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ROCK PUSHING AND

SAMPLING UNDER ROCKS

ON MARS
VIKING SCIENCE TEST LANDER

This full-scale model with fully operational lander camera and surface-sampler subsystems 

was installed adjacent to a large sand box representing the area in reach of the surface 

sampler. The Science Test Lander was used during the mission to develop and verify surface-sampler commands. Circular S-band radio antenna of lander is 0.76 meter across. Locations of cameras and surf ace-sampler subsystems are shown in figure 1.
Rock Pushing and 

Sampling Under Rocks 

on Mars

By H. J. MOORE, S. LIEBES, JR., D. S. CROUCH, and L. V. CLARK

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1081

Prepared on behalf of the

National Aeronautics and Space Administration

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1978
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY 

H. William Menard, Directorof Congress Cataloging in Publication Data 

Rock pushing and sampling under rocks on Mars

(Geological Survey Professional Paper 1081)

"Prepared on behalf of the National Aeronautics and Space Administration."

Bibliography: p. 20-21

I. Life on other planets. 2. Mars (Planet)--Geology. 3. Viking Mars Program. I. Moore, Henry J.

II. United States. National Aeronautics and Space Administration. III. Series: United States.

Geological Survey. Professional Paper 1081. 

QB54.R518 574.999'23 78-13085

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402

Stock Number 024-001-03008-6
CONTENTS

Page

Abstract ______________________________________________ 1

Introduction ____________________________________________ 1

Surface Sampler Subsystem components ___________________________ 2

Stereophotogrammetry ______________________________________ 3

Science Test Lander _______________________________________ 5

Criteria for rock selection ____________________________________ 6

Rock-pushing strategy _____________________________________ 10

Sampler motor currents and rock movement _________________________ 11

Sampling results _________________________________________ 14

Scientific value __________________________________________ 17

Summary and conclusions ____________________________________ 18

References cited __________________________________________ 20

ILLUSTRATIONS

Page

FRONTISPIECE. Viking Science Test Lander.

FIGURE 1. Diagram of a Viking lander showing Surface Sampler Assembly components

	and camera locations _________________________________________________ 2

2. Surface-sampler collector head _______________________________________________ 2

3. Schematic illustration of a Viking lander showing location of cameras, sampler arm or boom, and

	Lander Aligned Coordinate System _________________________________________ 3

4. Schematic illustration of interactive video-stereophotogrammetry station _____________________ 3

5. Stereopair of pictures of Notch rock after nudge ____________________________________ 4

6. Plot of fifth V-Profile from the left in figure 5 _____________________________________ 5

7. Graph showing range uncertainty with horizontal range for paired 0.04° resolution images ___________ 6

8. Plan view of Viking Lander 2 and status of sample field at end of Primary Mission ________________ 7

9. Camera 2 picture showing first rocks considered for pushing _____________________________ 8

10. Chart showing factors, scores, and weightings used in selection of rocks _______________________ 8

11. Graph showing estimates of weights of rocks that could be pushed _________________________ 9

12. Chart showing additional considerations for selection of rocks ____________________________ 11

13. Pictures showing sequences of events at "Bonneville Salt Flats" ____________________________ 13

14. Sequence of pictures showing history of Badger (rock 3) _______________________________ 14

15. Plan view showing movement of Badger (rock 3) ____________________________________ 15

16. Sequence of pictures showing Notch (rock 7) ______________________________________ 16

17. Plan view showing movement of Notch (rock 7) ____________________________________ 17

18. V-Profile along sampler arm azimuth of 201° showing surface and original location of Badger (rock 3) _ _ _ _ 18

TABLES

TABLE 1. Sampler sequences used for rock pushing and sampling under rocks ________________________ 12

2. Comparison of scientific results from samples acquired from under rocks and samples directly exposed to the

atmosphere and sun __________________________________________________ 19

ROCK PUSHING AND SAMPLING 

UNDER ROCKS ON MARS

By H. J. MOORE, 1 S. LlEBES, JR.,2 D. S. CROUCH,3 and L. V. CLARK4

ABSTRACT

Viking Lander 2 acquired samples on Mars from beneath two 

rocks, where living organisms and organic molecules would be protected from ultraviolet radiation. Selection of rocks to be moved 

was based on scientific and engineering considerations, including 

rock size, rock shape, burial depth, and location in a sample field. 

Rock locations and topography were established using the computerized interactive video-stereophotogrammetric system and plotted on vertical profiles and in plan view. Sampler commands were 

developed and tested on Earth using a full-size lander and surface 

mock-up. The use of power by the sampler motor correlates with 

rock movements, which were by plowing, skidding, and rolling.

Provenance of the samples was determined by measurements 

and interpretation of pictures and positions of the sampler arm. 

Analytical results demonstrate that the samples were, in fact, from 

beneath the rocks. Results from the Gas Chromatograph-Mass 

Spectrometer of the Molecular Analysis experiment and the Gas 

Exchange instrument of the Biology experiment indicate that 

more adsorbed(?) water occurs in samples under rocks than in 

samples exposed to the sun. This is consistent with terrestrial arid 

environments, where more moisture occurs in near-surface soil under rocks than in surrounding soil because the net heat flow is toward the soil beneath the rock and the rock cap inhibits evaporation. Inorganic analyses show that samples of soil from under the 

rocks have significantly less iron than soil exposed to the sun.

The scientific significance of analyses of samples under the rocks 

is only partly evaluated, but some facts are clear. Detectable quantities of martian organic molecules were not found in the sample 

from under a rock by the Molecular Analysis experiment. The Biology experiments did not find definitive evidence for Earth-like living organisms in their sample. Significant amounts of adsorbed 

water may be present in the martian regolith. The response of the 

soil from under a rock to the aqueous nutrient in the Gas Exchange 

instrument indicates that adsorbed water and hydrates play an important role in the oxidation potential of the soil. The rock surfaces 

are strong, because they did not scratch, chip or spall when the 

sampler pushed them. Fresh surfaces of soil and the undersides of 

rocks were exposed so that they could be imaged in color. A ledge of 

soil adhered to one rock that tilted, showing that a crust forms near 

the surface of Mars. The reason for low amounts of iron in the samples from under the rocks is not known at this time.

INTRODUCTION

During the Primary Viking Mission,5 Lander 2 acquired soil samples from beneath two rocks, where 

any living organisms and organic molecules would be 

protected from ultraviolet radiation. The acquisition 

of the samples required that the rocks be pushed away 

exposing the surface beneath them. Pushing rocks by 

remote control amid a dense field of other rocks 

(Shorthill and others, 1976; Moore and others, 1977a) 

some 363 million km away is a complex feat. Few people expected such a profusion of rocks on Mars, and 

the soil sampler was not designed for pushing rocks. 

Some of the rocks presented obstacles to the sampler 

and others were targets; consequently a detailed accurate knowledge of the topography and rock locations 

within reach of the sampler was mandatory for successful operations.

The purpose of this paper is to (1) describe the procedures used to push the rocks and the problems encountered, (2) show that the samples did, in fact, come 

from under the rocks, and (3) indicate the scientific 

value of acquiring samples from under the rocks.

ACKNOWLEDGMENTS

The authors are indebted to the National Aeronautics and Space Administration and countless individuals who made the Viking Mission a resounding 

success. The Viking Project was managed by James S. 

Martin and his staff at NASA Langley Research Center, Hampton, Virginia and the Viking landers were 

built by the Martin Marietta Corp., Littleton, Colo. 

Work was partly performed under NASA order L9714 (H. Moore) and contract NAS-1-9682 (S. 

Liebes).

'U.S. Geological Survey, Menlo Park, Calif.

Department of Genetics, Stanford University Medical Center, Stanford University, 

Stanford, Calif.

3Martin Marietta Corp., Littleton, Colo. 

4NASA Langley Research Center, Hampton, Va.

5 The Primary Mission is defined by the interval of time from the landing of Viking 1 on 

Mars, 20 July 1976, to 11 November 1976; the Viking spacecraft have continued to operate during the Extended Mission which ends in April 1978 (Soffen, 1976).
ROCK PUSHING AND SAMPLING UNDER ROCKS ON MARS

SURFACE SAMPLER SUBSYSTEM 

COMPONENTS

One of the major subsystems aboard the two Viking 

Landers is the Surface Sampler Subsystem (frontispiece and fig. 1). This subsystem was designed to acquire, process, and deliver surface material samples to 

the Biology, Molecular Analysis, and Inorganic Analysis experiments and to provide support for the Surface 

Physical and Magnetic Properties investigations (Soffen and Snyder, 1976). Biological analyses are conducted using three instruments (Klein and others, 

1972,1977): (1) Pyrolitic Release, (2) Labeled Release, 

and (3) Gas Exchange. The Gas Exchange instrument 

measures gases evolved from soil in the presence or 

absence of an aqueous nutrient, using gas chromatography. Molecular analyses are conducted using a Gas 

Chromatograph-Mass Spectrometer (GCMS) (Biemann and others, 1976, 1977). Inorganic analyses are 

conducted using an X-ray Fluorescence Spectrometer 

(XRFS) (Clark and others, 1976).

