You can get web absolute url and concatenate it with "/SitePages/Tickets.aspx".
On Client side:
<script type="text/javascript">
var YOUR_URL = _spPageContextInfo.webAbsoluteUrl + "/SitePages/Tickets.aspx";
Response.Redirect(YOUR_URL);
</script>
On Server side:
SPWeb curWeb = SPContext.Current.Web;
string YOUR_URL = curWeb.Url + "/SitePages/Tickets.aspx";
Response.Redirect(YOUR_URL);