Mars Pathfinder will carry an alpha-proton x ray spectrometer (APX) for the determination of the elemental chemical composition of Martian rocks and soils. The instrument will measure the concentration of all major and some minor elements, including C, N, and O at levels above typically 1 percent

Economou, T.

Rieder, Rudi

Waeke, H.

English

NASA Technical Reports Server

36 Mars Pathfinder tanding Sire Workshop 
N95- 161 99 
MAJA VALLES AND THE CHRYSE OUTFLOW COMPLEX 
SITES. J. W. Rice, Department of Geography, Arizona State 
University. Tempe AZ 85287, USA. p \ 
c Mala Valles Region: This candidate landing site is located at 
19"N, 53.5"W near the mouth of a major outflow channel, Maja 
Vedra Valles. This region has been mapped in detail by Rice and 
De Hon and is in press as a USGS 1:5oO,OOO scale geologic map. 
The advantages to this site are the following: Two distinct channel 
forms (outflow and dendritic valley network) in one location. These 
channels were formed by different processes. The outflow channels 
are believed to have formed by catastrophic release of water and the 
valley networks by surface runoff and or sapping. The ideal landing 
site, if it could be pinpointed, would be on the fan delta complex 
located at the terminus of the three channels (Maja, Maumee, and 
Vedra Valles). The fan delta complex would be a fairly smooth 
surface with shallow slopes. 
Water was impounded behind the wrinkle ridge system, Xanthe 
Scopulus, forming a temporal lake. This paleolake bed would also 
present itself as a safe landing site, perhaps similar to playas. Once 
the wrinkle ridges were breached the water flowed northeastward 
in the direction of the Viking I lander, some 350 km away. 
Objectives to be analyzed in this region are ( I )  origin and 
paleohydrology of outflow and valley network channels, (2) fan 
delta complex composition (this deposit located in this area is one 
of the few deposits identified at the mouths of any channels on the 
planet), and (3) analysis of any paleolake sediments (carbonates, 
evaporites). Another advantage to this area will be any blocks and 
boulders that were plucked out and carried along the 1600-km 
course of Maja Valles. These samples would provide a virtual grab 
bag of lithologies. For example, the oldest mappable rock unit (Nb. 
Noachian basement material) and the Hesperian ridged plains (Hr) 
are cut by Maja Valles before it empties into Chryse. It can be argued 
that we will not know their exact location, which is true, but it will 
provide us with information about the variety of rock types on Mars 
by only landing in one site. Other questions to be investigated in the 
area are the origin of wrinkle ridges by viewing ridge walls that were 
incised by the outflow, streamlined islanddbars; whether they are 
erosional or depositional, and if the location pennits view channel 
wall stratigraphy, fan delta stratigraphy, and perhaps send the rover 
up a channel mouth near the end of its mission. 
This site is below the 0-km elevation datum, within the latitude 
restrictions (19ON), and all the objectives stated above are within 
the 150-km landing error ellipse. This region is also imaged at 
resolutions of 40-50 m/p. 
The Chrsye Outflow Complex Region (Ares, Tiu, Mawrth, 
Simud, and Shalbatana Valles): The overall philosophy and 
objectives described above for the Maja Valles region apply here as 
well. The primary objectives here would be outflow channel dynam- 
ics (paleohydrology) of five different channel systems. One question 
to be answered might be whether all outflow channels are of the 
same origin and type. They are probably all somewhat different in 
terms of duration, age, source, and perhaps even origin. The grab  
bag philosophy of various rock types being deposited near channel 
mouths would apply here also. The site is located at I S O N .  35OW. 
However, the longitudinal coordinate can be relaxed or slid farther 
to either side of 35OW. Sliding the ellipse farther to the east would 
I Valles, and two "valley network" channel systems, Maumee and 
allow investigations of Mawrth Valles. The region near the mouth 
of Mawrth Valles would be of interest because this area contains 
material that appears to have been dissected, thus exposing the 
stratigraphy of what may possibly be deltaic sediments. 
N95-,1@00 -* 
d T E  VALLES SITE. J. W. Rice, Department of Geography, 
Arizona State University, Tempe AZ 85287, USA. 
This site is located at 16ON, 177OW on the flood plains of Marte 
Valles, which is perhaps the youngest channel system on Mars. 
However, the coordinates for the landing site are flexible. Moving 
the site more to the southwest would allow investigations of pos- 
sible lacustrine sediments. The channel extends for about 3000 km 
