NASA revealed the Artemis II rocket experienced an "unexpected development" involving the rocket's flow of helium, which is required for launch. Subscribe to ABC News on YouTube: https://abcnews.visitlink.me/59aJ1G ABC News Digital is your daily source of breaking national and world news, exclusive interviews and 24/7 live streaming coverage. Download the ABC News app for the latest headlines and alerts: https://abcnews.go.com/devices Watch 24/7 coverage of breaking news and live events on ABC