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NASA NTRS2016

Development of the NASA MCAT Auxiliary Telescope for Orbital Debris Research

The National Aeronautical and Space Administration (NASA) has recently deployed the Meter Class Autonomous Telescope (MCAT) to Ascension Island. MCAT will provide NASA with a dedicated optical sensor for observations of orbital debris with the goal of statistically sampling the orbital and photometric characteristics of the population from low Earth to Geosynchronous orbits. Additionally, a small auxiliary telescope, co-located with MCAT, is being deployed to augment its observations by providing near-simultaneous photometry and astrometry, as well as offloading low priority targets from MCAT's observing queue. It will also be available to provide observational measurements to the Space Surveillance Network for the United States Air Force.

Frith, James↗
NASA NTRS2007

A Comparison of Three Catastrophic On-Orbit Collisions

Orbital debris environment models, such as NASA's LEGEND model, show that accidental collisions between satellites will begin to be the dominant cause for future debris population growth within the foreseeable future. The collisional breakup models employed are obviously a critical component of the environment models. The Chinese Anti-Satellite (ASAT) test which destroyed the Fengyun-1C weather satellite provided a rare, but not unique, chance to compare the breakup models against an actual on-orbit collision. Measurements from the U.S. Space Surveillance Network (SSN), for debris larger than 10-cm, and from Haystack, for debris larger than 1-cm, show that the number of fragments created from Fengyun significantly exceeds model predictions using the NASA Standard Collisional Breakup Model. However, it may not be appropriate to alter the model to match this one, individual case. Two other on-orbit collisions have occurred in the past which have produced significant numbers of debris fragments. In September 1985, the U.S. conducted an ASAT test against the Solwind P-78 spacecraft at an altitude of approximately 525 km. A year later, in September 1986, the Delta 180 payload was struck by its Delta II rocket body in a planned collision at 220 km altitude. Although no Haystack data is available in 1985-6 and very few debris pieces were cataloged from Delta 180 due to its low altitude, measurements were collected in dedicated tests by phased array radars in the SSN in the days after each test. This paper will examine the available radar data from each test and compare and contrast the results with model predictions and with the results from the more recent Fengyun ASAT test.

Stansbery, Gene↗
NASA NTRS2011

Engineering and Technology Challenges for Active Debris Removal

After more than fifty years of space activities, the near-Earth environment is polluted with man-made orbital debris. The collision between Cosmos 2251 and the operational Iridium 33 in 2009 signaled a potential collision cascade effect, also known as the "Kessler Syndrome", in the environment. Various modelling studies have suggested that the commonly-adopted mitigation measures will not be sufficient to stabilize the future debris population. Active debris removal must be considered to remediate the environment. This paper summarizes the key issues associated with debris removal and describes the technology and engineering challenges to move forward. Fifty-four years after the launch of Sputnik 1, satellites have become an integral part of human society. Unfortunately, the ongoing space activities have left behind an undesirable byproduct orbital debris. This environment problem is threatening the current and future space activities. On average, two Shuttle window panels are replaced after every mission due to damage by micrometeoroid or orbital debris impacts. More than 100 collision avoidance maneuvers were conducted by satellite operators in 2010 to reduce the impact risks of their satellites with respect to objects in the U.S. Space Surveillance Network (SSN) catalog. Of the four known accident collisions between objects in the SSN catalog, the last one, collision between Cosmos 2251 and the operational Iridium 33 in 2009, was the most significant. It was the first ever accidental catastrophic destruction of an operational satellite by another satellite. It also signaled the potential collision cascade effect in the environment, commonly known as the "Kessler Syndrome," predicted by Kessler and Cour-Palais in 1978 [1]. Figure 1 shows the historical increase of objects in the SSN catalog. The majority of the catalog objects are 10 cm and larger. As of April 2011, the total objects tracked by the SSN sensors were more than 22,000. However, approximately 6000 of them had yet to be fully processed and entered into the catalog. This population had been dominated by fragmentation debris throughout history. Before the anti-satellite test (ASAT) conducted by China in 2007, the fragmentation debris were almost all explosion fragments. After the ASAT test and the collision between Iridium 33 and Cosmos 2251, the ratio of collision fragments to explosion fragments was about one-to-one. It is expected that accidental collision fragments will further dominate the environment in the future.

