NASA and the Psyche team declined interview requests until an independent review of mission delays had been completed. At last month’s press conference, Laurie Glaese, chief of NASA’s planetary science division, said agency officials will make a decision on next steps based on that review in the coming months. But WIRED has spoken with other experts about options for sending a probe deep into the solar system, even if it can’t get past it to Mars.
Parker, for example, thinks it might be possible for Psyche to reach its asteroid by relying more on the spacecraft’s solar electric propulsion system. This system contains solar arrays that will unfold the size of a tennis court, converting sunlight into electricity to power Psyche’s Hall’s motors, efficient, long-lasting devices that emit a blue glow.
Using the Falcon Heavy for launch is another advantage, Parker says, because it will give the spacecraft more kinetic energy to start with compared to smaller rockets, meaning that less solar power must come in the way. He believes that focusing on power from takeoff and from the onboard propulsion system would give mission planners some flexibility about launch times, potentially allowing them to make the flight without relying on Mars alignment.
Another option for a spacecraft that needs to speed up is to overtake Earth. That was the option chosen for the European Space Agency’s Rosetta spacecraft, which was launched in 2004 on a mission associated with the comet, says Andrea Acomazzo, the agency’s chief of solar system and exploratory missions. During the probe’s 10-year journey, it gained speed through three flights of Earth and then swung by Mars before taking a direct line to Comet Churyumov-Gerasimenko and deploying an Philae probe to it.
Rosetta’s team faced two additional challenges: The comet had a moving elliptical orbit rather than a circular orbit like most asteroids, which made its speed and velocity difficult to match. And the researchers wanted to plan the trip so that Rosetta and its landing companion would meet the comet when it’s not too close to the sun, where it’s most active, pulling out bits of ice and dust and complicating the descent that already would have been difficult to pull off.
Engineers design a spacecraft with launch and trajectory options in mind, and in this case, some flights around Earth were the best course. “You start at the goal, then work backwards,” Akumazu says. “You have three sources of energy: the primary energy of the rocket, the energy in the fuel tanks of the spacecraft, and the energy that you can get from the planetary swing. It’s kind of manual work done by my colleagues who have been trying to find the optimal solution.”
Parker points out that the usefulness of a planetary swing depends on the spacecraft’s trajectory geometry, so it’s not always an option. But he agrees that they can be useful, especially when the destination is far away. “Asteroid missions in the main belt are challenging, and they consume a lot of fuel,” he says. “Psyche could have launched directly to its target with a larger launch vehicle, a smaller spacecraft, or a different engine,” but that could increase costs or reduce the scientific exploration that can be accomplished once the spacecraft arrives. NASA plans to orbit the probe around the asteroid for at least 21 months while it is photographed and use a magnetometer to search for remnants of a magnetic field, which may indicate that it was originally the core of a planet.