Browse Topic: Spacecraft guidance

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Docking System Enables Safe Rendezvous in SpaceTBMG-3561412/1/2019
Even though it has been done many times before, the docking maneuver between two objects in space is always a delicate and potentially dangerous procedure. The speed is extremely high (about 28,000 km/h in the case of the International Space Station, or ISS), and corrections are difficult. When the two objects are about to meet, maneuvering thrusters can no longer be used since their exhaust plumes can cause damage. To prevent harm, cargo transporters are caught by a robotic arm installed in the ISS and berthed manually. Manned spacecraft, on the other hand, dock directly in a computer-controlled process.
Ray Optics Simulation of Inertial Navigation SystemsTBMG-3328511/1/2018
Attitude detection is a crucial element in aircraft and spacecraft navigation. The motion of an aircraft consists of a translational component (motion of its center of mass with respect to the Earth) and a rotational component (rotation of the aircraft around its center of mass). Attitude detection is the measurement of the rotational component of the aircraft's motion, and depending on the mission this measurement might need to be extremely accurate. Advances in computer simulation technology have made it easier than ever to set up high-fidelity numerical simulations of inertial navigation and attitude control systems of the type typically found aboard aircraft and spacecraft.
Advanced Numerical Integration Techniques for High-Fidelity SDE Spacecraft SimulationTBMG-238962/1/2016
Simulation study is an integral part of the validation of navigation algorithms for spacecraft. While it is possible to come up with an estimate of a navigation algorithm’s performance with a low-fidelity system model, the mathematical analysis is intractable for higher-fidelity models that include fuel slosh, flexible booms, sensor saturation, etc. Thus simulation study is a vital step in validating navigation algorithms before an actual satellite is launched.
Wald Sequential Probability Ratio Test for Space Object Conjunction AssessmentTBMG-222066/1/2015
When a maneuverable spacecraft confronts a potentially unsafe conjunction with another space object, its operators must decide whether to maneuver to mitigate the risk of a collision. Such decisions may not be straightforward, since the operators must balance their confidence in the predictions that detected the conjunction, the actual likelihood of a collision, any risk inherent in performing the maneuver, interruptions to the mission’s ongoing operations, and long-term consequences such as depletion of consumable propellant. The most common metric for assessing the risk associated with a conjunction is the collision probability.
Advanced Navigation Strategies for Asteroid Sample Return MissionsTBMG-212761/1/2015
Sample-return missions to primitive solar system bodies (asteroids, comets, and planetary satellites) can provide a wealth of scientific information and insight into the composition and origins of the solar system. Recent interest in primitive body missions has been driven by the possibility of human near-Earth object missions, Earth conjunction analysis, and scientific discovery. Precision navigation to acquire a sample from a primitive solar system body and return it to Earth presents unique challenges beyond traditional Earth-based and interplanetary missions.
Three-Axis Attitude Estimation With a High-Bandwidth Angular Rate SensorTBMG-156712/1/2013
A continuing challenge for modern instrument pointing control systems is to meet the increasingly stringent pointing performance requirements imposed by emerging advanced scientific, defense, and civilian payloads. Instruments such as adaptive optics telescopes, space interferometers, and optical communications make unprecedented demands on precision pointing capabilities. A cost-effective method was developed for increasing the pointing performance for this class of NASA applications.
Spacecraft Guidance, Navigation, and Control Visualization ToolTBMG-109249/1/2011
G-View is a 3D visualization tool for supporting spacecraft guidance, navigation, and control (GN&C) simulations relevant to small-body exploration and sampling (see figure). The tool is developed in MATLAB using Virtual Reality Toolbox and provides users with the ability to visualize the behavior of their simulations, regardless of which programming language (or machine) is used to generate simulation results. The only requirement is that multi-body simulation data is generated and placed in the proper format before applying GView.
Safe Onboard Guidance and Control Under Probabilistic UncertaintyTBMG-96094/1/2011
An algorithm was developed that determines the fuel-optimal spacecraft guidance trajectory that takes into account uncertainty, in order to guarantee that mission safety constraints are satisfied with the required probability. The algorithm uses convex optimization to solve for the optimal trajectory. Convex optimization is amenable to onboard solution due to its excellent convergence properties.
