3D-DOS

3D-DOS is an experiment that shall characterize the radiation environment aboard the ISS. The international community celebrated the station’s 20th birthday last year, so you would expect ours is not the first experiment pursuing that objective. And indeed, radiation sensors have been an integral part of spacecraft instrumentation for decades. But we will need better technologies than currently available for future endeavors into deep space.

First things first, though: Why is a thorough understanding of the space radiation environment so important after all?

The international space community has shifted its attention away from the ISS and towards the manned exploration of deep space. The station is still heavily utilized for basic research under microgravity conditions—even more so than during the first years of its existence—but the research is increasingly conducted and financed by private companies rather than by national space agencies. Instead, missions to the Moon and to Mars are today’s focus of publicly funded space programs. In recent years, a number of high-profile missions has been proposed around the world. In cooperation with the European Space Agency and other ISS partners, the U.S. space agency NASA plans to build a Gateway station in lunar orbit. After originally floating the idea, ESA’s director general Johann-Dietrich Wörner has repeatedly reiterated his support for an international Moon Village on the lunar surface. Actors from industry plan privately funded missions to the Moon and Mars. SpaceX’s Elon Musk even talks about the permanent colonization of Mars before the turn of the century.

While considerable effort is being put into the development of the infrastructure necessary to achieve such feats, relatively little is known about the medical implications of deep-space missions. Especially the effects of prolonged exposure to the heightened levels of radiation are not well understood. Long-term medical studies cannot be conducted on Earth because our planet’s atmosphere and magnetosphere protect us from most of the cosmic and solar radiation. Some studies can be performed on the ISS, even though Earth’s magnetic field still provides substantial shielding against radiation at the station’s orbital altitude. Indeed, this natural protection is what allows astronauts to safely live in space for months at a time in the first place. Lacking a deeper understanding and the appropriate means of artificial shielding, long-term space missions without such protection must still be considered too risky.

To learn about the health risks of exposure to the space radiation environment, astronauts are examined regularly during and after their stay in space. In addition, the local radiation environment inside the spacecraft must be monitored constantly to be able to examine whether observed biological effects can be attributed to radiation exposure or to other environmental conditions, such as the lack of gravity. To achieve this, a multitude of different sensors is being operated aboard the ISS. So far, no single instrument can provide a full picture of the radiation environment. Even the combined data of all instruments does not yet deliver the required level of accuracy. Another issue is that most current instruments are rather large and bulky—which is especially problematic aboard spacecraft, where space is at a premium and every kilogram brought into orbit costs five-figure sums of (taxpayer) money.

Our goal is to develop radiation sensors that provide more information and better measurements than current devices but are smaller, lighter, and easier to use at the same time. 3D-DOS utilizes the research we have been conducting as doctoral students throughout the past years but will be the first time our instruments fly into space.

The monitoring of radiation doses astronauts receive is a crucial aspect of every manned space mission. Due to the unpredictable nature of the space radiation environment and the severe health risks associated with it—ranging from short-term cognitive impairment at relatively low doses to an increased risk of developing cancer to the fatal form of acute radiation syndrome at very high doses—deep-space missions are not possible without it. Radiation sensors must therefore be considered an integral part of every spacecraft’s life support system.

So far, the space industry’s focus has primarily been the quick, inexpensive, and reliable access to space. Now we must ensure that we can keep our astronauts safe on trips to the Moon or to Mars. We hope that our instrument can contribute to these efforts by providing some of the necessary data.

Through our research at TUM, we were able to demonstrate that the technologies we intend to employ in 3D-DOS work. We must now use the knowledge we acquired to develop the concept for a new class of radiation sensors that can reliably operate in space. This process will require us to build several prototypes that we must test in the laboratory and at particle accelerator facilities. Once we have arrived at a final design, we must build and test the flight model of the experiment and an identical version that stays in our laboratory for troubleshooting purposes. Only then are we ready to hand over the experiment for shipment to the ISS.

