A Mission to Five Near Earth Objects in 2030
Adam Hibberd
We at i4is, together with our collaborators on the Phase I NIAC (NASA Innovative Advanced Concepts) at Space Initiatives Inc., have been contemplating precursors to the ultimate mission of sending laser sails to swarm our nearest neighbouring star, Proxima Centauri. A summary of the NIAC can be found here.
To be sure the mission to the planet Proxima b, orbiting Proxima Centauri, as detailed in this NIAC, is a significant number of decades away from coming to fruition (approx. 3 decades). Thus we must await the predicted technological developments to be realised first.
Meanwhile there is no reason why we can't countenance more parochial precursor missions as a lead-up to this target planet. The spacecraft to be developed for the NIAC are sail craft, more specifically laser sail craft, and have been christened 'Coracles'.
As a stepping stone to our Proxima b ambitions, it is reasonable to suppose that these Coracles are fashioned out of material available now, and since lasers powerful enough to reach Proxima Centauri are out of the question at the moment, we can suppose instead that they are pushed by photons from the Sun, i.e. that they are solar sails.
But what would present a suitable and worthwhile precursor mission for these Coracles to undertake? A most compelling case can be made for Near Earth Objects (NEOs), a fraction of which are 'mini-moons' of Earth, by which we mean Earth-Trojans, asteroids co-orbital with Earth, and the such-like.
I discovered from this CNEOS catalogue that there are around 100 such objects encountering Earth in the year 2030 alone, and if in one Coracle mission we wish to flyby 5, say, of them, that introduces a total number of permutations of approximately 868277728000 trajectories. That's a shockingly large number, how on Earth can we derive all the feasible trajectories from this, feasible in the sense that we wish to minimize the total DeltaV required to travel along the trajectories?
This is a challenge I felt I was up to and the first step was to filter out (or prune) all the permutations which might involve high DeltaVs - by removing NEOs with high eccentricities, high inclinations, and so on. This reduced the number to 792.
Having completed this task, I adopted the Non-Linear Problem (NLP) solver NOMAD to optimise the remaining 792 combinations and I then applied MIDACO to these solutions found by NOMAD.
Hoorah! The result was success, with two trajectories discovered from these 792 which had DeltaVs around 0.5 km/s (or 500 m/s). One of these trajectories can be found in the two animations below, which represent the same mission but the first one is heliocentric and the second one is geocentric.
