The Artemis II crew is expected to briefly go silent once they pass the midpoint of their 10-day voyage.
Astronauts Reid Wiseman, Victor Glover, Christina Koch and Jeremy Hansen began their lunar flyby mission on Wednesday (April 1) and are scheduled to splash down back on Earth on Friday (April 10).
So far, the flight has stayed on track. The upcoming phase will take them to a historic milestone, with the crew set to travel farther from Earth than any humans have ever gone as Orion closes in on the Moon.
But one moment of the journey will be particularly tense: a roughly 40-minute stretch when the Moon itself blocks the radio links used by NASA’s Deep Space Network. During that window, the spacecraft and mission control will be unable to communicate.
If a problem occurs while the capsule is hidden behind the lunar surface, the astronauts won’t be able to call Earth for assistance until the signal returns.
Speaking to the BBC, Glover previously said: “When we’re behind the moon, out of contact with everybody, let’s take that as an opportunity.
“Let’s pray, hope, send your good thoughts and feelings that we get back in contact with the crew.”
That communication blackout is expected to begin as the Orion capsule slips behind the Moon at about 6.47pm ET (11.47pm UK time).
While out of contact, the crew will be at their closest point to the lunar surface and will use the time to log observations. However, visibility is limited inside the capsule, so only two astronauts can watch at once.
The trajectory depends on the Moon’s gravity to swing Orion back toward Earth. Mission teams anticipate signal and voice contact will be restored at around 7.27pm ET (00.27 UK time).
At a briefing on Sunday (April 5), Artemis II ascent flight director Judd Frieling emphasized that the temporary blackout does not mean the craft is drifting without command.
“We absolutely know physics is going to take them back to us,” he declared.
In total, the flight is a 685,000-mile round-trip and represents humanity’s first crewed journey to the Moon in more than 50 years, since Apollo 13 in 1970.
Apollo 13 reached 248,655 miles from Earth, while Artemis II is projected to top out at about 252,757 miles.
The most hazardous portion is expected during the return home, when Orion will hit Earth’s atmosphere and endure temperatures as high as 3,000°F.
Once the capsule slows sufficiently, parachutes will open for the final descent. The crew is set to land in the Pacific Ocean off San Diego, where NASA and the US Navy will recover the spacecraft and astronauts.