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Managing Life Support Systems Using Procedures

Article  · July 2007   with   7 Reads DOI: 10.4271/2007-01-3026 AbstractInternational Space Station life support hardware is controlled mainly from the ground by executing standard operating procedures. While some on-board software exists for safety purposes, most commands are sent from ECLSS ground controllers to achieve mission objectives. This will prove unwieldy for extended operations with increasing time delays. This paper presents a new approach to encoding standard operating procedures that provides a path to greater autonomy in life support operations. Software tools will allow for adjustable automation of procedures from either the ground or on-board. The Cascade Distiller System (CDS) being tested at NASA Johnson Space Center is used as an example system.

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Join for free Figures 07ICES-206 Managing Life Sup port Syste ms Us ing Proce dur es David Ko rtenka mp, R. P eter Bon asso and Debra Schreck e ngh ost TRACLabs Inc a t N ASA J ohns on Space Center , Hous ton T X 77 058 Copyright © 2007 SAE I nternation al ABS TRA CT Intern ation al Space S tation li fe supp ort h ardw are is contro lled m ainly fro m the gr ound by ex ec uting sta nda r d opera ting procedur es. Whi le s o me on- board softwa re exis ts for sa fety pur pos e s, mo st co m mands are s e nt from EC LSS ground c ontro llers to ach ie ve miss io n objective s . Th is wil l p rov e unwiel dy for ex tend ed opera tions w ith inc reas ing ti me delays . This pape r pres ents a new ap proac h to encodi ng sta nda rd opera ting p roce dures that pr ovide s a pa th to gr ea t er autono my in life suppor t opera tions . Software tools w ill allow for ad jus table au tom ation of p roc edure s from ei th er the grou nd or o n-bo ard. The C asc ade Dis tiller Sys tem (CD S) being tes ted a t N ASA J ohns on Spac e Cen ter is used as a n exa mp le sy s tem . INTRO D UC TIO N Fligh t con troller s an d cr ew me mber s r ely o n sta nda r d opera ting pr oced ures to con trol l ife s uppor t sy ste m s. For spac e shuttle a nd spac e sta tion thes e proce dur es are currently authored in Micros oft Wor d and manua l ly exec uted us ing sy ste m co m mand a nd co n trol d ispla y s. For station this requir es a full-ti me ECLSS g rou nd contro ller interac ting wi th an Atm osp here a nd Cons umables Eng in eer (AC E) in the “ back roo m” f or most ac tivi ties . Th e pro cedu res are used to c alibra te sens ors , chec k s moke a la rms , per for m o xy g en replen ish men ts (called repr ess es) , a nd s tart up and sh ut down ECLSS eq uip ment . Pro cedu res are a lso us ed to diagnos e malfunct ions in ECLSS e quip ment . Wh i le most proce dures can be per formed by either gro u nd contro llers or crew members, they are typical ly performed on t he gr ound when a t all p oss ible. T h is requir es send ing literally thou sand s of comman ds p er year from the ground to sta tion ECLSS sys te ms. We are develop ing proce sse s and tools tha t will al lo w proc edur es to be author ed and exec uted in an adju st ab ly autono mous fashion . Adjus table auto ma tion means th at the hu man may cho ose at run- time w ha t par ts of the proc edur e sho uld be ex ecu ted au tono mous ly an d wh at parts s hould be exec uted man ually . An exec uti on engine ma nages the in terac tion be twee n the h u man a nd the underly in g sys tem . We ha ve also dev elope d a ne w proc edur e repr esen tation la ngu age ca lled PRL tha t captur es the addi tiona l in form atio n n eces sar y to exec ute proc edur es autono mous ly . PROCE D URE RE PRE SE NT ATI O N Proced ures are c urre ntly