Preliminary Mission Analysis Tool (PMAT)Educational Software for Satellite Mission Design

Siti Fariza Mohd Dahlan, Illyia Mohd YusofSchool oj"Aerospacc Engineering

Universiti Sains Mal(J\'siaEngineering CampusJ430() Nibong Teba/.

Pulau Pinan.g, Malc(l'siaTel: +604-5937788 ext 6509/6502

Fax: +604-5941026Email: fariza(akng.uslll.mv;illviallzJcng.usm.mv

( I) INTRODUCTIONABSTRACT

Satellite 17HSSWn design and analysis involvescomplex calculations and repeated tasks indetermining the relevant parameters slich as orbitdetermination. field of vie\\.' and calculations on theeffects o.lpertllrbations. The experience in perjormingmanual calculations could contribute to practicalunderstanding 0.1' space physics and theories:however. the process is time consuming and pron.e tohuman errors. Buying a commercial so./twa~-epackagethat provides similar capabili(l' may be an option:nevertheless. such idea is cost(l' and the so./'tware maynot be tailored to a specific requirement.This paper presents an ejfortfocused Oil developing amission design so.ltware aimed fo promote betterltndersfanding and e.fficiency in design and analysistechniques .for students who speciali:zes inASfronCtufics Engineering whilsf reducing thedep~/1dencies towards the cO/1/mercial o.fF-the-she(j"sojh-l'are (COTS). The soItH'are is fargeted to .facilitateQI1a1.l'ficai aspect of the design process in the .form of'computer aided inferactiol1 (elf) and compufer basedlearning (eBL).

The olltcome of this research is a graphicalsatellite mission design und analysis so./"n,'arepackage for educational purposes either for teachingaid orjbr students' lIsage. The research does not onlyprovide opportuf7i(v ./01' students to contribute theirskills i/1 the devclopmenf process but also acts as aplatjhr/1/ for them to beffer IIl/ders/ancl fhe process (~l

safelli/e lJIissiOil design.

Key1l'ords: S'il11ulatiof"1. safe/lile missio/l design

Malaysia is fast becoming a capable satellitemanufacturing country with the recent deveLopment ofRazakSat satellite. The move to manufacture thenational satellite is seen to bolster the need for morelocal scientists in areas relnted to spacecraftengineering. Any spacecraft development must startfrom a list of requirements and translated to a set ofmission design by responsible engineers. Missiondesign involves planning for the right flightcharacteristics in order to satisfy the requirements.Orbital design and analysis are among the prerequisitesteps to be taken before moving to higher hierarchy ofsatellite design phases. Here is where scientists willdetermine the best orbital location for a satellite toreside whilst reducing transpotiation cost to the lowestpossible.

The time taken for a thorough mission planningand analysis can be reduced from nine months to threemonths with the use of good computer software.Nowadays, there exist many freeware, shareware andcommercial satellite mission design and analysissoftware in the market. The best software could costdearly to an organization. Developing equivalentsoftware could be painstaking and time consuming.Nevctiheless, the process is seen wOlihwhile as thedevelopment process itself is a learning process. Alleducator whom assimilates knowledge could bettertransmit his/her knowledge through softwaredevelopment, while students could benefit from thehands-on experience gained during the process.

1.../.9

Terms Definition

Semimajor Axis - Half the distance between the twopoints in the orbit that are f:lIthest apartApogee/Perigee Radius - Measured from the centerof the Earth to the points of maximum and minimumradius in the orbitApogee/Perigee Altitude - Measured from the"surface" of the Earth (a theoretical sphere with aradius equal to the equatorial radius of the Earth) tothe points of maximum and minimum radius in theorbitPeriod - The dur:ltion of one orbit, based on assumedtwo-body motionMean Motion - The number of orbits per solar day(86.400 secl24 hour). based on assumed two-bodymotionEccentricity - The shape of the ellipse comprising theorbit. ranging between a perfect circle (eccentricity =

0) and a parabola (eccentricity = I)Inclination - The angle between the orbital plane andthe Ealth1s equatorial plane (commonly used as areference plane for Earth satellites)

