of 3
498
J.
SPACECRAFT
VOL.
28,
NO.
5
Mars
Observer:
The
Next
Mars
Mission
Arden
L.
Albee*
California
Institute
of
Technology,
Pasadena,
California
91125
and
Frank
D.
Palluconit
Jet
Propulsion
Laboratory,
California
Institute
of
Technology,
Pasadena,
California
91109
The
next
mission
to
Mars,
called
Mars
Observer,
will
be
launched
in
September
1992.
After
the
capture
of
the
spacecraft
by
the
planet
and
the
adjustment
into
a low,
Sun-synchronous,
polar-mapping
orbit
in
late
1993,
observations
will
continue
for
a Mars
year
(687
days).
The
scientific
mission
centers
around
global
geoscience
and
climatology
observations
of
the
Mars
atmosphere,
surface,
and
interior.
The
seven
experiments
carried
by
the
spacecraft
involve
gamma-ray
spectroscopy,
magnetometry,
surface
and
atmospheric
imaging,
atmospheric
sounding,
laser
altimetry,
gravity
mapping,
and
thermal
emission
spectroscopy.
All
experiments
contain
micro-
processors,
which
will
be
controlled remotely
from
the
investigator's
home
institution.
The
long
planned
period
of
continuous
24
hi
day
observation
promises
a rich
harvest
of
global
and
seasonal
information.
Mars
Observer
stands
between
the
initial
exploration
of
Mars
and
the
more
intensive
explorations,.
possibly
involving
human
beings,
that
are
only
now
being
planned.
Introduction
T
HE
scientific
activity
of
the
Mars
Observer
mission
is
or-
ganized
around
the
twin
themes
of
geoscience
and
clima-
tology.
Full
mapping
operations
will
begin
late
in
1993
and
will
continue
for
a full
Mars
year
(687
days)
through
the
fall
of
1995.
This
long
period
will
provide
sufficient
time
to
examine
the
full
range
of
seasonal
behavior
and
to
thoroughly
map
the
planet.
Background
Mars
is
the
most
closely
examined
of
any
planet
other
than
the
Earth.
Over
20
space
vehicles
have
been
sent
to
the
vicinity
of
Mars
in
either
a flyby,
orbiter,
or
landed
mode, the
most
re-
cent
being
the
Soviet
Phobos
II
Orbiter
in
1989.
A
key
objec-
tive
in
this
exploration
involves
understanding
the
origin
and
subsequent
evolution
of
Mars
in
the
context
of
its
nearest
neighbors,
Earth
and
Venus.
These
three
terrestrial
planets
formed
in
the
same
region
of
the
solar
system
at
the
same
time,
but
they
have
subsequently
followed
quite
different
evolutionary
paths.
For
example,
the
surface
atmospheric
pressure
at
Venus
is
90
times
that
of
Earth's,
but
on
Mars
the
surface
pressure
is
less
than
one-hundredth
that
of
Earth's.
The
atmospheres
of
both
Venus
and
Mars
are
dominated
by
the
greenhouse
gas,
carbon
dioxide,
and
they
are,
thus,
of
considerable
interest
since
this
gas
also
figures
prominently
in
concerns
about
climate
change
on
Earth.
Although
the
Martian
atmosphere
is
thin
by
terrestrial
stan-
dards,
it does
contain
measurable
amounts
of
water
vapor.
At
times,
the
Martian
relative
humidity
reaches
1000Jo;
leading
to
formation
of
water
clouds,
fogs,
and
frost
in
addition
to
car-
bon
dioxide
clouds
and
frost.
However,
it cannot
rain
on
Mars
at
present
because
the
atmospheric
pressure
is
too
low
for
liq-
uid
water
to
be
stable.
Apart
from
water
vapor
in
the
atmo-
sphere,
water
is
also
known
to
exist
on
Mars
in
the
extensive
northern
permanent
polar
cap.
Surprisingly,
the
smaller
Received
Dec.
11,
1989;
revision
received
Oct.
2,
1990;
accepted
for
publication
March
30,
1991.
Copyright
©
1991
by
the
American
In-
stitute
of
Aeronautics
and
Astronautics,
Inc.
The
U.S.
Government
has
a royalty-free
license
to
exercise
all
rights
under
the
copyright
claimed
herein
for
Governmental
purposes.
All
other
rights
are
reserv-
ed
by
the
copyright
owner.
