The best way we've found to send requests to HTTPS is this:
RewriteEngine on
RewriteCond %{HTTPS} off
RewriteRule (.*) https://%{SERVER_NAME}/$1 [R,L]
Copy and paste these lines at the top of your .htaccess file. This works for any domain/sub-domain, since Apache will replace %{SERVER_NAME} with the domain of the current request.
