UCRL-JC- 128641

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Description of ARAC’S Real-TimeModeling Support to the Mars

Pathfinder and Cassini Missions

J.C. Pace

This paper was prepared for submittal to the

10th Joint Conference on the Applications of Air Pollution Meteorologywith the Air & Waste Management Association

Phoenix, AZJanuu?y 11-16,1998

October 1997

This is a preprint of a paper intended for publication in a journal or proceedings. YSince changes may be made before publication, this preprintis made available with ‘the understanding that it will not be cited or reproduced without the permission of the 7author.

DISCLAIMER

This document was prepared as an account of work sponsored by an agency ofthe United States Government. Neither the United States Government nor theUniversity of California nor any of their employees, makes any warranty, expressor implied, or assumes any legal liability or responsibility for the accuracy,completeness, or usefulness of any information, apparatus, product, or processdisclosed, or represents that its use would not infringe privately owned rights.Reference herein to any specific commercial product, process, or service by tradename, trademark, manufacturer, or otherwise, does not necessarily constitute orimply its endorsement, recommendation, or favoring by the United StatesGovernment or the University of California. The views and opinions of authorsexpressed herein do not necessarily state or reflect those of the United StatesGovernment or the University of California, and shall not be used for advertisingor product endorsement purposes.

2.1 DESCRIPTION OF ARAC’S REAL-TIME MODELING SUPPORTTO THE MARS PATHFINDER AND CASSINI MISSIONS

John C. Pace” *Lawrence Livermore National Laboratory, Livermore, California

1. INTRODUCTION

The Mara Pathfinder and Caasinimiaaions, conducted by the National Aeronauticsand Space Administration (NASA) to study Marsand Saturn, have radioactive materials On boardboth spacecraft to supply heat and electricalpower. Although the risk of a releaae of radioactivematerial from either mission was very small,federal plans call for the Department of Energy(DOE) to provide emergency response supporiduring the launch of any NASA mission involvingradioactive materiala.

For Mars Pathfinder and Caaaini, DOEassigned the task of emergency responsediaperaion modeling to the Atmospheric ReleaseAdvisory Capability (ARAC) at the LawrencaLivermore National Laboratory (LLNL). The role ofARAC was to provide pre-launch guidance aboutwhere hazardous material would have gone ifreleased, and in the event of an accident toprovide refined calculations to help determine themagnitude of the release. This paper describeshow ARAC carried out this mission.

2. DESCRIPTION OF MARS PATHFINDER ANDCASSINI MISSIONS

The Mara Pathfinder mission, whichlaunched from Cape Canaveral on 3 Decdmber1996, landed the Mats Sojourner rover (Fig 1) onMare on4July1997. The rover has sent backawealth of new information about Mare, includingspectacular pictures of the planet’s surface.

The Cassini mission, scheduled for launchin October 1997, will enter orbit around Saturn inJuly 2004. As it approaches Titan, Saturn’s largestmoon, Cassini will release the Huygens probe,which will descend through Titan’s atmosphere.Caesini will orbit Saturn for four years.

3. NUCLEAR ASPECTS OF THE MISSIONS

Nuclear material waa used for kth thesemissions. For Mars Pathfinder, a small amount of

Corresponding aufhor address: John C. Pace, L-103, P.O. Box 808, Atmospheric SciencesDivision, Lawrence Livermore National Lehmtory,Livermore CA 94551; e-mail jpace @arec.llnl.gov.

Plutonium-238 (Pu-238) was used in threeRadioisotope Heater Units (RHUS) to supply heatto the rover% electronic circuits. Also the rover’sAlpha Proton X-Ray Spectrometer (APXS)contains Curium-244 (Cm-244). The APXSstimulated rock and soil targets with alphaparticles emitted by the Cm-244 and recorded theresulting alpha, proton, and X-Ray spectra emittedfrom the sample to determine the composition ofthe targets. The total amount of nuclear materialon board the spacecraft was 7.3 g of Pu-238 and.00093 g of Cm-244, but safety analyses predictedthe release in the highly unlikely event of anaccident would be only .0031 g of Pu-236 and.00054 g of Cm-244.

Figure 1. Rover on the surface of Mars.

Substantially more radioactive materialwas used for Caasini. Heat was supplied by 129RHUS, each containing 2.56 g of Pu-238, andelectrical power waa supplied by threeRadioisotope Thermoelectric Generators (RTGs),containing a total of 32,700 g of Pu-238. TheRHUS and RTGs were extremely well built,designed to withstand almost any catastrophicevent, so even in the event of an accident undermost conditions no nuclear material would be

released. In the rare cases where a release couldoccur, the total amount of released Pu-238 waspredicted to be between .56 g and 360.14 g,depending on the accident scenario.

