The German ESA astronaut Alexander Gerst has been on the International Space Station (ISS) for over a month, and he has been conducting experiments that scientists have sent into space for him. This week, his activities included putting on two small tracking devices, which allow researchers from the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) to track his movements. This technology can be used to locate people in space, but also in mines and other hard-to-reach places. Gerst has also taken radiation meters with him into space. These monitor the radiation that the astronauts are exposed to, and give them a warning if necessary.
Tracking astronauts on the ISS
On 12 July 2018, the 'Wireless Compose' experiment followed Alexander Gerst for 30 minutes as he moved around the Columbus Laboratory on board the ISS. The autonomous indoor positioning system offers the possibility of tracking people or even robotic systems in hard-to-reach places – or astronauts on long-term space missions. This would allow them to be located and rescued quickly in the event of an emergency. On the ISS, Gerst started the experiment by switching on all five of the 'anchor motes' in the Columbus laboratory. These small boxes, measuring approximately 10 centimetres across, receive the signal from the mobile tracking device and are the fixed point (or anchor) for calculating its position.
Indoor tracking in extreme environments
At the DLR Institute of Space Systems in Bremen, Christian Strowik, one of the two principal investigators (PIs) for the experiment, has a sudden shock; two of the 'anchor motes' are indicating a malfunction. "It is quite possible that the photovoltaic cells are not providing enough power, so the devices switch to battery operation, which can take a few seconds," he says, hopefully. Alexander Gerst floats over to the 'anchor motes' a second time and gives the all clear; the devices are now all showing a green light. The astronaut puts on the mobile tracking devices – one on his ankle and the other on his upper arm. For around 30 minutes, the researchers record his movement data. During this period, Gerst carries out his normal programme of tasks, in this case maintenance work in the Columbus laboratory. "Our goal is to capture Alexander Gerst's movements on the ISS in three-dimensional space. In our experiment, we are tracking not only his location, but also the speed and rotation rate of his movements," says Strowik.
Assistance with automatic inventory checking
For wireless data transmission on the ISS, researchers use what is referred to as ultra-wideband, as it covers a very broad frequency range of 500 megahertz. Ultra-wideband is often used for indoor communications, as its low spectral power density means that it does not disrupt other frequency ranges and it is resistant to reflections within the ISS. After 35 minutes, Gerst takes off the tracking device and floats over to the five 'anchor motes' to switch them off again.
The results from the ISS are relayed to Earth during the next data transmission, and the two DLR researchers begin their analysis. In addition to tracking people or objects, in the long-term the system will also be able to be used as an aid for inventory-taking: "The system is still in its early stages of development; in future, the devices will be much smaller and lighter. Objects equipped with them could transmit their location and be automatically added to the inventory," says Martin Drobczyk, the other PI for the experiment. In addition to the ISS, the system is currently also being tested in the DLR's EDEN ISS greenhouse.
DOSIS measuring devices monitor radiation dose
In the DOSIS 3D experiment, Thomas Berger and his team from the DLR Institute of Aerospace Medicine are constantly monitoring the dose of cosmic radiation to which astronauts on the ISS are exposed. Alexander Gerst brought a total of 11 packages of radiation measuring equipment with him on the Soyuz spacecraft when he embarked on his mission to the ISS on 8 June 2018. Just three days later, on 11 June, he delivered the five-by-five-centimetre orange measuring devices to the Columbus laboratory, where they are held in place with hook-and-loop fasteners.
Two hundred times higher radiation exposure
Radiation exposure in space is many times higher than that on Earth. In order to make more accurate estimates of the dose of high-energy particle radiation received during a long-term mission, the radiation in the Columbus laboratory has been measured continuously since 2009, allowing Berger to draw upon a long-term dataset: "On average, we measure a radiation dose of 700 microsieverts per day, which is more than 200 times the dose at the surface of Earth. We know from this that the shielding on the ISS is already much better than it was for Space Shuttle missions or on the Russian Mir space station."
Warning in the event of danger
Since the beginning of spaceflight, recording radiation exposure has been an indispensable part of every related scientific programme, in particular for manned missions. Various passive and active radiation measurement devices have been developed over recent decades for use in space. The long experience of the DLR Institute of Aerospace Medicine has played a key role in developing such technology. Passive dosimeters give a value for the radiation as a total over time, while active dosimeters measure real-time rates of exposure. "The active measurement devices warn the crew in the event of a solar particle event, when their radiation exposure can suddenly rise sharply. If this happens, the astronauts have to retreat into the better-shielded areas of the ISS for a certain amount of time," explains Berger.
Google Street View for science
In conjunction with the company ThinkSpace, Berger and his team have developed a tool that can be used interactively to display the readings from individual DOSIS measuring devices on a website, in a similar way to Google Street View. "This is the first experiment to make its measurement results readily accessible to the general public. The aim is to allow more data relating to experiments on the ISS to be made available in this way."