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ESA’s contributions to the ISS. MPLM is highlighted in pink; the other ESA-provided items for Partner elements are in light blue. Right: MPLM remains berthed only while the Space Shuttle is docked to the Space Station – the spaceplane is omitted here for clarity.(ESA/Alenia Aerospazio)
Environmental Control & Life Support forthe Multi-Purpose Logistics Module
D. Laurini & A. ThirkettleESA Directorate of Manned Spaceflight & Microgravity, ESTEC, Noordwijk, The Netherlands
K. BockstahlerDaimlerChrysler Aerospace AG/Dornier, Friedrichshafen, Germany
IntroductionAssembly of the 470-tonne ISS began at theend of 1998 with the mating of the first twomodules in orbit. Although assembly will not becompleted until 2004, productive work aboardthis outpost will begin in early 2000. This will require a regular flow of equipment,materials and consumables delivered by arange of vehicles. Other items, such as theresults of experiments, will need to be returnedto Earth.
the MPLM prime contractor, Alenia Aerospazio,with the ECLS Subsystem for the three MPLMFlight Models. The estimated saving to eachprogramme is more than 25 million Euros.
The ECLS Subsystem was designed to satisfyboth MPLM and Columbus. The contract wasawarded by ESA in early 1996 to DornierSatellitensysteme of DASA, and the deliveriesof all MPLM ECLS engineering models,associated Ground Support Equipment and thethree Flight Model sets, with minor exceptions,were completed in 1998. The Columbus ECLSdeliveries are planned for 1999.
MPLM ECLS SubsystemMPLM is a unique part of the overall ISSlogistics scenario: it is the only logistics modulecapable of transferring complete InternationalStandard Payload Racks (ISPRs) to and fromthe ISS. The module will be berthed at Node-2(Node-1 on its debut mission in mid-2000)using the Station or Shuttle robot arm.
Equipment will be transferred by Station and/orShuttle crew members, and this is where ESA’scontribution to MPLM is critically important.The Agency-supplied ECLS Subsystem willmaintain comfortable conditions for threeastronauts to work in the modulesimultaneously for the projected MPLM missionlength of two weeks. Drawing on Stationresources, the ECLS controls the module’sinternal environment to provide a safe, sea-level‘shirtsleeve’ environment.
In particular, it must provide: temperature andhumidity control; atmosphere pressure control;fire detection and suppression; contaminationmonitoring and control.
Temperature and Humidity ControlThe ECLS Subsystem collects fresh air from
ESA has provided the Environmental Control and Life Support (ECLS)Subsystem for Italy’s Multi-Purpose Logistics Module (MPLM)contribution to the International Space Station (ISS). In exchange, theItalian Space Agency (ASI) is providing a derivative of the MPLMprimary structure for ESA’s Columbus ISS laboratory module.Considerable savings have been achieved by the development andqualification of common hardware – more than 25 million Euros foreach project. MPLM’s ECLS Subsystem is described here, withemphasis on its similarity to the version used by Columbus.
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Europe is providing two crucial elements of thisferry network. ESA’s Automated TransferVehicle (ATV) and its mixed cargo will belaunched on Europe’s large Ariane-5 rocket.Italy is separately contributing the Multi-Purpose Logistics Module (MPLM) to becarried in the Space Shuttle’s payload bay.
