Spacecraft could use sat-nav for directions to the moon

Sat-nav, where’s the nearest service station? (Image: NASA/SIPA/REX Shutterstock)

At the next space station, turn left. Efforts to repurpose GPS and other navigation satellites to help spacecraft reach the moon are under way, and could bring about an increase in lunar-bound traffic.

You can’t just point your rocket at the moon and be sure of getting there in one piece – you need to navigate. “It’s not possible to predict the trajectory accurately,” says Vincenzo Capuano of the Swiss Federal Institute of Technology in Lausanne (EPFL), Switzerland. “That’s why you need to know where the spacecraft is.”

Currently, spacecraft communicate with tracking stations on Earth, such as NASA’s Deep Space Network, to monitor their positions. But these large radio antenna facilities are expensive to run, and there are a limited number dotted around the planet. If we’re ever going to send spacecraft to the moon on a regular basis, we’ll need a more autonomous system.

Fly me to the moon

Enter GPS. Some spacecraft in low Earth orbit, around the level of the International Space Station, already use GPS to navigate, but missions to the moon fly well above the GPS satellites. That’s a problem, since the transmitters point down, towards Earth.

Now Capuano and his colleagues have figured out that spacecraft on their way to the moon could use signals from GPS satellites on the distant side of Earth to navigate. The signal is much weaker, but they’ve calculated that combining signals from US GPS satellites with those from Galileo, a European navigation system currently under construction, would be enough for a lunar trip. “You would save a lot of money because you don’t need a lot of people working in the ground stations,” says Capuano.

The team is also developing more powerful GPS receivers to pick up this weaker signal, which could in turn have benefits on Earth – standard smartphone receivers struggle to get a location inside buildings or other built-up areas, so new devices could mean better navigation.

Journal reference: Acta Astronautica, DOI: 10.1016/j.actaastro.2015.06.007

By Jacob Aron

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