(2) PROBLEM DEFINITION

Experiences gained in early 200 I from the Schoolof Aerospace Engineering. Universiti Sains Malaysiain taught courses ESA 11 1 - Introduction to AerospaceEngineering (Astronautics section), ESA164 - FlightMechanics and design electives courses indicate thatstudents encounter difficulties in understandingrudimentary theories associated to space mechanics.lecturers often have to spend more time and energy toprepare visual aided pictorial and models depicting thesolar system and satellite orbits to get the messagethrough. Although limited in evelY aspect (especiallyin describing derived terms and of course limitation ofthe material used) this method has transpired certainextend of interest that leads to self-learning of spaceelements. Nevertheless, students cannot fully benefitfrom these techniques due to the complexity of thesubject as lecturers tend to simplify things up andexamples are limited on special cases only.

A more comprehensive and robust technique hasto be employed based on one-to-one or step-by-stepapproach in order to promote self-learning. Thephysical models and motions described can bedepicted in the computer without limitation. Anymotions can be simulated in the computer as well ashelp items for new lIsers.

The primary objective is then to develop asatellite mission design software as a tool to promote

better understanding and self-learning of spacemechanics and to facilitate tlnalysis aspects of thedesign process for undergraduate students.

FUlther enhancement will be conducted(depending on the availability of grants) coveringaspects of constellation. perturbation and Ealth shape.These aspects will be beneficial for master levelstudents majoring in astronautics engineering andspace sCIences.

(3) REQUIREMENTS BASELINE

The main purpose of this study is to identify basicrequirements in the form of need and then to formulatea total solution for every need. The idea here is touncoyer, invent. concoct and/or devise a broadspectrum of ideas and alternatives for missions fromwhich new projects can be selected.

A loosely stmctured examination of needs mustbe upheld in a small cluster consisting of interestsubject (users), direct benefactors and third-pilltybenefactors.

In this study, four main categories which consistof needs analysis, system operational requirements.system maintenance concept and functionalrequirements are carried OLlt.

(3.1) Need Analysis

Referring to the problems faced by the group ofstudents. the actual need is to develop a moresystematic model to effectively promote betterunderstanding in space mechanics. Students wouldlearn better through graphical representation and bestthrough step-by-step approach. The design of thesoftware should be in such that answers can beimmediately seen after the execution of a set of data.Students should also be furnished with a set of defaultdata for comparison with user input data. The tinalresult should be in the form of computer aidedinteraction (CAl) and computer based learning (CBl).

(.3 .~) System Operational Requirements

Whilst physical models and pictorial images needpapers, scissors and a good artistic hand, therequirements of the proposed solution consist of acomputer and a good projector for large audience. Onthe other hand, the development of the PMATsoftware requires GUI based design using MATLABwith Simulink and Visual C++ software, and arelatively better computer and brainpower for codingpurposes in MATLAB am! C languages. The end

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product con~ists of ~nly ~n execu~able file and somehelp itinerarIes. ThIS software will be tested on thelatest computer technology using Windows operating

system.

(3.3)System Mi.lintcnance Concept

This aspect of requirement will be furtherenhanced as we gain more input from prospectiveusers and benefactors. A more reliable system canonly be obtained after corrections and enhancement tothe existing software are made in the future based onthe following criteria:• User/Benefactor level of knowledge

• User-program interface

• Ergonomics• Auto-assistance (help file) and• User-friendliness

(3.4)Functional Requirements

The development of the PMAT software isloosely based on the European Cooperation for SpaceStandardization on Space Engineering for Softwaredeveloper documentation. the ECSS-E-40A. Acomprehensive top-down diagram wiIl be presentedlatter in this paper depicting all functions required bythe end user. The concept of the software willtherefore inherit those highlighted by the ECSS-E-40Astandards.

(4) SOFTWARE REQUIREMENTS ANALYSIS

An analysis of the software requirements, or so­called requirements baseline was conducted based onthe needs analysis presented earlier. At this stage.functionalities of the software. software architectureand software technical specifications were outlined.

understanding complex theories. as well as mISSIondesign activities. Apalt from that the software shall beuser-friendly, that is. it should be simple enough to beused by entry level students. In addition, tool tips andhelp files will be madc available to facilitate softwareusage.

