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NASA NTRS2016

Lightforce Photon-Pressure Collision Avoidance: Efficiency Analysis in the Current Debris Environment and Long-Term Simulation Perspective

This work provides an efficiency analysis of the LightForce space debris collision avoidance scheme in the current debris environment and describes a simulation approach to assess its impact on the long-term evolution of the space debris environment. LightForce aims to provide just-in-time collision avoidance by utilizing photon pressure from ground-based industrial lasers. These ground stations impart minimal accelerations to increase the miss distance for a predicted conjunction between two objects. In the first part of this paper we will present research that investigates the short-term effect of a few systems consisting of 20-kilowatt-class lasers directed by 1.5-meter-diameter telescopes using adaptive optics. The results found such a network of ground stations to mitigate more than 85 percent of conjunctions and could lower the expected number of collisions in Low Earth Orbit (LEO) by an order of magnitude. While these are impressive numbers that indicate LightForce's utility in the short-term, the remaining 15 percent of possible collisions contain (among others) conjunctions between two massive objects that would add large amount of debris if they collide. Still, conjunctions between massive objects and smaller objects can be mitigated. Hence, we choose to expand the capabilities of the simulation software to investigate the overall effect of a network of LightForce stations on the long-term debris evolution. In the second part of this paper, we will present the planned simulation approach for that effort. For the efficiency analysis of collision avoidance in the current debris environment, we utilize a simulation approach that uses the entire Two Line Element (TLE) catalog in LEO for a given day as initial input. These objects are propagated for one year and an all-on-all conjunction analysis is performed. For conjunctions that fall below a range threshold, we calculate the probability of collision and record those values. To assess efficiency, we compare a baseline (without collision avoidance) conjunction analysis with an analysis where LightForce is active. Using that approach, we take into account that collision avoidance maneuvers could have effects on third objects. Performing all-on-all conjunction analyses for extended period of time requires significant computer resources; hence we implemented this simulation utilizing a highly parallel approach on the NASA Pleiades supercomputer.

space debris mitigation↗

NASA NTRS2014

A Framework for Dimensioning VDL-2 Air-Ground Networks

This paper describes a framework developed at MITRE for dimensioning a Very High Frequency (VHF) Digital Link Mode 2 (VDL-2) Air-to-Ground network. This framework was developed to support the FAA's Data Communications (Data Comm) program by providing estimates of expected capacity required for the air-ground network services that will support Controller-Pilot-Data-Link Communications (CPDLC), as well as the spectrum needed to operate the system at required levels of performance. The Data Comm program is part of the FAA's NextGen initiative to implement advanced communication capabilities in the National Airspace System (NAS). The first component of the framework is the radio-frequency (RF) coverage design for the network ground stations. Then we proceed to describe the approach used to assess the aircraft geographical distribution and the data traffic demand expected in the network. The next step is the resource allocation utilizing optimization algorithms developed in MITRE's Spectrum ProspectorTM tool to propose frequency assignment solutions, and a NASA-developed VDL-2 tool to perform simulations and determine whether a proposed plan meets the desired performance requirements. The framework presented is capable of providing quantitative estimates of multiple variables related to the air-ground network, in order to satisfy established coverage, capacity and latency performance requirements. Outputs include: coverage provided at different altitudes; data capacity required in the network, aggregated or on a per ground station basis; spectrum (pool of frequencies) needed for the system to meet a target performance; optimized frequency plan for a given scenario; expected performance given spectrum available; and, estimates of throughput distributions for a given scenario. We conclude with a discussion aimed at providing insight into the tradeoffs and challenges identified with respect to radio resource management for VDL-2 air-ground networks.

Aviation↗

NASA NTRS1976

The Lageos satellite

The fundamental concept of Lageos is a long-lived, dense, electrically and mechanically inert spherical satellite with its surface speckled with retroreflecting cube corners, designed such that range measurements between duly equipped laser ground stations and the satellite are possible with an ultimate accuracy of 2 cm when data from a single satellite pass are appropriately averaged. The Lageos concept requires that the satellite be placed in an orbit for which an ephemeris can be determined ultimately to 5 cm rms uncertainty for a 24-hour arc. These required satellite characteristics should allow the several geodynamic motions experienced by ground stations to be determined typically with 2 cm accuracy.

