EM-1: NASA managers request ambitious changes to debut SLS/Orion mission
Just months after changing Exploration Mission -2 (EM-2) into an asteroid rendezvous mission, NASA managers have issued a Change Request to alter the debut flight of the Space Launch System (SLS) with Orion. The change would result in Orion being sent 70,000 km past the Moon on a 25 day flight.
As SLS undergoes its Preliminary Design Review (PDR), a new – and highly detailed – 116 page Concept Of Operations (CONOPS) document (available to download in L2) has finally provided extensive details into the ongoing Exploration Roadmap planning effort.
Based on the creation of Design Reference Missions (DRMs), the document covers both crewed and uncrewed mission templates for SLS, Orion and Deep Space Habs (DSHs) all the way through to landings on Mars. Additional notes (L2) also point to negotiations with the Jet Propulsion Laboratory (JPL) for a SLS-launched science mission (to be covered in a specific article at a later date).
The first SLS-based roadmap was based only on the initial cost and schedule estimates for evolving the Heavy Lift Launch Vehicle (HLV), through to its 130mt capability – as ordered by Congress in the 2010 Authorization Act.
With the requirement for Orion to be a back-up to NASA’s commercial crew effort, the first launch of SLS was technically advanced to 2017 – a date it remains on track to achieve. Meanwhile, the first NASA crewed commercial launch (USCV-1) has since slipped over two years and is threatening to slip further – potentially after SLS/Orion’s EM-1 debut – should funding levels fall below requested levels.
However, it remains a highly unlikely scenario that the first SLS/Orion mission will be to the ISS, not least because it is classed as unthinkable that a crew would ride uphill on the debut launch of the HLV.
Planning documentation continues to reference the ISS DRM as an option, but manifests have always pointed towards the first SLS/Orion launch being an uncrewed Exploration Mission (EM-1), which was baselined a validation flight that would send Orion on a 7-10 day mission around the Moon.
SLS and Orion would then endure a four year gap – again, mainly due to the advanced 2017 debut relating to ISS crew back up – before repeating a version of EM-1, this time as a CLO (Crewed Lunar Orbit) flight, with four astronauts spending three to four days orbiting our nearest neighbor, as opposed to heading directly home after passing around the Moon – a flight known as Exploration Mission -2 (EM-2).
Much to the surprise of some people deeply involved with SLS and Orion, the order came down from NASA HQ to realign EM-2, based around a 2019 mission tasked with hunting down and capturing an asteroid that would then be placed in the vicinity of the Moon within one to two years. EM-2 is also known as the Asteroid Redirect Crewed Mission (ARCM).
The 2019 mission would require the launch of an Asteroid Retrieval Spacecraft (ARS) via an Atlas V in its 551 configuration, setting sail for an asteroid that would be “small enough” and relatively close by. EM-2 would then launch a crew of two astronauts to meet up and conduct EVAs on the asteroid.
Deemed as fulfilling President Obama’s wish of investigating a Near Earth Asteroid (NEA) by the middle of the 2020s, subsequent political hearings have seen some lawmakers complain about the mission’s lack of public interest, through to questioning the technical viability of the initial mission outline and its schedule.
EM-1 Change Request:
As part of a potential reaction to that initial feedback, an order to evaluate an alteration of 2017’s EM-1 was recently sent from NASA HQ to the SLS and Orion teams.
The order – known as a “Change Request” – calls for the replacement of the Uncrewed “Lunar Flyby Tactical DRM” with a “Distant Retrograde Orbit (DRO) Tactical DRM”, citing the mission would directly aid the new EM-2 asteroid objectives.
“Un-crewed DRO flight to demonstrate trajectory performance and increased flight duration for future Asteroid Redirect Crewed Mission (ARCM) as well as high speed entry and select integrated systems performance prior to crewed flight,” noted the EM-1 Change Request outline (L2).
While the new EM-1 flight would technically still be to the Moon, the change would result in Orion passing 70,000km past the lunar surface, as opposed to the original plan to enter a Low Lunar Orbit (LLO). The mission would also be much longer, such as the extended 10 day trip to the target destination.
“This mission utilizes a single Block 1 (70mt) SLS with an ICPS (Interim Cryogenic Propulsion System) and Orion to go beyond Earth orbit and test critical mission events as well as demonstrate performance in relevant environments. This DRM is designed such that the Orion flies a mission profile similar to what might be used in a future ARCM,” added the latest CONOPS document, which provides a detailed outline of the new mission.
“Requires an SLS lift capability of 70mt to an insertion orbit of -87 x 241 km. This DRM requires SLS to deliver a payload insertion mass of 58 mt to an insertion orbit of 41 km x 1806 km. This higher orbit mission is more stressing than a LEO mission, so it envelopes it.”
Following the previously outlined Ground Operations, Launch and Ascent of the SLS with Orion, the uncrewed Orion would be prepared for its Trans-Lunar Injection (TLI) burn, that would be conducted by the Delta Cryogenic Second Stage (DCSS), acting as the ICPS.
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“The ICPS performs the TLI burn to place the Orion on a lunar free return trajectory to execute a lunar flyby gravity assist maneuver that will target a DRO, and the Orion separates from the ICPS,” added the On Orbit Operations outline in the CONOPS for new EM-1 mission proposal.
“The ICPS maintains a stable attitude following separation to ensure no re-contact, after which the ICPS performs any necessary maneuvers for safe disposal.”
During transit, the Orion – now on its own – would perform a translational burn to accomplish a powered lunar flyby gravity assist maneuver that targets the DRO. Once at the DRO arrival point, Orion would then perform a translation burn to establish the DRO orbit of approximately 70,000 km with the spacecraft also performing Trajectory Correction Maneuver (TCM) burns as required.
Orion would then spend six days in the DRO, before making the return leg.
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“Upon completing the DRO portion of the mission, Orion performs a departure burn to place the spacecraft on a trajectory to execute a return lunar flyby gravity assist maneuver,” added the CONOPS presentation.
“Orion uses this trajectory to propel around the Moon, and then performs a return flyby burn resulting in a nine day transit back to Earth.”
At the conclusion to the 25 day mission, Orion would then re-enter at high velocity, conducting a major test of its heatsheild.
“The Orion return trajectory is designed to achieve a maximum Earth return velocity. Required tactical capability is 11.2 km/s; expected maximum achievable Earth return velocity from this DRM is approximately 11 km/s.”
A decision point on converting the Change Request into the EM-1 baseline is expected later this year.
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