(4.2) Software Architecture

The software is a module based appl ication. thusmore modules can be added for future expansion.Modules planned for preliminary requirements arebased on spacecraft mission elements which are:a) Subject or mission to accomplishb) Orbital elementsc) Space segment: payload and subsystemd) Launch Segmente) Ground Segmentf) Communication Stnlctureg) Mission Operation

The modules are interdependent between one andanother in order to acquire a complete analysis on thepreliminary requirements. However. in the tirst phaseof the project, all mission elements listed above areanalyzed and programmed as a general overview.Detail analysis of important modules. such as theOrbital Elements. Space Segment and CommunicationStructure, are done in the second phase of the project.

(4.3) Technical Specification

Due to time limitation. some software constraintswere identified and shall be rectified in future phase ofthe project. Some orbital parameters. such as the typeof coordinate system, graphical images or somesimulation data were made constant due to theseconstraints. Greater flexibility is hoped to be achievedin future phases. Since the software runs on modularbasis, default values are made available.

(5) DESIGN ENGINEERING PROCESS

Table I Dejcllllt Values./or General OrbitalCalculatiuns

(4.1) Software Functionalities

To cater the needs analysis presented earlier, thissoftware will tackle mainly on the weaknesses ofconventional way of teaching orbital mechanics andspacecraft design courses. The first phase of theproject will be focusing on the fundamentals of spacemission design. Apalt from being a teaching tool forlecturers in conducting their space mechanics relatedcourses, the software is targeted to aid students in sclf­learning of fundamental concepts in orbital mechanics.

As the software will be based on a GUI concept,the theories learned in class can easily be visualizedand understood, thus shall increase time efficiency in

ParameterPropagatorCoordinate TypeCoordinate SystemAnimation St~lIt TimeAnimation Stop TimeAnimation Step SizeOrbit Epoch

Ty eConstantConstantConstantVariableVariableVariableVariable

ValueTwo BodyClassicalJ2000

151

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· f.:lJ: <lOO"""

-. P"'''''''C''r~I~..-._

·;~~~·l

..~.JA ..lfiOdt9: i·

:-I; r L.... A.<.cnllo.lo .J'll-d09 i

:~ ..:J:· ~ .-.rod<\) TJIl~ I

.......... ':"'_,':,::~.:i .OJ'1.rt'(Vt rI P.,,1fOe .-7' ~.,.. :

~ ..:.LJ .:J t· l_~~ .._.._.._".._~~J

:.r.,~Wr.~ ...... _. -=:.:·r il<l-l '~T+

L. _-:::~~d.~=~,~.)J

Fig. 2 Orbit Orientation Module

Only two input parameters are required to create acustom orbit. As such, the first parameter selecteddetermines the input parameter needed in the second.

The second module allows user to defineimpol1ant initial orbital parameters of a satellite orbit.The expected Olltput of the process is a 2-D graphicalsimulation of the orbit based on th~ informationgathered from lIser. U'::ier has an option to choose oneof the following predefined orbits:

a) Critically inclinedb) Critically inclined sun synchronousc) Geostationaryd) Molniyae) Repeating ground tracef) Repeating sun synchronousg) Sun synclu'onous

or, a custom defined orbit.

The design process is dependent on the softwarerequirements as discussed above. A'::i such. thesoftware requirements baseline will be used as inputsto the design process. Any new functionalities requiredwill then not be considered, and shall be broughtforward only to the next phase of the project. Thedesign process life cycle include designing of softwareitems, coding, testing and integration of software units.

A thorough top-level architecnlral design iswritten in the form of seven inter-dependent mainmodules as mentioned earlier. Users are asked to inputa set of variables in the first module which will thenoutput another set of variables to the second moduleand so on. Though the sequence of operations isinvisible to users, the order of each module should benoted in order to obtain a detail analysis. This featurealso aims to facilitate users to the step-by-step processof designing a preliminary mission. However, eachmodule can still be executed independently, in whichcase default values will be used where necessary.

