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Establishing a proto-LTC with Two-Way Satellite Time Transfer (TWSTT) at the Moon

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Description

This ECI project seeks to address these critical timing needs to develop a system 
capability for a “proto”- coordinated lunar time (LTC) scale and determine its 
empirical relationship with the standard terrestrial time scale. Complementary 
efforts are focused on defining an interoperable framework for communication, PNT, 
and auxiliary services in cislunar space (known as LunaNet) or advancing low TRL next 
generation highly stable clock technologies (such as the Spaceflight Compatible Optical 
Atomic Strontium Ion Clock, or OASIC). This proposed concept is focused on the 
development of a low small size, weight, and power (low SWaP) clock ensemble using 
flight-rated COTS parts to be deployed on the lunar surface, and the long-distance twoway satellite time transfer (TWSTT) procedure necessary for defining and tracing the
lunar time relationship to UTC. This is a key technological effort because it will establish 
a feasible means to close the current gap in lunar timing service infrastructure in the 
next 3-5 years. Systems designed to obtain and distribute measurements of proper
lunar time from the lunar surface are needed by lunar PNT systems such as LCRNS.
The steady increase in missions going to the Moon will continue to strain the ground 
station infrastructure to meet cislunar missions’ needs for ranging, Doppler, and timing, 
when in view. The availability of a timing source providing a stable LTC reference to
users on the lunar surface and in orbit can: 1) improve the navigation solutions of 
cislunar and lunar surface missions, when used as a source for the LunaNet PNT 
services, thereby unifying the distribution of a common lunar reference system 
commensurate with LTC; 2) reduce the timing burden on cislunar users by allowing 
them to use lower SWaP receivers, clocks, and processing power since the LTC time 
broadcast by the LunaNet Service Provider (LNSP) nodes are orbiting the same central 
body, are close by, and can more frequently provide time updates through the one-way 
broadcast; 3) serve as the foundation to establish a common time system for the 
Moon, analogous to International Atomic Time (TAI) or UTC on Earth.
 

Benefits

The decades ahead will witness monumental advances in the exploration of cislunar 
space. Following the success of Artemis I and the Commercial Lunar Payload Services
(CLPS), subsequent missions will return astronauts, robotic explorers, and science 
instruments to lunar orbit and the lunar surface, with the goal of establishing an 
enduring human presence on the Moon and vibrant lunar ecosystem in preparing for
Mars. Critical to these endeavors will be establishing a time system at the 
Moon, to perform experiments of fundamental physics, testing predictions of 
relativity, and support a permanent presence on the lunar surface and 
sustained activities from private industry and government. The establishment of a 
Coordinated Lunar Time (LTC) is essential to enable safe navigation in cislunar 
space long term and facilitate interoperability between lunar assets and with 
Earth. The development and maintenance of a LTC at the moon will mature the 
technology and establish the processes necessary build and maintain a system for 
Mars. NASA’s Space Communications and Navigation (SCaN) program is working to 
enhance and develop new network assets for the Artemis program. The Lunar 
Communications Relay and Navigation System (LCRNS) includes a proposed Global 
Navigation Satellite System (GNSS)-like constellation of relay satellites to provide 
communication and PNT services primarily at the Moon’s South Pole region. The 
constellation has three phases of deployment beginning in 2026 and ending in 2029
after the deployment of a minimum of 4 nodes in the constellation. However, the initial 
LCRNS node(s) may be limited to mathematically defined offsets from the Earth 
standard Coordinated Universal Time (UTC) which could introduce timing errors, since 
no proper clock yet exists on the lunar surface to obtain empirical measurements. A 
clock or ensemble of clocks on the lunar surface can measure a realized time on 
the lunar geoid and be the first to establish LTC for the Moon. Like the GNSS 
constellations at Earth, the LCRNS nodes can broadcast the realized LTC time to users 
on the surface and in cislunar space around the South Pole. In turn, this capability 
will reduce the Size, Weight, and Power (SWaP) of user’s receiver, clock, and 
processing requirements for time transfer in the same way GNSS receivers are 
small and ubiquitous on Earth [5]. The positive outcome to achieve safe navigation 
based on realized LTC can not be overstated.
 

Details

ProgramEarly Career Initiative (ECI)
Start date2026-04-01
End date2027-09-30

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How to get involved

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