ASTROtir – A multi-purpose thermal infrared camera

Spacecraft relative navigation with an omnidirectional vision sensor

Precise relative GPS navigation is essential technology for rendezvous and formation flying of spacecraft in Low Earth Orbit. Key design issues of precise relative GPS navigation software are studied and a novel formulation is proposed for the mission which requires high accuracy when the separation distance is up to several km. The navigation filter estimates float navigation solutions by extended Kalman filter with elaborate dynamics models, and resolves ambiguities of integer carrier phase biases to achieve high accuracy fix navigation solutions. A relative navigation software with the proposed formulation is implemented and evaluated in two different ways. One is a test using spacebourne GPS receivers and a GPS signal simulator to evaluate the performance and sensitivity of the software against variation of parameters. The other is a test using actual telemetry data from Gravity Recovery and Climate Experiment (GRACE) to demonstrate the software performance. The design, implementation, and results of the evaluation are presented and discussed on this paper.

PRISMA is a technology demonstration mission for satellite formation flying and in-orbit servicing. The space segment comprises the fully maneuverable Main minisatellite and the smaller Target satellite in a low Earth orbit at 700-km altitude. A key mission objective is to demonstrate onboard, fully autonomous, robust, safe, and precise formation flying of spacecraft. This is accomplished by spaceborne global positioning system navigation, guidance, and control functionalities for the maintenance of the relative motion between the two spacecraft. An innovative estimation approach employs a common Kalman filter for the absolute states of Main and Target, which accounts for the interdependency of absolute and relative navigation without the need for an explicit relative state. As a result, the onboard navigation system provides absolute and relative orbit information in real time with a position accuracy of 2 and 0.1 m, respectively. The formation control achieves accuracies of a few tenths of meters with minimum usage of thrusters. The guidance and control concept is detailed with emphasis on a relative eccentricity and inclination vector separation strategy. The paper derives estimates of the expected relative orbit control performances based upon realworld simulations using typical global positioning system receiver and propulsion system characteristics.

Geostationary satellites play a key role in observing the spatial and temporal variations in surface and atmospheric features, which are important for monitoring short-term weather. While limited in spatial resolution compared to low-earth orbiting satellites, geostationary platform provides a significant advantage. The primary advantage is the ability to characterize the radiance by obtaining numerous views of a specific earth location for any time of day. This allows the production of a composite image to monitor short-term weather better. It will be shown that only 14% of days were missed in retrials, compared to the likely miss rate of 60-70% of a polar orbiting satellite. Mie theory is applied to calculate scattering characteristics of dust particles, and analyze dust channel selection of meteorological satellite. It can be seen that the visible channel is the primary channel available for dust aerosol observation. Also, the shortwave channel has some sensitivity to aerosols. Therefore, optically thick dust can have significant effect on infrared radiation. The radiative temperature of dust in shortwave infrared and longwave infrared is different also because emissivity is the function of wavelength. We compare the emissivity of rock, soils, vegetation, water and ice in shortwave and longwave channel, referring to the paper of John W. Salisbury. It can be seen that the different emissivity of soils is the most obvious. We apply difference of two wave bands to distinguish dust storm. The practical difference image proves the point. Geostationary orbit satellite is main tool in distinguishing short time weather phenomena such as dust storm due to its observational frequency and range.

An occulter is a spacecraft with a precisely-shaped optical edges which flies in formation with a telescope, blocking light from a star while leaving light from nearby planets unaffected. Using linear optimization, occulters can be designed for use with telescopes over a wide range of telescope aperture sizes, science bands, and starlight suppression levels. It can be shown that this optimization depends primarily on a small number of independent nondimensional parameters, which correspond to Fresnel numbers and physical scales and enter the optimization only as constraints. We show how these can be used to span the parameter space of possible optimized occulters; this data set can then be mined to determine occulter sizes for various mission scenarios and sets of engineering constraints.

