Imagine a spacecraft embarking on a daring journey to intercept a comet from beyond our solar system. This is not just any comet, but the iconic 3I/ATLAS, currently hurtling away from us at an incredible speed. But here's the catch: to catch up with this interstellar traveler, scientists propose a risky move. They suggest firing the spacecraft's booster rockets during an extremely close encounter with the sun, using the sun's gravity to gain the necessary velocity.
The plan is to launch this mission in 2035, aiming to reach 3I/ATLAS by 2085 at a staggering distance of 732 astronomical units (AU) from the sun. That's 732 times farther than the Earth's distance from the sun, or approximately 68 billion miles! To put it into perspective, our most distant space probe, Voyager 1, is currently only 170 AU away after a similar flight time. But this mission aims to go much further, much faster.
The key to this ambitious plan lies in a concept called the Oberth effect, named after the Austro-Hungarian rocket scientist Hermann Oberth. He introduced this idea in 1929, explaining how a spacecraft can gain more velocity by firing its engines at the point of closest approach to a gravitating body, like the sun. And this is the part most people miss: the Oberth effect is already used in many launches, but the proposed mission to 3I/ATLAS would involve a unique, straight-out Oberth maneuver, a major rocket burn at the sun's closest approach during a flyby.
The sun, being the most massive body in our solar system, offers the perfect opportunity to utilize the Oberth effect. But this requires the spacecraft to get incredibly close, within 3.2 solar radii from the sun's center. That's equivalent to about 0.015 AU, deep inside the solar corona. NASA's Parker Solar Probe has braved similar conditions, approaching the sun within 0.04 AU and enduring temperatures of 2,500 to 2,600 degrees Fahrenheit.
The spacecraft for this mission would require a robust heat shield, similar to the carbon-composite shield on the Parker Solar Probe, but with additional layers of aerogel for insulation. This heat shield would protect the spacecraft as it performs the solar Oberth maneuver, accelerating it to unprecedented speeds.
The mission's trajectory is carefully calculated by software engineer and creator of the Optimum Interplanetary Trajectory Software, Adam Hibberd. His calculations show that the most efficient launch window would be in 2035, after first flying out to Jupiter to slow down the spacecraft and then loop back towards the sun. This counterintuitive maneuver is necessary to shed velocity, as any spacecraft launched from Earth already has Earth's orbital motion, which would cause it to overshoot the sun at high speeds.
The spacecraft's mass is estimated to be around 1,100 pounds, similar to NASA's New Horizons mission to Pluto. However, the heat shield's weight must be accounted for, as it is a crucial component. The team suggests using two or three solid-rocket boosters, such as the Starship Block 3s with nine Raptor 3 engines, to provide the necessary thrust for the solar Oberth maneuver.
The mission's duration depends on the delta-V achieved during the maneuver. A delta-V of 5.19 miles per second would result in a 50-year journey for a flyby of 3I/ATLAS. But if we can push the delta-V to 6.43 miles per second, the rendezvous could happen in just 30 years. This is not an impossible feat, as NASA's Dawn spacecraft achieved a similar delta-V after separating from its booster rocket.
Given the high speeds involved, a flyby is the only feasible option, rather than entering orbit around the comet. But why chase 3I/ATLAS when there will soon be easier interstellar comet targets to reach? The researchers argue that the desire to explore these unique objects may persist, even as more are discovered. And if a mission is ready to launch, conventional methods could be used to reach newly discovered comets.
The European Space Agency's Comet Interceptor mission, set to launch in late 2028 or early 2029, is designed to wait for a suitable interstellar comet target before being dispatched. This mission highlights the growing interest in exploring these cosmic visitors. And while the solar Oberth maneuver may not be necessary for all interstellar missions, it could still prove valuable for exploring the outer solar system, including the theorized Planet Nine, or even for sending telescopes to the far reaches of our solar system.
The 3I/ATLAS comet continues its journey away from us, but the development of spacecraft trajectories using solar Oberth maneuvers opens up exciting possibilities for exploring the outer solar system. And who knows, perhaps one day we'll have the technology to catch up with these interstellar travelers and unlock their secrets.
