https://www.cnet.com/news/nasa-parker-solar-probe-delays-mission-to-explore-the-sun/

The Parker Solar Probe was scheduled to blast off atop a United Launch Alliance Delta IV Heavy rocket from Florida's Kennedy Space Center in the early hours of Saturday morning.

But as the rocket waited on the launchpad, the countdown was frozen twice and the launch delayed for over 45 minutes. As a result, the mission missed its planned launch window. The plan is to try again in 24 hours.