repr esen ted in na tur al languag e on a human- reada b le display (se e Figure 1). They a re intende d for hu man cons um ptio n not co mpu ter cons umpt ion. Thu s , the repres enta tion do es not su pp ort adjustab le auto mation . Telemetry and com mand i ng infor mation is no t encod ed in the proc edur e. We have been develop in g a new proc edu re repr esen tation cal led the Procedure Repres en tati on Langua ge (PRL ). This l angua ge ke eps the us er- frie nd ly display for ma t of cur rent proc edur es bu t au gme nts i t w i th content-b a sed infor mation (e. g. , goa ls, re sour ces , pr e-cond itions , post-c ond it ions, e tc .) requ ired for mo re autono mous exec ution. PRL also allows for proce dur es to b e writ ten in a mo re modular fas h ion , wi th lar g er proc edur es compos ed of sma ll procedu re “frag men t s'” that ac co mpli sh spec ific tasks . I n this wa y , n e w proc edur es ca n be eas ily cr eated and v erified as hardw are configura tions change . Ou r pr oced ure repr esen tation language is an in tegra tion of an autom ated exec u tion langua ge dev e loped a t N ASA called PLEX IL [1] a nd the e xis tin g Interna tional Spac e Station (ISS) p roc edure r epres en tatio n. Bo th of the s e repr esen tations an d ou r n ew PRL ar e s che mas wri tten in the Exte ns ible Mar kup La ng uage (X ML). STRUCTU RE OF A PROC EDU RE The basic s truc ture of a p roc edure as represe nted in PRL is : Meta data: I nclud es a u n ique ide n tifier , th e pr ocedu re name , the proc edur e au thor, da te, etc . Automa tion da ta: Includes the fo llowin g: • Start c ond it ions: a bo olean exp ress ion t hat w hen evalua ted to false me ans tha t the pr oced ure shou ld wai t unti l the boo lea n ex pres sion is true before s tar ting • Pre -con dition s: evaluate d af ter the s tar t cond ition a nd i f fals e then exit the proc edur e immedia tely with failur e • Pos t-cond itio ns : ev alu ated af ter a pr oce dure is done a nd i f it eva lua tes to fa lse then the proc edur e has failed • End con ditions : evalua ted con tinuo usly and when it is true ex ecu tion of the pro cedu re is finish ed • Inv arian t c ondi tions : mus t rema in true during the entire exec ut ion o f the proc edure ; oth erw ise the proc edur e fails • R esou rce s: any r esou rces (time , fuel , c rew memb ers, power , tools , etc .) requir ed for exec ution o f this proc edur e Para meters : De clara tions o f any data tha t is pas sed to the pr oced ure fro m wha tever is call ing the pro cedu re Loca l Var iables : Dec lara tions o f a ny variab le s u s ed internal to the proc edure ExitMode s : D efini tion o f exp lic it proc edur e e xit mode s , spec ifying proced ure succ es s or fa ilure , and givi ng optiona l desc ri ptio n o f the reaso n for ex iting ProcTi tle : Proce dure nu mbe r a nd title InfoSta tement : Speci fies ex pla natory infor mation (e. g. notes, cau tions , warn ings) t hat mig ht b e ne eded or desir ed by a h uma n exec utor Step: A st ep is the bas ic or ganizin g s tructure of a proc edur e. A proce dure c an con tain on e or more s tep s and eac h step cons is ts of the follo wing par ts : • Auto ma tion d a ta: As ab ove exc ept r epl ac e the word “proc edur e'” wi th “step'” • Step title and unique iden ti fier • Infor ma tion to be disp layed to the user be fore this step is execu ted in manual oper a tions • A block , w hich can be ordere d (i.e., exec ute d in sequ ence ) or unordere d (i.e., execute d in any order ). A bloc k c an als o con sis t o f a n If-The n state men t, a For-Eac h st atemen t o r a Wh ile state men t. Ins ide of a block ar e: o Automa tion da ta , as abo ve ex cep t for block s o Ano ther bloc k allow in g for arb itrar y