEA missions. Other rationale only points towards the opportunities to take non-NASA astronauts along for the ride, as payback for contributing towards the mission.
“The capability to support a crew of four allows for increased crew capabilities to have multiple EVA sortie teams on a mission, the appropriate crew skill mix for longer duration missions, and intra-vehicular activity (IVA) crew support to extra-vehicular activity (EVA) crewmembers. These crew capabilities can be especially important for missions with long comm delays to Earth, which will increase the needs for crew autonomy,” the document added.
“Support for four crewmembers also increases the opportunity for domestic, commercial, and international partnerships by allowing for a mixed crew from different agencies that have provided significant contributions to a mission.”
The ESD add that smaller crews may be more desirable, with the Orion systems designed with that in mind.
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“The capability for the architecture to support two or three crew is driven by the need to accommodate smaller crews for missions in which there is a need to substitute crew for other mass to meet that mission’s objectives. The capability for the architecture to support crew sizes of two or three crew will drive the design so that the systems do not require more than two crew to perform operations.”
The ESD also add that there may be missions where no crewmembers are required, along with the long duration missions where the Orion would be without a crew for an extended amount of time, or sent in-situ in Mars orbit, waiting for its role as the entry vehicle at the end of the mission.
“Zero crew is not specified in the requirement because the requirement is not intended to drive the capability to perform the complete set of DRMs autonomously without crew,” the document continued. “However, there are DRMs that demonstrate new capabilities that have no crew, as well as there are subsets of DRMs where habitable elements of the architecture are left untended.”
At the opposite end of the scale, the ESD believe a crew of six would ride on Orion for a Mars mission – although this would only be for the ascent, rendezvous and entry portion of the mission – with the bulk of the mission seeing the crew take up residence on the Mars Transport Vehicle (MTV) habitable module.
“Crew size of six derives from initial crewed missions to the Mars surface, which will have more significant needs for autonomy from Earth based support and will require an even greater set of skills within the crew than the earlier DRMs,” added the document.
However, interest continues to grow on the potential near-term Lunar Sortie missions, and more so the potential of hosting all exploration missions via the proposed ISS-built Exploration Platform, sent out to a location at the preferred Earth-Moon Lagrange point (EML2).
Orion flights to such an Exploration Gateway/Platform would involve the crew riding on the spacecraft during the entire flight both to and from the platform, utilizing the 21 days of the total active mission duration requirement.
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