Friday saw our final EVA. The ultimate challenge for everybody involved and a culmination of all the hard work and learning of the past two weeks.

The wireless network was pushed to the limit: the chosen site was over 3 miles from the Hab and was situated within a narrow canyon (Lith Canyon) often more than 30 ft deep. The weather was very hot so as astronauts we were also being physically pushed in the difficult conditions, but I must say the fans and water provided by the backpack was wonderful relief.

The two of us started above the canyon using the voice recognition system to "track (our) location every 60 seconds". This sent a message back to our 'Personal Agents' so that our GPS co-ordinates were monitored each minute. From this point on we were limited to less than 2 hours for our EVA which made it seem more realistic as on Mars, astronauts would have time constraints based on things such as the amount of oxygen that would be available to them.

The first site looked to be covered with wood chips to start with and I was able to create a name for this location. This would provide a useful tool for a geologist so that they could name a location based on some morphology that reminded them of something and this would aid recollection of a site greatly. Brent took a photo or two of the area and was able to use speech recognition to have the images downloaded from his camera and ftp'd to the Hab - very impressive on our wireless network. I was able to create voice notes and a sample bag and associate them with each other and the location name I had created.

We faced a few problems on entering the canyon as not everywhere received a radio signal. This meant that we could use a number of functions (i.e. create sample bag/ voice note etc.) but they were stored on the minibooks in our backpacks until we were within reach of the signal. This made the functionality a little difficult but we still go the chance to see some interesting sedimentary units within the canyon. The top half of the 30-40 ft head of the canyon contained very noticeable lenses of sandstones and conglomerates. The conglomerates graded normally from coarser clasts at the base of the lenses. These features are typical (on Earth) of relatively high energy, wandering, river channels. Beneath these units, finer grained material (silts and muds) was found, again with the red coloration typical of this area. The finer sediments indicate lower energy waters (higher sea level perhaps, marine environment) and these were the older beds so the cliff section shows that there was a progressive decrease in sea-level and a change from more marine to fluvial environments.

We started to move further down the canyon and I tried to get a drink of water but in rearranging my backpack, my water carrier had been placed in a way so as to stop the flow of water, so Brent had to come to my rescue and unfasten it. This shows a strong dependence on your field partner that would be necessary in a true Mars EVA.

Next we found more conglomerate beneath the muds and silts and took more notes, sample bags and images. The systems that are in place for us to use at the moment have been designed with geologists in mind and as such are adapted to our way of thinking in the field and the methods by which we collect our data. For example, we can list the locations, voice notes and sample bags we have created and we can replay voice notes so at a later time these can be associated with a specific sample or location.

After the conglomerate we hit a dead end, or at least it was for us as astronauts. We came upon a bench in the rock about 1 m above the next part of the canyon floor. Without suits this would likely have not caused a problem but movement is very restricted within the suits and we were carrying heavy and expensive equipment! Another point of note is that from the aerial images we had looked at prior to going to that field site, we had no idea that such an obstacle existed. This illustrates how an EVA has to be adaptable at short notice, I feel.