Designing star trackers to meet micro-satellite requirements

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2006.Includes bibliographical references (p. 179-187).Star trackers provide numerous advantages over other attitude sensors because of their ability to provide full, three-axis orientation information with high accuracy and flexibility to operate independently from other navigation tools. However, current star trackers are optimized to maximize accuracy, at the exclusion of all else. Although this produces extremely capable systems, the excessive mass, power consumption, and cost that result are often contradictory to the requirements of smaller space vehicles. Thus, it is of interest to design smaller, lower cost, albeit reduced capability star trackers that can provide adequate attitude and rate determination to small, highly maneuverable, low-cost spacecraft. This thesis discusses the analysis used to select hardware and predict system performance, as well as the algorithms that have been employed to determine attitude information and rotation rates of the spacecraft. Finally, the performance of these algorithms using computer simulated images, nighttime photographs, and images captured directly by star tracker prototypes is presented.by Kara M. Huffman.S.M

The design and implementation of a stellar gyroscope for accurate angular rate estimation on CubeSats

Thesis (MEng)--Stellenbosch University, 2015.ENGLISH ABSTRACT: Until recently, small form factor satellites (such as CubeSats) relied almost exclusively on micro electromechanical system (MEMS) gyroscopes for attitude propagation purposes. Unfortunately, the nature of MEMS gyros is such that they exhibit a measure of bias drift. This drift must be compensated for, a task for which stellar gyros have proved to be exceptionally useful. Stellar gyros are satellite subsystems capable of inferring three-axis attitude propagation based on the displacement of a series of stars between successive image frames. Their design is analogous to that of star trackers, using many of the same hardware designs and algorithms. When used in combination with MEMS solutions, stellar gyros provide not only a means for drift compensation, but also a measure of functional redundancy with regard to attitude propagation. This thesis presents the design and implementation of stellar gyroscope algorithms capable of operating alongside existing orientation algorithms on traditional star tracker hardware. The CubeStar star tracker module is used as development platform. The proposed stellar gyro solution retains CubeStar’s existing star extraction algorithms, while investigating alternative methods for star centroiding in addition to the existing centre of gravity (CoG) approach. A dynamic proximity based matching algorithm is suggested to determine star correspondence between image frames. Finally, various well established estimation algorithms are considered for the purpose of rate determination, including singular value decomposition (SVD), Davenport’s q-Method and weighted least-squares (WLS). An initial evaluation of the proposed algorithms is made based on simulations in the MATLAB environment. Simulation results are confirmed through means of practical tests, performed on a simulated night sky in a controlled environment. With a focus on low angular rates, results suggest reliable operation up to ±1 deg/s in all three axes of rotation. As expected for stellar imaging solutions, angular rates estimated in both cross-boresight axes are almost an order of magnitude more accurate than the corresponding estimates in the boresight axis itself.AFRIKAANSE OPSOMMING: Mikrosatelliete, soos CubeSats, het tot onlangs byna uitsluitlik op mikro elektromeganiese (MEMS) vibrerende struktuur giroskope staatgemaak vir die meet van hoeksnelhede. Ongelukkig is die aard van MEMS giroskope sodanig dat hierdie metings afsette toon wat al hoe verder van hul werklike waardes verskuif. Daar moet gekompenseer word vir hierdie verskuiwing, ’n taak waarvoor stergiroskope besonder geskik is. Sterrebeeld gebaseerde giroskope (of bloot gewoon stergiroskope) is satelliet substelsels wat daartoe in staat is om ’n satelliet se oriëntasie in drie dimensies te propageer deur gebruik te maak van die verplasing van ’n reeks sterre tussen twee opeenvolgende beelde. Hulle ontwerp in terme van beide hardeware en algoritmes is soortgelyk aan dié van stervolger kameras. Stergiroskope kan ook saam met MEMS toestelle gebruik word. Hulle verskaf beide ’n metode om te kompenseer vir verskuiwings in MEMS metings sowel as ’n funksionele alternatief met betrekking tot hoekafskatting. Hierdie tesis beskryf die ontwerp en implementering van ster giroskoop algoritmes wat in staat is om hand-in-hand met bestaande oriëntasie algoritmes op tradisionele ster volger hardeware te funksioneer. Die CubeStar stervolger module is as ontwikkelings platform gebruik. Die beoogde stergiroskoop ontwerp behou CubeStar se bestaande ster ontginnings algoritmes. Verskeie metodes benewens die bestaande swaartepunt benadering word wel ondersoek vir die bepaling van ster sentroïedes. Die korrespondensie tussen opeenvolgende sterbeelde word bepaal deur middel van ’n dinamiese nabyheid gebaseerde passings algoritme. Ten slotte word verskeie algoritmes oorweeg vir die afskatting van ’n satelliet se hoeksnelhede. Dit sluit in enkelvoud waarde ontbinding (SVD), Davenport se q-metode en ’n geweegte kleinste kwadraat (WLS) benadering. Die voorgestelde algoritmes is ge-evalueer op grond van simulasies in die MATLAB omgewing. Praktiese toetse is uitgevoer op ’n gesimuleerde sterrebeeld om simulasie resultate te bevestig. Met ’n fokus op lae hoeksnelhede dui resultate op betroubare afskatting teen hoeksnelhede van tot ±1 grade/s rondom al drie rotasie-asse. Soos verwag van ster kameras is die hoekafskattings rondom die transversale asse ’n orde meer akkuraat as die ooreenstemmende afskattings rondom die optiese as

