of 16
JOURNAL
OF
GEOPHYSICAL
RESEARCH,
VOL.
97,
NO.
E5,
PAGES
7665-7680,
MAY
25,
1992
Mars
Observer
Mission
A.
L.
ALBEE
California
Institute
of
Technology,
Pasadena
R.
E.
ARVIDSON
McDonnell
Center
for
Space
Sciences,
Washington
University,
Saint
Louis,
Missouri
F.
D.
PALLUCONI
Jet
Propulsion
Laboratory,
Pasadena,
California
The
Mars
Observer
mission
will
extend
the
exploration
and
characterization
of
Mars
by
providing
new
and
systematic
measurements
of
the
atmosphere,
surface,
and
interior
of
the
planet.
These
measurements
will
be
made
from
a low-altitude
polar
orbiter
over
a period
of
I Martian
year,
permitting
repetitive
observations
of
the
surface
and
of
the
seasonal
variations
of
the
atmosphere.
The
mission
will
be
conducted
in
a manner
that
will
provide
new
and
valuable
scientific
data
using
a
distributed
data
system
that
minimizes
operational
complexity
and
cost.
INTRODUCTION
The
Mars
Observer
spacecraft
will
be
placed
into
orbit
about
Mars
in
August
1993
(Figure
1).
After
4 months
of
trim
maneuvers
to
come
into
a circular
orbit,
the
spacecraft
will
begin
mapping
the
atmosphere,
surface,
and
interior
for
at
least
1 Martian
year.
The
primary
geoscience
objectives
for
Mars
Observer
include
the
global
definition
of
the
topogra-
phy
and
gravitational
fields,
global
determination
of
the
elemental
and
mineralogical
character
of
surface
materials,
and
determination
of
the
nature
of
the
magnetic
field
around
Mars.
The
primary
climatology
objectives
are
the
determi-
nation
of
the
time
and
space
distribution,
abundances,
sources,
and
sinks
of
volatile
material
and
dust
over
a
seasonal
cycle,
as
well
as
the
delineation
of
atmospheric
structure
and
dynamics.
Mars
Observer
will
provide
a basic
global
understanding
of
Mars
as
it
exists
today
and
will
provide
a framework
for
understanding
its
past.
It will
also
establish
a base
of
knowledge
for
future
Mars
missions,
including
network
science,
returned
samples,
and
an
even-
tual
piloted
landing.
This
paper
is
an
overview
of
the
Mars
Observer
mission.
Emphasis
is placed
on
summarizing
key
science
objectives,
and
providing
high-level
descriptions
of
the
spacecraft,
mapping
orbit,
and
mission
operations.
Further,
we
provide
an
overview
of
science
analysis
and
archiving
functions.
Note
that
each
Mars
Observer
instrument
is
described
in
detail
in
a suite
of
papers
included
in
this
issue
and
authored
by
members
of
the
respective
instrument
teams.
More
detailed
information
on
the
mission
elements
and
the
space-
craft
can
be
obtained
from
a group
of
technical
papers
[Allbee
and
Palluconi,
1991;
Beerer
and
Roncoli,
1991;
Blume
et
al.,
1991;
Erickson
and
McKinley,
1991;
Esposito
et
al.,
1991;
Halsell
and
Bollman,
1991;
Komro
and
Hujber,
1991;
Malin
et
al.,
1991;
McCleese
et
al.,
1986;
McKinley,
1991;
Palocz,
1991;
Potts,
1991].
Copyright
1992
by
the
American
Geophysical
Union.
Paper
number
92JE00342.
0148-0227/92/92J
E-00342505.00
MISSION
OVERVIEW
Mars
Observer
will
be
launched
on
a Titan
III
rocket
from
Cape
Kennedy,
Florida,
in
September
1992.
Figure
1 pro-
vides
an
overview
of
the
mission.
After
an
11-month
transit,
the
spacecraft
will
be
injected
into
an
elliptical
orbit
about
Mars
with
a periapsis
near
the
north
pole.
The
orbit
will
then
be
adjusted
through
a series
of
maneuvers
to
a near-circular,
near-polar,
Sun-synchronous
orbit
with
an
average
altitude
of
400
km
and
0200/1400
LT
equatorial
crossing
times.