from southeastern Elysium Planitia into western Amazonis Planitia. 
This system appears to originate within the knobby cratered mate- 
rial around Cerberus Rupes, a set of en echelon fractures that extend 
for more than 1000 km. Crater counts indicate that this system is 
Amazonian in age. This channel may have also acted as a spillway 
between paleolakes located in Elysium and Amazonis Planitia. The 
young age of this channel warrants investigation because of climatic 
implications for fluvial activity in recent geologic time. The paucity 
of craters makes this an excellent site in terms of safety require- 
ments. Detailed work by Tanaka and Scott indicate that embayed 
craters larger than 1 km diameter appear embayed by the channeled 
plains unit, suggesting that it is only tens of meters thick. This 
material contributed to the resurfacing of the northern lowlands of 
the planet. Some of the objectives stated previously for the Maja 
Valles Region would also apply to this site (grab bag of rock types, 
etc.). This site is below the 0-km datum, located at 16ON. and has 
the young channeled plains, bars, terraces, and streamlined albedo 
patterns located within the 150-km landing error ellipse. Resolution 
coverage in some areas is as high as 13 d p .  
1 -  L N95- 16201 .-; :' . / y  
ALPHA PROTON X-RAY SPECTROMETER. R. Riederl, 
H. Wbke', and T. Ekonomou2, IMax-Planck-Institut fiir Chemie. 
Mainz, Germany, Wniversity of Chicago, Chicago IL 60637, USA. 
Mars Pathfinder will carry an alpha-proton X-ray spectrometer 
(APX) for the determination of the elemental chemical composition 
of martian rocks and soils. The instrument will measure the concen- 
tration of all major and some minor elements, including C. N. and 
0, at levels above typically 1%. 
The method employed consists of bombarding a sample 50 mm 
in diameter with alpha particles from a radioactive source (50 mCi 
of 240Cm) and measuring ( I )  backscattered alpha particles (Ruther- 
ford backscatter = RBS mode), (2) protons from A( ,p)B reactions 
(proton mode) and (3) characteristic X-rays emitted from the sample 
(X-ray mode). In RBS mode all elements with atomic mass greater 
than four are registered, thus permitting normalization of results to 
100% concentration. This feature permits accurate quantitative 
analysis independent (within limits) of the actual measurement 
geometry. Data obtained from proton and X-ray modes are used to 
enhance selectivity of the RBS mode for the rock-forming elements 
Mg, AI, and Si and for heavier elements (K and Ca. Fe-group): 
https://ntrs.nasa.gov/search.jsp?R=19950009786 2020-06-16T08:53:04+00:00Z
LPI Technical Report 94-04 37 
Resolving power in the RBS mode is determined by the energy 
spread of the alpha source and the range of backscatter angles 
observed by the detectors. These parameters in turn determine the 
number of backscattered alpha particles per unit time. In the present 
design the use of proton and X-ray data permits us to trade selectiv- 
ity for sensitivity. 
The instrument has a long standing space heritage, going back to 
the days of Surveyors V, VI, and VI1 (1968-1969) and Phobos 
(1988). The present design is the result of an endeavor to reduce 
mass and power consumption (Surveyor 10 kg/lO W, Phobos: 
2.7 kgl2.5 W, this instrument: 0.6 kgl0.3 W); four instruments are 
scheduled to fly on the Russian Mars ‘94 mission: two on penetrators 
(without X-ray mode) and two on small stations (including the X- 
ray mode, using “room temperature” mercuric iodide detectors 
provided by the University of Chicago). These are currently being 
calibrated and prepared for integration. 
The instrument for Mars Pathfinder will be a duplicate of the 
instruments for the Mars ‘94 small stations but with minor changes. 
It consists of a sensor head, incorporating the alpha sources, a 
telescope of silicon detectors (35 and 700 m thick) for the detection 
of alpha particles and protons and a mercuric iodide X-ray detector 
with preamplifier, and an electronics box (80 x 70 x 60 mm) 
containing a microcontroller-based multichannel spectrometer. The 
sensor head will be mounted on the rear of the Mars Pathfinder 
Microrover on a deployment mechanism that permits placement of 
the sensor in contact with sample surfaces inclined at any angle from 
horizontal to vertical, thus permitting measurement of the compo- 
sition of soil and rock sample. The electronic box will be contained 
in the microrover’s ‘‘warm’’ container and will communicate with 
the microrover control system through a standard RS 232 serial 
interface. 
- - :  ,’. I. y / , I - ’  ... 
ATMOSPHERE STRUCTURE 
STRUMENT FOR MARS PATHFINDER. A. Seiff, San Jose 
State University Foundation, Mail Stop 245-1, NASA Ames Research 
Center, Moffett Field CA 94035, USA. 
The MESUR Science Definition Team recommended that all 
