Review of: "A Robotic Subsurface Explorer" JPL, Brian Wilcox, PI Reviewed by: Dimitrios Apostol.opoulos ------------ Objectives & Justification Summary: ----------------------------------- Develop a device which can maneuver in the regolith of planetary bodies, penetrating sub-meter to tens of meters depending on soil properties, and making in-situ measurements of soils. The subsurface composition of planetary bodies (focus: Mars) is of great scientific interest. Of special importance is the possible search for fossil life in lakebeds on Mars. Approach & Technical Presentation of the Concept: ------------------------------------------------- Short vehicle description: Thin wall outer tube is pushed through the soil by means of two auger bits, one in the front and one in the back. The self-tapping- screw-type front auger will engage the soil ahead of the vehicle, loosen the material and push it in an annular cavity between the outer wall and the cylindrical payload volume. The counter-rotating rear auger will recompact the soil and provide thrust to the front auger to continue "drilling". Piezoelectrically actuated flap-type vanes in front of the vehicle enable steering. A thin two-wire and fiber optic tether which is paid out from the vehicle provide communication with the lander. EM and ultrasonic sensors detect rock inclusions ahead of the explorer. Scientific payload includes Raman and mass spectroscopy, analytical chemistry, and micro-imaging instruments. This is a 5 kg-class vehicle. They have estimated power for probing into plaster to be 5 Watts (used a 13/16" auger bit, @ 40 RPM, and 0.012"/sec feed-rate). Power will be transmitted via high-voltage, thin gauge wires. Serial communication at 9600 baud. (Proposal goes into a lengthy conversation on the selected science instruments and measuring methods). Logistics & Milestones: ----------------------- FY97: stand-alone augers, external tubes, tether spool; torque measurements to control vehicle heading; develop or/and calibrate instruments FY98: testing of vehicle navigation and hazard avoidance; implement Raman spectroscopy; rework systems FY99: Testing in non-homogeneous soils; rework systems FY00: Implement mass spectroscopy; performance evaluation leading to flight version. Budget: $400K/FY97, $500K/FY98, $500K/FY99, $500K/FY00 Total: $1.9M 4 YEARS My comments: ------------ 0. "Exotic" concept. Authors underestimate challenges of subsurface tethered, screw-type locomotion. No immediate need for such vehicle. Focus should be placed on capable planetary surface vehicles, with appropriate subsurface sensing (contact or non- contact). Why not use mini-penetrometers that were so successful during the Apollo era? If the argument is depth, I do not think that their 5 kg-tethered vehicle can "drill" more than 1/2 meter! I would NOT vote for this proposal. more: 1. The program objective is clear and well supported throughout the proposal. They propose a very challenging task. It appears that they have done some work on vehicle configuration, and even more work on instrument selection. 2. Program justification is weak. This is not a high priority technology for NASA division with tight budget. Throughout the proposal they allude to conversations with Code S people, such as Pete Ulrich, who appear to be supportive of the idea. 3. Experiments with a single auger bit do not mean much. Controlled soil displacement could only be appreciated by building a model of the vehicle. Also, what happens to the tether which is subjected to higher and higher tension as the vehicle maneuvers in the subsurface? 4. Milestones and budget do not make sense. Vehicle design and most of development and testing happen during the first year, but the budget is the lowest. To do such a project it will cost at least three times more of what they are asking. 5. Dual-use potential is limited. This is a highly specialized vehicle-tool and I do not see how much can be done with a 5 kg in relevant coring/drilling applications. Scaling such a concept is a non-linear process...