Connie Carrington

Orbital Express Advanced Video Guidance Sensor

In May 2007 the first US-sponsored fully autonomous rendezvous and capture was successfully performed by DARPAs Orbital Express (OE) mission. For the following three months, the Boeing ASTRO spacecraft and the Ball Aerospace NEXTSat performed multiple rendezvous and docking maneuvers to demonstrate some of the technologies needed for satellite servicing. MSFCs advanced video guidance sensor (AVGS) was a near-field proximity operations sensor integrated into ASTROs Autonomous Rendezvous and Capture Sensor System (ARCSS), which provided relative state knowledge to the ASTRO GN&C system. AVGS was one of the primary docking sensors included in ARCSS. This paper provides an overview of the AVGS sensor that flew on orbital express, a summary of the AVGS ground testing, and a discussion of AVGS performance on-orbit for OE. The AVGS is a laser-based system that is capable of providing bearing at midrange distances and full six degree- of-freedom (6-DOF) knowledge at near ranges. The sensor fires lasers of two different wavelengths to illuminate retro- reflectors on the long range target (LRT) and the Short Range Target (SRT) mounted on NEXTSat. The retro- reflector filters allow one laser wavelength to pass through and be reflected, while blocking the other wavelength. Subtraction of one return image from the other image removes extraneous light sources and reflections from anything other than the corner cubes on the LRT and SRT. The very bright spots that remain in the subtracted image are processed to provide bearing or 6-DOF relative state information. AVGS was operational during the Orbital Express unmated scenarios and the sensor checkout operations. The OE unmated scenarios ranged from 10 meters to 7 kilometers ending in either a docking or a free-flyer capture. When the target was pointed toward the AVGS and in the AVGS operating range and field-of-view (i.e. along the approach corridor of the NEXTSat), the AVGS provided full 6-DOF measurements. The AVGS performed very well during the sensor check-out operations, effectively tracking beyond its 10-degree Pitch and Yaw limit-specifications. AVGS also provided excellent performance during the unmated operations, effectively tracking its targets, and showing good agreement between the SRT and LRT data. The AVGS consistently exceeded the tracking range expectations for both the SRT and LRT. During the approach to re-mate in scenario 3-1 recovery the AVGS began tracking the LRT at 150 m, well beyond the OE specified operational range of 120 meters, and functioned as the primary sensor for the autonomous rendezvous and docking. For all scenarios, the AVGS was used while ASTRO was in the approach corridor to NEXTSat, and during close proximity operations and docking.

Evaluation and comparison of space solar power concepts

Abstract The SSP Exploratory Research and Technology (SERT) program undertaken by NASA in the 1999–2000 timeframe was the third in a recent series of NASA sponsored studies of Space Solar Power (SSP) that began with the 1995 SSP “Fresh Look” Study, and was followed by the SSP Concept Definition Study in 1998. In all three studies, a major focus has been on identifying system concepts, architectures and technologies that may ultimately produce a practical, economically viable source of electrical power to help satisfy the worlds growing energy needs. As part of the SERT program, members of the study team developed several new and innovative SSP concepts that sprung from a desire to address the problem areas of previous system concepts with new technology and system solutions. In the previous SSP studies it has been shown that systems analyses and sensitivity studies are key to understanding the merits of different system concepts and technologies, particularly with respect to their impact on the mass and cost of space hardware and their ultimate economic impact on the cost of SSP-produced electricity. Enabled by analytical models and tools developed over the series of SSP studies, seven different system concepts as well as different technology choices within these concepts were quantitatively compared with one another on the basis of the mass and cost metrics suggested above. Accompanying sensitivity studies have permitted examination of how variations in the projected capabilities of different technologies could affect conclusions drawn from these analyses. This paper summarizes the results of these analytical efforts and from those results, identifies the most promising SSP concepts, including their key technologies and their comparative advantages and disadvantages.

The Abacus/Reflector and Integrated Symmetrical Concentrator: Concepts for Space Solar Power Collection and Transmission

New energy sources are vital for the development of emerging nations, and the growth of industry in developed economies. Also vital is the need for these energy sources to be clean and renewable. For the past several years, NASA has been taking a new look at collecting solar energy in space and transmitting it to Earth, to planetary surfaces, and to orbiting spacecraft. Several innovative concepts are being studied for the space segment component of solar power beaming. One is the Abacus/Reflector, a large sun-oriented array structure fixed to the transmitter, and a rotating RF reflector that tracks a receiving rectenna on Earth. This concept eliminates the need for power-conducting slip rings in rotating joints between the solar collectors and the transmitter. Another concept is the Integrated Symmetrical Concentrator (ISC), composed of two very large segmented reflectors which rotate to collect and reflect the incident sunlight onto two centrally-located photovoltaic arrays. Adjacent to the PV arrays is the RF transmitter, which as a unit track the receiving rectenna, again eliminating power-conducting joints, and in addition reducing the cable lengths between the arrays and transmitter. The metering structure to maintain the position of the reflectors is a long mast, oriented perpendicular to the equatorial orbit plane. This paper presents a status of ongoing systems studies and configurations for the Abacus/Reflector and the ISC concepts, and a top-level study of packaging for launch and assembly.