Relative Navigation of Satellites in Formation Using Monocular Model-Based Vision

This chapter describes recent advancements in the areas of guidance, navigation, and control of distributed spacecraft systems or spacecraft formation flying of swarms of 100-gram class spacecraft and planetary landing. A review of advances in perception technologies for on-board hazard detection and terrain relative navigation is presented. The second part of this chapter is devoted to the discussion of innovative research on spacecraft swarms. Spacecraft swarms, comprised of hundreds to thousands of small spacecraft will push the frontier of the existing formation flying concepts by maximizing the benefits of distributed spacecraft systems. Novel control strategies of handling such a large spacecraft network are presented by employing synchronization control on adaptive graphs and probabilistic swarm guidance strategies. Furthermore, new filtering techniques that enable tracking of a large number of space objects are discussed.

Spacecraft formation flying has received an enor- mous amount of attention over the past few years as a promising alternative to monolithic- and often large- space structures. Balanced optimal energy control of such distributed space systems guarantees maximum lifetime for these missions and hence is of great importance in mission feasibility studies. In this paper, an optimal control strategy for two and three spacecraft distributed space systems that are commanded to attain new relative coordinates, is proposed, guaranteeing balanced energy consumption among the spacecraft. We will delineate on the relevant mission scenarios both in deep space as well as in close proximity to a gravitational force field as in Earth's orbit. Index Terms— Formation flying, balanced energy reconfig- urations, optimal control

Anomaly detection for a noncooperative satellite is a fundamental and significant step in space situation awareness. To effectively detect the abnormal state of an on-orbit satellite, this article proposes a novel generative adversarial network with a time–frequency (TF) spectrum (TF-GAN). First, the TF spectrum of radar echoes is acquired, and the artificially selected features are extracted from the TF spectrum of the normal state of the on-orbit satellite. Second, the proposed model is trained to learn the TF spectrum latent representation and the pre-extracted features. Then, the trained model can distinguish abnormal samples from the normal ones and output the evaluated anomaly score. Finally, the proposed TF-GAN is compared with several GAN-based methods. Experiments show that the accuracy and F1-score of the TF-GAN are superior to those of the comparison methods, and the anomaly scores of abnormal and normal classes are more separable.

Collision Probability with Gaussian Mixture Orbit Uncertainty

The first Visible Infrared Imager Radiometer Suite (VIIRS) instrument was successfully launched on-board the Suomi National Polar-orbiting Partnership (SNPP) spacecraft on October 28, 2011. Suomi NPP VIIRS observations are made in 22 spectral bands, from the visible (VIS) to the long-wave infrared (LWIR), and are used to produce 22 Environmental Data Records (EDRs) with a broad range of scientific applications. The quality of these VIIRS EDRs strongly depends on the quality of its calibrated and geo-located Sensor Date Records (SDRs). Built with a strong heritage to the NASA's EOS MODerate resolution Imaging Spectroradiometer (MODIS) instrument, the VIIRS is calibrated on-orbit using a similar set of on-board calibrators (OBC), including a solar diffuser (SD) and solar diffuser stability monitor (SDSM) system for the reflective solar bands (RSB) and a blackbody (BB) for the thermal emissive bands (TEB). On-orbit maneuvers of the SNPP spacecraft provide additional calibration and characterization data from the VIIRS instrument which cannot be obtained pre-launch and are required to produce the highest quality SDRs. These include multi-orbit yaw maneuvers for the characterization of SD and SDSM screen transmission, quasi-monthly roll maneuvers to acquire lunar observations to track sensor degradation in the visible through shortwave infrared, and a driven pitch-over maneuver to acquire multiple scans of deep space to determine TEB response versus scan angle (RVS). This paper pro-vides an overview of these three SNPP calibration maneuvers. Discussions are focused on their potential calibration and science benefits, pre-launch planning activities, and on-orbit scheduling and implementation strategies. Results from calibration maneuvers performed during the Intensive Calibration and Validation (ICV) period for the VIIRS sensor are illustrated. Also presented in this paper are lessons learned regarding the implementation of calibration spacecraft maneuvers on follow-on missions.

