From: Haughton-Mars Project (HMP)
Posted: Sunday, July 28, 2002
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Keith begins to drill a hole through upper ground layers with an electric drill powered by a portable generator
Keith drilling through the permafrost layer
Aircraft cable connecting the greenhouse to rebar anchors
Turnbuckle connecting aircraft cable and rebar
Keegan Boyd adds rocks to the base of the greenhouse
Keith sitting in front of the Mess Tent with Keltey (L) and Quimmiq (R)
The greenhouse and its support platform itself weigh well over two tons. All told, taking the weakest components of the new anchoring system into account, this would add well over a ton of additional 'hold down' force.
We were already rather confident in the ability of the greenhouse to stay put - even in high winds. Winds can exceed 100 kph here during the worst weather. I was standing inside the greenhouse the other day when the weather station (sample weather report) showed 70 kph winds blowing outside. You could not feel the slightest vibration in the greenhouse. Indeed, I was surprised at just how quiet it was inside given the howling wind outside.
The drill I used was flown in specially from Resolute for this task. Several day before, two geophysicists from the University of Calgary were digging pilot holes around camp in preparation for surveys they were going to do. I asked them if they'd like to dig one in back for the greenhouse so I could see where the permafrost was. After about half a meter they struck solid ice: permafrost.
Given the depth and angle of the holes I needed to drill - and the amount of frozen ground I'd drill through, I was confident that the anchors would provide adequate strength.
Drilling though the thawed soil was rather straightforward. There was no mistaking the permafrost when I hit it. At this point I needed to put my entire body weight - and all the strength I could muster to help force the drill through the remaining permafrost. After half an hour or so I was done.
Permafrost is defined as soil or rock that remains below 32F/0C for two or more years. It is formed when the ground cools sufficiently over the course of winter to produce a frozen layer that remains frozen throughout the following summer. Permafrost is defined by its composition but rather by the temperature it retains over the course of a year. Permafrost can range widely in its composition. It can contain over 30% ice or contain almost no ice at all. It can lie underneath several meters of snow or be found underneath surface areas with little or no snow.
Nearly a quarter of Earth's exposed surface has permafrost beneath. Estimates by the Geological Survey of Canada show that permafrost on Devon Island can be between 100 and 500 meters thick. While we have yet to drill on Mars, it is almost certain (based on satellite observations) that large amounts of water ice are found below the surface of Mars - as permafrost.
On Devon Island the upper half-meter or so of the surface thaws in the summer. However the frozen layer beneath serves to keep the melted water at or near the surface. As such, you need to build things differently here than you would further south. We built our greenhouse atop multiple wooden block footings placed directly on the ground so as to allow the entire structure to 'float' as the ground thaws and then freezes each year.
We went out of our way to minimize disturbances to the area immediately around the greenhouse. The upper, active layer of ground here is vulnerable to environmental damage. Tracks left by airplanes or motorized vehicles can persist for many, many years. As such, great care is taken by the HMP team to be thoughtful about where they traverse the surface. ATV trails have been established in heavily traveled areas and everyone makes certain to stay within these tracks whenever possible. If a region can be reached on foot, then every attempt is made to do so.
Marks left in the permafrost by human activity can persist for a very long time - centuries in some cases. Given the very slow pace at which life grows in this environment, and the thin grasp it has on survival in the first place - it can taken an immense period of time for life to erase these points of damage.
Contrast this with the marks made by humans on the lunar surface. Since the 1960's it has been commonly expressed that the footprints left by the Apollo astronauts will last for "a million years". This was based, no doubt, on a quick guess by someone familiar with models of micrometeoroid erosion of the lunar surface. This is the only 'weathering' process that could serve to erode these footprints. While more refined models developed since may expand or contract this value, it is certain that humanity's tracks will persist for an immense period of time.
|Quicktime panorama: Center of Base Camp 19 July 2002. 360 degree pan. R-L: Office Tent, Mess Tent, webcam, Comm Tent, Argo ATV, Tool Tent, The Fortress, Airstrip, Greenhouse, Tent City [Download]|
Unlike the human marks made in the arctic, which we'd all like to avoid making - and remove if at all possible - the marks made by humans on the Moon may, in contrast, become something we seek to preserve. Picture future lunar tourists wanting to see the Apollo 11 landing site for themselves and you can quickly imagine what steps would have to be taken to keep them from stomping all over history. Similar concerns confronted the discoverers of ancient hominid footprints found in volcanic ash in Africa.
One world's human damage is another's history.
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