Otto Koudelka

BRITE-Constellation: Nanosatellites for Precision Photometry of Bright Stars

BRITE-Constellation (where BRITE stands for BRIght Target Explorer) is an international nanosatellite mission to monitor photometrically, in two colours, the brightness and temperature variations of stars generally brighter than mag(V) ≈ 4 with precision and time coverage not possible from the ground. The current mission design consists of six nanosats (hence Constellation): two from Austria, two from Canada, and two from Poland. Each 7 kg nanosat carries an optical telescope of aperture 3 cm feeding an uncooled CCD. One instrument in each pair is equipped with a blue filter; the other with a red filter. Each BRITE instrument has a wide field of view (≈24°), so up to about 15 bright stars can be observed simultaneously, sampled in 32 × 32 pixels sub-rasters. Photometry of additional fainter targets, with reduced precision but thorough time sampling, will be possible through onboard data processing. The BRITE sample is dominated by the most intrinsically luminous stars: massive stars seen at all evolutionary stages, and evolved medium-mass stars at the very end of their nuclear burning phases. The goals of BRITE-Constellation are to (1) measure p- and g-mode pulsations to probe the interiors and ages of stars through asteroseismology; (2) look for varying spots on the stars surfaces carried across the stellar disks by rotation, which are the sources of co-rotating interaction regions in the winds of the most luminous stars, probably arising from magnetic subsurface convection; and (3) search for planetary transits.

A novel approach for symbol timing estimation based on the extended zero-crossing property

Carrier- and data-blind recovery of the symbol timing is of paramount importance in digital receivers, i.e., detailed knowledge about carrier frequency and phase or any pilot sequences is not necessary for proper operation. In this context, feedforward algorithms are particularly useful in packet-oriented systems, where rapid and stable acquisition of the major transmission parameters is essential for subsequent processing stages. In the current paper, we propose a novel approach for blind estimation of the symbol timing, which needs just one or two samples per symbol. The new method is characterized by introducing a second filter in parallel to the receiver matched filter. Under Nyquist conditions, this filter exhibits an impulse response satisfying the extended zero-crossing property, i.e., it vanishes for all integer multiples of the symbol period, including the origin! Using this idea for a suitably designed timing estimator, it is shown that the annoying jitter floor - typical for most timing estimators and caused by pattern noise - can be avoided.

Blind symbol timing recovery in the presence of IQ mismatch and DC offset

Recovery of the symbol timing is of paramount importance in digital receivers. In this context, carrier-blind and non-data-aided algorithms are of particular interest, with Oerder-Meyr and Gardner algorithms as most prominent examples. On the other hand, it is to admit that direct-conversion receivers represent a most attractive solution for modern communication systems, which is mainly due to their small package size and the reduced power consumption. Scanning the open literature, it turned out quickly that waveform-related topics, like pulse shaping and symbol timing recovery, have not been addressed so far with regard to direct-conversion receivers. Motivated by this background, this particular issue is investigated in the current paper. The focus is on the estimator and detector characteristic of Oerder-Meyr and Gardner algorithms, but also on the jitter variance as the major figures of merit in this respect.

Parameter estimation for link adaptation on land-mobile satellite links

Propagation conditions on a land-mobile satellite (LMS) link may change within the round-trip time. While for slowly fading channels the signal-to-noise ratio (SNR) is the most important figure of merit to adapt the related transmission parameters, this does not hold true for mobile channels in general. Additional information about the signal-to-interference ratio (SIR) and the Doppler spread of the fading component are typically necessary for successful link adaptation techniques. In this paper, we address carrier recovery as well as estimation of SNR, SIR, and Doppler spread for a Loo-Fontan channel, which is in the open literature frequently considered as a suitable model for LMS links. The focus is on the performance of an estimation framework, which we identified in a precursor study to be appropriate for correlated Rice channels. This developed framework is extended to LF conditions and verified by simulation results.

Nanosatellites—the BRITE and OPS-SAT missions

Nanosatellites are spacecraft in the mass range between 1 and 10 kg providing a fast and low-cost possibility to test new technology in Space and gain flight heritage. The first Austrian nanosatellite TUGSAT-1/BRITE-Austria, successfully launched in 2013, and a follow-up ESA mission are described in this paper.ZusammenfassungNanosatelliten sind Weltraumobjekte mit einer Masse zwischen 1 und 10 kg. Sie bieten eine rasche und kostengünstige Möglichkeit, neue Technologien im Weltraum zu erproben und Flugerfahrung zu sammeln. Der erste österreichische Satellit TUGSAT-1/BRITE-Austria, der erfolgreich 2013 gestartet wurde, und eine Nachfolgemission der ESA werden in diesem Artikel beschrieben.