Liou, Jer-Chyi↗
NASA NTRS1982

Signalling characteristics in satellite-aided land mobile communications

The feasibility of land mobile radio communications has been demonstrated by a large number of experiments with NASA's ATS satellites. Significant differences in the propagation characteristics of satellite and terrestrial mobile signal paths were observed in the experiments. Terrestrial paths are best in cities where they can provide frequency reuse and assure communication by bouncing signals around obstructions. Satellites may be best in thinly populated areas because they eliminate the need for many tower mounted relays. The satellite paths do not have the severe Rayleigh fading that limits the range and signal quality of terrestrial paths if the satellite is above approximately ten degrees elevation, a value easily achieved for the United States. The experiments verified that high quality voice communications and other functions, such as data transmission and vehicle position surveillance, are easily accomplished through geostationary satellites with vehicle transmitter power and antenna gain no different than those of terrestrial mobile communications.

Anderson, R. E.↗
NASA NTRS1988

CCD scanning for comets and asteroids

Some populations of objects in the solar system are still poorly known, and the long-range goal of this program is to improve that situation. For instance, the statistics of Trojan asteroids are uncertain, while previous serveying indicates there is an appreciable systematic difference between the L-4 and L-5 regions, which is hard to explain. Researchers are developing for this goal a new technique of sky surveillance, namely scanning with a charge coupled device (CCD). With its quantum efficiency and wavelength range greater than that of photographic plates, the CCD should be especially valuable for fast-moving objects such as near-Earth asteroids. A 320 x 512 pixel CCD has been in operation since 1983 on a telescope that is dedicated during the dark half of each month to sky surveillance, that is the Spacewatch Telescope which is the 91-cm Newtonian reflector of the Steward Observatory on Kitt Peak. The system was found to be of special value for astrometry. The telescope drive is turned off at a selected distance west of the object and the scan is continued such that the number of astrometric standards is optimized. Because the drive is off, the effects of refraction practically vanish.

Gehrels, Tom↗
NASA NTRS2013

The NASA Meter Class Autonomous Telescope: Ascension Island

The Meter Class Autonomous Telescope (MCAT) is the newest optical sensor dedicated to NASA's mission to characterize the space debris environment. It is the successor to a series of optical telescopes developed and operated by the JSC Orbital Debris Program Office (ODPO) to monitor and assess the debris environment in (1) Low Earth Orbit (LEO), (2) Medium Earth Orbit (MEO), and (3) Geosynchronous Orbit (GEO), with emphasis on LEO and GEO altitudes. A joint NASA - Air Force Research Labs project, MCAT is a 1.3m optical telescope dedicated to debris research. Its optical path and sensor yield a large survey fence at the cutting edge of current detector performance. It has four primary operational observing modes, two of which were not computationally feasible a decade ago. Operations are supported by a sophisticated software suite that monitors clouds and weather conditions, and controls everything from data collection to dome rotation to processing tens of gigabytes of image data nightly. With fainter detection limits, precision detection, acquisition and tracking of targets, multi-color photometry, precision astrometry, automated re-acquisition capability, and the ability to process all data at the acquisition rate, MCAT is capable of producing and processing a volume and quality of data far in excess of any current (or prior) ODPO operations. This means higher fidelity population inputs and eliminating the multi-year backlog from acquisition-to-product typical of optical campaigns. All of this is possible given a suitable observing location. Ascension Island offers numerous advantages. As a British overseas territory with a US Air Force base presence, the necessary infrastructure and support already exists. It is located mid-way between Brazil and Africa at 7.93S latitude and 14.37 W longitude. With the Ground-based Electro-Optical Deep Space Surveillance (GEODSS) asset in Moron, Spain shutting down, this presents access to the sky from a unique latitude/longitude for an optical telescope. Constant trade winds from the SSE, originating from Africa, give promise to a steady laminar airflow over an island, a trait sought after to create stable atmospheric and good astronomical 'seeing' conditions with very low annual rainfall values. This combination of attributes created the necessary compelling argument to redirect MCAT to its final destination: Ascension Island.