The Surface Sampler Subsystem consists of four 

major components: (1) the Acquisition Assembly, 

which acquires the samples and delivers them to the 

desired experiments; (2) the GCMS Processor, which 

receives samples from the Acquisition Assembly, 

grinds the material to a particle size less than 300 /on, 

and delivers metered 1-cm3 samples to the GCMS; (3)

S-band radio antenna

X- ray fluorescence funnel 

Biology processor 

GCMS processor 

Camera 1

Acquisition 

assembly 

Integral gimbal 

Boom housing 

Furlable boom 

Surface-sampler Collector head

control assembly

(internally mounted)

Footpad 2

Nominal

sampling field

~12m2

Upper lid

the Biology Processor, which accepts samples from 

the Acquisition Assembly, sieves the material to a particle size less than 1,500 jum, and delivers metered 

7-cm3 samples to the Biology experiments; and (4) the 

Control Assembly, which receives digital commands 

from the spacecraft computer and controls the operation of and handles the data from the other three 

components. Samples are delivered to the XRFS 

through a funnel with a 1.25-cm screen. The Acquisition Assembly, with its control electronics, and the 

spacecraft computer were the major components involved in the rock-pushing sequences.

The Acquisition Assembly consists of a boom unit 

and collector head. The boom unit consists of (1) an 

extendable and retractable furlable boom capable of 

extending the tip of the collector head to a maximum 

of 3.45 m from the boom housing and (2) an integral 

gimbal capable of 288° horizontal (azimuth) movement and 74° vertical (elevation) movement. The collector head (fig. 2) consists of a stationary lower jaw 

for digging into the surface and a movable upper jaw 

for retaining the sample. The collector head can deliver a bulk sample directly to the appropriate experiment in the upright position, or it can be rotated 180° 

and the upper lid (in the inverted position) vibrated at 

4.4 or 8.8 Hz to deliver the sample through a 2-mm 

sieve in the collector head lid.

The Surface Sampler Subsystem is automatically 

controlled by the spacecraft computer and Surface 

Sampler control electronics. Typical sampling sequences generally require that 40-100 discrete commands be executed; the longest sequence to date 

required the execution of 344 commands. Real-time 

command control and camera monitoring of the boom 

is impossible due to the one-way radio transmission 

time between Earth and Mars, which was about 20

Inflight retainingtab

Primary sieve 

(2000*i)

Solenoid actuator/

vibration

(4.4 or

180° rotation 

motor (internal)

Surface contact switch 

Rotation position switch 

-(internal)

"Secondary sample 

retention area

-Magnet 

array

-Temperature sensor 

(external)

5 CENTIMETERS 10

FIGURE 1. Surface Sampler Assembly components and camera locations. FIGURE 2. Surface-sampler collector head.
STEREOPHOTOGRAMMETRY

minutes during the Primary Mission. Therefore, the 

entire sequence to be executed must be generated and 

verified on Earth, transmitted to the spacecraft, and 

stored in the lander's computer until the specified execution time. When the sequence is executed, the 

computer sequentially transmits each coded digital 

command and waits a specific interval of time (precomputed to allow sufficient time for execution) before issuing the next command. If the command is not 

successfully completed, or a "no-go" signal is generated by an unsafe operation, the computer terminates 

power to the Surface Sampler and stops the sequence 

until corrective commands are transmitted from 

Earth.

Surface samples are acquired by moving the boom 

to the desired azimuth and extension distance and 

lowering it until the collector head contacts the surface. At that point, the collector head pivots about a 

ball joint, which activates a switch and terminates the 

downward movement. Sampling is then carried out by 

opening the collector head lid, extending the boom 

forward 15-20 cm, closing the lid, and delivering the 

sample to the desired experiment by another series of 

commands.

STEREOPHOTOGRAMMETRY

The prompt generation of accurate and suitably formatted topographic information was a prerequsite for 

choosing sample sites and rocks to be pushed and for 

planning sampler sequences. An interactive computerized video-stereophotogrammetric system (Liebes 

and Schwartz, 1977) was used for this purpose. The 

system, created to support the Viking Lander Imaging 

Team and to serve general project needs, was developed by one of the authors (Liebes) in collaboration 

with A. A. Schwartz of the Jet Propulsion Laboratory.

The primary input to the system was the digitally 

encoded imaging data returned by the Viking lander 

cameras (Huck and others, 1975; Mutch and others, 

1972). Figure 3 schematically illustrates the nominal 

locations of the camera photogrammetric reference 

points, the placement and articulation of the surface 

sampler boom or arm, and the alignment of the 

Lander Aligned Coordinate System.

The stereophotogrammetry system consists of three 

basic elements: (1) computer hardware, (2) computer 

software, and (3) a stereo station. The computer hardware is that of the Interactive Image Processing Facility (Levinthal and others, 1977) at the Jet 

Propulsion Laboratory. A computer software applications program, called RANGER, supports the system. 

The stereostation is illustrated schematically in figure 

4. A pair of video monitors face one another from opposite ends of a table. Images displayed on the monitors are simultaneously viewed through a centrally 

located scanning stereoscope. The left and right members of a stereoimage pair are routed, under the control of RANGER, to the left and right video monitors, 

respectively. The stereoscope enables a photogrammetrist to fuse the image pair into an apparent threedimensional image of the martian scene.

Camera geometric calibration files developed by M. 

R. Wolf of the Jet Propulsion Laboratory (Patterson 

and others, 1977) help RANGER to accurately associate a viewing vector in the Lander Aligned Coordinate

(NOTE: E = COMMANDED ARM EXTENSION)

0.411 m

FIGURE 3. Schematic illustration of a Viking lander indicating location of cameras, sampler arm or boom, and Lander Aligned 

Coordinate System.

FIGURE 4. Schematic illustration of interactive video-stereophotogrammetry station. Video monitors rest on table. Left and right 

camera stereoimage data are directed from computer to left and 

right monitors, respectively. Three-dimensional cursor is controlled by trackball device (TB). Video image routing and analog image are controlled by switchbox (SB).
ROCK PUSHING AND SAMPLING UNDER ROCKS ON MARS

System with each image point. RANGER provides the 

photogrammetrist with an artificial "3-space mark" 

consisting of an appropriately coupled pair of point 

cursors overlayed on the two video images. The pair of 

marks fuse to produce a single mark in the apparent 

three-dimensional image. The photogrammetrist can 

move the mark in a continuous manner through the 

martian scene. RANGER can be commanded to constrain the mark to any surface, which enables the photogrammetrist to generate arbitrary profiles of the 

relief such as elevation contours, vertical profiles, 

transverse profiles, etc.

Support for the sampler activities was invariably 

provided in the form of sets of profiles (called V-Profiles) representing the intersections of the martian relief with planes containing the azimuth axis of the 

sampler boom. The profile data were stored in computer data sets. Products consisted of photographs of 

the stereoimage pairs and overlaid profiles, and plots 

of the V-Profiles. Figure 5 illustrates a stereopair recorded after the sampler nudged Notch rock. The 

white lines represent 10 profiles that were generated 

along boom azimuth intervals of 0.5° to quantify the 

results of the nudge, to provide a basis for planning 

the subsequent attempt to displace Notch substantially, and to acquire a sample for Biology from beneath the rock. Figure 6 is a plot of the fifth profile 

from the left in figure 5. Sets of such V-Profiles enabled constraints such as the area accessible to the 

sampler (sample field) and detailed rock shapes to be 

established. The commands required to execute any 

desired sequence would be determined directly from 

these plots (Clark and others, 1977). The profile formatting program (implemented by R. N. Philips of 

the Jet Propulsion Laboratory) operated under multiparameter control that permitted variable grid intervals, measurement systems, and scales. Full-size VProfiles were frequently plotted to aid modeling of 

sample areas in front of the Science Test Lander, 

which is discussed in the following section.