In late 1995, ESA’s Council authorised the‘Arrangement Between the European SpaceAgency and the Italian Space Agency on theExploitation of Common Features of thePressurised Modules Developed by theParties’. The goal was to avoid the duplicationof development efforts by sharing commonfeatures on ESA’s Columbus laboratory andASI’s MPLM. This led to ASI providing ESA andthe Columbus prime contractor, DASA, with aderivative of the MPLM primary structure forColumbus. In exchange, ESA provided ASI and
This article is abbreviatedfrom the ESA brochureBR-143 ‘Supporting Life:Environmental Control andLife Support for the Multi-Purpose Logistics Module ofthe International SpaceStation’. An electronic versionwill be posted athttp://esapub.esrin.esa.it/
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The layout of MPLM’s environmental control and life support subsystem (Dornier)
The ECLS is seen here partially installed inside the MPLMEngineering Qualification Model. The white box at right is the cabinfan assembly. Although the ducting is not connected, air is fed intothe module by the lines of silver diffusers at top, and taken outthrough the grids at bottom (Alenia Aerospazio)
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Most of the ECLShardware is housed inMPLM’s forward endcone (Dornier)
The first MPLM Flight Model (‘Leonardo’) in Alenia Aerospazio’s cleanroom in Turin.Air is drawn into the module through the IMV port to the left of the hatch; if the hatchis closed, it exits via the port to the right. The holes in the upper conical area are forhousing different valves
The cabin fan assemblyundergoing a random
vibration test during itsqualification phase
the Station/MPLM Inter Module Ventilation(IMV) Interface, distributes it throughout thecabin and then returns it to the ISS forrevitalisation. The air enters through a port tothe right of the hatch in the forward end cone,and normally exits via the open hatch.
Ventilation is provided throughout the habitablevolume to prevent dangerous pockets of staleair, and the temperature is monitored. Thehumidity and temperature are controlled fromthe Station Node.
The required airflow of 468 m3/h is provided bya single fan assembly in the forward end cone.The air is distributed by ducting and diffusers intwo branches along the upper cabin – fourdiffusers on each side. Each diffuser emitsabout 51 m3/h to produce the required cabinair movement. A further 30 m3/h is routed fromeach branch along the roof into the aft cone.Restrictor grids in the diffusers and restrictors inthe outlets to the aft cone adjust the flows.
The air is sucked from the module via returngrids in the lower stand-offs. The two branchesare mixed in a junction duct and led back to thefan inlet, where the Station supply is added. Arestrictor in the return duct ensures thepressure is lower than at the IMV supplyinterface, so air continues to be sucked fromthe Station.
Normally, air flows back to the Station throughthe open hatch. If the hatch is closed, the airtravels through the separate dedicated IMVreturn duct. To isolate the module from theStation, a motorised valve in each of the IMVsupply and return ducts closes off the airflow.
MPLM’s cabin air is also monitored by atemperature sensor.
Cabin Ventilation TestA cabin ventilation qualification test wasperformed using a full-scale cabin simulator/mock-up. The two photographs show the testarticle with equipment installed for air speed
and temperature measurements. The testverified that the cabin comfort requirementshave been achieved: air speed is 0.076-0.203 m/s within at least 67% of the habitablevolume, except near the diffuser outlets. Theoptimum airflow for injection through each ofthe eight cabin air inlet diffusers was found tobe 51 m3/h.
Atmosphere Pressure ControlThe total atmospheric pressure is monitored,and MPLM’s data management systemtransmits an emergency signal to the ISS ifMPLM’s air pressure strays beyond pre-setlimits. Pressure valves protect the module’sstructural integrity and support firesuppression.
Positive Pressure Relief Assembly (PPRA)MPLM’s structure is designed to handle apressure differential of 1.034 Earth-atmospheres (1048 hPa). To prevent it fromreaching this level, the valve in the PPRA opensand vents air from the cabin when the pressuredifferential rises to 1.014 atm (1027 hPa). This‘crack pressure’ can be reached when theMPLM is isolated, for example, inside theShuttle during launch, when the internaltemperature might increase becauseequipment is powered up without activecooling.
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A cabin ventilationqualification test on a full-
scale cabin mockup atDornier showed that the
required air speed of0.076-0.203 m/s in at least
67% of the habitablevolume had been achieved
The Positive PressureRelief Assembly bleeds offair if the pressure climbstoo high. The unit mountedinside MPLM is at left. Thevalve can be closedmanually by the handle atleft or by the remotely-controlled electric motor atright. The unit mountedoutside MPLM is at right
Total Pressure MonitorMPLM is equipped with three redundantpressure sensors for monitoring the module’sinternal air pressure. They are designed for anabsolute pressure measurement range of0.0010–1.0856 atm (1–1100 hPa) with anaccuracy of about 0.0158 atm (16 hPa).
