Is it possible to make summary mandatory?
Short Answer

Yes, you can require the summary field be populated before it can be sumbitted.

Details

Implement hook_form_FORM_ID_alter() in a custom module.

hook_form_FORM_ID_alter(&amp;$form, &amp;$form_state, $form_id) {
   $form['body'][LANGUAGE_NONE][0]['summary']['#required'] = TRUE;
}


This assumes that you are taking the standard "body" field and requiring that it's summary be entered before submission.