PMM Leonardo: The Final Permanent U.S. Module for the ISS

by Chris Gebhardt

Arriving at Pad 39A on Thursday, prior to marking a significant milestone for not only the Space Shuttle/International Space Station Program, but also the U.S. space program in general, the flight of PMM Leonardo – the premiere payload element for Discovery’s final flight – to the ISS will mark the delivery and installation of the final permanent module from the United States for the orbital outpost.

Leonardo: Workhorse of the MPLM Fleet:

Named after the famed Italian renaissance inventor Leonardo da Vinci, construction on Multi-Purpose Logistics Module 1 (MPLM 1) – or Flight Module 1 – commenced in April 1996.

Contracted as part of the original ISS agreement between the international partners, Leonardo, like the two other MPLMs, was constructed by the Italian Space Agency. After the completion of primary construction in August 1998, Leonardo was loaded onto a Beluga aircraft and delivered to the Kennedy Space Center, FL.

From there, final construction was completed and various tests performed to formalize Leonardo’s certification for flight ahead of its inaugural mission on Space Shuttle Discovery as part of the STS-102 flight in March 2001.

Liftoff of Leonardo in Discovery on STS-102 marked the first of 10 MPLM flights to date – seven of which have been conducted with Leonardo; MPLM Raffaello (MPLM 2) picked up the other three MPLM flights, with Donatello unfortunately receiving no flight assignments following the restructuring of the Shuttle manifest in the wake of the 2003 Columbia accident.

Upon return of STS-102, Leonardo was quickly reconfigured for flight five months later on STS-105 – also on Space Shuttle orbiter Discovery.

During STS-105, Leonardo was used to deliver six Resupply Stowage Racks, four Resupply Stowage Platforms, and two new scientific experiment racks for the Destiny lab. Two new science racks and EXPRESS (Expedite the Processing of Experiments to the Space Station) Racks 4 and 5 were also delivered by STS-105 via Leonardo and greatly increased the science capability of the ISS.

Leonardo was then returned to Earth with Discovery where it was deserviced and prepared for its next mission, the STS-111 flight on orbiter Endeavour in June 2002. During this flight, Leonardo was used to transport new experiment racks and three stowage and resupply racks to the ISS.

STS-111 would also mark the final time Leonardo would fly due to the suspension of Space Shuttle flight operations following the loss of Shuttle orbiter Columbia and the STS-107 crew on February 1, 2003. In fact, it would not be until July 2006 that Leonardo would once again be called upon to ferry supplies, experiments, and equipment to the International Space Station.

Returning to active service on July 4, 2006 with the launch of Space Shuttle Discovery and the STS-121 mission, Leonardo carried numerous supplies meant to restart the process of stockpiling the ISS with needed supplies that, while present on ISS, had not been as prevalent during the Space Shuttle Program stand down after Columbia and the year-long stretch between STS-114 and STS-121.

But perhaps Leonardo’s biggest role to date came during her next flight on the STS-126 mission in November 2008 aboard orbiter Endeavour. The near 16-day mission (Leonardo’s longest single-flight duration mission) saw Leonardo carry the final equipment needed for expanding the International Space Station’s crew from three people to six people.

To accomplish this task, Leonardo was launched with a gross weight of 28,100 lbs – 14,000 lbs of which were accounted for by supplies and equipment for the ISS. With no other MPLM flight currently scheduled to exceed this launch weight, Leonardo holds the record for heaviest MPLM flight.

Among the items Leonardo carried to the Station on STS-126 were two new crew quarters racks, a second galley, a second Waste and Hygiene Compartment, the advanced Resistive Exercise Device, two water reclamation racks, new experiments, and a GLACIER (General Laboratory Active Cryogenic ISS Experiment Refrigerator) unit.

After a California landing, Leonardo was returned to the Kennedy Space Center in December 2008 with Endeavour and prepared for its role in the August 2009 flight of Discovery and mission STS-128.

Launching seconds before the stroke of midnight on August 28, 2009, Discovery and Leonardo carried the final pieces of equipment to ease the living conditions of the Station’s six-member crew. Included in Leonardo’s launch manifest were three life support racks, one Crew Quarters for Kibo, a new treadmill named after comedian Steven Colbert, and an Air Revitalization System ultimately destined for Node-3.

Finally, Leonardo was returned to the Kennedy Space Center in September 2009 following the California landing of Discovery. Upon return to KSC, Leonardo was prepared for what would ultimately be its final mission to space as a Multi-Purpose Logistics Module.

