The Moon, Mars, and Beyond
David S. Adlis
NASA will send a new generation of explorers to the moon, and then on to Mars and other destinations in the solar system. Aerospace is providing its unique expertise to help in this endeavor.
NASA's plan for human exploration of the solar system—the Constellation program—includes a series of missions to return astronauts to the moon (see sidebar, NASA's Vision for Space Exploration). A centerpiece of this plan is the Orion capsule, which will fly atop the Ares I crew launch vehicle. Orion will be similar in shape to the Apollo spacecraft that took Americans to the moon in 1969–1972, but significantly larger; it will accommodate four crew members on missions to the moon, and six on missions to the International Space Station or Mars. For missions to the moon, an Ares V cargo launch vehicle will precede Orion into low Earth orbit, bringing with it the Earth departure stage and the lunar module. Orion will dock with the lunar module, and the Earth departure stage will propel both on their journey to the moon. Upon reaching the moon, astronauts will use the lunar landing craft to visit the surface, while the Orion spacecraft stays in lunar orbit. Once the lunar mission is complete, the astronauts will return to Orion using a lunar ascent module. They will then use the service module main engine to break out of lunar orbit and head back to Earth.
 (NASA) |
Ares I uses a single five-segment solid rocket booster, a derivative of the space shuttle's four-segment solid rocket booster, for the first stage. A liquid-oxygen/liquid-hydrogen J-2X engine derived from the engine used on Apollo's second stage will power the Ares I second stage. Ares V will use RS-68 liquid-oxygen/liquid-hydrogen engines mounted below a larger version of the space shuttle's external tank along with two five-segment solid propellant rocket boosters for the first stage. The upper stage will use the same J-2X engine as the Ares I. Orion borrows its shape from the capsules of the past, but takes advantage of 21st-century technology in computers, electronics, life support, propulsion and heat-protection systems. For example, Orion will reenter Earth's atmosphere using a newly developed thermal protection system, with parachutes to further slow its descent.
Ares I Development
Aerospace is supporting several aspects of NASA's Ares I development efforts. For example, NASA plans to conduct test flights of various vehicle configurations early in the development cycle to increase confidence in, and reduce risk for, the final vehicle configuration. Aerospace is supporting the two earliest test flights, as well as the main Ares I program itself.
Comparisons of previous, current, and future human spaceflight launch vehicles. Aerospace provided a quick-look assessment of the flight dynamics and flight control aspects of the Ares I (and Ares I-X, which is not pictured) launch vehicles, particularly with respect to flight control algorithms. (NASA/John Frassanitno and Associates) |
NASA's first test flight is called Ares I-X. It will provide an early opportunity to evaluate hardware, facilities, and ground operations associated with the Ares I and gather critical data during ascent of an unmanned, simulated Orion and Ares I launch vehicle stack. The Ares I-X test vehicle will use a four-segment solid rocket motor from the shuttle program in place of the five-segment version that will fly on Ares I. It will have mass simulators for the entire upper portion of the vehicle forward of the solid rocket motor. The avionics boxes and flight software are being provided by Lockheed-Martin and are of Atlas V heritage. By preserving the Ares I vehicle's outer dimensions and mass while using existing propulsion and avionics systems, NASA can perform a useful, relatively simple test that will provide valuable engineering data early in the program. Aerospace is performing several independent verification and validation analyses in support of the Ares I-X flight test. The disciplines involved include fluid mechanics, thermal, loads/dynamics, structures, mechanical systems, flight software, guidance, navigation, controls, and vibro-acoustics. To date, more than 50 Aerospace engineers have supported the program in various degrees. The Ares I-X launch is expected to take place in the summer of 2009. Aerospace will be involved through the flight readiness review process and postflight analyses.
The second test flight, named AA-1, will solely test the ascent abort subsystem and is expected to fly in mid 2010. Aerospace's current involvement in the AA-1 test flight is significantly less than for Ares I-X, and primarily focuses on fluid mechanics and loads/dynamics. Aerospace experts in these disciplines are also providing in-line consulting support to the main Ares I program to assist NASA with their wind tunnel test programs and vehicle-coupled loads predictions. These efforts take advantage of knowledge gained in supporting Ares I-X.