Johnson, C. W.↗

NASA NTRS1999

Modem Characterization Through a Wideband, Hard-Limited Ka-Band Satellite Channel

NASA is using a commercial customized TDMA/FDMA bandwidth on demand modem for use with the Advanced Communications Technology Satellite (ACTS) to highlight the numerous services and experiments that can be performed using small Ka-Band terminals. Characterizing the modems proved challenging due to the characteristics of the satellite transponder. The ACTS channel is hard-limited and up to 900 MHz wide. The channel has some unusual dynamic properties due to the satellite and antenna system, which make modem testing through the satellite challenging and the test requirements stringent. The satellite Multi-Beam Antenna (MBA) has a 1 hertz oscillation induced by the momentum wheel, which causes the transmit antenna pattern to move slightly. This results in a 1 hertz oscillation in the ground station receive power, with amplitude changes up to 1 dB depending on terminal location within a spot beam and associated gain slope. In addition, ACTS experiences a solar induced "thermal event" each day. This "thermal event" occurs when the sun heats the antenna support structure causing the transmit and receive reflectors to mispoint. This results in a slowly decreasing or increasing power density at the ground station receiver as the antenna pattern moves off bore-site. This paper describes the method used to fully characterize the TDMA/FDMA modem through the ACTS wideband, hard-limited transponder. In particular, techniques are discussed for conducting RF measurements on such a channel, the affect that the thermal characteristics and 1 hertz variations have on the accuracy of the results, and suggested means to minimize the error and provide useful and valuable data.

Reinhart, Richard C.↗

NASA NTRSDate not supplied

Near Rectilinear Halo Orbit Determination with Simulated DSN Observations

This paper presents the results of a high-fidelity simulation of spacecraft orbit determination in a near rectilinear halo orbit (NRHO). Others in the literature have examined this problem with linear covariance analysis, but the highly-nonlinear dynamics of this orbit challenge the assumptions underlying such analyses. The present work builds on similar analysis performed by other authors to contribute a fuller understanding of the operational requirements for NRHO navigation. The present work serves as a check to the assumptions of previous studies and an independent verification of those results. The results from the literature are extended by quantifying the space of orbital states from which a spacecraft with given control authority can safely return to the nominal path. Spacecraft state uncertainty estimates are evaluated as a function of time. Simulated range and range-rate measurements with the Deep Space Network (DSN) ground stations are used to model orbit determination accuracy. Orbit maintenance maneuvers are performed using both short-horizon and long-horizon stationkeeping targeting. Monte Carlo analysis of orbit determination and stationkeeping is performed. This paper quantifies the achievable state uncertainty with deep space network (DSN)-only range and range-rate observations. This paper also addresses requirements on the frequency of DSN observation periods and correlates ground contact frequency with navigation accuracy. The results of several related studies are presented and discussed: the effect of missing ground station passes, the effect of missing stationkeeping maneuvers, the sensitivity of the spacecraft state estimate to realistic error sources, and stationkeeping propellant budget.

Nathan L Parrish↗

NASA NTRS2013

Proposed US Contributions to LOFT

Proposed US Enhancements include:Tantalum X -ray collimator, Additional ground station, Large Observatory for X-Ray Timing (LOFT) instrument team participation, US science support center & data archive, and Science enabled by US hardware. High-Z material with excellent stopping power. Fabricated using a combination of laser micromachining and chemical etching. Known technology capable of producing high-aspect ratio holes and large open fractions. Reduces LOFT LAD background by a factor of 3. Telemetry formats for LOFT based upon RXTE/EDS experience. Ground system software and strategies for WFM based upon RXTE/ASM automated pipeline software. MSFC engineering trade studies supporting the Ta collimator. Burst alert triggers based upon Fermi/GBM and HETE-2. Science Enhancements Enabled by US Hardware include: Tantalum collimator: Reduces background by factor of 3. Improves sensitivity to faint sources such as AGN. Eliminates contamination by bright/variable sources. outside the LAD field of view. US Ground Station: Enables continuous telemetry of all events from the WFM. Allows LAD to observe very bright >500 mCrab sources with full event resolution.

