This paper presents some alternate mission strategies to the 90-Day Study approach. Emphasis is placed on the lunar portion of these missions, although some discussion relevant to Mars is required. First a review of the 90-Day Study approach is presented. Two alternate approaches are then provided. The first emphasizes exploration of both the Moon and Mars prior to committing to a permanent outpost. This exploration strategy provides detailed information about the planets allowing for more efficient system designs and outpost emplacement. The second strategy emphasizes aggressively expanding human presence into the solar system. This approach relies on using the local resources to the maximum extent possible to reduce the resupply requirement from Earth.
On July 20, 1989, President Bush defined which of the numerous exploration pathways to take: First complete Space Station Freedom, and then back to the Moon to stay, and then on to Mars.
In the fall of 1990, NASA initiated an agency-wide study to define the President's Moon-Mars program. The results of this study were presented to the National Space Council via the "Report of the 90-day Study on Human Exploration of the Moon and Mars." The purpose of this report was to aid the National Space Council in development of a strategic plan. This report does not represent the only or best way to accomplish the President's initiative, but rather is one feasible approach.
This paper will discuss some alternate mission approaches to achieving President Bush's vision, emphasizing the lunar mission phase. Before discussing some alternate lunar mission strategies, a brief review of the 90-day mission strategy is provided.
The first step toward missions to the Moon begins with the Robotic Phase, during which essential data about the lunar surface is gathered. This information will support the design and development of the surface systems, and transportation systems, and pre-planning activities prior to the actual human missions. The information gained from the robotic missions will aid in site selection and certification activities for the lunar outpost. Several factors, including the scientific interest of the site, potential resources that may be available, and operations must be considered. Robotic missions additionally provide a strategic opportunity to demonstrate key technologies, such as aerobraking, landing accuracy, hazard avoidance, and autonomous rendezvous and docking. Demonstrations of these technologies potentially can reduce total program cost by spreading risk.2
The next step in the lunar portion of the exploration strategy is the Emplacement phase. This phase is significant to the overall exploration strategy because it establishes the first permanent foothold on another planetary body. The objective of this phase is to establish a permanent presence on the Moon and begin developing the knowledge base on how to live and work on a non-terrestrial body. Emphasis centers on emplacing simple equipment and instruments and laying the foundation for later more complex surface operations by testing prototypes of future systems. Space Station Freedom supports the initial flight test of the lunar transportation system including vehicle integration, checkout, launch support, and inspection after flight. As the Emplacement Phase concludes, SSF capabilities have expanded to maintain and service the first reusable elements of the lunar transportation system.
The objective of the Consolidation Phase, the next step in the 90-Day Study exploration strategy, is to expand the permanent presence on the Moon and increase the knowledge base on how to live and work in space. During this phase the outpost capabilities are dramatically expanded, particularly in the area of pressurized volume. A constructible habitation module is erected at the outpost to provide large pressurized volumes for both habitation and scientific research. This habitat provides the capability to test long-duration exposure to partial gravity in preparation for the upcoming missions to Mars. Reducing dependence on Earth takes on paramount importance in both making capabilities available to initiate Mars exploration, and developing confidence in operational strategies and hardware. This is accomplished by relying on more efficient systems, such as life support and outpost operations, and by testing prototypes of lunar resource production plants to be operated in the Operation Phase. Experience is gained in carrying on day-to-day activities in the absence of continual Earth supervision and guidance, thereby reducing the operational ties to Earth.
Figure 1. - The 90-Day Study mission strategy.
The objective of the last phase, the Operation Phase, is to curtail emplacement of new lunar facilities while at the same time developing independence from Earth. Local resources, such as lunar oxygen production at the outpost, can be used to fuel the lunar excursion vehicles. This off-loading reduces the mass required in low Earth orbit for each flight of the lunar transportation system. The Space Station Freedom facilities are expanded to support the assembly and processing of the first Mars vehicles. Further expansion of the lunar outpost infrastructure is curtailed in order to open operational, logistic, and funding "wedges" to accomplish the missions to Mars.
Figure 2. - Spectrum of mission strategies.
