NASA managers have created new mandates for future exploration systems, as the Agency continues to refine a capability-driven approach to its exploration aspirations. Working in tandem with NASA’s latest conceptual Design Reference Missions (DRMs), the requirements detail the capabilities required of the Orion crew vehicle, Space Launch System (SLS) and Ground Systems Development and Operations (GSDO).
Concepts and Capabilities:
NASA’s Human Exploration and Operations Mission Directorate’s (HEOMD) latest stipulations focus on future space and ground systems, which include the Space Launch System (SLS), Orion crew vehicle and Ground Systems Development and Operations (GSDO), and are based on NASA’s “capability-driven framework” for exploration.
The capability-driven framework requires that NASA select celestial destinations based on future space and ground systems’ capabilities rather than designing space and ground systems’ capabilities based on destinations.
The HEOMD requirements are part of NASA’s general Exploration Systems Development (ESD) effort. ESD documentation – available in L2 – details a series of conceptual design reference missions (DRMs) that use planned program capabilities to reach a multitude of potential destinations. DRMs are arranged in a hierarchy of complexity.
Tactical DRMs, which include lunar flybys and lunar orbit missions, use only the earliest variants of NASA’s planned systems. Strategic DRMs, such as missions to near-Earth asteroids (NEAs), use upgraded systems along with conceptual, currently undeveloped systems.
Finally, Architectural DRMs encompass NASA’s long-term goals, such as Mars surface missions, and use systems with the highest-planned upgrades along with conceptual systems.
The destinations encompassed in DRMs drive the stated HEOMD requirements for future NASA systems.
Laying the Groundwork:
The starting line for all of NASA’s current DRMs is GSDO, which includes the infrastructure needed to transport, assemble and launch SLS, Orion and other elements needed for exploration. In addition, GSDO will be tasked with the recovery of crews and their vehicles.
NASA’s manifest for future manned missions requires that GSDO meet regular launch rates. According to ESD documentation, GSDO must maintain a launch rate of one launch every two years for Tactical-level missions. Strategic-level missions must maintain a launch rate of one to three launches per year.
Despite requiring an eventual three SLS launches per year, ESD documentation includes a caveat to the launch rate’s upper limit, stating, “3 launches per year is not considered to be a sustainable rate and is not to be construed as a production capability. During these periods, nominal flight activity will be suspended to enable this surge capability. Storage of assets may be required for a 3 launch DRM.”
Today, NASA’s GSDO is preparing to meet the requirements set by the HEOMD. Kennedy Space Center (KSC), for instance, is readying its Vehicle Assembly Building (VAB), crawler-transporters, Mobile Launcher (ML) and Launch Pad 39B for the arrival of SLS and Orion.
Liftoff of the Future:
SLS, which will loft NASA’s exploration crews and payloads into orbit from KSC’s Pad 39B, is NASA’s next heavy-lift launch vehicle.
Currently on track for a December 2017 debut, SLS initially will be required to lift 70 metric tons of payload to low Earth orbit (LEO), with an eventual lifting requirement of 130 metric tons of payload to LEO, ESD documentation states.
Refinements to the evolution are continuing, not least with the Upper Stage – per additional L2 documentation – which will surround a series of planned upgrades, including a stretched first stage, advanced boosters, upgraded RS-25 engines, and an upgraded cryogenic propulsion stage (CPS) that is currently into long-term evaluations.
The Block 1, 1B and 2B will be the likely evolving family of HLVs, which will eventually use the Exploration Upper Stage (EUS), completely removing the J-2X from ever flying with SLS.
The Block I SLS will enable Tactical-level missions, and the 105-metric-ton Block IB SLS will facilitate Strategic-level missions. Finally, the Block II SLS will enable Architectural-level missions.
Once in Orbit:
The Orion crew vehicle is the centerpiece of in-space activities for NASA’s future manned exploration missions. Salvaged from the defunding of the Constellation Program (CxP), Orion is the primary craft that future NASA crews will use for launch, transit and re-entry.
Orion, which is scheduled for a December, 2014 maiden test flight, will feature a crew module (CM) constructed by Lockheed Martin and a service module (SM) constructed by Astrium, manufacturer of ESA’s Automated Transfer Vehicles (ATVs) – for at least the EM-1 mission.
According to ESD requirements, Orion must support at least four crew members with its initial capabilities, with an eventual goal of supporting a crew of six.
In an example from ESD documentation, a crew of four would allow two astronauts to conduct an extra-vehicular activity (EVA) while two of their crewmates support them from within Orion.