Engineers conduct a hot-fire test of subscale main injector hardware at NASA's Marshall Space Flight Center to support development of the RS-68 engine for Ares V. An Aerospace study on the possibility of using RS-68 engines in place of the Space Shuttle Main Engine (SSME) contributed to NASA's decision to retire the SSME. (NASA) |
Environments, Loads, and Structural Dynamics
As a member of the Ares I Loads Panel, Aerospace provided a comprehensive assessment of the state of the art in loads analyses. This included analysis of the liftoff and atmospheric flight loads needed to design the launch vehicle and its payload. As part of this effort, Aerospace provided an in-depth review and documentation of the equations used in combining the various load contributors encountered during atmospheric flight. For the critical buffet loads—caused by the formation and interaction of shock waves, shock-wave oscillations, flow separation, and attached turbulent boundary layers—Aerospace developed the loads analysis methodology. In addition, Aerospace supported development of Ares I and Ares I-X buffet forcing functions, and later supported the buffet wind-tunnel test for Ares I-X and the planning of such a test for Ares I. Aerospace independently analyzed the Ares I-X wind-tunnel test data and developed buffet forcing functions and developed procedures to remove from the data features related to the test that would not occur in flight.
During transportation in the launch configuration and prior to liftoff, launch vehicles can experience severe loads caused by ground winds. Aerospace performed independent structural margin assessment of the Ares I-X aft end for ground wind loading. Similarly, Aerospace provided independent verification and validation of thermal analyses, including troubleshooting the models and assessing the adequacy of case definitions, and conveyed lessons learned regarding EMC, EMI, and lightning.
With Ares I using a lengthened version of the space shuttle solid rocket motor, NASA had predicted that motor thrust oscillations could induce response levels that approach, or exceed, the limits deemed acceptable for human flight. Because of Aerospace's experience with respect to this phenomenon for several launch vehicles, Aerospace was asked to assess the analysis methodology used by NASA. Aerospace analyzed space shuttle thrust-oscillation data and developed independent analysis spectra for the motor pressure oscillations—with close attention to data-acquisition fidelity, time scaling, and statistical behavior. Aerospace also provided expertise with respect to the potential for a pogo-like interaction between the motor thrust oscillations and structural responses. As a result of increased understanding of the thrust oscillation problem, NASA is now modifying the design of Ares I to provide additional damping of ascent vibrations. Aerospace also assessed roll-out and on-pad structural margins, provided independent assessment of mass properties, and performed structural-modes uncertainty analyses.
The Orion crew exploration vehicle. (NASA) |
Orion Avionics
Since the fall of 2007, Aerospace engineers have worked alongside NASA engineers focusing on the Orion avionics subsystem, which includes the hardware and software components for flight software, communications and tracking, command and data handling, instrumentation, and crew displays and controls. Orion avionics will operate with crew oversight, similar to the space shuttle, but will also have to support unmanned operations. The Orion contractor team has been conducting trades studies to generate avionics subsystem requirements for both modes of operation. The space shuttle avionics were developed in the late 1970s and early 1980s and rely on electronic components of that era. But the last 18 years have brought significant electrical power savings and computational power that can be incorporated into avionics design. Advances in high-reliability avionics based on commercial fly-by-wire aircraft can be applied, as well as improvements in radiation susceptibility. In addition, whole new families of parts that support flexible designs such as field-programmable gate arrays (FPGAs) have become available. Methods for enhancing the reliability and robustness of avionics bus architectures are also under consideration. The Orion design team is balancing these opportunities with the typical concerns for spacecraft mass and power allowances as it finalizes its planning before the preliminary design review.
Aerospace has been active in the areas of engineering design, development, and testing for the Orion spacecraft, including technical discipline support, engineering analysis, technical insight, technology assessments, and programmatic support. Aerospace is supplementing NASA's systems engineering and integration team and is serving as co-chair of the avionics requirements team, charged with requirements analysis and oversight. Part of these duties entails analysis and planning for the test and verification being developed for Orion. Aerospace has also provided specialized engineering support, such as radiation environment definition and effects analysis and expertise with phased-array antennas and electrical, electronic, and electromechanical parts. Aerospace is also involved with analysis of security protocols for communications between the Orion spacecraft and the ground.