*Project
Scientist,
Mars
Observer
Project.
tDeputy
Project
Scientist,
Mars
Observer
Project,
Mail
Stop
264-627.
southern
permanent
polar
cap
is
covered,
even
during
south-
ern
summer,
by
carbon
dioxide
frost
and
is
not
a source
of
water
for
the
atmosphere
at
present.
Ample
evidence
exists,
in
the
form
of
very
large
flood-type
channels
and
loosely
integrated
drainage
networks,
that
water
in
large
amounts
was
present
on
the
Martian
surface
in
the
past.
What
happened
to
it?
Current
thinking
places
some
of
this
water
beneath
the
surface
in
a frozen
state
while
some
has
escaped
as
vapor
and
has
been
carried
off
into
interplanetary
space
by
erosion
of
the
Martian
atmosphere
in
the
solar
wind.
Unraveling
the
history
of
water
on
Mars
is one
of
the
underly-
ing
motivations for
the
Mars
Observer
mission.
If
we
can
understand
the
behavior
of
the
atmosphere
at
present,
we
can
more
confidently
extrapolate
backward
in
time
to
understand
conditions
at
earlier
epochs.
The
thinness
of
the
Martian
atmosphere
is
an
advantage
for
a variety
of
remote
sensing
experiments
because
it permits
a
nearly
unobstructed
view
of
the
surface
from
orbit.
Its
thin-
ness
even
permits
some
measurements,
like
gamma-ray
spec-
troscopy,
which
are
not
possible
from
Earth
orbit
because
of
absorption
of
the
emitted
gamma
rays
by
our
thicker
atmo-
sphere.
It
is
fortunate
that
measurements
of
surface
properties
can
be
made
from
orbit
because,
although
Mars
is
a smaller
planet
than
Earth,
its
144
x
10
6
km
2
surface
area
is
equal
to
the entire
continental
area
of
the
Earth.
For
a long
time
to
come,
remotely
sensed
data
will
be
the
only
type
we
will
have
from
many
regions
of
Mars.
The
surface
of
Mars
is
especially
important
in
understand-
ing
the
evolution
of
the
terrestrial
planets
because
parts
of
its
surface
preserve
direct
evidence
of
processes
going
back
all
the
way
to
the
period
of
late
bombardment
following
planetary
formation
(about
4 billion
years
ago).
The
first
U.S.
mission
to
Mars,
Mariner
4,
returned
images
of
this
moonlike,
heavily
cratered
region
of
Mars.
On
Earth,
this
early
bombardment
record
has
been
either
erased
or
heavily
modified.
Sea
floor
creation
and
subsequent
subduction
has
erased
most
traces
of
the
Earth's
early
oceanic
crust,
and
on
the
continents
erosion
has
been
nearly
as
effective.
Subduction
of
the
crust
appears
to
be
absent
on
Mars,
and
erosion
has
been
considerably
less
effective.
In
this
sense,
the
early
history
of
Mars
is
more
open
to
inspection
than
is
the
early
history
of
Earth.
Key
Mission
Elements
The
scientific
plans
for
the
Mars
Observer
mission
are
or-
ganized
around
a set
of
spacecraft
and
mission
choices
that
are
SEPT.-OCT.
1991
MARS
OBSERVER:
THE
NEXT
MARS
MISSION
499
being
applied
for
the
first
time
to
a planetary
mission.
A
low-
altitude,
near-circular,
near-polar,
and
near-Sun-synchronous
orbit
has
been
selected
for
mapping
the
planet.
Each
aspect
of
this
orbit
contributes
to
the
measurement
opportunities.
The
low
altitude
(400
±
25
km)
produces
higher
spatial
resolution
and
improved
signal-to-noise
ratios
for
some
experiments.
The
near-circular
orbit
(eccentricity
<
0.01)
allows
nearly
uniform
spatial
resolution
at
all
latitudes
and
longitudes,
facilitating
intercomparison
of
measurements
from
different
locations.
The
near-polar
orbit
(inclination
of
93
deg)
permits
observa-
tions
to
be
made
at
all
latitudes
and
longitudes
and
is
the
key
to
a global-mapping
mission.
The
near-Sun-synchronous
orbit
(2
p.m.
sunward
equator
crossing
time)
makes
possible
repeated
observations
at
the
same
time
of
day,
thereby
making
it possi-
ble
to
separate
diurnal
and
seasonal
behavior.
This
orbit
also
readily
accommodates
continuous
observation
from
experi-
ments
that
must
use
radiators
to
cool
detectors.
Mars
Observer's
Sun-synchronous
orbit
is
similar
to
that
used
by
the
LANDSAT,
Spot,
and
NOAA
terrestrial
polar
orbiters.
