If you're going to spend millions of dollars on a spacecraft, you might as well try to cram in as much as possible. With that in mind, ESA has now detailed the side mission it's planning for the asteroid-visiting spacecraft Hera. After the main work is complete, the probe will test out some new autonomous navigation systems, which should help future spacecraft get around without relying on ground control all the way back on Earth.
Hera is part of a planetary defense test known as the Asteroid Impact and Deflection Assessment (AIDA), which as the name suggests is designed to figure out how we might go about nudging a potential Earth-bound space rock off-course. The target is a binary asteroid called Didymos, which consists of a tiny 160-meter-wide (525-ft) rock orbiting a larger, 780-m (2,560-ft) asteroid.
The mission itself is also kind of a binary system, involving two spacecraft. The NASA-designed DART probe is made to smash into the smaller rock, with the aim of ever-so-slightly altering its orbit. But of course, the problem there is that DART won't be around to watch what happens next.
And that's where Hera comes in. Currently being designed by ESA, the craft will enter orbit around Didymos and look out for changes in the smaller rock's orbit, as well as investigate the crater left behind on its surface.
But that's not all. ESA has previously alluded to the craft's self-driving abilities, and now the space agency has revealed just how that will work. Hera will function using three different autonomous modes, depending on its distance of Didymos.
"If you think self-driving cars are the future on Earth, then Hera is the pioneer of autonomy in deep space," says Paolo Martino, Hera's lead systems engineer. "While the mission is designed to be fully operated manually from [the] ground, the new technology will be tested once the core mission objectives are achieved and higher risks can be taken."
The first mode will be tested on approach, when the asteroid just looks like any other star. To identify it, Hera will take multiple images of the rock to register its motion against the background starfield. That said, at this stage the craft won't be entirely autonomous – since it's too valuable to risk before its main mission is complete, this will be more of a secondary test.
The second mode will be used for the bulk of the mission, when Hera is within 30 to 8 km (18.6 to 5 mi) of the surface of Didymos. At this stage, the craft's camera will use the hard-to-miss reference point of the larger asteroid to figure out where it is.
"This mode depends on having the big asteroid smaller than our overall camera field of view, and detecting the contrast of its edges giving way to the space beyond," says Massimo Casasco, a guidance, navigation and control (GNC) engineer at ESA. "We take advantage of its roughly-spherical shape to fit it within a circle and estimate the line-of-sight distance between the spacecraft and the asteroid 'centroid'."
The third mode is the toughest one to pull off. Kicking in when the craft is too close to see the whole asteroid, the camera will instead look for surface features to try to navigate.
"This will be a matter of imaging the same features – such as boulders and craters – in different pictures to gain a sense of how we're moving with respect to the surface, combined in turn with other information including onboard accelerometers for dead reckoning and the thermal infrared camera for overflying the asteroid's night side," says Jesus Gil Fernandez, another ESA GNC engineer.
If the mission is successful, similar self-driving tech could eventually find its way into future spacecraft. Ideally, it would eventually free up ground teams from having to oversee every minor step of a spacecraft's movement.
Hera is currently in the detailed design work phase, and is due to be presented to Europe's space ministers in November. If all goes to plan, it should launch in 2023. A test can be seen in the video below.
Source: ESA
