(U) Structural Systems

(The effects of any budget/program decisions made since the information was collected during 1997-98 are NOT reflected in the National Security Space Road Map (NSSRM).)

Overview: (U)
(U) The goal of this subthrust is to enhance the capability and performance of the payload by reducing the mass of necessary structural support and thermal bus susbsystems. The approach to meeting this goal includes the application of advanced composite materials to both satellite and launch vehicle structural components, the research and development of higher heat flux thermal bus components, and the ability to test new structural materials in a realistic simulation of the space environment.  The ultimate aim is to satisfy the Air Force's needs for lower cost and lighter weight spacecraft and launch vehicle systems.

Description: (U)
(U) The objective of this area is to reduce spacecraft weight by 40% and satellite structural weight by 50% through the application of advanced composite materials and processing techniques.  Light-weight satellite components and bus structures enable designers to increase the useful payload carried.  Light-weight structures may also enable the use of smaller, lower cost launch systems.  We are also pursuing programs that improve fabrication and assembly techniques at lower costs, increase flexibility in satellite integration, investigate the effects of the hostile space environment on advanced materials, and reduce system complexity by integrating electrical sub-systems into the load-bearing structure.

(U)  Composite Joining Technology:  Develop and demonstrate fabrication processes and assembly technologies to improve and further enable joining of composite structural assemblies for Air Force surveillance/commu-ni-ca-tions space systems.  Joining technologies must be understood to avoid premature failures, excess weight, and cost.

(U)  MightySat Satellite Bus:  Design and fabricate a composite satellite bus structure using advanced composite materials and innovative structural designs to improve payload mass-fraction, reduce satellite assembly time, and reduce overall satellite costs.

(U)  Multi-Functional Structure Technology:  Establish a design philosophy for incorporating the ground and power planes, communication bus, and data transmission lines into the spacecraft structure.  This will be achieved through the design, fabrication, test, and evaluation of sub-scale and demonstration integrated electronic structures.  Payoffs include a significant reduction or elimination of cable harnesses, connectors, and component enclosures with a corresponding increase in payload mass-fraction.

(U)  Spacecraft Structure/Components:  Design, fabricate, and test through flight acceptance satellite structural components using advanced composites and innovative design.  Initially this effort is focused to support "in-house" Phillips Lab satellite programs such as MSTI and Mighty Sat.

(U)  Advanced Integrated Structures:  Design and fabricate a standard satellite bus structure using advanced composite materials and structural designs to improve payload mass-fraction, reduce satellite assembly time, and reduce overall satellite costs.  The standard bus structure will incorporate the developed technologies of multi-functional structure, light-weight solar arrays, carbon-carbon thermal radiator, precision optical bench, advanced light-weight antenna structure, and E-beam processing.

(U)  Light-Weight Rigid Solar Arrays:  Design, fabricate, and validate composite isogrid structural panels for large, rigid solar array substrates.  Payoffs include weight savings over  fixed face sheet/honeycomb core construction and increased solar cell efficiency due to improved heat transfer.

(U)  Carbon-Carbon Thermal Radiator:  Design, fabricate, demonstrate, and test advanced carbon-carbon conventional and deployable radiators.  Initial efforts will be directed at substituting conventional aluminum face sheets with carbon-carbon composite materials.  Payoffs include significant increase in thermal efficiency and decrease in structural weight.

(U)  Advanced Composite Radiator:  Demonstrate a spacecraft radiator with sufficiently high conductivity to significantly reduce the complexity and cost of structural radiators.  New result will be reduced weight, reduced cost, and increased reliability.  Hardware demonstration will prepare the concept for future flight demonstration.

(U)  Deployable Composite Radiator:  Demonstrate thermal continuity through deployable articulated structural radiator via the design, fabrication, and demonstration of a high power dissipating, deployable composite radiator.  Hardware demonstration will prepare the concept for future flight demonstration.

