Spacecraft exploring cislunar space lack an always-available global positioning service, forcing missions beyond geosynchronous Earth orbit to rely heavily on NASA’s Deep Space Network, according to MIT Lincoln Laboratory researchers. Because all DSN ground antennas are located on Earth, their separation is small compared to the scale of cislunar space, leaving distant spacecraft waiting hours for precise orbital locations and forcing user craft to actively transmit signals for measurement.
Why the Deep Space Network Struggles With Cislunar Navigation
Operating since the 1950s, NASA’s Deep Space Network relies on an international array of Earth-bound radio antennas that must manage a mounting queue of missions, according to MIT researchers. While the network has received technological upgrades over the decades, its surface-bound location creates an inherent geometric restriction. The distance between the two farthest spaced DSN telescopes reaches upwards of 17,600 kilometers, which is only a fraction of the 384,000 kilometers needed to reach the Moon.
This limited separation restricts the angular baselines available for orbit determination. Therefore, estimating orbital profiles for distant spacecraft can take hours, and the network supports only a few missions at a time, according to MIT Lincoln Laboratory. Furthermore, unlike terrestrial GPS which passively sends data for users to receive, the DSN requires user spacecraft to actively emit signals for measurement.
How MIT’s LightHOUSE Concept Plans to Fix Deep Space Tracking
To combat these limitations, researchers at MIT Lincoln Laboratory are developing a deep-space navigational system known as the Light High-Orbit Utility Signal Emitter, or LightHOUSE, according to project documentation. The concept calls for launching a fleet of three satellites into ultrahigh orbits about 1.6 million kilometers (roughly one million miles) above Earth’s surface—farther than the distance to the Moon.
“Satellites in cislunar space have limited access to support resources, even though orbits at and beyond the geosynchronous belt are increasingly important for various missions,” says Aaron Greenberg, a technical staff member in the Laser Communications Group at MIT Lincoln Laboratory. “The Moon is reemerging as a strategic priority for national security. Nearly all space missions require some degree of precision navigation and timing, but no global positioning system exists in this domain. Here is where LightHOUSE is intended to step in, expanding critical and reliable communication and navigation services across this vast region.”
Placing the beacon satellites at this extreme altitude creates an extremely long baseline, allowing slight changes in a spacecraft’s position to register as much larger changes in relative distance. This geometry lets engineers capture orbital profiles much faster than current DSN methods. Additionally, the high orbital path allows satellites to peer behind the far side of the Moon, preventing radio blackouts like the nerve-wracking 40-minute silence experienced during the Artemis II mission.
Pro Tip: Free-space optical communications—laser links through space—form the technological backbone of the LightHOUSE architecture, building on laboratory work demonstrated through NASA-sponsored programs such as TBIRD and O2O.
Optical Communications and Beacon-Driven Navigation
LightHOUSE borrows heavily from the GPS philosophy by placing the primary technical burden on the beacon satellites rather than on user spacecraft, according to MIT researchers. The beacons would carry telescopes with tens-of-centimeter diameters and laser transmitters, using imaging against the stellar background to estimate each user spacecraft’s three-dimensional position and velocity.
“This concept hinges on a cooperative ranging capability enabled by free-space optical communications,” says Timothy Yarnall, an associate leader of the Laser Communications Group. “This technology area is one in which the Laboratory is a global leader, as evidenced by the recent O2O success during Artemis II. The Laboratory’s experience with radiation hardening of digital focal plane array technology will also enable the sensitive receivers and star cameras — like the camera built by the Advanced Imager Technology Group for NASA’s Psyche mission — that this concept relies upon.”
By shifting transmission duties to the high-orbit beacons, deep-space craft would no longer need to carry powerful radio antennas to communicate with the DSN, freeing up payload space for other mission tools. However, user spacecraft would still need a mechanism to communicate their data base to home stations.
Did You Know? Much of the funding for LightHOUSE development has come from internal research and development money administered through the Lincoln Laboratory’s portfolio in optical systems technology, as the project has not yet been adopted by a major space agency or private company.
Frequently Asked Questions
What is cislunar space?
Cislunar space refers to the volume of space between Earth and the Moon, which is experiencing a significant increase in traffic and infrastructure complexity.
Why can’t spacecraft in deep space use standard GPS?
Standard Global Positioning System signals do not reach beyond Earth’s immediate orbit because GPS satellites are constrained to medium Earth orbits designed for terrestrial users.
How does the Deep Space Network currently track distant spacecraft?
The DSN uses a network of large radio antennas on Earth’s surface that communicate via radio frequencies, requiring user spacecraft to actively transmit signals that take hours to process.
Who is developing the LightHOUSE system?
Researchers from the Laser Communications Group and Advanced Capabilities and Technologies Group at MIT Lincoln Laboratory are developing the LightHOUSE concept.
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