NASA's Mars Pathfinder Project requires a Ground Data System (GDS) that supports both engineering and scientific payloads with reduced mission operations staffing, and short planning schedules. Also, successful surface operation of the lander camera requires efficient mission planning and accurate pointing of the camera. To meet these challenges, a new software strategy that integrates virtual reality technology with existing navigational ancillary information and image processing capabilities. The result is an interactive workstation based applications software that provides a high resolution, 3-dimensial, stereo display of Mars as if it were viewed through the lander camera. The design, implementation strategy and parametric specification phases for the development of this software were completed, and the prototype tested. When completed, the software will allow scientists and mission planners to access simulated and actual scenes of Mars' surface. The perspective from the lander camera will enable scientists to plan activities more accurately and completely. The application will also support the sequence and command generation process and will allow testing and verification of camera pointing commands via simulation

Kim, Jacqueline H.

Sacks, Allan L.

Weidner, Richard J.

English

NASA Technical Reports Server

N95- 15978
•_. _• 4•
USING VIRTUAL REALITY FOR SCIENCE MISSION PLANNING:
A MARS PATHFINDER CASE
Jacqueline H. Kim, Richard J. Weidner, Allan L. Sacks
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, CA 91109
ABSTRACT
NASA's Mars Pathfinder Project requires a Ground Data System (GDS) that supports both an
engineering and a science payload with reduced mission operations staffing, and short planning
schedules. Also, successful surface operation of the lander camera requires efficient mission planning
and accurate pointing of the camera.
To meet these challenges, the GDS Team designed a new software strategy that integrates virtual
reality technology with existing JPL Navigational Ancillary Information Facilities (NAIF) and image
processing capabilities. The result is an interactive, workstation-based application software that provides a
high resolution, 3-dimensional, stereo display of Mars as if it were viewed through the lander camera. The
design, implementation strategy and parameter specification phases for the development of this software
have already been completed, and the prototype has been tested. When completed, this software will
allow science investigators and mission planners to access simulated and actual scenes of Mars' surface.
The perspective from the lander camera will enable scientists to plan activities more accurately and
completely. The application .also will support the sequence and command generation process, and will
allow testing and verification of camera-pointing commands via simulation of the sequence.
This paper describes the architecture and characteristics of this science mission planning software
now under development for Mars Pathfinder, including output from the prototype. Also, it addresses
possible uses of this software by other planetary missions.
INTRODUCTION
The Mars Pathfinder Project is the first of NASA's
Discovery Program missions. Discovery-class
means low development cost ($150 Million or
less), short development time (3 years or less),
and focused science objectives. The Mars
•Pathfinder mission is the first lander mission
since Viking in 1976. During the Viking Mission,
many of the mission operations activities were
labor-intensive, costly and time consuming,
especially in the area of science mission
planning for the imaging system. The Pathfinder
Ground Data System (GDS) Team provided the
functional design for a new software that
eliminates much of the labor intensive work in
mission planning for the lander imaging system,
Imager for Mars Pathfinder (IMP).
The resulting software, named SIMP (Simulator
for IMP), creates a "virtual Mars environment=on
a workstation using high resolution, 3-
dimensional, stereographic display of Mars
terrain and atmosphere. This innovative use of
workstation-based virtual reality enables
scientists and mission operation's staff to plan
the observations easily and accurately. This
application supports the sequence and
command generation process; as well as
verification of the generated sequence.
The first prototype of the SIMP was tested
recently and received favorable reviews by
scientists as well as mission operations team.
The prototype will go through several tests and
refinement within the next 12 months. The
SIMP can also be used for other future lander
missions, such as landers in the Mars Program,
with little modification.
MISSION DESCRIPTION
The Mars Pathfinder project development began
in October 1993.
The spacecraft will be launched during the 1996
Mars opportunity (between December 5, 1996
and January 3, 1997), on a Delta II launch
37
https://ntrs.nasa.gov/search.jsp?R=19950009563 2020-06-16T09:09:48+00:00Z
i_ '• < :_
vehicle. The spacecraft will spend 6 to 7 months
in cruise using a type I trajectory, and will land on
Mars on July 4, 1997. The surface mission on
Mars will be completed by August 1997.
