Space situational awareness

As the spacefaring community is well aware, the increasingly rapid proliferation of man-made objects in space, whether active satellites or debris, threatens the safe and secure operation of spacecraft and requires that we change the way we conduct business in space. The introduction of appropriate protocols and procedures to regulate the use of space is predicated on the availability of quantifiable and timely information regarding the behavior of resident space objects (RSO): the basis of space domain awareness (SDA). Yet despite five decades of space operations, and a growing global dependence on the services provided by space-based platforms, the population of Earth orbiting space objects is still neither rigorously nor comprehensively quantified, and the behaviors of these objects, whether directed by human agency or governed by interaction with the space environment, are inadequately characterized. In response to these challenges, the University of Arizona (UA) has recently established the Space Object Behavioral Sciences (SOBS) Division of its Defense and Security Research Institute (DSRI) with a mandate to carry out research, education, and operational support to spacecraft operators. The SOBS Division builds on UA's heritage as a world leader in space science. By way of examples, UA, with a total research portfolio exceeding $600M per year, operates more than 20 astronomical telescopes on two continents, leads NASA's $800M OSIRIS-REx asteroid sample return mission, and has been deeply engaged in every US mission to Mars without exception. Key goals of the SOBS Division are to develop a capability to predict RSO behavior, extending SDA beyond its present paradigm of catalog maintenance and forensic analysis, and to arrive at a comprehensive physical understanding of non-gravitational forces that affect the motions of RSOs. Without seeking to provide a universal solution to global SDA needs, SOBS nonetheless concentrates resources to advance the state-of-the-art in astrodynamic research toward those ends. Solutions to these problems require multidisciplinary engagement that combines space surveillance data with other information, including space object databases and space environmental data, to help decision-making processes predict, detect, and quantify threatening and hazardous space domain activity. To that end, the division engages and integrates talent and resources from across the UA, including the Colleges of Science, Engineering, Optical Sciences, and Agriculture & Life Sciences. As activity ramps up over approximately the next three years, the SOBS Division will directly support the creation of timely knowledge of the space environment by drawing on a worldwide network of sensors processed through existing UA cyberinfrastructure. In addition, the SOBS Division will also provide a real-world training ground for current and future workers in the field through certificate programs and postgraduate degrees.

" In space, no one can hear you scream, " as the tagline from the sci-fi film Aliens goes. But what if there were a way of " hearing " in space, moving in-space video from the Silent Era to a more contemporary cinematic experience? How could this capability be applied to shape future spacecraft and mission designs? Such a capability can be effectively incorporated into a 3U CubeSat using a measurement technique called Remote Acoustic Sensing (RAS). " RASSat " uses advanced optical sensors to view and recover audio from distant objects that have weak optical modulations produced by local sound and vibration sources; the modulated light sources and the RAS sensor are passively coupled at the speed of light, yielding a variety of interesting sounds across the entire human auditory range. RAS field demonstrations and analyses have identified and characterized terrestrial sound sources observable from LEO, along with associated acousto-optic modulation mechanisms. RASSat sensitivity is such that both day and night strong, easily detectable terrestrial acousto-optic emitters abound, and applications to Space Situational Awareness and planetary exploration are also evident. This paper provides an overview of the RAS measurement technique and recent terrestrial demonstrations, and highlights key RASSat design features, performance capabilities and applications.

As the spacefaring community is well aware, the increasingly rapid proliferation of man-made objects in space, whether active satellites or debris, threatens the safe and secure operation of spacecraft and requires that we change the way we conduct business in space. The introduction of appropriate protocols and procedures to regulate the use of space is predicated on the availability of quantifiable and timely information regarding the behavior of resident space objects (RSO): the basis of space domain awareness (SDA). Yet despite five decades of space operations, and a growing global dependence on the services provided by space-based platforms, the population of Earth orbiting space objects is still neither rigorously nor comprehensively quantified, and the behaviors of these objects, whether directed by human agency or governed by interaction with the space environment, are inadequately characterized. In response to these challenges, the University of Arizona (UA) has recently established the Space Object Behavioral Sciences (SOBS) Division of its Defense and Security Research Institute (DSRI) with a mandate to carry out research, education, and operational support to spacecraft operators. The SOBS Division builds on UA's heritage as a world leader in space science. By way of examples, UA, with a total research portfolio exceeding $600M per year, operates more than 20 astronomical telescopes on two continents, leads NASA's $800M OSIRIS-REx asteroid sample return mission, and has been deeply engaged in every US mission to Mars without exception. Key goals of the SOBS Division are to develop a capability to predict RSO behavior, extending SDA beyond its present paradigm of catalog maintenance and forensic analysis, and to arrive at a comprehensive physical understanding of non-gravitational forces that affect the motions of RSOs. Without seeking to provide a universal solution to global SDA needs, SOBS nonetheless concentrates resources to advance the state-of-the-art in astrodynamic research toward those ends. Solutions to these problems require multidisciplinary engagement that combines space surveillance data with other information, including space object databases and space environmental data, to help decision-making processes predict, detect, and quantify threatening and hazardous space domain activity. To that end, the division engages and integrates talent and resources from across the UA, including the Colleges of Science, Engineering, Optical Sciences, and Agriculture & Life Sciences. As activity ramps up over approximately the next three years, the SOBS Division will directly support the creation of timely knowledge of the space environment by drawing on a worldwide network of sensors processed through existing UA cyberinfrastructure. In addition, the SOBS Division will also provide a real-world training ground for current and future workers in the field through certificate programs and postgraduate degrees.

