Multiple space agencies are gearing up to send missions to the Moon in the near future. These missions will not only see astronauts return to the Moon for the first time since the end of the Apollo Era; they will also lead to a sustained human presence on the Moon. This includes infrastructure such as habitats, power systems, transportation, and research facilities. Much of this research will be unprecedented, since NASA, China, Russia, and other space agencies plan to build their bases on the far side of the Moon.
For one thing, the far side of the Moon is “radio-quiet,” meaning that it is not subject to radio interference from terrestrial sources. This makes the environment the perfect place to conduct radio astronomy research, including the new CosmoCube satellite currently under development at the University of Cambridge. Using the Moon as a natural shield, this satellite will listen for faint whispers (the 21-centimeter line) emitted by hydrogen atoms that existed between the Big Bang and the period known as “Cosmic Dawn.”
This period has historically been completely inaccessible to astronomers, earning it the nickname “Cosmic Dark Ages.” During this period, which lasted from ca. 380,000 years to 1 billion years after the Big Bang, the only light visible to astronomers today is the Cosmic Microwave Background (CMB), the afterglow of the Big Bang, or the 21-centimeter radiation emitted by all the neutral hydrogen that filled the Universe. About 50 million years later, the first stars and galaxies formed, gradually reionizing the neutral hydrogen.
The far side of the Moon offers protection from terrestrial radiation and a fabulous location to study radiation from the earliest moments of the evolution of the Universe. Credit: NASA
This period, known as “Cosmic Dawn,” effectively ended the Dark Ages and made the Universe “transparent,” i.e., visible to optical instruments today. With missions like the Wilkinson Microwave Anisotropy Probe (WMAP) and the ESA’s Planck mission, astronomers can visualize and study the CMB. Thanks to Hubble, Webb, and ground-based interferometry telescopes, astronomers have also been able to study the earliest galaxies in the Universe emerging from the Dark Ages. But the period between them remains inaccessible.
For Earth-based telescopes, detecting signals from 13.5 billion years ago is extremely difficult since Earth’s upper atmosphere (the ionosphere) blocks the frequencies, while radio towers, satellites, and other telecommunication sources create radio-frequency interference (RFI). But as the CosmoCube team describes in a paper that appeared in Nature Astronomy, the satellite will be shielded from all Earth-based RFI as its orbit takes it behind the far side of the Moon.
The satellite will accomplish this by operating at extremely low frequencies (10 to 50 MHz), far outside the range of ground-based telescopes. During its two-hour orbit, the probe will have roughly 40 minutes to listen for echoes from the early Universe. Over a primary mission lasting two years, the probe will build up 1000 hours of data on what astronomers consider the “final frontier” of astronomy and cosmology. The information this reveals will improve our understanding of how the Universe transitioned from being dark and nearly empty to transparent and filled with bright objects.
In addition, CosmoCube will also explore the role Dark Matter played in the formation of the first galaxies. “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,” said Professor Eloy de Lera Acedo from Cambridge’s Cavendish Laboratory, the lead author on the study.
This infographic offers a schematic view of the evolution of the Universe, which unfolds in four dimensions. Credit: ESA
Once in orbit, the CosmoCube will deploy a long, lightweight radio antenna sensitive enough to detect the 21-centimeter signal. When the data is received on Earth, the team will use advanced Bayesian statistical analysis to remove foreground noise, such as natural radio emissions from the Milky Way. They will also use computer simulations and in-flight measurements to determine how the antenna responds to different parts of the sky, allowing them to remove any remaining distortions. Said de Lera Acedo:
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. 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. 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.
However, there’s a bit of a snag. With multiple space agencies planning on utilizing the radio-quiet environment of the Moon’s far side, it may not be long before it’s no longer quiet. This presents an additional challenge for a mission already facing the hazards of operating in a hostile environment with extreme temperature swings and no atmosphere. Luckily, challenges like these call for innovative thinking that often yields creative solutions. Said co-author Dr Will Grainger from STFC RAL Space:
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. 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.
Among CosmoCube’s featured instruments is a state-of-the-art, fully integrated miniature radiometer that uses RF-Systems-on-Chip (RFSoCs), the latest in analog and digital technology. Surrey Space Technology Limited (SSTL) is developing the space platform (‘SSTL-21’), with funding from the UK Space Agency, and the research team hopes to launch CosmoCube within the next five years. Instrument development is well underway, with functioning lab prototypes and environmental testing in progress.
They are also collaborating with industry partners, including Portsmouth University and STFC RAL Space. The CosmoCube team also participated in the recent ESA mini-Fast missions Call for Ideas, which seeks out concepts for medium-size, fast, and cost-effective missions of opportunity. “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,” said de Lera Acedo.
Further Reading: University of Cambridge, Nature Astronomy
