Microgravity Investigation and Crew Reaction in 0-Gravity (MICR0-G) is a joint project of MIT, NASA, Politecnico di Milano University, the Italian Space Agency (ASI) with contributions from the French Space Agency (CNES).
The objective is to develop an integrated system of advanced kinematic and kinetic instruments for the International Space Station (ISS) to make precise measurements of the forces and moments exerted by the astronauts and to characterize human motor strategies and postural behavior in weightlessness. The astronaut-induced forces and moments will be measured by an advanced version of Dynamic Load Sensors flown on the Space Shuttle and on Mir. The astronaut motions will be measured by ELITE-S2, an enhanced version of the real-time opto-electronic motion analysers ELITE-S and Kinelite.

The primary objective of the MICR0-G project is to record and store for later analysis the forces and moments applied by the crew onto the space station during nominal intra-vehicular activities and to provide real-time feedback to the crew on the magnitude of the applied loads. Therefore the crew members will more easily and rapidly adapt their behaviour in microgravity.
The secondary objective is to record and store force and moment data of human subjects for scientific investigations.

The advanced sensors will reflect on-orbit experience with original sensors but attempt to take advantage of the drastic increase in computing hardware and software capabilities to produce a far more robust, flexible, and mobile payload system.
The latest features of the advanced load sensors are summurazied herein:

• Minimized size (24x24x8 cm) and weight (less than 4kg per sensor).
  
• Acquisition and processing of data in real-time as well as immediate feedback to the astronauts.
  
• Use of wireless communication enhancing global mobility and flexibility of the system.
  
• Maximum use of commercial off-the-shelf (COTS) technologies to reduce development and production costs.
  
• Simplification of the operations for the astronauts.
  
• Enhanced hardware and software reliability to eliminate the likelihood of unallowable system failures.
  

Each advanced sensor consists of two parts: the Sensor Mechanical Unit (SMU) and the Sensor Electronics Unit (SEU). The SEU has the same footprint (24x24cm) as the sensors and is about 6cm high. The following figure illustrates a sensor and its electronics contained in a case screwed up underneath the sensor (the so-called SEU includes the electronics and the case):

The SMU and its SEU Screwed Up Underneath

Advanced Sensors Architecture

• Post-flight tests of the original sensors returned from Mir revealed an excellent overall quality and accuracy. Therefore, NASA decided to keep the same design of the load cells (SRU). As part of the final design, the top plate of the sensors will incorporate a LED device to provide real-time feedback to the astronauts on the magnitude of the applied loads. This slight modification of the enclosure is the only difference between the first and the second generation of load sensors.
  
  
  
  First Generation of Sensors

• The Sensor Electronics Unit (SEU) incorporates similar, but more advanced, electronics than the original ESM contained. It achieves a reduction in size and mass by a factor of eight in comparison to the MODE ESM.
  
  The SEU consists of the following main components:
  • Signal conditiong Board
  • A/D converter
  • Central Processing Unit (CPU)
  • PC-Card Module
  • Wireless PC-Card
  • Power Supply Components
  • LED Device
  
  The signal conditiong board is a customized electronic board designed to have the same footprint (9.0x9.6cm) as PC/104 boards.
  
  
  Customized Signal Conditioning Board
  The remaining electronics (namely the A/D converter, the CPU and the PC-Card module) are PC/104 boards. The PC/104 form factor defines how to repackage desktop PC functions in a manner that satisfies the ruggedness, reliability, and size constraints of embedded systems. Therefore, PC/104 offers a full hardware and sotware PC-compatible architecture, but in the form of compact (9.0x9.6cm), self-stacking, modules.
  
  
  
  Advanced Sensors PC/104 Stack

• Finally the network is based on Proxim RangeLAN2 PC-Cards using RF connectivity in the 2.4 GHz frequency band. The central laptop computer as well as each Sensor Eletronics Unit incorporates one of these PCMCIA cards. The sensors utilize the TCP/IP protocol to send data to the wireless LAN enabled central laptop and to implement additional networking capabilities such as monitoring or time synchronization.
  The whole system composed of the sensors and the central laptop can be integrated into the ISS wireless network or can be organized into a stand-alone LAN.