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Space shuttle navigation analysis

A detailed analysis of space shuttle navigation for each of the major mission phases is presented. A covariance analysis program for prelaunch IMU calibration and alignment for the orbital flight tests (OFT) is described, and a partial error budget is presented. The ascent, orbital operations and deorbit maneuver study considered GPS-aided inertial navigation in the Phase III GPS (1984+) time frame. The entry and landing study evaluated navigation performance for the OFT baseline system. Detailed error budgets and sensitivity analyses are provided for both the ascent and entry studies.

Jones, H. L.↗

Autonomous Optical-only Navigation for Deep Space Missions

Navigation of spacecraft for interplanetary missions is typically performed on the ground using a two-way radio link to obtain the necessary tracking data. Due to the limited number of antenna capable of tracking these spacecraft, it would be advantageous to have a navigation capability that is entirely self-contained onboard a spacecraft. A camera mounted on a spacecraft is theoretically capable of enabling self-navigating spacecraft, and has been demonstrated in limited circumstances in past missions. Fundamentally, the technique involves using various natural or artificial targets as observational beacons to determine the observers position in space. In this paper, the technique of optical-only navigation is described, including discussions of what types of observations are used, and results of analysis showing the accuracies achievable for various mission types across the Solar System is discussed.

Bhaskaran, Shyam↗

Autonomous Navigation for Deep Space Missions

Navigation (determining where the spacecraft is at any given time, controlling its path to achieve desired targets), performed using ground-in- the-loop techniques: (1) Data includes 2-way radiometric (Doppler, range), interferometric (Delta- Differential One-way Range), and optical (images of natural bodies taken by onboard camera) (2) Data received on the ground, processed to determine orbit, commands sent to execute maneuvers to control orbit. A self-contained, onboard, autonomous navigation system can: (1) Eliminate delays due to round-trip light time (2) Eliminate the human factors in ground-based processing (3) Reduce turnaround time from navigation update to minutes, down to seconds (4) React to late-breaking data. At JPL, we have developed the framework and computational elements of an autonomous navigation system, called AutoNav. It was originally developed as one of the technologies for the Deep Space 1 mission, launched in 1998; subsequently used on three other spacecraft, for four different missions. The primary use has been on comet missions to track comets during flybys, and impact one comet.

navigation↗

Navigation of space VLBI missions: Radioastron and VSOP

In the mid-1990s, Russian and Japanese space agencies will each place into highly elliptic earth orbit a radio telescope consisting of a large antenna and radio astronomy receivers. Very long baseline interferometry (VLBI) techniques will be used to obtain high resolution images of radio sources observed by the space and ground based antennas. Stringent navigation accuracy requirements are imposed on the space VLBI missions by the need to transfer an ultra-stable ground reference frequency standard to the spacecraft and by the demands of the VLBI correlation process. Orbit determination for the mission will be the joint responsibility of navigation centers in the U.S., Russia, and Japan with orbit estimates based on combining tracking data from NASA, Russian, and Japanese sites. This paper describes the operational plans, the inter-agency coordination, and data exchange between the navigation centers required for space VLBI navigation.

Ellis, Jordan↗

Navigation and EDL for the Mars Exploration Rovers

A viewgraph presentation on Deep Space Navigation, and Entry, Decent, and Landing (EDL) for Mars Exploration Rovers is shown. The contents include: 1) JPL Spacecraft Operating across the Solar System; 2) 2003 - 2004: The Busiest Period in JPL's History; 3) Deep Space Navigation Will Enable Many of the New NASA Missions; 4) What Exactly is Navigation vs. GNC for Deep Space?; 5) Cruise and Approach: Why is Deep Space Navigation So Difficult?; 6) Project Importance of GNC: Landing Site Selection; 7) Planetary Communications and Tracking; 8) Tracking Data Types; 9) Delta Differential One-Way Range (deltaDOR); 10) All Solutions Leading up to TCM-4 Design; 11) Entry Flight Path Sensitivities; 12) MER Navigation Results; 13) Atmospheric Entry Targeting and Delivery; 14) Landing Ellipse Orientation; 15) MER Landing Site Trade Example; 16) Entry, Descent and Landing: Entry Guidance or What Things Do We NOT do for MER Landings (but we will later...); 17) Entering Martian Space 8:29 p.m. PST (ERT); 18) Entry, Descent and Landing; 19) Entry, Descent and Landing: Terminal Guidance; 20) The Challenge Going from 12,000 mph to Zero in Less Than Six Minutes; 21) Spirit Landing Location; 22) Entry, Descent and Landing: The Future; 23) Powered Descent Time-Line; and 24) Updated Sky Crane Maneuver Description. A short summary is also given on planetary guidance, navigation and control as it pertains to EDL systems