The
mapping
orbit
has
a
118-min
period
with
a
7-sol
near-repeat
ground
track
(a
sol
is
a Martian
day,
about
5%
longer
than
an
Earth
day).
Each
7-sol
cycle
will
be
system-
atically
offset
from
the
next,
and
as
a result,
the
planet
will
be
repeatedly
mapped
in
26-sol
cycles,
with
a
58.6-km
nominal
path
separation.
Orbit
trim
adjustments
will
make
it
possible
to
obtain
uniform
coverage
during
the
course
of
the
mission,
with
an
ultimate
spacing
of
ground
tracks
at
the
equator
of
3.1
km.
The
mapping
orbit
meets
the
planetary
protection
requirement
that
the
unsterilized
spacecraft
not
impact
the
planet
before
the
year
2039
(NASA
Management
Instruction,
NHB-8020).
The
spacecraft
provides
a
three-axis
stabilized,
nadir-
oriented
platform
for
continuous
observations
of
Mars.
During
at
least
1 Martian
year
(687
Earth
days)
of
observa-
tions,
the
instruments
will
acquire
data
in
a
systematic
program
of
global
mapping.
Table
1 provides
a summary
of
instruments
and
their
capabilities.
The
normal
observation
sequence
will
be
to
record
continuously
for
24
hours
and
to
then
play
the
data
back
in
one
10-hour
link
to
a 34-m
NASA
Deep
Space
Network
tracking
station.
In
addition,
approx-
imately
every
3 days,
a real-time
link
will
be
used
to
transmit
data
at
a relatively
high
rate.
With
this
mission
overview,
we
now
discuss
the
major
science
objectives
that
guided
the
mission
design
and
instru-
ment
selections.
SCIENCE
OBJECTIVES
The
primary
Mars
Observer
science
objectives
are
to
(1)
determine
the
global
elemental
and
mineralogical
character-
7665
7666
ALBEE
ET
AL.:
MARS
OBSERVER
MISSION
INTERPLANETARY
CRUISE
TO
MARS
LASTS
NEARLY
ONE
YEAR
INSERTS
INTO
AN
INTERMEDIATE
ELLIPTICAL
POLAR
ORBIT
AT
MARS
USES
THE
TRANSFER
ORBIT
STAGE
FOR
INTERPLANETARY
INJECTION
LAUNCHES
ON
TITAN
III
IN
SEPTEMBER
1992
OBSERVES
MARS
FROM
THE
MAPPING
ORBIT
FOR
ONE
MARTIAN
YEAR
--
687
DAYS
Fig.
1.
Mission
outline
for
the
3.4-year
duration
of
the
Mars
Observer
mission.
istics
of
surface
materials;
(2)
define
the
global
topography
and
gravity
fields;
(3)
establish
the
nature
of
the
magnetic
field;
(4)
determine
the
time
and
space
distribution,
abun-
dance,
sources,
and
sinks
of
volatile
material
and
dust
over
a seasonal
cycle;
and
(5)
explore
the
structure
and
dynamics
of
the
atmosphere.
These
objectives
and
the
mission
itself
are
derived
from
the
recommendations
of
the
Solar
System
Exploration
Committee
(SEEC)
[1983,
pp.
95-99].
All
the
objectives
require
mapping
that
results
in
derived
data
sets
that
have
spatial
and
temporal
dimensions.
For
the
geoscience
objectives
the
intent
is
to
generate
a suite
of
products
that
depict
surface
and
subsurface
characteristics
as
a function
of
latitude,
longitude,
elevation,
and
season.
For
many
climatology
objectives
the
data
sets
will
be
orga-
nized
by
latitude,
longitude,
altitude,
and
season.
As
a
result,
this
mission
will
obtain
a systematic
global
character-
ization
of
Mars,
as
it exists
today.
This
characterization
will
also
help
us
to
understand
the
geologic
and
climatologic
history
of
Mars
and
the
evolution
of
its
interior
and
surface
and
will
provide
bases
for
comparison
with
Venus
and
Earth.
Geoscience
The
first
three
science
objectives
listed
above
involve
measurement
of
geological,
geochemical,
and
geophysical
quantities.
Mars
is a single-plate
planet,
with
a surface
area
that
is
slightly
larger
than
the
combined
area
of
all
the
plates
that
make
up
Earth's
continents.