The
orbit
period
is
118
min.
This
permits
sampling
at
two
times
of
day
for
13
longitudes
each
Martian
day.
The
Mars
Observer
spacecraft
will
maintain
a
nadir-
pointing
orientation
for
the
entire
mapping
mission,
so
that
each
experiment
will
be
able
to
view
Mars
continuously
for
an
entire
Martian
year.
The
spacecraft
will
support
this
con-
tinuous
data
collection
with
onboard
tape
recorders.
A
daily
playback
to
Earth
is
planned
for
Mars'
recorded
data,
along
with
supplemental
real-time
data
transmissions
for
high-data-
rate
experiments.
Several
experiments
that
need
to
look
in
more
than
one
direction,
e.g.,
atmospheric
sensors
that
need
to
look
from
the
nadir
point
to
the
limb,
will
use
internally
driven
electronic
or
mechanical
articulation.
The
science
instruments
will
weigh
approximately
150
kg.
The
average
total
science
instrument
power
consumption
will
be
about
121
W.
This
level
of
power
will
be
continuously
available
to
the
science
complement
for
the
duration
of
the
mapping
mission.
The
number
of
bits
of
recorded
data
returned
each
day
depends
on
the
Earth
to
Mars
distance
and
will
range
from
a low
of
3.5 x
10
8
bits/day
when
Mars
is
far-
thest
from
the
Earth
to
a high
of
1.4
X
10
9
bits/
day
near
op-
position.
Every
experiment
will
be
controlled
by
a microprocessor
contained
within
the
instrument.
Throughout
the
long
map-
ping
mission,
the
investigators
will
remain
at
their
home
insti-
tutions
and
will
command
their
instruments
remotely
from
these
locations
through
an
operations
center
at
the
Jet
Propul-
sion
Laboratory
(JPL)
and
the
NASA
Deep
Space
Network.
In
the
same
way,
data
returned
from
each
experiment
to
JPL
will
be
electronically
sent
to
investigators
at
their
home
institu-
tions.
Taken
together,
these
various
factors-orbit,
space-
craft,
instruments,
and
operations
arrangements-maximize
the
experimental
opportunities
within
the
context
of
a mission
of
modest
cost.
Science
Objectives
There
are
five
scientific
objectives
for
the
Mars
Observer
mission.
The
first
three
encompass
the
geoscience
objectives
and
involve
measurements
of
the
surface
and
interior
(gravity
and
magnetics).
The
remaining
two
contain
the
climatology
objectives
and
involve
measurement
of
the
atmosphere
and
surface.
These
objectives
are
1)
to
determine
the
global
ele-
mental
and
mineralogical
character
of
the
surface
material;
2)
to
define
globally
the
topography
and
gravitational
field;
3)
to
establish
the
nature
of
the
magnetic
field;
4)
to
determine
the
time
and
space
distribution,
abundance,
sources,
and
sinks
of
volatile
material
and
dust
over
a seasonal
cycle;
and
5)
to
explore
the
structure
and
aspects
of
the
circulation
of
the
at-
mosphere.
Experiments
and
Instrumentation
Each
of
the
seven
experiments
selected
for
the
mission
con-
tributes
to
meeting
one
or
more
of
the
scientific
objectives.
These
experiments
are
described
in
the
following.
The
gamma-ray
spectrometer
(GRS)
detects
gamma
rays
emerging
from
within
and
near
the
Martian
surface.
These
high-energy
photons
are
created
by
the
natural
decay
of
radioactive
elements
or
are
induced
by
cosmic
rays
that
in-
teract
with
atoms
in
the
atmosphere
and
surface.
The
GRS
measures
the
energy
distribution
of
these
photons,
and
the
ex-
periment
team
will
use
this
information
to
establish
the
amounts
of
each
element
present
in
the
atmosphere
and
sur-
face
material.
Elements
such
as
potassium,
uranium,
thorium,
calcium,
magnesium,
aluminum,
iron,
and
others
can
be
mea-
sured
in
the
top
meter
of
the
surface.
Although
the
spatial
res-
olution
of
this
experiment
is
low
(generally
>
300
km
for
most
elements),
it
is
the
only
remote
means
of
directly
establishing
elemental
surface
composition.
The
instrument
also
incor-
porates
a neutron
spectrometer
for
the
measurement
of
the
in-
tensity
of
thermal
and
epithermal
neutron
flux.
