Four of IOtech's Personal Daq data acquisition systems were used in the ARED Instrumentation Box

Adapted from an article that appeared in
NASA Tech Briefs, August 2005

One of the primary ways astronauts have to maintain bone density during long-duration space flights is resistive exercising, such as weight lifting. Walking, impact exercise, and weight lifting can maintain bone density on Earth because the body is working against gravity. But on the International Space Station (ISS), the effect of gravity isn’t felt in the gravity-free environment, so astronauts must simulate it with resistance exercise.

Devices currently in use on the ISS do not collect as much information as the scientists would like, and they are aging. The equipment will be replaced with a next-generation Advanced Resistive Exercise Device (ARED), which is being built at NASA’s Johnson Space Center in Houston, TX. The equipment will provide astronauts with more exercises and larger loads. The exerciser is a full-body exerciser that simulates free weights, similar to a home gym. It lets astronauts perform cable and bar-type exercises for a single hand, leg, or limb.

In addition, a suite of instrumentation is included on the exerciser to collect research for use on future flights such as long-duration missions to Mars. This data will enable the scientists to monitor, predict, and improve the exercise regimen, as well as better understand the entire biological impact on the astronauts’ bodies.

NASA has developed numerous instrumentation systems but none were easy to adapt to this application. Rather than design a custom unit, they opted to modify a commercial off-the-shelf (COTS) data acquisition system and add it to the exercise device. The primary requirements for the system included low power operation, a USB port, high accuracy, and low cost.

NASA selected a new instrumentation system that includes four Personal Daq^™ data acquisition systems per exercise device. The suite contains 14 different sensors, which constitute 22 channels of data exclusively for gathering position information and force from load cells as the astronauts exercise. To increase bandwidth and gather the 22 channels of data, the Personal Daqs are mounted directly to the exercise device. All channels measure load cells except two, which are rotational displacement. NASA has several different load cells, typically 0 to 500 pounds and 0 to 1,000 pounds. The displacement sensors are variable-inductance types that measure ±60° of rotation.

To eliminate potentially hazardous materials, including plastics that outgas or support the most remotely possible fire condition, NASA repackages all COTS equipment to get the hardware ready for flight. Repackaging also removes some of the connectors on the circuit boards and reconnects the wires directly to the solder pads to eliminate mechanical interface metal enclosure along with the power supply, signal conditioning, and the USB hub.

Twenty-four Personal Daqs were purchased to satisfy 15 years worth of instrumentation needs for the exerciser program. In many cases, NASA purchases COTS hardware all at once for use in the duration of a project—preferably from the same lot or production line—since no one can guarantee that the same hardware will be available again.

Eight Personal Daqs are scheduled for flight—four for the primary acquisition system and four spares packaged in another complete box called an AIB (ARED Instrumentation Box), which simply can be plugged in if the primary AIB should fail.

NASA engineers wrote a custom software package embedded in National Instruments^™ LabVIEW^® to handle the required data acquisition tasks. The package is directly interfaced to the Personal Daq. Additionally, engineers embedded a data –reduction tool, also in LabVIEW, that pulls the data an out and sends it to a flat ASCII file. When they want to analyze the data, they use a variety of third-party analysis software packages.