Are missions to the Sun particularly relevant to our interstellar ambitions? At the current state of our technology, the answer is yes. Consider Solar Cruiser, which is the planned NASA mission using a solar sail that could maintain non-Keplerian orbits, allowing it to investigate the Sun’s high latitudes. And throw in the European Space Agency-led Solar Orbiter, which left our planet early Monday (UTC) on a United Launch Alliance Atlas V rocket, lifting off from Launch Complex 41 at Cape Canaveral Air Force Station in Florida. Herewith the gorgeous arc of ascent:
Image: Launch of the ESA/NASA Solar Orbiter mission to study the Sun from Cape Canaveral Air Force Station in Florida on Feb. 9, 2020. Credit: Jared Frankle.
Missions to the Sun allow us to explore conditions close to a star and, significantly, deep in its gravity well, where interesting things can happen. When we discuss one way of propelling a sail beyond the heliosphere, the irony is that an Oberth maneuver, which takes place at a few solar radii, can bring additional chemical propulsion online at perihelion to extract the maximum push. So in propulsive terms, we go to the Sun in order to get flung from the Sun at highest speed. If we want to get beyond the heliosphere fast and with today’s tools, the Sun is a major factor.
Solar Orbiter is not, of course, designed around interstellar matters, but the synchronicity here works well for us. The more data about conditions near the Sun, the better for what we will want to do in the future. Günther Hasinger is the European Space Agency’s director of science:
“As humans, we have always been familiar with the importance of the Sun to life on Earth, observing it and investigating how it works in detail, but we have also long known it has the potential to disrupt everyday life should we be in the firing line of a powerful solar storm. By the end of our Solar Orbiter mission, we will know more about the hidden force responsible for the Sun’s changing behavior and its influence on our home planet than ever before.”
And, I would add, we’ll know a great deal more about how spacecraft operate inside Mercury’s orbit. Moreover, think about all the interesting maneuvers that have to take place to make this happen. Three gravity assists come into play as Solar Orbiter goes for the Sun, two of them past Venus in late 2020 and August of 2021, and one past Earth in November of 2021. The first close pass of the Sun will be in 2022, at about a third of an AU, with the gravity of Venus being used to push Solar Orbiter up out of the ecliptic plane. Ulysses achieved an inclined orbit in 1990, but Solar Orbiter will be carrying cameras allowing us to directly image the Sun’s poles, a role for which Ulysses was not equipped. The spacecraft is to reach an inclination 17 degrees above and below the solar equator.
Solar Cruiser and Solar Orbiter have much to teach us about interstellar possibilities, as does, for that matter, the continuing Parker Solar Probe mission. Along the way we learn, in addition to the significant science return about the Sun itself, about how spacecraft cope with being subjected to the solar wind and the temperatures of passage near the Sun. We learn about heat shielding and how to minimize what is needed so as to maximize payload. Solar Orbiter will face temperatures of up to 500º C, 13 times that experienced by satellites in Earth orbit.
So if we’re thinking deep space today, we should also be thinking about heliophysics. Our best bet at getting a successor to the Voyager missions well beyond the heliosphere and at significantly higher speeds that Voyager 1 is a close solar pass and propulsive kick that will demand deep knowledge of conditions at perihelion. Solar Orbiter’s 10 scientific instruments will measure electric and magnetic fields, passing particles and waves, solar atmospheric conditions and the outflow of material.
All these are factors as we contemplate the close approaches that will fling solar sails into the Kuiper Belt. In not many years, we could build a ‘sundiver’ mission that would make for great heliophysics as well as data from deep space — two missions in one.