Adam Hibberd
The third interstellar object is causing a bit of a stir. What could it be exactly?
Judging by its predicted path, we should get a ring-side view of it from Earth, except for an important viewing outage as it approaches perihelion - the closest approach to the Sun - simply because it will be blocked by it (i.e. it will have a low solar elongation).
It could be argued that a mission would be entirely unnecessary from a scientific standpoint, as its nature should be known and fully understood by the time it disappears off into the distance again, having completed its express tour of our Solar System.
The same cannot be said for 1I/'Oumuamua, the first interstellar visitor to our abode, which was visible for less than 2 months and has left a mountain of unanswered questions in its wake. But the news isn't good for 3I/ATLAS from a purely astrodynamical stand point either - because a mission to it, as I shall show, is totally infeasible.
Take the pork-chop plot which I provide below, and which my software Optimum Interplanetary Trajectory Software (OITS) has generated. This, I remind you, is the characteristic energy, C3, expressed in colour, of a direct mission to 3I/ATLAS, given any launch date and flight duration.
Thus the lower the C3 (and the deeper blue the colour), the more feasible mission, and conversely the higher the C3 (the more yellow the colour), the less feasible the mission. We find absolutely NO colours after July of this year, meaning we can NO LONGER send a DIRECT mission to this curious interstellar visitor.
But what about an INDIRECT mission? The news isn't great there either.
Two options present themselves, a JUPITER OBERTH, where we travel to Jupiter and deliver all our thrust at the closest approach - perijove - to this planet. This can easily be shown to require FAR TOO much 'DelatV' (or velocity increment) from the propulsion system to be even remotely feasible.
Or alternatively what about a SOLAR OBERTH?
A Solar Oberth Manoevure comprises a low perihelion and applying all your thrust at this point. It turns out the best way of achieving a low perihelion is by travelling to Jupiter first, thus this means we are constrained in our launch opportunities by the precise alignment of Jupiter with Earth and the target, 3I/ATLAS.
Unforunately, the next alignment is around 26th September of this year, so FAR TOO SOON, to launch a mission - see my animation below (or go to my YouTube channel here). The subsequent alignment to this will be in 2038, 12 years (and one Jupiter period) later, when 3I/ATLAS will have receded much farther away, meaning a mission will be much harder to realise, since the DeltaVs will be much larger.
So altogether this interstellar object is one huge problem for a space mission designer, and it's just as well we have two other examples of interstellar objects on our 'to-do' list, and with the now-fully operational Vera C. Rubin telescope, hopefully the prospect of many more to come.