For Mars missions, a crew would experience an average communication delay of 20 minutes, with the added obstacle of being months away from a return to civilization. Therefore, NASA specifies that Orion accommodate a diversely-skilled crew of six for Mars surface missions.
In addition, Orion will be capable of missions with as few as two crew members, with the mass freed by fewer crew allowing for extra cargo, according to ESD documentation.
While NASA envisions the development of a Deep Space Habitat (DSH) to house crews for long-duration missions, Orion alone will be capable of supporting a crew of four on missions lasting 21 days or less, ESD documentation states.
The 21-day requirement was originally developed for CxP’s lunar surface missions, but ESD documentation states that it remains tentatively valid for the new program’s potential lunar surface missions.
ESD requirements stipulate that Orion’s propulsion systems be capable of a change in velocity, or delta-v, of 1340 m/s. The delta-v requirement, which essentially outlines the extent of Orion’s ability to maneuver in space, is based on the delta-v required for lunar missions and missions to Earth-Moon Langrangian points.
Orion’s delta-v capability will provide an emergency return option in the event of an abort within cis-lunar space, the space between geostationary orbit and lunar orbit. Currently, Orion’s required delta-v only accounts for Tactical DRMs, and will be adjusted for Strategic DRMs as they become more defined by NASA.
In addition to safely transporting crew, Orion also will be able to return cargo, such as scientific samples and experiments, from its destinations.
For an Orion vehicle with a crew of two or three, NASA stipulates a return cargo capacity of 250 kg, while a four-crew member Orion will have 100 kg of return cargo capability.
Although the Orion SM’s primary role lies with supporting Orion’s CM, ESD requirements stipulate that the SM have the standalone capability to support unmanned cargo flights for strategic-level DRMs. According to ESD documentation, unmanned Orion SM flights could make use of specific Orion CM components such as avionics without using the entire CM.
ESD documentation also outlines the need for audio and motion imagery during exploration missions, citing motion imagery inadequacies discovered by the Columbia Accident Investigation Report.
In addition to assisting post-flight engineering analysis of vehicles, future missions’ audio and motion imagery will play a role in NASA’s education efforts. ESD documentation states, “the Architecture needs to support Science, Technology, Engineering and Mathematics (STEM) and public outreach as well as flight crew operational health care, through downlink of synchronized audio and motion imagery.
“This includes in-cabin and external real-time, near real-time and streaming audio and motion imagery feed of major human-interest events and crew activities.”
Requirements for Return:
For Orion’s return to Earth, the HEOMD requires that the vehicle’s heat shield have a reentry velocity capability of no less than 11.2 km/s for tactical DRMs and no less than 11.5 km/s for strategic DRMs.
Orion’s reentry requirements are based on direct reentries from orbits beyond LEO. However, it will not be capable of the velocities required for Mars missions, which will require a more capable version of the heat shield.
While NASA considered the possibility of missions entering LEO before reentry to lessen the load on Orion’s heat shield, a pre-entry insertion to LEO was found to be prohibitively taxing on fuel, according to ESD documentation.
Following reentry and landing, Orion will be able to sustain a crew for up to 24 hours until recovery. NASA’s 24-hour requirement factors in the possibility of off-target landings.
Meanwhile, the nominal post-landing recovery of crews and their vehicles will be a requirement of GSDO, which will use ships and helicopters to reach crews within 2 hours of splashdown. In the event of an off-target landing, GSDO would shift to search and rescue operations.
The ESD team’s requirements include thresholds for the incidence of loss of crew (LOC) events, which ESD documentation defines as “death of or permanently debilitating injury to one or more crew members.”
While LOC thresholds are calculated for Orion and SLS, no such thresholds are established for GSDO. “LOC risk contributed by the GSDO Program is expected to be small as compared to flight elements,” ESD documentation states.
Currently, the only LOC thresholds calculated by the ESD team are based on Exploration Mission 2 (EM-2), which is planned for 2021 and will consist of an SLS-launched crewed Orion rendezvousing with a robotically captured asteroid in lunar orbit.
For ascent on EM-2, ESD documentation states that the probability of LOC is 1 in 1400 for Orion and 1 in 550 for SLS. Orion’s LOC threshold for Earth entry, descent and landing is 1 in 650, according to ESD documentation.
ESD documentation states that further LOC thresholds will be calculated as more missions are developed.
(Images: Via L2 content from L2’s SLS specific L2 section, which includes, presentations, videos, graphics and internal – interactive with actual SLS engineers – updates on the SLS and HLV, available on no other site. Other images via NASA)
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