Autonomous GN&C for Spacecraft Exploration of Comets and AsteroidsTBMG-872111/1/2010
A spacecraft guidance, navigation, and control (GN&C) system is needed to enable a spacecraft to descend to a surface, take a sample using a touch-and-go (TAG) sampling approach, and then safely ascend. At the time of this reporting, a flyable GN&C system that can accomplish these goals is beyond state of the art. This article describes AutoGNC, which is a GN&C system capable of addressing these goals, which has recently been developed and demonstrated to a maturity TRL-5-plus.The AutoGNC solution matures and integrates two previously existing JPL capabilities into a single unified GN&C system. The two capabilities are AutoNAV and G-REX. AutoNAV is JPL’s current flight navigation system, and is fairly mature with respect to flybys and rendezvous with small bodies, but is lacking capability for close surface proximity operations, sampling, and contact. G-REX is a suite of low-TRL algorithms and capabilities that enables spacecraft operations in close surface proximity and for performing sampling/contact. The development and integration of AutoNAV and G-REX components into AutoGNC provides a single, unified GN&C capability for addressing the autonomy, close-proximity, and sampling/contact aspects of small-body sample return missions.
Enhanced Pseudo-Waypoint Guidance for Spacecraft ManeuversTBMG-336911/1/2008
An enhanced version of the scheme reported in “Pseudo-Waypoint Guidance for Proximity Spacecraft Maneuvers” (NPO-42753), NASA Tech Briefs, Vol. 31, No. 6 (June 2007), page 73 was developed. To recapitulate: the scheme provides algorithms for guidance and control (G&C) of a spacecraft maneuvering near a small astronomical body. The open-loop guidance problem is solved in advance or in real time by use of the pseudo-waypoint generation (PWG) method. Feedback control is implemented to track PWG trajectories, in a manner that enables updating of G&C in a model-predictive manner. The scheme includes silent periods following each thruster firing.
Pseudo-Waypoint Guidance for Proximity Spacecraft ManeuversTBMG-19466/1/2007
A paper describes algorithms for guidance and control (G&C) of a spacecraft maneuvering near a planet, moon, asteroid, comet, or other small astronomical body. The algorithms were developed following a model- predictive-control approach along with a convexification of the governing dynamical equations, control constraints, and trajectory and state constraints. The open-loop guidance problem is solved in advance or in real time by use of the pseudo-waypoint generation (PWG) method, which is a blend of classical waypoint and state-of-theart, real-time trajectory-generation methods. The PWG method includes satisfaction of required thruster silent times during maneuvers. Feedback control is implemented to track PWG trajectories in a manner that guarantees the resolvability of the open-loop-control problem, enabling updating of G&C in a provably robust, model-predictive manner. Thruster firing times and models of the gravitational field of the body are incorporated into discretized versions of the dynamical equations that are solved as part of an optimal-control problem to minimize consumption of fuel or energy. The optimal- control problem is cast as a linear matrix inequality (specifically a secondorder cone program), then solved through semi-definite-programming techniques in a computationally efficient manner that guarantees convergence and satisfaction of constraints.
A Robotic System as an Alternative to the Air-Bearing System for Spacecraft Simulator2006-01-20477/17/2006
A system emulation that can be used for testing a spacecraft control system with all of its hardware in place, in a 1-g laboratory environment, is presented. The system is comprised of a manipulator whose end-effector rigidly grasps a functional spacecraft, a six-axis force/moment (F/M) sensor placed at the interface of the spacecraft and the manipulator, and a control system. The controller takes the values of the force/moment as well as the manipulator's joint angles and velocities and issues torque command to drive the manipulator so that the motion of the spacecraft model in the presence of external forces replicates 0-g motion dynamics of a flight spacecraft. The control system can also modify the inertial properties of the spacecraft so as to match those of an actual spacecraft, even if the latter is flexible and the former is rigid. The stability of the overall system is analytically investigated, and the results show that the system remains stable provided that the inertial properties of two spacecraft are different. Important practical issues such as calibration and analysis of the sensitivity to noise and disturbance are also presented. Finally, the concept of the 0-g emulation of spacecraft is demonstrated by conducting an experiment using a robotic testbed at the Canadian Space Agency (CSA).
Aghili, Farhad, Namvar, Mehrzad
Simplified Optics and Controls for Laser CommunicationsTBMG-827/1/2006
A document discusses an architecture of a spaceborne laser communication system that provides for a simplified control subsystem that stabilizes the line of sight in a desired direction.
Simplified Optics and Controls for Laser CommunicationsTBMG-121027/1/2006
A document discusses an architecture of a spaceborne laser communication system that provides for a simplified control subsystem that stabilizes the line of sight in a desired direction. Heretofore, a typical design for a spaceborne laser communication system has called for a high-bandwidth control loop, a steering mirror and associated optics, and a fast steering mirror actuator to stabilize the line of sight in the presence of vibrations. In the present architecture, the need for this fast steering-mirror subsystem is eliminated by mounting the laser-communication optics on a disturbance-free platform (DFP) that suppresses coupling of vibrations to the optics by ≥60 dB. Taking advantage of microgravitation, in the DFP, the optical assembly is free-flying relative to the rest of the spacecraft, and a low-spring-constant pointing control subsystem exerts small forces to regulate the position and orientation of the optics via voice coils. All steering is effected via the DFP, which can be controlled in all six degrees of freedom relative to the spacecraft. A second control loop, closed around a position sensor and the spacecraft attitude-control system, moves the spacecraft as needed to prevent mechanical contact with the optical assembly.
