  Front end of a CW linac of the Project X contains an H source, an RFQ, a
medium energy transport line with the beam chopper, and a SC low-beta linac
that accelerates H- from 2.5 MeV to 160 MeV. SC Single Spoke Resonators (SSR)
will be used in the linac, because Fermilab already successfully developed and
tested a SSR for beta=0.21. Two manufactured cavities achieve 2.5 times more
than design accelerating gradients. One of these cavities completely dressed,
e.g. welded to helium vessel with integrated slow and fast tuners, and tested
in CW regime. Successful tests of beta=0.21 SSR give us a confidence to use
this type of cavity for low beta (0.117) and for high-beta (0.4) as well. Both
types of these cavities are under development. In present report the basic
constrains, parameters, electromagnetic and mechanical design for all the three
SSR cavities, and first test results of beta=0.21 SSR are presented.
