7th ESA Workshop on Advanced Space Technologies for Robotics and Automation 'ASTRA 2002' ESTEC, Noordwijk, The Netherlands, November 19-21, 2002

Transcription

1 µ'hh'ul GULOOWRROSURWRW\SHDQGGULOOLQJV\VWHP GHYHORSPHQWIRU0DUVVRLOVDPSOLQJDSSOLFDWLRQV (5H3*0DJQDQL7<OLNRUSL *&KHUXELQL 7HFQRVSD]LR6S$ 9LD0RQWHIHOWUR0LODQR0,,WDO\ (PDLOHUH#WHFQRVSD]LRLW *DOLOHR$YLRQLFD6S$ $2OLYLHUL 9LD$(LQVWHLQ&DPSL%LVHQ]LR),,WDO\ (PDLOJLRYDQQLFKHUXELQL#RIILFLQHJDOLOHRILQPHFFDQLFDLW,WDOLDQ6SDFH$JHQF\ /RFDOLWj7HUOHFFKLD0DWHUD07,WDO\ (PDLODQJHORROLYLHUL#DVLLW,1752'8&7,21 The DeeDri program is funded by the Italian Space Agency (ASI) for the NASA Mars Exploration Mission. Within this program a core sampler mechanism is foreseen to collect Mars surface and subsurface soil samples and release them to the scientific instruments or storage system on the planetary landing vehicle. Tecnospazio and Galileo Avionica have developed a prototype of the core sampler mechanism. This prototype, and the associated testing, will allow important verifications to support both a final core sampler design as well as system configuration aspects. The drilling tool prototype consists of a hollow steel tube equipped with an auger thread on outer surface and a drill tip at the lower end. The tool drills a hole 35-mm in diameter and its central part (piston) can be withdrawn so to form a volume to allow sample core to be collected inside this opening. The core sample collected is approximately 14-mm in diameter and 25-mm in length. The mechanism allows collecting not only core samples but also powder-like samples. The tool diameter can be scaled down to allow drilling and sampling functionality with a lower demand of power and force/torque actions. Parallel to the prototype tool development a design work is done in Tecnospazio, following the drill system requirements discussion undergoing in NASA, to develop complete drilling systems for Mars application. The Single- Rod design is a low-mass (7-kg) system with one single tool capable to reach 1-meter depth. The system includes extensive instrumentation to collect information during drilling process, and several electrical and optical lines are fedthrough down into the drill rod for down-hole science and instrumentation, as well as to operate an active sample collecting device included into the drill tool. Structural design of the Single-Rod design reflects the experience Tecnospazio has gained during development of the SD2-drill for the Rosetta-mission. The Multi-Rod design is a more complex extendible drill with 10 pieces of drill rods. One or more of the rods can be replaced with a specific drill tool. Different variants of Multi-Rod design have been evaluated, each allowing a specific penetration depth with an overall envelope range form 2 to 5 meter. In the next of the article a specific solution for 2.5 meter is shown. '5,//6<67(0&21),*85$7,216 Two different DeeDri system conceptual designs are presented: œ A Single-Rod -design suitable for 1-meter depth œ A Multi-Rod -design suitable for 2.5-meter depth Both concepts make use of a special drill and sampling tool developed on purpose for Mars drill; as pointed out in the introduction a prototype of this tool has been manufactured and tested with different materials. The Multi-Rod design makes use of a specifically developed drill pipe coupling concept based on thread, like the couplings of most of the conventional fully automatic rock drilling machines. Among several different connecting schemes the thread turned out to be most reliable with least risk for unintended release of the rod or failure to couple. 1

2 The threaded coupling can not be accidentally opened (in which case the complete drill string might be lost) by pulling, pushing or clock-wise twisting, or by any combination of these. However, autonomous release of the coupling during counter-clockwise rotation presents a naturally built-in safety mechanism that allows release of the drill rod in case it should get stuck in soil. The coupling is equipped with an electrical feed-through for 10 lines to facilitate active drilltool operations and other down-hole instrumentation. Both concepts include a slip ring assembly (10 to 15 lines depending on concept) and a flex-cable assembly to transfer power and data between s/c and possible drill tool instrumentation. In addition the systems provide means to measure drill thrust, drilling torque and drill depth, and also means to support the moving parts during s/c launch. Components selected for the concepts design are either known to readily be available space-qualified ( connectors, motors, resolvers) or are commercial high-quality products available on the shelf (slip ring assembly, force sensors, bearings) which can be considered applicable for space application with specific adjustments. 6LQJOH5RG'HVLJQ This design aims for high reliability and low mass by using one single drill tool without any disposable or interchangeable components. The single-rod design drilling a hole 25-mm in diameter up to 1- m depth has dimensions 1251-mm x 220-mm x 155-mm, and it weighs 7322 grams (3D-model calculated mass without margin), including an active motor operated sample collection tool inside the drill rod, but excluding screws and nuts, external cabling, positioning mechanism and control electronics. The collected sample is to be ejected for separate sample storage or sample processing system on S/C-platform, after which sampling procedure can be repeated thus allowing multiple sampling in several desired locations or varying depths.) In addition to electrical feed-through the system includes also an optical rotary feed-through (2 lines) for optical data transfer between drill tool and spacecraft. Fig. 1. The Single-Rod drill (1-m depth). Complete redundancy of the system may be achieved by duplicating complete drill assembly. 2