Mapping
of the
144
x 106
km
2 of Martian
surface
will
occur
over
the
full
Martian
year
planned
for
the
mission.
The
Martian
crust
includes
high-
altitude,
heavily
cratered
uplands
in
the
southern
hemi-
sphere
and
lower,
sparsely
cratered
plains
in
the
northern
hemisphere
(Figure
2).
The
Tharsis
Plateau
is a 4-
to
10-km-
high,
4000-km-wide
zone
of
relatively
young
volcanic
flows
and
large
volcanic
constructs
that
straddles
the
Martian
TABLE
1.
Characteristics
of
the
Mars
Observer
Instruments
Instrument
Mass,
Measurements
kg
Average*/
Peak
Power,
W
Data
Rate
bits/s
Gamma
ray
spectrometer
(GRS)
Mars
Observer
camera
(MOC)
Thermal
emission
spectrometer
(TES)
Mars
Mars
Observer
laser
altimeter
(MOLA)
Ultrastable
oscillator
(USO/RS)
Magnetometer/electron
reflectometer
(MAG/ER)
Pressure
modulator
IR
radiometer
(PMIRR)
Mars
Balloon
Relay
Experiment
(MBR)
primary/secondary
gamma
rays,
bursts
at
0.2-10
23.2
MeV
and
neutrons
to
10
keV
Imaging-narrow
and
wide
fields
at œ10,
3.5
m
for
0.5-
21.4
0.9/xm,
at œ6.5,
11.3
mm
for
blue
and
red
(0.4-
0.45
and
0.58-0.63
um)
interferometer
at
6-
to
50-urn
spectral
range
and
14.1
broadbands
at
0.3-3.0
and
4.5-100
um
topography-74-cm
focal
length
telescope
sends
and
25.9
receives
1.06-um
laser
pulse;
150-m
footprint
at
2-m
timing
accuracy
oscillator
provides
precision
frequency
reference
for
1.3
radio
science
measurements
during
occultations
magnetic
fields
in
the
range
from
16
to
65536
nT;
5.4
electrons
in
the
range
from
1 to
10
keV
six
IR
channels
between
7.0
and
46.5
um
with
40.9
pressure-modulated
CO2
and
H20
channels;
albedo
at
0.3-3.0
um
signal
relay
receiver;
interrogating
at
437
MHz;
7.7
receiving
at
401
and
406
MHz
14.0/34.9
7.5/25.7
13.2/18.3
23.1/30.2
2.2/4.2
4.6/4.6
34.1/34.7
9.0/9.05
665
700/2856/9120
(29260)RT?
688/1664/
(4992)RT•
618
N/A
324/648/1296
156
N/A
*Average
is
orbital
average.
?RT
is
real-time
rate.
ALBEE
ET
AL..'
MARS
OBSERVER
MISSION
7667
..
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--
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Fig.
2.
Viking
image
mosaic
of
the
contact
between
the
cratered
uplands
and
the
northern
plains
centered
on
the
Mangala
Vailis.
Mangala
cuts
through
heavily
cratered
terrain
and
ends
at
the
escarpment
between
the
cratered
upland
and
the
plains.
The
smooth
rolling
plains
to
the
northwest
may
be
ignimbrite
deposits.
This
is a mosaicked
digital
image
model
(MDIM)
at
approximately
6 ø south
latitude;
150
ø west
longitude.
Frame
width
is about
1000
km.
equator.
Annual
and
permanent
ice
and
associated
layered
deposits
occur
near
each
pole.
Further,
bedrock
has
been
modified
by
crustal
and
surface
processes
to
produce
can-
yons
and
channels,
chaotic,
fretted,
and
hummocky
terrains,
and
the
surface
is
covered
with
a thin
veneer
of
aeolian
and
locally
derived
soils.
Mars
Observer
data
will
be
used
to
understand
the
distri-
bution
of
chemical
elements
and
minerals
on
the
Martian
surface
in
relation
to
the
age,
origin,
nature,
and
weathering
of
the
surface
rocks.
Simultaneous
global
mapping
of
the
gravitational
field,
the
surface
topography,
and
the
magnetic
field
will
improve
our
understanding
of
both
the
surface
and
the
interior
of
Mars.