Wilson-Hodge, Colleen↗

NASA NTRS2017

Human-Autonomy Teaming in a Flight Following Task

The NATO HFM-247 Working Group is creating a summary report of the group's activities on human-autonomy teaming. This chapter is a summary of our at NASA Ames work toward developing a framework for human-autonomy teaming (HAT) in aviation. The purpose of this project was to demonstrate and evaluate proposed tenets of HAT. The HAT features were derived from three tenets and were built into an automated recommender system on a ground station. These tenets include bi-directional communication, automation transparency, and operator directed interface. This study focused primarily on interactions with one piece of automation, the Autonomous Constrained Flight Planner (ACFP). The ACFP is designed to support rapid diversion decisions for commercial pilots in off-nominal situations. Much effort has gone into enhancing this tool not only in capability but also in transparency. In this study, participants used the ACFP at a ground station designed to aid dispatchers in a flight following role to reroute aircraft in situations such as inclement weather, system failures and medical emergencies. Participants performed this task both with HAT features enabled and without and provided feedback. We examined subjective and behavioral indicators of HAT collaborations using a proof-of-concept demonstration of HAT tenets. The data collected suggest potential advantages and disadvantages of HAT.

bi-directional communication↗

NASA NTRS2012

Availability Estimation for Facilities in Extreme Geographical Locations

A value added analysis for the Reliability. Availability and Maintainability of McMurdo Ground Station was developed, which will be a useful tool for system managers in sparing, maintenance planning and determining vital performance metrics needed for readiness assessment of the upgrades to the McMurdo System. Output of this study can also be used as inputs and recommendations for the application of Reliability Centered Maintenance (RCM) for the system. ReliaSoft's BlockSim. a commercial Reliability Analysis software package, has been used to model the availability of the system upgrade to the National Aeronautics and Space Administration (NASA) Near Earth Network (NEN) Ground Station at McMurdo Station in the Antarctica. The logistics challenges due to the closure of access to McMurdo Station during the Antarctic winter was modeled using a weighted composite of four Weibull distributions. one of the possible choices for statistical distributions throughout the software program and usually used to account for failure rates of components supplied by different manufacturers. The inaccessibility of the antenna site on a hill outside McMurdo Station throughout one year due to severe weather was modeled with a Weibull distribution for the repair crew availability. The Weibull distribution is based on an analysis of the available weather data for the antenna site for 2007 in combination with the rules for travel restrictions due to severe weather imposed by the administrating agency, the National Science Foundation (NSF). The simulations resulted in an upper bound for the system availability and allowed for identification of components that would improve availability based on a higher on-site spare count than initially planned.

Fischer, Gerd M.↗

NASA NTRS1998

Autonomous Satellite Command and Control Through the World Wide Web

The Automated Space System Experimental Testbed (ASSET) system is a simple yet comprehensive real-world operations network being developed. Phase 3 of the ASSET Project was January-December 1997 and is the subject of this report. This phase permitted SSDL and its project partners to expand the ASSET system in a variety of ways. These added capabilities included the advancement of ground station capabilities, the adaptation of spacecraft on-board software, and the expansion of capabilities of the ASSET management algorithms. Specific goals of Phase 3 were: (1) Extend Web-based goal-level commanding for both the payload PI and the spacecraft engineer. (2) Support prioritized handling of multiple (PIs) Principle Investigators as well as associated payload experimenters. (3) Expand the number and types of experiments supported by the ASSET system and its associated spacecraft. (4) Implement more advanced resource management, modeling and fault management capabilities that integrate the space and ground segments of the space system hardware. (5) Implement a beacon monitoring test. (6) Implement an experimental blackboard controller for space system management. (7) Further define typical ground station developments required for Internet-based remote control and for full system automation of the PI-to-spacecraft link. Each of those goals are examined. Significant sections of this report were also published as a conference paper. Several publications produced in support of this grant are included as attachments. Titles include: 1) Experimental Initiatives in Space System Operations; 2) The ASSET Client Interface: Balancing High Level Specification with Low Level Control; 3) Specifying Spacecraft Operations At The Product/Service Level; 4) The Design of a Highly Configurable, Reusable Operating System for Testbed Satellites; 5) Automated Health Operations For The Sapphire Spacecraft; 6) Engineering Data Summaries for Space Missions; and 7) Experiments In Automated Health Assessment And Notification For The Sapphire Microsatellite.