This
mea-
surement
in
conjunction
with
gamma-ray
spectroscopy
allows
exploration
of
the
stratigraphy
of
carbon
and
hydrogen
in
the
upper
1-2
m
of
the
surface.
Cosmic
gamma-ray
spectra
will
also
be
recorded
when
the
gamma-ray
flux
reaches
a threshold
level.
Triangulation,
using
gamma-ray
detectors
in
other
parts
of
the
solar
system,
will
permit
location
of
these
cosmic
gamma-ray
bursts.
The
magnetometer/electron
reflectometer
(MAG/ER)
is
designed
to
detect
the
presence
of
both
global
and
local
mag-
netic
fields.
Mars
is
now
the
only
planet
from
Mercury
to
Nep-
tune
whose
magnetic
field
has
not
been
measured.
The
magnetometer
can
detect
the
presence
of
a magnetic
field
directly,
and
the
electron
reflectometer,
in
conjunction
with
the
magnetometer,
can
deduce
the
strength
of
the
magnetic
field
in
the
region
closer
to
the
planet
than
the
spacecraft
by
measuring
the
properties
of
electrons
incident
on
the
instru-
ment. Previous
measurements
at
Mars
indicate
that
a global
magnetic
field,
if
present,
is
weak.
Recent
magnetic
and
parti-
cle
measurements,
made
by
the
Soviet
Phobos
II
mission
in
1989,
also
supported
the
view
that
if
a magnetic
field
is
present
it
is
very
weak.
The
task
of
the
magnetometer
team
will
be
to
sort
out
the
many
processes
that
can
produce
a magnetic
field
and
to
successfully
identify
the
actual
field
generated
by
pro-
cesses
inside
Mars.
The
Mars
Observer
camera
(MOC)
consists
of
two
wide-
angle
assemblies,
which
can
photograph
the
planet
from
limb
to
limb,
and
one
narrow-angle
(1.4
m/pixel)
system.
The
wide-
angle
cameras
will
return
low-resolution
images
of
the
entire
planet
every
day
to
provide
a record
of
the
weather
on
Mars.
These
cameras
will
also
return
moderate-resolution
images
(of
order
300m/pixel)
of
the
surface
by
returning
only
the
central
portion
of
the
wide-angle
images
through
editing
done
on-
board
the
spacecraft.
The
high-resolution
system
will
selec-
tively
return
images
from
areas
where
key
questions
can
be
better
understood
through
detailed
knowledge
of
surface
mor-
phology
and
albedo.
Because
of
the
volume
of
returned
data
involved
in
the
high-resolution
imaging,
even
with
data
com-
pression,
only
a few
tenths
of
1117o
of
the
Martian
surface
will
be
examined
with
this
mode.
A
daily
global
image
of
Mars
in
the
visible
will
provide
for
the
first
time
an
unbiased
assess-
ment
of
atmospheric
phenomena.
As
an
example,
it
will
be
possible
to
develop
statistical
information
as
a function
of
lati-
tude,
longitude,
and
season
for
local
dust
storms.
This
will
permit
an
assessment
of
the
role
of
local
storms
in
the
forma-
tion
of
global
dust
storms,
should
a global
storm
occur
during
the
period
of
Mars
Observer
measurements.
The
very
high-
resolution
measurements
will
provide
a critical
test
of
ideas
in-
volving
climate
change.
Suggestions
that
ponded
water
or
con-
tinental
scale
glaciers
have
shaped
large
areas
of
the
surface
can
be
tested
by
looking
for
the
associated
small-scale
features,
i.e.,
beaches
and
eskers,
that
accompany
such
processes.
The
pressure
modulator
infrared
radiometer
(PMIRR)
will
obtain
data
about
atmospheric
structure
and
dynamics
by
making
measurements
primarily
in
the
thermal
infrared
wave-
length
region.
This
instrument
will
concentrate
its
mea-
surements
at
the
limb
of
Mars,
where
the
path
through
the
at-
500
A.
L.
ALBEE
AND
F.
D.
PALLUCONI
J.
SPACECRAFT
mosphere
from
the
location
of
the
spacecraft
is
greatest.
PMIRR
will
scan
upward
from
the
limb,
sounding
the
atmo-
sphere
to
produce
altitude
profiles
of
temperature,
pressure,
water
vapor,
dust
opacity,
and
cloud
composition.
These
mea-
surements
will
be
used
by
the
PMIRR
experiment
team
to
ex-
amine
the
structure
and
circulation
of
the
atmosphere
as
a
function
of
latitude,
longitude,
season,
and
altitude.