With a base funding of 180,000 € we can develop an experiment with the full basic functionality of the sensors we intend to test and cover all expenses required operate 3D-DOS aboard the ISS. If we reach at least 240,000 €, we can add high-resolution silicon-based tracking detectors to the sensors, which would allow us to determine the directional dependence of radiation with a much higher precision. If we reach the funding goal of 265,000 €, we would even be able to use radiation-hardened components for the control and data acquisition electronics of 3D-DOS—an absolute must for high-reliability sensors that shall one day operate aboard spacecraft beyond Earth orbit!

3D-DOS shall demonstrate new technologies for monitoring the radiation environment in spacecraft and habitats. Current sensors are oftentimes quite large and bulky because the underlying technologies and detection principles make it hard to miniaturize the devices. On top of that, many sensors are only sensitive to particular parts of the radiation spectrum. Consequently, a multitude of sensors must be used to cover the complete spectrum, taking up more space than required for newer, more compact devices.

Our concept combines the advantages of several sensor into one device. The three dosimeters of 3D-DOS can measure the flux protons and other charged particles, which cause a significant portion of the radiation exposure in space, but are also sensitive to neutrons and gamma rays. This allows us to precisely monitor the radiation environment at the instrument’s location. We can also determine the directionality of incoming radiation in the dosimeters’ fields of view. With its three sensors 3D-DOS can thus help to better assess the shielding effectiveness of the station’s outer walls than currently possible. Such data can help to significantly improve the shielding layouts of future spacecraft.

We use state-of-the-art materials and sensors to build our dosimeters. Some components have already been tested in space, others are so new that we are one of the first groups using them. We have already performed many tests in our laboratories to make sure we know how to reliably operate these components—now it is time for us to make the next step and bring them into space!

Our team mostly consists of PhD students working in the fields of physics and astronautics. All of us had the opportunity to work on space missions during our studies, among them the MOVE-II nanosatellite that was launched into space on December 3, 2018. Together, we have also participated in the REXUS/BEXUS student program organized by the German Aerospace Center (DLR) and the Swedish National Space Agency (SNSA). During the program, we performed an experiment aboard a stratospheric research balloon launched from Esrange Space Center in northern Sweden.

Martin J. Losekamm

M.Sc. – Project management and hardware development

Martin holds a M.Sc. in Applied and Engineering Physics from TUM and now works as a PhD student at the Institute of Prof. Stepan Paul. His research interest is the development of instrumentation for spacecraft.

Thomas Pöschl

M.Sc. – Data analysis and reconstruction

Thomas holds a M.Sc. in Nuclear, Particle and Astrophysics from TUM. Currently, Thomas is doing his PhD research at TUM, focusing on the development of real-time analysis algorithms for space radiation monitors and other particle detectors.

Nicolas Appel

M.Sc. – Software development

Nicolas holds a M.Sc. in Informatics from TUM. He works as a PhD student at the Institute of Prof. Ulrich Walter, developing signal-processing and communication electronics for spacecraft.

Sebastian Rückerl

M.Sc. – Software development

Sebastian also holds a M.Sc. in Informatics from TUM and is a PhD student at Prof. Walter’s group. In cooperation with Nicolas, he is developing signal-processing and data-handling electronics for satellites.

Verena Eiblmeier

B.Sc. – Hardware development

Verena received her B.Sc. in Physics from the Ludwig Maximilian University of Munich and is currently pursuing her M.Sc. studies in Nuclear, Particle and Astrophysics at TUM. Her work on 3D-DOS is part of her Master’s thesis at Prof. Laura Fabbietti’s group.

We have successfully demonstrated the underlying technologies and working principles of the 3D-DOS sensors in numerous tests at TUM and Paul Scherrer Institute, a research institution and particle-accelerator facility in Switzerland. That is why we are confident that our experiment will work!

With 3D-DOS, we will employ our research for operational space radiation dosimetry for the first time. For us, the experiment is the first step in demonstrating that we can produce a new class of radiation monitors that rely on state-of-the-art technologies and are more robust and less expensive than current devices. We hope that 3D-DOS, if it is successful, can pave the way for a wider use of our sensors—possibly even aboard spacecraft that will fly to Mars or other planets! That would be our small contribution to the exploration of outer space.