Whispers from the dark ages

“400 thousand years after the big bang, everything went dark. For 400 million years the galactic recipes that make life as we know it possible concocted in complete darkness. Those essential and creative Dark Ages remain the largest mystery known to the astronomy community. Astronomers are now looking to the Moon for an advantageous new vantage point to listen for whispers from the universe’s most productive and secretive era.”

The only thing missing here is the tune from Star Wars or some other blockbuster about outer space. Microelectronics experts Dr. Chris Verhoeven of EWI Faculty and Dr. Mark Bentum of the University of Twente are scientists, but they might just as well have been screenplay writers. The above paragraph is an excerpt from their paper ‘Echoes from the dark’, which they wrote to enthuse the public, fellow researchers and financiers for project OLFAR, Orbiting Low-Frequency Antennas for Radio Astronomy.

OLFAR is a joint project of the University of Twente, TU Delft, Radboud University and ASTRON, the Netherlands Institute for Radio Astronomy. It aims to develop a space-based radio telescope, consisting of dozens of nanosatellites circling the Moon. These satellites must fly in a swarm approximately 100 kilometres in diameter to synthesise a large radio aperture.

With an aperture array, the researchers want to look for radiation from the hydrogen of that era, so-called hydrogen red-shifts. These red-shifts may be the only faint signals left from the ‘dark ages’ before the stars started to shine. The scientists will have to scan the radio frequency band below 30 MHz. Our Earth atmosphere reflects these waves back into space. Searching for signals just outside our atmosphere won’t do either because any faint outer space signal would dissolve in the cacophony of human radio-activity. Hence the idea of deploying an ultra-long wavelength aperture array at the dark side of the moon, where there are no disruptive signals.

Many hurdles must be overcome before such a network of nanosatellites can be realised. One of them, however, seems to have been mostly overcome; the navigation and time-keeping of the satellites. Or at least the accompanying maths. To be able to interpret the measurements from distant swarms of nanosatellites, it is paramount that the relative positions of each one of the satellites within the swarm are precisely known. This involves some harsh mathematics, which has recently been solved by PhD student Raj Thilak Rajan and his supervisor Dr. Alle-Jan van der Veen, who is the head of the Circuits and Systems group at the Electrical Engineering, Mathematics and Computer Science faculty. Rajan will defend his thesis titled Relative Space-Time Kinematics of an Anchorless Network later this year.

The idea is that the mobile and asynchronous satellites will send radio signals to each other and that they will record the respective local transmission and reception times. These measurements are enough to estimate the time-varying relative distance and relative position. An additional problem is that the atomic-clocks aboard all the satellites slightly drift in time. So minute differences in clocks must be taken into account. Similarly, the relative velocity and acceleration of the satellites must be estimated without any absolute information on space and time. In his algorithms, Rajan tackled these issues.

The TU Delft work on OLFAR doesn’t only consist of developing navigation algorithms. The University has extensive experience in making nanosatellites. TU Delft students from different faculties developed two satellites. Delfi-C3, was launched in April 2008 and, although designed for a year of active service, still functions. She is nicknamed the Old Lady. And then there is Delfi-n3Xt (Delfi Next) launched in 2013. These satellites only measure 10 by 34 centimetres – a little larger only than a milk carton. Talks are now ongoing between the TU Delft Space Institute and the Indian Space Research Organisation for a possible collaboration that should result in even more nanosatellites sent into space.

Hitching a ride with the Chinese

OLFAR is about to reach another milestone. Researchers at Radboud University, ASTRON and the Delft company Innovative Solutions in Space are to develop a new instrument that will be on-board the Chinese Chang’e4 satellite that will be placed in an orbit behind the moon in 2018. Hopes are that this device will detect these long sought after radio signals below 30 MHz from the dark ages. The signal will not be able to determine where the radio waves come from, for that, a collaborative swarm is needed, but detecting the signals in itself would be a big step forward.

The partnership agreement with the Chinese National Space Administration was signed last June. According to an ASTRON press release, the radio antenna is the first Dutch-made scientific instrument to be sent on a Chinese space mission. “This instrument will help us find answers to vital questions concerning the origin of the universe,” said Gert Kruithof from ASTRON.

Radboud University astronomers Dr. Heino Falcke and Dr. Marc Klein Wolt are the scientific advisors for the project. “The instrument we are developing will be a precursor to a future radio telescope in space,” said Klein Wolt, director of the Radboud Radio Lab, in the press release. “We will ultimately need such a facility to map the early universe and to provide information on the development of the earliest structures in it, like stars and galaxies.”