@article{oai:nipr.repo.nii.ac.jp:00002220,
 author = {Zagorodnov,V.S. and Kelley,J.J. and Koci,B.R.},
 journal = {Memoirs of National Institute of Polar Research. Special issue},
 month = {Mar},
 note = {P(論文), Directional Drilling (DD) technology can be used in deep glacier boreholes to obtain additional ice cores from any depth and create supplemental boreholes for geophysical research on glacier ice properties under natural conditions. Experimental directional drilling was done using an antifreeze thermal electrical drill (ATED) in a PICO test well. A special device called a whipstock was used for the deflection of the ATED in previously-drilled borehole. The test demonstrated that a whipstock deployed in the main borehole permits directional drilling to obtain extra ice core. The experimental whipstock was placed 25cm above the bottom of the 4.5m deep borehole. The ATED was inclined in previously-prepared cavity to an angle of up to 3°. When the second borehole reached a depth of about 6m from the whipstock it had no inclination. The distance between axes of the main and secondary boreholes was about 0.3m. The whipstock was frozen into the main borehole during directional drilling experiment and afterwards, it was heated electrically and removed from the hole.},
 pages = {165--171},
 title = {Directional drilling},
 volume = {49},
 year = {1994}
}