(U)  Advanced Communication Antenna Structure:  Reduce on-orbit weight and increase pointing accuracy through design, fabrication, and dem-on-stration of an antenna and its support structure fabricated from advanced composite materials.  Hardware demonstration will prepare the concept for future flight demonstration.

(U)  Space-Based Antenna Structure:  Design, fabricate, validate, and incorporate for a flight experiment a lightweight deployable antenna reflector.  Payoffs include weight savings over conventional antenna mesh technologies and increased dimensional stability due to reduction in thermal strains and fabrication imperfections.

(U)  Advanced Composite Solar Array:  Design, fabricate, validate, and incorporate into a flight experiment lightweight composite structural panels for large, rigid or flexible solar array substrates.  Also included into the solar array panel will be embedded wiring to transfer the power from the solar cells to the spacecraft.  Payoffs include weight savings over conventional face sheet/honeycomb core construction and conventional wiring techniques, and increased solar cell efficiency due to improved heat transfer.

(U)  Electron Beam Processing Technology:  Develop and assess electron beam curing of composite materials as an alternative to conventional processing methods.  Processing of large spacecraft and launch vehicle structures, as well as dimensionally precise/complex composite space structures at potentially lower cost, are possible.

(U)  SAMMES:  Design, fabricate, and test through multiple flight experiments various components used to measure the space environment in different Earth orbits.  This effort will be used to characterize the effects of the space environment on different materials and satellite components, provide comparison with ground testing, and validate analytical models.  

(U)  Combined Space Effects:  Conduct ground simulation tests of spacecraft materials degradation in the low earth orbitÔs environment.  Determine the synergistic effect of atomic oxygen, ultraviolet radiation, hypervelocity debris and energetic charged particles, acting simultaneously, on the mass loss of spacecraft materials.  Compare analytic models with ground simulation results using space experimental data as controls.

(U)  Launch Vehicle Structures:  The objective of this area is to reduce launch vehicle costs and weights by at least 50% and cut lead times by a third through the application of advanced composite materials and structural designs.  Light-weight launch vehicle structures manufactured using advanced composite materials enable existing and next-generation space launch systems to carry more payload into orbit.  In addition, these structures may be manufactured using techniques that can substantially reduce costs and/or lead times compared to conventional methods.  Programs are also being pursued that address vehicle health monitoring, i.e., systems capable of processing data from traditional non-destructive evaluation sources as well as on-board sensors for determining launch readiness.

(U)  Advanced Payload Shroud:  Design, develop, and manufacture a composite isogrid demonstration article that will provide the enabling technology for full-scale development of shrouds for the Titan, Delta, Atlas, and/or next generation expendable launch vehicles.  The integration of acoustic damping material into the process will also be given consideration.  The use of composite isogrid shrouds gives potentially 40% weight and 40% cost savings.

(U)  Advanced Interstage & Adapter:  Design, develop, and manufacture a composite isogrid demonstration article that will provide the enabling technology for full-scale development of interstages and adapters for the Titan, Delta, Atlas, and/or next generation expendable launch vehicles.

(U)  Advanced Interstages, Adapters, and Payload Shrouds:  Through design, fabrication, and test, demonstrate the scaleability and payoffs of composite isogrid cylinders for launch. 

(U)  Reusable Composite LH2 Tank:  Design, fabricate, and test a composite tank that can retain liquid hydrogen without the use of a metallic liner.  Issues that will be addressed are permeability, microcracking, boss/case interface, and insulation system.  The weight reduction achieved by using composite materials is critical to the success of a reusable launch vehicle system.

(U)  Acoustical Attenuation of Composite Launch Structures:  Demonstrate the acoustical attenuation or damping of composite structures through the use of both passive and active damping techniques.  Suppressing the payload environment through the use of passive and active damping will result in lighter weight launch vehicles by eliminating the need for heavy acoustical blankets and a quieter, safer ride for the satellite.