The abort motor manifold for Orion's launch abort system is readied for a hydro proof test to validate engineering models about how it will respond to induced pressure and vehicle flight loads. Aerospace compiled historical data on solid rocket motors with an eye toward developing reliability comparisons for the launch abort system motors. (NASA) |
Safety and Mission Assurance
Aerospace has been providing independent assessments for NASA in the area of safety and mission assurance for a number of years, and an increasing number of these have been in support of the Constellation program. For example, the extremely long and slender profile of the Ares I and I-X launch vehicles provides a challenging environment for control design. To aid in test and verification, Aerospace provided a quick-look assessment of the flight dynamics and flight control aspects of the launch vehicle, particularly with respect to flight control algorithms, and specifically recommended additional instrumentation for structural mode identification.
A launch abort system will sit atop the Orion crew module to provide safe escape for astronauts in an emergency. The system will have three different solid rocket motors for abort, jettison, and attitude control. Aerospace compiled historical data on solid rocket motors with an eye toward developing reliability comparisons for the launch abort system motors. Aerospace engineers used design data to summarize the characteristics and risks to better define the uncertainties associated with these motors when making a reliability estimate. The analysis further summarized best practices for solid rocket motors developed through decades of experience. In addition, Aerospace independently reviewed the vendor qualification plans and provided NASA with specific recommendations to enhance mission assurance.
Unlike the Apollo crew module, each Orion crew module is expected to be refurbished and reused up to ten times. Aerospace performed an initial investigation into reusability parameters to build a framework for a comprehensive reusability trade study and risk evaluation. Components of this assessment included program reusability requirements, flight-rate considerations, a comparison with the space shuttle reusability experience, landing scenarios, and capsule reusability parameters. Aerospace recommended using this initial investigation as a guide to performing a comprehensive trade study at the NASA Headquarters level.
Aerospace reviewed the planning processes described by Constellation documentation and compared them with the processes used to develop other space systems. This review identified issues related to the software lifecycle and the various development, configuration-management, sustainment, and day-of-launch roles. Aerospace also identified metrics needed to calculate software turnaround times and minor-versus-major changes to software between launches and on the day of launch.
The ability of an electronics system to provide insight into its status is highly beneficial in spaceflight. Spacecraft operators need insight into critical aspects of a system in the event of problems, and such insight can be achieved by folding self-test information from subsystems or components into the operational telemetry channel. Higher-level functions that implement autonomy—such as integrated vehicle health management systems or fault detection, isolation, and recovery functions—can benefit from improved self-test capability. Also, launch processing costs could be reduced if self-testing were to provide reliable information without requiring unit removal. Using historical and recent developments in Department of Defense launch vehicles and spacecraft, Aerospace investigated the costs and benefits of avionics self-test capability for crew exploration and launch vehicles, including modeling approaches for evaluating self-test costs against launch vehicle availability.
To identify any residual risk associated with electrical assembly workmanship requirements, Aerospace compared ANSI standards with NASA standards and provided detailed commentary on similarities and differences. Specific to the Orion service module, Aerospace investigated failures and anomalies due to workmanship of propulsion strip heaters, internal tank heaters, solar array and antenna deployment mechanisms, wiring harnesses, and avionics cold plates and provided recommendations for mitigating and preventing them.
A model of the integrated crew module and launch vehicle sits in one of four wind tunnel facilities used by NASA. Aerospace supported the buffet wind-tunnel test for Ares I-X and the planning of such a test for Ares I. Aerospace independently analyzed the Ares I-X wind-tunnel test data. (NASA/Boeing) |
Aerospace assessed NASA quality assurance requirements and significant data deliverables, such as acceptance-data package content, and compared them with those used for national security space programs. The initial comparison revealed major differences between NASA requirements and military requirements, and highlighted areas of potentially significant cost savings for NASA without additional risk. Primary recommendations included the restructuring and reduction of program safety, reliability, and quality assurance requirements and documents—including the consolidation of quality assurance requirements—and the establishment of electronic access to verification information in lieu of copious hard-copy documentation.
