how can I write a whitespace into a MASTER_SITE_SUBDIR?

[wen heping]

Hi, all:

  How can I write a whitespace into a MASTER_SITE_SUBDIR?
  Because a package's fetch address is something like:
     http://....../atutor 1.6.3/atutor-1.6.3.tar.gz

  Thanks at advance.

wen