Deep-Space Ranging Using Pseudonoise CodesTBMG-67607/1/2002
A report discusses aspects of a ranging system in which the distance between the Earth and a spacecraft is determined from the difference between the phases of (1) modulation on a radio signal trans- mitted to the spacecraft and (2) a replica of the modulation transmitted back to Earth by a transponder on the spacecraft, received at Earth a roundtrip- light-time after the original transmission. The system correlates the transmitted and return modulation for different phase shifts. The phase shift for which the correlation is maximum is deemed to be related to the round-trip signal-propagation time and, hence, to the distance. The modulations used in prior such systems were sequential square-wave tones or repeating pseudo- noise tones, but not both in the same system. A proposed improvement would equip a ranging system to use either square-wave or pseudonoise tones. The report presents mathematical analyses and comparisons of the performances of square-wave and pseudonoise ranging. It is shown that in comparison with the existing system using sequential square-wave tones, a system using a set of pseudonoise codes would perform better (in terms of integration time and variance in distance) and could be configured and operated more easily.
Black Jack GPS ReceiverTBMG-73506/1/2001
The Black Jack (BJ) receiver is the revolutionary flight Global Positioning System (GPS) receiver developed by NASA to fill future needs for orbit-based GPS science. These range from a receiver to determine precise (1-cm radial accuracy goal for JASON-1) orbits, to missions using the GPS signals for remote sensing of the Earth's atmosphere. The BJ receiver follows the TurboRogue space receiver, which was successfully used in collaboration with engineers and scientists at JPL on five satellite missions. While the TurboRogue was initially designed as a high-accuracy ground receiver, the BJ was designed from the start as an instrument for use from orbit. The BJ contains many innovations to better suit it to this application. In order to simplify the analog electronics, it directly samples the amplified and filtered RF (radio-frequency) signal. This sampling produces two sample streams in quadrature for improved SNR (signal-to-noise ratio). The BJ semicustom Application Specific Integrated Circuit (ASIC) uses a full matrix switch so that inputs from multiple antennas can be directed to any of 48 tracking channels. Other ASIC capabilities are telemetry reception, tone tracking, and precise time tagging of external events. Although the receiver is designed as a science instrument rather than for mission-critical operation, it does contain innovative features such as the capability to operate in a bit-grab mode. In the event the highly-redundant digital processing fails, the main processor stops, or the spacecraft can no longer power the GPS receiver, the BJ can turn on for less than a second every hour, and still transmit data to the ground allowing sub-100-m orbit determination. The BJ receiver is designed with excess processor capacity to allow it to perform non-GPS functions; for example, on the GRACE mission, the BJ controls an intersatellite K-band link and also processes the output of a star camera to determine spacecraft attitude.
Using Rayleigh Scattering To Measure Spacecraft AttitudeTBMG-300969/1/1999
Two reports describe a Rayleigh-scattering attitude sensor (RSAS) - an optoelectronic instrument for determining the orientation of a spacecraft. An RSAS comprises a telescope/video-camera/image-digitizer combination that is mounted on the spacecraft and that captures images of the limb of the Earth in 355-nm-wavelength sunlight that has been Rayleigh-scattered from the atmosphere. (At 355 nm, the atmosphere scatters strongly but does not absorb significantly.) A computational model of the 355-nm radiance of the atmosphere as a function of altitude, lighting conditions, and viewing angle is then used to extract, from the image data, an estimate of the angle between the line of sight of the RSAS and the nadir.
Development of Flight Software for Small Explorer SpacecraftTBMG-301079/1/1999
A report describes a continuing program of development of flight software for the attitude-control system (ACS) and the command-and-data-handling (C&DH) system of a prototype standard spacecraft of the Small Explorer (SMEX)-Lite class. Both the C&DH and ACS parts of the software are designed to run on a single reduced-instruction-set computer (RISC) with a peripheral component interface (PCI) bus architecture. The software consists of VxWorks tasks written in C++. Various components of the software have either been developed anew or redesigned from heritage code written for prior spacecraft missions.
