48th International Conference on Environmental Systems ICES-2018-214 8-12 July 2018, Albuquerque, New Mexico Inter-Module Ventilation Changes to the International Space Station Vehicle to Support the Bigelow Expandable Activity Module

1 Kevin M. Braman0F The Boeing Company, Houston, Texas

The Bigelow Expandable Activity Module (BEAM) was berthed to the International Space Station (ISS) as part of a two year study on the feasibility of expandable volumes for habitability. The BEAM is not outfitted with heaters for thermal control of the wall surfaces. To ensure that the module remains above the station dew point Environmental Control and Life Support System (ECLSS) Inter-module Ventilation (IMV) must be maintained between the Node 3 volume and the BEAM. This paper will describe the details, challenges, and modifications to the ECLSS on ISS and their interaction with BEAM.

Nomenclature: CDRA = Carbon Dioxide Removal Assembly cfm = Cubic Feet per Minute ECLSS = Environmental Control and Life Support System ESA = European Space Agency FOD = Foreign Object Debris FIT = Failure Investigation Team HEPA = High Efficiency Particulate Air IMV = Inter Module Ventilation ISS = International Space Station JEM = Japanese Experiment Module MER = Mission Evaluation Room NPRV = Negative Pressure Relief Valve RMO = Remote Manual Override THC = Temperature and Humidity Control USOS = United States On-Orbit Segment

I. Introduction

An agreement between the National Aeronautics and Space Administration (NASA) and Bigelow Aerospace allowed for the berthing of an expandable module to the ISS. This paper describes the modifications to the ISS ventilation system that were required for the proper operation of the BEAM once installed. The paper does not cover the specifics of the inflation of the BEAM.

1 Environmental Control and Life Support System Engineer, The Boeing Company, [email protected] ICES-2018-214

II. Overview of System The USOS comprises seven main modules: Node 1, Node 2, Node 3, Airlock, US Lab, Columbus, and JEM. The modules mix atmosphere through fan-driven IMV with paths through both ducting and open hatchways. The ISS Program determined that the BEAM would be installed at the Aft berthing port of the Node 3 module (as shown schematically in Figure 1), which had been unused since Node 3 arrived to the ISS in 2010. The Aft ventilation is designed for an IMV Fan to push air into an attached module from the Aft-Port side of the bulkhead. The return air would travel either through an open hatch or through the Aft-Starboard bulkhead IMV ducting that is routed to the HEPA Plenum in the deck midbay of Node 3 and is subsequently filtered before returning to the Node 3 volume. The Node 3 Cabin Fan that provides ventilation for the Node 3 Module and pulls air through the HEPA Plenum does not provide a negative pressure head for the air returning from the Node 3 Aft-Starboard IMV ducting (i.e., from the BEAM).

Figure 1 Node 3 to BEAM IMV Functional Schematic

The concept of operations for the BEAM, unlike most modules on the ISS, is to remain with the hatch closed when the crew is not actively performing operations in the BEAM. One of the main reasons for this operational decision is because the BEAM hatch is designed to be a cover plate held in place by four bolts nominally, and when opened the hatch is a free-floating part. Thus, to close the BEAM hatch during an emergency would require significantly more time than the standard ISS hatch (which rides on a wheel-and-track system and closes quickly). Consequently, BEAM ventilation is generally provided through the IMV ducting for both supply and return air. For thermal control, ISS modules have shell-heaters that prevent the wall temperatures from dropping below the dew point of the Station atmosphere, thereby precluding condensation on the shell. The design of the BEAM did not allow for wall-heaters, and therefore the thermal control is dependent on the air flow over the interior surfaces. Due to this constraint, the air flow provides a critical function for the BEAM, as discussed later in this paper.

III. Integration of IMV Valves

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When Node 3 was being prepared for flight, the Aft hatch was outfitted with IMV Valves designed and built by Carleton Technologies Inc. During ground testing it was discovered that the Carleton Valves did not properly communicate with ISS computers. All previous modules had been outfitted with Honeywell built IMV valves and did not have similar communication issues. Since there were no plans to have a berthed module or visiting vehicle at Node 3 Aft at the time of launch, the decision was made to replace the IMV valves with Negative Pressure Relief Valves (NPRV) for the Aft Port and Starboard bulkhead feed-through connections. Following the discovery of communication issues with the Carleton IMV Valves an investigation was performed and it was discovered that a change to the valve electronic board would correct the issue. Modification kits were created for the fleet of ten Carleton (now known as Cobham) IMV Valves that corrected the issue and allowed for the valves to be used on-orbit. Two Cobham IMV Valves were outfitted with a modification kit, each for use at the Node 3 Aft location. When the IMV Valve needs to be operated manually, this is done using a Remote Manual Override (RMO). The initial build of the Node 3 module included RMO (Figure 2) installation for the Aft Port and Starboard locations. When the IMV Valves were discovered to be faulty and removed, they were disconnected from their associated RMOs, and the RMOs remained installed. Therefore, when the IMV Valves were flown to the Station there were already RMOs installed and available to be connected to the IMV Valves.

