Universe Today
Cislunar space is already getting crowded. And with that crowding comes infrastructure complications. One is navigation - there is no Global Positioning System available when you're not on the globe. Finding a spacecraft’s exact orbital path relies on networking with the Deep Space Network (DSN), a set of telescopes originally developed in the 1950s to communicate with spacecraft far afield. DSN itself is already getting overwhelmed with managing all of the missions requesting its time, so getting a precise orbital location currently can take hours. But researchers at MIT’s Lincoln Laboratory think they might have a solution for this - launching a fleet of three satellites to collectively create a deep-space navigational system known as the LIght High-Orbit Utility Signal Emitter - LightHOUSE.
To be fair to the DSN, it has done a remarkable job keeping up with the times. However, despite all the technological upgrades it's received over the decades, there’s one thing that it has yet to be able to cope with - its Earth-bound location. Despite being as far as possible on the surface of the Earth - with the distance between the two farthest spaced telescopes reaching upwards of 17,600km - that is still only a fraction of the distance needed to get to the Moon (384,000km), let alone Mars.
To combat this inherent restriction, the MIT researchers plan to put the satellites that comprise the network in orbit at about 1.6 million kilometers above Earth’s surface. That is farther than the distance from the Earth to the Moon - and there are several good technical reasons for doing so.
Fraser and Pamela discuss the DSNFirst, it allows for an extremely long “baseline” - i.e. the distance between two of the satellites is a large fraction of even interplanetary distances - at least to Mars and Venus. This allows slight changes in the position of the spacecraft to register as much larger changes in the relative distance between the orbiting satellites - allowing engineers to capture orbital profiles much faster than the current best efforts of the DSN.
Second, it allows for satellites to peer behind the far side of the Moon. The Artemis II mission recently highlighted the nerve-wracking 40 minute radio silence that happens when spacecraft reach the isolated far side. With an orbital path that takes it beyond the Moon itself, some of LightHOUSE’s satellites will be available to provide precise positioning even in that remote locale - with the caveat that they would then also contribute to the radio frequency noise that is starting to impinge on the relatively pristine lunar far side already.
A third feature of LightHOUSE doesn’t have to do with its positioning, but does have to do with its features. Currently, deep space craft are required to carry powerful radio antennas to communicate with DSN. Operating those antennas requires precious electrical power, and carrying them crowds out other potential payloads that could have otherwise been utilized on the mission. With LightHOUSE, the burden of transmission lies with the “beacon” satellites - they will be the ones sending high energy signals to the various spacecraft asking for positional updates, though those spacecraft will still need a way to communicate their data base to their home base station.
NASA video describing the DSN.Optical communications are actually the technological backbone of LightHOUSE. Lincoln Lab has been iterating and improving upon free-space optical systems for years, most recently with the O2O optical communications system on the Artemis II mission, and the successful test of Psyche’s Deep Space Optical Communications (DSOC) network. These technologies would provide the basis for LightHOUSE’s communications and tracking system, though there’s still more work to be done if it was to be implemented.
Currently, that path towards implementation remains dark. Much of the funding for the efforts so far has come from internal R&D money from the Lincoln Lab itself - and the project hasn’t been adopted by any major space agency or private company that could make it a reality. But that doesn’t mean it won’t some day be. Ultimately, as deep space continues to get busier, we will eventually need to either massively update or completely replace the DSN - it’s only a matter of time. And maybe LightHOUSE will play a role in what that solution looks like.
Learn More:
MIT - High-orbit satellites could light the way for travel to the moon
UT - Tracking Deep Space Probes With GEO Satellites Improves Uptime
UT - NASA's Top 5 Technical Challenges Countdown: #4: Improved Navigation
