NASA is hoping to launch its twin Grail spacecraft this morning, after a temporary delay because of poor weather.
“The countdown remains in the T-4 hold,” says NASA’s latest bulletin. “Upper level winds were reported in the ‘red’ range, so the launch team is targeting this morning’s second window at 9:16 am EDT.”
The launch of the Delta 2 rocket carrying the probes was initially scheduled for 8:37 am. Moving to this second launch window means it will head out on a 99-degree angle, a more southerly trajectory than would have been the case earlier.
The two Grail probes are designed to examine the interior of the moon and its gravitational field. They will fly in tandem orbits around the moon for several months, measuring its gravity field in great detail.
The new information should help establish possible future spacecraft landing sites, as well as improve understanding of the moon’s interior and its thermal evolution, as well as throwing light on the moon’s history of asteroid collisions.
At liftoff, the rocket’s first-stage engine and six of its nine strap-on solid rocket motors will ignite, and the rocket will rise up over the Atlantic Ocean. The remaining three rocket motors will be ignited shortly after the first six burn out.
Next, the second stage, which will provide 9,645 pounds of kick for Grail, will begin the first of two scheduled burns.
Shortly after ignition of the rocket’s second stage, the Delta’s 30-foot-long nose cone will separate and be jettisoned. It will then enter a ‘parking orbit’ at about 90 miles up.
Finally, the Delta’s second stage will begin a second burn, placing Grail on its desired trajectory to the moon. The Grail-A spacecraft will then begin its separation process from the Delta’s second stagewith the Grail-B spacecraft separating about eight minutes later.
It’ll reach the moon about three-and-a-half months later.