nesting o f bloc ks in a step o Instruc tions , which are limited to the follow ing:  Comma nd i n struc tion, w hich send s an elec tronic co mma nd to the sys tem bein g con trolled  Ensure ins truc tion, wh ich c heck s to value of a tele metry vari able agains t a targe t a nd , if the v alue is n o t cor rect then issu es a comm and tha t shou ld mak e it corr ect  Input ins truc tion, w h ich ass igns extern al data (from a cr ew me mber , telemetry , e tc.) to a local va r iable  Manual ins truc tion , wh ich as ks a human to iss ue a co m mand  Physic al device ins truction , which ask s a crew membe r to phy s ic ally mani pulate a dev ice  Wait ins truc tion , w hich w aits for either a se t period of time or un til a boolean exp res sion e valua tes to true, wh ichev er co mes first  Proced ure c all, wh ic h can be block ing (i.e ., the curr ent pro cedu re paus es until the called pr oce dure finish es) or non- block ing (i .e ., the two proc edur es c ontinue to run in parallel  Stop, pause and resu me proce dure, which effec ts the exec ution o f the cur rent proc edure • The las t c om ponen t of a step is a c ondi tion al branc h, which cont ains a set of b ool ean expr ess ions paired w ith a goto step or e xi t proc edur e c ommand that is e xec uted if the boolean expr ess ion is true. Th e de faul t is to go to the n ext step if n o cond itio nal bran ch is given. This r epres en tatio n ca ptures th e co nten t and in tent of the p roc edure a lo ng wi th s a fety rules (or condit ion s) under wh ich the proc edur e an d its compone n ts ar e to be exec uted. PROCEDUR E EXA MPLE Figure 1 sho ws the first s tep of a multi-step ISS ECLSS proc edur e to ac tiva te the atmos pher e r evita lizat i on sys tem. The pr oce dure is n ine teen page s long a nd is pres ented to the hu man or the c rew me mber exa ct ly as show n in Figur e 1 . In Step 1, wh ich is ti tled “ Verify i ng Rac k Power” the firs t s ev eral line s ar e ins tructions on how to nav iga te to the c orr ect pa ge o f the ISS co mm a nd and control d isplay s . Transla ted, i t tel ls the per s on exec uting the proc edur e to go to the U S La b page , t h en the ECLSS page , then the AR Rac k p age then look for the labe l “L AB AR Rac k Ove rview ” on tha t pag e , t h en find the “ Rac k Loc ation L AB1D6 – ( Entire R ack )” label and selec t RPC M LA 2B C RPC 0 1 . After selec ting th at the use r s hould s ee a c ommand button l abeled “RPC Posi tion” w ith the wor d “ Clos e” in it. They shou ld hi t th at button an d v erify tha t the tele metry talkb ac k r eads ‘ Cl ’ . Assu ming the verify is cor rec t they move on to the ne xt instruc tion in th e proc edure , w hich is a nother nav igat i on through c omman d and con trol pag es and ano th er comma nd. I t is e as y to se e h ow , ov er ni neteen page s , it c an g et very tedious to enter c om man ds man ua lly a nd move your attention betwee n the proce dure and the comma nd a nd c on trol disp lay s. SYS T E M REPR ESE N TA TIO N Proced ures des cr ibe the proc ess es by which a de vice or sys tem is oper ated or de bugge d. Th ey a re or ien ted towards achiev ing so me tas k or goa l. They do n ot desc ribe the d evic e or s ys tem . How eve r, a repr esen tation of the sy ste m is neces sar y for proc edu r e exec ution. Th at is , a rep rese n tation o f all o f the pos si b le comma nds , teleme try , s ta tes, sta te trans ition s , conn ections and taxono my of the dev ice or sys te m is requir ed to su pport pr oced ure au thoring an d exe cutio n. This rep res ent ation is differe n t fro m the pr oced u re repr esen tation des cribe d in the prev ious sec tion . COM M ANDS AND TEL EME TRY The repr ese ntation o f com man ds and te leme