Lars Alminde

Educational value and lessons learned from the AAU-CubeSat project

In September 2001 Aalborg university started the AAU-cubesat project that reached it climax when the student built satellite was launched into space on the 30th of June 2003 on top of a former Russian ICBM. AAU-cubesat was among the first five satellites to be launched that are built within the cubesat concept that prescribes a satellite with dimensions 10/spl times/10/spl times/10 cm and mass one kilogram. These constraints clearly limits the possibilities for the satellite in terms of possible scientific missions, but on the other hand: by building satellites of this size a technology push is created that in the future will help to reduce the size of both scientific and commercial satellites and thus help to drive down the launch cost. In this paper described the overall architecture of the AAU-cubesat in order to show what a pico-satellite can be and demonstrate all the fields of engineering which must come together to built a student satellite like the AAU-cubesat. Results from the operation phase will be stated, and recommendations on further work on pico-satellite designs will be given. In addition as the project has been carried through by students then the educational value of the project will be addressed as well.

A strategic approach to developing space capabilities using Cubesat technology

This paper describes the main problems associated with developing a space technology capacity from scratch using a Cubesat approach. The paper goes on to describe development of the GomSpace-α platform, and how it can help support a strategic capacity building approach in a cost-effective manner with low risk.

The AAU-Cubesat Student Satellite Project: Architectural Overview and Lessons Learned

Abstract In September 2001 Aalborg university started the AAU-cubesat projectthat reached its climax when the student built satellite was launched into space on the 30th of June 2003 on top of a former Russian ICBM. AAU-cubesat was among the first five satellites to be launched that are built within the cubesat concept that prescribes a satellite with dimensions 10x10x10cm and mass one kilogram. This paper will describe the overall architecture of the AAU-cubesat in order to show what a pico-satellite can be and demonstrate all the fields of engineering which must come together to built a student satellite like the AAU-cubesat. Results from the operation phase will be stated, and recommendations on further work on pico-satellite designs will be given. In addition as the project has been carried through by students, the educational value of the project will be adressed as well.

A danish perspective on problem based learning in space education

This describes the goals of the Student Satellite Program at Aalborg University (AAU), and the means for implementing it, namely a concept called problem based learning, which is the cornerstone in education at AAU. AAU has, within the last decade, chosen to focus strongly on education in space technology, not because the country lacks aerospace engineers, but because space projects require the students to think about systems rather than individual modules, while providing problems that are technically challenging for the students to solve. This combination makes the graduates very attractive for industry in general, and not only for the space industry

A Quantized State Approach to On-line Simulation for Spacecraft Autonomy

Future space applications will require an increased level of operational autonomy. This calls for declarative methods for spacecraft state estimation and control, so that the spacecraft engineer can focus on modeling the spacecraft rather than implementing all details of the on-line system. Celebrated model based methods such as Kalman filtering techniques and Model Predictive Control (MPC) rely on an on-line model of the system under control that can be simulated in faster than real-time. This becomes a severe challenge when the paradigm of modeling employed is that of hybrid systems where discrete and continuous dynamics co-exists. This paper describes the design and implementation of an efficient engine for simulation of hybrid systems, specifically tailored for on-line applications. The simulation engine, contrary to traditional simulations systems, does not rely on discretisation of time, but instead it works on a discretized state-space where the update of states is determined by a projection of points in time where the trajectory enters a new region. With this approach each state in the model is integrated separately, meaning that sparsity is exploited well. In addition hybrid transitions are located conservatively, i.e. without the need to ever “roll back” the simulation in time.

The SOPHY framework: simulation, observation and planning in hybrid systems

The goal of the SOPHY framework (Simulation, Observation and Planning in Hybrid Systems) is to implement a multi-level framework for description, simulation, observation, fault detection and recovery, diagnosis and autonomous planning in distributed embedded hybrid systems. A Java-based distributed, hybrid simulator is implemented to demonstrate the virtues of SOPHY. The simulator is set up using subsystem models described in human readable XML combined with a composition structure allowing virtual interconnection of subsystems in a simulation scenario. The performance of the simulator has shown to be very dependent on the way its distributability is utilised revealing both the limitations and strengths introduced by delegating computation tasks in a distributed architecture.

OBJECTIVE DIRECTED CONTROL USING LOCAL MINIMISATION FOR AN AUTONOMOUS UNDERWATER VEHICLE

Abstract This paper presents a new method for control of complex MIMO plants based on a quantised state description. The control algorithm solves a minimisation problem for a set of user defined convex control objective functions with the plant dynamics as a constraint. The solution makes use of local linear models that are effectively calculated by propagating the state on-line using a quantised state description. The method is demonstrated on a model of an autonomous underwater vehicle.

An automated test framework for experimenting with stochastic behavior in reconfigurable logic

In this paper, we present an automated test framework for the characterization of stochastic behavior in logic circuits. The framework is intended as a platform for experimenting with and providing statistics on digital architectures given behavioral uncertainties at the gate-level. As an experimental platform, we propose to use an FPGA due to the proven value of reconfigurable architectures in design space exploration. We hypothesize that stochastic behavior can be introduced in FPGAs using external noise sources; a fact that is later confirmed by characterizing the behavior of an FPGA IO block subject to voltage/frequency scaling and Vdd-noise. The framework provides easy interfacing with laboratory equipment, design of experiment capabilities and automatic test execution, thus providing a powerful tool for characterizing stochastic behavior in reconfigurable logic.

ADS-B in space: Decoder implementation and first results from the GATOSS mission

ADS-B is increasingly used for air traffic control in areas covered by terrestrial receivers; however, its limited range makes it unsuitable for other areas such as the oceans. To overcome this limitation, it has been proposed to receive ADS-B signals from low earth orbit nano-satellites and relay them to the terrestrial receivers. This paper gives an overview of the GATOSS mission and of its highly-sensitive ADS-B software-defined radio receiver payload. Details of the design and implementation of the receivers decoder are introduced. The first real-life, space-based results show that ADS-B signals are indeed successfully received in space and retransmitted to a terrestrial station by the GATOSS nano-satellite orbiting at 700+ km altitudes, thus showing that GATOSS is capable of tracking flights, including transoceanic ones, from space.

Empirical verification of fault models for FPGAs operating in the subcritical voltage region

We present a rigorous empirical study of the bit-level error behavior of field programmable gate arrays operating in the subcricital voltage region. This region is of significant interest as voltage-scaling under normal circumstances is halted by the first occurrence of errors. However, accurate fault models might provide insight that would allow subcritical scaling by changing digital design practices or by simply accepting errors if possible. To facilitate further work in this direction, we present probabilistic error models that allow us to link error behavior with statistical properties of the binary signals, and based on a two-FPGA setup we experimentally verify the correctness of candidate models. For all experiments, the observed error rates exhibit a polynomial dependency on outcome probability of the binary inputs, which corresponds to the behavior predicted by the proposed timing error model. Furthermore, our results show that the fault mechanism is fully deterministic - mimicking temporary stuck-at errors. As a result, given knowledge about a given signal, errors are fully predictable in the subcritical voltage region.