3 0XOWL5RG'HVLJQ The Multi-Rod design aims for a reduced system height that would fit inside a more restricted volume on a small-sized planetary exploration vehicle. Fig. 2. Multi-rod drill (2.5-meter depth). The drill rod is divided into up to ten separate drill pipes that are stored on a carousel inside the drilling system. The system provides some versatility since some of the drill pipes may be replaced with additional drill tools having perhaps different designs for different sampling operations. Introduction of a carousel and drill string extending/retrieval-system adds, however, quite many separate functions and increases overall complexity and weight of the system. The multi-rod design presented aims to drill into depth of 2.5 meters with a drill string consisting of ten drill pipes 23-mm in diameter. The current design is sized 540-mm x 175-mm x 175-mm weighing about 8300 grams (3D-model calculated mass without margin, excluding external cabling, positioning mechanism and control electronics. Penetration depth of 3 m can be achieved by making the system 5-cm higher (with some mass increase). Instead, for a reduced 1-meter drilling depth height of the system can be reduced to 390-mm which reduces system mass roughly 400 grams. Components selected for the design are commercial high-quality products available off-the-shelf. Preliminary motor and gearbox selection is based on selecting a large motor and gearbox to guarantee sufficient performance margin. Further analyses in detailed design phase may reveal that smaller motors and gearboxes may be sufficient, and total envelope and mass may be reduced. '5,//722/352727<3($1'7(675(68/76 The baseline tool schematics is shown in Fig. 3. It includes: œ main tube with external auger, provided with cutting bits; œ central piston, rotating together with the external auger; it can be uplifted upon command so to create a volume available for sample housing; it is also provided with cutting bits; œ shutters (or a single shutter), which can be activated upon command and have (has) the purpose to both detach the root of the sample from the soil and contain the sample (either solid or powder). The shutter(s) can be activated only when the central piston is uplifted and a sample (e.g. core) is contained in the dedicated volume; œ actuator(s), to move the central piston and the shutters. Acquisit. Chamber Central Piston Shutters Actuator Central Piston Actuator Auger Shutters Drill Bit Acquired Sample Fig. 3. Drill tool schematics (with 2 shutters). The tool drills holes 35-mm in diameter and 250 mm depth and the core sample collected is 14 mm in diameter and 25 mm in length. 3

4 In the following figure 4 some views of the Core Sampler mechanism are given: the first two images give the overall view before the insertion of the mechanism inside the auger. The third image (bottom right) shows the tip retracted in coring configuration, herein, as well as in the following, a 1 FRLQLVVKRZQWRJLYHGLPHQVLRQDOUHIHUHQFHV7KHIRXUWK one (bottom left) shows the bucket in closed position, after the sampling phase. Fig. 4. Detail images of the sampling tool. 'ULOO7LS The drill tip is constituted by two parts, a central piston and an outer tip, both equipped with polycrystalline diamond cutting bits. The central piston of the tool can be withdrawn inside the tool in order to form a volume to allow sample core to be collected inside this opening. Fig.5. The outer tip with 4 polycrystalline bits and a complete drill tip The central piston tip is equipped by a hard-alloy central spike, that is essential to initiate the hole when drilling is started 4