The Mars Pathfinder mission's primary objective
is to demonstrate the low cost engineering
technology involving the cruise, entry, descent,
and landing system required to place a payload
on the Martian surface in an operational
configuration. In addition, the lander carries a
micro-rover as a technology instrument. The
lander deploys the rover upon opening of the
solar panels. The rover will be driven off of the
solar panel after deployment of the solar panel.
The flight system consists of four main parts: 1)
Aeroshell, parachute, and airbag Entry, Descent,
Landing (EDL) System (See Figure 1), 2) Self
righting, tetrahedral lander (See Figure 2),
3)Active thermal system for the lander (See
Figure 3), and 4)Free ranging rover.
Figure 1 illustrates the EDL sequence. The
spacecraft is enclosed within an aeroshell during
cruise. After entering into the Martian
atmosphere, a parachute is deployed to reduce
the impact speed. Just before the landing, air
bags are inflated to cushion the impact, and the
parachute is jettisoned away from the lander
position.
The lander carries a significant science payload.
There are several science instruments relating to
atmospherics, meteorology, geology and
imaging. Imager for Mars Pathfinder is the main
science instrument, and it consists of a stereo
camera with color image capability. The imaging
system is located near the center of the lander
and is controlled.by a set of motors. Figure 3
shows the lander and its payload.
i_;ili:i_._ii:;'_i'_:'_:_ ............................... " _._i;
ii_ii..'..'!;::i!_!!!$_:_:"
i:_:)'-.,.... ,.':" _:':':':_
Figure 2 - Artist's Conceptualization of the
Lander on the Surface of Mars
Figure I - Mars Pathfinder Entry, Descent,
Landing (EDL) Sequence
MISSION PLANNING FOR VIKING AND
MARS PATHFINDER CAMERA
In order for scientists to control the camera, they
need to specify approximately 32 different
parameters, ranging from ephemeris information
to optimum data compression ratio. The most
basic parameters are displacement angle in
azimuth and elevation direction (i.e. targeting
parameters), and the location of the Sun.
During Viking mission operations, image mission
planning was achieved by using the "Skyline
drawings", timeline, and many hours of intensive
calculations of essential quantities. Although
this system served its purpose well, this was a
labor-intensive, time consuming and inefficient
process.
38
: l_rP-_ D4_ C-ALT._;ET
i
Figure 3 - Pathfinder Lander Configuration
F_ure 4 showsthe actualSkylineDrawings used
by the Viking Lander-I, during Sol-0 and So1-1.
(A "Martian sol"is a solar day for Mars which is
equivalent to 24.66 Earth solar hours.) The"
Skyline Drawings show image outlines on a
rectilineargridwhose horizontal axis represents
_' the azimuth and the vertical axis representsthe
elevation.
Yr.-1
SOlO
! .p... : .
_. i°i
(x[_ i vl_
Figure 4- Skyline Drawings Used in the Viking
LanderMission
The Viking Lander Timeline, shown in Figure 5,
was also usedas a mainpartof missionplanning.
This timeline shows the Viking Lander-l's
missionactivitiesduringSol 22. As one can see,
these resources are unsuitable to use for new
missions like Mars Pathfinder, considering
advanced technologythat is availabletoday.
The proposalforthe image mission planningtool
for the Pathfinder was to create a _irtual Mars'
environment. The idea isto simulatethe camera
usinga workstationsuch as Silicon Graphics or
Sun. The simulator creates a virtual Mars
environmenton a workstationscreen, displaying
3-dimensional, stereographic images of Mars'
terrain as well as its atmosphere. The scene
created should look as if it were seen by the
camera. This idea utilizes existinghardware and
enta_sonlya small cost. The scenes of Mars will
be viewed with stereo viewing devices already
widelyavailable.
: ----'-'== o t._NI_R. I.EX.AL TIME, HIZ..5Feo_ NgDNI6HT
,
P---_
i_r°
_EI5.
