The X-43C was intended to be a larger follow-on to the current X-43A Hyper-X. It was canceled a few days ago.

The review, completed last week, assessed each program for its applicability to NASA's new space exploration goals (DAILY, March 18.) The X-43C "did not fit our particular needs at this particular point for an exploration systems development program," exploration office head Rear Adm. Craig Steidle told lawmakers during a House Space and Aeronautics subcommittee hearing in Washington March 18.

The X-43C was a larger follow-on to the X-43A "Hyper-X" demonstrator, which is scheduled to make its second Mach 7 flight attempt on March 27 (DAILY, Feb. 18). The exploration office will fund the X-43A for a third flight attempt at Mach 10 if it performs well in its second flight, according to Steidle.

NASA's hypersonics efforts were part of its Next Generation Launch Technology (NGLT) program, which was inherited by Steidle's office when it was formed in January. Hypersonics work at NASA will continue, Steidle said, with NASA's Office of Aeronautics paying for procurement and the exploration office paying for other expenses.

From what I've read, if this flight is successful, there may be one more flight with the goal of reaching Mach 10. I don't know about any other planned X-43 flights.