4. ARAC SYSTEM

The ARAC mission is to provide timelyand creddbleadvisories for radiological(and other)hazardous releases to the atmosphere. Btiefly, theARAC system simulates the release of somematerial in the atmosphere and predicts itsmovement downwind. The system calculates theconsequences to health of the release, based onknown characteristicsof the material.

. ARAC has been designed to respond innear-real-time to releases anywhere worldwide.The flexible ARAC system has been used formany types of actual or exercise events (nuclearpower plants, weapons, volcanoes, missilelaunches, oil fires, and many others). For non-routine applications such as support to NASAlaunches, ARAC’S support is improved ifequipment is deployed and plans are made beforeany potential release.

The ARAC system (Sullivan et al., 1993)uses topographical and meteorological data togenerate a time-varying series of three-dimensional mass adjusted wind fields, which areused to drive the ADPIC Lagrangian particledispersion model. ADPIC is a three-dimensionalmodel which accountsfor the effects of spatial andtemporal variation of mean wind and tutt)ulence,gravitational settling, dry and wet deposition, andinitialplume buoyancy and momentum.

ARAC personnel use horizontal andvertical cross-sections through the plume alongwith other displays to study and evaluate thestructure of the plume, in order to decide whetherthe models are working optimally. Examples froma simulated release made in real time before theMars Pathfinder launch (Figs 2 and 3) showcomplicated patterns due to strong wind shearwithinthe model domain. As discussedearlier, thissimulationinvolveda very small amount of Pu-238(0.0031 g); the corresponding consequence plotswill be presented below.

The ARAC models have been extensivelyevaluated during many field tracer studies, and theresults show the system is highly accurate whenthe source term is well known and themeteorological conditions are well represented(Foster and Dickerson, 1990). ARAC’S systemallows use of multiple sources of meteorologicaldata, and ARAC used different types ofmeteorological data for Mars Pathfinder andCassini, as discussed below.

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Figure 2. Overhead view of ARAC particlepositionsfor Mars Pathfinder calculation,2 hr aftersimulated release at 0658 UTC on 4 Dec 96.Abscissa and ordinate scales are UniversalTransverse Mercator (UTM) distances, equivalentto km.

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mo m 640 800 m

Figure 3. Side views of ARAC particles for MarsPathfindercalculation, 2 hr after simulated releaseat 0656 UTC on 4 Dec 96. (lop) View from eastto west. (Bottom) View from south to north.Vertical scale is m AGL.

5. HOW ARAC PLOTS WERE USED

ARAC generated pre-launch plots for bothmissions, and was prepared to perform additionalcalculationsif there had been an actual release.

The purpose of the pre-launch plots wasto provide guidance to NASA response officialsabout where a release would go if it occurred.They u?%d this information to pre-deploy fieldmeasurement teams, who would have sampledthe air and ground to define the radioactive cloud(where did it go, when did it get there, and howmuchwas in it) had there been an a release.

If there had been an accident, ARACwould immediately have made new calculationsbased on the actual time of the accident, using ormodifying the pre-defined release scenario asappropriate. As field measurement reportsbecame available, this informationwould be inputto the ARAC models, which would be re-run withadjustments so the predictions matched themeasurements. In this way, ARAC would helpdeterminethe magnitude of the release.

6. ARAC PREPARATIONS FOR MARSPATHFINDER

For both missions, ARAC did not modelthe explosivecloud rise that would occur duringanaccident involving a rocket. Instead, ARAC usedthe results of previous NASA and DOE studieswhich predicted the configuration of the stabilizedcloud following the dissipation of the immediateheat and buoyancy effects, and the distributionofthe radioactive material in the cloud. Because thesource terms were well-specified, the primarychallenge for ARAC was to represent the complexwind patterns in the Cape area.

ARAC used two meteorological datasources for its Mars Pathfinder calculations:forecasted vertical wind profiles (which wereremarkably accurate) generated by a forecaster ofthe U.S. Air Force’s 45th Weather Squadron atCape Canaveral Air Station (CCAS), and weatherobservations from the many sensors arrayedaround the Cape (over 40 instrumented, multi-level meteorological towers, rawinsondesoundings, and a 50 MHz profiler). Theseobservations are collected automatically by theCCAS Meteorological Interactive Data DisplaySystem (MIDDS). ARAC retrieved them using adial-in modem connection and inserted them intoits operationalworldwide meteorologicaldatabase,facilitatingtheir use in its model system.

An important advance was needed inARAC’S system to use data from the multi-levelmeteorological towers at the Cape. Previously

ARAC used only the lowest level from thosereported at a tower. To use all the data availablefrom the Cape, ARAC created new algorithmswhich use data from all levels from the full verticalextent of all towers.

