This gem requires NAIF's CSPICE toolkit. This can be downloaded from:

To compile, you will need to go into the cspice/lib directory and copy cspice.a to libcspice.a so that gcc can find it. Then you will need to pass to extconf the flag --with-cspice-dir=/path/to/cspice

Using the gem command, this might look like:

gem install --local naif-spice.gem -- --with-spice-dir=/path/to/cspice

The CSPICE library is statically linked. It doesn't matter where you unarchive it for compiling.