A University of Arizona-led mission set to probe the mysteries of the faint universe made a major stride toward launch with the announcement of the successful completion of the spacecraft "bus" assembly on Feb. 25. The bus is the housing that will provide the structure, power and other systems that will enable the mission to carry out its work. 

Featuring a space telescope developed at the U of A's Steward Observatory, Aspera will study galaxy evolution through observation of ultraviolet light. Led by Carlos Vargas, an assistant astronomer at Steward Observatory, Aspera will study the so-called circumgalactic medium, the diffuse matter surrounding galaxies, which may contribute to the birth of stars and planets.

"Gas is the fuel needed to make stars," said Vargas, who serves as the mission's principal investigator. "We have a good understanding of how much gas there must be in galaxies to explain how many stars we see, but we've searched far and wide and still cannot find most of it."

Likely, the "missing" gas can be found in the circumgalactic medium, Vargas explained. The circumgalactic medium is invisible in optical wavelengths. Aspera will be the first mission to gather and map the incredibly faint ultraviolet light signatures that come from nearby galaxies.

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"Why do we care about that? Because every star that has formed, every planet that's formed, and all life on those planets must come from matter somewhere," Vargas said.

The mission derives its name from the Latin word for "difficulty" or "hardship," because astronomers have never been able to successfully observe the hot gases that compose the circumgalactic medium. Aspera could be the first to do so.

The spacecraft consists of a microsatellite built by Toronto-based Space Flight Laboratory, or SFL. In early 2026, the roughly 120-pound satellite is scheduled to launch into orbit, from where it will detect "fingerprints "of light from the enigmatic gases that surround galaxies.

A key aspect to the technical success of Aspera – and the reason SFL was selected for spacecraft development – is the importance of a high-performance spacecraft bus in a compact platform. The SFL spacecraft bus that will house the Aspera telescope is roughly the size of a mini fridge. It is studded with solar panels that will power the systems onboard, from controlling the spin of the satellite to maintaining temperatures for the sophisticated instrumentation onboard. 

The compact design of the bus is one of its assets: SFL's microsatellite platforms minimize launch cost without sacrificing performance. The Aspera mission is funded by the NASA Astrophysics Pioneers Program, which launched in 2020 to cultivate compelling astrophysics science at a lower cost using smaller hardware.

Vargas credits the small satellite revolution for making the Aspera mission possible. Just 10 years ago, he said, such a space astronomy mission would not have been financially viable with traditional satellites.

"Big science can now be done on small platforms, and the University of Arizona and Steward Observatory are big players in the SmallSat revolution." said Vargas. "Our partnership with SFL makes that possible."

Established in 1998, SFL has developed 86 operationally successful smaller satellite missions totaling more than 370 cumulative years in orbit. Another 21 spacecraft are now under development by SFL, which offers a complete suite of nano-, micro- and small satellites.