Mars Exploration Rover (MER)↗

James Webb Space Telescope Navigation Optimization Challenges

The James Webb Space Telescope (JWST) is a NASA flagship mission launched on December 25, 2021. The early orbit phase was highlighted by three midcourse correction burns that were performed to maneuver the vehicle into a libration orbit at the second Sun-Earth-Moon (SEM) libration point (L2). During the coast to L2, the vehicle’s primary observatory and sunshield were deployed. Once the tennis-court-sized sunshield was unfurled and tensioned into place, the large area exposed to solar radiation pressure (SRP) dictated that the SRP force model would need to account for the vehicle’s geometry, reflective properties, and orientation relative to the Sun. Following the insertion of JWST into its L2 libration orbit on January 24, 2022, the commissioning phase for the vehicle’s observatory commenced along with the first cycle of routine station-keeping maneuvers. The NASA Goddard Space Flight Center’s Flight Dynamics Facility (FDF) provides navigation services for the JWST mission. The FDF serves as the prime or backup navigation operations center for more than 30 active missions spanning a wide array of flight regimes performing orbit determination, maneuver planning, trajectory optimization, and tracking data evaluation. Definitive orbit determination for JWST is performed by the FDF using an Extended Kalman Filter (EKF) to estimate the vehicle’s trajectory and reflective properties using Deep Space Network (DSN) TRK-2-34 tracking data and spacecraft attitude telemetry. For the purposes of orbit prediction and station-keeping maneuver targeting, the sensitivity of the SRP force to the vehicle’s orientation requires that predictive attitude information must be incorporated to generate accurate orbit predictions and maneuver plans. Predictive attitude plans are provided to the FDF by the JWST Spacecraft Operations Center (SOC). Short-term (28 day) orbit predictions are propagated using a Short Range Attitude Plan (SRAP) to model the vehicle’s future attitude states for up to a week. SRAP attitude data is highly reliable, as it reflects finalized planned attitude states that the vehicle will be commanded to attain during the ensuing week. A Long Range Attitude Plan (LRAP) can be implemented to model predicted attitude states beyond one week, but these predictions are tentative and subject to revision due to changes in science operations plans. Instead, a conservative approach of applying a Sun-Pointing Neutral (SPN) attitude configuration is utilized for long-term (2 year) orbit predictions where reliable planned attitude data is not available. SPN attitude mode aligns the net SRP force along the JWST-to-Sun vector where it becomes independent of the vehicle’s angle of rotation about this vector, defined as the Sun yaw. Given the dynamic instability of the libration orbit, station-keeping thrust must be applied in either the sunward or anti-sunward direction to balance the resulting orbit. The attitude constraints of the vehicle also impose limits on the available pointing directions for station-keeping thrusters. The thrusters cannot be aligned with the optimal pointing direction for sunward maneuvers, rendering sunward maneuvers to be significantly less fuel efficient than anti-sunward maneuvers. Consequently, station-keeping maneuvers must be targeted to balance the orbit while ensuring that the next maneuver will also be performed in the anti-sunward direction to optimize propellant usage. When targeting a station-keeping maneuver, the attitude and SRP modeling configuration which is applied to the predicted post-maneuver trajectory will dictate the direction of the subsequent station-keeping maneuver, assuming nominal propulsion system performance. If the predicted post-maneuver attitude states result in an SRP model which under-predicts the cumulative SRP impact on the post-maneuver orbit, a targeted anti-sunward maneuver will be larger than necessary and the next maneuver will need to be executed sunward in order to compensate. In contrast, an anti-sunward maneuver which is targeted using an SRP model which over-predicts the cumulative SRP impact will achieve station-keeping while ensuring that the next maneuver will likewise be performed anti-sunward. For this reason, station-keeping maneuvers are targeted while applying the SPN attitude mode, as this mode entails the largest possible SRP area cross-section and therefore a larger modeled cumulative SRP impact. This paper documents the NASA Goddard Space Flight Center’s FDF support for JWST on-orbit operations and the analysis projects undertaken utilizing the experiences and data accumulated throughout the first full year of routine science operations. The results of these analysis efforts have been used to implement improvements to orbit prediction accuracy and maneuver efficiency which have the potential to prolong the lifespan of JWST to continue to conduct ground-breaking infrared astronomy for decades to come.