try is nece ssa ry so t hat the pr oced ure au thor k nows wh at atomic ele men ts ar e a vailab le to co nstruc t a proc edure . Further mor e, t he ex ecutive (man ual or auto ma ted) mu st know how to get teleme try fro m, or send a co mma nd to, the con trolled s yste m and in w h at for ma t. Ideally th is repr esen tation of c om mands and teleme try shou ld co me from t he h ardw are designe r o r v endor . W e ha ve chos en an indus try stand ar d repr ese ntati on c alled XML Teleme tric and Co mm and Excha nge (XTC E) (http: //sp ace .omg.org /xtce /index .htm) for re pr esen ti ng comma nds a nd tele me try . We neede d to make s igni fican t modifica tions in how we used XTC E to a cco mmod a te the au thoring a nd exec ution o f gen er ic procedur es. Ge ner ic proc edur es are thos e in wh ic h th e actua l de vice b eing o pe rated is not know n unti l the pro cedu re is exec uted. In that c as e, the a c tual co m mands and tele me try are not kn o wn either. Fo r exa mple , there migh t be a pr oced ure to calibr ate a s moke de tec tor, whic h w orks for any s mo ke detector . Wh en a s pec ific smok e detec tor is c alibra t ed the co mm ands an d te lem etry w i ll n ee d to b e link ed to that device . How eve r, wh en t he p roc edure is wr it ten the comma nds a nd te leme try nee d to be gen eric for all smok e de tec tors . W e hav e e x tended XTCE to include a “type” tag tha t a llows for crea ting ge ner ic class es o f devic es tha t all sha re the s a me c o m mands a nd telemetry . STAT ES The repr ese ntation of s tates an d s tate tra nsit ions is nece ssa ry so tha t the pr oced ure au thor can re feren c e them in p re-c ondi tions and pos t-cond itions ( e .g., do n' t do this proc edur e wh en the dev ice is in this s tate) and so that the exe cut ive can chec k these s tates w he n exec uting the proce dure. T he s tate repre sent atio n o f a devic e cou ld come ea rly i n i ts des i gn be fore t he hardw are impleme nta tion and be for e s pecif icatio n of comma nds and t ele me try. This would allow for ear ly deve lopmen t and test ing of p roce dures aga in st a s ta te model of the dev ice. Whi le we co uld extend XTC E to add s ta te in for ma tion, w e fel t th at a sep ara te repr esen tation would be mor e po we rful . We ha v e chos en State Char t XML (SCX M L) (http: //www .w3 .org /TR/s cx ml/) for repr esen ting s tat es and s tate trans i tions . TAXONO M Y A syste m rep res en ta tion als o need s to inc lude the compon en ts o f the s ys tem a n d the rel atio nship betwe en compon en ts in s o me kin d o f tax onomy . There are t wo kinds of relat ionsh ip s we expe ct to captur e . Fir st there is a hierar chic al rela tionsh ip betw een sp acec r aft compon en ts. For ex amp le, a spac ecra ft c ons is ts o f many s yste ms - - pow er, life s uppor t, navig a tion, propu lsion , etc . Eac h s ys tem has m any s ubsy ste ms a nd subs ys tems hav e co mponen ts (v alve s , tan ks , sw itche s , etc.). Hierar chy a nd conta in ment ar e impor tan t t o repr esen t in orde r to al low for e fficient displ ay a nd Figure 1 : The f irst step of a n ISS ECLSS proce dure reas oning. The s ec ond kind of rel atio ns hip is conn ectivi ty be tween s pac ecr aft co mpone n ts . F or example , the outpu t of an oxy gen g enera tion sys tem may be conn ected to an ox ygen s torage tan k. Conne ctivity is i mpor tan t to rep res en t s o tha t s ituat i on awar enes s display s can be buil t for hum ans . We are st ill in the pr oces s o f de ter minin g a ppr opria te repr esen tations -- ex is ting sta nda rds suc h as X ML Metad ata Intercha ng e (XMI) (http: //www .o mg.org / techno logy /doc umen ts /for mal/xm i. htm) m ay be appr o priate . PROCE D URE E XE CU TIO N Proced ures c an be ex ecu ted au tono mous ly us ing an executio n en gi ne, which i nterpr e ts the proc edu re repr esen tation an d issu es c om ma nds to the un derly i ng sys tem. T he re has bee n a great de a l o f rese arch in the last de cade on proc edura l ex ecution sys tems , with s o me of t he more prominen t bein g PRS [2 ], R APS [3], and APEX [4 ]. T he Space Statio n pr ogram a ls o has a proc edur al ex ecu tion sy s tem c alled Ti meli ner fro m Drap er Laboratorie s. Wh ile underly ing imple men tati on details may chan ge , all proced ural ex ecu tives ha v e simi lar fu nc tions : 1) they have a librar y o f a p plica b le proc edur es; 2 ) they choo se proc edur es tha t a re eligi b le to r un by ma tch ing s tar t and pre-c ondi tion s wi th sys te m states an d teleme try in r eal-t ime ; 3) they d eco mpo s e hierar chic al pr oce dures i nto sub- pr oced ures ; 4) th ey dispatc h com mands to lo w er lev el con trol pr oce sse s; and 5) they moni tor for re levan t sta tes in the sy ste m . ADJUST A BLE AUTO NO M Y Adjus table autono my a llo ws a proc edur e to be exe cut ed either by a hu man , but au tom atio n or by b oth. The go al is to mini mize the need for h u man i nter ac tion whi le maxi mizing the a bil ity for hu man s to in terv ene in proc edur e exec ution. Adjus tab le autono my mus t be addre sse d fro m the beg inn ing by iden ti fying wha t p ar ts of a pro cedu re ( i.e., ste ps and ins tructions) migh t be exec uted auton omo usly a nd wha t par ts mu st b e exec uted by a human. Manual exec ution is requir ed for parts of the p roc edure tha t hav e n o ele c tron ic comma nds . It is als o re quired for p ar ts o f the proce du re that have no ins trumen ta tion to d e term ine i f exec uti on was su cce ss ful. We h ave ide ntified three b as ic levels of autom ation for proc edur es : • Man ual : The com mand is dispa tch ed o r a c tion is performed by a huma n w ith a ll tele metry ver ification done by a human • Auto ma tic: The co m mand is d is pa tched autom atica lly or the teleme try is v erif ied autom atica lly • C onse nt: C o m mand is dis pa tched auto ma tically , but only a fter appr ova l by a hum an After iden ti fying a nd s toring in the PRL ho w di ffere nt parts of a procedur e could be execu ted, the en d u s er interfa ce (s ee nex t s ec tion) is us ed to mark w h ether a step or ins tructio n sho uld b e ma nual , auto ma tic o r requir e co nsen t b efore ex ec u tion be gins . The s e ass ign ments mus t no t con fl ict wi th the pre -au thoriz ed level of autono my for a p roc edure s tep or i nstru ct ion. As the proc edur e is ex ecu ted, the ex ecut ion en g in e res pects the end user ’ s de s ires an d guide s the en d us er through the vario us manu al and con se nt act ions. PROCEDUR E TR AC K ING Proced ures w ill c on tinue to be exe cuted manual ly in upco ming space missio n s. Th ere will be a c tions that can only be do ne by a per son for p hy sic al or ope ra tion al reas ons. This po ses p roble ms for an a djus tab ly autono mous ap proac h to proc edure ex ecu tion. In a purely auto ma ted ap pr oac h the exec utiv e kn ows exa c tly what is b ein g d one and w hat the status is . H owev er, if some parts o f the pro cedu re are man ual , then th e cur rent execu tion status w ill need to be inferr ed from telemetry or by direc t query to the end u ser. T he proc edur e tracking proce ss doe s this inferen ce . It us es all a vai lable da ta to deter mine w hich s tep o f th e proc edur e is being e xec uted a nd wh a t the ex ecu ti on status is. I t the n ma kes th is ava ilab le to o ther p roc ess e s suc h as the execu tive and the end us er d isplay . GRAPHI