Laying the Groundwork for Artemis: Key Recommendations from a 1972 Orbital Operations Study

In May 1972, North American Rockwell published their comprehensive Orbital Operations Study conducted under NASA contract. The objective was to identify and analyze potential earth orbital operational interactions between space elements in the 1980s timeframe. The study established 11 representative mission models encompassing 117 potential element-to-element interactions between 25 different orbital elements. It then defined 14 generic interfacing activities to scope the range of operations that could occur between element pairs during these interactions.

Key findings, recommendations, and design influences from the analysis of each interfacing activity are summarized below.

Mission Analysis:

• The 11 representative mission models covered a broad spectrum of anticipated space activities in the 1980s, including emplacement, retrieval, and servicing of satellites, space stations, orbital propellant depots, cislunar vehicles and other assets.
• 14 generic interfacing activities were defined to categorize all potential operations between element pairs, such as mating, orbital assembly, payload deployment and retrieval, rendezvous, propellant transfer, crew transfer, etc. Each element pair interaction was mapped to the applicable interfacing activities.
• 117 distinct element-to-element interactions were identified from the mission models, involving 25 different orbital elements such as the Earth Orbital Shuttle (EOS), Space Tug, Research and Applications Modules (RAMs), Modular Space Station (MSS), Orbital Propellant Depot (OPD), Reusable Nuclear Shuttle (RNS) and others.

Mating:

• Direct docking, using a common but versatile docking port design, was recommended as the preferred approach for mating of all element pairs except those involving small satellites. Key features included 100-400 ft-lb energy attenuation, a 0.4 ft/sec maximum closing velocity, and automated soft capture.
• An adapter, or an extendable manipulator arm on the logistics vehicle, was proposed for mating of small satellites unable to accommodate a standard docking port.
• A laser scanning radar on the active logistics vehicle was recommended to assist alignment and final closure for docking, supplemented by visual cues.

Orbital Assembly:

• Direct docking was found adequate for assembly of multi-module orbital elements like space stations, orbital propellant depots, and cislunar vehicles. Mating ports at both ends of modules facilitated flexible assembly sequences.
• A manipulator arm on the EOS was desirable for space station assembly to provide an extra degree of control and safety margin, although not absolutely required. Grapple fixtures on modules were recommended.
• Special assembly jigs or fixtures, delivered by the EOS, might be needed for assembly of large structures like antennas or solar arrays.

Payload Deployment and Retrieval:

• A pivoting deployment mechanism was preferred for handling single large payloads on the EOS, while a manipulator arm was better suited for deploying and retrieving multiple smaller payloads on the same mission.
• A standard 4-point payload retention system in the EOS cargo bay was proposed, with adjustable latches to secure most payloads. Some unique payloads could require mission-specific retention hardware.
• An airlock or tunnel to enable EOS crew access to the payload bay was desirable, provided as a mission kit. Many payloads would benefit from servicing, reconfiguration or inspection by the crew before deployment or after retrieval.

Communications:

• S-band with omnidirectional antennas was recommended as the primary communications link for all elements, both space-to-space and space-to-ground, with VHF providing a backup.
• High data rates exceeding 1 Mbps required a Ku-band link through the Tracking and Data Relay Satellite System (TDRSS). Elements generating such high data volumes needed a steerable Ku-band dish antenna.
• The TDRSS and ground networks would need expansion and upgrades to handle the large number of user spacecraft and high data throughputs anticipated. Scheduling systems for shared access and onboard data storage for delayed transmission would be essential.

Rendezvous and Stationkeeping:

• The EOS should have an autonomous rendezvous and stationkeeping capability using star trackers, horizon scanners, and a laser radar, to enable independent quick-response operations.
• Ground control could manage the rendezvous phase for most missions, handing off to autonomous systems for the final approach and stationkeeping. Unmanned elements could rely entirely on ground control except for close proximity operations.
• A space-based control center, such as the MSS, could provide relative navigation support for co-orbiting free-flyers, enabling more responsive operations than relaying through the ground.

Propellant Transfer:

• Fluid transfer from a dedicated tanker vehicle delivered by the EOS directly to the user vehicle was preferred over exchanging modular propellant tanks.
• Linear acceleration provided by thrusters on the tanker was recommended for propellant settling during transfer. The transfer should occur with the tanker and user vehicle free-flying as a mated pair, detached from the EOS.

