A rebel alliance: the small mission collaboration between ESA and ISAS
“Instead of every ten or fifteen years, what about sending smaller and cheaper missions every few years to do something simpler, but still of scientific interest?” Carnelli recalls asking as a young engineer at the headquarters of the European Space Agency in Paris. “And I was looked at as a martian.”
Ian Carnelli is the Head of the Systems Department at the European Space Agency (ESA). The Systems Department is responsible for the “In-Orbit Demonstration projects” that include the Proba-3 mission, which recently hit the headlines for creating the first artificial solar eclipse.
The Proba missions are designed to be low cost missions with a fast development timeline to test new technology. Proba-3 demonstrated high precision formation flying, where two satellites maintained a relative position to millimetre precision. Aligned with the Sun, one satellite was an equipped with a large disc to cast a shadow over its partner in order to create a solar eclipse in orbit. The second satellite was then able to observe the solar corona, the outermost layer of the Sun’s atmosphere that is only visible during a total eclipse.
It was the Proba-style of mission that Carnelli wanted to try with scientific exploration. However, there was a problem.
“At the time, it was difficult to conceive that a mission coming from the technology world would seek a collaboration with science,” explains Carnelli.
The Martians on Earth
Back at ESA in 2010, small technology-focussed missions such as the Proba satellites, and the very ambitious space science flagship missions such as the comet chaser, Rosetta, were considered separate endeavours. When Carnelli proposed a small mission on the same scale as a Proba but with a scientific focus, he was treated as an alien by almost everyone in the room.
“Our team in the Systems Division thought these small missions had a lot of potential beyond engineering demonstrations,” recalls Carnelli. “But when I proposed our idea, the only person in the room who was fine-tuning with me on the concept was Masaki.”
Visiting Paris from Japan, Fujimoto Masaki was attending the same meeting as Carnelli. Fujimoto would became the Director General at the JAXA Institute of Space and Astronautical Science in 2025. But at this moment, he was a professor in the ISAS Department of Solar System Sciences, which was celebrating the return of the first Hayabusa mission from asteroid Itokawa.
“Hayabusa raised the bar for planetary exploration for three reasons,” says Carnelli. “The first reason was that it was going to an asteroid and staying there for a long period of time, gathering the support and interest of the scientific community. It was a mission that advanced asteroid science. The second reason was that this was a very fast and very cheap mission. And the third reason was that it was extremely ambitious. Hayabusa, and later Hayabusa2, really wrote a page of space history.”
Carnelli felt that Hayabusa shared the spirit of the Proba missions, but with a journey that went beyond Earth orbit and into deep space. Fujimoto and Carnelli discussed the scientific potential of frequent small missions during the coffee break. But international collaborative missions were considered the jurisdiction of the ESA space science flagships, leaving no pathway for ISAS and ESA to work together on an innovative smaller design.
Then in 2019, ESA opened a new Directorate. It was a program that required scientific observations and international collaboration, but where the missions could be small and must be swiftly developed because the targets were close but fast moving. The program name was “Space Safety” and one of the main topics was planetary defence.
Protecting the Earth from a major collision with an asteroid or comet had been gathering interest at ESA for a number of years. Carnelli had been the technical officer on a proposal for a double spacecraft mission as part of the In-Orbit Demonstration fleet called “Don Quijote”, in which one spacecraft would attempt to deflect an asteroid via an impact while a second spacecraft observed the result.
While the mission was not selected for launch by ESA, the concept gained international attention. In 2011, the Johns Hopkins University Applied Physics Laboratory in the USA proposed developing the impact spacecraft. That mission became the NASA “Double Asteroid Redirection Test” (DART). Carnelli and his team put forward a new proposal for the observing spacecraft to ESA, this time as a single spacecraft mission called the “Asteroid Impact Mission” (AIM).
The proposal for AIM was seriously considered, and the mission concept was put to the ESA Council at Ministerial Level in 2016, the highest decision-making body at ESA.
“There were ministers saying yes, we should absolutely do it,” remembers Carnelli. “But the majority said no.”
The concept was rejected.
“That was a big setback,” says Carnelli. “I actually thought at that point we could give up. But the scientists motivated us to give it one last try.”
That final try came in 2019, when the redesigned mission was once again put before the ESA Council. The proposal was accepted, with the mission name “Hera”. ESA opened the Space Safety program, formally created a planetary defence sector for which Hera would be the cornerstone mission.
The Hera collaboration
Hera was a small-scale mission with a short development time but with a scientific mandate to explore an asteroid and validate the asteroid deflection technique. The barriers to collaboration gone, Carnelli returned to ISAS. It was perfect timing, as ISAS was planning to formally create a planetary defence team within JAXA.
