International Resupply Vehicles Impact ISS On-Orbit Stowage

by Pete Harding

The recent flurry of Visiting Vehicle (VV) activity at the International Space Station (ISS) has created a logistics challenge for ISS managers, who are tasked with meticulously choreographing where and when the new cargo will be stowed aboard the ISS.

Current ISS Stowage Overview:

An ISS Stowage Status document, available to download in full on L2, outlines the current stowage situation on ISS, showing just how packed the orbital outpost currently is.

According to the document, Node 3’s Overhead, Forward and Aft hatch areas are filled with cargo, and the Port endcone area contains “smelly trash”.

There are no stowage racks available in Node 3, while Node 1’s four stowage racks are volumetrically full, with the Overhead hatch area being used for food, and the Deck hatch area being used for overflow cargo destined for the Permanent Multipurpose Module (PMM).

The Airlock’s (A/L’s) stowage bags and corridor space is filled by Extravehicular Activity (EVA) gear.

In the US Lab, all stowage racks are volumetrically full, with the rest of the space being taken up by science payload hardware. The two stowage areas in Node 2’s DC to DC Conversion Unit (DDCU) racks are volumetrically full. Node 2’s Overhead and Deck hatch areas, usually reserved for stowage, are currently clear due to HTV-2 operations.

The cargo from these two areas is being stored in Node 2’s Forward endcone. The Forward endcone will need to be cleared of cargo prior to the arrival of STS-133 on 26th February, as the stowage will block access to Node 2’s Forward hatch, which leads to Pressurised Mating Adapter-2 (PMA-2), to which the Shuttle docks.

All stowage racks in the Columbus Orbiting Laboratory (COL) are volumetrically full, as is the Starboard endcone. All rack stowage is taken up by European Space Agency (ESA) cargo, apart from the Zero-G Stowage Rack (ZSR) rack fronts, which are currently clear. 

Also, all US stowage racks in the Japanese Pressurised Module (JPM) are volumetrically full, as are the Japan Aerospace Exploration Agency (JAXA) stowage racks. The NASA ZSR rack fronts are currently clear. The Japanese Logistics Platform’s (JLP’s) four US ZSRs are volumetrically full, although some stowage space exists on the rack fronts.

This stowage backlog is partly being caused by the delay of the PMM, which was originally scheduled to arrive at the ISS in November last year, before being delayed to December, and then February. The need for the PMM is clearly shown in the Stowage Status document, especially due the high volume of VVs arriving at the ISS over the next month.

Visiting Vehicles:

Kicking off the busy period of VV activity was the arrival of Japan’s H-II Transfer Vehicle-2 (HTV-2) on 27th January.

HTV-2 carried 6,000 kg of cargo to the ISS, which includes two brand new science racks, the Gradient Heating Furnace (GHF) “Kobairo” and the Multipurpose Small Payload Rack (MSPR). Both GHF and MSPR were transferred to the ISS last week, and were installed in JPM rack bays Forward 3 and Aft 4 respectively.

Also aboard HTV-2 is a large quantity of Cargo Transfer Bags (CTBs), some stowed in the six HTV Resupply Racks (HRRs), and some stowed in specially modified stand-offs that usually contain lighting and ventilation systems.

Hot on the heels of HTV-2 was Russia’s Progress M-09M/41P, which successfully docked to the ISS at the Docking Compartment-1 (DC-1) Nadir port on 30th January. 41P carried 2,500 kg of cargo to the ISS, which included 20 CTB Equivalents (CTBEs) of NASA cargo, which is planned to take 20 crew hours to unload and stow. Unlike HTV-2, 41P’s cargo is not dependent upon the PMM.

Europe’s Automated Transfer Vehicle-2 (ATV-2) is currently scheduled to launch on 15th February and dock to the ISS on 23rd February, delivering around 7,500 kg of supplies to the ISS. ATV-2 will carry 80 CTBEs of NASA cargo and 20 CTBEs of ESA cargo.

However, due to the large volume of cargo already created by HTV-2 and 40P, ATV-2’s cargo will not be unloaded until Expedition 27 begins on 16th March. This is because ATV-2’s cargo is dependent upon the PMM, which should be available to stow ATV-2 cargo by the time Expedition 27 begins.

PMM – a dedicated stowage room for ISS:

The PMM is scheduled to be delivered to the ISS aboard Space Shuttle Discovery during the STS-133/ULF-5 mission in February. Discovery is currently scheduled to launch on 24th February, one day after the ATV-2 docking. Following Discovery’s docking to the ISS on 26th February, the PMM will be installed onto the ISS, which will greatly enhance the ISS’s stowage capability by providing a dedicated volume for cargo.

The PMM’s stowage layout during on-orbit operations will change considerably from its cargo layout during launch.

For launch, the PMM will carry seventeen racks in total, consisting of six Resupply Stowage Platforms (RSPs), five Resupply Stowage Racks (RSRs), three flat-packed Zero-G Stowage Racks (ZSRs), two Integrated Stowage Platforms (ISPs), and ExPrESS Rack-8 (ER-8). Robonaut 2 (R2), nestled inside its Structural Launch Enclosure to Effectively Protect Robonaut (SLEEPR), will be carried in the Aft 4 (Aft side of PMM, rack bay number 4) RSP.

Following the PMM’s berthing to the ISS and ingress, a fast-paced set of operations will begin to quickly reconfigure the PMM for on-orbit operations. The reconfiguration operations will consume 300 hours of crew time. The fast pace of the operations is required in order to gain the maximum amount of down-mass from HTV-2 before it departs the station.

