Researchers at Radboud University Nijmegen have started a preparatory program for a radio telescope on the moon. Such a telescope, which would be comparable to the LOFAR telescope on Earth, would, for the first time, enable researchers to measure radiation generated shortly after the Big Bang. This radiation cannot be measured by radio telescopes on Earth, as our atmosphere absorbs it and because we produce a lot of radiation ourselves at the same frequencies. Using a radio telescope on the moon (or in space), we can detect this primordial radiation and from it we are able to investigate the distribution of hydrogen in the cosmos in the period directly following the Big Bang. As the universe expands the wavelength of this early radiation is stretched out as well, so by looking at different frequencies (i.e. wavelengths) one would get images of the distribution of the hydrogen at different points in time. Eventually, this would produce a ‘movie’ of the changing distribution of hydrogen in the universe. With such a radio telescope on the moon, we could map the initial stages in the evolution of the first stars and galaxies, which would evolve to the universe as we observe it today, comparable to a movie of the first steps of your child.

Radio technology on Earth has been successfully tested for many years, but placing one or more antennas on the moon (or in space) involves special requirements regarding the weight, dimensions, power consumption, as well as the processing and transfer of data. Toward this goal and as an important exercise, the team at Radboud University has designed a radio-payload for Stratos II+ rocket. The Stratos II+ rocket is holding an antenna to intercept radio signals below 12 MegaHertz and a digital receiver, both developed in Radboud Radio lab at Radboud University Nijmegen.

Space-like environment
Radiation immunity and signal processing requirements are essential for space design electronics. Furthermore building a radio telescope on the moon involves special requirements regarding the weight, dimensions, power consumption, as well as the processing and transfer of data. To achieve building such a telescope, the experiment aboard the Stratos II+ rocket is an important initial step, as it gives us the unique opportunity to test the digital receiver we developed in a space-like environment. The electronics should be low power, reliable optimized in size and robust against vibrations. The payload had already gone through the vibrations tests and the results were quite promising.

Demonstrating the technology
One of the primary goals of the current experiment is to demonstrate the functionality of the technology. The rocket will be loaded with equipment for power supply and with equipment to record and analyze the data produced by the antenna. If all the equipment survives this test, it might be used in a professional space mission in time.

The Radboud Radio Lab team uses the 50-centimeter antenna to measure the radio-frequency interference (RFI) in the atmosphere, and how the strength of this signal increases as the rocket climbs to an altitude of 50 kilometers. Using this, the astronomers hope to obtain a clearer understanding of the amount of RFI that can be expected in space.

Technical Capabilities

This payload mainly includes a radio antenna, analogue front-end circuit and a high performance digital receiver that has been build by the researchers at Radboud Radio Lab. The digitizer is a novel minimal design of a receiver for space radio astronomy, which will be used for future radio projects like SKA or “LOFAR on the moon”. This digitizer is made in a cube-sat size and provides us with a low-power and high-performance multiprocessor hardware/software system for radio astronomy experiments.

The electronics including the analogue front-end, digital back-end and the power module

On the top layer of the digitizer, there is the power module attached, which provides the supply voltage of the whole electronics (analogue and digital circuits). The middle layer is the processing unit and the bottom unit is analogue to digital convert ADC board.

Analogue front-end circuit designed and integrated

The Radboud radio payload, has several unique specifications, e.g.: The hardware is a unique design in terms of power requirement and computation performances, as a high-speed dual-core ARM-based processor is utilized for computation purpose, while dynamic supply voltage and frequency scaling could be applied for power reduction. This hardware setup is accompanied with a high-resolution ADC module, adaptive matching circuit and front-end analogue electronics.

• Provides a dual-core fast (1Gz) processing hardware for implementation of the data processing algorithms for data analysis of the antenna signals;
• Minimal size design of the digitizer, as already mentioned, which by including the power supply unit
• The power consumption is minimized in both software and hardware. – Dynamic frequency scaling technique has been added as an extra solution to dynamically adjust the speed and power consumption depending of the processing demands. This feature saves energy when not the maximum processing is required. In fact, this feature allows the two processors to switch between frequencies  (up to 1GHz speed) depending on the processing demands;
• Running under two operating systems OS: Linux and Android. This will open a broad opportunity for the digitizer to be used in different circumstances. The Linux kernel of the OS is also created based on the already existing open source Linux kernels. It is therefore compatible with all the other Linux-based software packages and programming languages.

Integration of the payload into the capsule of the Stratos II+ rocket

Radio interferometry experiment
In addition to the mentioned science goals, the antenna on-board Stratos II+ will be used for an interferometric measurement to determine the location of the rocket very precisely, where the antenna is one part of an array of antennas on the ground.

Three core-stations are designed to be located in the launch site, each with a predefined and known distance from each other and from the rocket launch pad. Combining with a reference transmitter antenna together with the antenna on-board the rocket, and using the radio interferometry techniques, we are able to precisely localize the rocket with pinpoint accuracy.

(For more information contact the project leader, Dr. Hamid Reza Pourshaghaghi:  H.Pourshaghaghi@astro.ru.nl)