The cameras can record at resolutions of either 

0.04° or 0.12°. The curves in figure 7, which illustrates 

theoretical uncertainty of range, apply to a pair of 

0.04° images. Uncertainties will be two times as great 

when one image is at 0.04° and the other is 0.12° resolution, and three times as great for a pair of 0.12° resolution images. Uncertainty at any field point is here 

defined to be the radial dimension in plan view of the 

diamond-shaped region of overlap of wedges radiating 

out from each of the cameras, with wedge apex angles 

equal to the camera resolutions. Error caused by the 

calibration data and by thermal movement of the

FIGURE 5. Stereopair of pictures of Notch rock after nudge. Notch rock is about 25 cm wide 

and 11 cm high. Profiles (white lines) are in planes radiating from the azimuth gimbal 

axis spaced 0.5° apart. These reproductions have been subjected to differential enlargement and relative rotation to facilitate stereoviewing. Sampler boom visible at top with 

its shadow below. Vertical bar in left image is artifact of transmission.
SCIENCE TEST LANDER

cameras and shifts of the lander amount at most to 

0.06° of image displacement, suggesting that a reasonable measure of operational ranging error is typically 

that shown in the figure. Within the stereoportion of 

the sample field, this uncertainty is typically about 2 

or 3 cm.

SCIENCE TEST LANDER

An important simulation facility was available at 

the Jet Propulsion Laboratory during the Viking mission for developing and verifying all of the commands 

to be executed on Mars by the Viking surface sampler.

DRY/TIME 75?94/050006 COMMANDED RZIMUTH RNGLE 106.00 

L2.RDSC. S45BB2. 545BB2. L 1 292, JNBOi I DENT 18

LflCS Z-RXIS (INCHES) .i................... i ...

100 90 80 

LRCS r-RXIS (INCHES)

70

120 110 100 

RZIMUTH GIMBRL RXIS (INCHES)

90

jPL/IMfiGF °ROCESS!NC LRSURflTPRY

FIGURE 6. Plot of fifth V-Profile from the left in figure 5. Gaps in 

profile correspond to regions not visible to both cameras. Note 

that the fillet at the base of the rock was not disturbed during 

the nudge. Sampler commands of azimuth, extension, and elevation required for subsequent rock push and sample acquisition were derived from such plots. The "range data set name" 

for the family of profiles appears beneath the Julian day and 

time in the top margin. The "IDENT" number designates the 

particular profile member of the set. The boom azimuth associated with the profile plane is indicated in the upper right 

corner. The X, Y, and Z coordinate scales appear in the plot

margins. The Y and Z scales plotted on the V-Profile are azimuth-angle dependent (see fig. 3). The perpendicular distance 

in the Y-Z plane from the axis of the azimuth gimbal is indicated at the bottom. Each of the concentric curves denotes the 

position of the collector head tip at a given extension distance; 

that is, the curve the tip would describe as the boom is raised 

and lowered. These curves are here labeled with the associated 

extension distance (in inches). The diagonal fan of rays indicates the path of the collector head tip as the boom is extended 

at the indicated elevation angles.
ROCK PUSHING AND SAMPLING UNDER ROCKS ON MARS

10 

HORIZONTAL RANGE, cm

FIGURE 7. Range uncertainty with horizontal range for paired 

0.04° resolution images.

The key element of this facility, the Science Test 

Lander, was a full-scale Viking lander with fully operational cameras and surface sampler (frontispiece). 

The Science Test Lander was installed adjacent to a 

large sandbox which represented the area on Mars 

within reach of the sampler (the sample field). The 

subsystems were manually controlled by test equipment and, in the case of the surface sampler, by a 

small programmable computer. Two 10-kw tungstencarbide lights were available for simulating martian 

lighting conditions during imaging tests.

Computer control of the sampler was essential to 

simulate and validate each sampler sequence. The sequences could thus be witnessed by scientists as well 

as engineers and managers responsible for assuring 

the safety of the sequence. The computer also provided data like that which would be returned during 

execution of the sequence on Mars. Surface-sampler 

data include commanded and achieved boom positions, discrete measurements of motor current and 

temperature, and switch positions. Although the surface-sampler data do not contain any timing information, it was possible to determine timing from a 

detailed analysis of the lander computer's memory as 

a continuous timed-tagged record of command and 

data traffic. This record permitted determination of 

the rates of travel of all motors, considered a measure 

of subsystem health. It was also a valuable diagnostic 

tool for understanding anomalous behavior of the 

sampler subsystem, and it was especially useful for 

evaluating the results of rock-pushing sequences.

After the landing of Viking Lander 1 on July 20, 

1976, the Science Test Lander was configured to simulate as closely as possible the conditions at the site.

The modeling was done by personnel of the U.S. Geological Survey using the images returned from the 

lander and photogrammetric analyses of the images. A 

sand mixture was used for the soil, and the simulated 

rocks were made of styrofoam. An accurate representation of the surface topography including rock locations was considered essential to developing and 

verifying safe and meaningful sampler sequences. 

Support imaging was also validated using the Science 

Test Lander. The real-time imaging display was particularly useful during the modeling work.

The Science Test Lander was reconfigured after the 

landing of Viking Lander 2 on September 3, 1976. 

Simulation of the second landing site took on an added importance when it was decided to search for martian organic matter and biota by acquiring samples 

from under rocks instead of from the exposed surface 

material. This necessitated an extensive program to 

develop rock-push sequences. The sample field was 

carefully surveyed for candidate rocks that met certain scientific and boom-capability criteria. Three 

rocks were selected for the sampler to attempt to 

move. Full-scale V-Profiles and contour maps of the 

target rocks were provided to the NASA/ 

Manned Spacecraft Center's Lunar Receiving Laboratory, which prepared two models of each rock (one 

of plaster of paris and the other of epoxy resin) simulating extremes of their estimated weights on Mars. 

The rocks were positioned in front of the Science Test 

Lander using full-scale V-Profiles. These rocks were 

used in exhaustive tests to develop the proper techniques for rock pushing.

CRITERIA FOR ROCK SELECTION

Rocks that were eligible for pushing were limited to 

the sample field (fig. 8), which was defined using sampler extensions less than 279 cm (110 in.), angles of 

boom elevation greater than -38.1°, and boom azimuths between 90° and 250° (fig. 3). This excluded a 

number of promising rocks because they were either 

too far away, too close to the spacecraft, or on the left 

edge of the sample field. Five rocks (Nos. 1 through 5 

in figs. 8 and 9) were considered first because they had 

been imaged by both cameras in high resolution early 

in the mission, whereas high-resolution coverage in 

stereo was not available in other areas. Each rock was 

rated from 1 to 4 in each of 11 factors, and each factor 

was weighted by importance.

The eleven factors were defined as follows: (1) Reliability: Was the rock deeply buried or near the surface so that it would move when pushed? (2) 

Obstructions: Were there objects behind the rock that 

might interfere with its motion? (3) Size: Was the 

weight of the rock small enough for it to be moved? (4)
CRITERIA FOR ROCK SELECTION

VIKING LANDER 2

3. MR. BADGER (MOVED)

6. BONNEVILLE

1 METER FOOTPAD 1

PPT

ROCKS (ONLY SELECTED ROCKS 

ARE SHOWN). ROCKS 1 THROUGH 8 

WERE CANDIDATES FOR MOVING. 

LARGE ARROWS FOR ROCKS 3 AND 

7 INDICATE DIRECTION MOTION; 

DASHED LINES INDICATE ORIGINAL 

POSITION. ROCK A WAS STRUCK BY 

FOOTPAD 3 DURING LANDING. 

SHROUD WAS EJECTED FROM SURFACE SAMPLER, STRUCK ROCK B; 

THE SURFACE AT C, AND CAME TO 

REST AT D.

ARROWS INDICATE TRACE OF 

FLIGHT PATH ON SURFACE 

DURING LANDING.

SURFACE ERODED BY ENGINE 2

1/11/77

FIGURE 8. Plan view of Viking Lander 2 and status of sample field at end of Primary Mission. Locations of selected rocks, sample 

acquisition trenches, and ejected shroud are shown. Original positions and positions of rocks 3 and 7 after pushing are indicated. 

Plane of plan view is parallel to upper surface of lander oody (spacecraft Y-Z plane).

Accessibility: Were there objects in front of the rock 

that would interfere with the ability of the surface 

sampler to reach the rock or the area exposed after it 

moved? (5) Grippability: Was the character of the surface of the rock such that the surface sampler would 

not slip off? (6) Breakability: Would the rock break 

when moved? (7) Purchase: Was the shape and orientation of the rock on the surface favorable for moving? 