Design and evaluation of a digital processing unit for satellite angular velocity estimation

A satellite's absolute attitude and angular rate are both important measurements for satellite missions that require navigation. Typically, these measurements have been made by separate sensors, with star cameras being used to determine a satellite's absolute attitude, and gyroscopes being used as the primary rate sensors. Recently, there have been multiple efforts to measure both of these quantities using only the star camera, however the work primarily involves solutions where the optical sensor and the unit that processes the images are separate integrated circuits. Operation in this modality requires the use of chip to chip communication in order to estimate angular rate from star tracker images, which can lead to an increase in system power, a degradation in performance, and increased latency. The goal of this thesis is to consolidate the sensing and processing into a single integrated circuit. The design and evaluation of a digital processing unit that estimates angular rate and facilitates the realization of image sensor and processor integration is presented. The processing unit is implemented in UMC's 130 nm process, has an area of 10 mm × 200 μm, and consumes 8.253 mW of power

Modeling, image processing and attitude estimation of high speed star sensors

Attitude estimation and angular velocity estimation are the most critical components of a spacecraft's guidance, navigation and control. Usually, an array of tightlycoupled sensors (star trackers, gyroscopes, sun sensors, magnetometers) is used to estimate these quantities. The cost (financial, mass, power, time, human resources) for the integration of these separate sub-systems is a major deterrent towards realizing the goal of smaller, cheaper and faster to launch spacecrafts/satellites. In this work, we present a novel stellar imaging system that is capable of estimating attitude and angular velocities at true update rates of greater than 100Hz, thereby eliminating the need for a separate star tracker and gyroscope sub-systems. High image acquisition rates necessitate short integration times and large optical apertures, thereby adding mass and volume to the sensor. The proposed high speed sensor overcomes these difficulties by employing light amplification technologies coupled with fiber optics. To better understand the performance of the sensor, an electro-optical model of the sensor system is developed which is then used to design a high-fidelity night sky image simulator. Novel star position estimation algorithms based on a two-dimensional Gaussian fitting to the star pixel intensity profiles are then presented. These algorithms are non-iterative, perform local background estimation in the vicinity of the star and lead to significant improvements in the star centroid determination. Further, a new attitude determination algorithm is developed that uses the inter-star angles of the identified stars as constraints to recompute the body measured vectors and provide a higher accuracy estimate of the attitude as compared to existing methods. The spectral response of the sensor is then used to develop a star catalog generation method that results in a compact on-board star catalog. Finally, the use of a fiber optic faceplate is proposed as an additional means of stray light mitigation for the system. This dissertation serves to validate the conceptual design of the high update rate star sensor through analysis, hardware design, algorithm development and experimental testing

