ALBERT

Description: Some of the most noteworthy missions in space exploration have occurred in the last two decades and owe their success to on-orbit servicing. The tremendously successful Hubble Space Telescope repair and upgrade missions, as well as the completed assembly of the International Space Station (ISS) and its full utilization, lead us to the next chapter and set of challenges. These include fully exploiting the many space systems already launched, assembling large structures in situ thereby enabling new scientific discoveries, and providing systems that reliably and cost-effectively support the next steps in space exploration. In-orbit servicing is a tool--a tool that can serve as the master enabler to create space architectures that would otherwise be unattainable. This paper will survey how NASA's satellite-servicing technology development efforts are being applied to the planning and execution of two such ambitious missions, specifically asteroid capture and the in-space assembly of a very large life-finding telescope.

Description: Some of the most noteworthy missions in space exploration have occurred in the last two decades and owe their success to on-orbit servicing. The tremendously successful Hubble Space Telescope repair and upgrade missions, as well as the completed assembly of the International Space Station (ISS) and its full utilization, lead us to the next chapter and set of challenges. These include fully exploiting the many space systems already launched, assembling large structures in situ thereby enabling new scientific discoveries, and providing systems that reliably and cost-effectively support the next steps in space exploration. In-orbit servicing is a tool-a tool that can serve as the master enabler to create space architectures that would otherwise be unattainable. This paper will survey how NASA's satellite-servicing technology development efforts are being applied to the planning and execution of two such ambitious missions, specifically asteroid capture and the in-space assembly of a very large life-finding telescope.

Description: One of the long-term exploration goals of NASA is manned missions to Mars and other deep space robotic exploration. These missions would include sending astronauts along with scientific equipment to the surface of Mars for extended stay and returning the crew, science data and surface sample to Earth. In order to achieve this goal, multiple precursor missions are required that would launch the crew, crew habitats, return vehicles and destination systems into space. Some of these payloads would then rendezvous in space for the trip to Mars, while others would be sent directly to the Martian surface. To support such an ambitious mission architecture, NASA must reduce cost, simplify logistics, reuse and/or repurpose flight hardware, and minimize resources needed for refurbishment. In-space servicing is a means to achieving these goals. By designing a mission architecture that utilizes the concept of in-space servicing (robotic and manned), maximum supportability can be achieved.

Description: One of the long-term exploration goals of NASA is manned missions to Mars and other deep space robotic exploration. These missions would include sending astronauts along with scientific equipment to the surface of Mars for extended stay and returning the crew, science data and surface samples, and equipment to Earth. In order to achieve this goal, multiple precursor missions are required that would launch the crew, crew habitats, return vehicles and destination systems into space. Some of these payloads would then rendezvous in space for the trip to Mars, while others would be sent directly to the Martian surface. To support such an ambitious mission architecture, NASA must reduce cost, simplify logistics, re-use and or re-purpose flight hardware, and minimize resources needed for refurbishment. In-space servicing is a means to achieving these goals. By designing a mission architecture that relies on the concept of in-space servicing (robotic and manned), maximum supportability can be achieved.

Description: No abstract available

Description: This paper describes the landmark measurement system being developed for terrain relative navigation on NASAs Asteroid Redirect Robotic Mission (ARRM),and the results of a performance characterization study given realistic navigational and model errors. The system is called Retina, and is derived from the stereophotoclinometry methods widely used on other small-body missions. The system is simulated using synthetic imagery of the asteroid surface and discussion is given on various algorithmic design choices. Unlike other missions, ARRMs Retina is the first planned autonomous use of these methods during the close-proximity and descent phase of the mission.

Description: The NASA initiative to collect an asteroid the Asteroid Robotic Redirect Mission (ARRM) is currently investigating the option of retrieving a boulder off an asteroid, demonstrating planetary defense with an enhanced gravity tractor technique and returning it to a lunar orbit. Techniques for accomplishing this are being investigated by the Satellite Servicing Capabilities Office (SSOO) and NASA GSFC in colloboration with JPL, NASA, JSC, LaRC, and Draper Laboratories Inc. Two critical phases of the mission are the descent to the boulder and the Enhanced Gravity Tractor-enhanced gravity tractor demonstration. A linear covariance analysis was done for these phases to assess the feasibility of these concepts with the proposed design of the sensor and actuaor suite of the Asteroid Redirect Vehicle (ARV). The sensor suite for this analysis will include a wide field of view camera, Lidar, and a MMU. The proposed asteroid of interest is currently the C-type asteroid 2008 EV5, a carbonaceous chondrite that is of high interest to the scientific community. This paper will present an overview of the analysis discuss sensor and actuator models and address the feasibility of descending to the boulder within the requirements as the feasibility of maintaining the halo orbit in order to demonstrate the Enhanced Gravity Tractor-enhanced gravity tractory technique.