(8) Sampleability: Would the exposed surface be 

easily sampled? (9) Visibility: Would the exposed surface be visible to the cameras? (10) Surface area: 

Would the newly exposed area be large enough to collect samples unmixed with surface materials previously exposed to solar ultraviolet radiation? (11) 

Iconoclasticity: Were there any emotional reasons 

why the rock should be moved?

Each factor was weighted by relative importance 

(fig. 10), and surface area, visibility, and sampleability 

received the largest weightings because of their scientific importance. Large surface areas reduce the
ROCK PUSHING AND SAMPLING UNDER ROCKS ON MARS

FIGURE 9. Camera 2 picture showing first rocks considered for pushing: (1) ICL, (2) Mr. Toad, (3) Mr. Badger, (4) Mr. Rat, and (5) Mr. 

Mole. Rock 6 (Bonneville) was considered for pushing later in the mission. Dimensions of rocks given in figures 10 and 12.

FACTOR

1. Reliability

2. Obstructions

3. Size

Mass

4. Accessibility

5. Grippability

6. Breakability

7. Purchase

8. Sampleability

9. Visibility

10. Surface Area

0

cm (cm)

11. Iconoclasticity

RATING 

WT

4

3

4

3

2

1

2

5

5

5

1

TOTAL SCORE 

(140 IS PERFECT)

NAME / NUMBER

ICL 

1

3 (12)

3 (9)

3 (12)

16.7kg

4 (12)

3 (6)

3 (3)

2 (4)

4 (20)

4 (20)

4 (20)

648(18 x 36)

4 (4)

122

Mr. TOAD 

2

4 (16)

4 (12)

4 (16)

11.5kg

2 (6)

4 (8)

3 (3)

4 (8)

2 (10)

2 (10)

1 (5)

225(15 x 15)

1 (1)

95

Mr. BADGER 

3

3 (12)

4 (12)

4 (16)

11.5kg

4 (12)

4 (8)

3 (3)

3 (6)

2 (10)

1 (5)

2 (10)

360(24 x 15)

1 (1)

95

Mr. RAT 

4

2 (8)

4 (12)

4 (16)

9. 9 +kg

4 (12)

3 (6)

1 (3)

4 (8)

4 (20)

4 (20)

2 (10)

306(18 x 17)

1 (1)

116

Mr. MOLE 

5

1 (4)

4 (12)

1 (4)

25. 9 +kg

4 (12)

4 (8)

2 (2)

1 (2)

4 (20)

4 (20)

3 (15)

810(30 x 27)

1 (1)

100

FIGURE 10. Factors, scores, and weightings used in selection of rocks to be moved for acquiring samples under rocks. Rock 1 (ICL) 

received the highest scores because of large weighting of scientifically important factors: surface area, visibility, and sampleability. 

Iconoclasticity, a humorous factor, did not affect the outcome.
CRITERIA FOR ROCK SELECTION

chances of mixing and contamination of the underrock sample with material that had been exposed to 

the sun. Good visibility allows an opportunity to assess the results of the sampling. Sampleability is the 

fundamental scientific requirement. The three rocks 

nearest the spacecraft (ICL, Mr. Mole, and Mr. Rat,6 

in figs. 8 and 9) received high scores in visibility and 

sampleability because the newly exposed surfaces 

would be favorably oriented to the cameras and the 

surface sampler if they moved (fig. 10). Because of 

their location and orientation on the surface, their 

surface areas could be determined. ICL clearly had 

the largest surface area 18 cm at right angles to the 

surface-sampler azimuth plane and 36 cm along it, so 

that the chances of acquiring an unmixed sample from 

beneath it would be good. Rocks farther from the spacecraft generally had low scores, partly because of 

their location and partly because of their orientation 

on the surface, which reduced the observer's ability to 

estimate the dimension of the rock away from the spacecraft. Mr. Toad (rock 2) had the smallest estimated 

surface area because of its narrow base (fig. 9); considering width alone, it was too small. Visibility and sampleability were scored low because Toad was relatively 

far from the spacecraft, and the upper surface of the 

rock was barely visible, showing it was tilted away 

from the spacecraft. Mr. Badger (rock 3) had low 

scores for the same reasons. The visibility score for 

Badger was lowest of all because its orientation indicated the exposed surface would be difficult to view 

and dimensions difficult to estimate. Evidence for this 

unfavorable orientation was fourfold: (1) V-Profiles 

showed the surface adjacent to the rock was inclined 

and could not be viewed, (2) the upper surface of the 

rock was invisible, (3) the visible upper edge of the 

rock was convex upward and parallel to a crude layering midway in the rock, and (4) the undersurface of 

the rock was visible at the tip nearest the spacecraft. 

This orientation resulted in low scores for sampleability and a conservative estimate of its dimension in a 

direction away from the spacecraft.

Rock size (weight) and reliability were the chief engineering considerations. Estimates of the weight of 

rock that could be pushed were made assuming frictional sliding (fig. 11). For frictional sliding and boom 

angles constrained by the local surface and sampler 

capabilities, rocks as heavy as 90 and 160 Newtons (N) 

could be pushed. If moderate plowing occurred, the 

weights might be about 40 N less. Rock weights were

WEIGHT OF ROCK, Ibs

20 30

WEIGHT OF ROCK THAT 

CAN BE PUSHED ASSUMING 

SLIDING FRICTION 

(tan 6 = 0.6, F = 30 Ibs)

100 120 140 

WEIGHT OF ROCK, NEWTONS

6 Names were assigned to rocks in order to aid memorization of the geometry of the 

sample field. Rocks 2 through 5 were named after characters in Kenneth Grahame's 

book The Wind in the Willows (1961), and others were simply named. The origin of the 

name of rock 1 (ICL) is noted later, in footnote 7.

FIGURE 11. Estimates of weights of rocks that could be pushed by 

the sampler assuming frictional sliding.

estimated from the dimensions, shapes, and an assumed density of 3,000 Kg/m3. Such a density is reasonable for massive mafic rock (Baird and others, 

1976) but is somewhat excessive if the rocks are, in 

fact, vesicular. As an example, ICL's estimated weight 

was about 62 N assuming an ellipsoidal shape and 

should have moved provided that excessive plowing 

(because of burial) would not be required. With the 

exception of Mr. Mole (rock 5), the other four rocks 

would move if excessive plowing was not required. 

Mole was not only heavier than about 97 N, but it was 

also deeply buried (fig. 9) and would require plowing; 

thus it received low scores on reliability and size. Toad 

was clearly the most reliable because of its small base 

compared to its upper part. Mr. Rat (rock 4) appeared 

to be partly buried. In the other factors, only Toad 

scored low in accessibility because Mole and Rat 

would interfere with sample acquisition. ICL scored 

low in obstructions because there were two small rocks 

behind it. The curved and relatively smooth surfaces 

of Rat and ICL indicated the surface-sampler collector head might slip while pushing, but there were 

some pits on the surface so that the teeth of the collector head would probably grip and stay with the rock. 

Because many of the rocks appeared to be vesicular, it 

was possible that they might be fragile and break if 

they did not move when the sampler pushed them. 

Thus, partly buried rocks, such as Rat and Mole, received low scores in breakability. High scores for purchase were given to Toad and Rat because their large 

height-to-base ratios would provide mechanical advantage for rolling. In contrast, Mole scored low because of its small height-to-base ratio. The fact that 

Badger was tilted away from the lander resulted in a 

relatively high score for purchase.
10 ROCK PUSHING AND SAMPLING UNDER ROCKS ON MARS

The weighted scores tipped the balance in favor of 

ICL rock as the first choice. Here, the factors weighted 

on scientific goals were important. ICL's high score in 

"iconoclasticity," a factor introduced to help many 

tired members of the Viking Flight Team retain their 

sense of humor and relax, did not affect the outcome.7

Subsequent rock selections considered the same 11 

factors as well as others (fig. 12). Bonneville (rock 6) 

and Notch (rock 7), two of three new candidates, were 

selected to be nudged (fig. 8). Bonneville had moved 

previously during a sample acquisition for the Inorganic Analysis experiment, and the surface that would 

be exposed after it moved would be shaded at the 

planned time of sample acquisition for Biology. The 

rock was in an area where the boom housing obscured 

the field of view of camera 1, and so there was no stereoscopic coverage. Notch won out as the push candidate because its location was well-known, its shape 

provided favorable grippability, its location provided 

good visibility, and the surface in front of it was not 

disturbed by previous acqusitions (as was the case for 

Bonneville), which reduced chances of contamination. 

Surface area, visibility, and sampleability were ample 

for Notch.