To facilitate usage, the software will be based onGraphical User Interface (GUI) fonnat. Each modulewill have animation window, parameters inputpanel and an animation control panel. Parametersinput panel accepts user input for relevant spacemechanics and mathematical calculations. A report onthe calculations perfomled can be viewed by just aclick on a button in the animation control panel. Anyorbital simulation based on the initial input parametersand back-end data processing can be launched fromthe animation control panel and the graphicalsimulation will automatically be displayed in theanimation window.

5.1 Module I: Subject Table 2 Available Pairs ofParameters

The software requires user to specify the subjectto be detected or mission to be performed by thesatellite. Users need to define the criteria for thesubject to be viewed such as the coverage ;.Irea andspatial resolution.

First Parameter

Semimajor axisApogee RadiusApogee AltitudPeriodMean Motion

Second Parameter

EccentricityPerigee RadiusPerigee AltitudEccentricityEccentricity

1 - Subject Characteristic - (b~~ .~.~

Tdr.:(J~t : padi ':["1)

SlJbJecr:. : P"ldl3i~~ 1)[ "'h~ .:iubJt-:.-r: : l).O~ (J

111e CO'J'~r:Qq'e ;).rr;·~ ft:-Z: l'-:II.U: Zl.1b1 ~ct : 1000 mTIle ~CC"U:'3CV Y':I\l 10Ilsh to )bset:ue : 10 iJeqfr.:e({\len~y "t Ob3nc·'HL(·n : 1'; per ':layHel.qht of the r:a,(IJ~t: : 350 II.

Fig. I £xcerptji-o/1/ Subject Report

(5.2) Module 2: Orbital Design

Orbit plane changes can be viewed by choosingthe kind of transfer orbit required. for example,Hohmann Transfer or Bielliptical Transfer.

In order to view the orientation of the orbit planein space, two Keplerian elements, represented by thefollowing parameters, are required:• Right ascension of the ascending node (RAAN):

The angle in the Ea11h's equatorial plane measuredeastward from the vernal equinox to the ascendingnode of the orbit,

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5.6 Final Result

5.3 Module 4: Communication Architecture

4.1 - ComlTh."'IIld Link Budget . ~h'~~

In this module. users will be guided tlU'ough thesubsystems analysis: attitude determination andcontrol, communication, command and data handling.power. thermaL structure. guidance and propulsion. (n

each subsystem analysis. the elements to be used orspeciticd parameters arc to be determined andcalculated,

5.5 Module 6: Spacecraft Bus

Two analyses will be done in this module. whichare to calculate the power budget and the mass budgetfor the whole spacecraft. For this purpose, the payloadpower estimation calculated in the earlier module willbe used. However. basic assumptions need to be madeto calculate the approximations.

5.4 Module 5: Mass Budget

Fig. 5 Excerpt o.lReport Analysis on Link Budget

Uphllk Frequency = S GH::TLm3111.l:l:er p.)\,Ter = 10. clBlJTrallSlIlt te [ Lllle La::" = -1 'lBTra1l3llllt Antenna Beolll.ll.dth = 10 d"!q

·;-Jtp'.-r I,~ I V,,,Ic>;..:t Ilr',k !;<I.r:h,~I' Itu'l$' I :~i' 'to 1;11..;' ~·-,:I'•.'f I, "Clnd I.r_-;"IJt?L}

In this module. the software will perform the linkbudget analysis for the specified mission. which is thecommand link budget and telemetry and data linkbudget.

Step 4: link BudgetName of Mssion ; glonass2Cleated: L8·Aug-2003

Space segment module lets USCI' to select suitablepayload for the spacecraft mission and then to estimatepayload's size. The software will calculate the aperturesize and apeliure ratio of the payload based on thewavelength and resolution required.

Mean anomaly. Argument of Time past ascendingnode, Time past perigee.

(5.3 )Module 3: Space Segment

./

de of the a~n?:~''= node: The Earth-fixed;.,~_ .... fthc ar;.cendlr.:::: :Jode.

~ v' _. ,." l of perigee: J:--e angle. In the 'plane of:- "11't I~ o-rbit. ber;"~:1 the ascending nodeto J C·7 h' . d .. . crigee of t e :,trolL measure In thep .,'on ()(the ~telllte s. :=JOIlon.~~.

