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NASA moves PMM to make room for CCP spacecraft

Permanent Multipurpose Module (PMM) alongside Progress/Soyuz. Photo Credit: NASA

The Permanent Multipurpose Module (PMM) alongside a docked Soyuz spacecraft were photographed by an Expedition 26 crew member on March 1, 2011. Photo Credit: NASA

With plans to have privately-produced spacecraft ferry crews to the International Space Station (ISS) picking up speed, NASA re-positioned the Permanent Multipurpose Module (PMM) from the Unity Module (Node 1) on the orbiting laboratory to the port side of the Tranquility Module (Node 3). The transfer was completed at 9:08 a.m. EDT (13:08 GMT) and utilized the station’s robotic manipulator “Canadarm2” to move the station component to its new home.

The PMM was scheduled to be detached by robotics flight controllers at the Mission Control Center at NASA’s Johnson Space Center on Wednesday, May 27. It was robotically relocated from the Earth-facing port of the Unity Module on the International Space Station to the forward port of the Tranquility Module using the Canadarm2 robotic arm to maneuver the 11-ton module a short distance to its new location – the next step to reconfigure the complex for the future arrival of U.S. commercial crew vehicles.

Expedition 43’s commander, NASA astronaut Terry Virts, along with flight engineer Scott Kelly (who will be conducting a year-long stay aboard the ISS) handled the unbolting and re-positioning of the PMM. Virts and Kelly had closed the hatch to the module on Tuesday, May 26. The move got underway starting at approximately 8 a.m. EST on Wednesday, May 27. The hatch to the module was reopened at its new location on Thursday, May 28.

Image Credit: NASA

This illustration shows the previous location (blue) of the Permanent Multipurpose Module (PMM) on the International Space Station (ISS) and the new location where it was repositioned (green) during the May 27 move.
(Click to enlarge) Image & Caption Credit: NASA

Many of the components on the space station are modular in nature, allowing them to re-positioned. NASA’s fleet of shuttle orbiters, which carried out most of the heavy lifting in terms of the station’s construction, were retired in 2011.

Basically, the module relocation procedure – which will, in future, involve relocating multiple modules and components from their current Space Shuttle optimized positions – on the ISS is necessary to provide an additional docking port for future commercial crewed vehicles. At this time, only one docking port is available.

Nevertheless, future Commercial Crew vehicles will require two docking ports. This is because, currently, NASA operates a “rental car” model of Commercial Crew transportation – ISS astronauts fly to the station, their vehicles remain at the space station during their stay, and then they return to Earth aboard the same vehicle.

Image Credit: NASA

Previous PMM location. (Click to enlarge) Image Credit: NASA

This method of transportation to the ISS means that only one Commercial Crew vehicle is present at any given time, since one vehicle departs before another arrives – known as an indirect handover.

Furthermore, this situation also means that one Russian crewman will always be required to fly on a Commercial Crew vehicle so that one NASA crewman can continue to fly on a Soyuz, in order to maintain a constant U.S. presence aboard the ISS when no Commercial Crew vehicle is docked at the station.

Photo Credit: NASA

Close-up view of the PMM. (Click to enlarge) Photo Credit: NASA

However, NASA is not currently planning on using the ‘taxi’ model – involving dedicated pilots flying the incoming ISS crew to the station and returning with the outgoing crew – in what is known as a direct handover.

The main reason for this round of restructuring the space station to create two docking ports is the requirement for a backup docking port in addition to the primary port – in case it ever fails – while still preserving the ‘taxi’ model option at a future time should it be required.

Now that NASA is focusing on returning to the business of space exploration, the space agency is not abandoning the station, however. Rather, it is handing off responsibility of keeping the ISS properly staffed and supplied with cargo to the private firms involved in the Commercial Crew Program – SpaceX, Boeing, Blue Origin, and SNC. Two of those aerospace firms, SpaceX and Boeing, who were awarded the Commercial Crew Transportation Capability (CCtCap) contract, have developed and produced the (crewed) Dragon and CST-100 spacecraft, respectively. NASA and their commercial partners are hoping to conduct the first flights of these spacecraft as early as 2017.

New location of the PMM. Image Credit: NASA

The ISS as of May 27, 2015, shows the newly relocated PMM, two Soyuz vehicles, and a Progress resupply vehicle. (Click to enlarge) Image & Caption Credit: NASA

The PMM, originally named “Leonardo” by the Italian Space Agency that supervised its manufacture, was one of three cargo modules used to haul supplies back and forth from the station during Space Shuttle assembly missions. The PMM was launched for the last time to the station on the final flight of the Space Shuttle Discovery on Feb. 24, 2011, and was installed on Unity five days later. The PMM is 22 feet (6.7 m) long, 14 feet (4.27 m) in diameter, and has a mass of almost 11 tons; it has an internal volume of more than 2,400 cubic feet (68 m3).

To date, the PMM has been used as the station’s supply depot.

Video courtesy of ReelNASA

Video courtesy of NASA



Jason Rhian spent several years honing his skills with internships at NASA, the National Space Society and other organizations. He has provided content for outlets such as: Aviation Week & Space Technology,, The Mars Society and Universe Today.

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