WiSe-Net – tomorrow's technologies in miniature format
The environmental conditions on board the International Space Station ISS are strictly controlled; there are only very slight variations in temperature, humidity, air pressure and light intensity. The composition of the atmosphere is also extremely stable. The 'residents' must be aware of any changes immediately. The German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) installed the Wireless Sensor Network (WiSe-Net) experiment on board the ISS to develop reliable miniature sensors that take precise measurements of the ISS environment and will help make the Space Station even safer. Now, the first measurement campaign using the experiment, developed in collaboration with Airbus Defence and Space (ADS) has been completed – more successfully than originally anticipated.
A long-term experiment
The original plans had been to keep the small sensor network in operation on board the Space Station for just six weeks. So Volker Schmid, ISS Programme Manager at the DLR Space Administration, and the ADS developers working with Project Manager Hans-Jörg Beestermöller, calculated the battery life accordingly.
Instead, the experiment’s initial measurement campaign in the European Columbus module on the ISS ran for almost 10 weeks – from New Year's Eve 2014 until 12 March 2015. Here, WiSe-Net utilised the infrastructure of the DLR magnetic field experiment MagVector/MFX. These two systems were transported to the ISS on board the ATV-5 transfer vehicle in July 2014, as part of German ESA astronaut Alexander Gerst's 'Blue-Dot' mission. "Apart from a brief interruption, the four sensors collected data round-the-clock. WiSe-Net has helped us acquire precise knowledge of the environmental conditions in the Columbus Laboratory," says Schmid, who is in charge of the project at DLR.
The data show a clear pattern
WiSe-Net consists of a network of four sensors the size of MP3 players. They collect data relating to temperature, humidity, air pressure and light intensity, and use wireless connections to transmit the readings to a base station. The sensors are fitted at various points in the Columbus module. Besides the data itself, the system also provides statistics on the quality of the wireless network. Data packages are compiled at regular intervals and transmitted back to Earth via the ISS communication channels. Is it possible to infer a pattern for the ISS based on this data? "The assessment over a period as long as 10 weeks shows a clear pattern – confirming that normal conditions prevail. The temperature is almost exactly 24 degrees Celsius, humidity is 45 percent and air pressure 1002 hectopascals – all of them normal readings," says Beestermöller, summing up the results. "We only observed a fluctuation in all three of these parameters on 3 January 2015. Here, humidity and air pressure rose sharply, while the temperature dropped. We still have to find out why this happened."
Monitoring the crew by measuring light
The wireless sensors measure more than just these three environmental parameters. They also record light intensity. "This shows when the crew members are working in the Columbus module, and how much. The light intensity is a fairly simple method of tracing the crew's routine workday, and also its rhythm. The sensors are extremely sensitive, so we can see which sensor is responding and to what degree – and this tells us where the day's main activities took place," explains Beestermöller.
Tracking down hazardous gases
The WiSe-Net sensors are also able to warn the crew of – and protect against –potential threats. Gas leaks pose another source of danger on board the Space Station. As a reminder, the astronauts and flight controllers were startled by an alarm on 14 January, indicating that highly toxic ammonia had leaked into the US-European section of the station. Ultimately, it was a false alarm caused by a computer malfunction. Nevertheless, an astronaut equipped with a respirator was forced to enter the section and read the values 'by hand', as the Space Station is currently not fitted with any instruments to track down potential leaks. "WiSe-Net could remedy this situation. We intend to fit the next-generation sensors with a gas detection system. They will record the values, and each sensor will identify the precise concentration in its immediate vicinity. We will then be in a position to accurately localise any potential leak. Once this is in place, astronauts will no longer be required to don respirators and conduct measurements in a danger zone," explain Schmid and Beestermöller with a view to the future.
Future miniaturised technology will be even better
Their ideas do not stop there; there are plans to equip the next-generation WiSe-Net 2 sensors with systems capable of 'harvesting' lost energy to recharge their batteries, or even make them entirely superfluous. Excess energy is normally converted into heat and released; it dissipates and cannot be recovered. The same principle applies to light. "What is referred to as energy harvesting is a promising field for technological research. It would be useful if we were able to recover this lost energy on board the ISS. This is precisely what we plan to do in the follow-up project WiSe-Net 2," say Beestermöller and Schmid.
Interestingly, the Blue Dot mission was the first time that two industrial experiments were installed on the ISS whose hardware was financed without public funds. WiSe-Net is one of them. "These industrially-motivated experiments will become more common," says Volker Schmid.