function createOrder()
{
    var contentRequest = $.ajax({
        url     : '/orders/create',
        method  : 'POST',
        data    : '',
        success : function( data, status, xhr )
        {
            // Detect the header change in 'create.php' here,
            // perhaps update the history/current url.
        }
};

<?php
$NewOrder = Order::CreateNew();

header("Location: /orders/edit?orderID=$NewOrder->ID");
?>