PMIRR
can
also
do
atmospheric
sounding
in
a nadir-looking
mode
and
make
surface
measurements
in
this
mode
as
well.
The
band
selection
permits
full
radiation
budget
measurements
in-
cluding
the
solar
reflected
and
Mars
emitted
components.
The
Mars
Observer
laser
altimeter
(MOLA)
fires
pulses
of
infrared
light
(1.06
J.!m)
at
the
surface.
From
a laser,
by
meas-
uring
the
travel
time
of
the
reflected
pulse,
it
is
possible
to
measure
the
distance
from
the
spacecraft
to
the
surface
with
a
precision
of
several
meters.
By
combining
this
measured
dis-
tance
with
the
distance
from
the
center
of
the
planet
to
the
spacecraft,
obtained
from
orbit
reconstruction,
the
experi-
ment
team
can
gradually
reconstruct
the
entire
global
topog-
raphy
of
Mars.
Although
topography
is
basic
to
understanding
the
geophysics
and
geology
of
Mars,
our
absolute
knowledge
of
this
quantity
is
no
better
than
a kilometer
for
much
of
the
surface.
The
high
precision
of
the
Mars
Observer
altimeter,
coupled
with
accurate
orbits
based
on
improved
knowledge
of
the
gravity
field,
will
provide
a many-fold
improvement
in
understanding
topographic
relationships.
As
a byproduct
of
this
altimetry,
the
surface
reflectivity
at
1.06
J.!m
will
be
known
for
each
of
the
6 x
10
8
measurement
locations.
In
the
radio
science
(RS)
investigation,
the
experiment
team
will
use
the
spacecraft
telecommunications
system
and
ground
station
receiving
equipment
to
probe
the
atmosphere
and
grav-
ity
field
of
Mars.
By
carefully
monitoring
changes
in
the
fre-
quency
of
the
radio
signal
from
the
spacecraft
as
it
moves
around
Mars,
the
effect
of
the
gravity
field
on
the
spacecraft
velocity
can
be
determined.
Changes
in
the
radio
signal
as
the
spacecraft
passes
in
and
out
of
occultation
by
Mars,
as
viewed
from
Earth,
are
used
to
construct
high-resolution
temperature
profiles
of
the
atmosphere.
The
pole-to-pole
coverage
and
low
altitude
of
the
Mars
Observer
orbit
will
permit
a significant
improvement
in
understanding
the
gravity
field
of
Mars.
The
radius
of
Mars
will
be
accurately
established
at
each
of
the
oc-
cultation
points,
providing
an
independent
means
of
checking
the
accuracy
of
the
laser
altimetry.
The
thermal
emission
spectrometer
(TES)
operates
prima-
rily
in
the
thermal
infrared
portion
of
the
electromagnetic
spectrum.
The
nature
of
radiation
from
the
Martian
surface
at
these
wavelengths
depends
on
temperature,
surface
mineralogy,
and
other
factors.
The
investigation
team
will
use
spectrometer
measurements
to
determine
the
thermal
and
mineralogical
pro-
perties
of
the
surface.
The
instrument
will
also
provide
data
about
Martian
atmospheric
properties,
including
cloud
type
(carbon
dioxide
or
water
ice)
and
dust
opacity.
TES
is
the
third
experiment
(along
with
PMIRR
and
RS)
to
make
atmospheric
measurements.
The
differing
atmospheric
data
sets
obtained
by
these
three
instruments
will
permit
intercomparison
of
the
results
of
different
measuring
techniques,
thus
greatly
strength-
ening
confidence
in
the
accuracy
of
the
results
obtained.
TES
uses
a 3 x 2
(three
detectors
crosstrack)
detector
array
in
each
of
its
operating wave
bands.
The
spatial
resolution
of
each
de-
tector
is
3 km.
It will
be
possible
to
map
the entire
surface
over
the
course
of
the
mission.
Like
PMIRR,
TES
carries
wave
bands
permitting
full
radiation
budget
measurements.
Mars
Balloon
Relay
In
addition
to
these
seven
experiments,
the
spacecraft
will
carry
an
eighth
device,
supplied
by
the
French
Centre
Na-
tionale
d'Etude
Spatiales,
which
will
support
the
penetrators
and
landers
of
the
Soviet
Mars
1994
mission,
when
that
space-
craft
reaches
Mars
in
the
fall
of
1995.
The equipment
carried
by
the
Mars
Observer
spacecraft
consists
of
a receiver/trans-
mitter
combination
operating
continuously
at
frequencies
near
400
MHz.
