NASA’s Artemis II mission, beginning April 1, will mark humanity’s return to deep space with a crewed journey around the Moon. But during this mission, there will be a phase often referred to as a “period of loss”, a moment when communication between the spacecraft and Earth temporarily breaks down. Despite the ominous name, this is a planned and well-understood part of lunar missions.

What is the “period of loss”?

The “period of loss” refers to a temporary loss of communication signal between the Orion spacecraft and Earth. This happens when the spacecraft passes behind the Moon relative to Earth, physically blocking radio signals.

NASA expects this blackout to last around 40 minutes. During this time, no voice, video, or telemetry data can be transmitted between the astronauts and mission control because the Moon itself acts as a barrier to communication signals.

This is not a malfunction or failure. It is a predictable limitation of current space communication systems, which rely on line-of-sight radio links.

Why it happens during Artemis II

Artemis II follows a lunar flyby trajectory, where the Orion spacecraft travels around the far side of the Moon before returning to Earth.

When Orion moves behind the Moon, it enters a region where Earth-based communication networks such as NASA’s Deep Space Network cannot reach it. Even with advanced systems, including experimental laser communication payloads, the fundamental issue remains the same: signals cannot pass through the Moon.

This is why every crewed lunar mission, including those during the Apollo era, experienced similar communication blackouts.

How it impacts the Artemis II mission

Operationally, the impact is significant but manageable. During the blackout:

• Mission control cannot monitor real-time spacecraft data
• Astronauts cannot communicate with Earth
• Any unexpected issue must be handled autonomously by the crew

This places a greater emphasis on crew training and onboard systems. Artemis II astronauts are trained to operate independently during this phase, relying on pre-planned procedures and automated systems.

At the same time, the spacecraft continues to function normally. Navigation, propulsion, and life-support systems operate without needing constant input from Earth.

What could happen during this phase

Several outcomes are possible during the period of loss, most of them routine:

• In the nominal scenario, nothing unusual occurs. The spacecraft completes its trajectory behind the Moon, re-emerges, and communication is restored. This is the expected outcome and the one NASA plans for.
• A second scenario involves minor anomalies. If a small issue arises, such as a system fluctuation, the crew is expected to handle it independently until communication resumes.
• A more critical scenario, while unlikely, would involve a major system issue during the blackout. In such a case, astronauts would need to rely entirely on onboard systems and training until contact is re-established. This is why Artemis II is considered a test mission, designed to validate both human and system performance in deep space conditions.

Why this phase matters

The period of loss is not just a limitation. It is also a test. Artemis II is the first crewed mission beyond low Earth orbit in over 50 years, and operating without continuous ground support is a key capability for future missions.

As NASA moves toward long-duration missions to the Moon and eventually Mars, communication delays and blackouts will become more common. Artemis II provides an opportunity to evaluate how crews and systems perform under these conditions.