TheBRITEConstellation Nanosatellite Mission: Testing, Commissioning, and Operations

Abstract

BRITE (BRIght Target Explorer) Constellation, the first nanosatellite mission applied to astrophysical research, is a collaboration among Austria, Canada and Poland. The fleet of satellites (6 launched; 5 functioning) performs precise optical photometry of the brightest stars in the night sky. A pioneering mission like BRITE -with optics and instruments restricted to small volume, mass and power in several nanosatellites, whose measurements must be coordinated in orbit -poses many unique challenges. We discuss the technical issues, including problems encountered during on-orbit commissioning (especially higher-thanexpected sensitivity of the CCDs to particle radiation). We describe in detail how the BRITE team has mitigated these problems, and provide a complete overview of mission operations. This paper serves as a template for how to effectively plan, build and operate future low-cost niche-driven space astronomy missions. and multi-filter capability, for a sample of the brightest stars, which tend to be the most intrinsically luminous (i.e., massive and/or highly evolved). BRITE Constellation extends the parameter space of space photometry missions, with nearly all-sky coverage in two wavelength ranges of hundreds of the most luminous stars in the Galaxy -all at relatively low cost (Weiss et al. 2014) . Three partner nations (Austria, Canada and Poland) each contributed a pair of nanosatellites (mass 7 kg; 3-axis-stablized). The BRITE network is designed to collect optical photometry of millimagnitude precision (Popowicz et al. 2016, in prep; hereafter Paper III) in light curves of high cadence (20 -25 s between consecutive exposures) and long duration (up to 6 months) through red and blue filters. The features of the six BRITE nanosatellites are listed in Table 1; only five are currently operating in orbit. The Austrian satellites are UniBRITE (UBr) and BRITE-Austria (BAb), the Polish are BRITE-Lem (BLb) and BRITE-Heweliusz (BHr), and the Canadian are BRITE-Toronto (BTr) and BRITE-Montréal (BMb, which did not deploy correctly into orbit); where r and b refer to the satellites equipped with red and blue filters, respectively. This is Paper II in a series of publications that address the technical aspects of the BRITE mission. The first paper in the series, Weiss et al. (2014), shall hereafter be referred to as Paper I. This paper provides a comprehensive history of the development of BRITE, the overall design of each satellite, and an explanation of the objectives that have been the driving forces behind the mission. Paper III in the series will be a description of the BRITE data reduction pipeline. BRITE's prime directive is to observe bright stars (V ≤ 4 mag), and shed light on their internal and surface dynamics. Among the benefits that BRITE offers are:• A test bed for future astronomical surveys with small satellites. The combination of cutting-edge science with small low-cost instruments in space has come ≈ $600 million price tag (Borucki 2016), albeit with many more limitations, providing the opportunit...

Let there be more variability in two γ Cas stars

“…The observations of BZ Cru took place in 2016 Feb-May during a run dedicated to the Crux-Carina I field; the data were downloaded from the public archives 5 . The 4 s exposures were taken in the chopping mode (Pablo et al 2016). Aperture photometry of the star was obtained from the pipeline described by Popowicz et al (2017) and corrected for instrumental effects according to the procedure presented by Pigulski (2018).…”

Machine learning search for variable stars

“…One may be interested in identifying stars more variable than the Sun (McQuillan, Aigrain & Roberts 2012) or the ones showing periodic variability (Debosscher et al 2009(Debosscher et al , 2011) -these problems require a different set of light curve features than the ones considered here. The variability detection approach presented here will likely not be useful for space astroseismology missions like MOST (Walker et al 2003), BRITE (Weiss et al 2014, Pablo et al 2016, Popowicz et al 2017) and the upcoming transit photometry mission CHEOPS (Broeg et al 2013) as they observe (with superior accuracy) only one or few stars at a time.…”

Studying the photometric and spectroscopic variability of the magnetic hot supergiant ζ Orionis Aa

“…During this Orion II observing campaign, approximately the first 40% of the observations were taken by BAb and BTr, and then the two Polish BRITE nano-satellites, BLb and BHr, took over. For some satellites, tests were performed to investigate whether onboard stackings of multiple, consecutive CCD images improved the data quality (Pablo et al 2016). This led to various observing cadences being adopted throughout the Orion II campaign, although each individual observation occurred with an exposure time of 1.0 s. Table 2 lists the various BRITE observations of ζ Ori, taken during the Orion I and Orion II campaigns.…”

“…1. However, even after correction, differences remain in the data quality for ζ Ori between the various BRITE nano-satellites (Pablo et al 2016). …”

“…This PSF has a shape which heavily depends on the orientation with the optical axis, and strongly differs from an airy disk for targets that fall close to the edge of the CCD (see Fig. 6 of Pablo et al 2016, for the effect on the PSF with the orientation with respect to the optical axis). Therefore, the time dependent temperature variations produce a time dependent PSF shape, causing a correlation between flux and the CCD centroid position of the PSF (which was the provided metadata diagnostic).…”