NASA has banned Chinese citizens with US visas from participating in agency programs — a dramatic escalation in the space race between China and the United States. It occurs as China gears up to send a crewed mission to land and potentially establish a habitat on the moon, about which the Trump administration has expressed increasing alarm.

The new policy began September 5, and its effects have since rippled across the sprawling agency, according to two people at NASA who spoke on the condition of anonymity for fear of retribution.

The change affects hundreds of scientists and researchers, many of whom are funded by NASA to conduct their work in climate science, space and other disciplines.

It is not clear if there was a specific incident that prompted this crackdown. When CNN asked N

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