Under ESA contract an industrial consortium including Aboa Space Research Oy (ASRO), the Astronomical Institute of the University of Bern (AIUB), and the Dutch National Aerospace Laboratory (NLR), proposed the observation concept, developed a suitable sensor architecture, and assessed the performance of a space-based optical (SBO) telescope in 2005. The goal of the SBO study was to analyse how the existing knowledge gap in the space debris population in the millimetre and centimetre regime may be closed by means of a passive optical instrument. The SBO instrument was requested to provide statistical information on the space debris population in terms of number of objects and size distribution. The SBO instrument was considered to be a cost-efficient with 20 cm aperture and 6°field-of-view and having flexible integration requirements. It should be possible to integrate the SBO instrument easily as a secondary payload on satellites launched into low-Earth orbits (LEO), or into geostationary orbit (GEO). Thus the selected mission concept only allowed for fix-mounted telescopes, and the pointing direction could be requested freely. Since 2007 ESA focuses space surveillance and tracking activities in the Space Situational Awareness (SSA) preparatory program. Ground-based radars and optical telescopes are studied for the build-up and maintenance of a catalogue of objects. In this paper we analyse how the proposed SBO architecture could contribute to the space surveillance tasks survey and tracking. We assume that the SBO instrumentation is placed into a circular sunsynchronous orbit at 800 km altitude. We discuss the observation conditions of objects at higher altitude, and select an orbit close to the terminator plane. A pointing of the sensor orthogonal to the orbital plane with optimal elevation slightly in positive direction (0°a nd +5°) is found optimal for accessing the entire GEO regime within one day, implying a very good coverage of controlled objects in GEO, too. Simulations using ESA's Program for Radar and Optical Observation Forecasting (PROOF) in the version 2005 and a GEO reference population extracted from DISCOS revealed that the proposed pointing scenario provides low phase angles together with low angular velocities of the objects crossing the field-of-view. Radiometric simulations show that the optimal exposure time is 1-2 s, and that spherical objects in GEO with a diameter of below 1 m can be detected. The GEO population can be covered under proper illumination nearly completely, but seasonal drops of the coverage are possible. Subsequent observations of objects are on average at least every 1.5 days, not exceeding 3 days at maximum. A single observation arc spans 3°to 5°on average. Using a simulation environment that connects PROOF to AIUB's program system CelMech we verify the consistency of the initial orbit determination for five selected test objects on subsequent days as a function of realistic astrometric noise levels. The initial orbit determination is possible. We define requirements for a correlator process essential for catalogue build-up and maintenance. Each single observation should provide an astrometric accuracy of at least 1"-1.5" so that the initially determined orbits are consistent within a few hundred kilometres for the semimajor axis, 0.01 for the eccentricity, and 0.1°for the inclination.