“It was clear that ISAS should build the thermal imager,” says Carnelli. “We didn’t have an instrument of that sort ready for Hera, but ISAS had flown a thermal imager on Hayabusa and Hayabusa2. There was a good heritage. I flew to Japan and signed the agreement.”
A thermal infrared imager views the temperature a celestial body. In the case of an asteroid, viewing how quickly the hot and cold regions vary provides information regarding the surface structure of the asteroid as well as clues to its composition. The Thermal InfraRed Imager (TIRI) for Hera was developed by ISAS and a Belgium European team, and was launched onboard Hera in 2024.
The destination for Hera was the asteroid Dimorphos, which had been hit by the DART spacecraft in 2022. Dimorphos poses no threat to the Earth, but by assessing the changes wrought by the DART impact after arrival in 2026, Hera will provide valuable data about the deflection in case we ever need to apply a shove to in-coming asteroid. The TIRI was tested as Hera passed Mars, snapping thermal images of the red planet and the outer moon, Deimos.
“My only regret is that Masaki didn’t make it to the launch or Mars flyby,” chuckles Carnelli. “I told him that he owes me! But it was an amazing experience.”
With the pathway finally open to collaboration on small missions, Carnelli looked for a new opportunity to combine the ESA and ISAS teams. That opportunity was asteroid Apophis.
The Ramses joint venture
Apophis is a roughly 375m asteroid on a trajectory to make a close approach to the Earth in April 2029. While a collision with the Earth has been ruled out, the size and proximity of the asteroid represents a once-per-thousand year event.
A mission to examine Apophis is effectively a unique opportunity to study how asteroids are affected by the Earth’s gravity at close quarters. It is science that will reveal more about the structure of asteroids, and could be essential in a deflection attempt.
Costs for the Hera mission had actually come under budget. Carnelli suggested that the remaining funds could be used to rebuild the Hera spacecraft and send this sibling to Apophis. Copying a spacecraft design is a very cost-effective way of developing a mission. ESA had direct experience of the benefits, having successfully launched the Rosetta Mission, Mars Express, and Venus Express with similar architectures.
“I said, let’s do the same with Hera,” says Carnelli. “We build it again, we send it to Apophis!”
The mission concept became Ramses: the Rapid Apophis Mission for Space Safety.
An Asteroid Apophis rendezvous leveraged the benefits of small, fast missions to conduct science impossible to achieve through the traditional space science flagships. It was an idea that had strong appeal to both ESA and ISAS. In addition to providing a second thermal imager, ISAS would also provide light-weight solar arrays for the spacecraft, and discussions are also underway to launch the mission on the JAXA H3 rocket. While Hera had been a collaboration between ESA and ISAS, Ramses was to be a joint mission.
“The relationship between ESA and JAXA has always been extremely strong,” explains Carnelli. “But now the intention is to have truly joint missions, because we share the same values, the same interest, and similar skills. This is especially true in the field of planetary defence, with JAXA’s incredible tradition of small body missions that completely aligns with the ESA plan for the planetary defence program, and eventually, our exploration program.”
The international nature of the collaboration in planetary defence missions is also a valued component for both ESA and ISAS. Should an asteroid pose a threat to the Earth, the decision to act would have to be decided by an international forum, as the consequences of a mistake could place another region of the planet in danger. Working groups exist within the United Nations to rehearse the situation through simulations and set up protocols for information sharing.
“Asteroids have no borders!” notes Carnelli.
Joint missions between countries to study asteroids such as Apophis provide a powerful way to share information and develop effective joint teams. However, the story of the ESA and ISAS collaboration in planetary defence reveals that a successful partnership does not start with an official bilateral agreement, but is built on the shared aspirations of the people within the agencies.
“The signed letter is the last step,” says Carnelli. “Masaki and I shared the same values and vision for space exploration, and we always worked with full transparency. It built trust that we would do whatever we could to help each other to realise this vision. It’s a story of a fantastic international relationship, but also a deep friendship.”
Martians to Mars?
Looking beyond Ramses, Carnelli is eager to explore the limits of small, fast missions such as Hayabusa, Hera, and Ramses. One target could be the exploration of Mars, designing smaller and faster missions to cover more regions of the red planet. ISAS is already active in this area, developing new landing technology that could bring a light rover more easily to the Martian surface.
“I think that’s the boundary we’re exploring now,” says Carnelli. “It’s Mars. I think you could do some interesting Mars missions with these type of small and fast spacecraft.”
Further information:
The RAMSES mission (external site)
The DART mission (external site)
The HERA mission (ESA site / JAXA site)
On Cosmos:
July 5: the day the world was due to end
Avoiding the 7 minutes of terror: the next generation of space technology to head to Mars
Protecting our home world: the planetary defence mission fleet
Following the DART mission to protect our planet
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