External Stowage Platform-2 (ESP-2)
The External Stowage Platform-2 (ESP-2) is an external pallet that can securely hold up to eight critical spare parts or Orbital Replacement Units (ORUs) for the International Space Station (ISS). Space Shuttle Discovery will carry ESP-2 to the ISS on STS-114 in May 2005. An Extravehicular Activity (EVA) or spacewalk, will be required to install the pallet on the mission's ninth day.
Each of the ESP-2 storage sites has a Flight Releasable Attachment Mechanism (FRAM) used by astronauts to secure or release the ORUs and other equipment stored on the pallet. Electrical power for the pallet and its contents is provided by the ISS. Most of the ORUs have heaters to keep their internal components from getting too cold while stored on the ESP-2. The pallet also has handrails and attachment points for tethers and foot restraints used by the astronauts. The ISS robotic arm can be used to move the large ORUs stored on the pallet, but astronauts can move smaller parts during a spacewalk.
ESP-2 is the second in a series of storage pallets on the ISS. ESP-1 was installed on ISS flight 5A.1 in March 2001 and is mounted on the aft portion of the U.S. Laboratory, Destiny. ESP-1 is smaller than ESP-2 and has two ORU storage sites. Node 1, Unity, provides power to the ESP-1, which in turn makes power available to both ORU storage areas. ESP-2 is derived from an Integrated Cargo Carrier (ICC), an equipment carrier designed for use in the payload of the orbiter. ESP-2 was adapted for deployment on the ISS by developing a device to attach it to the ISS airlock. Development has already begun on ESP-3, which will be launched on ISS flight 13A.1 (STS-118) and attached to the P3 truss.
During the first of three spacewalks planned for Discovery's mission, astronauts will remove the ESP Attachment Device (ESPAD) from ESP-2 and mount it to the ISS airlock using the ISS robotic arm. During the third spacewalk of the mission, the ISS robotic arm will move ESP-2 from the orbiter payload bay and attach it to the ESPAD. After the mechanical/structural work for the ESP-2 is completed, astronauts will connect primary and secondary power cables to the ISS. Primary power for ESP-2 comes from Node 1 and secondary power comes from the S0 truss.
ESP-2 launches with the following ORUs:
- Flex Hose Rotary Coupler (FHRC) -- Provides two isolated paths for distribution of ammonia between the ISS radiators and the rest of the station. The FHRC is a component of the Thermal Radiator Rotary Joint which rotates the radiators aboard the S1 and P1 trusses.
- Main Bus Switching Unit -- Used for power distribution, circuit protection and fault isolation on the space station' s power system.
- Utility Transfer Assembly -- Manages electrical power flow from the solar arrays to the space station.
- Video Stanchion Support Assembly -- Used by astronauts during a spacewalk to mount video cameras and lights on the ISS structure for remote viewing of external parts of the ISS during the assembly process.
Future shuttle missions will deliver these ORUs for storage on the ESP-2:
- Battery Charge / Discharge Unit (BCDU) (ISS flight ULF1.1, July 2005) -- The BCDU charges batteries and provides conditioned battery power to power buses during eclipse periods.
- Pump Module Assembly (PMA) (ISS flight ULF1.1, July 2005) -- The PMA provides pressure to transport ammonia throughout the space station' s cooling system. It also regulates mixing of warm and cold ammonia to control ISS temperature loops.
- SPACEHAB/Oceaneering Space Systems-Extended Deployable (SHOSS-ED) Box (ISS flight ULF1.1, July 2005) -- The SHOSS Box is a storage container for the DC to DC Converter Unit-Coldplate (DDCU-CP) and Main Bus Switching Unit-Coldplate (MBSU-CP). When mounted on the ESP-2 it can be used to store ORUs or other ISS hardware.
ESP 2 Statistics:
Project Integrator: Boeing
Major Contractors:
- ICC -- SPACEHAB Inc.
- ESPAD -- Oceaneering Space Systems
- Power Cables -- Boeing
- ORUs -- Boeing, Honeywell, Lockheed Sunnyvale, and Loral
- ORU FSE -- Boeing and Oceaneering Space Systems
Purpose: ESP-2 is an unpressurized external storage pallet with eight attachment sites capable of holding up to eight ISS spare parts and assemblies. The pallet also has handrails and attachment points for tethers and foot restraints that astronauts can use while working with the ORUs on the ESP-2.
Weight: Empty structure weighs about 5,900 lbs. (2676.19 kg.). At launch with ORUs and other equipment, ESP-2 will weigh about 7,500 lbs. (3401.94 kg.).
Dimensions: about 12 ft. x 16 ft. x 9 ft. (3.65 m x 4.9 m x 2.74 m)
Structure: An Integrated Cargo Carrier (ICC) is the basic structure of ESP-2 with eight FRAM sites attached. The ESPAD structure connects the ESP-2 to the ISS airlock trunnion pins. Two power cables connect to Node 1 (Unity) for primary power and the S0 truss for backup power to the ESP-2. Each ORU has an active FRAM to attach the ORU to the passive FRAM site mounted on the ESP-2.
Construction: Integration of the ORUs with their Flight Support Equipment (FSE) onto the ICC was performed by SPACEHAB, Inc. at Cape Canaveral, FL. Once the ORUs were integrated onto the ESP-2 by SPACEHAB, the entire assembly was transferred to Kennedy Space Center's Space Station Processing Facility for final processing.
Installation: Attached to the Quest Airlock on the International Space Station during ISS flight LF1 (STS-114) in May 2005.