Kansas State University

Coordinated Tasks

MOTIVATION

This work is part of a NASA EPSCoR project at Kansas State University titled “Biosensor Networks and Telecommunication Subsystems for Long Duration Missions, EVA Suits, and Robotic Precursor Scout Missions.” Current space suits primarily monitor ECG signals. Synergistically, we have seen many wireless biosensors appearing in the commercial market. This study looks at applying similar technology in future suits. These sensors will provide more biomedical data and be easier to adapt as well as less expensive than their wired counterparts.

UNDERSTANDING SPACE SUIT ENVIRONMENT

Before adding any elements to the space suit, we needed to understand its radio properties. In an effort to learn more about the layers of the suit, the team visited the Kansas Cosmosphere and Space Center in Hutchinson, KS. During the visit, they saw archived Apollo-era suits and did initial testing on the suits’ radio characteristics (see below). The Thermal Micrometeoroid Garment (TMG) is designed to protect astronauts from micrometeoroids and space debris and to maintain a safe in-suit temperature. The aluminized-mylar layers used should also keep any radio signals inside the suit. To verify this, we contacted ILC Dover and received a sample of current-generation suit material. Using a car key-fob radio transmitter, we tested the sample and found the signal to indeed be blocked by the suit materials. In addition to the TMG, the Liquid Cooling and Ventilation Garment (LCVG) is of interest for potential energy harvesting applications. The LCVG wicks away perspiration and removes excess heat generated by the astronaut. The temperature difference between the LCVG and the astronaut's skin could be converted from heat to electrical power to avoid concerns about the use of battery power within the oxygen-rich suit environment.

BUILDING A SPACE SUIT

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As part of an effort to understand the propagation of waves in the space suit, we built a full-scale model. We purchased two different metallic fabrics and metallic Velcro. A pattern was developed based on a picture of the EMU Suit. To help fill out the suit, we used sewing hoops. The knee joints also utilized hoops to create an interlocking joint. All other joints are attached using Velcro. The model suit was then used to measure in-suit propagation.

MODEL SUIT TESTING

To give a first-order approximation of the real suit, we used our full-scale model for testing. In addition to the suit, the test subject put on two layers of sweatshirts and sweatpants to account for the air gap and prevent the antenna from making contact with the suit. Bubble wrap was used around the neck and hands for the same reasons. A transmit radio and a receive radio were placed on the body in various locations (see table). The receiving radio has an received signal strength indicator (RSSI) output. The RSSI output is used to determine power levels. From the difference in power levels we can start to understand the path loss. Since the antennas are not matched, the received power is degraded by mismatch loss. Hence, the levels below are conservative estimates. The full data set shows that travel through the torso results in losses larger then desired. However, the torso is the most central location, and thus all signals will most likely be coming to or from an antenna on the chest or back. From these initial measurements, the signal from any sensor is expected to be strong enough to be received.

ELECTROMAGNETIC SIMULATIONS

One way to understand the space suit environment is through electromagnetic (EM) simulations. We are using EMPro for our EM simulation. A simplified model of the body was built out of five cylinders (one for the torso and one for each arm and leg). The body model inside is made using three layers: skin, fat, and muscle with thicknesses of 1 mm, 3 mm, and 40 mm, respectively . The muscle thickness is slightly modified to fill the interior of the cylinders. A similar model made of aluminum functions as the Thermo-Micrometeoroid Garment. The aluminum cylinder’s radius is 4 cm larger than the body cylinder’s radius. Initial findings indicate agreement between the electromagnetic simulations and lab tests with the model suit. For example, with the arms spread straight out the electromagnetic simulation indicated a 77.9 dB path loss, while lab tests indicate a 87.5 dB path loss. The difference between these two values can be attributed to experimental error.

ENERGY HARVESTING