Lederer, S. M.↗
NASA NTRS2016

Do Astronauts have a Higher Rate of Orthopedic Shoulder Conditions than a Cohort of Working Professionals?

Occupational surveillance of astronaut shoulder injuries began with operational concerns at the Neutral Buoyancy Laboratory (NBL) during Extra Vehicular Activity (EVA) training. NASA has implemented several occupational health initiatives during the past 20 years to decrease the number and severity of injuries, but the individual success rate is unknown. Orthopedic shoulder injury and surgery rates were calculated, but classifying the rates as normal, high or low was highly dependent on the comparison group. The purpose of this study was to identify a population of working professionals and compare orthopedic shoulder consultation and surgery rates.

Laughlin, Mitzi S.↗
NASA NTRS2014

Assessing the Risk of Disc Heniation Related to Landing Impact Following Long-duration Spacecraft

Previous research has shown that crewmembers returning on the Space Shuttle have an increased incidence of herniated nucleus pulposus after spaceflight. This increased risk is thought to be related to disc volume expansion due to unloading and prolonged exposure to microgravity. Although there is an increased risk of disc herniation in Space Shuttle astronauts, it is unknown if dynamic landing loads further contribute to the risk of herniation. To determine if dynamic loads increase the risk of incidence, data from crewmembers (excluding cosmonauts) returning on the Soyuz spacecraft will be compared to Space Shuttle astronauts. These data will be obtained from the Lifetime Surveillance of Astronaut Health (LSAH) Project at NASA. Severity and incidence after spaceflight will be mined from the data, and statistical analyses will be used to determine if Soyuz crewmembers have a higher incidence of disc herniation than Space Shuttle crewmembers. The results are expected to show no difference between Space Shuttle and Soyuz crewmembers, indicating that higher dynamic loads on landing and long-duration spaceflight do not significantly increase the risk of disc herniation. If no difference is shown between the two crewmember populations, then disc volume expansion due to microgravity does not significantly increase the risk of injury due to dynamic loads for deconditioned crewmembers. Any risk associated with deconditioning would be primarily due to bone structure changes and resulting bone strength changes. This study is an important first step in determining whether the spinal disc plays a role in injury due to dynamic loads.

Somers, J. T.↗
NASA NTRS2012

The Effects of Solar Maximum on the Earth's Satellite Population and Space Situational Awareness

The rapidly approaching maximum of Solar Cycle 24 will have wide-ranging effects not only on the number and distribution of resident space objects, but also on vital aspects of space situational awareness, including conjunction assessment processes. The best known consequence of high solar activity is an increase in the density of the thermosphere, which, in turn, increases drag on the vast majority of objects in low Earth orbit. The most prominent evidence of this is seen in a dramatic increase in space object reentries. Due to the massive amounts of new debris created by the fragmentations of Fengyun-1C, Cosmos 2251 and Iridium 33 during the recent period of Solar Minimum, this effect might reach epic levels. However, space surveillance systems are also affected, both directly and indirectly, historically leading to an increase in the number of lost satellites and in the routine accuracy of the calculation of their orbits. Thus, at a time when more objects are drifting through regions containing exceptionally high-value assets, such as the International Space Station and remote sensing satellites, their position uncertainties increase. In other words, as the possibility of damaging and catastrophic collisions increases, our ability to protect space systems is degraded. Potential countermeasures include adjustments to space surveillance techniques and the resetting of collision avoidance maneuver thresholds.

