Multi-Purpose Space Tug Vehicle AIAA 2015-3893

1. Multi-Purpose Space Tug VehicleAIAA 2015-3893 51th AIAA/ASME/SAE/ASEE Joint Propulsion Conference Orlando, Florida John W. Robinson, Propellant Supply Technology, Seal Beach, California Russel E. Rhodes, Kennedy Space Center, Florida Robert Bell, Robert Bell and Associates, Highlands Ranch, Colorado July 27-29, 2015

2. Multi-Purpose Space Tug Vehicle Major Goals • In-space Reusable Space Tug operation • Satisfy earth orbit transfer functions for necessary space infrastructure development • Initiate implementation of in-space architecture for Sustained Manned Space Habitation • Provide a technology demonstrator to support flight hardware qualification for propulsion components for future on-orbit, moon and planetary operations. • Apply SPST study results to Space Tug design employing choices consistent with expected architecture requirements and goals. • Long term in-space operation with the capability to interact with necessary evolving architecture • Test bed to demonstrate long term operation and qualification of propulsion hardware for future in-space propulsion needs • Workhorse element in the infra-structure development. • Propellant transfer with repeated on orbit refueling will be one of the key requirements to demonstrate

3. Multi-Purpose Space Tug Vehicle Why Reusable Multi-purpose Tug? • Early entry of in-space based architecture element in budget constrained environment • Utilize to support construction of future in-space based architecture node • Begin demonstration of reusable in-space based flight hardware / technology demonstrator • Workhorse Space Tug Vehicle will support in-space architecture construction for manned habitation of space / space infra-structure support • 20 year life and refueling demonstration plus critical flight hardware in-space qualification • Provide Earth orbit transfer functions • Interim flight support for moon and near-earth space missions • Establish routine space operations through-out the Earth-Moon system

4. Multi-Purpose Space Tug Vehicle Key Concepts, Definitions, and Background • Space Tug takes basic design elements from previous flown systems • 20 year life and long-duration space missions including up to 30 days active maneuver time plus 12 month’s quiescent mode. • Engine, adaptor, thermal protection and avionics systems are designed to be upgradeable • Constructed of advanced materials and equipped with a docking device and robotic arms • Future missions include exploration of a near Earth asteroid, moon based support trips and return safely to Earth • Future need ...no clear plan • SPST has been developing a Roadmap for Long Term Sustainable Space Exploration and Habitation. which consist of an all in-space based architecture • The Space Tug vehicle is an early entry in the all space-based architecture • The Multi-Purpose Space Tug Vehicle is intended to do a variety of functions • Support of the overall space architecture • Provide a means of docking with the ISS and other elements as needed providing an in-space development platform while the in-space architecture evolves.

5. Multi-Purpose Space Tug Vehicle KEY CONCEPTUAL DESIGN REQUIREMENTS • Reusable long term (20 yr) in-space operation with on-orbit fuel transfer for sustained operation • Deliver Cargo/Payloads to required orbits based on mission needs • Test-bed for propulsion hardware for long in-space architecture components. • LOX/Hydrogen long duration storage main propellant • Subsystem built with provision for on-orbit upgrades incorporated into design • Pollution free exhaust environment. • Maximize dormant life without re-fueling (Goal of 5 years) • Minimum fluids and pressurant types required • In-space upgrade capability for engine ,power and control systems • Ability to carry two robotic arms • Vehicle equipment and avionics in boattail and universal docking adapter. • Fairing around the top of the engine installation and tankage for micrometeoroid and space debris protection.

6. Multi-Purpose Space Tug Vehicle PROPELLANT AND PROPULSION : • Choice of propellant • Cryogenic (LOX/LH2) selected over storable, solids, or hybrids. • Hign performance propellants with selected mixture ratio and less dense than slush or gelled propellants

7. . Multi-Purpose Space Tug Vehicle Overall Mission Support Requirements • Support future in-space architecture elements and missions to send spacecraft to the MOON, VENUS, ASTEROIDS and MARS both un-manned and manned • Provide Orbital Maneuvering Propulsion (insertion/circularization, de-orbit & Trans-lunar/mars injection) and Reaction Control Propulsiond • Provide for the following functions: • On-board propellant storage; cryogenic on-board propellant and hardware conditioning for engine start • Propellant management (residuals, fuel bias, margins); engine start; engine shutdown • Propellant acquisition/settling • Tank feed; fluid pump/pressure transfer • Propellant inlet/intake management; nozzle exhaust gas management • Propellant/hardware thermal management • Engine control & health management • Propulsion power generation.

8. Multi-Purpose Space Tug Vehicle Space Tug will be in continual operation and maintained for many years with docking provisions to a space ground node for maintenance and servicing on-orbit; and, will be able to support a broad range of missions

9. Multi-Purpose Space Tug Vehicle Multi-Purpose Space Tug has a number of subsystem elements that form the integrated vehicle configuration. Initial design effort will focus on the Propulsion Design elements for the vehicle. Future papers will address the Propulsion System detailed design and overall vehicle including structures & materials, G&C, design & docking mechanisms, thermal control, power and communications.

