Adam Hibberd
3I/ATLAS, the interstellar object, is in the Solar System and making its presence known, not only to astronomers but also to the world's media. My paper with Avi Loeb and Adam Crowl examined the hypothesis that 3I/ATLAS might be alien technology, go here. I confess this paper has been somewhat of a hit!
Though controversial, perhaps, nevertheless I invite you to read it without the prejudice which might have formed as a result of representations of it, or should I say misrepresentations of it, from social media coverage.
Meanwhile I muddle on with my research, this time on the various challenges of mounting a spacecraft mission to this strange object.
You may already be aware, since I have made it quite clear on previous blog posts, here for example, that a direct mission to 3I/ATLAS is quite impossible, since it was discovered too late. Just to repeat the logic, look at the Figure below which is the relevant 'Pork Chop' plot in question, do read the aforementioned post for more detail.
With this revelation, is there any way at all possible a spacecraft could be sent to intercept this object? Possibly not directly, but indirectly, using a combination of gravity assists (GAs) for example?
So enters the stage my wonderful software OITS (Optimum Interplanetary Trajectory Software), designed specifically to model interplanetary spacecraft GAs and also OBERTH MANOEUVRES.
As a reminder the fastest speed an object travels when it is orbiting a hugely more massive object, is at the PERIAPSIS point, or in other words at the closest approach it makes to this massive object. This means given a certain DeltaV capability of the spacecraft (i.e. a velocity increment available from an onboard propulsion system), then to MAXIMISE the change in kinetic energy of the spacecraft, this available thrust should all be delivered at this periapsis point. This will slingshot the spacecraft away at huge speed from the aforementioned massive body, and onwards to catch the target. Go to my animation here to demonstrate the Solar Oberth Effect, or look at the video below.
Now, it may not have escaped your notice that the most massive body in our Solar System is the Sun, and so one should expect a SOLAR OBERTH MANOEUVRE to be precisely the optimal trajectory of choice to enable a spacecraft to catch up with the object, in this case 3I/ATLAS, in minimum time. Note also that by the time of launch of the spacecraft, 3I/ATLAS will be receding rapidly from the Sun at a huge speed upwards of 58 km/s, so this is a question of catch-up as is invariably the case for Oberth Manoeuvres.
My software was designed so that it could model Solar Oberth Manoeuvres, so look at the figure below where I have examined a Solar Oberth to 3I/ATLAS in some depth.
It turns out that the next BIG opportunity for a Solar Oberth will be with a launch on 26th September 2025, which is far too soon to be of any practical use.
Yet nonetheless these results are still informative as they should also hold for future Solar Oberth trajectories, so beyond that 26th September 2025 deadline. Solar Oberths have a 12 year cycle of launch windows, since they involve a passage to Jupiter, which happens to realign with the Sun and 3I/ATLAS every 12 years, this being Jupiter's orbital period.
We find in the figure above that the optimal distance from the Sun's centre for a Solar Oberth is at about 8.5 Solar Radii (as a reminder, for 'Oumuamua it was 6 Solar Radii). This perihelion distance requires least DeltaV at the Oberth to catch up with 3I/ATLAS, eventually arriving in the space of 30-odd years from launch. This is optimal from purely an ASTRODYNAMICAL point of view.
Nonetheless even at this minimum DeltaV option, the Solar Oberth Manoeuvre DeltaV is quite a stretch for a chemical propulsion system, and would require at least 2 stages, more likely 3 stages to deliver it.
Scientia ad Sidera!