A mini satellite, roughly the size of a small carry-on suitcase, will travel to the far side of the Moon to listen for "whispers" from 13.5 billion years ago, aiming to answer one of cosmology's biggest questions. Scientists from the University of Cambridge will lead an international team using the CosmoCube satellite to investigate the "cosmic dark ages," a period of about 150 million years before the universe's first stars emerged.
The target signal is the 21-centimetre line, emitted by hydrogen atoms during the era between the Big Bang's afterglow and the Cosmic Dawn, when nuclear fusion ignited the first stars. This period has never been directly observed.
"Aside from the science, what makes our mission unique is its size: we’re probing the earliest, deepest parts of the dark ages that others don’t reach, but with a compact, relatively low-cost platform," said Prof Eloy de Lera Acedo, from Cambridge’s Cavendish Laboratory.
Earth-based telescopes struggle to detect the faint signal due to the ionosphere blocking relevant frequencies and interference from radio, satellites, and telecommunications. CosmoCube will utilize the Moon as a natural shield; when orbiting the far side, it will be shielded from Earth's noise for approximately 40 minutes in each two-hour orbit.
The two-year mission is expected to yield 1,000 hours of data on this unexplored epoch, shedding light on the universe's transition from a dark, empty state to its current form. It may also help understand dark matter, the mysterious force holding galaxies together.
"This emission from hydrogen after the Big Bang, but before the first stars, will hopefully allow us to understand the role of dark matter in the early universe, how it worked to pull together hydrogen into the first stars and galaxies," explained Prof de Lera Acedo, lead author of a paper on the project published in Nature Astronomy.
With funding from the UK Space Agency, the CosmoCube mission is targeted for launch within five years. It will operate at extremely low frequencies (10-50MHz), far beyond the reach of ground-based telescopes, relying on the Moon's far side as its "fortress of solitude."
"There’s no other place where you can get the sort of shielding you need to detect such a faint signal, while at the same time looking at the whole of space," said Prof de Lera Acedo, who is also affiliated with the Kavli Institute for Cosmology in Cambridge. "The far side of the Moon is really the only option: it solves multiple problems at once, opening a clear window to the very early universe."
Upon reaching the lunar far side, CosmoCube will deploy a long, lightweight radio antenna sensitive enough to detect the 21-centimetre signal. In orbit, it will use a "Dicke switched" calibrator, flipping between the sky and internal reference sources, to correct its electronics and cancel out internal noise that could be mistaken for cosmic signals.
Advanced Bayesian statistical methods will be employed on Earth to remove foreground noise, primarily radio emissions from our own galaxy. The team will also use computer simulations and in-flight measurements to reconstruct antenna response and subtract distortions.
Other missions from the US, India, and other countries are also planned to leverage the Moon's radio silence, making time of the essence.
Surrey Space Technology Limited (SSTL) is developing the CosmoCube platform, featuring a miniature radiometer using the latest RF-Systems-on-Chip (RFSoCs) technology. Instrument development and environmental testing are underway, with collaboration from industry partners.
Academic partners include Portsmouth University and STFC RAL Space in the UK, with participation from EU countries like Malta. The CosmoCube team recently submitted a proposal for the European Space Agency’s mini-Fast missions Call for Ideas.
"CosmoCube is aiming to do some ambitious science from a very small satellite in a challenging environment, and to do that requires some clever design techniques," said co-author Dr Will Grainger, from STFC RAL Space. "We’ve worked with the project partners to develop representative models of the satellite and its payload. These have been tested in our facilities to ensure the thermal performance allows the payload to operate and perform the required sensitive measurements under the different temperature conditions it will experience whilst in orbit around the Moon. In the future, we hope to further develop the full payload in preparation for a full mission."
Prof de Lera Acedo, a fellow of Selwyn College, Cambridge, added: "This could be a real UK success story: the hardware, the software, the implementation and the technology is all being developed here, and it could help us answer one of the most profound questions in the universe."
The project is supported by the UK Space Agency, the Kavli Foundation, and the Science and Technology Facilities Council.