Combining
these
distinctly
different
measurements
in
a single
mission
exploits
their
inherent
synergism
and
allows
us
to
realistically
address
such
global
problems
as
Mars'
bulk
composition,
the
degree
of
differen-
tiation
of
the
planet,
the
chemical
and
mineralogical
compo-
sition
of
the
crust
and
mantle,
and
the
nature
and
cause
of
the
planet-wide
dichotomy
of
uplands
and
plains.
The
K/U
ratio
for
Mars
will
be
determined
by
the
gamma
ray
spectrometer
(GRS)
and
will
provide
an
important
con-
straint
on
bulk
composition.
Uranium
provides
an
index
for
those
elements
that
tend
to
condense
from
the
solar
nebula
at
high
temperatures;
potassium
is
an
index
for
elements
with
lower
condensation
temperatures;
yet
both
behave
similarly
in
magmatic
processes.
Thus
the
K/U
value,
cou-
pled
with
other
elemental
ratios,
provides
a means
of
recon-
structing
the
bulk
composition
of
the
planet.
The
content
of
these
two
elements
in
the
crustal
material
also
gives
an
indication
of
the
degree
of
differentiation
of
the
planet,
7668
ALBEE
ET
AL.'
MARS
OBSERVER
MISSION
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...... •::::•;•.•::
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•":
Fig.
3.
Viking
Lander
image
of
soil
and
bedrock
at
the
Lander
2 site.
Panorama
is generated
from
high-resolution
(0.04
• angular
resolution)
data.
estimates
of
the
amount
of
volatiles,
including
water,
that
have
outgassed
from
the
planet,
and
places
constraints
on
the
thermal
evolution
models.
A major
question
to
be
addressed
by
Mars
Observer
is the
nature
and
cause
of
the
planet-wide
dichotomy
into
old
cratered
upland
and
sparsely
cratered
plains.
Mars
Observer
will
determine
chemical
and
mineralogical
differences
be-
tween
the
two
regions,
how
the
crust
and
lithosphere
differ
beneath
the
two
regions,
and
what
is
the
nature
of
the
boundary.
These
estimates
will
lead
to
a much
better
under-
standing
of
the
nature
of
the
dichotomy,
what
caused
it,
and
when
it
occurred.
The
volcanoes
of
Mars
are
well
known,
but
we
have
little
information
on
the
chemistry
and
mineralogy
of
the
lavas.
This
information
would
be
of
use
to
infer
the
composition
of
the
mantle,
the
depth
of
origin
of
the
magma,
and
whether
magmas
have
undergone
differentiation
during
passage
from
the
source
region
to
the
surface.
Mars
Observer
will
also
provide
the
data
to
tell
if there
are
regional
differences
in
composition
that
might
result
from
differences
in
source
rock
or
depth
of
origin
of
the
magmas.
Mapping
of
the
gravity
and
topographic
fields
will
lead
to
better
understanding
of
volcanic
processes
and
the
thermal
evolution
of
the
interior
of
Mars.
Lithospheric
thickness
will
be
determined
from
the
deformation
of
the
crust
by
large
volcanoes,
as
reflected
in
the
topographic
and
gravity
field
data.
Thermal
conditions
in
the
interior
will
be
modeled
based
on
the
degree
and
depth
of
isostatic
compensation
of
features
such
as
craters,
canyons,
and
volcanoes.
Increase
in
the
depth
of
compensation
with
the
age
of
features
would
suggest
that
the
lithosphere
has
thickened
with
time.
Mag-
netic
measurements
will
indicate
whether
conditions
in
the
core
today
can
sustain
a planetary
dynamo;
local
remnant
magnetism
may
establish
whether
and
when
such
conditions
existed
in
the
past.
Much
of
the
Martian
surface
is
covered
with
soils
that
are
a
combination
of
local
and
aeolian
materials,
including
highly
altered
components
(Figure
3).
Tentative
identifica-
tions
have
been
made
of
specific
absorption
bands
seen
in
telescopic
observations,
but
we
actually
know
very
little
about
the
chemistry
and
mineralogy
of
the
surface.
Mars
Observer
will
provide
basic
characterization
of
these
mate-
rials.
We
particularly
want
to
understand
the
role
of
water,
its
form
(adsorbed,
ice,
in
minerals,
etc.),
and
whether
water-containing
minerals
are
forming
currently
or
are
"fos-
sil"
from
past
climates.