MESUR probes, including Pathfinder, carry an ASYMET experi- 
ment, in order that no opponunity be lost to characterize the atmos- 
phere of Mars in passing through it. The experiment was thus 
included on Pathfinder from the start (February 1992), but on an 
essentially noninterference basis: It was to make no unusual de- 
mands on the spacecraft. A Science Advisory Team appointed by 
NASA Headquarters in September 1993 fmt met on November 3 to 
initiate formal science participation, and the level of activity has 
since been high. The instrument passed its Preliminary Design 
Review on February 28. 
The structure of the atmosphere is measured during entry and 
descent; meteorological parameters, pressure, temperature, and 
wind velocity are collected during the mission lifetime after land- 
ing. The structure experiment has two phases. During high-speed 
entry, from 160 km to near 8 km (where the parachute is deployed), 
accelerometers define the density structure. In the parachute de- 
scent, atmospheric pressure and temperature are measured until 
airbags are deployed -150 m above touchdown. Entry phase pres- 
sures are obtained by integrating measured densities assuming 
hydrostatic equilibrium (the technique used on the Viking and 
Pioneer Venus missions and to be used on the Galileo Probe); the 
equation of state then yields temperatures. The sensors employed 
are guidance-quality accelerometers, Tavis and Vaisalla pressure 
sensors, and chromel-constantan thermocouples with platinum re- 
sistance thermometers at their cold junctions. 
Constraints imposed do not allow the descent phase sensors to 
project outside the lander envelope, nor are the accelerometers in an 
optimum configuration about the center of gravity. The Science 
Advisory Team (SAT) is exploring the effects of these limitations, 
but they should not prevent the acquisition of valuable data. 
The meteorology measurements were originally limited to pres- 
sure and temperature, but were extended to include winds because 
of the apparent simplicity of the hardware. The measurement reso- 
lution will be 256x better than that of Viking, which was resolution 
limited. Temperature measurements at three elevations above the 
surface. and wind measurements at two heights (if affordable within 
available lander resources), will define profiles not available from 
the Viking instrument. Rapid sampling for 5 midhr will define both 
diurnal and seasonal variations and turbulence. Consideration is 
being given to sampling over selected I-hr intervals for better 
definition of fluctuations. Pressure sensors are s h a d  with the ASI. 
Temperature sensors are chromel-constantan thermocouples of 75- 
pm wire diameter. Wind is sensed from the convective heat loss of 
heated wires. Sensors have been designed and evaluated analyti- 
cally. They will be evaluated experimentally and refined if neces- 
sary from tests at Mars surface conditions in the Mars Wind Tunnel 
at NASA Ames Research Center (operated by Arizona State Univer- 
sity). 
To move them away from thermal influence of the lander elec- 
tronics, the temperature and baseline wind sensor are mounted on 
the whip antenna, which communicates with the rover, about 1 m 
away from the lander COR. The wind sensor and primary tempera- 
ture sensors are about 0.5 m above the surface; two other tempera- 
ture sensors are 0.25 m and 0.125 m above the surface. ’IRe second 
wind sensor is proposed to be mounted on the low-gain antenna, 
about 1 m above the surface. Pressure sensors are in the Warm 
Electronics Box in the lander core. The temperature profiles will 
differentiate between stable and convective near-surface condi- 
tions, and define atmospheric heating rate. Wind profiles will like- 
wise discriminate stable from unstable conditions, and define near- 
surface shear, as well as provide a valuable input to boundary layer 
models. 
The greatest concem we have for the descent phase results from 
the restriction against external deployment of the temperature sensor 
(for reasons of air bag safety). The sensor must sample atmosphere 
flowing through the lander rather than around it, at velocities well 
below the descent velocity. This slows sensor response time, e.g., to 
-4 s if the internal velocity (yet to be established) is 1 mls. For the 
entry phase, the major problem is correction of measured accelera- 
tions for angular inputs at off-center of gravity locations. For landed 
meteorology, the major concern is the design of the wind sensor to 
work sensitively at extremely low power levels in the low-density 
atmosphere and define wind directions. Problems of thermal con- 
tamination are also inevitably present. 


Alpha proton x ray spectrometer

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server