ROCK-PUSHING STRATEGY

The Acquisition Assembly was not designed for 

moving rocks on Mars. Therefore, when the request 

was made to obtain samples from under rocks after 

the Mars landing, appropriate sequences using the existing capabilities of the Acquisition Assembly had to 

be developed rapidly.

Two ways of moving rocks were considered: (1) positioning the collector head on the rock in such a manner that the backhoe could be used to drag the rock 

when the boom was commanded to retract and (2) positioning the collector head in front of the rock and 

pushing the rock forward by extending the boom. The 

boom can push or pull with a force of approximately 

178-213 N before the motor load capability is exceeded causing decoupling of its magnetic clutch.

Tests using the Science Test Lander indicated the 

pushing technique was the most feasible. The major 

difficulty encountered was the accuracy required to 

push the rock at an optimum point judged from imaging to be the center of gravity. The command resolution of the boom is 0.6° in azimuth and elevation, and 

0.6° cm in the extend and retract directions. Addition7 ICL rock was named after an acronym for Initial Computer Load. Prior to landing, the 

spacecraft computers had stored commands for an automatic mission in the event that 

the lander could not be commanded. Had this occured, the spacecraft would have tried 

to collect a sample from a point just beyond ICL, but would have failed. Thus, ICL was 

an "iconic clast" that deserved to be pushed.

ally, gear backlash and gravitational and thermal deflection of the boom increased the possible aiming 

inaccuracies. Although the gravitational deflection 

could be calculated, the thermal bending of the thinwalled steel boom could not be predicted with sufficient accuracy to guarantee that the collector head 

would not contact the surface in front of the rock and 

push exposed surface material into the sample site 

during the forward thrust.

A strategy of rock pushing was ultimately selected 

that provided the best way to move the rock without 

contaminating the sampling site. The accuracy of azimuth positioning was improved by comparing the 

boom-command coordinates of previously excavated 

trenches with the V-Profile azimuths of the centerlines of the trenches measured using the camera stereoimages. Appropriate command corrections were 

made as required. The azimuth backlash effect was 

predictable because the lander is tilted 8.2° in a westerly direction (Shorthill and others, 1976; fig. 8). 

Thus, the azimuth backlash consistently produced actual boom azimuths that were about 0.6° smaller than 

the commanded azimuths. Backlash in the extend and 

retract directions was negligible. The relatively large 

potential errors in the elevation axis (boom thermal 

bending, gravitational deflection, and overtraveling 

after motor cutoff) were eliminated by first commanding the boom to the surface until movement was terminated by actuation of the ground contact switch. 

This command was followed by an elevate command 

which was controlled by timing rather than by position achieved. Knowledge of the elevation rate of 

travel enabled calculation of the time required to lift 

the collector head tip above the surface a known 

amount. This technique nullified the effect of boom 

deflections in the upward direction. The final sequence adopted for the mission consisted of the following steps generally performed over a period of 10- 

15 Martian days:

1. Swing the boom to the desired azimuth (as determined from V-Profile data and corrected for calibration and lander tilt).

2. Extend the boom such that the tip would be positioned approximately 2-3 cm in front of the rock 

after lowering it (as determined from V-Profile 

data).

3. Deelevate the boom to activate the surface contact 

cutoff switch.

4. Elevate the boom (usually for 1-2 seconds) to position the collector head at the correct vertical position in front of the rock.

5. Extend the boom approximately 7-8 cm to verify 

"moveability" of the rock by subsequent imaging 

and boom telemetry data.
SAMPLER MOTOR CURRENTS AND ROCK MOVEMENT 11

NAME/ NUMBER

SIZE Width 

Depth 

Height 

Mass

ADVANTAGES

DISADVANTAGES

Iconoclasticity

Mr. RAT 

4

18 cm 

17 cm 

11 cm 

9.9 kg

Has V-Profile 

data stereoscopic cove rage

Near ICL 

rock (1) which 

didn't move

Partly buried

1

BONNEVILLE 

6

22 cm 

15-22 cm 

5-6 cm 

6-8.4 kg

Appears to have 

moved during 

XRFS Sol 30 dig

Newly exposed area 

shaded at 0600

Monoscopic coverage 

Area in front of 

rock "messed-up" 

by GCMS (Sol 21) 

and XRFS (Sol 29, 

30) Frenches

0

NOTCH 

7

25 cm 

25 cm 

11 cm 

10. 7-20. 3 kg

Appears to be 

unburied

Has V-Profiledata 

stereoscopic coverage

0

OTHER 

8

25 cm 

25 cm 

13 cm 

9.5-19.1 kg

Has V- Profile 

data stereoscopic 

coverage

Rock along SSAA 

gimbal axis 

presents possible 

hazard

0

FIGURE 12. Additional considerations for selection of rocks to be nudged 9r pushed for the second sample acquisition beneath a rock for

the Biology Experiment.

6. Position the boom such that the rock and collector 

head could be stereoimaged and subsequent VProfiles could be generated showing the new position of the rock.

7. Position the collector head at the new relative position (steps 1 through 4).

8. Extend the boom 20-25 cm (depending on dimensions of rock) to completely displace rock from 

original site. Verify rock movement by imaging and 

repeat steps 7 and 8 if required.

9. Perform a backhoe sequence at the original site of 

the rock to remove possible exposed material, followed by performance of a normal sampling sequence.

Details of the rock-push sequences used on Mars are

listed in table 1.

SAMPLER MOTOR CURRENTS 

AND ROCK MOVEMENT

Motor currents, inferred from variations in lander bus 

currents, were sampled at a rate of 4 kilobits per second in the engineering data format (Format 5). This

resulted in a current sample every 0.19 seconds and a 

current resolution of 0.039 amperes. Typical motor 

currents have a base current of about 0.2 amperes, 

normally a high current transient at motor start, a noload condition during a gear transfer, and then a rise 

in current due to extension. Currents are converted to 

force by subtracting the base current of 0.2 amperes 

from the total motor current measurements, calculating the wattage from known voltages (typically 31.8 

Vdc) and then using calibration data (Crouch, 1976) 

which gives ^20 Newtons/watt. Thus, the resolution 

in force is about 25 N.

Motor currents during nudging, pushing, and sampling correlate with movements of the sampler and 

the rocks as viewed and measured using the pictures. 

This correlation is vividly illustrated by the Sol 29 acquisition for the Inorganic Analysis experiment (fig. 

13). The acquisition stroke extended to the buried 

base of Bonneville, which was displaced upward about 

0.4 cm as shown by comparison of pre- and post-sample pictures of the rock. The surface sampler extends 

at a rate of about 1 in. (2.54 cm) per second. The duration of high current (« 6.7 s, fig. 13) represents an extension near 6.7 in. (17 cm), which is in good
12 ROCK PUSHING AND SAMPLING UNDER ROCKS ON MARS

[Engineering units are reported in inches because of use during mission and in final surfacesampler report (L. V. Clark and others, 1977). CW, clockwise; CCW, counterclockwise as 

viewed in fig. 8; est., estimated]

Rock Sol'

Command 

description

Position 

achieved Comments

TABLEl. Sample sequences used forrock pushing and sampling under rocks agreement with the Commanded extension of 6.4 in.

	(16.3 cm). Thus, the increase in current at the end of 

	the Sol 29 sample acquisition is certainly due to the 

	interaction of the surface sampler and soil with

______________________________ Bonneville rock. The current increase corresponds to

ICL 30 Azimuth cw __ __ 186.6° TO nudge rock. a force of about 50 N, a value about twice the estiExtend __________75.4in. Est distance to rock 77.4- ^^ ^^ Qf ^ ^^ (22_^ N) ^ & deelevation

(-)33.2° Surface contact. angle of —29°, the horizontal component of force is

'm£ ZS?———* _« about 44 N. Because the rock moved upward, a lifting

in.; motor clutched: est. force force of about 22-31 N was required. The horizontal

Badger 34 Azimuth CW _______201.1° S^S^tT" f°TC* TMCt°T dOn« * lTM *?&** 3°° *>«*** ^ ^

Extend __ _ __ _ 84.4 in. Est. distance to rock 87.4 in. face sampler is 37.5 N, and its vertical component is 22

SKT.:::::::!-)^ SST"* N> or near the estimated weight of the rock.