Multi-Sensor Testing for Automated Rendezvous and Docking Sensor Testing at the Flight Robotics Lab

The exploration systems architecture defines missions that require rendezvous, proximity operations, and docking (RPOD) of two spacecraft both in low earth orbit (LEO) and in low lunar orbit (LLO). Uncrewed spacecraft must perform automated and/or autonomous rendezvous, proximity operations and docking operations (commonly known as ARD (2) CEV-specific trajectories designed to test performance during CEV-like approach and departure profiles; and (3) sensor characterization tests designed for evaluating sensor performance under more extreme conditions as might be induced during a spacecraft failure or during contingency situations. This paper describes the test development, test facility, test preparations, test execution, and test results of the multi- sensor series of trajectories.

SPARTAN: A High-Fidelity Simulation for Automated Rendezvous and Docking Applications

bd Systems (a subsidiary of SAIC) has developed the Simulation Package for Autonomous Rendezvous Test and ANalysis (SPARTAN), a high-fidelity on-orbit simulation featuring multiple six-degree-of-freedom vehicles. SPARTAN has been developed in a modular fashion in Matlab/Simulink to test next-generation automated rendezvous and docking guidance, navigation, and control algorithms for NASA’s new Vision for Space Exploration. SPARTAN includes autonomous state-based mission manager algorithms responsible for sequencing the vehicle through various flight phases based on on-board sensor inputs and closed-loop guidance algorithms, including Lambert transfers, ClohessyWiltshire maneuvers, and glideslope approaches The guidance commands are implemented using an integrated translation and attitude control system to provide 6DOF control of each vehicle in the simulation. SPARTAN also includes high-fidelity representations of a variety of absolute and relative navigation sensors that may be used for NASA missions, including radio frequency, lidar, and video-based rendezvous sensors. Proprietary navigation sensor fusion algorithms have been developed that allow the integration of these sensor measurements through an extended Kalman filter framework to create a single optimal estimate of the relative state of the vehicles. SPARTAN provides capability for Monte Carlo dispersion analysis, allowing for rigorous evaluation of the performance of the complete proposed AR&D system, including software, sensors, and mechanisms. SPARTAN also supports hardware-in-the-loop testing through conversion of the algorithms to C code using Real-Time Workshop in order to be hosted in a mission computer engineering development unit running an embedded real-time operating system. SPARTAN also contains both runtime TCP/IP socket interface and post-processing compatibility with bdStudio, a visualization tool developed by bd Systems, allowing for intuitive evaluation of simulation results. A description of the SPARTAN architecture and capabilities is provided, along with details on the models and algorithms utilized and results from representative missions.

Modular, Reconfigurable, High-Energy Technology Development

The modular, reconfigurable high-energy (MRHE) technology demonstrator project was to have been a series of ground-based demonstrations to mature critical technologies needed for in-space assembly of a high-power high-voltage modular spacecraft in low Earth orbit, enabling the development of future modular solar-powered exploration cargo-transport vehicles and infrastructure. MRHE was a project in the high energy space systems (HESS) program, within NASAs Exploration Systems Research and Technology (ESR&T) Program. NASA participants included Marshall Space Flight Center (MSFC), the Jet Propulsion Laboratory (JPL), and Glenn Research Center (GRC). Contractor participants were the Boeing Phantom Works in Huntsville, AL, Lockheed Martin Advanced Technology Center in Palo Alto, CA, ENTECH, Inc. in Keller, TX, and the University of AL Huntsville (UAH). This paper presents an overview of the MRHE Phase I activities at MSFC and its contractor partners. The assembly demonstration in the Lockheed Martin Advanced Technology Center (LMATC) Robot-Satellite facility was a major Phase I accomplishment. Three robot-satellites successfully demonstrated rendezvous & docking, self-assembly, reconfiguration, adaptable GN&C, deployment, and interfaces between modules. ENTECHs Phase I technology maturation accomplishments include material recommendations for radiation-hardened Stretched Lens Array (SLA) concentrator lenses, and a design concept and test results for a hi-voltage PV receiver. UAHs accomplishments include Supertube heat-pipe test results, which support estimates of thermal conductivities at 30,000 times that of an equivalent silver rod. MSFC performed systems trades and developed a preliminary concept design for a lOOkW-class modular reconfigurable solar electric propulsion transport vehicle. Boeing Phantom Works in Huntsville performed assembly and rendezvous and docking trades and launch vehicles and orbit analysis. A concept animation video was produced by SAIC, which showed rendezvous and docking and SLA-square-rigger (SLASR) deployment in LEO.