We
may
then
infer
how
water
is
cycled
during
the
current
seasonal
and
obliquity
cycles
and
whether
significantly
different
climates
in
the
past
are
re-
quired
to
explain
the
formation
of
the
soil
materials.
Under-
standing
the
abundance
of
volatile-containing
materials
will
lead
to
improved
estimates
of
the
amount
of
water
and
other
volatiles
outgassed
from
the
planet
and
provide
clues
as
to
when
the
outgassed
volatiles
were
removed
from
the
atmo-
sphere
by
escape
or
becoming
fixed
in
the
regolith.
Mars
Observer
also
provides
an
opportunity
for
mapping
the
planet-wide
distribution
of
ice
in
near-surface
material.
Ice
is believed
to
be
a major
component
in
the
polar-layered
terrain
(Figure
4),
detectable
by
Mars
Observer
from
both
compositional
and
gravity
information.
Ice
may
also
be
present
near
the
surface
at
high
latitudes,
its
limit
varying
with
the
season.
Detection
of
ice
will
depend
upon
its
being
close
enough
to
the
surface
such
that
seasonal
changes
can
be
discerned.
Detection
of
liquid
water
is
not
expected,
but
aberrant
conditions
might
allow
seepage
to
the
surface.
Such
a discovery
would
lead
to
significant
reassessment
of
how
water
is
circulated
about
Mars.
Finally,
more
precise
determination
of
topography
and
gravity
will
lead
to
a more
complete
understanding
of
almost
every
geologic
process
that
has
affected
the
surface.
Our
current
understanding
is based
largely
on
surface
morphol-
ogy
and
is
hindered
by
the
lack
of
quantitative
information
against
which
different
ideas
can
be
tested.
Better
informa-
ALBEE
ET
AL.'
MARS
OBSERVER
MISSION
7669
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Fig.
4.
Viking
Orbiter
image
mosaic
centered
on
the
north
pole
and
showing
the
residual
north
polar
cap,
layered
deposits,
and
the
dark
circumpolar
area
of
sand
dunes.
This
is a Mars
digital
image
mosaic
(MDIM)
with
approximately
1500-km
frame
width.
tion
on
slopes
will
lead
to
a better
understanding
of
fluvial
erosion
and
emplacement
of
lavas.
Comparison
of
present-
day
slopes
with
original
slopes
as
inferred
from
the
gradients
of
lava
flows
or
channels
will
provide
information
on
defor-
mation
rates.
Better
information
on
gravity
patterns
of
craters
and
on
crater
depths,
rim
heights,
and
ejecta
thick-
ness
will
lead
to
a more
complete
understanding
of
cratering.
In
summary,
acquisition
of
chemical,
mineralogical,
grav-
itational,
and
elevation
data
by
Mars
Observer
will
improve
our
understanding
of
almost
every
aspect
of
Martian
geol-
ogy.
However,
the
main
impact
will
be
an
improved
under-
standing
of
global
problems
rather
than
local
geologic
pro-
cesses,
although
regional
studies
will
be
utilized
to
address
global-scale
problems.
Improved
understanding
of
the
plan-
et's
bulk
composition,
the
composition
of
the
crust
and
mantle,
the
thickness
of
the
lithosphere,
the
thermal
state
of
the
interior,
and
the
planet's
outgassing
history
will
inevita-
bly
follow
from
Mars
Observer.
This
will
be
the
mission's
main
geoscience
legacy.
Climate
The
fourth
and
fifth
Mars
Observer
science
objectives
address
volatile
(carbon
dioxide
and
water)
and
dust
cycles
and
the
Martian
atmosphere.
The
emphasis
will
be
on
seasonal
variations;
hence
the
use
of
the
term
climatology.
An
understanding
of
the
current
climate
of
Mars
will
permit
us
to
better
assess
how
currently
active
processes
(weather-
ing,
erosion,
atmospheric
transport,
and
dust
deposition)
are
modifying
the
surface.
If
we
are
able
to
understand
the
current
climate,
we
may
more
confidently
project
this
knowledge
back
in
time
to
periods
when
the
Martian
orbit,
axial
characteristics,
and
atmospheric
pressure
were
differ-
ent.
In
principle,
determination
of
the
daily
as
well
as
the