5 'ULOO7RRO2SHUDWLRQ To describe the sequence of operations of the drill tool, reference is made to Fig The sequence starts as shown in sketch 1, with the drill tool in a normal drilling configuration, i.e. the central piston is in drill position and the shutters are (necessarily) open; 2. In order to start a sample acquisition, the drill tool is arranged as in sketch 2: the central piston is uplifted and the shutters are still open; 3. The drilling action is then continued to perform actual coring till filling of the sample volume, as shown in sketch 3; 4. The shutters are then commanded to close, while the drill tool still rotates, so that a core sample is detached from the soil and fully encapsulated in its container, as shown in sketch 4; 5. The drill tool leaves the bore hole and brings the collected sample, as in sketch 5 6. Finally, the sample is discharged into the container, sketch 6. The system can collect samples starting just below the surface up to the maximum depth that depends on the drill tool length. The collected samples can either be directly discharged into the ports of scientific instruments for in situ analysis or, if required, stored in dedicated sample containers, for example mounted on carousels (these not included in DeeDri Single-Rod or Multi-Rod designs presented in previous section). Drilling to reach Sampling Depth Central Piston in upper position Core Forming Core Cutting (closing Shutters) Drill uplift 6 Sample Discharge Fig. 6. Sample collection and discharge sequence. 7HVW(TXLSPHQW The test equipment, illustrated in fig.7, was an especially for purpose developed drilling system that provides axial thrust and guidance and drill rotation. The system includes a slip-ring assembly to transfer 12 power and signal lines from control system to the drill tool under testing. The following table describes system diagnostics capabilities. 7KHRXWSXWLQIRUPDWLRQWKDWWKHPDFKLQHSURYLGHVLQFOXGHV,QDGGLWLRQWKHPDFKLQHSURYLGHVDELOLW\WR œ Drill motor voltage œ Drill motor current œ Drill motor encoder signal frequency (with external measuring device) œ Thrust motor voltage œ Thrust motor current œ Thrust motor encoder signal frequency (with external measuring device) œ Axial location of the drill (i.e. drilling depth) œ Thrust load with a load cell located under the sample. Table 1. Test system diagnostics capabilities œ Feed power to tool motor (with external power source) œ Read input current for tool motor (with external measuring device) œ Read and indicate state of the limit-switches on tool 5

6 Fig. 7, Test equipment The drilling and sample collecting tests were carried into several materials: Sand, Gas Concrete, Tuff and Travertine. The table below presents the averaged test results and describes performance of this sampling tool prototype, and some collected samples are shown in the following photographs of fig.8. 3URSHUW\ 6DQG *DVFRQFUHWH 7XII 7UDYHUWLQH Material density (g/cm^3) Drill Thrust (kgf) Drill Torque (Nm) Drill RPM Drill Feed Rate (mm/min.) 'ULOOLQWDNHSRZHU: Table 2. Drill tool performance in different materials. 6

7 Sand Gas concrete Tuff Travertine Fig. 8. Some collected samples. 6SHFLILF'ULOOLQJ3RZHU Some detailed results of the test done into Travertine are collected in the following graphs in figures 10 and 11. In order to determine cutting efficiency with respect to different speed of rotation or thrust, a variable called Specific Drilling Power (SDP) [W/(mm/min.)] was defined. SDP indicates how much power [W] is needed to achieve a corresponding speed of penetration [mm/min.]. Naturally SDP depends on properties of material being drilled into, drill bit geometry, drill rotation speed, drill axial thrust and drilling method (rotary, percussive or rotary-percussive). In these tests material, drill bit and drilling method were kept unchanged, and effect of drill rotation speed and thrust force on energy efficiency was being studied. The test was repeated also for other materials. With given drill rotation speed a higher thrust gives higher efficiency, or smaller Specific Drilling Power in terms of power intake vs. speed of penetration. Energy needed to make a hole depends on grain size developed. Energy used to separate a single grain derives from material shear strength and the surface area that connects the grain to base material. In rotary drilling material is removed in fine powder where size of grains is very small, and overall grain surface area is high leading to high energy consumption. With a higher thrust bigger cuttings are removed from the material, which gives better energy efficiency. Increase of rotation speed tends to decrease size of the cuttings (i.e. lower energy efficiency) unless thrust is increased accordingly. &21&/86,21 The prototype design and testing activities so far performed pointed out good performances compatible with the constraints of a landing mission on Mars. A full verification of a possible drill system for Mars requires further design, prototyping and testing activity in order to cover all involved issues like reliability of multi-rod mounting/dismounting operation, wear of drill tool under prolonged drilling operations, and behavior of long tools in heterogeneous subsurface. Tecnospazio is presently performing an activity on behalf of ASI aiming at an extensive design and verification of the drilling system leading to a complete and successful feasibility demonstration. 7

8 ' " &!# %$ $ # "! H IC GB FE E D 45,00 40,00. $ - * *)+,,, ( 35,00 30,00 25,00 20,00 0,00 0,20 0,40 0,60 0,80 1,00 1,20 1, Fig. 9. Specific drilling power with respect to feed rate at 5 different drill rotation speed OO EN JM L M M LKJ ABCD / : ;6< 3= >@? X Y65 Z S : [ 015 \ 37 S]R367 96^`_ ;65 7 3RU2`Y67 Q 3`T : ;6< 3`7 Sà : 015 3RU b P 5 7 Q QR5 0 : ; : 7 019S6T 3 3RU= V /8W4? Fig. 10 Specific drilling power with respect to input power at 5 different drill rotation speed in Travertine. 8