Flight Dynamics↗

Recent Successes and Future Plans for NASA's Space Communications and Navigation Testbed on the International Space Station

Flexible and extensible space communications architectures and technology are essential to enable future space exploration and science activities. NASA has championed the development of the Space Telecommunications Radio System (STRS) software defined radio (SDR) standard and the application of SDR technology to reduce the costs and risks of using SDRs for space missions, and has developed an on-orbit testbed to validate these capabilities. The Space Communications and Navigation (SCaN) Testbed (previously known as the Communications, Navigation, and Networking reConfigurable Testbed (CoNNeCT)) is advancing SDR, on-board networking, and navigation technologies by conducting space experiments aboard the International Space Station. During its first year(s) on-orbit, the SCaN Testbed has achieved considerable accomplishments to better understand SDRs and their applications. The SDR platforms and software waveforms on each SDR have over 1500 hours of operation and are performing as designed. The Ka-band SDR on the SCaN Testbed is NASAs first space Ka-band transceiver and is NASA's first Ka-band mission using the Space Network. This has provided exciting opportunities to operate at Ka-band and assist with on-orbit tests of NASA newest Tracking and Data Relay Satellites (TDRS). During its first year, SCaN Testbed completed its first on-orbit SDR reconfigurations. SDR reconfigurations occur when implementing new waveforms on an SDR. SDR reconfigurations allow a radio to change minor parameters, such as data rate, or complete functionality. New waveforms which provide new capability and are reusable across different missions provide long term value for reconfigurable platforms such as SDRs. The STRS Standard provides guidelines for new waveform development by third parties. Waveform development by organizations other than the platform provider offers NASA the ability to develop waveforms itself and reduce its dependence and costs on the platform developer. Each of these new waveforms requires a waveform build environment for the particular SDR, helps assess the usefulness of the platform provider documentation, and exercises the objectives of STRS Standard and the SCaN Testbed. There is considerable interest in conducting experiments using the SCaN Testbed from NASA, academia, commercial companies, and other space agencies. There are approximately 25 experiments or activities supported by the project underway or in development, with more proposals ready, as time and funding allow, and new experiment solicitations available. NASA continues development of new waveforms and applications in communications, networking, and navigation, the first university experimenters are beginning waveform development, which will support the next generation of communications engineers, and international interest is beginning with space agency partners from European Space Agency (ESA) and the Centre National d'Etudes Spatiales (CNES). This paper will provide an overview of the SCaN Testbed and discuss its recent accomplishments and experiment activities.Its recent successes in Ka-band operations, reception of the newest GPS signals, SDR reconfigurations, and STRS demonstration in space when combined with the future experiment portfolio have positioned the SCaN Testbed to enable future space communications and navigation capabilities for exploration and science.

SOFTWARE DEFINED RADIO↗

Extending the ICRF to Higher Radio Frequencies

The ICRF forms the basis for all astrometry including use as the inertial coordinate system for navigating deep space missions. This frame was defined using S/X-band observations over the past 20+ years. In January 2002, the VLBA approved our proposal for observing time to extend the ICRF to K-band (24 GHz) and Q-band (43 GHz). The first step will be observations at K- and Q-bands on a subset of ICRF sources. Eventually, K- and Q-band multi-epoch observations will be used to estimate positions, flux density and source structure for a large fraction of the current S/X-band ICRF source list. This work will benefit the radio astronomy community by extending the VLBA calibrator list at these bands. In the longer term, we would also like to extend the ICRF to Ka-band (32 GHz). A celestial reference frame will be needed at this frequency to support deep space navigation. A navigation demonstration is being considered for NASA's Mars 2005 mission. The initial K- and Q-band work will serve to identify candidate sources at Ka-band for use with that mission.

Jacobs, C. S.↗

Challenges of Space Station navigation

A description of the main navigational challenges posed by the Space Station program is given. Among the specific navigational problems addressed are: attitude reference control for payload support applications; traffic control system requirements; navigational system for proximity operations; and the development of automated navigation systems. Navigational problems associated with solar array and radiator orientation are discussed in detail. A schematic diagram of the Space Station reference configuration is provided.

Pixley, P. T.↗

Space Shuttle navigation validation

The validation of the guidance, navigation, and control system of the Space Shuttle is explained. The functions of the ascent, on-board, and entry mission phases software of the navigation system are described. The common facility testing, which evaluates the simulations to be used in the navigation validation, is examined. The standard preflight analysis of the operational modes of the navigation software and the post-flight navigation analysis are explained. The conversion of the data into a useful reference frame and the use of orbit parameters in the analysis of the data are discussed. Upon entry the data received are converted to flags, ratios, and residuals in order to evaluate performance and detect errors. Various programs developed to support navigation validation are explained. A number of events that occurred with the Space Shuttle's navigation system are described.