Johnson, Nicholas L.↗
NASA NTRSDate not supplied

Distributed Vision Sensing of Small Uncrewed Aircraft Systems in Urban Traffic Corridors

The NASA Advanced Air Mobility mission will enable widespread low altitude passenger travel, cargo delivery, and a variety of public services through the development of Uncrewed Aerial Systems (UAS) operations. Ensuring safe, autonomous operations in densely populated environments requires careful consideration towards hazards including other aircraft, infrastructure, and evolving weather. Small Uncrewed Aerial Systems (SUAS) present a unique hazard to UAS operations as they share airspace and may be readily operated in a non-cooperative fashion. This work investigates distributed sensing of SUAS traversing an air traffic corridor in an urban setting. This work develops a distributed vision detect and track strategy at NASA Langley Research Center. Three nodes, each with at least one global shutter camera, are distributed around a traffic corridor to surveil flight operations for two SUAS performing low altitude flight operations. Each node is equipped with a GPS and cellular modem to enable timestamping and remote control of acquisition. Node one faces a traffic roundabout with buildings in the background and achieves 99% surveillance coverage for two SUAS against building and tree backgrounds at ranges 50 to 130m. The second node points down Langley Boulevard with trees and buildings in the background and achieves 99% coverage at separation distances between 70 and 180m. The analysis for the second node is limited to ranges below 180m due to low contrast against dark, tree backgrounds. Finally, the third node points down Langley Boulevard from another perspective and achieves 99% coverage at ranges 60m to 200m against mostly building with a few sections of trees in the background.

Chester V Dolph↗
NASA NTRS2000

Forecasting disease risk for increased epidemic preparedness in public health

Emerging infectious diseases pose a growing threat to human populations. Many of the world's epidemic diseases (particularly those transmitted by intermediate hosts) are known to be highly sensitive to long-term changes in climate and short-term fluctuations in the weather. The application of environmental data to the study of disease offers the capability to demonstrate vector-environment relationships and potentially forecast the risk of disease outbreaks or epidemics. Accurate disease forecasting models would markedly improve epidemic prevention and control capabilities. This chapter examines the potential for epidemic forecasting and discusses the issues associated with the development of global networks for surveillance and prediction. Existing global systems for epidemic preparedness focus on disease surveillance using either expert knowledge or statistical modelling of disease activity and thresholds to identify times and areas of risk. Predictive health information systems would use monitored environmental variables, linked to a disease system, to be observed and provide prior information of outbreaks. The components and varieties of forecasting systems are discussed with selected examples, along with issues relating to further development.

Disease Outbreaks↗
NASA NTRS2009

Spatial Analysis of West Nile Virus: Predictive Risk Modeling of a Vector-borne Infectious Disease in Illinois by Means of NASA Earth Observation Systems

West Nile Virus is a mosquito-borne virus of the family Flaviviridae. It infects birds and various mammals, including humans, and can cause encephalitis that may prove fatal, notably among vulnerable populations. Since its identification in New York City in 1999, WNV has become established in a broad range of ecological settings throughout North America, infecting more than 25,300 people and killing 1133 as of 2008 (CDC,2009). WNV is transmitted by mosquitoes that feed on infected birds. As a result, the degree of human infection depends on local ecology and human exposure. This study hypothesizes that remote sensing and GIS can be used to analyze environmental determinants of WNV transmission, such as climate, elevation, land cover, and vegetation densities, to map areas of WNV risk for surveillance and intervention.

Renneboog, Nathan↗
NASA NTRSDate not supplied

Lessons Learned on Mega-Constellation Deployments and Impact to Space Domain Awareness

The breakneck expansion of multi-payload launches in low Earth orbit (LEO) has seen significant escalation over the last three years in the Space Domain Awareness (SDA) enterprise. The uptick in satellite deployment frequency, gradation of mega-constellation deployments utilizing electric propulsion, and surge in metric observation density from the Space Surveillance Network (SSN) have driven major system enhancements to ensure spaceflight safety. Beginning with the launch phase, new tactics, software, and procedures have been developed over the last few years to optimize the tasking of the SSN and ensure custody of all recently launched satellites that are added to the space catalog. Ensuring appropriate tasking levels were pivotal during the satellite separation phase, which necessitated updates to the mission systems for improved delineation between clustered satellites in a short window of time. The improved incorporation of utilizing satellite owner/operator-provided ephemeris coupled with critical code improvements have revolutionized how we maintain custody of Earth orbiting objects. The exponential population growth of Low-Earth orbiting satellites have also increased the quantity of Conjunction Data Messages sent out to partners such as the Trajectory Operations Group (TOPO) in Johnson Space Center. We will discuss the need for continued collaboration between the National Aeronautics and Space Administration (NASA) and other mega-constellation satellite operators to safeguard human spaceflight operations. Lastly, we will discuss how mega-constellations are driving best practices for safe operations across the space community.