Identification and characterisation of the growing population of resident space objects (RSOs) in orbit around
Earth is central to current and future Space Traffic Management and Space Situational Awareness (SSA)
activities. Research at University of New South Wales (UNSW) Canberra Space seeks to assist this effort
through combining optical measurements of selected RSOs with numerical astrodynamics modelling techniques
to extend the information that can be inferred about an RSO from its photometric light curve signature.
The initial phase of this research comprised two three-month observation campaigns, which were completed in
July 2018. A collection of photometric light curves was obtained using different nodes of the Falcon Telescope
Network (FTN) for the Buccaneer Risk Mitigation Mission (BRMM) 3U CubeSat. The BRMM was launched in
2017 as a joint mission between UNSW Canberra Space and the Defence Science and Technology Group
(DST). While BRMM is a pathfinder for the future Buccaneer Main Mission whose primary objective will be
the calibration of the Jindalee Operational Radar Network (JORN), it also serves as a stepping stone in building
Australian space capability. For BRMM one of the mission objectives was to perform photometric experiments
to contribute to SSA research and development efforts via dynamic on-orbit manoeuvres. This paper reports on
the initial analysis of the photometric light curves central to the SSA mission goal. The material properties and
dynamic attitude motion of the BRMM during the FTN observations are known, with rotational body rates
commanded from 0.2 to 5 degrees per second about multiple combinations of body axes to build a
comprehensive database of light curves for analysis. Further variation in the light curve database is provided by
observations obtained prior to solar panel and antenna deployment.
A set of 70 light curves was obtained during the observational campaigns, with each light curve signature
containing a bulk change in intensity over time due to the change in range as BRMM approaches the FTN node
on its Low Earth Orbit (LEO) trajectory. Superimposed on the mean intensity change are characteristic peaks
and troughs produced by reflections from individual facets of the spacecraft, the magnitude and frequency of
which are highly dependent upon the spacecraft’s attitude and body rate. Samples from the light curve database
are presented with the attitude data downlinked from the spacecraft to assess light curve variations with attitude
and spin rate of the spacecraft.
Supporting the optical data are numerically simulated light curves, generated by applying the Ashikhmin-
Premože Bidirectional Reflectance Distribution Function (BRDF) Model for the BRMM geometry using a high-
fidelity 6 Degree of Freedom (DOF) orbit propagator supported by the Orekit orbit propagation library for
computations related to time systems, coordinate frames, and gravitational perturbations. The performance of
the numerical simulation was evaluated by superimposing the attitude profile reported by the spacecraft
telemetry on top of the propagated orbit to provide a one-to-one comparison between the measured and
simulated light curves for select cases.
A preliminary investigation into the feasibility of using the simulation tool to infer attitude dynamics from a
given light curve signature is also presented. A candidate set of simulated light curves was generated by
numerically propagating a set of initial attitude states and constant body rates through the observation window.
The results were searched to find the case that provided the best fit to the observed light curve. A further study
was initiated to investigate the errors introduced by the assumption of a constant body rate throughout the
observation for the simulated light data.

A full-wafer, 10,580 $\times$ 10,560 pixel (95 $\times$ 95 mm) CCD was designed and tested at Semiconductor Technology Associates (STA) with 9 um square pixels and 16 outputs. The chip was successfully fabricated in 2006 at DALSA and some performance results are presented here. This program was funded by the Office of Naval Research through a Small Business Innovation in Research (SBIR) program requested by the U.S. Naval Observatory for its next generation astrometric sky survey programs. Using Leach electronics, low read-noise output of the 111 million pixels requires 16 seconds at 0.9 MHz. Alternative electronics developed at STA allow readout at 20 MHz. Some modifications of the design to include anti-blooming features, a larger number of outputs, and use of p-channel material for space applications are discussed.

Maintaining space situational awareness requires an understanding of friendly and opposing force capabilities. This paper presents work towards a flexible and accurate framework for modeling rendezvous and proximity operations (RPO) within an existing simulation environment. The authors present several spacecraft close proximity maneuvering and perching techniques modeled with a high-precision numerical integrator using full force models and closed-loop control with a fuzzy logic intelligent controller to command the engines. Maneuvers, fuel use, and other parameters are documented and compared. An innovative application to design, simulate and analyze proximity and perching maneuvers, already in use for operational satellites performing other maneuvers, has been built. The system has been extended to develop closed-loop control laws to maneuver spacecraft in close proximity to another, perch and stare, conduct self-inspection, docking and other operations applicable to space situational awareness, space based surveillance and operational satellite modeling. The fully integrated end-to-end trajectory ephemerides are available from the authors in electronic ASCII text by request.

Space situational awareness (SSA) is vital for international safety and security, and the future of space travel. By improving SSA data-sharing we improve global SSA. Computational ontology should provide one means toward that goal. This paper develops the ontology of the SSA domain and takes steps in the creation of a Space Situational Awareness Ontology. It follows (Rovetto, 2015) and outlines objectives, requirements and desiderata; and describes the SSA domain and discipline of ontology. The purposes of the SSA ontology are to explore the potential for ontology development and engineering to (i) represent SSA data, general knowledge, and domain objects, (ii) clearly annotate and express the meaning of that orbital, near-earth and deep-space da-ta, and (iii) foster SSA data sharing among SSA actors and space object catalogs. By improving global SSA via actionable data- and knowledge-exchange, we can achieve the broader goals (and motivations) of (iv) advancing our capacity for planetary defense from near- or deep-space ob-ects, and (v) improving spaceflight safety for future generations.