(U)  K3B Thermoplastic Structures:  Demonstrate the use of K3B thermoplastic materials for use in fabricating a reusable composite LH2 cryogenic tank.  Since the K3B thermoplastic is a high temperature material, fewer thermal protection systems are required, thereby minimizing the operational and manufacturing cost associated with a reusable launch vehicle system.

(U)  Integrated Vehicle/Engine Thrust Structure:  Develop and test advanced composite manufacturing technologies for application to the tubular members and connections of truss-type structures.  These structures will be employed to mount and support rocket engines on next-generation launch vehicles.

(U)  Launch Vehicle Structures:  Design, fabricate, and test through flight acceptance launch vehicle structural components using advanced composites and innovative design.  Initially this effort is focused to support the Phillips Lab SSTO reusable launch vehicle programs.

(U)  Computer Aided Flaw Detection (NDE of SRBs):  Select, integrate, and demonstrate non-destructive inspection/evaluation (NDI/E) systems and techniques, and develop computer software for automated health assessment of solid rocket boosters for both in-process evaluation and age-life determination.

(U)  Cryogenic Propellant Tank:  Demonstrate that reusable composite cryogenic tanks will meet the lightweight, operability, and life requirements of stringent launch and space environments.  New composite structural materials that are impact resistant and resist cracks and delaminations when exposed to extreme and cyclic conditions will be explored.  Payoff to the Air Force includes reduced cost of manufacturing fuel tanks that are light, reliable, and reusable.

(U)  Conformable Propellant Tank:  Design, fabricate, test, and integrate into a flight experiment a conformable cryogenic propellant tank that meets the current design of the NASA/AF SSTO vehicle.  Some of the proposed vehicle concepts include designs that require propellant tanks that are not the standard right circular cylinder.  This program will look into fabricating a propellant tank with a conformable geometry.

(U)  Thermal Bus Management:  This area focuses on developing and demonstrating thermal control technologies associated with the following system drivers:

a)  Operational use of high power density devices (high power density electronics and diode lasers).

b)  Operational use of high temperature power systems (NaS batteries).

c)  Minimize vehicle weight and heater power to achieve launch vehicle step-down.

d) Transport of increasingly larger amounts of heat with minimal temperature drop using a centralized thermal bus.

(U)  Key technical challenges for heat transfer and dissipation technologies include:  understanding the parameters that allow for rapid, reliable start-up and longer term operation of two phase capillary devices in a zero-g and adverse-g environment; developing low cost advanced materials that allow for dissipation of heat fluxes from microelectronic devices; developing capillary wicks smaller than 1 micron pore size to provide 1-g robustness; and developing flexible or rotateable joints that allow for the efficient transport of heat from a high power surface area-limited spacecraft bus outward to a deployable radiator.  Requirements within these areas include 0-g operability (most heat transfer approaches require two-phase fluids), very low weight, high thermal conductivity values, radiation/atomic oxygen survivability, and ease of integration.  As with cryogenic coolers, a high confidence level in the reliability and performance of these technologies must be established prior to operational utilization.  As such, substantial ground characterization (performance and endurance characterization) in concert with fully integrated flight experiments are  required.  To this end, Phillips Laboratory, in cooperation with industry and NASA, is leading the conduct of laboratory characterization, ground demonstrations, and flight experiments.  

(U)  1)  Component Thermal Control Development Program:  This program is focusing on the thermal control of high temperature and high power density components.  To enable the use of high temperature devices such as NaS batteries, we are developing passive, high temperature operation (600 K and above) heat pipes. Early FY95 concluded extensive ground characterization of several heat pipe designs.  The focus of this activity was to find the best combination of reliability and performance.  Now in FY96, an experiment via the Shuttle Hitchhiker program will be integrated and flown to evaluate 0-g issues associated with micro-gravity fluid behavior. Spacecraft developers are unable to thermally control next generation electronic devices via traditional design approaches.  As such, a cooperative program with the Phillips Laboratory electronics division has been established to address this problem.  A key aspect of this program is the completion and demonstration of a laboratory test bed in early FY97.  This test bed will allow us to jointly study high power density thermal control issues and the effectiveness of several thermal control approaches (including micro-channel cooling, and the use of high conductivity materials).  Long-term objectives include integrated demonstrations of new electronic devices with appropriate thermal control techniques.