Description: A control system has been designed to keep a balloon-borne scientific instrument pointed toward a celestial object within an angular error of the order of an arc second. The design is intended to be adaptable to a large range of instrument payloads. The initial payload to which the design nominally applies is considered to be a telescope, modeled as a simple thin-walled cylinder 24 ft (approx.= 7.3 m) long, 3 ft (approx.= 0.91 m) in diameter, weighing 1,500 lb (having a mass of .680 kg). The instrument would be mounted on a set of motor-driven gimbals in pitch-yaw configuration. The motors on the gimbals would apply the control torques needed for fine adjustments of the instrument in pitch and yaw. The pitch-yaw mount would, in turn, be suspended from a motor mount at the lower end of a pair of cables hanging down from the balloon (see figure). The motor in this mount would be used to effect coarse azimuth control of the pitch-yaw mount. A notable innovation incorporated in the design is a provision for keeping the gimbal bearings in constant motion. This innovation would eliminate the deleterious effects of static friction . something that must be done in order to achieve the desired arc-second precision. Another notable innovation is the use of linear accelerometers to provide feedback that would facilitate the early detection and counteraction of disturbance torques before they could integrate into significant angular-velocity and angular-position errors. The control software processing the sensor data would be capable of distinguishing between translational and rotational accelerations. The output of the accelerometers is combined with that of angular position and angular-velocity sensors into a proportional + integral + derivative + acceleration control law for the pitch and yaw torque motors. Preliminary calculations have shown that with appropriate gains, the power demand of the control system would be low enough to be satisfiable by means of storage batteries charged by solar batteries during the day.

Description: Spacecraft sating designs generally have minimal goals with loose pointing requirements. Safe pointing orientations for three-axis stabilized spacecraft are usually chosen to put the spacecraft into a thermally safe and power-positive orientation. In addition, safe mode designs are required to be simple and reliable. This simplicity lends itself to the usage of analog sun sensors, because digital sun sensors will add unwanted complexity to the safe hold mode. The Global Precipitation Measurement (GPM) Mission Core Observatory will launch into lower earth orbit (LEO) at an inclination of 65 degrees. The GPM instrument suite consists of an active radar system and a passive microwave imager to provide the next-generation global observations of rain and snow. The complexity and precision of these instruments along with the operational constraints of the mission result in tight pointing requirements during all phases of the mission. To ensure the instruments are not damaged during spacecraft safing, thermal constraints dictate that the solar pointing orientation must be maintained to better than 6.5 degrees. This requirement is outside the capabilities of a typical analog sun sensor suite, primarily due to the effects of Earth's albedo. To ensure mission success, a new analog sensor, along with the appropriate algorithms, is needed. This paper discusses the design issues involving albedo effects on spacecraft pointing and the development of a simple, low-cost analog sensor and algorithm that will address the needs of the GPM mission. In addition, the algorithms are designed to be easily integrated into the existing attitude determination software by using common interfaces. The sensor design is based on a heritage, commercial off-the-shelf analog sun sensors with a limited field-of-view to reduce the effects of Earth's albedo. High fidelity simulation results are presented that demonstrate the efficacy of the design.

Description: For many years scientists have been utilizing stratospheric balloons as low-cost platforms on which to conduct space science experiments. A major hurdle in extending the range of experiments for which these vehicles are useful has been the imposition of the gondola dynamics on the accuracy with which an instrument can be kept pointed at a celestial target. A significant number of scientists have sought the ability to point their instruments with jitter in the arc-second range. This paper presents the design and analysis of a stratospheric balloon borne pointing system that is able to meet this requirement. The foundation for a high fidelity controller simulation is presented. The flexibility of the flight train is represented through generalized modal analysis. A multiple controller scheme is introduced for coarse and fine pointing. Coarse azimuth pointing is accomplished by an established pointing system, with extensive flight history, residing above the gondola structure. A pitch-yaw gimbal mount is used for fine pointing, providing orthogonal axes when nominally on target. Fine pointing actuation is from direct drive dc motors, eliminating backlash problems. An analysis of friction nonlinearities and a demonstration of the necessity in eliminating static fiction are provided. A unique bearing hub design is introduced that eliminates static fiction from the system dynamics. A control scheme involving linear accelerometers for enhanced disturbance rejection is also presented. Results from a linear analysis of the total system and the high fidelity simulation are given. This paper establishes that the proposed control strategy can be made robustly stable with significant design margins. Also demonstrated is the efficacy of the proposed system in rejecting disturbances larger than those considered realistic. Finally, we see that sub arc-second pointing stability can be achieved for a large instrument pointing at an inertial target.