A Versatile Rock Melting System For the Formation ... - The Black Vault

following critical paths or intersectingsmall targets.B. Development of Attitude-Control SensorsSeveral approaches to the developmentof sensors, deviation indicators, and alignment-controlsystems are being investigated.The deviation indicator (01) shown conceptuallyin Fig. 19will flash a light onthe control console to alert tbe operatorthat the hole-forming assembly has deviateda predetermined amount in a given quadrant(viewed from the stem-advancer end).Thesignal is generated when the cantileveredsection of the inner tube is contacted bythe outer housing after a predetermined deflection.This approach is similar to thatof a simple torque—trench indicator.The development of a deviation sensor(DS) can choose among several possibilities:• Laser optical systems are currentlyin use for aligning tunnel-boring machines;however, although the HFA will probably deviatemore than one diameter in a guidancecontrolcycle and although the use of alaser is therefore questionable, these systemswill be reviewed for possible adaptationof the HFA.• Inertial guidance systems are widelyused for navigation and attitude-controlsystems.These systems will also be reviewed.• Gyrostabilizers are extensivelyused for navigation, attitude control, and9-11bore-hole surveying.They will be reviewedfor possible applicati n for inclusionin the HFA.A preliminary review indicatesthat hole size and length of timeto melt a hole may restrict their use toattitude and directional control.• Surface triangulation of a seismicsource in the HFA may be a method to determinehole deviation.Results to datehave not been promising, but a state-of-theartreview should reveal whether sufficientprogress has been made to accurately trackan HFA.• Triaxial dc magnetometers are inuse for attitude-sensing and navigation.In one current application the deviceis following the path of a directionaldrilling tool and signals any deviationsof a bore hole in conventional oil, gas,and water drilling, or in guiding thedrilling of life-support holes to trappedminers. A review of this system will determineits adaptability for HFA use.C. Examples of Deviation SensorsTwo possibilities discussed above areused to illustrate the sensor section ofthe HFA, the surface display, and the operator'suse of the display to initiatecorrective action (see Figs. 19, 20, and 21)An open-loop sensing and control system isconsidered adequate for the length of holespecified in Section III.The relatively simple deviation indicatorshown in Fig. 19 can alert theoperator if the HFA is deviating in a givenquadrant. A section of the inner tube isbuilt as an independent cantilever beam byusing a flexible bellows connection. Fourcontacts are placed around the inner tubewith a small initial standoff clearancefrom the tube. Deflection of the outerhousing, forced by hole deviation, willcause contact between the inner tube andone of the four contacts. Closing of thecontact will light up a corresponding signalon the control console. Correctiveaction can then be initiated either by rotatingthe advancing stem to equalize mechanicalalignment, or by using an alignment-controlsection in the HFA. Physicalorientation of the advancing stem is maintainedby aligning and clamping fiducialprotractors that are attached to the stemsection at the stem advancer.A triaxial magnetometer sensor candetect rotation of its axes relative to aninitial ori'entation. Figure 20 showsschematically the use of a triaxial magnetometeras the deviation sensor for a13