This paper describes a novel concept for optical interrogation, communication, and navigation between spacecraft platforms. The technique uses a gimbaled laser source on a pursuer spacecraft and an array of solid-state, multiple quantum well modulating retroreflectors on a target spacecraft. The sensor system provides high-bandwidth optical communication, centimeter-level relative positioning, and better than arc-minute-level relative attitude of the target platform with minimal sacrifice in target size, weight, and power. To accomplish the relative navigation, each target retroreflector return is modulated with a unique code sequence, allowing for individual discrimination of the detected composite signal at the pursuer location. Experimental results using a dual-platform, multi-degree-of-freedom testbed provide verification and demonstration of the concept, highlighting its potential for applications such as inter-spacecraft rendezvous and capture, long-baseline space interferometry, and formation flying.

In this brief we present a new approach to fine relative position control in satellite formation flying. We focus on a situation involving two spacecraft, one of which (the “chaser”) is actively controlling its position with respect to the other (the “target”). The goal of the approach is to use the minimum number of thruster firings in order to keep the chaser following its reference position within a certain tolerance. We first present a method based on the matching pursuit (MP) algorithm, which proves to provide a solution to this problem in the open-loop case. Moreover, we show that a closed-loop version of the controller can be obtained as well by turning the method into a model predictive control (MPC) strategy, thanks to the fact that the computational cost of the method is small. An example of application is shown at the end for a mission scenario inspired by the PROBA3 mission, which is currently under development.

In this study, submillimeter level accuracy K-band microwave ranging (MWR) equipment is demonstrated, aiming to verify the detection of the Earth’s gravity field (EGF) and digital elevation models (DEM), through spacecraft formation flying (SFF) in low Earth orbit (LEO). In particular, this paper introduces in detail an integrated BeiDou III B1C/B2a dual frequency receiver we designed and developed, including signal processing scheme, gain allocation, and frequency planning. The receiver matched the 0.1 ns precise synchronize time-frequency benchmark for the MWR system, verified by a static and dynamic test, compared with a time interval counter synchronization solution. Moreover, MWR equipment ranging accuracy is explored in-depth by using different ranging techniques. The test results show that MWR achieved 40 m and 1.6 m/s accuracy for ranging and range rate during tests, using synchronous dual one-way ranging (DOWR) microwave phase accumulation frame, and 6 m/s range rate accuracy obtained through a one-way ranging experiment. The ranging error sources of the whole MWR system in-orbit are analyzed, while the relative orbit dynamic models, for formation scenes, and adaptive Kalman filter algorithms, for SFF relative navigation designs, are introduced. The performance of SFF relative navigation using MWR are tested in a hardware in loop (HIL) simulation system within a high precision six degree of freedom (6-DOF) moving platform. The final estimation error from adaptive relative navigation system using MWR are about 0.42 mm (range/RMS) and 0.87 m/s (range rate/RMS), which demonstrated the promising accuracy for future applications of EGF and DEM formation missions in space.

In the context of space situational awareness, orbit determination and maneuver detection pose considerable challenges given the ever increasing number of noncooperative satellites that perform unspecified maneuvers at unknown epochs. A new metric is proposed for maneuver detection here, based on measurements from a single surveillance radar. Data from the radar track are leveraged to derive this metric; it can flag the occurrence of a maneuver since the last time a satellite was observed. In the scenarios considered in this work, the main challenge is having just a few available observations in between long propagations. Thus, a realistic quantification of uncertainty becomes crucial; Gaussian mixtures are chosen for this work. The propagated state is compared against the radar track data to compute a well-known cost metric, the evidence in Bayes’s update, similar to the Mahalanobis distance (MD). The contribution of this work lies in using the variation of the cost metric across track points to define a new maneuver detection metric. The focus is on testing this new metric in diverse and realistic scenarios to gain practical intuition about its performance and limitations. The preliminary results are promising, simultaneously improving upon the classical MD at maneuver detection and reducing false positives.