Project Lyra: A Solar Oberth at 10 Solar Radii

Adam Hibberd

I have recently returned my attention to the Solar Oberth mission to ‘Oumuamua.

For readers not familiar with this celestial body, 1I/’Oumuamua was the first interstellar object to be discovered passing through our Solar System, is now out of range of our most powerful telescopes and has left scientists with many questions in its wake. A mission to this very strange object, Project Lyra, would seem an ideal way of answering all these questions.

Since a high heliocentric velocity would be needed to catch up with it, such a mission would stretch the limits of current and near-term chemical propulsion technology. However we at i4is have found that it would indeed be feasible. As well as there being several potential feasible mission scenarios to get to 'Oumuamua (as discovered by our research), one of the most investigated and compelling options for such a mission is known as the Solar Oberth Manoeuvre, where the chemical rocket is ignited at a very low perihelion to the Sun, on the order of a few Solar Radii (SR) where one SR is about 695700 km.

In turn, a low perihelion is achieved by the spacecraft flying to Jupiter and then losing all its tangential velocity there, as it turns out that this is the most efficient method of achieving a low perihelion, i.e. the one that uses least ΔV, and so fuel, from the chemical rocket engines.

Various previous studies highlighted a Solar Oberth at 6 SR was the most promising course of action, launching from Earth in a 2030-2033 timeframe and arriving at the destination ‘Oumuamua some 22 years later.

Ecliptic Plan view of Projet Lyra with Solar Oberth at 10 Solar Radii

However because a 6 SR perihelion might be problematic for various reasons, mainly the requirement of a heavy heat shield to protect the craft from the huge solar flux from the Sun, instead I decided to increase that perihelion to 10 SR, which is precisely what will be achieved by the NASA Parker Solar Probe and thus allows exactly the same heat shield technology to be exploited.

Having set to work on this task, which involved running my Optimum Interplanetary Trajectory Software (OITS) development, I found that a mission with a 10 SR perihelion is indeed feasible, though for various reasons has a longer overall flight duration, and a slightly higher total ΔV requirement.

I hope you agree that although there are many, many other strategies for launching a mission to ‘Oumuamua (just refer to Google scholar, ‘Project Lyra’), the Solar Oberth is by far the most daring, challenging and pleasing to the eye.

I provide with this blog, two alternative animations of this mission, the first a plan view from above the Solar System’s ecliptic plane (the plane of the Earth’s orbit), and the second a sideways view from along the ecliptic plane, so that an idea of the out-of-ecliptic component of the trajectory can be appreciated.