Czech institutions and companies are involved in the design, implementation and operation of the European Space Agency's (ESA) Hera mission. Hera is part of the first ever planetary defence test and will evaluate the consequences of the collision between the US DART spacecraft and the 170-metre Dimorphos asteroid orbiting the larger 800-metre Didymos asteroid. In cooperation between Brno University of Technology, the Geological Institute of the CAS and Huld, a programme has been prepared to evaluate the quality of the scientific data acquired on board the Milani cubesat (in the main picture), one of two smaller probes that will be launched from the Hera mother probe upon arrival at the target planet. The Institute of Astronomy of the CAS, in collaboration with foreign colleagues at several observatories using large telescopes, is working on a precise description of the Didymos-Dimorphos system after the DART probe's impactor and before the arrival of Hera. Dimorphos was discovered on November 20, 2003 by Petr Pravec from the Astronomical Institute of the CAS.
The Hera mission is currently scheduled to launch after problems with the Falcon 9 launch vehicle on October 7, 2024 at 16:56 our time just launched by Falcon 9 from the Cape Canaveral Spaceport in Florida, USA. The aim of the mission is to explore the Didymos-Dimorphos binary asteroid after it was hit by the US DART probe in September 2022. The Hera probe will reach the Didymos asteroid after two years of space travel. Along the way, it may pass close to the planet Mars. Orbiting the 780-metre-high Didymos is its moon, the 170-metre-high Dimorphos. The DART probe just hit Dimorphos, causing it to change its orbit around the larger Didymos. The Hera mission consists of a main spacecraft and two small cubesats, comparable in size to a shoebox, which Hera will carry to the target asteroids. This will be the first time the asteroids will be studied in detail by small and relatively inexpensive probes. Cubesat Juventas carries primarily miniaturized radars to determine the geophysical characteristics of the Dimorphos moon. It will thus map its internal structure and gravitational field. Cubesat Milani carries the miniaturized Finnish ASPECT hyperspectral camera, which will image asteroids in the visible and infrared part of the spectrum, as well as the Italian VISTA dust particle detector. The current plan is for both cubesats to land on the asteroids at the end of their mission.
ASPECT smart camera
The ASPECT hyperspectral camera will be able to image both asteroids in a wide range of light, 15 times wider than the colour range visible to the eye. Hyperspectral observations are key to understanding the composition of both asteroids, their origin and to assessing the effects of the impact of the US DART probe in the Planetary Defence Test, but they generate a high volume of data. Not all of the images will be transferable from a small spacecraft like cubesat Milani to Earth; realistically, it is expected that about 10 (hyperspectral) images can be sent to Earth. Therefore, key images need to be selected as soon as they are acquired. For this reason, ASPECT is equipped with its own on-board computer with performance comparable to a smartphone. The Faculty of Information Technology of Brno University of Technology, the Geological Institute of the CAS and the company Huld have developed unique programs for the on-board computer ASPECT to evaluate the quality of hyperspectral images immediately after their acquisition.
"In order to successfully create an accurate high-resolution mineralogical map, we need to be sure that all the transferred images acquired by ASPECT are of the required quality," Says Tomas Kohout from the Institute of Geology of the CAS responsible for the evaluation of the images.
The program first automatically detects whether the target asteroid was fully in the field of view and evaluates the sharpness of the images. It then selects the best quality images for transmission to Earth and compresses them to reduce the volume of data transmitted as much as possible. If the software decides the photo is not worth sending to Earth, it will store it on the lander in an archive and send only the quality information it finds. Scientists will then use this information to decide whether to reshoot the scene or use one of the stored images.
"When you have limited data transfer options and you want to map both asteroids, plus the initial testing and calibration of the instrument, you can't afford to waste it. So the only solution is to analyse the quality of the science data obtained directly on the spacecraft," says the author of the quality assessment software used Tomas Kasparek from Brno University of Technology.
No other camera on Hera is equipped with a comparable smart image quality detection program, and it is this advanced solution developed in the Czech Republic that makes ASPECT a unique smart camera.
New state of the Didymos-Dimorphos system after the DART probe impact
The DART probe's impact on Dimorphos in September 2022 changed its orbit around Didymos, but it also caused other changes in the binary system. "In addition to the ejection of material from Dimorphos and its subsequent escape from the system, or partial redeposition onto Didymos and Dimorphos, there was also a change in the shape of Dimorphos and an excitation of its rotation," Says Petr Pravec The current orbit of Dimorphos around Didymos is uncertain due to the dynamical interaction between the rotation of Dimorphos and its orbit (the so-called spin-orbit interaction), and possibly due to the interaction with the residual material around these two bodies. An international team led by Pravec is working to refine the description of Dimorphos' current orbit. They are using large telescopes of 3-10 metres at several observatories around the world to obtain the necessary data. They will complete the relevant photometric measurements of the Didymos-Dimorphos system in March next year and, after evaluation and analysis, will refine the current status of this binary system. Pravets concludes: "The resulting refined description of the orbit of Dimorphos, in addition to a better understanding of the dynamical interactions in this binary system, will be much needed to plan the initial phases of Hera's operations after its arrival at Didymos-Dimorphos in December 2026."
Probe launch:
Start time and date: 7 October at 16:52 CEST
Launch pad SLC-40, Cape Canaveral Space Force Station, Florida
Rocket: Falcon 9
Primary payload: the Hera spacecraft + 2 CubeSats
Cargo weight: 1 081 kilograms
Orbit: Heliocentric
For Czech viewers it will provide Kosmonautix.cz live broadcast from the start, starting about 30 minutes before the start, around 16:20 CEST.
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