Something else you can try...
When you launch from the Liberty, don't hyper immdediately to the first battle area. Funny thing about this mission...the Hurrim don't show up til about 20 seconds after you do, but the shuttle keeps moving. In other words, if you delay your hyper in, the shuttle will be much closer to it's hyper point when the Hurrim arrive and you will have a much better chance of getting it to safety. Don't delay your hyper to the second area though, the Hurrim won't wait for you there!