The sensor uses a diaphragm that deflects inproportion to the applied pressure. Thisdeflection is coupled to a resistive strain gaugebridge circuit, which sends a signal to theMPLM data management system fortranslation into a pressure reading.
Fire Detection and SuppressionThe prospect of fire breaking out in the moduleis reduced by careful selection of non-flammable materials and by controllingpotential ignition sources. The next level ofprotection and fire localisation is achieved bynormal housekeeping monitoring of poweredequipment to detect anomalies in temperatures,voltages and currents, for example, that couldtrigger a fire. If an anomaly is found, theaffected equipment is switched off andredundant equipment is activated. Also, airflowin areas housing powered equipment would behalted by turning off the fan, specifically toavoid feeding any fire with oxygen. The fan canbe switched on/off by the crew from any otherISS module or by ground controllers.
There is a portable extinguisher for the crew tofight fires in the forward end cone where mostof MPLM’s powered equipment is located. Thatarea is divided into three compartments, so that
The assembly provides ‘two-failure tolerance’by using three valves in parallel, any one ofwhich can do the job. Two are housed in afeed-through plate in the upper area of theforward cone; the third is mounted directly inthe cone’s lower area.
Each assembly comprises a power-independentpneumatic pressure relief valve and a butterflyshut-off valve, installed in series. The shut-offvalve can be closed electrically by a brush-type28 V DC motor or by manual override; thisisolates the assembly in case the pneumaticrelief valve or motor fail.
Ground controllers or Space Station crews canuse the electric motors to deactivate thesystem when it is not required. For example,when MPLM is docked with its hatch open andthe Station is providing overall pressure control.
Negative Pressure Relief Assembly (NPRA)MPLM’s internal pressure might fall belowexternal pressure during ground operations,launch abort or nominal reentry. This negativedifferential is prevented from reaching thestructure’s design level of 0.0336 atm (34 hPa)by the NPRA.
This NPRA consists of a set of pneumatic,power-independent valves. As this capability isneeded mainly during launch and reentry –when MPLM is unmanned – manual override isunnecessary. Three of these valves aremounted directly in the forward cone’s lowerarea; two are positioned in the aft conebulkhead.
The redundant cover on each is one-failuretolerant against leakage to space duringnominal on-orbit mission phases, when thepneumatic portion of the valve is not needed.This phase can last up to 15 years for theColumbus module.
Cabin Depressurisation Assembly (CDA)The CDA can vent the cabin air to space in lessthan 10 minutes as an integral element of theMPLM/ISS/Columbus fire suppression scheme.It consists of two separate units on the samefeed-through plate as the two PPRAs inMPLM’s forward cone upper area. Each isequipped with two butterfly shut-off valves,arranged in series so that the failure of one valve does not cause unexpecteddepressurisation or prevent closure afterintentional venting. A 28 V DC brush motoroperates each valve on command from the ISSdata management system via MPLM’s datamanagement system. Manual override isunnecessary because they would be activatedonly when the module is unmanned.
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A single Duct SmokeDetector (DSD) on a cabin
air duct alerts the MPLMdata management system if
it detects smoke
the carbon dioxide from a single extinguisherwould reduce the oxygen concentration in anyone below the minimum (10.5% by volume)necessary for sustaining a fire.
As a last resort, the hatch would be closed toisolate the module before the cabin air isdumped via the CDA.
Fire Suppression TestsFull-scale mock-ups of the three forward conecompartments, where most MPLM poweredequipment is located, were built to verify that afire can be suppressed with a Station portablefire extinguisher. During early fire suppressiondevelopment tests, the importance of leakagebetween the module shell and compartmentclose-out panels was identified. Great care wastherefore taken in simulating those leakageareas.
The qualification tests were performed with themock-ups in two orientations in order toeliminate the influence of gravity. It was shownthat the fire could be suppressed in two sidecompartments, but leakage was too high in thethird compartment, in the lower part of theforward cone, to achieve the low oxygen level.The sealing was improved and the qualificationtest for that compartment was successfullyrepeated.
Cabin Air Contamination Monitoring andControlThe cabin air’s major constituents and tracegas contamination are measured by theStation’s ECLS equipment. Samples of thecabin return air are periodically drawn into theStation via a dedicated tube.