Compact pixel architecture for CMOS lateral flow immunoassay readout systems

A novel pixel architecture for CMOS image sensors is presented. It uses only one amplifier for both integration of the photocurrent and in-pixel noise cancelation, thus minimizing power consumption. The circuit is specifically designed to be used in readout systems for lateral flow immunoassays. In addition a switching technique is introduced enabling the use of column correlated double sampling technique in capacitive transimpedance amplifier pixel architectures without the use of any memory cells. As a result the reset noise which is crucial in these architectures can be suppressed. The circuit has been designed in a 0.35-μm CMOS technology and simulations are presented to show its performance

CSTARS: Cryogenic CMOS Optical Star Tracking

CMOS and sCMOS image sensors are a cost-effective alternative to the more common CCD based experimental sensors. While often being less favored than CCDs at room temperature, CMOS image sensors have a better performance at lower temperatures and are the only of the two highly used technologies that is viable at cryogenic temperatures. This paper discusses development iterations of the star tracking rocket attitude regulation system (CSTARS). This includes discussions of the cryogenic operation of CMOS sensors as well as operating in and interfacing with a NASA sounding rocket as a star tracking system. Both iterations of the project have proved effective in operating sCMOS image sensors at cryogenic temperatures with low read noise. Star tracking has also been successful in the second iteration of the system, which is scheduled to fly with the CIBER-2 sounding rocket experiment. A successful flight with CIBER-2 would prove the readiness of sCMOS sensors for cryogenic operation in a real world application

Circuits and Systems for Lateral Flow Immunoassay Biosensors at the Point-of-Care

Lateral Flow Immunoassays (LFIAs) are biosensors, which among others are used for the detection of infectious diseases. Due to their numerous advantages, they are particularly suitable for point of care testing, especially in developing countries where there is lack of medical healthcare centers and trained personnel. When the testing sample is positive, the LFIAs generate a color test line to indicate the presence of analyte. The intensity of the test line relates to the concentration of analyte. Even though the color test line can be visually observed for the accurate quantification of the results in LFIAs an external electronic reader is required. Existing readers are not fully optimized for point-of-care (POC) testing and therefore have significant limitations. This thesis presents the development of three readout systems that quantify the results of LFIAs. The first system was implemented as a proof of concept of the proposed method, which is based on the scanning approach without using any moving components or any extra optical accessories. Instead, the test line and the area around it, are scanned using an array of photodiodes (1 × 128). The small size of the pixels gives the system sufficient spatial resolution, to avoid errors due to positioning displacement of the strip. The system was tested with influenza A nucleoprotein and the results demonstrate its quantification capabilities. The second generation system is an optimized version of the proof of concept system. Optimization was performed in terms of matching the photodetectors wavelength with the maximum absorption wavelength of the gold nanoparticles presented in the tested LFIA. Ray trace simulations defined the optimum position of all the components in order to achieve uniform light distribution across the LFIA with the minimum number of light sources. An experimental model of the optical profile of the surface of LFIA was also generated for accurate simulations. Tests of the developed system with LFIAs showed its ability to quantify the results while having reduced power consumption and better limit of detection compared to the first system. Finally, a third generation system was realized which demonstrated the capability of having a miniaturized reader. The photodetector of the previous systems was replaced with a CMOS Image Sensor (CIS), specifically designed for this application. The pixel design was optimized for very low power consumption via biasing the transistors in subthreshold and by reusing the same amplifier for both photocurrent to voltage conversion and noise cancellation. With uniform light distribution at 525 nm and 76 frames/s the chip has 1.9 mVrms total output referred noise and a total power consumption of 21 μW. In tests with lateral flow immunoassay, this system detected concentrations of influenza A nucleoprotein from 0.5 ng/mL to 200 ng/mL

Science Mission Directorate TechPort Records for 2019 STI-DAA Release

The role of the Science Mission Directorate (SMD) is to enable NASA to achieve its science goals in the context of the Nation's science agenda. SMD's strategic decisions regarding future missions and scientific pursuits are guided by Agency goals, input from the science community including the recommendations set forth in the National Research Council (NRC) decadal surveys and a commitment to preserve a balanced program across the major science disciplines. Toward this end, each of the four SMD science divisions -- Heliophysics, Earth Science, Planetary Science, and Astrophysics -- develops fundamental science questions upon which to base future research and mission programs