(._CM5
_RAY #._Sc.A
#ROE
II_Ar=ING
Figure 5- Vildng Lander Timeline
DESIGN OF SIMP
The SIMP design approach was different from
the traditional approach at JPL. The decision
was made to start the design without a detailed
functional requirement document or schedule.
Instead, this software development relied on
close interaction between team members. This
approach allows all team members to understand
the purpose of the task, and the significance of
their roles toward accomplishing the task. Most
importantly, each member is completely
responsible for his contribution to this task, but
39
¸¸!¸.,,¸
,r _
at the same time, to work as a cooperative team
member.
The design phase of development began with a
meeting between representatives of the Ground
Systems, Image Processing, Science, and SIMP
implementation team. During this initial meeting,
the purpose and functions were identified, and
concepts for creating a virtual Mars were
proposed. In addition, the description of the
mission, launch schedule and mission
operations plan were discussed. The design
team agreed that providing a comprehensive
user's guide and a software description would be
the only necessary documentation. The design
team also decided that incorporating
NAIF/SPICE is an appropriate approach to get
ancillary information. (The description of
NAIF/SPICE is attached as Appendix A.)
After a few months, the initial prototype was
completed. The design team presented the
prototype to scientists for a review, and found
the prototype to be satisfactory in terms of
meeting a foreseen necessary functions for
mission planning. At this point, the
implementation team decided to proceed with
detailed developmentof SIMP, including some
additional requested functionality. Figure 6
shows the prototype of SIMP.
SIMP creates a virtual Mars environment by
displaying either single or mosaic images, in
stereo view. There is an option to display either
the Mars local coordinate reference or lander
center coordinate reference on the border of the
scene. Graphical display of azimuth and
elevation angle, field of view and field of regard
(ranges within the camera can move) are placed
below the scene. In addition, there are text
display of other parameters such filter and
exposure information. On the scene, motor step
grid and field of view are overlaid for quick
reference.
: , L
Figure 6 - Display from SIMP Prototype
4O
,i ':'/ !" L/ ;
, . , ,.j
i .i:: _'
PLAN FOR TESTING AND REFINEMENT
It is our plan to refine SIMP through continuous
communication between GDS, the
implementation team and the science team.
Also, SIMP is schedule to be connected to the
camera engineering model to test the real-time
interface and its accuracy.
W'rthinthe next month, the design team of SIMP
will participate in a special test activity, in
cooperation with the science team. The
Principal Investigator of the camera at the
University of Arizona will create a pseudo-Mars,
named Mars Garden, by designing an area
according to available Mars data. The
engineering model of IMP will be mounted within
the Mars Garden and will be connected to a
control system. At that time, SIMP will be
connected to the control system to simulate the
mission operations environment. This test will
give us useful accuracy data as well as usability
information about SIMP.
Figure 7 is a conceptual model of Mars
Pathfinder's uplink (command) system.
SEQGEN and SEQTRAN are sequence
processing software currently used at JPL.
SASF and SSF are input files for SEQGEN and
SEQTRAN. As shown, SIMP will provide
planning function as well as validation of the
designed sequence. During next phase of Mare
Pathfinder's system testing, SIMP will be placed
within the uplink system to be integrated with the
rest of the G["_"
tim' TeamII,
SlMP
Generate ]
Real Time
Commands
I SASF as input]to SEQGEN I_
¢
SSF as input ]to SEOTRAN
[ f
._ pCommand Subsyste_
] programs) l
POTENTIAL USE BY FUTURE LANDER
MISSION
Figure 7-
Currently, there is a proposed plan to repeatedly
launch landers as Mars to conduct various
scientific investigations. SIMP can be used to
simulate any camera or remote sensing
instrument on any of the future landers, with little
modification. The only foreseeable modification
required will be to generate SPICE kemel files
for spacecraft and the camera. SIMP is
independent of landing location or mission
dates.
