The arrival of 3I/ATLAS in our solar system spawned multiple proposals for a rendezvous mission to study it up close. As the third interstellar object (ISO) ever detected, the wealth of information direct studies could provide would be groundbreaking in many respects. However, the mission architecture for intercepting an interstellar comet poses numerous significant challenges for mission designers and planners. Chief among them is the technological readiness level (TRL) of the proposed propulsion systems, ranging from conventional rockets to directed-energy propulsion (DEP).

So far, mission proposals have focused on chemical rockets launched from Earth, like NASA's Janus mission and the ESA's Comet Interceptor, or on existing missions like the Juno probe adjusting their trajectories to rendezvous with it. In a recent paper, researchers from the Initiative for Interstellar Studies (i4is) propose foregoing a direct transfer mission that would launch from Earth today. Instead, they demonstrate how a mission launching in 2035 could intercept 3I/ATLAS using an indirect Solar Oberth maneuver.

The main challenges for a direct mission to rendezvous with 3I/ATLAS stem from the target object's celestial mechanics, its high heliocentric speed, and the late initial detection. The first issue effectively rules out a rendezvous mission that relies on an onboard propulsion system to match the comet's velocity, thereby enabling a prolonged close-up study of the body. As a result, a flyby mission is the preferred option. However, the second and third considerations rule out a direct mission because the optimal launch date had already passed before it was detected. As Hibberd summarized these for Universe Today via email:

"For the direct mission, the object 3I/ATLAS was detected too late, when it had already travelled inside the orbit of Jupiter, and with a velocity in excess of 60 km/s. It turns out, this was after the optimal launch date for a direct mission to intercept it. One paper found that there would even have been difficulties for a ‘Comet Interceptor’ spacecraft had it been already loitering at the sun/Earth L2 point when 3I/ATLAS was discovered."