Future space telescopes are being designed to be easier to service, with a focus on overcoming challenges such as remote locations and limited fuel. The new approach includes safe close-range operations and efficient trajectory planning, potentially extending the lifespan of existing missions such as James Webb and Gaia.
Space telescopes are becoming more sustainable thanks to new designs focused on maintainability. Researchers drew inspiration from missions such as the James Webb Space Telescope and ESA's Gaia to develop maintenance plans for future space observatories.
"Although the next generation of large space telescopes are designed with maintainability in mind, significant challenges remain during implementation," explained Siegfried Eggl, professor of aerospace engineering at the Grainger School of Engineering at the University of Illinois at Urbana-Champaign.
A major challenge is distance. The modern telescope is located at the Sun-Earth Lagrange point L2, about one million miles from Earth. While this location moves in sync with the Earth, making it somewhat easier to reach, transporting materials is time-consuming and expensive due to the distance. Despite these challenges, Lagrangian point L2 provides a quiet, low-distraction environment that greatly enhances the impact of missions like Gaia, and Egger believes the effort is worth it.
"Gaia is like a spinning cylinder with solar panels," Egger said. "It's encapsulated so it's not damaged, but after a decade wandering outside, it's running out of fuel. Luttwik-Bomena devised a novel concept that adds a spider "Gaia will be decommissioned soon, so there won't be enough time to get access to it, but James Webb may still have a chance, and since it will still be operational for a few years, they may decide to extend its mission."
He explained that the mirrors of the James Webb Telescope are unshielded segmented mirrors, some of which have been damaged when struck by micrometeorites. The entire mirror diameter of JWST is 6 meters. The next large telescope will be twice this size.
"We're trying to stay ahead of the curve so we can replace broken mirrors etc. in a planned way. If we don't do that, it's like buying an expensive sports car and throwing it away when it runs out of gas."
Another area of work for Bomena is safe close work.
"Spacecraft being sent to repair or refuel a telescope need to be braked upon arrival," Bomena said. "Using thrusters to slow down is like pointing a blowtorch at a telescope. You don't want to do that to a delicate structure like a telescope mirror. How do we do that without burning the entire mirror?"
Robyn Woollands, also a professor of aerospace engineering at the University of Illinois, said one of their main goals with this work is to find a trajectory to get there cheaply without relying on large, costly rockets.
"Fortunately, getting there is feasible thanks to some hidden highways in the solar system. We have a trajectory that is optimal for the size of the spacecraft needed to repair JWST," she said.
PhD student Alex Pascarella has developed a new technique that quickly samples the solution space, thereby reducing computational time. "The novelty is that we combine two different approaches to trajectory design: dynamical systems theory and optimal control theory," he said.
Traditional approaches to orbit design in multi-body systems such as the Sun-Earth system rely on computing the invariant manifold of the orbit—the manifold is the path in space that naturally leads a spacecraft to a given orbit. This is a great approach that has been used successfully for decades in both academic research and practical applications.
"When you're trying to rendezvous with a target spacecraft at a specific location in space/time, as opposed to reaching a target orbit, and you're dealing with a low-thrust spacecraft that has its engines working for a long time, as opposed to a spacecraft with a more powerful thruster that has its engines working for a short time, it becomes a little challenging. "Our technique is based on a slightly different idea," Pascarella said: "We first study the solution space by propagating samples of the solution - either without any thrust or using a very simple thrust control law - and then we note how close they are to our desired destination."
He adds that because the type of orbit they are trying to achieve creates manifolds, they know that at least some of the initial guesses will be close to the ideal orbit: "After mapping the initial solution, we use optimal control theory to generate optimal end-to-end trajectories. Optimal control allows us to find trajectories that start near Earth and rendezvous with our space telescope in the shortest possible time. Initial sampling of the solution space is fundamental - optimal control problems are notoriously difficult to solve, so we need a suitable initial guess."
The plan to repair/fuel Gaia is a complete design that can be implemented, while the James Webb telescope will require more engineering, Egger said.
Compiled from /ScitechDaily