Several alternate approaches are currently being studied by NASA. To illustrate some of the differences between the approaches, two strategies will be discussed here: Exploration Emphasis, and Expanding Human Presence. The first of which emphasizes continued exploration of the Moon and Mars prior to emplacing an outpost, and the second emphasizes aggressively expanding human presence into the solar system.
Geologic field work is a key factor in this approach. It provides the opportunity for humans to perform local investigations of the lunar surface, allowing them to further understand the planetary processes, geologic formations, and planetary history. But geologic field work is a complex and iterative process, usually requiring human interaction. Astronauts will do some of the field work, but much of it can be done by teleoperated robotic field geologists under the complete control of trained geologists at the landing site or possibly on Earth.5 These robotic field geologists, or Teleprospectors, are robotic vehicles which imitate many functions of their human counterparts including stereoscopic vision and manipulation of arms. They can also provide additional capabilities such as infrared and X-ray mapping for sample identification, and sample storage and return. The Teleprospectors provide humans access to many regions of the lunar surface without risking the complexities of human missions.
Figure 3. - Exploration emphasis mission strategy.
Human missions to multiple surface sites are conducted at a global scale, allowing for the discovery of new formations and increasing the information returned from each mission. These missions to the lunar surface are similar to the Apollo missions, but are longer in duration. The extended surface stays, two to six weeks, provide ample time for the crews to perform extensive geologic field work, emplace scientific packages, and perform technology demonstrations, such as utilizing the local resources to manufacture usable products. The revisit benefit of this strategy whereby the human explorers have the capability to return to previously visited sites provides additional flexibility. For instance, pre-deployed scientific packages, which may be in remote areas, can be routinely maintained, adjusted, serviced, and resupplied. This revisit capability also allows explorers to return to previously visited sites to perform more detailed geologic field work.
The Exploration Emphasis strategy imposes unique requirements on the transportation systems, foremost of which is providing access to the entire surface of the Moon. The staging location for the vehicles can impose significant constraints on the missions. For instance, staging the missions from an equatorial orbit about the Moon limits the landing sites to a narrow band about the equator. On the other hand, staging from polar lunar orbits opens up access to any point on the lunar surface, but launch opportunities to these orbits are less frequent.
Staging from a location, such as a lunar libration point, can remove some of these operational constraints, specifically by providing routine access to the entire lunar surface. Libration points are fixed locations in the Earth-Moon system where the gravitational attraction of the Moon equals the gravitational attraction of the Earth. There are five such points in the Earth-Moon system. The cis-lunar (L1) and trans-lunar (L2) libration points provide unique opportunities for conducting missions to the Moon. The L1 and L2 libration points are relatively close to the Moon and they provide a common and continual staging location from both the Earth and the lunar surface.
Exploration of the entire surface of the Moon and Mars provides an extensive knowledge base of these planetary bodies. Commitment to an outpost location following a particular emplacement approach would depend on the conclusions drawn from the many exploration missions. This strategy provides flexibility in emplacing and designing the outposts. For instance, outpost functions, such as habitation, power, ISRU production, and science, can be designed to take maximum advantage of the local environment.
The Expanding Human Presence approach begins with the Robotic Exploration Phase (see Figure 4). During this phase telerobotic science will be conducted for the purpose of identifying and supporting the selection of the outpost site. The location of the site is critical not only because it must be easily accessible, but also because the outpost must be capable of supporting numerous surface activities. For example, the resources contained in the regolith surrounding the outpost are critical in an aggressive in-situ resource utilization (ISRU) program. This is probably the most demanding requirement on the outpost location for this type of strategy since developing self-sufficiency by utilizing the local resources is a key goal. Data from orbiting robotic vehicles and samples returned by telerobotic rovers will provide an opportunity to fully characterize the surface while at the same time provide caches of lunar regolith to use in developing the ISRU production plants here on Earth.
Figure 4. - Expanding human presence mission strategy.