Christian Ramos↗
NASA NTRS2024

Herpesviruses in Saliva and Their Clinical Significance

Saliva has been used as a source of biological markers for a wide spectrum of normal and disease states for a long time. It is a non-invasive, easily accessible, and self-collected body fluid that contains a variety of measurable biological substances. While mostly water, saliva also contains ions, carbohydrates, proteins and peptides, exfoliated cells, nucleic acids, and microorganisms. Saliva can reflect tissue levels of some natural substances and a large variety of molecules introduced for therapeutic use, emotional status; hormonal status, immunological status, neurological effects, and nutritional and metabolic status. It can also be used to monitor a variety of drugs including marijuana, cocaine, and alcohol. It is the most cost-effective approach for screening large population in community mass screening programs and for longitudinal sampling of hospitalized individuals aimed at monitoring viral load dynamics and treatment response. During the COVID-19 pandemic, scientific evidence emerged indicating that molecular tests performed on saliva have diagnostic sensitivity and specificity comparable to those observed with nasopharyngeal swabs for SARS-CoV-2 RNA detection. The presence of IgA and IgG antibodies at the mucosal level has been demonstrated to influence the progression of viral infection and the severity of clinical manifestation. As saliva contains both respiratory secretions and immunological components, it has wide applications, ranging from clinical diagnostics to post-vaccine disease burden and immunity surveillance.

Douglass Diak↗
NASA NTRSDate not supplied

Lessons Learned on Mega-Constellation Deployments and Impact to Space Domain Awareness

The breakneck expansion of multi-payload launches in low Earth orbit (LEO) has seen significant escalation over the last three years in the Space Domain Awareness (SDA) enterprise. The uptick in satellite deployment frequency, gradation of Mega-constellation deployments utilizing electric propulsion, and surge in metric observation density from the Space Surveillance Network (SSN) have imposed major system enhancements to ensure spaceflight safety. Beginning with the launch phase, new tactics, software, and procedures have been developed over the last few years to optimize the tasking of the SSN and ensure custody of all recently launched satellites that are added to the space catalog. Ensuring appropriate tasking levels were pivotal during the satellite separation phase, which necessitated updates to the mission systems for improved delineation between clustered satellites in a short window of time. The improved incorporation of utilizing owner operator provided ephemeris coupled with critical code improvements have now revolutionized how we maintain custody of earth orbiting objects. The exponential population growth of low-Earth orbiting satellites have also increased the quantity of Conjunction Data Messages sent out to partners such as the Trajectory Operations Group (TOPO) in Johnson Space Center. We will discuss the need for continued collaboration between the National Aeronautics and Space Administration (NASA) and other Mega-Constellation Satellite Operators to safeguard Human Space Flight operations. Lastly, we will discuss the increase in reentry reporting for satellites falling back to Earth’s atmosphere, and the challenges associated with these events.