BRITE-Constellation: Nanosatellites for precision photometry of bright stars

BRITE-Constellation (where BRITE stands for BRIght Target Explorer) is an international nanosatellite mission to monitor photometrically, in two colours, brightness and temperature variations of stars brighter than V≈ 4, with precision and time coverage not possible from the ground. The current mission design consists of three pairs of 7 kg nanosats (hence ”Constellation”) from Austria, Canada and Poland carrying optical telescopes (3 cm aperture) and CCDs. One instrument in each pair is equipped with a blue filter; the other, a red filter. The first two nanosats (funded by Austria), are UniBRITE, designed and built by UTIAS-SFL (University of Toronto Institute for Aerospace Studies Spaceflight Laboratory) and its twin, BRITE-Austria, built by the Technical University Graz (TUG) with support of UTIAS-SFL. They were launched on 25 February 2013 by the Indian Space Agency, under contract to the Canadian Space Agency. Each BRITE instrument has a wide field of view (≈ 24 degrees), so up to 15 bright stars can be observed simultaneously in 32 x 32 sub-rasters. Photometry (with reduced precision but thorough time sampling) of additional fainter targets will be possible through on-board data processing. A critical technical element of the BRITE mission is the three-axis attitude control system to stabilize a nanosat with very low inertia. The pointing stability is better than 1.5 arcminutes rms, a significant advance by UTIAS-SFL over any previous nanosatellite. BRITE-Constellation will primarily measure pand g-mode pulsations to probe the interiors and ages of stars through asteroseismology. The BRITE sample of many of the brightest stars in the night sky is dominated by the most intrinsically luminous stars: massive stars seen at all evolutionary stages, and evolved medium-mass stars at the very end of their nuclear burning phases (cool giants and AGB stars). The Hertzsprung-Russell Diagram for stars brighter than magV=4 from which the BRITE-Constellation sample will be selected is shown in Fig. 1. This sample falls into two principal classes of stars: (1) Hot luminous H-burning stars (O to F stars). Analyses of OB star variability have the potential to help solve two outstanding problems: the sizes of convective (mixed) cores in massive stars and the influence of rapid rotation on their structure and evolution. (2) Cool luminous stars (AGB stars, cool giants and cool supergiants). Measurements of the † Member of the BRITE-Constellation Executive Science Team (BEST) ‡ M. Chaumont, Cordell Grant, J. Lifshits, A. Popowicz, M. Rataj, P. Romano, M. Unterberger, R. Wawrzaszek, T. Zawistowski & BEST

Satellitenkommunikationssysteme und ihre anwendung

ZusammenfassungSeit mehr als 20 Jahren wird am Institut für Nachrichtentechnik und Wellenausbreitung (INW) gemeinsam mit dem Institut für Angewandte Systemtechnik (IAS) an der Untersuchung und Entwicklung fortschrittlicher Satellitenübertragungsverfahren und-systeme gearbeitet. Datenkommunikationssysteme für den Rechnerverbund, Video- und Audiokommunikation wurden unter Einsatz leistungsfähiger Modulations-, Codier- und Vielfachzugriffsverfahren entworfen und im praktischen Einsatz getestet und verbessert.Der nachfolgende Beitrag gibt einen Überblick über die Eigenschaften von Satelliten und die Schlüsselprojekte, die im Auftrag der Europäischen Weltraumorganisation ESA und der EU durchgeführt wurden.AbstractFor more than 20 years advanced satellite communications methods and systems have been investigated and developed at the Department of Communications and Wave Propagation (INW) and the Institute of Applied Systems Technology (IAS). Data communications systems for computer networking, video and audio dissemination were designed, tested and improved, using powerful modulation, coding and multiple access techniques.The following contribution presents an overview of the properties of satellites and key projects which have been carried out under contracts by European Space Agency and the European Union.

Space and satellite technology

Univ.-Prof. Dr. Wolfgang Bösch Over the last decades Space and satellite technology has increasingly become part of our daily lives, be it regular weather forecasts based on satellite images, the multitude of TV channels distributed via satellites or the navigational GPS support we find in almost every car—not to mention the many other services and science missions that are based on modern satellite technologies. Austria has a long tradition especially in the area of Space research and technology. The first Austrian Space object, a measurement probe for ionospheric research, was launched on 26 November 1969 on board of a Norwegian sounding rocket. In 1981 Austria became an associate member of the European Space Agency ESA and has been a full member since 1987. Austria contributes to the mandatory and optional ESA programs. The annual Space expenditures amount to 65 million Euro (including the national Space program ASAP and the contribution to EUMETSAT). Regarding the optional programs Austria focuses on its strengths, both in industry and academia. Earth observation, satellite communications and satellite navigation as well as integrated Space applications constitute the majority of the projects contracted to Austrian companies, universities and research organizations. In the area of satellite communications Austria has significantly contributed to ESA missions such as OTS, OLYMPUS, ARTEMIS and most recently ALPHASAT. In 2013 Austria became a “launching state” with the successful orbiting of the first Austrian satellite BRITE-Austria/TUGSAT-1 and its companion UniBRITE. In this special edition of the e&i journal particular aspects of satellite technology and applications are addressed. The first paper by Manfred Wittig discusses the past, presence and future of intelligent communications payloads, “switchboards in the sky”, which improve communications and service efficiency. The second paper by Michael Schmidt et al. presents the design of a satellite ground station for Q/V-Band (40/50 GHz) and the communications and propagation experiments which are conducted using ESA’s largest telecom satellite, ALPHASAT. The paper by Qi Luo focuses on intelligent antenna technology for mobile satellite communications which can increase the channel capacity, spectral efficiency and coverage. Norbert Frischauf’s paper addresses aeronautical applications of satellite navigation systems such as GPS, GALILEO and others which aim at improving air transport safety. The paper by Otto Koudelka presents two examples of demanding nanosatellite missions, namely BRITE, a small satellite constellation for asteroseismology, and OPS-SAT, an ESA project to demonstrate in orbit novel technology and new operational concepts.