Pass search paramters to jqGrid via $_POST/$_GET

Question

I'm loving jqGrid, but stuck on one thing.

Am trying to send parameters to the jqGrid page via $_POST/$_GET, but not able to force the jqGrid instance to initialize with results filtered by said parameters.

Have tried hardcoding like:

jQuery("#list").jqGrid({
....
});

 //load passed search terms
 $("#list").setGridParam({url : 'https://domain.com/get_missions.php' +
     '?_search=true&nd=1277984344302&rows=10&page=1&sidx=mission_id&sord=asc' +
      '&searchField=mission_code&searchString=INTCH0023423&searchOper=cn'})
 .trigger("reloadGrid");

but no joy. The jqGrid doesn't want to refresh with the new URL.

(yes, calling and receiving pages are SSL)