Extend __ _ __ __ 96.5 in. Rock translated, tilted, and During the nudgC Of Bonneville, SUrfaCC Contact WaS

f^^rwTnfunt made on the rock as shown by the deelevation angles

rock. (table 1) and by the pictures (fig. 13), which show the

Retract__________8,oin. '^^^^^ collector head resting on the rock after it extended.

pier. The high motor currents during the last part of the

Badger 37 Azimuth CW —— ——— 200.5° To push rock, second try. rmHtrA Iflctprl flhrmt 09 <SPf>nnH<S wHifh rPnrP<*Pnt<* Extend______89.iin. Est. distance to rock 90.6 in. nuQge lasted aoout u.z seconas, wmcn represents

(->29.4° Surface contact. about 0.5 cm of travel. This is consistent with about 1

ioL28 in° ££S*«»u» of 97-98 cm upward motion on the face of the rock which was

in. along 2oo.5o ; may have estimated from the pictures and suggests a pivot point

Jhl^mards^1'1116 *"* On edg6 °f the r°ck» which is ab°Ut h&lf BS hlgh &S

237 Azimuth cw _ ___ 201.1° TO acquire sample. wide, farthest from the spacecraft. After retraction,

Extend —— __—_ 93.0 in. Est. distance to rock 95 in. fae rock returned approximately to its prenudge posiDeelevate _______ (-)28.8° Surface contact. . . , , . ^ , , . . , . „

Retract ________84.1 in. Trench to clear away any tlOn CaUSing QCDHS IrOm plOWCd material in the Tim OI

surface contaminants. tne previous trench to fall into that trench (fig. 13).

Elevate ________(-)20.5° *1 . ... ... v °

Extend _____87.o in. ICL, the first choice candidate, did not move, as

Deeievate ———— (-)3o.o° Surface contact. demonstrated by comparing8 prenudge and postnudge

Bonne- Extend __________93.6 in. Sample acquisition. . , 1,1 i •

vme 45 Azimuth cw ____ 217.5° TO nudge rock. images taken by the same camera, photogrammetnc

Extend —————99.1 in. Soi 29 XRFS extension of measurements, and motor currents. Relatively small

99.4 in. moved rock. , „ , - ,

Deeievate ______ (-)25.6° Elev. indicates surface sam- motor Currents Were measured for about 3 SCCOnds,

pier contact on rock. after which they rose to a value corresponding to a

Elevate __ _____ (-)26.2° Images show collector head . nnn -KT n ^i i ^

tilted back and on rock. force of about 200 N above the normal extension curExtend —————103.0 in. Rock feii back after exten- ren^ The current duration compares favorably with

sion. Points on front surface ,. ,. t * n n r • /r- /-» A \j«^ j.ii moved i cm upward. the estimated 2~2.5-m. (5-6.4 cm) distance to the

Notch 45 Azimuth ccw _ _ _—105.8° TO nudge rock. rock. Two hundred Newtons is close to the decoupling

Extend ___ __ _ 84.1 in. Est. distance to 86.2 in. ,. ,. ,•• i , ttno r»i o XT\ rpr Deeievate _ J__ J__\-)K.\° Surface contact. force for the sampler motor (178-213 N). The maxiEievate — _——(-)22.4° By timing. mum horizontal component of force on ICL was 153-

Extend ————— 87.8 in. Left edge of rock displaced < <->r> XT T-» T/-^T j_- A. j A. • t. /-»r» XT i

about ^5 in (38 cm) p 183 N. Because ICL was estimated to weigh 62 N, only

Notch 51 Azimuth cw ————106.4° TO push rock. about 67 N should be required to push it if simple slidExtend 86.7 in. Est. distance to rock • • j/ ,. •^•ii\ TIT J.T- • n

--------- 87.7-88in. mg is assumed (see equation in fig. 11). If the sin 6

(-)2i.s° Surface contact. term in the equation is ignored, 37 N should be reS to. Ro7TMZsiat*d and rotated quired to push the rock. Thus ICL must be cemented

clockwise. or more deeply buried than initial interpretations inNotch 51 Azimuth 107.1° To acquire sample. j. , j T , . , .•> .•> , ,1 .j Extend _V_~_V_V_V_"93.6 in. dicated. It is noteworthy that there was no evidence

Deeievate —_—(->2o.5° Surface contact. for chipping, spalling, or scratching of ICL as a result

Retract 78.1 in. Trench to clear away debris. -.•• ,, ,, ij.i i mi « j- -j i j. J.T. Elevate I" " 1.." "(-)i5.5° °f tne attempt to push the rock. The individual teeth

Extend _————88.0 in, of the lower jaw of the collector head have an area near

Deeievate (—)21.8° Surface contact. ., „ j , /..i j ^irv8xT/o _______Extend _ _ _"::::::_ 94.6 in. sample acquisition. 1 mm*, and so stresses of the order of 108 N/m2 were

' Sol is martian day from start of mission; day of touchdown is Sol 0. The duration of a CXCrtcd by the Collector head. ThuS, it appears that

martian day is about 24.65 hours. the SUrfaCC Of the TOCk is Strong.

2 Sequence was repeated because of failure to obtain level full indication; achieved elevations were (-)29.4° and (-)30.6° for surface contacts; level full indication was obtained prior to second delivery. Elevation increase indicates shallow 1.2 in. (3 cm) depth 'Viewing of two pictures taken of the same object at different times by one camera is a

for sample trench. sensitive way of detecting motion of the object.
SAMPLER MOTOR CURRENTS AND ROCK MOVEMENT

l^miti*^ liii"' 

.*-

13

SOL 21

GCMS SAMPLE 

ACQUISITION

SOL 29

XRFS SAMPLE 

TRENCH (1st PASS)

SOL 30

XRFS SAMPLE 

TRENCH (2nd PASS)

SOL 45 

NUDGE

SOL 45 

POST-NUDGE

0.2 -,

0.1 *•

0 -

(

J|

^^^^TM ^^^^ I

i r 1

-150

-100 0

t

-50 >

i i i i i i i "

) 4 8

TIME (sec)

SAMPLE (SOL 29)

MOTOR CURRENTS

. 0.2-,

FIGURE 13.—Sequence of events at "Bonneville Salt Flats." Bonneville (rock 6) is just beyond surface sampler in the left picture 

(Sol 21). Left picture shows sampler acquiring sample for the 

Molecular Analysis (GCMS) experiment on Sol 21. Next picture shows trench formed during the first pass of acquisition 

for XRFS on Sol 29; comparison of pre- and post-acquisition 

pictures shows Bonneville was displaced 0.4 cm upward; motor 

currents show increase at end of acquisition stroke and correspond to upward displacement of rock. The Sol 30 picture

Despite the initial setback of ICL, the sampler 

moved on to Badger (chosen over Toad). The weight 

of science considerations was relegated to lesser importance, a marginal decision in view of reduced visibility and sampleability. More importantly, Badger 

moved in a complicated way (figs. 14 and 15). Motor 

currents for the Sol 34 push of Badger correlate with 

the results. The rock was about 3 in. (7.6 cm) from the 

collector head tip at surface contact, which correlates 

with the duration of initially low currents (3 s). This 

was followed by large currents for 2.5 seconds, correlating with the estimated translation of 2.6-2.8 in. 

(6.5-7.0 cm), which may have been accomplished by

o.i -

1

" 15° w

- 100 o

-50 g 

0

0

TIME (sec) 

NUDGE (SOL 45)

(center) shows the second pass acquisition for XRFS; note 

trench has been cleaned of platy debris. Sol 45 picture (to 

right) shows collector head on Bonneville during nudge; note 

trench produced on Sol 30 is still clear of debris. Final picture 

at right shows sampler (upper center) and Bonneville after 

nudge; note debris propelled into trench by rock falling into its 

original position. Trenches are about 10 cm across. Motor currents for nudge (lower right) near end of stroke are larger than 

those for beginning of sample acquisition.

tilting, rather than sliding. Subsequent currents oscillate and correlate with the interval during which the 

sampler slipped down off the rock surface causing the 

rock to lean on it as it completed its extension (fig. 14). 

Most of the measured 69° counterclockwise rotation 

of the rock probably occurred in this last interval. Because the rock was leaning on the sampler as it retracted after the push, the collector head dug a trench 

along an azimuth oblique to the commanded azimuth. 

