Recent findings indicate that frequent, short-term crew exposure to elevated CO2 levels, combined with other physiological impacts of microgravity, may lead to a number of detrimental effects, including loss of vision. To evaluate the risks associated with transient elevated CO2 levels and design effective countermeasures, doctors must have access to frequent CO2 measurements in the immediate vicinity of individual crewmembers along with simultaneous measurements of their location in the space environment. To achieve this goal, a small, low-power wearable system that integrates an accurate CO2 sensor with an ultra-wideband (UWB) radio capable of real-time location estimation and data communication is proposed. This system would be worn by crewmembers or mounted on a free-flyer, and would automatically gather and transmit sampled sensor data tagged with real-time, high-resolution location information.
Prior CO2 measurements have been done with both wired and wireless sensors, but without real-time location information associated with the measurements. Some environment data are location-sensitive. Without location information, it is difficult to diagnose the source of the environment problem.
A UWB Time-of-Arrival (TOA) tracking and CO2 sensing system has been designed, implemented, tested, and proven feasible for providing the realtime and location-aware wireless CO2 sensor measurements, although the concept is applicable to other types of sensors. A microcontroller is leveraged to integrate a low-power CO2 sensor with a commercially available UWB radio system with ranging capability. In order to accurately locate problem places in a multipath intensive environment, a 3D UWB TOA tracking system with two-way ranging was proposed.
UWB technology has been exploited to implement the tracking system due to its properties such as fine time resolution and low-power spectral density. The TOA tracking method has been employed to fully utilize the accurate ranging capability of the UWB signal. Simulations show that the desired fine tracking resolution can be achieved for any size of proximity tracking with chosen system configuration “Twisted Rectangle” if the extension of the baseline radius in 3D is feasible. The Twisted Rectangle configuration has radios installed in different planes within the tracking space so there is no singularity problem.
Field tests demonstrate that this UWB tracking system can track the moving target in real time, and an inch-level tracking accuracy can be achieved with an update rate of 5 Hz. Environment data such as CO2 level can be wirelessly measured and automatically tagged with both time and location information. Although the initial effort is targeted to CO2 monitoring, the concept is applicable to other types of sensors to monitor more environmental parameters such as temperature, humidity, and radiation.