Adam Hibberd
I am tackling the challenging problem of rendezvous by a probe of Halley’s comet using Nuclear Electric Propulsion (NEP), and I am assisted by a very powerful and skillfull contributor in the form of AI.
NEP is a low thrust propulsion method with high ‘bang-for-your-buck’ (or specific impulse as we say in rocketry circles), and is about the only forseeable method of applying the necessary velocity change to match velocities with Halley at the huge distances from the Sun that we have in mind.
I laid down the law as to what approach we should use and that would be exploiting Pontryagin’s Maximum Principle (PMP).
PMP has the advantage of giving the THEORETICAL optimal trajectory, and not just a locally optimal solution contingent on the precise thrust vector formulation. Thus the answer we should get would be indisputably optimum.
But the next question would be, what exactly should we optimize? The obvious candidate is to minimize thrust time and therefore fuel mass-loss, but is not appropriate as a first step for reasons of sensitivity of the solution to the thrust cut-off time, every attempt at this approach failed.
But it was I who came up with the key breakthrough which was to try and maximize positive ‘Vz’.
For those who might be a bit confused at this point (as many of you no-doubt are), what the probe needs to do to catch up with Halley is do a gravity assist of Uranus and then swing downwards, way below the ecliptic plane – that means ‘Vz’ is initially negative, right?
The trouble is Halley is actually travelling upwards with a highly positive ‘Vz’ which means that the probe must do a huge U-turn in deep space, to make sure its velocity aligns with that of Halley.
That is a huge challenge but it so happens that when we applied precisely this objective – to maximize positive Vz achieved by the probe – to the PMP, the solutions began to look extremely promising, and this is no-doubt a massive stepping stone by which the overall aim of rendezvousing with Halley with minimum propellant-usage can be enabled.
The reason for this research shall become clear in the near future.