Radio-Source Tracker: Autonomous Attitude Determination on a Radio
Interferometric Swarm
Abstract
The development of satellite swarm technology offers new possibilities
for space studies and comes with new challenges. Among them is the need
of knowledge on the swarm topology and attitude, especially in the
context of space-borne radio interferometry. This paper presents an
algorithm that recovers the absolute swarm attitude autonomously. This
algorithm uses the imaging capability of a low frequency radio
interferometer that acts as a star-tracker using the main radio sources
in the sky. The Lost-In-Space (LIS) mode is presented in this paper.
This algorithm is studied through numerical simulations. This concept is
applied here to the kilometric wavelength spectral range (30 kHz – 1
MHz) but the technique can be extended to higher frequencies. Images are
reconstructed using an iterative Discrete Fourier Transform (DFT) at two
frequencies and using source subtractions. Pattern-matching is performed
with a voting system implemented on geometrical parameters defined by
triangles of sources. The radio sky in the working band is modeled by
extrapolating down observation of the sky at 50 MHz. The modeled
interferometer corresponds to the NOIRE (Nanosatellite pour un
Observatoire Interferométrique Radio dans l’Espace) concept study. The
accuracy on the recovered swarm attitude is measured for different
levels of noise in the interferometric visibilities. The simulation
shows that, the suggested algorithm can achieve an attitude knowledge
error lower than 1 arcmin for a swarm scale of 100 km. The requirements
in terms of memory and computation capability are discussed as well as
the limitations of the technique and the simulation.