Juventa's CubeSat: A radar flight to the center of asteroid Hera

“Asteroids today are collisional fragments of the building blocks of our entire solar system. If we can see how the interior of an asteroid is structured, we gain valuable insights into the evolution of the solar system and planetary defense,” explains Michael Kuipers, ESA’s Hera project scientist. “Is this asteroid a solid mass or a pile of rubble held together by gravity? The answer has practical implications for how approaching asteroids will deflect from Earth in the future.

The Juventas CubeSat, with dimensions of 37 x 23 x 10 cm, is operated by the Luxembourg company on behalf of the European Space Agency. Gomspace Supervised, the spacecraft was integrated at GomSpace's headquarters in Denmark. The company specializes in CubeSats, which are small, low-cost satellites assembled from standardized 10cm boxes, although they are typically intended for Earth orbit.

Building space

Jan Persson leads the Juventas project for GomSpace: “This is a completely different mission compared to the usual CubeSats we build and fly. Going beyond Earth orbit and out into deep space is a rare opportunity that requires close attention to detail. In addition, Juventus needs a sufficiently flexible navigation system To fly himself around an asteroid.

ESA's Hera asteroid mission is Europe's contribution to an international planetary defense experiment. After effect DART mission On the asteroid Demorphos, a moon of the larger asteroid Didymos, in 2022 — which changed its orbit around Didymos and sent a cloud of debris thousands of kilometers into space — Hera will return to Demorphos to get up close and personal with the crater left by the DART measurement. The mission will also measure the mass and composition of Dimorphos and Didymos.

Hera is scheduled to launch in October 2024, and has two CubeSats on board to take close-up images of the pair of asteroids: the Melanie hyperspectral mission will join Juventus. The trio will remain connected via an innovative communication system between satellites around asteroids.

The smallest radar in space

Juventas, named after the Roman daughter of Hera, may be small, but it has a big artistic imprint. The low-frequency radar instrument – the smallest radar system in space – was developed by the French Institute of Planetology and Astrophysics in Grenoble In the University of Grenoble Alpes And Technical University of Dresden Designed, with electronics from Imtronix Originates in Luxembourg. Radar signals are transmitted by quad antennas measuring 1.5 meters long, which is longer than the Juventus spacecraft itself and Astronica Contributed to Poland.

“The Juventas radar instrument (JuRa) is unique and will give the scientific community a rare insight into the composition of the asteroid,” explains Jan Persson. “It was greatly miniaturized to fit into the CubeSat housing. The biggest challenge was that the instrument inside the spacecraft generated a lot of heat, which our thermal design team at GomSpace was very interested in.”

Hera systems engineer Franco Pérez Lisi adds: “In order to fly itself, Juventas also has a visible light camera, lidar, star sensors for navigation and a cold gas propulsion system, as well as the radio link between satellites to share their positions and data with the split Hera.”

For a radar scan of the smaller asteroid, Juventas will enter a unique “self-stabilizing spacer orbit” around Didymos. This involves rotating parallel to the asteroid's day-night line, balancing the asteroid's weak gravity with the weak but constant pressure of sunlight itself – solar radiation pressure.

In fact, Didymos's gravity is so low that Juventus would be in orbit at just a few centimeters per second, and JuRa would use this low speed to send the same encoded signal to the asteroid multiple times, increasing the instrument's overall signal to noise ratio. The reflected signals are decoded and converted into a 3D image on the ground.

He came to earth

Once Juventas completes its radar monitoring, it will enter orbit around Dimorphos to begin the next phase of its mission: landing on the smaller asteroid. “We are still analyzing how best to do this, but our speed must be low enough, on the order of centimeters per second, for Juventus to land without jumping directly into space,” notes Jan Persson. “The accelerometers and gyroscopes on board will collect data at this moment.” To learn more about surface properties.When Juventus finally settles down, we want it to be in a stable configuration to power the spacecraft's second science payload, the GRASS gravimeter.

This first instrument to measure gravity directly on the surface of an asteroid, the Gravimeter for Small Solar System Objects, GRASS, was developed by the Royal Observatory of Belgium (Rob) with Spanish Emxis Company developed. The plan is to record how gravity on Demorphos changes over the course of its orbit around Didymos.

Both Juventas and Milani CubeSats have now joined the Hera mothership for testing at ESA's ESTEC Center in the Netherlands, the largest spacecraft testing facility in Europe. The trio will be placed in Maxwell's electromagnetic test chamber to verify that communications between the satellites are working as planned.