Validation of the SCARLET Advanced Array on DS11999-01-26308/2/1999
In October, 1998, the first of the NASA New Millennium Spacecraft, DS1, was successfully launched into space. The objectives for this spacecraft are to test advanced technologies that can reduce the cost or risk of future missions. One of these technologies is the Solar Concentrator Array with Refractive Linear Element Technology (SCARLET). Although part of the advanced technology validation study, the array is also the spacecraft power source. Funded by BMDO, the SCARLET™ concentrator solar array is the first spaceflight application of a refractive lens concentrator. As part of the DS1 validation process, the amount of array diagnostics is very extensive. The data obtained includes temperature measurements at numerous locations on the 2-wing solar array. For each individual panel, a 5-cell module in one of the circuit strings is wired so that a complete I-V curve can be obtained. This data is used to verify sun pointing accuracy and array output performance. In addition, the spacecraft power load can be varied from a small fraction of the array capability, up to maximum power. For each of the power loads, array operating voltage can be measured along with the current output from each wing. Preliminary in-space measurements suggest SCARLET performance is within one (1) percent of predictions made from ground data. This paper will discuss the results of the SCARLET in-space validation, including array performance as a function of changing solar distance and array performance compared to pre-launch predictions.
Stella, Paul M., Nieraeth, Donald G., Murphy, David M., Eskenazi, Michael I.
Program Generates Graphics To Help in Planning Space FlightsTBMG-298018/1/1999
The Mission Planning Graphical Tool (MPGT) computer program provides a mouse-driven graphical representation of data on a spacecraft and its environment, for use in planning a space flight. MPGT is designed to be a generic software tool that can be configured to analyze any specified Earth-orbiting spacecraft mission.
Documents on Flight Software for the SAMPEX SpacecraftTBMG-299217/1/1999
A collection of four documents contains information on various aspects of the flight software of the Solar Anomalous and Magnetospheric Particle Explorer (SAMPEX) spacecraft. The first document is part of a longer paper that presents design requirements for the software; the information in this part includes an introduction to the SAMPEX project and a brief description of the Small Explorer Data System (SEDS) - the onboard data-processing system utilizing the software. The second document is a completed form for submittal of the software to NASA's now-discontinued Computer Software Management and Information Center (COSMIC). The third document - apparently an attachment to the COSMIC form - is an outline that briefly describes the purpose, capabilities, and characteristics of the software. The fourth document is a complete paper that describes the software in somewhat more detail: The paper includes a brief historical introduction; an overview of the structure and functions of the software in relation to the SEDS hardware; and discussions of the impact, innovative aspects, and utility of the software.
Program for Conceptual Design of an Attitude-Control SystemTBMG-3230511/1/1998
A report describes the ACS Design Tool - a Macintosh- and PC-based computer program for evaluating conceptual designs of a spacecraft attitude-control system (ACS) within a computation time of about 15 minutes. Services provided by the program include computation of ACS performance and sizing of ACS equipment for 3-axis gravity-gradient- and spin-stabilized spacecraft; computation of pointing jitter; computation of star-acquisition probabilities; computations of inertial quantities; radiation-shielding computations; transformation of attitude coordinate frame; con- version of units of measure; estimation of cost of an ACS at either of two different levels of complexity and accuracy; information on project definitions and standards; and data bases on celestial bodies, thrusters, ACS equipment lists, and costs for JPL missions. Developed within the Microsoft Excel software environment, this program provides easy-to- use graphical user interfaces (GUIs), including pull-down menus, scroll/increment buttons, and general buttons. The program consists of six collections of subprograms, which are summarized in the report. The report includes examples of GUI displays for all of the subprograms.
Software for Navigation of a Spacecraft Flying in FormationTBMG-321617/1/1998
The Spacecraft Autonomous Navigation System using GPS for Earth Orbiters (SANS-GEO) computer program is designed to perform the navigation calculations that will enable the New Millennium Program's Earth Orbiter-1 (EO-1) spacecraft to fly in formation with the Landsat-7 (LS-7) satellite in orbit around the Earth. Scheduled to be launched in May 1999, the EO-1 will be required to follow 450±50 km behind the LS-7, and to keep its ground track within 3 km of the LS-7 ground track. Using data from an onboard Global Positioning System (GPS) receiver and empirical (purely kinematic) GPS navigation algorithms, SANS-GEO would compute parameters of the EO-1 orbit; these parameters would include rates of atmospheric-drag-induced decay. SANS-GEO would then utilize these parameters, along with the corresponding parameters and with maneuver plans generated remotely for the LS-7, to determine EO-1 velocity-change maneuvers needed to satisfy absolute orbital constraints (e.g., ground-track-repeat requirements) and/or relative orbital constraints (formation-flying requirements). The computed velocity-change maneuvers would be converted into commands for the EO-1 attitude-control system and thrusters.
Saturn V Instrument Unit6406381/1/1964
Weber, Fritz H.
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