Launching into the pre-dawn sky on Monday, April 5, 2010, Leonardo was once again transported to the ISS by Discovery. During the 15-day mission of STS-131, Leonardo was used to deliver food and science supplies to the ISS, the third and final Minus Eighty Degree Laboratory Freezer for ISS, a Window Orbital Research Facility, one Crew Quarters rack, a Muscle Atrophy Resistive Exercise rack, Resupply Stowage Racks, and Resupply Stowage Platforms.

Leonard: From MPLM to PMM:

With the landing of STS-131, Leonardo was transferred back to the Space Station Processing Facility where modifications and reconfigurations began immediately to convert Leonardo for permanent attachment to the ISS.

Some of these modifications included equipment removal to reduce the overall weight of Leonardo. These removals included the elimination of the Active Thermal Components in the forward endcone and the removal of utility plates, harnesses, water ducts, and “associated components from standoff Bays 1 and 2.”

These removals resulted in a net weight loss of 178.10 lbs.

Furthermore, several modifications were made to “facilitate on orbit maintenance,” notes the Mission and Stage Overview MOD FRR presentation available for download on L2.

These modifications included lengthening the forward endcone cable harnesses to allow for “panels to swing open without the need to disconnect multiple cable harnesses” and the inclusion of PIP pin capability in order to “replace non captive fasteners in the interface (will be inserted if we ever have to get to the avionics boxes behind the panels)” since PIP pins do not meet launch load requirements.

Additionally, the Permanent Multipurpose Module (PMM) Leonardo’s software was upgraded to account for the equipment that was removed as part of the MPLM to PMM weight reduction modifications.

“With the decision to remove several components inside PMM as a weight reduction effort, MPLM software was changed to account for the missing hardware,” notes the MOD FRR presentation.

However, several commands in the Mission Control Center will still exist for controlling the missing hardware on PMM Leonardo. This was done on purpose since STS-135 would – if funded – bring up the MPLM Raffaello, as would the STS-335 LON mission.

“Related to the PMM software generation, there are several commands in MCC for controlling that now missing hardware. Note that these MPLM commands were not deleted from the MCC command server to protect for a future flight (135) that may bring up an MPLM.”

STS-133 Specific Articles:

Therefore, to protect against the accidental selection and transmission of these commands to the PMM, MCC will “Type A” the commands to protect against this possibility.

Additionally, further modifications to Leonardo included the installation of upgraded MMOD (Micro Meteoroid Orbital Debris) shielding, the addition of a Planar Reflector at the request of JAXA, and the modification of the module’s Multi-Layer Insulation (MLI) to “upgrade the PMM Probability of No Penetration (PNP) to a level commensurate with other ISS modules (0.994).”

For the Planar Reflector, JAXA requested the addition of this component to the endcone area of the PMM to take the place to the reflector that was located on PMA-3 during HTV-1 approach operations. The new reflector will aide HTV-2 and subsequent HTV missions during their approach ops.

Moreover, the MLI upgrades will increase the ability of the PMM to handle potential MMOD impacts. As the MOD FRR presentation states, “If PMM PNP requirement = 0.995, USOS/ESA/JAXA MMOD risk would be 11% lower than if PMM PNP requirement = 0.99.”

In all, the PMM has an effect on the overall USOS/ESA/JAXA segment MMOD risk because of the module’s “relatively high-MMOD risk” due to its berthing location on the ISS. While the nextel/Kevlar MLI reduces the overall weight of the PMM, it conversely increases the MMOD risk. As such, the “PMM with MMOD PNP requirement = 0.99 would be highest risk module/element on USOS/ESA/JAXA.”

Nonetheless, with all of these modifications in place, the PMM Leonardo will add much-needed storage space on the ISS; however, that storage space won’t be available to the ISS crew immediately.

In fact, PMM Leonardo will be launched with a near full load of payloads. Following attachment to the ISS, the contents of the PMM will be emptied to the appropriate locations on ISS. Once JAXA’s HTV2 arrives in February, Leonardo’s now unnecessary launch hardware will be transferred to HTV2 for ultimate destruction in Earth’s atmosphere.

Once the launch equipment and racks have been removed, the PMM will then provide the needed stowage space for the ISS. However, “Activities to reconfigure the PMM following ULF-5 will span multiple [ISS crew] increments and will include relocating science (ER8, Robonaut) and relocating various NASA and ESA items into the PMM (CWCs currently stowed in the JEM, food containers, spares, payload hardware etc.),” notes the MOD FRR Mission and Stage Overview presentation.

In all, Leonardo will gain the distinct honor of being the only non-permanent module for ISS construction to be converted to and left on ISS as a permanent fixture. Even more fitting is the fact that Leonardo will be ferried to space for the final time on Discovery – the Shuttle orbiter on which it has flown the vast majority of its missions.

Images: NASA, Larry Sullivan ( Entertainment/STS-133 FRR Presentations via L2).

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