Figure 2 Honeywell IMV Valve and RMO Package

Installation of the IMV Valves was completed once the BEAM arrived, and the valves were checked for both commanded closing and opening along with manual operation with the RMO. One

3 International Conference on Environmental Systems ICES-2018-214 issue was discovered during the installation of the Aft Starboard IMV Valve: the flexible coupler was missing, which was expected to be installed to the ducting that meets up with the valve. Since IMV air flow with the hatch closed is a critical function for the BEAM Module, the ground team and the crew had to produce a makeshift coupler. The following section describes in detail the issue and the subsequent solution that the crew implemented.

IV. Aft Starboard IMV Coupler When it was discovered that the flexible coupler intended to make the connection between the Node 3 ducting and the newly installed IMV Valve was missing, a quick solution was required. There are spare flexible couplers aboard the ISS, but all of the couplers are for round-to-round connections that are aligned axially. The Node 3 Aft Starboard IMV ducting ends in an oblong shape, and the center of the duct is offset from the center of the circular IMV opening, thereby creating the need for a unique coupler design. During ground outfitting it was realized that the coupler initially designed and installed in Node 3 was found to be approximately 1 inch short, so it was removed. There was a non- conformance written and the as-delivered drawing was updated to reflect the absence of the coupler. Since there were no plans at the time of Node 3 delivery to support a module or vehicle at Node 3 Aft, much like the IMV Valve, there was no need for the coupler so the module was flown without a coupler. The ground team immediately investigated possible solutions so that IMV could be activated as soon as BEAM was ready for ingress. Following a Failure Investigation Team (FIT) meeting in the Mission Evaluation Room (MER) it was determined that a Kynar bag (a durable plastic material) could be used with the existing band clamps (intended to hold the flexible coupler in place),using kapton tape for additional stability. The crew was instructed to cut the bottom of a Kynar bag open and use the bag to complete the connection between the IMV valve and the ducting, as shown in Figure 3. Since this connection is not directly upstream from an IMV or Cabin Fan, the risk of a pressure differential causing a collapse of the coupler is greatly reduced and the coupler is expected to maintain a good IMV flow path. The crew has been asked to inspect the Kynar bag whenever they ingress the BEAM, and since the installation of the bag in May 2016, it has maintained its integrity. As of December, 2017, Thales Alenia Space Italia (TASI) was working towards launching a replacement coupler because the ISS Program has

4 International Conference on Environmental Systems ICES-2018-214 decided to keep the BEAM integrated with ISS and to use it for storage space. Since the mission length is now open-ended, a more permanent coupler is desired.

Figure 3 Kynar Bag Installed as IMV Sleeve Node 3 Aft Stbd

V. IMV Fan Each inactive IMV Fan on the ISS requires a periodic maintenance of operating for at least two hours every five years of being on-orbit, in order to maintain an even distribution of grease lubricant around the bearings. The fan installed at Node 3 Aft Port had never been operated since Node 3 arrived to the station in 2010, so in 2015 a Mission Action Request (chit) was written to operate the fan. Prior to operation, the crew had to remove the beta-cloth cover from the end of the ducting (that the beta-cloth was in place to prevent foreign objects from inadvertently entering the ducting) so the cloth would not get blown off to an unknown location behind the panels. Then the fan was operated for two hours while the crew confirmed that there was no off-nominal noise. Consequently, when the BEAM arrived in May of 2016, the IMV Fan was well within the periodic maintenance period and ready to operate continuously to provide ventilation to the BEAM to provide thermal conditioning for the walls.

