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The Canadian Space Agency has developed a multi-mission automated Collision Risk Assessment and Mitigation System (CRAMS). This paper describes the system and the challenges associated with its development and operation. The system receives e-mails and Conjunction Summary Messages (CSMs) from JSpOC, processes them and generates warning messages to the control centre when action is required based on predetermined thresholds. The system employs an approximate analytic probability model, and a conjunction geometry dependent hard body radius (HBR) for the primary object. The results of processing flight test data show accuracy extremely close to that of numerical integration in case of exact frame transformation. The limits of the simplifying assumptions for some transformations were also tested. To converge towards entry and exit (action -Stop action) criteria analysis was performed on past flight data and other data. The last challenge is the criterion on the quality of data given the fact that CSA receives only one or two data points before the time of conjunction. That implies that lack of sufficient data to test ability of covariance to predict miss distance variations for good quality data. One criterion was used for Radarsat-1 and Scisat based on not acting on any data of equivalent quality to that of TLEs. There has been previous decision not to act on TLE data after a visit and discussions with JSpOC.

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After suffering the failure of its magnetometer and all torque rods, the NEOSSat microsatellite has recovered operations through the use of novel attitude determination and control algorithms that utilize a minimal sensor and actuator suite. Following recovery, NEOSSat has regained the performance necessary to accomplish its near-earth object space surveillance mission with only a modest duty cycle reduction and adjustments to spacecraft operation planning. This paper provides a description of NEOSSat, its hardware failures, and discusses the development and implementation of the innovative flight software upgrades that facilitated its recovery. The paper expands the body of knowledge in GPS-based attitude determination and momentum management strategies for satellites.

Conjunction assessment of space objects in Low Earth Orbit (LEO) generally uses information collected by ground-based space surveillance sensors. These sensors track both the primary object (normally an active satellite) and the secondary object (typically space debris). The tracking data is used to update both objects’ orbits for collision risk assessment. The primary satellite’s involvement in this process is that of a satellite in jeopardy - the primary satellite does not usually contribute tracking data on the secondary as they are typically unequipped to do so. In this paper, an examination how an at-risk LEO primary satellite could obtain optical tracking data on a secondary object prior to the Time of Closest Approach (TCA) and assess its own collision risk without the need for additional ground-based space surveillance data is performed. This analysis was made possible by using in-situ optical measurements of space objects conjuncting with the Canadian NEOSSat Space Situational Awareness R&D microsatellite. By taking advantage of the near “constant-bearing, decreasing range” observing geometry formed during a LEO conjunction, NEOSSat can collect astrometric and photometric measurements of the secondary object in the time prior to TCA, or in the multiple half-orbits preceding TCA. This paper begins by describing the in-situ phenomenology of optically observed conjunctions in terms of the observing approach, geometry and detected astrometric and photometric characteristics. It was found that conjuncting objects are detectable to magnitude 16 and astrometric observations can be used for position covariances in the computation of probability of collision. Illustrative examples are provided. In orbits prior to TCA, in-track positioning error is improved by a factor of two or more by processing space-based observations on a filtered position estimate of the secondary. However, cross-track positioning knowledge is negligibly improved due to the inherent astrometric measurement precision of the NEOSSat sensor and the oblique observing geometry during conjunction observations. A short analysis of object detectability where star trackers could be used to perform similar observations finds that larger payload-sized objects would generally be detectable. However, smaller debris objects would require higher sensitivity from the star tracker if employed for optical conjunction derisk observations.