Badger did not move far enough on the first push, 

therefore a second push was executed on Sol 37. Unfortunately, motor currents were not obtained during 

this push. The pictures show two smooth tracks where
14 ROCK PUSHING AND SAMPLING UNDER ROCKS ON MARS

* "" '

SOLO 

PRE-PUSH

SOL 34 SOL 34 SOL 37 GCMSSOL37 

1st PUSH POST-1stPUSH POST-2nd PUSH SAMPLE TRENCH

FIGURE 14.—Sequence of pictures showing history of Badger (rock 

3). At left is rock prior to first push on Sol 34. Next picture (Sol 

34) shows Badger leaning on sampler which is fully extended 

and has been driven clockwise (to right); a small unplanned 

trench in front of rock was produced during push. Center picture (Sol 34) shows the trench excavated as sampler retracted; 

azimuth of trench is oblique to azimuths through gimbal axis.

the rock simply slid on the surface. The Sol 37 push 

was followed by a sample acquisition. Motor currents 

for this acquisition are relatively low and oscillatory 

when compared with other acquisitions (compare figs. 

13 and 15).

As noted above, the orientation of the surface with 

respect to the sampler was not expected to be favorable because it sloped away from the lander. Thus, the 

small motor currents measured during sampling are 

compatible with shallow trenching (« 3.5 cm deep) 

through an irregular surface inclined away from the 

lander.

The nudge and push of Notch (rock 7), followed by 

the acquisition, was the culmination of the under-therock sampling activities during the Primary Mission 

(figs. 16 and 17). On Sol 45, Notch was nudged by 

pushing on a protuberance on the left edge of the rock 

so that it would rotate to avoid early exposure. As 

planned, Notch rotated about an axis on the right center side of the rock. This movement displaced the protuberance about 3.8 cm (figs. 5,6, and 16). The motion 

may have been jerky, judging from the oscillating motor currents. The push before sunrise on Sol 51 was 

accompanied by about 47° of rotation and 9.5-10.5 in. 

(24-27 cm) of translation. The duration of high motor 

currents was about 10.5 seconds. A rapid rise in motor

Note thin "water line" ledge of soil adhering to left side of rock. 

Fourth picture (Sol 37) shows Badger after second push; note 

skid marks produced by sliding. Final picture shows second 

pass acquisition trench for sample under Badger; note floors of 

retraction trench (to clear contaminants) and acquisition 

trench are not visible because local surface slopes away from 

observer. Only end of sample trench is visible.

currents within 1 second shows that the sampler contacted the surface within 1 in. (2.5 cm) of the rock. 

Motor currents for the push were about 50 N larger 

than those during the sample acquisition. Periodically, they were 75-100 N larger. This may be compared with the estimated weight of the rock (40-76 

N). Since the higher estimate assumed a rectangular 

rock, it is probably too large. The lower weight allows 

for rounded edges but may be somewhat low. For simple sliding with a friction coefficient of 0.6 and using 

the equation of figure 11, a rock weighing 31 N could 

be pushed. If the sin 6 term, which allows for an increase in normal force by the sampler, is ignored, a 

rock weighing 40 N could be pushed. At times forces as 

large as 100 N were exerted and may correspond to 

some plowing, which is seen to be the case from the 

pictures.

SAMPLING RESULTS

Judgment on the provenance of the samples was relatively straightforward for Notch rock because it fulfilled the criteria of surface area, visibility, and 

sampleability, but this was not the case for Badger. 

The surface beneath Notch could be viewed directly 

on high-resolution pictures taken by both cameras. 

Direct views showed that the trenching designed to
INITIAL POSITION

VISIBLE

PART OF

ROCK INFERRED 

/ ROCK

SAMPLING RESULTS 

INTERMEDIATE

SURFACE SAMPLER 

CONTROL AZIMUTH

15

FINAL POSITION

SAMPLE

ACQUISITION

TRENCH

RETRACTION 

TRENCH

6 - 5 - 7 - 0cm/\40°TILT 12 - 15cm//20° TILT

MR. BADGER

69° 

ROTATION ROTATION

MOTOR CURRENTS

50 

I

0.2-1

0.1- 

t\-

_

__ ——— LJIT-TLT JITJl 

1^ 1

-100 o

1—

_n Z

or

0.2-1

0.1- 

njirr-ujuir-150

-100 

-50 

-n

10

SCALE (centimeters) TIME (sec)

PUSH (SOL 34)

TIME (sec)

SAMPLE (SOL 37)

FIGURE 15.—Plan view showing movement of Badger (rock 3). Left 

is Badger before movement; note view shadow and area of inferred rock; 201° is azimuth through sampler gimbal axis; a 

and b are points on rock. Center, Badger after first push; dotted line is original position; note short trench excavated by 

surface sampler while extending to rock; large trench produced during retraction while Badger leaned on surface samclear away possible contamination was successful and 

that the acquisition occurred in the correct place. 

Achieved positions of the sampler were in complete 

accord with interpretations of the pictures. For the 

sample beneath Badger, judgment was at best difficult. Visibility and sampleability were not as favorable as at Notch because of the slope of the surface. 

The situation was more seriously affected by the postsample acquisition pictures, one of which was a lowresolution (blue diode) picture and the other a highresolution picture. Both were taken at low sun elevation angles, which caused extensive shadowing. The 

chief evidence that the sample came from beneath the 

rock was provided by comparing the history and locapler; note trench is oblique to commanded azimuths; arrows 

below indicate motion; motor currents show approach to rock 

(0.6-4 s); the push (4-6.5 s); and push while Badger leaned on 

surface sampler (6.5-12.6 s). Last diagram shows final position 

of Badger; trench to clear contaminants; acquisition trench; 

arrows indicate motions; motor currents below are unusually 

low for sample acquisition.

tions of the rock along the azimuth axis of the sampler 

gimbal with achieved commands (fig. 18). Since this 

comparison indicated the sampler achieved the correct positions, the best estimate was that the sample 

did indeed come from soil originally beneath the rock. 

The outcome indicates that the low rating given to 

sampleability was appropriate. Two acquisition sequences were automatically performed because a 

"level full" signal was not obtained immediately after 

the first acquisition. Such a signal was obtained during the second acquisition sequence just before sieving 

of the sample into the Molecular Analysis soil delivery 

system. 

Analytical results of the samples by the Molecular
16 ROCK PUSHING AND SAMPLING UNDER ROCKS ON MARS

SOL 34 

PRE-NUDGE

SOL 45 

POST-NUDGE

SOL 51 

POST-PUSH AND ACQ.

FIGURE 16.—Sequence of pictures showing Notch (rock 7). At left is rock prior to nudge on Sol 45. Next picture shows rock after nudge; 

note small displacement at protuberance on left side of rock. Third picture shows Notch after push and sample on Sol 51; note 

backhoe trench walls, plowing marks, and sampled area, which was originally under rock.

Analysis Experiment and Biology Experiment are 

compatible with the judgment that the samples came 

from beneath the rocks. The amount of water evolved 

during heating from 50-200° C of material from beneath Badger is much larger (0.2 percent) than that 

evolved from the sample exposed to the sun and 

heated in one step to 200° C (^0.05 percent) (Biemann 

and others, 1977). Heating of both samples to 350° C 

and then 500° C evolved comparable amounts of water 

during each heating step (Biemann and others, 1977). 

The results of the Gas Exchange instrument of the Biology experiment are also compatible with relatively 

large amounts of water. Evolution (desorption) of N2, 

AT, C02, and Og from soil humidified in the presence 

of the nutrient in the Gas Exchange Instrument varies 

inversely with the mean water content of the original 

sample environment (Oyama and Berdahl, 1977). Reduced desorption of N2, Ar, and C02 from the sample

under Notch is attributed to larger amounts of adsorbed water (Oyama, 1977). Reduced 62 evolution is 

attributed to the hydration of alkaline-earth and alkali-metal superoxides to produce hydrated peroxides.