10. Multi-Purpose Space Tug Vehicle Tank Configuration Selection RL-10 & J-2 engines were used on many applications going back to Apollo .The Saturn I upper stage used a cluster of six RL-10 engine and the Saturn IB and Saturn V upper stages (designated S-IVB for both versions) possessed the larger diameter and mounted a single J-2 engines. S-IVB propellant mass was 87200 kilograms of LOX and 18000 kilograms of LH2 (with some variations depending on mission requirements). The volume of the lighter LH2 was much greater requiring a larger vessel to hold 225750 liters (69500 gallons), as compared with only 73280 liters (20150 gallons) of LOX. System integration issues determined the tank location.The tankage configuration we selected was concentric tanks thermally protecting the LH2 tank with the LOX tank. Engine System Various engine options and cycles were reviewed and the J2-X engine cycle was selected providing self sustaining engine subsystem elements and minimum interfaces with the feedsystem and desired high performance. .

11. Multi-Purpose Space Tug Vehicle Space Tug Design • Space Tug is designed for long term space operation and uses technology improvements needed to enable large quantities of cryogenic fluids to be stored in space for periods up to five years. • Reusable, space-based, cryogenic propulsion system • LOX/LH2 can enable self-pressurization of the propulsion system and are also fed to separate high pressure GLOX/GH2 tanks for pressurization and reaction control.(minimize fluids) • Pressurization of each propellant tank can be provided with pressurant gas either by an engine heat exchanger or the O2H2 burner, which draws oxidizer and fuel directly from the vehicle's LOX and LH2 tanks. • Lithium-ion batteries are considered for primary power in the Space Tug to eliminate on-orbit servicing of either a fuel cell system or an externally-deployed solar array system. • Combination of the low self-discharge rate of the lithium-ion batteries and the low boil-off rate of the cryogenic propellants will enable the Space Tug to be parked for extended periods of time while being immediately available for operation. • LOX/LH2 main propulsion engines utilize all the knowledge gain through the use of the RL-10 and J-2 families of engines which have been demonstrated successfully on many upper stages, including J2-X and RS-68 engines. • Externally-mounted micrometeoroid and space debris shields and multi-layer insulation to control solar heating

12. Multi-Purpose Space Tug Vehicle Space Tug Mission Capabilities • Space Tug Vehicle represents an early introduction of the in-space architecture that must be put into space for man to begin his journey and habitation of space as described in the series of papers on “Roadmap for Long Term Sustainable Space Exploration and Habitation. • Provide an early development of long life in-space hardware needed and begin qualifying essential hardware in advance of the necessary budget and political environment. • Missions and operations to be performed are summarized below: • Primary: • Retrieval of LEO objects and move to new orbits • Retrieval of Higher Orbit objects and move to lower orbit • Enable Space Based Enterprise by providing transportation support for re-supply, etc. • Docking capability with Space Station • Establish in-space propellant transfer • Upgraded major key in-space hardware, i.e. engines, power, etc. • Secondary: • Hardware demonstration for long term in-space use • Qualify long term in space critical hardware

13. Multi-Purpose Space Tug Vehicle Propellant Tank and Thermal Control • Existing cryogenic propulsion systems have reduced storage space with single LOX and LH2 tanks allowing minimum tank surface area and penetrations enabling the inevitable tank heating to be positively controlled. The space Tug tank design includes: • Concentric tank configuration providing additional thermal protection to the LH2 tank enclosed by the LOX tank. • Weight penalty is limited by the space based nature of the Space Tug vehicle deployment.. • Long term storage properly insulated should survive for 5 year life without refueling. • Issues to work include: • Propellant Feed • System Tank Supports • Pressurization Vent System • System Tank Supports

14. Multi-Purpose Space Tug Vehicle OPERATIONAL SUMMARY • The ground node and the spaced based architecture/reusable flight elements requirements have been identified for human habitation of space including: • Infrastructure necessary for the commercial expansion of space activities that will close the business case. • Space Tug to support all the architecture elements as they evolve. • Space Tug to be a working vehicle and provide a component test area to qualify in-space critical components. • Space propellant transfer is a critical technology and we intend to maintain the Space Tug in continual operation for many years with docking provisions to the space station for maintenance and servicing. • Conceptual design analyses indicate that the Space Tug can be developed using current technologies and operational deployment will provide • Substantial improvement in mobility and logistics, servicing and support, throughout the Earth-Moon system. • Infrastructure element that is paramount to encouraging commercialization in space. • Capability for missing element necessary to close the business cases on several applications such as satellite servicing, space debris removal, solar power for earth and space applications, and mining the moon or the asteroids. Conclusions • Accomplishments and current state of the art technology provide necessary resources needed to quickly and efficiently develops a usable, long-life, Multi-Purpose Space Tug • Data has been provided to support the development of the in-space based architecture. • Enable establishment of routine space operations throughout the Earth-Moon system. • Conceptual design analyses indicate that the Space Tug can be developed using current technologies. • Operational deployment will provide substantial improvement in mobility, logistics, servicing. • Provides support throughout the Earth-Moon system. • Will provide an early test bed to demonstrate and qualify flight critical hardware. • Ready to design, develop and deploy an in-space Multi-purpose Space Tug Vehicle.