Ultra-low-frequency radio astronomy observations from a Seleno-centric orbit: First results of the Longjiang-2 experiment

This paper introduces the first results of observations with the Ultra-Long-Wavelength (ULW) —- Low Frequency Interferometer and Spectrometer (LFIS) on board the selenocentric satellite Longjiang-2. We present a brief description of the satellite and focus on the LFIS payload. The in-orbit commissioning confirmed a reliable operational status...

Frequency Augmented Clock Synchronization for Space-based interferometry

Recently, an increase in distributed space systems and a rise in number of nodes in such systems is observed in numerous space applications, for example space-based interferometry. Such applications pose stringent demands on time synchronization which can be challenging to achieve for satellite networks that lack an absolute time reference...

Orbit design of a swarm for ultra-long wavelength radio interferometry with preliminary swarm and thruster sizing

Observing the universe in the Ultra-Long Wavelength (ULW) regime has been called the ‘last frontier in astronomy’—real imaging capabilities here are yet to be achieved. Obtaining an image of the sky in this frequency band can be done by employing a swarm of satellites that together act as an interferometer and collect the required imaging...

High-resolution radio astronomy: An outlook for Africa

Very Long Baseline Interferometry (VLBI) offers unrivalled resolution in studies of celestial radio sources. The subjects of interest of the current IAU Symposium, the Active Galactic Nuclei (AGN) of all types, constitute the major observing sample of modern VLBI networks. At present, the largest in the world in terms of the number of...

Autonomous Mission Planning for OLFAR: A Satellite Swarm in Lunar Orbit for Radio Astronomy

Orbiting Low Frequency Array for Radio Astronomy (OLFAR) is a radio astronomy mission that has been studied since 2010 by several Dutch universities and research institutes. The mission aims at producing sky maps by collecting cosmic signals at ultra-low wavelengths regimes, below the 30 MHz frequency band. A satellite swarm comprising more than...

A roadmap towards a space-based radio telescope for ultra-low frequency radio astronomy

The past two decades have witnessed a renewed interest in low frequency radio astronomy, with a particular focus on frequencies above 30 MHz e.g., LOFAR (LOw Frequency ARray) in the Netherlands and its European extension ILT, the International LOFAR Telescope. However, at frequencies below 30 MHz, Earth-based observations are limited due to a...

High Data-Rate Inter-Satellite Link (ISL) For Space-Based Interferometry

The inter-satellite link (ISL) in swarm and constellation missions is a key enabler in the autonomy of the mission. OLFAR (Orbiting Low Frequency Array for Radio astronomy) is one such mission where 10 to 50+ nanosatellites are placed in the Lunar orbit and perform astronomical observations from the far-side of the moon. Each of the...

Low-frequency observations using high-altitude balloon experiments (LOBE)

The frequency range below 30 MHz remains one of the last unexplored frequency ranges in radio astronomy However, Earth-based observations at these wavelengths are severely impeded, due to man-made radio frequency interference (RFI) and atmospheric opacity. To overcome this impediment, various space-based radio astronomy studies have been...

Efficient Calibration of Radio Interferometers Using Block LDU Decomposition

Having an accurate calibration method is crucial for any scientific research done by a radio telescope. The next generation radio telescopes such as the Square Kilometre Array (SKA) will have a large number of receivers which will produce exabytes of data per day. In this paper we propose new direction-dependent and independent calibration...

Relative Space-Time Kinematics of an Anchorless Network

Covariance matching techniques for radio astronomy calibration and imaging

The search for the answer to one of the most fundamental scientific questions, “How was the universe formed?”, requires us to study very weak radio signals from the early universe. In the last eighty years, radio astronomers have been able to use radio frequency observations for significant discoveries such as quasars, super massive Black Holes...

Radioastronomical image reconstruction with regularized least squares

Image formation using the data from an array of sensors is a familiar problem in many fields such as radio astronomy, biomedical and geodetic imaging. The problem can be formulated as a least squares (LS) estimation problem and becomes ill-posed at high resolutions, i.e. large number of image pixels. In this paper we propose two regularization...

Space-based aperture array for ultra-long wavelength radio astronomy

The past decade has seen the advent of various radio astronomy arrays, particularly for low-frequency observations below 100 MHz. These developments have been primarily driven by interesting and fundamental scientific questions, such as studying the dark ages and epoch of re-ionization, by detecting the highly red-shifted 21 cm line emission....

Farside explorer: Unique science from a mission to the farside of the moon

Farside Explorer is a proposed Cosmic Vision medium-size mission to the farside of theMoon consisting of two landers and an instrumented relay satellite. The farside of the Moon is a unique scientific platform in that it is shielded from terrestrial radio-frequency interference, it recorded the primary differentiation and evolution of the Moon,...

Spatial filtering of interfering signals at the initial Low Frequency Array (LOFAR) phased array test station

The Low Frequency Array (LOFAR) is a radio telescope currently being designed. Its targeted observational frequency window lies in the range of 10–250 MHz. In frequency bands in which there is interference, the sensitivity of LOFAR can be enhanced by interference mitigation techniques. In this paper we demonstrate spatial filtering capabilities...

Radio Frequency Interference Mitigation in Radio Astronomy

The next generation of radio telescopes is expected to be one to two orders of magnitude more sensitive than the current generation. Examples of such new telescopes are the Low Frequency Array (LOFAR), currently under construction in the Netherlands, and the Square Kilometer Array (SKA), currently in a concept study phase. Another trend is that...