In this series we’re exploring NASA’s top five challenges as detailed in its Civil Space Shortfall Ranking, which is basically NASA’s Christmas wish list. These are the technologies that NASA believes we need to develop if we want to go to space…and stay there.
Next we have number four: improved navigation.
We all take for granted our handy little cell phones, these magical rectangles that let us communicate instantly with anyone in the world…or scroll social media until our brains go numb. Related to that is the ease of navigation. Or you can plug in an address or drop a pin, and boom there you, the fastest route to grandma’s house. Oh yeah, and you always know what time it is, day or night or season of the year…so that you know you’re late for dinner.
All of this is easy for us to use because it was hard for someone else to create. To make a call, our cell phone connects to a nearby tower, of which there are approximately a bajillion, which is then connected to a vast globe-spanning network of wires and undersea cables. As for our position and navigation, that’s all handled by hundreds of satellites in orbit around the Earth, with several different networks: The United State’s Global Position System (the OG), Russia’s Global Navigation Satellite System, China’s BeiDou, and the European Union’s Galileo. We have all that, plus a host of regional and local space- and ground-based location services, all overlapping and working together to provide that pinpoint accuracy.
But in space, like on the Moon or Mars, we have…none of that. Zero. No GPS satellites, no globe-spanning networks. Just radio broadcasts from command centers here on Earth to tell our robots and crews what to do.
And so we have the next high priority challenge we have to navigate (ha, ha) to achieve a permanent presence in space: all that stuff, but in space. So what would this look like?
The most important step is to create a mini-GPS for the Moon, with a constellation of satellites doing for the Moon what they already do for the Earth. Plus we need to augment that with relay stations and repeaters at lunar bases or centers of exploration, because we probably won’t have enough signal strength to whip out our cell phones in the middle of Mare Vaporum. The hope is that our first generation of lunar GPS will be enough to match our first explorations, and then we can expand the system to match the needs of further lunar activities.
But in order to make that lunar GPS system, we need to deploy in space one critical piece of technology: atomic clocks. Atomic clocks are ultra-precise…well, clocks, that rely on the resonant frequency of atoms to monitor the passage of time. We already have atomic clocks in space, because every single GPS satellite has several of them onboard – that’s the key component to the entire navigation system. But for deep-space work we need to be much more sophisticated. Earth-based atomic clocks can get away with some uncertainty, because they are always cross-checking and correcting each other. That won’t be an option around the Moon or Mars, where a small network of satellites will have to keep perfect time.
Precise timing is necessary for pinpointing a satellite’s location. If you receive a signal from the satellite from a ground station, you need to know how long it took for you to receive the signal to figure out where the satellite is.
In June of 2019 NASA launched the Deep Space Atomic Clock, or DSAC, which operated for two years, maintain an accuracy of better than 1 nanosecond in 10 days – the means after ten years, the clock would only be off by a microsecond. NASA has recognized that to enable long-term deep-space activities,we need to be even more accurate than that.
Lunar and Martian spacecraft are going to have to be able to navigate autonomously, without human input. As a complement to a space-based GPS system, these spacecraft could also employ a few other tricks. One trick is called radiometric tracking, which uses incoming radio signals to judge the distance to the source of those radio signals. We already use this technique quite frequently, but it’s limited to one dimension: the direction towards the Earth, which is the origin of any radio signal that a spacecraft might pick up. Decades from now, we hope to have radio signals coming from lunar and Martian bases, and even asteroids, and a sufficiently sophisticated spacecraft might be able to pick up all these signals and figure out where it is in the solar system.
Speaking of weak radio signals, Lunar operations would benefit from our existing GPS network. Yes, those GPS satellites are aiming their signals down to the Earth, but some of that signal leaks out into outer space. We might be able to piggyback off that signal to at least get our navigation game started.