Cantwell, Brian↗

NASA NTRS2004

Research and Development in Optical Communications

A report in the form of lecture slides summarizes the optical-communications program of NASA s Jet Propulsion Laboratory (JPL) and describes the JPL Optical Communications Telescope Laboratory (OCTL) and its role in the program. The purpose of the program is to develop equipment and techniques for laser communication between (1) ground stations and (2) spacecraft (both near Earth and in deep space) and aircraft. The OCTL is an astronomical- style telescope facility that includes a 1-m-diameter, 75.8-m-focal length telescope in an elevation/azimuth mount, plus optical and electronic subsystems for tracking spacecraft and aircraft, receiving laser signals from such moving targets, and transmitting high-power laser signals to such targets. Near-term research at the OCTL is expected to focus on mitigating the effects of atmospheric scintillation on uplinks and on beacon-assisted tracking of ground stations by stations in deep space. Near-term experiments are expected to be performed with retroreflector-equipped aircraft and Earth-orbiting spacecraft techniques to test mathematical models of propagation of laser beams, multiple-beam strategies to mitigate uplink scintillation, and pointing and tracking accuracy of the telescope.

Wilson, Keith↗

NASA NTRS2008

Deep Space Mission Emergency Mode Downlink

This paper investigates telecommunications between a deep space mission satellite and the ground station during an emergency mode. Once emergency is detected, spacecraft is put into a safe mode, i.e., antenna to be used for emergency mode communications is pointed towards the sun and use total available power to transmit. There are many parameters affecting communications in this mode and these should be properly balanced to produce desired results. This paper explores the effectiveness of spacecraft antenna gain pattern in the emergency mode with respect to positions of the spacecraft, earth, Sun Earth Probe (SEP) angle at the receiving antenna, and the range of the spacecraft with respect to the ground station. The paper also provides parabolic reflector antenna diameter that should be used for emergency mode as a function of the satellite to sun range in the solar system.

Kantak, Anil V.↗

NASA NTRS2010

The Solar Dynamics Observatory: Your Eye on the Sun

The Solar Dynamics Observatory (SDO) was launched on February 11,2010 into partly cloudy skies over Cape Canaveral, Florida. SDO moved into a 28 degree inclined geosynchronous orbit over the longitude of the ground station in New Mexico. SDO is the first Space Weather Mission in NASA's Living With a Star Program. SDO's main goal is to understand and predict those solar variations that influence life on Earth and our technological systems. The SDO science investigations will determine how the Sun's magnetic field is generated and structured, how this stored magnetic energy is released into the heliosphere as the solar wind, energetic particles, and variations in the solar irradiance. The SDO mission consists of three scientific investigations (AIA, EVE, and HMI), a spacecraft bus, and a dedicated Ka-band ground station to handle the 150 Mbps data flow. SDO continues a long tradition of NASA missions providing calibrated solar spectral irradiance data, in this case using multiple measurements of the irradiance and rocket underflights of the spacecraft. The other instruments on SDO will be used to explain and develop predictive models of the solar spectral irradiance in the extreme ultraviolet. Science teams at LMSAL, LASP, and Stanford are responsible for processing, analyzing, distributing, and archiving the science data. We will talk about the building of SDO, its launch, and the data and science it will provide to NASA.

