Revolutionary Aerospace Systems Concepts Orbital Aggregation & Space Infrastructure Systems (OASIS) Preliminary Architecture and Operations Analysis FY2001 Final Report June 10, 2002 This page intentionally left blank. Foreword Just as the early American settlers pushed west beyond the original thirteen colonies, the world today is on the verge of expanding the realm of humanity beyond its terrestrial bounds. The next great frontier lies ahead in low-Earth orbit and beyond. Commercialization of space has recently been mostly limited to communications and remote sensing applications, but materials processing, manufacturing, tourism and servicing opportunities will undoubtedly increase during the first part of the new millennium. Discoveries hinting at the existence of water on Mars and Europa offer additional motivation for establishing a space-based infrastructure that supports extended human exploration of the solar system. If this space-based infrastructure were also utilized to stimulate and support space commercialization, permanent human occupation of low-Earth orbit and beyond could be achieved sooner and more cost effectively. The purpose of this study is to identify synergistic opportunities and concepts among human exploration initiatives and space commercialization activities while taking into account technology assumptions and mission viability in an Orbital Aggregation & Space Infrastructure Systems (OASIS) framework. OASIS is a set of concepts that provide a common infrastructure for enabling a large class of space missions. The concepts include communication, navigation and power systems, propellant modules, tank farms, habitats, and transfer systems using several propulsion technologies. OASIS features in-space aggregation of systems and resources in support of mission objectives. The concepts feature a high level of reusability and are supported by inexpensive launch of propellant and logistics payloads. The anticipated benefits of the synergistic utilization of space infrastructure are reduced mission costs and increased mission flexibility for future space exploration and commercialization initiatives. i This page intentionally left blank. ii Executive Summary The study was performed under the Revolutionary Aerospace Systems Concepts (RASC) activity led by the NASA Langley Research Center (LaRC). LaRC was chartered by the NASA Administrator to be the lead Center for evaluating revolutionary aerospace systems concepts and architectures to identify new mission approaches and the associated technologies that enable these missions to be implemented. Mission There are many challenges confronting humankind’s exploration of space, and many engineering problems that must be solved in order to provide safe, affordable and efficient in-space transportation of both personnel and equipment. These challenges directly impact the commercialization of space, with cost being the single largest obstacle. One method of reducing cost is to develop reusable transportation systems— both Earth-to-orbit systems and in-space infrastructure. Without reusable systems, sustained exploration or large-scale development beyond low-Earth-orbit (LEO) appears to be economically non-viable. However, reusable in-space transportation systems must be capable of both high fuel efficiency and “high utilization of capacity,” or economic costs will remain unacceptably high. Fixed infrastructures have been suggested as one approach to solving this challenge; for example, rotating tether approaches. However, these systems tend to suffer from high initial costs or unacceptable operational constraints. Another significant challenge is minimizing the in-space travel time for crewed missions. The risks associated with human missions can be significantly reduced by decreasing the time that the crew is in transit. Besides nuclear thermal propulsion systems and the inherent public concerns that accompany the use of these systems near the Earth, the propulsive system that provides a reasonably high thrust and short transit time is one that uses chemical propellants. One significant drawback to chemical systems is the relatively low specific impulse (Isp) requiring large propellant quantities to provide the velocity changes necessary to complete a mission. Solar electric propulsion (SEP) systems can provide high fuel efficiency but only at the cost of low thrust and transit times that are not compatible with crewed missions. An innovative concept that integrates the best features of both chemical and solar electric propulsive systems is proposed in this report. This concept appears to hold the promise of solving the issues associated with other approaches and may provide a new family of capabilities for future exploration and commercial development of near-Earth space and beyond. Study Summary An architecture composed of common in-space transportation elements was derived to support both human exploration and commercial applications in the Earth-moon neighborhood. Mission concepts utilizing this architecture are predicated on the availability of a low-cost launch vehicle for delivery of propellant and re-supply logistics. Infrastructure costs would be shared by Industry, NASA and other users. iii The Orbital Aggregation & Space Infrastructure Systems (OASIS) architecture minimizes point designs of elements in support of specific space mission objectives and maximizes modularity, reusability and commonality of elements across many missions, enterprises and organizations. A reusable Hybrid Propellant Module (HPM) that combines both chemical and electrical propellant in conjunction with modular orbital transfer/engine stages was targeted as the core OASIS element. The HPM provides chemical propellant for time critical transfers and provides electrical propellant for pre- positioning or return of the HPM for refueling and reuse. The HPM incorporates zero- boil off technology to maintain its cryogenic propellant load for long periods of time. The Chemical Transfer Module (CTM) is an OASIS element that serves as a high energy injection stage when attached to an HPM. The CTM also functions independently of the HPM as an autonomous orbital maneuvering vehicle for proximity operations such as payload ferrying, refueling and servicing. The Solar Electric Propulsion (SEP) Stage serves as a low thrust transfer stage when attached to an HPM for pre-positioning large/massive elements or for the slow return of elements for refurbishing and refueling. The Crew Transfer Vehicle (CTV) is used to transfer crew in a shirt sleeve environment from LEO to the L1 Earth–Moon Lagrange point and back as well as to the International Space Station (ISS) and any other crewed infrastructure elements. Parametric launch cost analysis of the OASIS architecture supporting NASA Lunar Gateway missions has demonstrated the potential cost advantage of this reusable architecture over an architecture with few reusable elements. When using today’s Space Shuttle for initial launch of the OASIS elements, the cross-over point where the OASIS architecture becomes more cost effective than non-reusable architectures is at approximately 8 lunar missions (4 to 4 ½ years assuming lunar missions every six months). If a high capacity, relatively low cost Delta IV-H is used for initial launch of OASIS elements, this cross-over point occurs at lunar mission #3 (1 ½ years). Analysis of commercial scenarios utilizing the HPM and CTM for satellite delivery and servicing show that a launch cost of $1,000/kg for propellant to re-supply the space-based elements is required for economic viability given a range of assumptions for element development costs and frequency of use. In these scenarios, Industry will leverage government investment in OASIS infrastructure development. Technology Identification A major assumption in support of the OASIS architecture is the availability of technologies to enable the routine and inexpensive launch of propellant to LEO. These technologies are being identified through NASA’s Space Launch Initiative (SLI). Many advanced technologies also are necessary to make an OASIS architecture a reality, including technologies specifically applicable to the HPM, CTM, CTV, and SEP Stage. With the proper funding levels, many of the technologies could be available within the next 15 years. Accelerated funding levels could make this timeline significantly shorter. The following is a brief description of some of the key technologies needed for the development of an OASIS architecture: iv • Zero boil-off cryogenic propellant storage system providing up to 10 years of storage without boil-off • Extremely lightweight, integrated primary structure and meteoroid and orbital debris shield incorporating non-metallic hybrids to maximize radiation protection • High efficiency power systems such as advanced triple junction crystalline solar cells providing at least 250 W/kg (array-level specific power) and 40% efficiency, along with improved radiation tolerance • Long-term autonomous spacecraft operations including rendezvous and docking, propellant transfer, deep-space navigation and communications, and vehicle health monitoring (miniaturized monitoring systems) • Reliable on-orbit cryogenic fluid transfer with minimal leakage using fluid transfer interfaces capable of multiple autonomous connections and disconnects • Lightweight composite cryogenic propellant storage tanks highly resistant to propellant leakage • Advanced materials such as graphitic foams and syntactic metal foams • Long-life chemical