Ragsdale, A.↗

A General Simulator Using State Estimation for a Space Tug Navigation System

A general simulation program is presented (GSP) involving nonlinear state estimation for space vehicle flight navigation systems. A complete explanation of the iterative guidance mode guidance law, derivation of the dynamics, coordinate frames, and state estimation routines are given so as to fully clarify the assumptions and approximations involved so that simulation results can be placed in their proper perspective. A complete set of computer acronyms and their definitions as well as explanations of the subroutines used in the GSP simulator are included. To facilitate input/output, a complete set of compatable numbers, with units, are included to aid in data development. Format specifications, output data phrase meanings and purposes, and computer card data input are clearly spelled out. A large number of simulation and analytical studies were used to determine the validity of the simulator itself as well as various data runs.

Boland, J. S., III↗

Experiment D005: Star occultation navigation

The usefulness of star occultation measurements for space navigation and the determination of a horizon density profile which could be used to update atmospheric models for horizon-based measurement systems were studied. The time of occultation of a known star by a celestial body, as seen by an orbiting observer, determines a cylinder of position, the axis of which is the line through the star and the body center, and the radius of which is equal to the occulting-body radius. The dimming percentage, with respect to the altitude of this grazing ray from the star to the observer, is a percentage altitude for occultation. That is, the star can be assumed to be occulted when it reaches a predetermined percentage of its unattenuated value. The procedure used was to measure this attenuation with respect to time to determine the usefulness of the measurements for autonomous space navigation. In this experiment, the crewmembers had to accomplish star acquisition, identification, calibration, and tracking. Instrumentation was required only for measurement of the relative intensity of the star as it set into the atmosphere.

Silva, R. M.↗

Applications of different design methodologies in navigation systems and development at JPL

The NASA/JPL deep space navigation system consists of a complex array of measurement systems, data processing systems, and support facilities, with components located both on the ground and on-board interplanetary spacecraft. From its beginings nearly 30 years ago, this system has steadily evolved and grown to meet the demands for ever-increasing navigation accuracy placed on it by a succession of unmanned planetary missions. Principal characteristics of this system are its capabilities and great complexity. Three examples in the design and development of interplanetary space navigation systems are examined in order to make a brief assessment of the usefulness of three basic design theories, known as normative, rational, and heuristic. Evaluation of the examples indicates that a heuristic approach, coupled with rational-based mathematical and computational analysis methods, is used most often in problems such as orbit determination strategy development and mission navigation system design, while normative methods have seen only limited use is such applications as the development of large software systems and in the design of certain operational navigation subsystems.

Thurman, S. W.↗

Deep Space Atomic Clock Technology Demonstration Mission Results

The Deep Space Atomic Clock (DSAC), a NASA Technology Demonstration Mission, was launched into low-Earth orbit on June 25, 2019 as a hosted payload aboard General Atomics’ Orbital Test Bed (OTB) spacecraft. The DSAC mission has been conducting a two-year demonstration of a mercury ion atomic clock to characterize its space-based performance and to validate its utility for deep space navigation and radio science. Analysis of the collected data using JPL’s GIPSY-OASIS software has shown DSAC’s AD at one-day to be near 310-15; much better than required AD of 210-14. Such low spacecraft clock errors will enable one-way radiometric tracking data with precision equivalent to or better than current-day two way tracking data, allowing a shift to a more efficient and flexible one-way deep space navigation architecture. To verify this, an analog deep space navigation experiment was performed using JPL’s operational navigation software (Monte). The experiment recovered orbit solutions with reduced data sets and geometric variations that are more representative of deep space missions, and showed that orbit determination using DSAC derived data is on par with more traditional two-way datatypes. As a technology demonstrator, DSAC’s development focus has been on maturing the mercury ion trap clock technology rather than achieving the smallest size, weight, and power (SWaP). Over the course of DSAC’s development the project has identified numerous improvements that could be made to significantly reduce SWaP for DSAC’s next version. Indeed, DSAC-2 was recently selected by NASA for further demonstration on the VERITAS mission to Venus. This work will review the DSAC technology, mission, and results from its two-year mission.

Wang, Rabi↗

Advancing Navigation, Timing, and Science with the Deep Space Atomic Clock

NASA's Deep Space Atomic Clock mission is developing a small, highly stable mercury ion atomic clock with an Allan deviation of at most 1e-14 at one day, and with current estimates near 3e-15. This stability enables one-way radiometric tracking data with accuracy equivalent to and, in certain conditions, better than current two-way deep space tracking data; allowing a shift to a more efficient and flexible one-way deep space navigation architecture. DSAC-enabled one-way tracking will benefit navigation and radio science by increasing the quantity and quality of tracking data. Additionally, DSAC would be a key component to fully-autonomous onboard radio navigation useful for time-sensitive situations. Potential deep space applications of DSAC are presented, including orbit determination of a Mars orbiter and gravity science on a Europa flyby mission.

radio science↗