Developed in the UK, the spacecraft is called CosmoCube. An international research team led by the University of Cambridge plans to place it in orbit around the Moon, where the lunar body could shield the satellite from radio interference produced on Earth.

From the Moon’s far side, CosmoCube will search for extremely faint signals left behind by the early universe. The mission could provide new insight into how the cosmos evolved from a dark, relatively empty place into the universe of stars, galaxies and large-scale structures we see today.

Searching for signals from before the first stars

Scientists call the target signal the 21-centimeter line. It comes from hydrogen atoms that existed after the Big Bang and during the dawn of the universe, before nuclear fusion began inside the first stars.

No one has directly observed this chapter in cosmic history.

The signal CosmoCube will study originated more than 13.5 billion years ago. Detecting it from Earth is extremely difficult because the planet’s ionosphere blocks the relevant radio frequencies from reaching ground-based observatories. FM broadcasts, satellites and telecommunications can also create interference strong enough to overwhelm these extremely weak signals.

The Moon offers a natural solution.

As CosmoCube passes behind the Moon, the lunar body will block radio noise from Earth for about 40 minutes during every two-hour orbit. Over the spacecraft’s expected two-year mission, researchers hope to collect approximately 1,000 hours of observations from one of the universe’s last largely unexplored epochs.

These measurements could help scientists understand how long it took for the first stars to form and how the early universe began developing the structures seen today.

The project is funded by the UK Space Agency, and researchers hope CosmoCube will launch within the next five years.

How CosmoCube could study dark matter’s early influence

CosmoCube is designed to investigate the period before the first stars formed. Researchers also hope its observations will provide new information about dark matter and its influence on the development of early cosmic structure.

Although dark matter cannot be seen directly, its gravitational effects are important for explaining how galaxies and other large structures are connected.

“We hope that the ejection of hydrogen after the Big Bang and before the formation of the first stars will help us understand the role of dark matter in the early universe and how hydrogen was drawn into the first stars and galaxies,” said lead author Professor Eloy de Lera Acedo of the Cavendish Institute at the University of Cambridge.

To reach this ancient era, CosmoCube will observe radio frequencies between 10 and 50 MHz. These frequencies are largely inaccessible to ground-based telescopes, making the Moon a particularly valuable location for early-universe research.

“Nowhere else can you get the shielding necessary to detect such a weak signal while observing the entire universe,” said de Lera Acedo, who is also affiliated with the Cavli Institute for Cosmology. “The far side of the Moon is really the only option. The far side of the Moon solves multiple problems at once and opens a clear window into the very early days of the universe.”

Using the Moon as a natural radio shield

After reaching lunar orbit, CosmoCube will deploy a long, lightweight radio antenna. As the spacecraft travels behind the Moon, the antenna will search for 21-centimeter hydrogen signals from the early universe while the lunar surface blocks radio interference from Earth.

Detecting such weak signals requires extremely high precision. CosmoCube will therefore use a “Dicke Switched” calibrator to continuously monitor and adjust its electronics. The system will alternate between observing the sky and measuring several internal reference sources.

This process is intended to identify and eliminate small changes and electronic noise produced by the spacecraft itself. Without that calibration, spacecraft noise could be mistaken for a signal from the early universe.

Researchers will carry out additional processing after the observations return to Earth. Advanced Bayesian statistical techniques will be used to separate the target signal from foreground radio radiation, including radio waves produced by our own galaxy.

Computer simulations and measurements collected during the mission will also help researchers reconstruct how CosmoCube’s antennas respond to different areas of the sky. Scientists can then correct any remaining distortions that could affect the results.

“What makes our mission unique, apart from the science, is its scale. We are using a compact and relatively low-cost platform while investigating the earliest and deepest parts of the Dark Ages that others cannot reach,” de Lera Acedo said.

A small satellite with an ambitious lunar mission

The radio silence available on the Moon’s far side could become increasingly valuable. The United States, India and other countries are also planning missions designed to take advantage of the unusually quiet radio environment there.

CosmoCube contains a highly integrated miniature radiometer that combines analog and digital technologies using radio-frequency system-on-chip, or RFSoC, technology.

The CosmoCube spacecraft platform, known as “SSTL-21,” is being developed in the United Kingdom by Surrey Space Technology Limited, or SSTL, a company specializing in small satellite manufacturing.

Development is already underway. Working prototypes have been built in the laboratory, environmental tests are being conducted, and researchers are collaborating with industry partners. UK academic partners include the University of Portsmouth and STFC RAL Space, while researchers from EU countries, including Malta, are also participating.

The CosmoCube team recently participated in a call for ideas for the ESA Mini Fast Mission. The proposed mission targets a cost of less than 50 million euros.

“CosmoCube aims to perform ambitious science from microsatellites in difficult environments, which requires smart design techniques,” said co-author Dr. Will Grainger of STFC RAL Space. “We have worked with our project partners to develop representative models of the satellite and its payload. These have been tested at our facilities and thermal performance has confirmed that the payload can operate and perform the required sensitive measurements under the various temperature conditions experienced in lunar orbit. In the future, we hope to further develop the complete payload in preparation for a complete mission.”

Could CosmoCube open a new window into cosmic history?

If CosmoCube succeeds, it could demonstrate that major discoveries about the early universe do not necessarily require enormous spacecraft.

Instead, small satellites operating in one of the quietest radio environments near Earth could give scientists access to cosmic eras that have previously been impossible to observe directly.

“This could be a real success story for the UK. The hardware, software, implementation and technology are all being developed here and could help answer one of the most profound questions in the universe,” de Lera Acedo said.

This research was supported by the UK Space Agency, the Kavli Foundation and the Science and Technology Facilities Council (STFC), part of UK Research and Innovation (UKRI). Eloy de Lera Acedo is a Fellow of Selwyn College, Cambridge.