The Hera team, and the GNC contribution

I am writing this article from the Frankfurt airport, coming back from the last business trip to ESOC, where yesterday the First Deep Space Maneuver of the Hera mission was successfully executed, injecting the spacecraft into its interplanetary trajectory. This marks the end of the so-called “Near Earth Commissioning Phase”, but maybe it is better to start from the beginning. 

The Hera mission concept was born in the early 2000s and changed several times of name during its evolution, but finally, in the Ministerial Council of 2019, this challenging mission was approved and its implementation phase started. The main mission objective is related to planetary defense, and specifically is to investigate the kinetic impactor technique. Hera will approach the binary asteroid system called Didymos and will study the effect of the impact of the DART spacecraft (from NASA) on the moon of the system. The goal is to understand how to defend the Earth, in case what happened to the dinosaurs happens again. To achieve its main purpose, Hera needed a state-of-the-art autonomous Guidance Navigation and Control System (GNC), that would allow its close proximity operations in a hostile environment, far from Earth and with an unknown and hardly predictable gravitational field. 

4 years, that was the time that industry and ESA had to design, develop, build, and test a new spacecraft, with brand new technologies, especially related to the GNC. Within GMV, we have been able to create a team that developed new standards, new processes, and a new agile way to work… all of this, while doing normal GNC subsystem development of course. Have you ever heard the expression “building a plane while it is flying”? Despite the lack of trust of the outside world, the GMV team managed to develop and deliver an excellent product, so we arrived in Summer 2024 proud of what we managed to do and convinced that the adventure was over… but it was only the beginning!

As per contract, GMV had to give support to what is called LEOP and NECP (“Low Earth Orbit Phase” and “Near Earth Commissioning Phase”). LEOP duration is very limited, in the case of HERA only 3 days, and the main purpose of this phase is to have the first contact with the spacecraft after launch, checking that all its primary units are properly functioning. During this phase, there is 24h monitoring from the ground, as the Hera team shall be able to react fast to any possible anomalies. You might have noticed that I referred to the Hera team, while before I only mentioned the GMV team. It is still not fully clear to me when that happened, and most likely it started even before the Summer 2024, but somehow ESA and the industry created a unified team, breaking all the walls of the standard interfaces. We all had the same purpose, to defy the rules of the “old space” standards (e.g. development time, cost) to make the Hera miracle happen. This concept became more and more clear to me during the LEOP Simulations. Starting in June, the Hera team traveled several times to ESOC (The European Spacecraft Operation Center) to simulate the LEOP scenario, and of course, the simulation was very realistic, full of failures that were injected by the SIM officers to train our issue detection and problem-solving skills. We were ready for LEOP, and more importantly, we built and consolidated a team in which we knew each other, our skills, and our limits, and we trusted the capability of this unified team, the Hera team.

Then, we finally approached the 7^th of October 2024, the day of the launch, but it seemed that a bigger force did not want Hera to fly. The spacecraft was ready in Cape Canaveral, Florida, but the Falcon 9 launcher, after an incredibly long sequence of successful launches, was grounded due to an issue. A few days before the nominal launch date, the FAA allowed the launch of Hera and I still remember the faces of the team, with huge smiles painted as if it was a sign that we would finally really do this. But the smiles did not last long, as a hurricane called Milton was forming in the vicinity of the spaceport, and it would have been a huge one! The hurricane would have arrived a few days later, but the weather conditions were prohibiting already, such that the day before launch we had an 85% of possibility of a no-go.

7^th of October, a friend of mine said that you have 50% to win the lottery, because there are only 2 possible results, to win or to lose. I said this to the team in the morning of the launch, because 50% sounded way better than 15%. Then something happened.. the same force that seemed to have destined Hera to ground, changed its mind and slowly the possibilities started to rise a few hours before the nominal lift-off. 15 became 20, that became 30, then the “doubtful” statical approach of my friend was applicable, and without even realizing it, at 16:52 and 11 seconds.. HERA was launched. The very same date that was fixed several months before, 1 day ahead of the schedule planned in the contract signed in 2020. Let’s also remark the support of the people of GMV who traveled to Florida to witness the launch, and all the GMV team that was essential for the GNC development, that was assisting live in a video call from Spain, Romania, and Portugal.

LEOP started. We had nominal acquisition of signal, and apart from some false alarms and some fine tuning to be performed, one by one all units woke up, stretched their arms, and started behaving perfectly! The spacecraft stayed some hours in what is called GNC Survival Mode, with the minimum set of GNC units in the loop. After that, more advanced and complex units have been used, like the Star Tracker and the Momentum Control Wheels. Everything was nominal, and we were so ahead of schedule that we also included additional activities, like firing every single thruster, one by one, checking their behavior and also the reaction of the spacecraft to their action (the feared Flexible modes). LEOP ends, not with a bang, but with a whimper.. with a moved voice that said: “LEOP is finished, and it has been a success”. I realized this only few hours later in the hotel, and I am glad, as it would have been quite embarrassing to show everybody how much I cried. One of the smoothest LEOPs of all time, with no major issues happening.. not even in the simulations such a smooth scenario ever existed. And that is the moment I started having my doubts.. do you know Matrix? But did not care, I do not care.. if this is a dream, please do not wake me up.

I remember my first year at university in Forlì, Bologna. I managed to approve all exams with the highest grades, but there was this very last one… I was already so happy, but I thought that this could be the perfect final piece, the cherry on the top. July 2007 I did that exam, and on Thursday 10^th of October 2024, Hera made history, proving in flight the most advanced vision-based autonomous navigation technology ever developed in an ESA mission. LEOP was over, but when you create such a powerful team, you have to expect the unexpected. Starting from an idea of ESA, we began to work on the adaptation of the HERA GNC autonomous technology (that should have been used on the Didymos asteroid ) for an Earth-Moon scenario. The only purpose was its validation, but the problem is that the scenario adaptation was not easy, and we had other priorities in the months before launch. Not to mention that Hera's relative speed with respect to Earth was such, that this rehearsal could only have been done 1 or 2 days after LEOP, where we were expecting to have way bigger problems than testing a new technology. Despite all of that, that night happened… and it was magical. The rehearsal was supposed to be pre-planned during a night communication passage, with nobody on console, but that night, the Dedicated Control Room was crowded with people from the industry, spacecraft controllers, and flight dynamic experts. The excitement was when we finally saw the first image of the Earth from the Hera camera and we had the proof that it was successfully used by her autonomous algorithms… it cannot be explained in words, but that.. that was the cherry on top.

Now we come back to the beginning of this article, the final stage of these first days in orbit, the Deep Space Maneuver. With this operation that closes the NECP, Hera, with its own thrusters, had to fire for almost 2 hours to be in a new trajectory that will lead her to Mars in March 2025. After using its gravitational push, she will be heading towards Didymos, for what is expected to be a very exciting close proximity operation phase at the asteroids.

Yesterday, someone asked me if, looking back, I can say that it was worth it.. all the work, all the personal commitment, all the suffering and the fights. I can finally smile, and say yes. It was worth it to be able to contribute to this amazing work of engineering that is now flying into deep space.. it was worth it, to have the chance to be part of the Hera team.

Author: Andrea Pellacani