SUMMARY
Through design and development of SIMP, the
Mars Pathfinder GDS has shown that an
innovative use of virtual reality concept
produced a high quality, re-usable tool for
science mission planning. The resulting tool will
accommodate scientists with •accurate
information when planning or validating their
mission sequence. Furthermore, this tool can
be used for any future landers regardless of time
or the destination of the mission.
Note:
The SIMP tool development is part of the Model
Based Planetary Tools Analysis Task funded by
Joe Bredenkamp of Code ST, NASA. This effort
described in this paper was performed at the Jet
Propulsion Laboratory, California Institute of
Technology under contract with NASA.
¢
ISEQGENI
SASF as an input [
to SIMP [
for verification ]
DCD
(DSN Command
Subsystem)
IMP Up/ink Process (Conceptual Model)
41
_•• : _i ¸
_ i _, _
, L•
/•
s•
APPENDIX A
"Kernel Knowledge"
NAIF/SPICE Description, published by NAIF
Group at JPL. (attached)
BIBLIOGRAPHY
Pathfinder Project Mission Plan (JPL D-11355),
Preliminary version, 1993.
Viking Lander Imaging Investigation: Picture
catalog of Primary Mission and Experiment Data
Record (NASA Reference Publication 1007) by
Robert B. •Tucker, published by NASA, 1978.
Mars Environmental Survey: Pathfinder and
Network, information material published by
NASAJJPL, 1993.
Mars Pathfinder Fact Sheet, information material
published by NASAJJPL, 1994.
Kernel Knowledge, information material
published by NAIF/SPICE Group at JPL.
: 42
- _•i ¸ •
Kernel
Knowledge
J_lll'mm_'lmmal_llmlemmla_.llmmmm_
Navigation
Ancillary
Information
Facility
43
{ L '¸¸_
• i •_!. i:
: L r ¸
Mapping SPICE
Kernels Into
Real Products
,aoe.me_m._mlml.lm._ mleD'wm
Kernels Kernel Files
"LogicalElements) (PhysicalFiles)
Historically, the ancillary
data needed to support
the planning and analysis
of observations made by
instruments on space-
craft have been organ-
ized into five logical ele-
ments-called kernels--
as shown in the left half
of the figure, and as de-
scribed in the table. The
acronym SPICE was
coined to refer tothese
kernels.
Kernel data are distrib-
uted in five kinds of files,
called kernel files, as
listed in thetable(right.)
Data from the S and the
Pephemeris kernels are
generally used together
(the stateof a spacecraft
is normally defined with
respect to a planetary
object), and may be
included in a single file.
Most kernel files are
originally produced by a
flight project, such as
Magellan, Galileo, or
Mars Observer. Updates
to these files could be
44
Kernel Contents
i
S Spacecraft
ephemeris
p Planet ephemeris
and constants
I Instrument
descriptions
C Camerapointing
Description
Positionand velocityof a spaeacraft
asa funnfien of time.
Positionand velocityof a planet, satelli
comet, asteroid, or the Sunas a functio_
of time. Also,eartugraphic constantsfL
Mat object.
Instrumentmounting alignment, intemaJ
timing, and other information neededto
interpretmeasurements made with an
instrument.
Theinertiai/y referenced attitude
(pointing)for an instrumentor other
spacecraft structureas a function of tim
E Events Spacecraft and instrument commands,
grounddata systemevent logs,and
experimenter's"ontebnok_'records.
File Format Description
SPK Binary Data from the $ kernel, or #ore the
ephemerisportion(Pephemecis ) of the
P kernel, or both.
Pcg Text Data from the constantsportion
(Pconstants) of the P kernel.
Ig Text Data from the ! kernel.
CK Binary Datafrom the C kernel.
Elf Text Datafrom the E kernel.
mm
produced both by the
project and by planetary
scientists during the
course oftheir analyses.
In addition, NAIF pro-
duces some SPK kernel
files containing planet,
satellite, comet, asteroid,
and Sun ephemerides for
general use. These kernel
flies are derived from
reference ephemerides
provided by the Jet Propul-
sion laboratory's Navigation
Syste,-m Section.
i_ _ ,ii:,
l/ ¸ _ .