Firstly, the ZSR currently located at the Lab Port 1 location will be moved to PMM Port 1. R2 will then be unpacked and stowed in the open rack bay at Lab Port 1. The flat-packed ZSR at PMM Starboard 3 will be moved to PMM Port 2 and its tent-like structure will be assembled. ER-8 will then be transferred from PMM Starboard 2 to Lab Port 4.

The flat-packed ZSR at PMM Starboard 4 will be moved to PMM Starboard 3 and assembled, while a ZSR will also be moved from PMM Starboard 1 to Columbus Forward 2 and assembled.

The six RSPs and two ISPs contained in the PMM will not be needed on-orbit, as their only purpose is to hold large cargo items in place during launch and entry. As these unneeded racks will take up valuable space inside the PMM, there is a strong desire to dispose of as many as possible, in order to free up space in the PMM for stowage.

Trash Disposal:

HTV-2 is currently scheduled to depart from the ISS on March 28th, roughly one month after the PMM’s arrival.

Given the fact that HTV-2 delivered two new racks to the ISS that were transferred into the JPM, HTV-2 will have two free rack bays for its departure (the Aft 1 and Forward 1 locations).

Documentation shows NASA has reached an agreement with JAXA that these two rack bays will accommodate two RSPs from the PMM, while each RSP will be loaded with cargo for disposal. Two ISPs from the PMM will also be disposed of on HTV-2, with each ISP strapped to the front of an HTV Resupply Rack (HRR) at the Starboard 1 and Port 2 locations.

The six remaining HRRs in HTV-2, as well as HTV-2’s stand-off containers, will also be packed with trash cargo.

It has also been noted that NASA will trash the “clamshells” (structural enclosures used to protect hardware during launch) for the following PMM-launched hardware: the Pump Package Assembly, Inlet ORU, Water Tank, Waste Water Tank, and R2’s empty SLEEPR.

According to another L2 document, other cargo NASA is planning to trash on HTV-2 includes: “6 large foam boxes inside the RSP locations, 4 M-01 bags worth of RFTA foam, 6 CTBEs of ISP launch foam, RSP filler foam, 2 large JAXA foam boxes, 3 CTBEs of common trash, 6 CTBEs of KTOs, HTV-2 M-bags of launch foam, foam box from the cylinder flywheels, filler foam pulled from inside NASA CTBs,HTV-2 rack filler foam, 6 CTBEs of CWC-I foam, 1 CWC-I metal box, RSP fences from the racks remaining in the PMM and 17 CTBEs of ballast”.

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In total, 55 percent of HTV-2 trash will come from the PMM. 85 percent of HTV-2’s trash will be foam. JAXA will need to produce a detailed breakdown of all trashed cargo inside HTV-2 prior to unberthing, as the cargo’s weight and distribution will affect the Center of Gravity (CG) of HTV-2. JAXA has already certified that none of the trashed cargo aboard HTV will pose a threat during HTV’s destructive re-entry.

Progress M-07M/39P, docked at Service Module (SM) Aft, will depart the ISS on 20th February. Progress M-08M/41P, docked at DC-1 Nadir, will undock from the ISS on 26th April. Together, 39P and 41P will dispose of 59 CTBEs of trash.

ATV-2 is not scheduled to undock from the ISS until June 4, whereupon it will dispose of a significant amount of cargo.

Longer-term logistics:

Looking to the end of 2011, ISS will continue to be a busy year for logistics operations, due to the now approved STS-135 mission, and the planned visits of new COTS (Commercial Orbital Transportation Services) vehicles.

STS-135, currently scheduled to launch on 28th June, will deliver a massive 14,000 kg of cargo to the ISS. The Raffaello MPLM will fly with its full complement of 16 racks, consisting of RSPs, RSRs and ISPs. A large amount of consumables will be transferred to ISS, including food, hygiene items, and clothing.

The MPLM will also take down a lot of unneeded items from ISS, as STS-135 will be the last chance to return a large amount of cargo to Earth before the Shuttle retires.

There is a strong desire to fly the STS-135 mission in order to ensure that the ISS is fully stockpiled throughout 2012 in the event that the commercial sector should suffer a setback with their resupply programs. The concern is that if the commercial sector suffers a setback in the post-Shuttle era, then the ISS may have to go down to a crew of three due to a lack of cargo delivery capability.

Thus, NASA managers are discussing a possible STS-135 launch in the August window, because flying as close to 2012 as possible will ensure a good stockpile of supplies throughout 2012.

At least one visit of SpaceX’s Dragon capsule, which has a cargo capacity of 3,310 kg, is planned to the ISS in 2011. Following on from COTS Demo Flight 1 in December 2010, Demo Flight 2 would test rendezvous operations with ISS, and Demo Flight 3 would be the first berthing of a Dragon to the ISS.

However, NASA is currently in discussions with SpaceX about the possibility of merging Flights 2 and 3, meaning that Dragon could berth to the ISS on Flight 2. In a December press conference, SpaceX CEO Elon Musk implied that if ISS logistics needed a boost, Demo Flight 2 could be loaded with non-essential supplies for the ISS crew. If the merger is approved, it is possible that two Dragons could visit ISS in 2011.

Orbital’s Cygnus vehicle, capable of launching 2,000 kg of supplies to the ISS, is tentatively planned to make its debut flight in December 2011

The benefit of adding the PMM to the ISS as a storage room will undoubtedly be seen in the post-Shuttle era, as a fleet of international governmental and commercial resupply vehicles continue to support the ISS’s crew, systems, and scientific experiments.

(All images courtesy L2 and NASA.)

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