C AL DI SP LA YS A ND E DITO RS Humans ar e an i mpor tan t pa r t o f the pr oced ure proce s s. They w ill be au thor ing proc edur es a nd they w ill be exec uting o r moni toring the autom ated execu tion of proc edur es. PROCEDUR E DI SPLA Y The hu man execu ting the pr oced ure w ill ne ed a d is pla y. Ideally , this d ispla y will look si milar to the ` `pap e r'' proc edur es of today , but allow for dire ct execut ion o f comma nds and d irec t dis play o f te leme try by the e nd user . Th e en d u ser interf ace will also hav e to displa y t he res ults of p roce dure trac ki ng by h ighl igh ting or oth erw i se noting s teps tha t ha ve bee n co mple ted, s teps tha t a re cur rently ex ecutin g, and s teps t hat are pe ndin g. Execu tion status , espe ci ally fai lures , will need to be made e xpl icit . Supp o rt for ad jus table au tono my r equir es an e asy wa y to note steps tha t sh ould b e do ne manua l ly and s teps tha t should be done au to mat ically . For a single pro cedu re being don e b y a single end us er the dis play requir e ments are not de mandi ng . H owev er, if we b eg in to ad dres s multiple p roce dures be i ng exec uted in paral lel by one or more e nd user s wi th interact ion bet wee n them , then a wider var ie ty of is su es arise . Thes e includ e notifica tion of the s tatus of o th er end us ers or exe cutives , inter rupt ion rea son ing , a nd multi-mod a l n o tificatio n. For ex amp le, a p roce dure m ay have a s tep that is a wai t for so me le ngthy per iod o f time (sa y one hour) at whic h point an en d us er co uld begin another p aral lel pr oced ure. A t the e nd of the hour t he end user would nee d to be n otified appro pr iate ly, f ind a break -po int in their ne w proc edur e, r eturn to the old proc edur e, get s ituated, and be g in ex ecu ting. In ano ther example , two en d users tha t ar e s epara ted by dis tan ce may be perfor ming a s ingle proc edure ( say an EV A astron aut a nd a gr ound c ontrol ler) and ne ed to coor dinate the ir activi ties . We have begun add res s i ng these iss ues in a sep ar ate pr ojec t [5] . Figure 2 sh ows a n end use r disp lay we dev eloped f or ISS proc edure s. Each bo x re pres en ts a ste p o f the proc edur e. Steps ca n b ranc h to o ther s teps ba s ed on their ou tco me. Di fferen t color s repre sen t the s ta tus a n d level of au tono my of e ach s tep. Gree n s teps a re comple te. Purple is the c urren t, manu al s tep. At the t op mess ages for the u ser are dis played a nd use r in put is reque sted. PROCEDUR E EDITING Proced ures will ne ed to be auth ore d, viewe d , ver ified, validated and mana ged by a va rie ty of peo ple , man y of who will not u nder sta nd XML o r o ther rep rese n tation s . We a re develo pin g a Proc edur e In tegra ted Deve lop me nt Environ men t ( PRID E) tha t will prov ide a n inte grated s et of too ls for d e aling w ith pr oced ures . These tools w ill allow for author ing , v erifyin g, v a lida ting and managi ng proc edur es. Author s w ill be ab le to gr aphic a lly des ign their proc edur e us ing p alet tes o f co m mands , te le metry and pr oced ure c ons tructs . Acces s to des ktop s ys tem simula tions wil l be integr ated with the PRID E tool f or ver ification and va lida tion a c tivi ties . A w ork flow s ys tem will also be in tegra ted with PRIDE to trac k proc edur e Figure 2 : A graph ic al end-us er di sp lay for a pro cedu re chan ges an d appr ovals . The PRIDE tool will al lo w authors to v iew the pr oced ure a s i t wil l a ppe ar to the e nd user . CASE ST UD Y NASA Jo hnso n Sp ace Center wi ll be cond uc ting tests in the spr ing and sum mer of 200 7 of a new water r eco very sys tem being built by Honey