, .... the SPICE
rl: : System
:! ...........................................................
• • • Scientist's Application Program • • •
Science
Results
: NAIl: .er_t. !s#e_J©Toolkit _oer_.r7
SPICEUB
• Project-
Inde_e_ent
Fortran.77
seinm_l#es
with dose.
mem_lse
tim mi_eno mnO •m
• COCtC_cmk* {_IIIP/
e_Srms
• Test * Part/#g
IssmwU_s
_RtbR_I_P_$.3n
withdese. •
me_tMJon •
I
(Optional)
ililllllllllll _
45
SPICE Helps Interpret
Sdence Instrument Data
The elements of the SPICE
system--kernel files and
software_are used to
support the planning and
analysis of space science
data.
A scientist'sapplication
program might use
picturesfrom the Mats
Observer Camera to help
determine the suitability.
of a particular region _s a
landing sitefora sample
returnmission. The
primary sclan_tic result
would be estimatesofpara-
meters thatdefinelocal
topography. A secondary
resultcould be improved
estimatesofprecisely
where the camera was
pointed when the pictures
were taken;thesedata
could be placed ina new
C-kernel file.
SPICELIB--the principal
SPICE software--isa
collectionof subroutines
written inANSI Fortran-77.
Some of thesesubroutines
read,write, and port binary
kernelfiles,and read text
kernel files. (Binary files
_e con'_ertedto an inter-
mediate text format for
trar_ferbetween various
computers.}
The remaining subrou-
tines use the information
contained in those files to
compute the geometric
quantities{vectors,anglas,
distances) needed toplan
observationsor to
interpret the data
returned from science
instruments,Each
subroutineincludesthe
informationneeded to
select and properly
integrate the subroutine
into the scientist's own
application programs.
The NAIF Toolkitconsists
of SPICELIB source code.
includingdocumentation,
plusthe following
additionalitems:
Cookbook Programs are
highly annotated, working
programs that illustrate
how SPICE kernels and
SPICELIB subroutines
may be used to compute
commonly requested
geometric quantities.
(Sample kernel files are
included.l
Testl_ognzrns can be
executed by a Toolkit
redpient to verify that the
Toolkit code has been suc-
cessfully ported tothe re-
clpient's own computer.
Utili_ Programs fall into
two categories. Some can
be used to examine and
convert binary, kernel files:
others can be used to gain
easy accessto descriptions
of SPICELIB subroutines.
Portlng lnsb'action.s
identify changes that nee
to be made when the
Toolkit is moved betwee_n
various computers.
SPICE Offers Wide
Applicability
The NAIF Toolkitcan be
used in planetary, spar.e
physics, and Earth sdenc
applications. R may be
augmented with project-
specific subroutines as
needed, with NAIF
normally providing this
code under project
funding.
Scientistsor engineers
pick needed Toolkit
subroutinesand combine
them with theirown
softwareto createan
applicationprogram.
(Toolkit users should no/
revise Toolkit subrou-
tines.)
When used in support of
•NASA flight project,
SPICE kernd files and
Toolkit software (includ-
ing augmentations), are
archived with science
instrument _tasets for
futurereference.
WhatisSPICE?
SPICE is a NASA information system for assem-
bling, archiving, distributing, and accessing
geometric and related ancillary information used
to plan space sdence observations and interpret
space science instrument data. This brochure
describes the content and use of the basic SPICE
system components.
The SPICE concept was defined by planetary
scientists, and is being implemented by the staff
of the Navigation Ancillary Information Facility
(NAIF) at the Jet Propulsion Laboratory, with
oversight by the science community.
Fundin# for development of the SPICE system is
provided by the Information Syster_ Branch and
the Solar System EzToloration Division of NASA 3
Office of Space Science and Applications.
Nacigatian Aecillary IMormation Facility
Jet Propulsion Laboratory
Mail 5"_p _0"1-1_£
480D Ca/t Grove Drive
Pasadena, California 91109
46


Using virtual reality for science mission planning: A Mars Pathfinder case

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