Carsten Scharlemann’s research while affiliated with University of Applied Sciences Wiener Neustadt and other places

CubeSats have a 65% success rate. Failures derive from design mistake or components malfunctions. To improve the success rate, Technical University of Dresden and FHWN (University of Applied Sciences Wiener Neustadt) developed GREATCUBE+, a software tool for the conceptual design of CubeSats. Its layered structure comprises three levels: empirical, where successfully flown missions are used for an initial tradeoff; analytical, where a design refinement is performed; and numerical, for the final assessment of the proposed architecture. The tool provides teams with information related to commercial off-the-shelf products which will satisfy the mission requirements. To turn this software into a universally applicable tool, it is possible to perform the design of CubeSat mission with many payload’s typologies such as attitude determination and control subsystem, telemetry telecommunication and command, onboard computer, propulsion unit and technology demonstration or scientific payloads. GREATCUBE+ has been validated using the information of existing CubeSats as baseline for its simulation. The achievable accuracy when comparing the simulated outcomes and the real design is of almost 100% for volumes, 90% for masses, and 80% for power generation. By implementing this tool during the conceptual development phase, it is hoped that teams could benefit in reliability thanks to the usage of flight proven equipment recommended via GREATCUBE+ together with a quicker development time.

CubeSats are a type of spacecraft which have become popular since the early 2000. They are known for their quick development time and low cost, when comparing them to larger satellites. However, there is a significant drawback which has been recorded during these years of operations, namely an high failure rate which turns almost half of them into space debris. The reasons behind these malfunctions are often attributed to flawed spacecraft design choices or failures of commercial off-the-shelf (COTS) products. To improve the design of CubeSats, several software tools for performing the conceptual design have been proposed. These tools are often limited in their capabilities and are not suitable for all types of CubeSat missions. To address this issue, the University of Applied Sciences Wiener Neustadt (FHWN) in cooperation with Technische Universität Dresden is developing a software tool called GREATCUBE+. Its goal is to increase the success rate of CubeSats by providing a satellite model which is composed of commercial-off-the-shelf (COTS) products backed up by empirical heritage, analytical proof, and numerical analysis. One of the main features of this tool is the ability of dealing with different typologies of payloads. GREATCUBE+ has been validated with various successful CubeSat missions and it provides design solutions with an accuracy of above 90% when it comes to CubeSat weights and volumes. Using this software, CubeSat design teams can proceed from the conceptual development to the testing and assembly phases quicker, hoping to result in higher quality CubeSats and fewer failures.

Based on its successful CubeSat mission PEGASUS, the University of Applied Sciences Wiener Neustadt (FHWN) is preparing its new CubeSat mission called CLIMB. CLIMB is a 3U CubeSat that will be launched to a low, circular orbit of about 500 km. Using a Field Emission Electric Propulsion (FEEP) system commercialized by the company ENPULSION, the satellite will be lifted to an elliptical orbit with its apogee around 1000 km – well inside the inner Van Allen belt. During its 1.5 yearlong ascent and its operation in the Van Allen belt, the satellite will continuously monitor the space radiation with a RadFET dosimeter payload and the impact on CLIMB’s subsystems. Comparisons with radiation testing on ground will allow the assessment of the capability of ground tests to predict effects of space radiation on CubeSat subsystems. The operation of the propulsion system will raise the satellite’s apogee on average 16 times a day. A comprehensive analysis has been conducted to assess its collision probability throughout its mission time. Using various tools, provided by ESA (CROC, MASTER and the DRAMA ARES python package), the collision probability for the entire mission duration (~3 years) was calculated to be 3.38 × 10-5, i.e. a magnitude smaller than the requested probability of 10-4. The second payload of CLIMB is an anisotropic magnetoresistance (AMR) magnetometer with a, for CubeSats high, sensitivity of about 10 nT RMS. The first results of measurements with this COTS based magnetometer are presented as well as experimental assessments of the satellite’s magnetic cleanliness. The benign thermal conditions on CubeSats operating close to Earth are complicated by the relatively high-power propulsion system onboard CLIMB. Detailed numerical analysis (ANSYS, ESATAN) and experimental verifications resulted in the identification of possible methods to deal with up to 18 W of dissipated electric power. The main heat sources are the thruster and the battery unit, during thruster operation

In tenuous plasma the floating potential of sunlit spacecraft reaches tens of volts, positive. The corresponding field disturbs measurements of the ambient plasma by electron and ion sensors and can reduce micro-channel plate lifetime in electron detectors owing to large fluxes of attracted photoelectrons. Also the accuracy of electric field measurements may suffer from a high spacecraft potential. The Active Spacecraft Potential Control (ASPOC) neutralizes the spacecraft potential by releasing positive charge produced by indium ion emitters. The method has been successfully applied on other spacecraft such as Cluster and Double Star. Two ASPOC units are present on each spacecraft. Each unit contains four ion emitters, whereby one emitter per instrument is operated at a time. ASPOC for the Magnetospheric Multiscale (MMS) mission includes new developments in the design of the emitters and the electronics. New features include the use of capillaries instead of needles, new materials for the emitters and their internal thermal insulators, an extended voltage and current range of the electronics, both for ion emission and heating purposes, and a more capable control software. This enables lower spacecraft potentials, higher reliability, and a more uniform potential structure in the spacecraft’s sheath compared to previous missions. Results from on-ground testing demonstrate compliance with requirements. Model calculations confirm the findings from previous applications that the plasma measurements will not be affected by the beam’s space charge. Finally, the various operating modes to adapt to changing boundary conditions are described along with the main data products.

Hydrogen peroxide is under investigation with regard to its potential to replace the presently used highly toxic oxidizers such as NTO or MON-3. Catalytically decomposed hydrogen peroxide results in a steam-oxygen mixture at elevated temperature and can be used either as a monopropellant or as an oxidizer in a bipropellant system. In order to achieve high decomposition efficiencies it is essential to understand and to be able to control the decomposition processes in detail. In particular, the choice of catalyst is one of the most essential issue in designing a propulsion system based on hydrogen peroxide. However a catalyst is defined by a multidimensional parameter matrix including the catalyst nature, diameter, length, inner and outer shape, heat capacity and conductivity of the carrier material, and, manufacturing method and many others. Reliable experimental investigation of a catalyst is a time consuming effort. To guide the experimental assessment, Fotec (formerly Austrian Institute of Technology - AIT) has developed an analytical model of the decomposition implemented into a numerical thermal model. The one dimensional decomposition model coupled to a finite element structural domain of the decomposition chamber is used to investigate the impact of the catalyst and, in addition, of the chamber structure on the decomposition behavior. Special focus is laid on the transitional behavior of hydrogen peroxide conversion to facilitate immediate start-up of the thruster system. The numerical results have been validated with experimental values. The comparison shows high accuracy of the predictions not only in the general decomposition behavior but also in intrinsic details such as the transitional behavior. Major findings of the model such as the existence of a radial temperature gradient across the catalyst have been experimentally validated. These findings point to an overestimation of experimentally determined decomposition performances, in the case of temperature measurements just downstream of the catalysts cental line. Another major finding is the identification of an mass flow overload threshold by the simulation, yielding a sudden decrease in decomposition performance after surpassing the threshold. This sudden decrease in decomposition performance has been experimentally verified.