Aerospace evaluated safety documentation for the Ares I system definition review, including the failure modes and effects analysis, probabilistic risk assessment, hazard analysis, fault tree report, and the safety, reliability, and quality assurance plan. This review showed some inconsistencies among documents, highlighted some assumptions that were potentially very nonconservative, and provided a list of potential hazards or issues that did not appear to be fully addressed.
NASA sought liquid rocket engine experts to review hazard reports for the Ares I upper-stage engine. Aerospace provided a detailed review—and a perspective from outside the NASA community. This outside perspective allowed experts who have reviewed and understood issues and resolutions with successful national security space systems to evaluate the assumptions and designs for Ares I rocket systems, providing valuable insight that might not be available in the NASA community to the same extent, given the limited number of liquid rocket engine designs they've been using for the past few decades.
Aerospace personnel served on an expert panel to provide an independent review of the certification requirements for the Orion heat shield for lunar return and the guidance, navigation, and control system for a skip entry. The team raised several issues and made recommendations on material selection and qualification as well as arc-jet flow field modeling techniques and facility upgrades.
Related Projects and Systems
Aerospace's extensive experience in test and verification was brought to bear in NASA's development of the Constellation Environmental Qualification and Acceptance Testing Requirements (CEQATR) document. The CEQATR is based on MIL-STD-1540, and Aerospace familiarity with this standard contributed greatly to baselining the new human spaceflight standard.
In support of NASA's Program Analysis and Evaluation office, Aerospace studied the possibility of using RS-68 engines in place of the Space Shuttle Main Engine (SSME). The results of this study contributed to NASA's decision to retire the SSME. The RS-68 was chosen as the propulsion system for Ares V, increasing performance to translunar injection and potentially saving billions of dollars over the life of the program.
Aerospace, as part of a national assessment of rocket engine test facilities and program needs over the next 14 years, performed a first-order assessment of the preliminary concept for the NASA Stennis Space Center A-3 Test Facility that will support the J-2X altitude simulation testing program.
Crew vehicle docked with lander and departure stage, leaving Earth orbit. (NASA/John Frassanito and Associates) |
Aerospace is part of the Lunar Dust Management Project core team that is chartered to identify and develop techniques for dust mitigation for extended human missions on the surface of the moon. Charged dust on the moon is abrasive, and it adheres to spacesuits and other surface systems, working its way into critical joints and other mechanisms. The abrasive dust can cause leaks in the spacesuits, degrade performance of other hardware, and reduce surface exploration and habitation times. Sufficient charge can build up to levitate particles, and even to violently eject them. As part of the core team, Aerospace developed the criteria for prioritizing dust mitigation technologies and recommended and performed detailed assessments of commercially available technologies that could be applied. These include removal methods such as mechanical brushing and gas blowing for large particles, electrostatic removal of small particles, and magnetic methods for magnetic fractions. In addition, mitigation techniques to prevent particle adhesion are also being evaluated, including design improvements (dust-repellent coatings and smooth surfaces), strippable coatings, and electrodynamic screens. To prevent the dust from being dispersed from the lunar surface, methods for surface stabilization are also being evaluated, similar to the techniques used by the DOD to prepare landing areas in desert regions.
NASA engineers are embarking on a number of high-profile spaceflight government-furnished equipment (GFE) projects for the Constellation program. In light of this, NASA is revitalizing its systems engineering processes. As part of this effort, Aerospace has been invited to participate in a number of milestone reviews to provide independent technical, cost, and schedule scrutiny to enhance the success of the projects. During the past year, Aerospace has supported milestone reviews for the Low Impact Docking System (LIDS), the Androgynous Peripheral Attach System (APAS), to LIDS Adapter System (ATLAS), the ISS to CEV Communications Adapter (ICCA), and the CEV Parachute Assembly System (CPAS). This has led to more rigor in products and entrance/exit criteria for the GFE reviews, thus reducing risk.
Conclusion
As NASA embarks on an ambitious new program for human spaceflight, including a new generation of launch vehicles, Aerospace's cross-agency and cross-program perspective and insight has proved to be a valuable resource. By virtue of its experience with new launch vehicles and space systems, and its uniquely independent role in national security space, Aerospace can provide a distinctive contribution to the Constellation program and help NASA ensure mission success.
Acknowledgment
The author thanks John Brekke and Alvar Kabe, as well as the Houston team, for their assistance in writing this article.
