Hera and CubeSats communicate with mission control

ESA’s Hera asteroid mission and its two CubeSats recently conducted a remarkable test, simulating their communication and interaction as if they were in the depths of space. This rehearsal took place within the foam pyramid-lined walls of the Agency’s Maxwell test chamber in the Netherlands, where the trio seamlessly shared data and ranging information. Simultaneously, the Hera mothership received commands from its mission controllers at the European Space Operations Centre (ESOC) in Darmstadt, Germany.

The testing occurred inside the Maxwell electromagnetic compatibility chamber, part of ESA’s ESTEC Test Centre, the largest spacecraft test facility in Europe. Maxwell’s 9-meter high metal walls shield it from all external radio interference, while its interior foam pyramids absorb all radio waves from the space systems being tested. This unique environment replicates the infinite void of space. As Franco Perez Lissi, the Hera CubeSats engineer, explained, “Once the door of Maxwell is closed, this becomes the only place where we can operate the antennas of Hera and its two CubeSats together freely and safely.”

Perez Lissi added, “For the rest of the mission’s test program, telecommands were being sent to the spacecraft via cables instead. We already have detailed models of how the connection to Earth and the inter-satellite links between the satellites will work, but this testing allows us to validate these models against reality.”

The testing extended to ESOC, enabling the Hera operations team based there to operate the spacecraft remotely and downlink telemetry and data via Hera’s 1.13-meter diameter High Gain Antenna, exactly as they will once Hera is in space. At once, Hera and its CubeSats were also communicating via dedicated inter-satellite links.

Manufactured by HPS in Germany and Romania, Hera’s High Gain Antenna boosts its X-band signal more than 4000-fold to reach distant Earth. The S-band inter-satellite links connecting Hera and its CubeSats, supplied by Tekever in Portugal with antennas from Anywaves in France, are much weaker, comparable to domestic wifi. Based on software-defined radio, these inter-satellite links serve a dual purpose:

• Exchanging data with Hera, which serves as a relay back to Earth
• Supplying ranging information, allowing the trio to know their precise relative positions at any given time, minimizing the risk of collision

The multi-point Doppler data provided through these inter-satellite links will also enable a more accurate measurement of the gravity fields of the Didymos and Dimorphos asteroids than Hera could achieve by itself.

“By having everything transmitting directly through the air, we’ve proved that all the links can run without interfering with each other,” explains Hera communications systems engineer Paolo Concari. “We actually expected to see some minor degradation but didn’t really find any – something called the ‘coupling factor’ where adjacent antennas can pick one another up – so ended up with very good performance.”

Hera is ESA’s first mission dedicated to planetary defense. Scheduled for launch in October of this year, Hera will embark on a journey to the Didymos binary asteroid system in deep space. Its primary objective is to conduct a close-up survey of the Dimorphos moonlet, which orbits the larger primary body.

Dimorphos has already made history as the first Solar System object to have its orbit intentionally altered by human intervention. This remarkable feat was achieved in 2022 when NASA’s DART mission intentionally impacted Dimorphos, altering its trajectory as part of a groundbreaking planetary defense experiment.

Hera’s mission is to gather crucial data about Dimorphos that is currently missing, enabling scientists to turn DART’s grand-scale experiment into a well-understood and potentially repeatable technique for planetary defense. By closely observing and analyzing the aftermath of the DART impact, Hera will provide invaluable insights into the effectiveness of such a kinetic impact approach for deflecting hazardous asteroids.

To maximize its data collection capabilities, Hera carries two deep space CubeSats, marking ESA’s first deployment of such miniaturized satellites beyond Earth orbit. These CubeSats, named Juventas and Milani, are equipped with specialized instruments and are designed to fly closer to the asteroid’s surface than the main Hera spacecraft, eventually landing on Dimorphos.

• Juventas carries a radar instrument to perform the first-ever radar probe of an asteroid’s internal structure, as well as a gravimeter to study the asteroid’s gravity field.
• Milani hosts a multispectral imager to survey the surface mineralogy of Dimorphos and a dust surveyor to analyze the asteroid’s dust environment.

The combined observations from Hera and its CubeSats will provide unprecedented insights into the composition, structure, and dynamics of this binary asteroid system. This comprehensive dataset will not only enhance our understanding of asteroids but also pave the way for more effective planetary defense strategies to protect Earth from potential asteroid impacts in the future.