wel l. The new s ys tem is called the Cas cade D istiller Sys tem (CDS). We are deve loping proc edur es for contro lling th e CD S usi ng t he tools des cr ibe d in this paper . We have e xpr ess ed the telemetry an d com mand s of the CD S in an XTC E file . We have written s ever al C DS pr oced ures in PRL a nd also encod ed th em in an e xec u tion engine called RAP S. The exec ution engine will exec ute the pr oce dur es agains t the CDS hardw are in an adjus tab ly autono mo us fashion . PRL allow s f or e asy e xpre ss ion o f the bas ic CDS oper ating para dig m. For ex ample, here is a pseu do-PRL snippe t f or s tar ting up the CDS (th e real PRL in XML is q uite v erbos e and d if ficul t to u nders ta n d withou t proper edi ting tools): Start Proc e dur e CD S Sta rtu p • Pr e-c ondit io ns : coola nt flowing AND va cuum pres sur e no minal AND feed tank full • St e p 1: Start Syst e ms 1. C omman d Ins truction : Star t dist iller water flowing a t 1200R PM 2. Exec ute Pro cedu re: Apply Vacu um To Al l Systems 3. Exec ute Pro cedu re: Fill Cold L oop Wit h D I Water 4. Exec ute Pro cedu re: Fill Hot Loo p With Feed 5. Exec ute Pro cedu re: Start Produ ct Flow ing • St e p 2: Wa it f or Sys t e m to St art 1. Wa it for : Produc t tank w eigh t i ncre ase End Proc ed ur e CD S Sta rt up The p re-c ondi tions ensur e th at the s ys tem is in the prope r s ta te for s tartu p. The first s tep has a c o mma nd instruc tion that is is sue d direc tly to the h ardw are . T he other four ins truct ions c all add itiona l proc edur es that d o var ious p arts of t he job and re turn to this pr oced u re when the y are d one. For e xa mple , the third in struc ti on calls a pr oce dure to fill t he cold lo op o f the CDS wi th de -ionized wa ter. This is done wi th a pr oce dure that turns a ser ies of v alves . Her e is some ps eudo -PRL for tha t proc edur e: Start Pr oc ed ur e Fill Col d Lo op With DI • Pre-con dit ion s: dis ti ller s peed EQ 120 0 R PM • Timeou t: 60 sec onds • St e p 1: Start DI Wat e r Flow in g 1. Exec ute Pro cedu re: Apply v acuu m to dis tiller sys tem 2. C omman d Ins truction : Open v alve to produ ct tank 3. C omman d Ins truction : Open DI wa ter valv e 4. Wa it for : Cold loop fille d 5. C omman d Ins truction : Clos e DI wa ter va lve End Proc ed ur e F ill Col d Lo op W ith DI This pr oced ure h as o n ly one s tep. I t has a preco nditi on that that dis tiller sy ste m b e ru nning with a speed o f 1200 RPM. Th e timeout s tates that th is p roc edure sho uld finish exe cuti ng in 60 s eco nds. If i t d oesn ’ t t he proc edur e ab orts with a fai lure . The firs t instru ct ion c al ls another proc edur e that applies vacuu m to t he disti ll er sys tem. The next two s teps o pen valve s . T he four th step wa its for a si gna l from the hardw are sy s tem tha t t he cold loop is filled . The fina l s tep c loses the DI valve . We ha ve id en tified s ever al doz en pr oce dures that w ill contro l the func tionin g of the C DS. These pr oce dur es conn ect v ia co mma nds an d se n sor s to the under ly i ng CDS v ia a hardw are inter face layer as defined i n the XTCE re pres en tation . Exec utio n is don e ma in ly autono mous ly us ing the ex ec ution engine , bu t the lev el of au tono my for mos t s teps ca n b e s et to manua l if desir ed. For example , in the pr eviou s proc edur e if Step 1 is s et to manual then a hum an w ould be res pons ib le for ex ecuting the vac uum p roce dure and o pening and clos ing a ll va lves . The ex ecutio n engine wo uld s till v erify pre- cond itions to ens ure sa fe oper a tion. In ad di tion to our wor k with the CD S w e have al so repr esen ted sever a l ISS Elec trical Power Sys te m (E PS) proc