No ARAC personnel or equipment weredeployed to supporl the Mars Pathfinder mission.All calculationswere carried out at LLNL, and plotsshowingARAC pre-launchcalculationswere faxedto NASA response personnel at the Kennedy ,Space Center (KSC). All these calculations werebased on a single pre-defined release scenario, sothe only day-to-day changes were due to use ofcurrent meteorological data, plus smalladjustments to accommodate the launch windowsbecominga few minutesearlier each day.

7. ARAC PREPARATIONS FOR CASSINI

ARAC’S preparations for Cassini weremuch more extensive because of the potential fora larger release. Four ARAC scientistsdeployed toFlorida, along with three ARAC computer systems.All model calculationswere done at LLNL, but theon-site personnel assisted in interpretation of themodel results and acted as interfaces to the staffat LLNL, describing current conditions andchanneling requestsfor support.

As with Mars Pathfinder, ARAC used thefull set of data from the MIDDS system for Cassinisupport. In additionto the data sources which hadbeen in place during Mars Pathfinder, five new915 MHz profilers were installed prior to Cassini.Thus ARAC had access to a very rich dataset,providing excellent’ resolution in the horizontal,vertical, and time, And, as before, the 45 WSsuppliedARAC with forecasted soundings.

ARAC developed a new software packageallowing display and editing of the tower,sounding, and profilerdata retrieved from MIDDS.Using this package ARAC personnel performedquality controlof the MIDDS data before their usein the ARAC models. The MIDDS data retrievaland all communications between LLNL and thedeployed personnel and equipment were doneover dedicated communications circuits providedby DOE’s Remote Sensing Laboratory (RSL).

An important new ARAC capability forCassini was provided by implementing the NavyOperational Regional Atmospheric PredictionSystem (NORAPS). NORAPS is a prognosticmodel developed by the Navy ResearchLaboratory, which has been used operationally forseveral years at the Fleet Numerical Meteorologyand Oceanography Center and which wassupplied to ARAC through an interagency supportagreement. To use NORAPS to support Cassini,ARAC accelerated the work needed to bring

NORAPS into an operational state at LLNL.NORAPS runs provided high-resolution, time-varying meteorologicaldata for the ARAC modelsdescribedabove.

ARAC therefore had access to four typesof meteorological data: forecasted soundings;MIDDS reports of local sensors; NORAPS outputand sutface and upper air observations from theregion, which ARAC collects routinelyfrom the AkForce ~lobal Weather Center. ARAC hasautomated procedures to retrieve, store, and useeach of these types, and can run its models withthese sources individuallyor in any mmbination.

Except for changes to accommodate thenew meteorological data sources, ARAC used itsexisting, well-tested, validated models to supportCassini. As with Mars Pathfinder, all ARACcalculations were based on pre-defined releasescenarios. However for Cassini ARAC modeledthree separate release scenarios, representingaccidents before the launch, during the first 5 secafter ignition,and from 5 to 143 sec after ignition.

5(IYR CEDE via Inhalation

8. ARAC PRODUCTS

The ARAC products for Mars Pathfinderpre-launch supporl were 50-Year CommittedEffected Dose Equivalent (CEDE), Total GroundDeposition, and Instantaneous Air Concentrationplots, all valid at 30 min intervalsout to 4 hr after asimulated release during each day’s launchwindow. The reason for generating plots valid atthese intewals was to illustratethe evolutionof therelease, allowing better response by emergencyresponders. However, this meant that more plotswere sent than were needed for pre-launchSUf)POrt tasks.

For Mars Pathfinder, ARAC generatedplots 24 hr, 3 hr, and 30 min before the launchwindow. Examples of these plots are at Figs 4 and5, showing the CEDE and deposition plots valid 4hr after a simulated release at the time of thelaunch. The predicted activity levels are extremely/ow. On the CEDE plot, the area extending southfrom the Cape shows areas with dose levelsbetween 0.1 and 1.0 mRem in 50 years. Forcomparison, normal background radiation fromterrestrial sources and cosmic rays is about 30-100 mRem per year. The deposition plot showsvalues about an order of magnitude smaller thanthe existingworldwidePu-238 depositionlevels.

For Cassini, ARAC also generated plots24 hr, 3 hr, and 30 min before the launch window.ARAC modeled each of the three releasescenarios at each product generation time, andsent the CEDE and deposition plots for eachscenario to NASA using a GeographicalInformationSystem operated by RSL.

Figure 4. Cumulative Effective Dose Equivalentplot valid 4 hr after simulated Mars Pathfinderrelease at 0658 UTC on 4 Dec 96. Values arewell below background.

TotalDepositkm

Figure 5. Ground Deposition plot valid 4 hr aftersimulated Mars Pathfinder release at 0658 UTCon 4 Dec 96. Values are well below background.