Testing the International Mechanism for Responding to an Asteroid Impact Threat

This paper describes the process and the results of a hypothetical exercise of one of the UN‐endorsed groups called the Space Mission Planning Advisory Group (SMPAG). It shows that this work advances the preparedness of the planetary defense’s community to react to near‐Earth object (NEO) hazards, making it directly applicable to this special issue of planetary defense. It develops operational frameworks for asteroid threat response and is directly linked to the scientific study and the threat mitigation from NEOs. As part of a hypothetical exercise prepared for the Planetary Defense Conference 2025, SMPAG has performed their work in a simulated impact threat scenario. SMPAG was notified by the International Asteroid Warning Network of a hypothetical potential impact of an asteroid in the year 2041 in August 2024. SMPAG then met regularly to discuss potential space‐based response to the threat: First in weekly meetings, and in October 2025 in a personal, two‐day meeting. After feeding back their conclusions to the exercise planning team, a second epoch (Epoch 2) was studied until the Planetary Defense Conference 2025. At this conference, a proposed response to the simulated threat was presented to a decision‐makers panel. This paper describes the process and the lessons learned for the first part, Epoch 1, of the hypothetical exercise. The study led to the recommendations to decision‐makers to (1) immediately start studying a flyby reconnaissance mission, (2) consider re‐tasking existing spacecraft for reconnaissance, (3) start designing a rendezvous reconnaissance mission using electric propulsion, (4) design a kinetic or ion beam mitigation mission, and (5) assess the risk of disrupting the asteroid when using a kinetic impactor. The main lessons learned are as follows: (1) A reasonable work package structure was developed that can mostly be reused in future threat scenarios. (2) The group is an advisory group, as the name says. As such, it is not meant to describe a decision strategy; rather, it can only provide recommendations. (3) The so‐called nuclear explosive device was debated heavily; no consensus on its recommended use or not was found. (4) Sufficient time for iterations within the delegations has to be provided even after a seemingly final recommendation has been written. (5) It was agreed that it is not possible for this international group to provide cost estimates in terms of money, as each agency has its own way of computing costs. Rather, an “effort” based on the number of needed launches and comparing missions to previously flown or studied ones was adopted.