Pesnell, William Dean↗

NASA NTRS2011

The Solar Dynamics Observatory: Your On-Orbit Eye on the Sun

The Solar Dynamics Observatory (SDO) was launched on February 11, 2010 into the partly cloudy skies above Cape Canaveral, Florida. Over the next month SDO moved into a 28 degree inclined geosynchronous orbit at the longitude of the ground station in New Mexico. SDO is the first Space Weather Mission in NASA's Living With a Star Program. SDO's main goal is to understand and predict those solar variations that influence life on Earth and our technological systems. The SDO science investigations will determine how the Sun's magnetic field is generated and structured, how this stored magnetic energy is released into the heliosphere as the solar wind, energetic particles, and variations in the solar irradiance. The SDO mission consists of three scientific investigations (AIA, EVE, and HMI), a spacecraft bus, and a dedicated Ka-band ground station to handle the 150 Mbps data flow. SDO continues a long tradition of NASA missions providing calibrated solar spectral irradiance data, in this case using multiple measurements of the irradiance and rocket underflights of the spacecraft. The other instruments on SDO will be used to explain and develop predictive models of the solar spectral irradiance in the extreme ultraviolet. Science teams at LMSAL, LASP, and Stanford are responsible for processing, analyzing, distributing, and archiving the science data. We will talk about the launch of SDO and describe the data and science it is providing to NASA.

Pesnell, W. Dean↗

NASA NTRS2013

Small Payload Launch Integrated Testing Services (SPLITS) - SPSDL

My experience working on the Small Payload Launch Integrated Testing Services project has been both educational and rewarding. I have been given the opportunity to work on and experiment with a number of exciting projects and initiatives, each offering different challenges and opportunities for teamwork and collaboration. One of my assignments is to aid in the design and construction of a small-scale two stage rocket as part of a Rocket University initiative. My duties include programming a microcontroller to control the various sensors on the rocket as well as process and transmit data. Additionally, I am writing a graphical user interface application for the ground station that will receive the transmitted data from the rocket and display the information on screen along with a 3D rendering displaying the rocket orientation. Another project I am working on is to design and develop the avionics that will be used to control a high altitude balloon flight that will test a sensor called a Micro Dosimeter that will measure the total ionizing dose absorbed by electrical components during a flight. This includes assembling and soldering the various sensors and components, programming a microcontroller to input and process data from the Micro Dosimeter, and transmitting the data down to a ground station as well as save the data to an on-board SD card. Additionally, I am aiding in the setup and development of ITOS (Integrated Test and Operations System) capability in the SPSDL (Spaceport Processing System Development Lab).

Intern↗

NASA NTRS2011

Diagonal-Axes Stage for Pointing an Optical Communications Transceiver

Traditional azimuth-elevation ("az-el") stages are used to point a variety of devices ranging from large optical telescopes to tank guns. Such a stage typically has an elevation stage having a horizontal axis mounted on an azimuth stage with a vertical axis. Both stages are often motorized. Optical communications transceivers often require two-axis motorized control, as when the communications link is between a ground station and an aircraft or satellite. In such applications, the traditional azimuth-elevation stage has two important drawbacks: a gimbal lock exclusion zone at zenith and susceptibility to pointing errors caused by backlash. Az-el stages in which the azimuth stage cannot rotate a full 360deg have the additional drawback of an azimuth exclusion zone. The diagonal-axes stage described here mitigates or eliminates all of these problems. Instead of one vertical axis and one horizontal axis, a diagonal-axes stage has two horizontal axes, both oriented at 45 to the trajectory of the target. For example, a ground station located on the equator tracking a satellite with an equatorial orbit would have one axis parallel to northeast and southwest, and the other axis parallel to northwest and southeast. The diagonal-axes stage is considerably less vulnerable to backlash. If it is correctly oriented, its axes rotate in only one direction during an overhead pass by a satellite. As a result, the effects of backlash may be inherently eliminated. If the gravity-induced torque on either axis changes during the pass, then backlash may become important during the part of the pass where the gravity torque, instead of opposing the motion of the stage, pushes the stage in the direction of motion. This can result in the loss of gear-to-gear contact in one or more stages of the gear reduction mechanism. In this case, a preload spring used to eliminate backlash need only be sufficiently strong to overcome the gravity torque, i.e. it need not overcome friction in the gear train. The diagonal-axes stage is not backlash-free for arbitrary target trajectories such as an aircraft might execute. If properly oriented for any particular satellite, however, it is backlash-free for all passes of that satellite, which will trace out parallel paths on the sky, and for all passes of any other satellite that are perpendicular to the first. It will also be backlash-free for some fraction of other satellite trajectories.

