X-63A, X-64A

[Andreas Parsch]

When the X-65A designation was announced by DARPA in May last year, X-plane enthusiasts had asked themselves what happened to X-63 and X-64 (the last published X-designation before 65 had been the X-62A "VISTA"). Well, you no longer need to ask .

AFRL has a research program for aerospike engines, called ARISE (Aerospike Rocket Integration and Suborbital Experiment), and is funding demonstrator rockets by two contractors - Invocon and ABL Space Systems. These demonstrators have been designated X-63A (ABL Space Systems) and X-64A (Invocon).

Sources:
- AFRL’s Rocket Lab Past, Present and Future
- DOD MDS records, delivered to me yesterday - unfortunately incomplete (I try to work with the FOIA office on that), but "good enough" in the X-63/64 case

 

[Stargazer]

Thanks a lot, Andreas! So, if we consider that "X-58" was skipped because of the Kratos XQ-58A Valkyrie, that leaves now only the X-52 slot missing from the list, right?

 

[Andreas Parsch]

Thanks a lot, Andreas! So, if we consider that "X-58" was skipped because of the Kratos XQ-58A Valkyrie, that leaves now only the X-52 slot missing from the list, right?

Both the XQ-58A and XQ-67A got their numbers from the X-series. Therefore, X-58 was skipped, and I think it's essentially certain, that X-67 will be skipped as well.

As for X-52, I'll just quote my own webpage :

The designation X-52A was requested in 2006 for a program to test active aeroelastic wing technology, but was disapproved because of possible confusion with the B-52 series. Instead the designation X-53A was allocated to the program.