Christian C Ramos↗
NASA NTRS2014

An Analysis of the FY-1C, Iridium 33, and Cosmos 2251 Fragments

The beginning of the year 2013 marks the sixth anniversary of the destruction of the Fengyun-1C (FY-1C) weather satellite as the result of an anti-satellite test conducted by China in January 2007 and the fourth anniversary of the accidental collision between Cosmos 2251 and the operational Iridium 33 in February 2009. These two events represent the worst satellite breakups in history. A total of 5579 fragments have been cataloged by the U.S. Space Surveillance Network (SSN), and almost 5000 of them were still in orbit in January 2013. In addition to these cataloged objects, hundreds of thousands (or more) of fragments down to the millimeter size regime were also generated during the breakups. These fragments are too small to be tracked by the SSN, but are large enough to be a safety concern for human space activities and robotic missions in low Earth orbit (LEO, the region below 2000 km altitude). Like their cataloged siblings, many of them remain in orbit today. These two breakup events dramatically changed the landscape of the orbital debris environment in LEO. The spatial density of the cataloged population in January 2013 is shown as the top blue curve. The combined FY-1C, Iridium 33, and Cosmos 2251 fragments (black curve) account for about 50 percent of the cataloged population below an altitude of 1000 km. They are also responsible for the concentrations at 770 km and 850 km, altitudes at which the collisions occurred. The effects of the FY-1C, Iridium 33, and Cosmos 2251 fragments will continue to be felt for decades to come. For example, approximately half of the generated FY-1C fragments will remain in orbit 20 years from now. In general, the Iridium 33 and Cosmos 2251 fragments will decay faster than the FY-1C fragments because of their lower altitudes. Of the Iridium 33 and Cosmos 2251 fragments, the former have much shorter orbital lifetimes than the latter, because lightweight composite materials were heavily used in the construction of the Iridium vehicle, leading to the higher area-to-mass ratios of the fragments.

Liou, J.-C.↗
NASA NTRS1990

Procedures for minimizing the effects of high solar activity on satellite tracking and ephemeris generation

We are currently experiencing a period of high solar radiation combined with wide short-term fluctuations in the radiation. The short-term fluctuations, especially when combined with highly energetic solar flares, can adversely affect the mission of U.S. Space Command's Space Surveillance Center (SSC) which catalogs and tracks the satellites in orbit around the Earth. Rapidly increasing levels of solar electromagnetic and/or particle radiation (solar wind) causes atmospheric warming, which, in turn, causes the upper-most portions of the atmosphere to expand outward, into the regime of low altitude satellites. The increased drag on satellites from this expansion can cause large, unmodeled, in-track displacements, thus undermining the SSC's ability to track and predict satellite position. On 13 March 1989, high solar radiation levels, combined with a high-energy solar flare, caused an exceptional amount of short-term atmospheric warming. The SSC temporarily lost track of over 1300 low altitude satellites--nearly half of the low altitude satellite population. Observational data on satellites that became lost during the days following the 13 March 'solar event' was analyzed and compared with the satellites' last element set prior to the event (referred to as a geomagnetic storm because of the large increase in magnetic flux in the upper atmosphere). The analysis led to a set of procedures for reducing the impact of future geomagnetic storms. These procedures adjust selected software limit parameters in the differential correction of element sets and in the observation association process and must be manually initiated at the onset of a geomagnetic storm. Sensor tasking procedures must be adjusted to ensure that a minimum of four observations per day are received for low altitude satellites. These procedures have been implemented and, thus far, appear to be successful in minimizing the effect of subsequent geomagnetic storms on satellite tracking and ephemeris computation.

Bredvik, Gordon D.↗
NASA NTRS2007

The Characteristics and Consequences of the Break-up of the Fengyun-1C Spacecraft

The intentional break-up of the Fengyun-1C spacecraft on 11 January 2007 via hypervelocity collision with a ballistic object created the most severe artificial debris cloud in Earth orbit since the beginning of space exploration. More than 900 debris on the order of 10 cm or greater in size have been identified by the U.S. Space Surveillance Network (SSN). The majority of these debris reside in long-lived orbits. The NASA Orbital Debris Program Office has conducted a thorough examination of the nature of the Fengyun-1C debris cloud, using SSN data for larger debris and special Haystack radar observations for smaller debris. These data have been compared with the NASA standard satellite break-up model for collisions, and the results are presented in this paper. The orbital longevity of the debris have also been evaluated for both small and large debris. The consequent long-term spatial density effects on the low Earth orbit (LEO) regime are then described. Finally, collision probabilities between the Fengyun-1C debris cloud and the resident space object population of 1 January 2007 have been calculated. The potential effect on the growth of the near-Earth satellite population is presented.

Johnson, Nicholas L.↗