Crew and Cargo Transfer:

• Pressurized crew transfer tunnels and hatches were recommended between all manned elements. A minimum 41-inch diameter clear opening was needed for cargo transfer and suited crew passage.
• Manual cargo transfer through hatches was acceptable in most cases, aided by mechanical assist devices like winches or rails if needed. Cargo modules in the EOS and logistics vehicles should be positioned for easy access and removal on orbit.
• An airlock module would be needed for the EOS crew to transfer to unpressurized elements. This could be provided as a mission kit when required.

Attached Element Operations:

• The EOS should provide attached payloads with access to standard utilities (power, thermal control, communications, etc.) through a standard interface. More extensive support should be provided by modular kits or a dedicated support module.
• The MSS should be designed from the outset to support attached elements as an in-space research and servicing facility, providing resources as well as change-out and repair.
• Tugs and cislunar vehicles had limited requirements for supporting attached elements, mainly providing survival power and monitoring during transient mated phases. No long-term support for payloads was needed.

The Orbital Operations Study provided a comprehensive analysis of the potential in-space interactions anticipated in the 1980s and beyond. It resulted in specific hardware and operational recommendations to enable the full range of advanced missions and servicing needs. Commonality and interoperability, in areas such as docking ports and utility interfaces, was a key emphasis. The EOS was identified as the primary logistics workhorse, requiring the most unique provisions and flexibility.

Relevance to Artemis Program

NASA’s Artemis program, aimed at returning humans to the Moon and establishing a sustainable long-term presence, shares many of the same challenges and objectives as the ambitious space infrastructure envisioned in this 1972 study.

Several of the study’s key recommendations remain highly relevant today and are clearly reflected in NASA’s Artemis architecture and plans:

• A common docking/berthing mechanism, the International Docking System Standard (IDSS), is baselined for all Artemis crew vehicles and habitation elements, enabling interoperability between international and commercial partners.
• The Gateway lunar outpost will serve as an aggregation point for lunar landers, logistics vehicles and future surface elements, analogous to the orbital propellant depot and space station concepts. It will provide power, communications, thermal control and other support services to visiting vehicles.
• Robotic manipulator arms are planned for the Gateway and for some Artemis logistics vehicles to assist with payload handling, spacecraft berthing, and lunar surface operations. This aligns with the study’s recommendations for manipulators on the MSS and EOS.
• Efficient transfer of cryogenic propellants, either in lunar orbit or on the lunar surface, is a key objective for sustainable Artemis operations. Fluid transfer from dedicated tanker vehicles is baselined, similar to the study’s propellant logistics approach.

However, the Artemis campaign also differs from the 1972 study’s proposed architecture in several important ways:

• Artemis is focused on cislunar space and the lunar surface rather than low Earth orbit infrastructure. The Gateway is a much smaller, more specialized outpost than the expansive space stations envisioned in the study.
• Artemis will leverage a range of advanced technologies that were not available in 1972, such as autonomous rendezvous and docking software, high-bandwidth optical communications, improved regenerative life support, in-situ resource utilization, fission surface power systems, and cryogenic fluid management.
• International collaboration and commercial partnerships play a central role in Artemis, with contributions of logistics services, lunar landers, rovers, surface habitats and other key elements. This approach shares costs and risks while fostering private innovation.
• Sustainability, reusability and scalability are core tenets of the Artemis architecture. This includes reusable lunar landers and surface systems, ISRU for propellant and consumables, modular expandable habitats, and an incremental buildup approach. The goal is an open architecture that can steadily grow with contributions from many partners.

Despite these differences, many of the fundamental technical challenges and operational needs identified in the 1972 Orbital Operations Study still apply to Artemis half a century later. The study’s emphasis on enabling a flexible, sustainable space transportation system through robust in-space logistics, interoperable interfaces, and efficient propellant management remains highly relevant as NASA works towards a permanent human presence on the Moon.

By building on the insights from seminal studies like this, while leveraging modern technologies and partnerships, Artemis is positioned to make the long-envisioned future of humans living and working in deep space a reality. However, significant work remains to fully address the multitude of challenges identified by this study and subsequent NASA efforts. With the Artemis missions of this decade as a foundation, NASA and its partners must continue to refine the technologies and operational concepts required for a sustained human presence on the Moon and eventual crewed missions to Mars. The findings and recommendations of the 1972 Orbital Operations Study provide a valuable reference point for this ongoing work.

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