Spring 2009

IFD Was the Answer for IceCube at the South Pole

Photo of Independent Frin Drill
The IFD assembled and ready to be moved to a site for drilling through the firn layer.

As the semi trailer pulled out of the PSL parking lot loaded with its cargo of  South Pole Icecube drilling equipment, no one knew just how important that cargo would turn out to be.  A bit behind schedule on November 28, 2006, the equipment still arrived at the Pole in plenty of time to make an impact on the 2006-07 drilling season.  The new Independent Firn Drill (IFD) was the reason for the big impact.

When the IFD arrived at the Pole around New Years Day 2007, the drilling season was well under way.  Up to that time, the first step after setting up the Icecube Enhanced Hot Water Drill (EHWD) at a new hole site was to melt a hole through the firn layer on top of the glacier.  The drill head and nozzle for drilling the deep ice did not work in the top firn layer which is porous compressed snow 40 m deep.  A special firn drill head was used but it sprayed and lost a lot of water into the snow using up a lot of liquid water and wasting the energy used to heat the water to try to melt through the firn.  Not a good idea when the only energy source is aviation fuel flown to the Pole from 850 miles away.  To conserve that water a totally different type of water-conserving drill head had to be used.  Changing from one drill head to the other, along with all the associated water recovery equipment, was very labor and time intensive. The IFD changed all that.

Now the drilling tower is positioned over a pre-drilled firn hole.  This has substantially reduced the time from tower set up to the start of deep ice drilling.  Other drilling improvements increased the number of holes drilled in the first IFD season from 8 to 13.  The drilling cycle was shortened enough with the IFD that the crew drilled 18 holes in ‘07-’08 and 19 holes in ’08-’09.

The IFD has precipitated this increase in deep hole drilling while requiring a minimum of labor.  For most of a firn hole drilling cycle, only one person is needed to operate the drill.  During a portion of that time, even that one person can be away from the drill for perhaps as much as an hour at a time while only periodic checks of drilling depth progress are monitored.  Moving the IFD from hole to hole takes two or three persons but can be done in as little as 30 minutes.  The IFD uses its own tank to store the Glycol/water mix that it uses as a drilling fluid. The fluid is continually pumped through the tank, hoses, and drill head and none is lost into the snow.  The heating is done with five, 30,000 Watt electric heating elements.  The 480 volt 3-phase power that the elements use is normally supplied by a generator separate from the ones that power the rest of the requirements at the Seasonal Equipment Site.  This allows firn drilling at locations far removed from other power sources.

Photo of PSL engineer Lee Greenler in the Independent Firn Drill
Mechanical Engineer Lee Greenler sitting inside IFD control booth monitoring drilling of firn hole.

The IFD allows the firn hole to be drilled in parallel with the deep hole drilling.  This has cut about 12 hours off the time. In addition to Lee Greenler’s fine design work, this year mechanical engineer Ken Kriesel did some work to improve reliability and instrument maker Darrell Hamilton implemented those changes at the Pole.

This last season a careful comparison was done between the calculated lifetime of an EHWD hole and the measured lifetime. The calculated shape of the hole versus time after drilling was done with a mathematical model created by Lee. The actual shape was determined by a device called a “hole logger” that could measure the size of the hole over its depth at several time intervals after drilling.  The two agreed quite well giving the drillers the confidence to drill smaller holes that had a smaller margin of error in freeze back rate. This saved enough fuel that it was possible to drill three additional holes, a total of 19, within the original allocated fuel budget.

Another major engineering improvement in the EHWD performance has been its reliability. Dan Wahl was involved in adding electrical slip rings to the reels that supply power to down hole pumps. Jeff Cherwinka worked on generator fuel supply, pressure relief installation, over temperature control, and stand alone operation. The reliability of the fuel system was greatly improved by eliminating air in the fuel lines by using a bottom feed fuel tank. The motor for the high pressure pumps was changed from permanent magnet motor to an oversized induction motor. These changes have greatly improved reliability. It did require building new pump stands and plumbing.

The partnership between PSL and Icecube that has seen 10 PSL employees make 15 trips to the South Pole is a strong one.  The IFD is another in the successes that that cooperation has brought about.  Both groups are seldom satisfied with resting on their laurels, however, and the end of the just completed season saw Icecube personnel testing a computer operating system that would require even fewer man hours of IFD supervision and shorten firn hole drilling time as well.  Refining that system will be one of the summer focuses for Icecube and PSL as they prepare for the 2009-2010 South Pole Drilling season.

IceCube Implementation Manager Tom Hutchings recently acknowledged PSL’s support and assistance to the IceCube drilling and installation efforts, “We’ve come to depend on the outstanding engineering and technical solutions PSL provides as well as the special skills and quality of each individual assigned to work with us.”

 

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