Regehr, Martin W.↗

NASA NTRSDate not supplied

Laser Communications Relay Demonstration: Experiments With Delay Tolerant Networking

The Laser Communications Relay Demonstration (LCRD) is a NASA mission that is presently providing a link between two optical ground stations on Earth and geosynchronous orbit; this capability will be extended to include a laser terminal on the International Space Station (ISS). From a practical perspective, LCRD provides a 1Gbps Ethernet link with an anticipated round-trip time of 4 seconds. Delay Tolerant Networking (DTN) is being used to transcend LCRDs capabilities from a point-to-point link to true network connectivity. Indeed, integrating the LCRD link into any network, such as one aboard the ISS, adds new hops and paths. In this paper, we detail DTN experiments conducted using LCRD to demonstrate how DTN and optical capabilities complement each other to enable the next generation of space communication modalities. We conclude with considerations on using LCRD to connect the ISS to the optical ground stations.

Alan Hylton↗

NASA NTRS2002

Low Power Transceiver

One of the FREESTAR experiments, the Low Power Transceiver (LPT) experiment is a low-power, lightweight software programmable transceiver prototype technology demonstration that is being developed by NASA as a low-cost S-band spacecraft navigation and communication device. The LPT prototype receives Global Positioning System (GPS) satellite signals for spacecraft navigation support and provides both forward and return, low-rate data communications links to the Merritt Island (MILA) and Dryden Flight Research Facility (DFRC) ground stations and to the Tracking and Data Relay Satellite System (TDRSS). The experiment is designed to demonstrate the system's ability to do simultaneous communications and navigation, as well as multi-mode communications and reconfiguration. LPT is managed by NASA's Goddard Space Flight Center and sponsored by NASA/HQ Code M. The LPT experiment consists of one thermally conductive box containing the electronics stack, three S-band antennas and one L-band antenna. The LPT payload uses general Orbiter services, including power control, command, and telemetry provided through the HHC avionics. On-orbit, the LPT payload will be primarily operated via direct communications between LPT and ground stations (MILA, WLPS, or DFRC) and/or TDRSS, with backup command and telemetry capability provided via the hitchhiker avionics and remote Payload Operations Control Center. During operations, LPT will utilize high Sband frequencies for communications. The LPT TDRSS (and GN) forward link (uplink) frequency is 2106.40625 MHz and their TDRSS (and GN) return link (downlink) frequency is 2287.5 MHz (utilizing Left-handed Circular Polarization to work with the TDRSS MA system). Two standard switch panel switches will be utilized to prohibit inadvertent operation of the antenna. An additional inhibit will be provided through the HH avionics power relay to the LPT.

Source record↗

DOE OSTI2022

Integrating Reanalysis and Satellite Cloud Information to Estimate Surface Downward Long-Wave Radiation

The estimation of downward long-wave radiation (DLR) at the surface is very important for the understanding of the Earth’s radiative budget with implications in surface–atmosphere exchanges, climate variability, and global warming. Theoretical radiative transfer and observationally based studies identify the crucial role of clouds in modulating the temporal and spatial variability of DLR. In this study, a new machine learning algorithm that uses multivariate adaptive regression splines (MARS) and the combination of near-surface meteorological data with satellite cloud information is proposed. The new algorithm is compared with the current operational formulation used by the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) Satellite Application Facility on Land Surface Analysis (LSA-SAF). Both algorithms use near-surface temperature and dewpoint temperature along with total column water vapor from the latest European Centre for Medium-range Weather Forecasts (ECMWF) reanalysis ERA5 and satellite cloud information from the Meteosat Second Generation. The algorithms are trained and validated using both ECMWF-ERA5 and DLR acquired from 23 ground stations as part of the Baseline Surface Radiation Network (BSRN) and the Atmospheric Radiation Measurement (ARM) user facility. Results show that the MARS algorithm generally improves DLR estimation in comparison with other model estimates, particularly when trained with observations. When considering all the validation data, root mean square errors (RMSEs) of 18.76, 23.55, and 22.08 W·m –2 are obtained for MARS, operational LSA-SAF, and ERA5, respectively. The added value of using the satellite cloud information is accessed by comparing with estimates driven by ERA5 total cloud cover, showing an increase of 17% of the RMSE. The consistency of MARS estimate is also tested against an independent dataset of 52 ground stations (from FLUXNET2015), further supporting the good performance of the proposed model.

54 ENVIRONMENTAL SCIENCES↗