By terrestrial analogy, larger amounts of water 

should be expected under rocks (Moore and others, 

1977b). Field and laboratory studies show that soil beneath rocks in a field of soil in an arid environment 

has detectably more adsorbed water at depths of 2.5- 

5.0 cm than soil exposed to the sun and atmosphere 

(Jury and Bellantuoni, 1976a, b). These studies indicate the net heat flow is toward the soil beneath the 

rocks, and so water vapor moves under the thermal 

gradient toward the area beneath the rocks. The rock 

cap inhibits evaporation. Also, ultraviolet radiation 

may dehydrate exposed soils (Huguenin, 1976).
SCIENTIFIC VALUE 17

3.0i

+ Z,

2.5m

2.0m

BIOLOGY "NOTCH" ROCK ACQUISITION

A. SEQUENCES

1. NUDGED ON SOL 45

2. PUSHED ON SOL51

3. SAMPLE ON SOL 51

____ a. BACKHOED TO CLEAN AWAY POSSIBLE CONTAMINATION ____ 

WITH EXPOSED SURFACE MATERIALS

b. COLLECTOR HEAD ELEVATED 18.0° UPTO REACH ACQUISITION 

POSITION AND PREVENT CONTAMINATION

c. ACQUISITION OCCURRED IN NEWLY EXPOSED SURFACE 

ORGINALLY UNDER ROCK

B. SAMPLER PROCEDURES AND RESULTS WERE OUTSTANDING — ESTIMATED 

TO BE BETTER THAN 90% OF SAMPLE FROM UNDER ROCK

0 20 

I

40 

I

60 cm

FINAL POSITION 

OF NOTCH ROCK

SCALE

ORIGINAL POSITION 

OF NOTCH ROCK

3.0m

REGION OF SAMPLE 

ACQUISITION

REGION OF 

BACKHOEING

1.0m

£ o.i -

1-150

(-100 §

> i

z

TIME (sec)

NUDGE (SOL 45)

MOTOR CURRENTS 

-d1 ——-^

3

TIME (sec)

PUSH (SOL 51)

pi 50

-100

-50 

0

r——Tl -100

-50 

0

TIME (sec)

SAMPLE (SOL 51)

FIGURE 17.—Plan view showing movement of Notch (rock 7). Short dashed lines indicate original position of rock, solid line indicates 

final position of rock. Arrows show motion of rock. Motor currents are plotted at bottom. Note motor currents during push (center) 

are larger than those for nudge (left) and sample (right).

SCIENTIFIC VALUE

The scientific value of the samples from under the 

rocks was considerable (see table 2).

1. There was no evidence for large quantities of organic molecules in the sample from the sunshielded soil beneath Badger (Biemann and others, 

1977).

2. Results from the Biology experiments did not produce convincing evidence for Earth-like living organisms that thrived in the protected environment 

beneath Notch (Horowitz and others, 1976, 1977); 

the possibility for life on Mars has not been excluded, however (Levin and Straat, 1976,1977). 

3. Results of the Inorganic Analysis experiment indicate substantially less iron in the samples from under Badger and Notch than in samples exposed to 

the sun and atmosphere (B. C. Clark and others, 

1977). The reason for the difference in iron content 

is not understood at this time; it may be the result
18 ROCK PUSHING AND SAMPLING UNDER ROCKS ON MARS

75 in

COLLECTOR HEAD AT 

START OF ACQUISITION

MR. BADGER

SURFACE SAMPLER 

AZIMUTH 201°

I__1 I I

105 100 95 90 85

DISTANCE FROM GIMBAL AXIS (INCHES)

FIGURE 18.—V-Profile along sampler arm azimuth of 201° showing surface and original location of Badger (rock 3), location after Sol 34 

push, and location after Sol 37 push. Surface sampler collector head is at position just before acquisition stroke; sample area and 

backhoe trench areas indicated by arrows. Sloping lines indicate deelevation angles; arcs are sampler extensions.

of sedimentation of magnetite-rich fine material 

from the atmosphere (Pollack and others, 1977) on 

exposed surfaces but not on covered surfaces.

4. The large amount of water (for Mars) evolved during heating of the sample from under Badger to 

200° C may represent adsorbed water. If this is the 

case and Mars is like the Earth, adsorbed water 

may be present at greater depths, where it is cooler. 

Such a result lends strong support to models of 

Mars and its atmosphere requiring adsorbed water 

(Fanale, 1976).

5. The response of the exposed and shielded soils to 

the Gas Exchange instrument is providing valuable 

insight on the chemical environment at the surface 

of Mars.

6. The surface sampler did not scratch, chip, or spall 

the rocks, showing their surfaces are hard.

7. Color pictures were obtained of freshly exposed soil 

beneath Badger as well as the underside of the 

rock.

8. The "water line" ledge of soil adhering to the side of

Badger (fig. 14) provides clear evidence of a nearsurface crust.

SUMMARY AND CONCLUSIONS

The dense field of rocks on Mars was not anticipated before the Viking landings, and pushing rocks 

was not in the plans. Successful pushing of the rocks 

and sampling from the newly exposed soils beneath 

them required the development of imaginative procedures based on a thorough understanding of scientific 

requirements and the variables related to the surface 

sampler. Of equal importance was an accurate knowledge of the locations of the rocks within the sample 

field.

The endeavor to collect samples from under rocks 

was entirely successful. Four lines of evidence support 

this: (1) The pictures show that samples came from 

soils originally beneath the rocks; (2) the sampler positions indicate that samples came from soils originally beneath the rocks; (3) by terrestrial analogy,
SUMMARY AND CONCLUSIONS 19

TABLE 2.—Comparison of scientific results from samples acquired from under rocks and samples 

directly exposed to the atmosphere and sun

Experiment

Observed quantities 

or items

Under-rock 

samples

Exposed Exposed

samples samples

(Lander 2) (Lander 1) Comments

Biology:

Gas Exchange _ _ predicted 

found 

predicted 

found 

predicted 

found 

predicted 

found

Ar(nmols) _____ 

Ar

N2

N2

02

02

CO2

CO2

39 

6

60

13

2.7

70-270

6,110

6,110

49 

4

76

30

3.4

190

7,750

7,750

62 

13

96

83

4.4

790

9,800

9,800

Pyrolytic Release

Labeled Release

I4C02 (disintegrations 

per minute).

N C02 (counts per 

minute).

Molecular Analysis _ _ Water (percent)

heated to— 50°C 

200°C 

350°C 

500°C 

500°C

<0.01 

0.2 

0.3 

0.8 

0.6

Inorganic Analysis __ Iron (percent) __________ «11.6-12.8

0.05

0.3

1.0

0.25

14.2 12.7-13.1

Predicted and observed 

nanomoles (nmols) of 

gas desorbed by humidification (Oyama 

and Berdahl, 1977; table 2). Differences in 

the Ar and N2 found 

in samples are attributed to amount of adsorbed water vapor, 

which is largest for under-rock sample and 

smallest at VL-1 site; 

amount of O2 evolved 

attributed to reaction 

of water vapor with 

superoxides and peroxides; O2 from under-rock sample 

probably near 70 

nmols; low O2 evolved 

because there was 

more water under 

Notch (rock 7).

Results from this instrument are poorly understood at this time; 

a biological interpretation of results is unlikely (Horowitz and 

others, 1977).

Results from this instrument are consistent 

with a biological response and restrict 

possible chemical reactions that might 

produce the results 

(Levin and Straat, 

1977).

No organic compounds 

related to the soil of 

Mars were detected; 

water analyses for 

Lander 1 were omitted 

because they are, at 

best, crude estimates 

(Biemann and others, 

1977).

Data on samples from 

under rocks not yet 

available; sample from 

under Badger (rock 3) 

contains 18 percent 

less iron than exposed 

samples at VL-2 site; 

sample from under 

Notch (rock 7) contains 10 percent less 

iron than exposed 

samples at VL-2 site 

(B. C. Clark and others, 1977); values for 

under-rock sample 

taken as 10 and 18 

percent less than 14.2 

percent.
20 ROCK PUSHING AND SAMPLING UNDER ROCKS ON MARS

TABLE 2.—Comparison of scientific results from samples acquired from under rocks and sample 

directly exposed to the atmosphere and sun—Continued

Experiment

Observed quantities 

or items

Under-rock 

samples

Exposed Exposed 

samples samples 

(Lander 2) (Lander 1) Comments

Physical properties:

Rock strength _____ Pictures 

and forces 

inferred from 

motor currents.

Soil structure 

(crust) _. . Pictures of disturbed 

rocks.

Lander Imaging Color Pictures of rock 

and soil.

ICL (rock 1) did not 

scratch, chip, or spall 

when forces of 200 N 

and stresses near 

108N/m2 were exerted 

on it; this indicates 

rock is strong and does 

not have a weak 

weathered rind.

Ledge of soil adhering to 

Badger (rock 3) proves 

the existence of thin 

crust near surface.

Color data not reduced; 

there are no obvious 

differences in color between under-rock and 

exposed soils.

more adsorbed (?) water should be in soils under rocks 

than in soils exposed to the sun; (4) soils from under 

the rocks contain less iron than those exposed to the 

sun and atmosphere.

The larger amount of water evolved during heating 

to 200°C from soil beneath the rock than from soil exposed to the sun and atmosphere as well as the Biology experiment results on the sample from under a 

rock lends strong support to theories requiring storage 

of water and volatiles in the martian regolith. Eventually, the results may lead to a reasonable assessment 

of equilibrium conditions between the water vapor in 

the atmosphere and the water in the regolith. Although not understood at this time, the difference between the amount of iron in soils from under the rocks 

and soils exposed to the sun and atmosphere should 

be explicable.

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