The communication layer for the OLFAR satellite swarm

Recently, new directions in astronomy are investigated as space observations tend to evolve from optical observations to the low-frequency domain. Ultra-long EM waves are the result of planetary emissions from outside and inside the solar system and of high-energy particle interactions. Exploring this band would create an image of our younger universe and uncover a lot of the so called astronomical dark ages(1)

Orbiting low frequency antennas for radio astronomy(OLFAR): Distributing signal processing

Recently, new and interesting science drivers have emerged in the ultra low frequency range of 0.3-30 MHz ranging from the epoch of re-ionization, exo-planets, ultra-high energy cosmic rays and studies of the astronomical dark ages. However at these wavelengths, ground based observations are severely limited due to ionospheric distortions below 50MHz, manmade interference, complete reflection of radio waves below 30MHz and even solar flares (1)

Swarm-to-earth communication in OLFAR

New science drivers have recently emerged in radio astronomy for observation of low-frequency radio waves, below 30 MHz. Exploring this frequency requires a space-based radio telescope with a very large aperture that is impossible to realize in a monolithic fashion. A distributed system consisting of a swarm of 50 or more nano-satellites is used to realize such an instrument. Equipped with low-frequency antennas, the very small spacecraft provide the needed aperture to capture and sample ultra-long electromagnetic waves. The distributed low-frequency telescope has to fulfill multiple tasks in which drawbacks such as the size and the limited power available are overcome by the large number of satellites. Sending the processed data to a base station is one of these aforementioned tasks that is critical for the functionality of the system. In our paper we analyze the challenges of downlinking data from a swarm of nano-satellites to Earth and propose a diversity scheme that helps the system to achieve its mission

Swarm to earth communication in OLFAR

New science drivers have recently emerged in radio astronomy for observation of low-frequency radio waves, below 30 MHz. Exploring this frequency requires a space-based radio telescope with a very large aperture that is impossible to realize in a monolithic fashion. A distributed system consisting of a swarm of 50 or more nano-satellites is used to realize such an instrument. Equipped with low-frequency antennas, the very small spacecraft provide the needed aperture to capture and sample ultra-long electromagnetic waves. The distributed low-frequency telescope has to fulfill multiple tasks in which drawbacks such as the size and the limited power available are overcome by the large number of satellites. Sending the processed data to a base station is one of these aforementioned tasks that is critical for the functionality of the system. In our paper we analyze the challenges of downlinking data from a swarm of nano-satellites to Earth and propose a diversity scheme that helps the system to achieve its mission

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

Antenna system design for olfar's inter-satellite link

Initiatives to perform space-based radio astronomy below 30 MHz have emerged recently, since novel technological developments have increased their feasibility. The Orbiting Low-Frequency Array for Radio Astronomy (OLFAR) project, one of these initiatives, aims to use a swarm of nano-satellites to implement an interferometric array in space. For its astronomical tasks, OLFAR requires that each satellite is able to establish a high-data-rate radio link with any other. We propose a design of the antenna system for these links, in which we present a design approach and describe an antenna configuration, a control strategy and individual antenna characteristics that satisfy OLFAR’s requirements