edur es in PRL. We h ave then e xec uted those proc edur es ag ains t a high- fidel ity s imulatio n o f th e IS S (ca lled ISS-in-a- box) to va lid ate t hat our appr oac h can Figure 3 : System arc hitec ture help enh ance s pac e s tation oper atio ns. Figure 3 s ho w s the bas ic sys te m arc hitec ture. The sys te m in the low er right ca n be the C DS or the ISS (or ISS simula tion) . T he interfa ce c onnec ts the exec ution e ngin e to the s ys tem. The ex ecu tion engine exe cutes procedur es, w hich are authored in PRIDE. The pr oce dure track er and end- us er display take da ta fro m the ex ecut ion eng ine and t he sys tem an d s how the us er the cur rent p roce dure s tat us and help the use r p er form ma n ual o pera tions or allow f or cons ent to be g iven . CONC LU SI O NS AN D FU TURE W ORK Proced ures ar e the means by whic h a ny space cr aft sys tem, includ in g life supp or t s ys tems , ar e o perate d. Curr ent operations are pred o minan tly manua l and a re time intens ive and err or-p rone . We are us i ng simula tions and gro und tes tbeds to v a lida te mo re autom ated ap proa ches to con trolli ng spa cec r aft sys tems . Th ese appr oach es w ill be nec ess ary as we deve lop lun ar out posts . The CD S sys tem wil l be o perated a t NASA JSC d uri ng the s pring and sum mer of 20 0 7. We will v alid ate o u r contro l a pproa ches using this s yste m. W e are als o re-authoring seve ral ex istin g ISS ECLSS p roc edure s in PRL and w ill ex peri ment wit h adjus table au tono mo us exec ution ag ains t a hig h-fid eli ty ISS si mulat ion. ACK NO W LE DGM E NT S This wor k wa s co nduc ted under NASA ’ s Ex plor ati on Techn ology Develop men t Progra m ’ s Spacecr a ft Autono my for Veh icles an d H abi tats p roj ec t. T he authors w ish to t hank the ir collea gues at N ASA A m es Res earc h C enter who particip ated in disc uss ion s under lyng many of the ideas presen ted in this p ap er, including Ari Jon sso n, Vand i Verma a nd Micha e l Dal al. The au thor s a lso w ish to than k S& K Aer ospa c e employe es Scott Bel l, Kev in Kusy , Tod Mila m, Arth ur Molin an d Ma ry Be th Huds on who w ork at N ASA J SC and i mple men ted many o f the so ftwar e p roc ess es desc ribed in this pa per . The a uthors als o a ckn owled ge Lui W ang of N ASA JSC and R ober t Phillips o f L3Co m a t NASA JSC for he lping cr ea te the Proc edu re Repr esen tation L angu age . REFER E NCE S 1. Vand i Ver ma, Ari Jons son , Corina Pas area nu , Re id Simmons an d Kan Tso , “ Plan Ex ecution Int erc hange Langua ge (PL EXIL) for Executable Pla ns and Comma nd Sequ ences ,” in Pro ceedi ng s of the Intern ation al Sympo siu m on Artifi cial Inte lligen ce, Roboti cs a nd Automa tion (i-S AIRAS) , 200 5 . 2. Mich ael P. George ff and Fra nco is Felix Ingrand , “Dec ision- making i n an Embe dded Reas on ing System ,” in Pro ceeding s of the Intern atio nal Joint Confere nce on Artifi cial In telligen ce, 1989 . 3. R . James F irby , “An I nve stig ation in to Reactive Plann ing in Co mplex Domains ,” in Pro ceedi ng s o f the Na tional Conferen ce o n Artifi cial Inte lligen ce, 1987. 4. Mich ael Free d , “ Mana ging Mu ltip le Task s in Complex , Dy na mic Environ ment s,” in Pro ceeding s o f the Na tional Conferen ce o n Artifi cial Inte lligen ce, 1998. 5. D ebra Schre cke nghos t, Carr ol l Thr ones bery , R. Peter Bo nass o, Da vid Kor tenka mp a n d C hery l Martin , “I ntellige n t Con trol of Life Suppor t for Space Missio ns ,” IE EE Intel ligen t Syste m s, 17(5 ) , 200 2 . CONT AC T The au thors may be co n tac ted t hroug h em ail at kor ten@tracl ab s.co m , bon as s o@trac labs .com a n d ghos t@ie ee.org

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