Calibration approach of the OLFAR space based radio telescope

In recent years, science drivers have emerged for radio astronomy in the frequency range between 0.3 and 30 MHz. Due to strong man-made radio frequency interference (RFI) and opacity and scintillation in the ionosphere, this is not possible on Earth. For this reason the Orbiting Low-Frequency Antennas for Radio Astronomy (OLFAR) project aims to develop a space-based radio telescope, consisting of 50 or more nano-satellites in a location far away from Earth. These satellites will be flying in a swarm approximately 100 km in diameter to synthesize a large radio aperture. As with any radio telescope, OLFAR will need to be calibrated. However the satellite swarm concept brings along several unique challenges for the calibration, which are outlined in this paper. An approach is proposed for the calibration using known calibrator sources and an alternating least squares (ALS) approach which solves for the complex receiver gains, the array response matrix, direction dependent antenna gains towards the calibrator sources and the receiver noise power. This paper provides proof of concept of the proposed calibration approach by means of Monte Carlo simulations.