::odulc wiJJ plot ,the :;atellite ~round. trac~ on-',urfacc accordmg :.0 the simulatIOn tune"',A fuJI repo~ o~ the result of orbital.. "1 can be VJewe-..: at the end of the

~i~

,..' of parameters ~.~--G.l be used to determinee location above me earth. The following'~ctcrg shall be use-.:i for such case:

-----_........ projec1ion of ~atelite. _~ _. . . :'-""'oc po~ition onto tn:1e

c:iIt:k .....-.. - ~a~..... I"'I""J O/~

..ut~ --.....~/: \ <;atdite,,/ ............ '.c..-'"Y location

./:::.:.~./~\/-[/../ /~\ ~ \~I

L_------:~---==---~__=~~+_-__l perigeeUlUf utt~ \... Eu1h )

......."'-.-,-_.... .///

J"= tIM itnClllQlll:r /'____~=_ etctd1C:~ _-----.-

;, ::Parameters Deten71ining Satellite Position

~ [j ~ Tll.le anomaly': fJ = Right ascension of ascending node

{II -. Argument of perigee/periap~i:;

I - Indination

I.>4 Parameters Determi/lil/!!, Orhit Orientation

.' I'llrameters determining satellite position:

15~

All results from each module are stored in HTMLdocuments during the process. Each HTML tilecontains the results from each module and all thesefiles are stored in a folder created during nmtime. Assuch, users can compare the results obtained from onemission to another for further analysis.

[6] VAUDATION AND VERIFICATIONPROCESS

The validation and veritication of the software istrivial in contirming that all requirements have beenmet and all design constraints discussed earlier arerespected. In this process, each software module willbe checked for validity of output, and consistency.The validation and verification plan shall be developedand carried out before the software can be deemed"qualified".

In conducting the process, the software shall beinstalled and evaluated in its operational environment.where the evaluation will be carried out by thesoftware developers as well as prospective users. Theresults obtained from this software will be comparedto the results obtained from other satellite softwareavailable in the market by using the same sets of data.

6.0 SOFTWARE APPLiCATION

Currently. some parts of the modules have beenidentified for further enhancement to include morefunctionality and to be more user-friendly. Since thesoftware is design for beginners in satellite missiondesign. a lot of default parameters will be incorporatedwhere suitable. Enhancements need to be done as tominimize the number of assumptions made in order toget better results.

Among the modules that have been identified forfurther expansion are Orbital Design andCommunication Architecture. All of these advancemodules will be developed separately before beingreintegrated tn the main software. One of theadvantages in this method is that these individualadvance modules can be used separately in coursessuch as Orbital Mechanics and SatelliteCommunication. The software as a whole shall beused in Spacecraft Design courses.

7.0 CONCLUSIONS

The development of this sottwarc is carried outwith respect to the needs of Astronautic Engineering

students in learning the process of earth observationsatellite mission design. Each software moduledeveloped has the potential to be made stand-alone toprovide more functionality and to be lIsed by moreadvanced users. Apart from being i.l teaching tool forlecturers in conducting their space' mechanics relatedcourses, the software is targeted to aid students in self­lCartlil1g of tile fLlndall1entai concepts of orbitalmechanics as well as to enhance the programmingskills of the students involve during the developmentprocess.

Acknowledgement

This research is P~lIt of the USM Short TermGrant "Preliminary Mission Analysis Tool: ASoftware for Satellite rvlission Design", ~OO 1-2003.

REFERENCES

[I] W. J. Larson & J. R.Werzr. Space MissionAna(l'sis lind Design. 2nd ed., Kluwer Academic.

London, 1995.

[2] C. D. Brown. Spacecrajt Mission Design,American Institute Aeronautics and Astronautics, Inc.Washington. 1992.[3] Vladimir A. Chobotov. Orbital Mechanics. 2 nd ed..American Institute of Aeronautics and Astronautics,Inc. Washington, 1996.[4] European Cooperation For SpaceStandardization.space Engineering Software. ESAPublications Division ESTEC. Netherlands, 1999.