Adam Hibberd
Towards the end of 2024 and beginning of 2025, I was asked by a friend from Space Initiatives Inc. (a US company), to look into the possibility of a mission from Earth to encounter 4-5 Near-Earth Objects (NEOs) and then return samples back to Earth. A ‘Grand Tour’ so-to-speak!
These samples would be collected at each encounter by using an impactor dispatched by the main spacecraft (designated as a ‘Coracle’) towards the current encounter asteroid. This Coracle would then travel through the plume from the resulting explosion, in the process collecting the sample in question with ‘aerogel’.
So I took all the NEOs to approach close to the Earth in 2030, and tried to derive a sequence with minimum overall cumulative ΔV, where ‘cumulative ΔV’ is defined as the sum of each velocity change to divert from one asteroid to the next.
As in most mathematical problems, assumptions need to be made, and this case was no exception. For instance would there need to be a ΔV at the first asteroid?
The answer is that the heliocentric speed at the first encounter could be so tailored such that the velocity of the Coracle would naturally take it to the second. Thus with this assumption, no ΔV would need be delivered. This would especially be the case if the Coracle were a simple solar sail spacecraft, since there would be plenty of opportunity between launch from Earth to arrival at the first asteroid to do precisely this.
See below for two videos of just such a Grand Tour with cumulative ΔV of only 0.5 km/s. One video is w.r.t. the Sun, and the other is of the same mission but w.r.t. the Earth.