A
receiver
attached
to
the
Mars
1994
landers
will
continuously
monitor
the
transmitter
frequency.
When
the
signal
strength
reaches
a threshold
value
indicating
that
the
Mars
Observer
receiver
is
close
enough
to
receive
data,
a trans-
mitter
on
the
lander
will
relay
scientific
and
engineering
infor-
mation
up
from
the
surface
to
the
receiver
on
the
spacecraft.
The
transmission
will
terminate
when
the
receiver
on
the
sur-
face detects
that
the
signal
from
the
Mars
Observer
transmitter
has
dropped
below
the
required
threshold.
The
data
relayed
up
from
the
Mars
1994landers
will
be
stored
in
the
large
solid-
state
memory
of
the
MOC,
where
it will
then
be
encoded
and
processed
for
return
to
Earth.
Mars
Observer
will
augment
the
return
of
data
from
the
landers.
The
primary
data
return
path
is
through
the
Soviet
Orbiter.
Organization
and
Scientific
Personnel
The
Mars
Observer
project
is managed
for
NASA
by
the
Jet
Propulsion
Laboratory.
NASA
Lewis
Research
Center
will
supply
the
Titan
III
launch
vehicle
through
a
commercial
launch
services
contract
with
Martin-Marietta
Commercial
Titan,
Inc.
NASA
Marshall
Space
Flight
Center
will
supply
the
upper
stage,
which
is
being
developed
by
the
Orbital
Sci-
ences
Corporation
and
built
by
the
Martin-Marietta
Astro-
nautics
Group.
The
spacecraft
is
being
developed
through
a
system
contract
with
the
General
Electric
Astro
Space
Divi-
sion.
Integration
of
scientific
instruments
with
the
spacecraft
began
in
July
1991.
The
seven
Mars
Observer
experiment
teams
were
selected
through
a NASA
announcement
of
opportunity
in
1985,
as
were
five
interdisciplinary
scientists.
Ten
Soviet
participating
scientists
will
join
the
scientific
effort,
and
the
Soviet
Mars
1994
balloon
experiment
team
will
include
several
American
participating
scientists.
In
the
year
before
launch,
Mars
Observer
will
select
a number
of
additional
participating
scien-
tists
through
an
open
NASA
research
announcement
to
be
released
in
1991.
The
participating
scientist
program
provides
.an
opportunity
to
enlarge
the
scientific
teams
during
the
data
collection
and
analysis
period.
Tracking
and
data
acquisition
for
the
mission
will
be
pro-
vided
by
the
NASA
Deep
Space
Network.
Launch
will
occur
from
launch
Complex
40
at
the
NASA
Kennedy
Space
Center
with
the
first
day
of
a 28-day
launch
window
opening
on
Sept.
16,
1992.
Summary
Mars
is
the
only
planet
in
the
solar
system,
other
than
the
Earth
and
its
Moon,
that
can
be
visited
and
personally
ex-
plored
by
humans
in
the
near
future.
The
presidential
Moon-
Mars
initiative,
announced
in
the
summer
of
1989,
increases
the
need
to
better
understand
the
Martian
environment.
Thus,
Mars
Observer
stands
between
the
initial
exploration
of
Mars,
already
carried
out
by
both
U.S.
and
Soviet
spacecraft,
and
the
more
intensive
examination
of
the
planet
with
robotic
sur-
face
rovers,
sample
returns,
and
human
beings,
which
are
pos-
sible
in
the
future.
Although
our
knowledge
of
Mars
is substantial,
it
is
trivial
when
compared
to
our
knowledge
of
Earth.
By
providing
global
measurements
of
the
Mars
atmosphere,
surface,
and
in-
terior
over
a full
Martian
year,
thus
recording
the
full
range
of
seasonal
behavior,
the
Mars
Observer
mission
will
consolidate
the
knowledge
gained
from
both
ground-based
studies
and
previous
spacecraft
missions,
add
extensive
new
mea-
surements,
and
provide
a strong
foundation
for
more
inten-
sive
investigations
of
Mars
in
the
future.
Acknowledgments
This
research
was
conducted
at
the
Jet
Propulsion
Labora-
tory,
California
Institute
of
Technology,
Pasadena,
CA,
under
contract
with
NASA.
The
authors
wish
to
thank
members
of
the
Mars
Observer
Project
Science
Group
for
pro-
viding
experiment
descriptions
used
in
the
preparation
of
this
paper.