Strong winds in the upper atmosphere forced NASA to scrub Thursday’s planned launch of its newest moon mission. The Gravity Recovery and Interior Laboratory is now set to lift off at 8:33 a.m. EDT or 9:12 a.m. PDT Saturday — but the weather is still not cooperating.

There’s about a 40 percent chance of favorable conditions for Saturday, the same initial forecast for Thursday, the space agency said. Upper level winds were in violation of the launch criteria and must calm down before NASA will send a rocket through them.

Grail is designed to study the gravity field and interior composition of the moon. Twin probes will fly in formation, monitoring tiny changes in the distance between then to discern the moon’s gravitational field.

They will take several months to arrive at the moon, ensuring they burn as much fuel as possible before arrival.