The objective of the next phase, the Emplacement Phase, is to gain the first permanent foothold on another planet while learning how to use the local environment as leverage in the remainder of the exploration process. The initial outpost emplaced on the lunar surface is a modest facility which supports the focused research program. Although a majority of the prototyping of the ISRU plants is performed on Earth, final verification and certification is conducted on the lunar surface. The ISRU processes include production of ceramics for fabrication of local pressurized facilities, oxygen for use in the transportation vehicles and life support system, soils for growing plants, and trace gases for life support. During this phase science activities are limited and focus on developing outpost self-sufficiency. This includes research in the areas of closed bio-spheres at the lunar outpost, and life science research related to the up-coming long-duration missions to Mars.
The outpost facilities are greatly expanded during the next phase, the Expansion Phase, by utilizing the local resources. Pressurized facilities including habitation areas, laboratories, maintenance rooms, and anterooms are constructed. In addition, oxygen extracted from the lunar surface is used in the life support system and as propellants in the transportation vehicles. As the capabilities for more advanced production are developed, finished products and spare parts can be produced locally, rather than supplied from Earth. Self-sufficiency is not only measured in physical terms, but is also achieved in intangible forms. As the outpost matures and operations become the norm rather than the exception, operational control will shift from the Earth to the outpost.
The thrust of the settlement changes during the Operation Phase. During this phase the aggressive push toward self-sufficiency is curtailed and other forms of activities take form. Certain features including scientific sorties and global access, which were delayed until self-sufficiency was established, will begin to provide detailed information on the history of the planets and solar system. Scientific research in disciplines other than life sciences, such as astrophysics and planetary geology, will thrive with heightened capabilities and initiatives. The accelerated growth process of the lunar base will provide the confidence and technological experience to initiate this process on Mars. A similar pattern will ensue: begin with a small community heavily dependent on the Earth and evolve into a nearly self-supporting, thriving establishment.
The robust and self-sufficient characteristics of this alternative provides unique downstream options. For instance, the initial outposts on the Moon and Mars can serve as the stepping stones for further exploration of the solar system. In addition, the technologies and techniques developed for these space settlements can be returned for use on Earth. For example, the wealth of information gained from establishing small eco-systems on planetary bodies will improve our knowledge about the Earth's environment. In addition, products and specialized goods can be exported from these settlements to other space-based users or to Earth.
First a review NASA's 90-Day Study was presented. The goal of the 90-Day study is to expand human presence into the solar system, resulting in missions to the surface of Mars. The strategy taken is an evolutionary one in which each step in the pathway - Space Station Freedom - lunar outpost - serves as the building-block or stepping-stone to the next.
The next alternative presented emphasizes exploration of the Moon and Mars prior to emplacing an outpost on either planet. This exploration approach provides an opportunity to expand man's knowledge, determining the best approach to take in developing and constructing an outpost. The exploration strategy in this approach is common for both the Moon and Mars - relying heavily on both human and robotic missions.
The goal of the last alternative is to aggressively expand human presence into the solar system, leading to human settlements. A key objective of this strategy is to reduce the resupply and operational support required from Earth by aggressively developing forms of self-sufficiency. The strategy for pursuing the expansion approach is evolutionary - relying on the Earth during the early phases, and later evolving the outpost to become nearly self-sufficient.
The alternatives presented represent just a few of the many options available which satisfy the President's vision. The final strategy will be chosen after further technical studies have been conducted and after much public debate has occurred.
2 Craig, M. K., "The Diverse Roles of Unmanned Precursors in Supporting Manned Missions to Mars." IAF-89-496, October, 1989.
3 "Planetary Exploration Through Year 2000," Part one of a report by the Solar System Exploration Committee of the NASA advisory council, 1983
4 Ryder, G., Spudis, P.D., and Taylor, G.J., "The Case for Planetary Sample Return Missions," EOS, Vol. 70, No. 47, November 21, 1989.
5 Taylor, G., J., Spudis, P. D., "A Teleoperated Robotic Field Geologist", Proceedings of Space 90, Engineering Construction and Operations in Space II, April 1990.
6 Fact Sheet from the Office of the Press Secretary, "U.S. National Space Policy," November 16, 1989.