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VI. Thermal Conditioning of BEAM Walls Using IMV Since the temperature of the walls of the BEAM is not controlled with heaters, convective heat transfer from ventilation is required to maintain the wall temperature above the station dew point. Per the Station specifications the ISS temperature is controlled between 65 – 80°F, and the dew point is maintained between 40 – 60°F. The Bigelow and NASA Thermal Analysis teams determined that with a nominal cabin temperature ≥65°F, and a nominal IMV flow of 12 cubic feet per minute (cfm), the BEAM wall temperatures will be maintained above 53°F, which is the highest dew point expected on the Station in the current configuration. The analysis further determined that the IMV flow could bias low as 90 cfm before the wall temperatures would drop below 53°F and risk condensate forming on the walls. Due to the critical nature of the IMV flow to the thermal control of BEAM, the Flight Rules were updated to require more frequent air velocity readings using the on-board Velocicalc meter and probe at the IMV inlet to the BEAM (i.e. every 90 days instead of the regular interval of 120 days). Due to the location of a strut over the inlet grille in Node 3 that leads to BEAM, the velocity readings cannot be taken with the measurement aide that allows for a single reading; rather twelve readings must be taken, as shown in Figure 4 (i.e. one measurement at each of the square openings in the inlet grille). The average of the twelve readings is used to determine the flow rate to the BEAM.

Figure 4 Velocity Reading Patern at Node 3 Aft Port

A computational fluid dynamics (CFD) analysis was used to determine that the direction of the air flow required to thermally condition the walls and the aft bulkhead. The details of that analysis will not be discussed in this paper. It should be noted that the simple straight IMV duct and the fact that the Node Aft Port IMV Fan does not have a silencer on the outlet side allows for the IMV flow to generally be greater than 120 cfm. Due to the conversion of the BEAM volume to be used for stowage, the IMV ducting had to be extended in November, 2017. This update did not significantly change the pressure loss, and the IMV flow remains above 120 cfm with a clean system.

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An IMV measurement of 66 cfm was obtained on August 24th, 2016. This was the first reading that was below the cleaning threshold of 90 cfm. Even though the IMV inlet screen is vacuumed by the crew during the weekly housekeeping, Foreign Object Debris (FOD) slowly builds up on the IMV Fan inlet flow-straightener and occludes the flow. When this happens the crew is instructed to open the IMV ducting at the fan inlet and vacuum off the flow-straightener to restore full flow. This clogging of fan inlets is a common occurrence on the ISS, and the cleaning procedure is performed as required. In September, 2017, the crew performed the standard velocity readings and found the IMV to have dropped to 45 cfm. The Node 3 Aft Port IMV Fan was inspected (see Figure 5) and cleaned by the crew, and the flow was restored to 143 CFM. Based on the analysis that led to the flight rule limiting the low flow rate to 90 cfm, there was concern that the BEAM wall temperatures may have decreased below the Station dew point. The BEAM contains temperature sensors whose data can be sent to the ground for processing. Following the low IMV reading and the subsequent fan cleaning this temperature data was evaluated. It was found that the lowest temperature during the reduced-IMV period was 59.5°F, and was recorded while the ISS was maneuvered for a Soyuz docking. Aside from the off-nominal orientation for docking operations, the temperatures recorded in the BEAM were above 64°F. Thus, even with half of the IMV flow, the wall temperatures in the BEAM remained above the station dew point. This data may lead to future adjustments to the minimum allowable IMV flow rate to BEAM, or an extension in the time allowed between IMV readings. Since the temperature data from the BEAM is not continuously monitored, and there are no operational constraints for ISS orientation, the initial conservative assumptions that lead to limiting the low flow rate to 90 cfm will remain for the time being.

Figure 5 IMV Fan Inlet at Node 3 Aft Port Occluded with Debris

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VII. Conclusion The changes to the ventilation system to support the BEAM have been completed and currently operate as expected. The changes to the ISS described in this paper include operating an IMV Fan which would otherwise be inactive, installing two Cobham IMV Valves, and adding a temporary IMV sleeve in the form of a Kynar bag. The ISS Vehicle Management has agreed to keep the BEAM longer than the 2 year test time, and utilize the volume for on-orbit stowage. The interior of the BEAM has already been outfitted with stowage bags, and spare hardware is being allocated for stowage within the BEAM. Due to the more permanent nature of the BEAM, the temporary Kynar bag IMV sleeve will be replaced with a standard rubber sleeve that TASI will manifest. Also, the thermal data and IMV velocity data will continue to be monitored and evaluated for possible relaxation of the measurement schedule, in the hopes of aligning the readings with the rest of the station readings. As the ISS continues to host payloads and next-generation exploration technologies, the ECLSS will continue to be modified to meet the needs as they arise. The ability to provide ventilation and heat rejection will be at the forefront of ISS utilization, as demonstrated in these BEAM activities.

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