The sampling line consists of a 1/4-inch(0.635 mm) diameter tube connected at oneend to the cabin air return duct upstream of thecabin fan, and at the other end to the forwardcone bulkhead. At the cabin end, a particle filter(mesh size 2 µm) screens out debris. A LineShut-Off Valve (LSOV) isolates the line from theStation. It is normally operated electrically by a28 V brush-type motor, but it is equipped witha manual override in case of motor failure.
Sharing with ColumbusESA developed the common ECLS under itsMPLM activities and procured the equipmentneeded for Columbus at recurring cost. Thedesign drivers of both projects were combined:each MPLM is designed for 25 flights, andreplaceable items on Columbus are designedfor 10 years on-orbit.
Existing Space Station hardware – such as theDuct Smoke Detector – was incorporatedwhere feasible. In other cases (CDA, NPRA,PPRA), designs used in NASA’s Space ShuttleOrbiter and ESA’s Spacelab were substantiallyimproved to meet the more stringentrequirements of the MPLM and Columbusprogrammes.
The Table summarises the hardware used inMPLM’s ECLS Subsystem and its commonalitywith Columbus and the ISS. It is clear thatcommon hardware has been used in mostitems.
Identical components used in both prog-rammes are the cabin air diffuser, cabin airtemperature sensor, IMV Shut-Off Valve, LineShut-Off Valve, NPRA, CDA and PPRA.
The Duct Smoke Detector was developed forthe ISS and is adopted by MPLM andColumbus not only to re-use existing hardware,but also to create similar alarm thresholdconditions over the whole station complex. ForMPLM, the detector was subjected to furtherqualification to cover the additional demandsimposed by repeated launches on the 25missions. All the others on the Station,including Columbus, are launched only onceand checked periodically on-orbit using theirinbuilt sensors. They can be replaced by thecrew if necessary.
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In exchange for the development of MPLM’sECLS Subsystem, the Columbus flight unit primary structure – directly derived fromMPLM’s design – is currently beingmanufactured under ASI’s responsibility. As therequirements for the two modules are sosimilar, the Columbus structure needs nodedicated qualification testing.
Considerable savings for both projects havebeen achieved by single development andqualification of common hardware – asignificant contribution to improving the afford-ability of manned space programmes. r
Identical cabin loop ducting is not feasiblebecause the modules have different internallayouts. However, the material and constructionof the single ducts and their incorporatedfeatures (such as mufflers) are similar and theexperience from the MPLM developmentefforts is directly applicable to Columbus.Common parts such as the flexible bellows forduct connection are also incorporated.
A common fan was not adopted because ofdifferent schedule, mass, volume, noise andoperational requirements. An existing ISS fanwas used for MPLM, already qualified within theStation programme, but subjected to furthertesting to cover the 25 MPLM missions. Inaddition, since the MPLM fan launch vibrationloads are higher than for the ISS, a fan dampingsystem was developed. For Columbus, a newEuropean fan is being developed.
ConclusionThe ECLS Subsystem for MPLM has beensuccessfully developed, and the hardware forthree module flight units delivered to ASI. Thiseffort forms part of the cooperation betweenESA and ASI aimed at improving the overallefficiency of industrial development for Europe’scontribution to the International Space Station.
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MPLM ECLS Hardware Commonality with Columbus and International Space Station
MPLM/ MPLM/ MPLM/Columbus ISS Columbus MPLM
Hardware Item Common Common Similar Dedicated Remarks
Cabin Fan Assembly/ X FDS not needed onFan Damping System X Columbus
Cabin Loop Ducting X
Cabin Air Diffuser X
Cabin Temperature Sensor X
IMV Shut-off Valve X
Negative Pressure XRelief Valve
Positive Pressure XRelief Valve
Cabin Depressurisation XAssembly
Total Pressure Sensor X Different Columbus andMPLM electrical interfaces
Sampling line X Line routing adapted tomodule; common samplefilter
Line Shut-off Valve X
Duct Smoke Detector X X ISS common item used onMPLM and Columbus
