What Time is it in Space?

In terrestrial affairs, time is a well-understood construct: it structures our daily routines, underpins global financial systems, and governs legal deadlines and obligations. However, once we leave the Earth, the concept of time becomes far more complex — both scientifically and legally. As space activities increase, the question “What time is it in space?” is no longer merely philosophical. It is a growing operational, legal, and regulatory challenge.

This article examines the multifaceted nature of timekeeping in outer space, particularly as it intersects with space law, international coordination, and emerging policy debates at the European, transatlantic, and global levels.

1. Coordinated Universal Time (UTC): The Current Reference Standard

Despite the relativistic nature of time in physics, human spaceflight to date has required standardized coordination — primarily through Coordinated Universal Time (UTC). The International Space Station (ISS), for instance, uses UTC as its official time reference. This was adopted by consensus between the major space agencies involved — notably NASA, Roscosmos, ESA, JAXA, and CSA — to enable unified scheduling between the various control centers involved.

From a legal standpoint, this reliance on UTC aligns with current practices under the Outer Space Treaty (1967), which calls for international cooperation and mutual assistance (Art. IX). However, UTC’s Earth-based nature raises questions when extended to interplanetary missions or permanent off-Earth settlements.

2. Planetary Timekeeping: Mars and the “Sol Problem”

The divergence between planetary rotations introduces operational challenges for missions to other celestial bodies. A day on Mars, known as “sol” on Mars, is approximately 24 hours and 39 minutes long, and has forced NASA and other space agencies to adapt. Mission teams working with Martian rovers such as Curiosity and Perseverance have operated on “Mars Time,” shifting their circadian rhythms to follow Martian sols for synchronization.

Although informal timekeeping systems exist, such as the Mars Sol Date (MSD) or the Local True Solar Time (LST), which is determined by the sun's position, there is no recognized international time standard for Mars. Notably, discussions have begun within scientific and legal communities regarding the need for standardized planetary timekeeping frameworks. These are expected to grow in importance as plans for crewed Martian missions under the NASA Mars Exploration Program progress.

3. Lunar Time and the ESA Proposal

A more immediate challenge concerns the Moon. With NASA's Artemis Program and the Artemis Accords envisioning a sustained human presence on the lunar surface and in cislunar space, time synchronization has emerged as a pressing operational and legal issue.

In early 2023, the European Space Agency (ESA) called for the development of a unified lunar time reference, following proposals made during ESA’s Moonlight initiative — a project aimed at establishing a dedicated lunar satellite navigation and communication infrastructure.

ESA engineers noted that clocks on the Moon tick slightly faster than on Earth, gaining roughly 56 microseconds per Earth day due to the Moon’s lower gravity. While this discrepancy may seem negligible, it has significant implications for autonomous operations, scientific experiments, and GNSS-based lunar navigation.

In response, ESA has proposed the establishment of a "common lunar reference time ", later named Coordinated Lunar Time (LTC). This proposal is under discussion with NASA, JAXA, and other Artemis signatories but has not yet been formalized under international law.

4. U.S. Legislative Initiative: The Celestial Time Standardization Act

In parallel to ESA’s proposals, the United States has also recognized the strategic importance of space-based timekeeping. In March 2025, a bipartisan legislative initiative was introduced in the U.S. House of Representatives: the Celestial Time Standardization Act (H.R. 2313). This bill mandates NASA to develop a standardized timekeeping system to support operations and infrastructure on and around the Moon and other celestial bodies.

The draft legislation notes the need for precise and consistent timekeeping to enable future lunar missions, deep-space navigation, and autonomous spacecraft operations. It also reflects the growing interdependence of legal, operational, and technological systems in space. If adopted, it would signal a major policy shift toward the institutionalization of off-Earth time standards within U.S. federal law — and possibly set a precedent for other national space agencies.

This legal development underscores the urgency of creating harmonized international approaches to timekeeping, especially given the increasing convergence of governmental and commercial activities in the cislunar domain around the globe.

5. Legal Considerations and the Need for a Regulatory Framework

The need for standardized timekeeping extends beyond technical and operational requirements. It carries profound legal implications, particularly in the context of:

Contractual obligations: Time coordination is essential in satellite operations, space services delivery, and launch scheduling.
Liability attribution: Under the Liability Convention (1972) and Registration Convention (1976), identifying the precise timing of incidents may affect legal jurisdiction and state responsibility.
Dispute resolution: Timestamping can be critical in litigation/arbitration and legal claims, especially with increasing private-sector participation in space disputes.

Despite these needs, international space law currently does not offer explicit guidance on time standards for outer space activities. Scholars have begun to advocate for multilateral coordination via forums such as the United Nations Committee on the Peaceful Uses of Outer Space (UNCOPUOS).

At the European level, the growing focus on satellite-based services (e.g., Galileo, IRIS²) and the emerging EU Space Act provide a valuable context for addressing time standardization as part of broader Space Traffic Management (STM) and situational awareness frameworks.

It remains to be seen whether the US draft bill (see point 4 above) or European initiatives, will gain momentum and whether NASA and ESA, joined by other space agencies, will jointly agree on a coordinated lunar time. As Dr. Ben Ashman, navigation lead for lunar relay development, part of NASA’s SCaN program, stated:

A shared definition of time is an important part of safe, resilient, and sustainable operations.

6. The Role of Time in Space Traffic Management

Timekeeping is a core enabler of Space Traffic Management (STM). Precise time coordination supports collision avoidance, orbital maneuver planning, and real-time data exchange between spacecraft and ground stations. As STM frameworks develop globally, time synchronization is becoming increasingly recognized as a foundational element.

The European Commission seems to acknowledge the role of time in ensuring interoperability and safety among actors in orbit as part of the EU's Space Traffic Management. For tracking space assets reliably and managing space traffic in different orbits, a coordinated time would be beneficial. Harmonized timekeeping systems — across jurisdictions, platforms, and organizations — will be essential for both national security and commercial operations.

Conclusion: Towards a Universal Time for the Universe?

As humanity transitions from occasional exploration to permanent presence in outer space, the need for standardized, legally recognized time references is becoming urgent. Whether on the Moon, Mars, or in deep space, time is more than a technical abstraction — it is a key pillar of governance, safety, and law.

Initiatives like ESA’s Lunar Coordinated Time and the U.S. Celestial Time Standardization Act suggest that national and international actors are beginning to converge on the importance of this issue. Future multilateral frameworks will need to account for both scientific precision and legal interoperability.

Time in space is a technical, operational, and legal need — and the time to regulate it on a global level is now.