(U)  2) Lightweight Thermal Bus Development Program:  Currently, a spacecraft's thermal bus is comprised of heat pipes (discrete devices that efficiently transport heat) and aluminum, structural radiators.  In general, weight savings cannot be achieved by further optimizing these two technologies.  As such, PL is pursuing the investigation and development of advanced heat transport systems, including the capillary pump loop (CPL) and a CPL alternative -- a Russian looped heat pipe (LHP), and the development of composite radiators (both structural and deployable).  If successfully developed and demonstrated, these technologies will provide weight savings of up to 50% and a potential reduction in power requirements of up to 50%.  The current emphasis of our advanced heat transport program, including CPL and LHP technology,  is characterizing behavior within these two systems and evaluating advanced system design approaches via a laboratory test bed. The continued focus of this program is developing advanced components such as evaporators, condensers, and fluid management systems.  In addition, we are cooperatively working with NASA and industry to demonstrate CPL and LHP technology applicable to very small satellites (< 50 watts).  

(U)  Because of large improvements in specific conductivity (a comparison of conductivity versus weight), constructing radiators out of composites should significantly decrease weight.  However, there are several issues related to fabrication, survivability, and spacecraft integration that must be satisfactorily addressed before these weight savings can be realized.  To this end, a cooperative program with the USAF Material Laboratory, the US Navy, and NASA has been established to pursue the development of a lightweight, composite radiator.  Key elements of this program include developing radiator coatings, fabrication techniques, and integration/ joining techniques.  In addition, extensive performance and endurance characterization will be performed at the component and system level.  Currently, we plan to have sub-scale components in test by FY96.  If successful, the development of a full-scale radiator will be completed, incorporating this technology with a CPL system.

(U)  3) Prototype Thermal Bus Development Model:  As mentioned above, current and near-term spacecraft require innovative, robust thermal control systems to maintain spacecraft components within the allowable temperature ranges utilizing a state-of-the-art centralized thermal bus.  As such, a new program that will address these issues and bring to light possible integration issues has been initiated in FY96 with TRW.  This program will provide: 1) the most reliable CPL architecture yet devised; 2) a lightweight, deployable thermal radiator usable with either a heatpipe or CPL thermal bus; and 3) improved electronic packaging and integration approaches that use high-thermal-conduc-tivity graph-ite materials for heat spreading. This 36-month program will culminate in the thermal test of an integrated prototype model that incorporates all of these components as well as two novel flat plate heatpipes.  The testbed will be delivered to Phillips Laboratory for further testing at the end of the program.

(U)  The development activities within this program will ultimately resolve many design and integration issues that have thus far hindered implementation of CPLs and deployable radiators on high-powered spacecraft.

(U)  Space Environmental Effects

(U)  Hypervelocity Impact on Thermal Protection Systems
Demonstrate the effects of hypervelocity impacts on the thermal protection system (TPS) to be used on a reusable launch vehicle (RLV) system.  Samples of the TPS will be impacted by hypervelocity particles to determine their survivability and ability to be reused.  In order for a RLV to be reusable, the TPS must be able to survive numerous flights prior to requiring replacement.

User Impact: (U)
(U) None.

Programmatics: (U)
(U) Concept/Technology.
	(U) IOC: 02/1996 (2QFY1996).

Related Initiatives: (U)
(U) None.

Related Requirements: (U)
(U) None.

Related Categories: (U)
(U) Space Vehicles Technology

Road Map Placements: (U)
(U) TECHNOLOGY- RDT&E.

Lead Office: (U)
(U) Air Force.

Date of Information: (U)
01 July 1997

(The effects of any budget/program decisions made since the information was collected during 1997-98 are NOT reflected in the National Security Space Road Map (NSSRM).)