External Storage Platforms ( ESP ) are three leaky components of the International Space Station , designed for external storage of bulky goods. Main purpose: storage of cargo delivered to the ISS, various elements and spare parts having the abbreviation ORU (from the English Orbital Replacement Units ). ORUs are stored on platforms until they need to be transferred to regular places, or to places instead of failed equipment. They are attached to the platforms using special rigging attachments ( FRAMs ), originally designed for Shuttles . Mounting devices are manufactured by Spacehab ( Eng. Spacehab )  . Some stored equipment requires power, so electricity is connected to the platforms.
The first platform was installed on the Destiny module body on March 13, 2001 , during the second space shuttle Discovery crew “STS-102” . Power is supplied from the Unity module . The platform has two FRAMs , on which they are permanently fixed:
- Direct Current Switching Unit ( DCSU );
- The pump control system ( PFCS ) is designed to control the flow of coolant ( ammonia ) in the secondary circuit of the thermal control system of the American station segment.
The second platform was installed on August 3, 2005 , on the Quest module , using the Shuttle Discovery "STS-114" robotic arm and two crew members of the ship during their third spacewalk. The platform was fixed to the module using a special mounting device ( ESP Attachment Device - ESPAD ). The mass of the platform is 2676 kg. The mass of stored ORU is 3400 kg. Like ESP-1, power is supplied from the Unity module .
The platform has eight FRAMs , on which are fixed:
- Power Switching Units ( Main Bus Switching Unit - MBSU )  ;
- Mobile conveyor ( Eng. Utility Transfer Assembly - UTA );
- Battery Charge / Discharge Unit ( BCDU );
- Pump Module Assembly ( PMA )  ;
- Additional deployable pressurized volume ( English Extended Deployable )  ;
- DC Switches ( Eng. Direct Current Switching Unit - DCSU )  ;
- Spare parts for the rotary support of the robot arm CanadaMarm2 ( Eng. Yaw Joint ORU for Canadarm2 );
- The bearing design of the gyrodin CMG-3 (from the English Control Moment Gyroscope ).
- In addition to this equipment, earlier (at start), an ORU was also installed on the platform, called Flex Hose Rotary Coupler - FHRC  ;
The third platform was installed on August 14, 2007, during the seventh day of the STS-118 Endeavor expedition. ESP-3 was the first platform to be installed using only the robotic capabilities of the shuttles and the ISS. The following were involved, respectively: an external video mooring system ( English External Berthing Camera System - BCS ) and a photoelectric remote manipulator ( English Photovoltaic Radiator Grapple Fixture - PVRGF ), on which four video cameras were installed, the video information from which came to the station.
The platform is mounted on one of the truss segments P3 .
Unlike other platforms, on the ESP-3 there are guide rails, places for attaching safety cables and limiters for the astronauts legs, which facilitate access to the equipment located on the platform.
Up to seven auxiliary elements and spare parts of the ISS can be installed on the eight available FRAMs . Since October 2007, the platform has secured:
- Battery Charge / Discharge Unit ( BCDU ) - designed to provide uniform power supply, in the absence of solar energy during night phases;
- Nitrogen Tank Assembly ( NTA ) tanks installed on S1 and P1 farms , which provide constant pressure of the coolant ( ammonia ) in the secondary circuit of the temperature control system of the American station segment;
- An additional articulation for the robotic arm ( Pitch Roll Joint - P / R-PJ ) is equipment provided by the Canadian space agency for the Canadaarm2 robotic arm.
- In addition to this equipment, earlier (at start), at the bottom of the platform was a spare battery module.
In addition, the Endeavor STS-118 crew installed a spare gyrodin CMG-3 (from the English Control Moment Gyroscope ) and its supporting structure. But on August 14, 2007, the Atlantis STS-122 crew dismantled it and installed it on the Z1 farm to replace the broken one; The supporting structure is transferred to the ESP-2 platform.
- Information about ESP-2 on the Boeing website. boeing.com Archived December 12, 2009 by Wayback Machine
- Power switching block - the first block was installed on August 3, 2005 during the STS-114 Discovery mission, the second block was installed on October 23, 2007 during the STS-120 Discovery mission
- Pump Module Assembly (PMA) - not to be confused with Pressurized Mating Adapters (PMA)
- Additional deployable pressurized volume - produced by SpaceHab and Oceaneering Space Systems
- DC switches - two switches were installed March 17, 2008 during the Invevor mission "STS-123"
- FHRC - unfortunately, no exact name, nor information about this equipment, other than the fact of its existence, has been found.