Papers by Tjorven Delabie
The CubeSpec mission
Space Telescopes and Instrumentation 2022: Optical, Infrared, and Millimeter Wave
Bringing High-precision Pointing Knowledge to CubeSats: A Compact Star Tracker
status: publishe
Astronomy & Astrophysics
Context. There is currently a niche for providing high-cadence, high resolution, time-series opti... more Context. There is currently a niche for providing high-cadence, high resolution, time-series optical spectroscopy from space, which can be filled by using a low-cost cubesat mission. The Belgian-led ESA/KU Leuven CubeSpec mission is specifically designed to provide space-based, low-cost spectroscopy with specific capabilities that can be optimised for a particular science need. Approved as an ESA in-orbit demonstrator, the CubeSpec satellite’s primary science objective will be to focus on obtaining high-cadence, high resolution optical spectroscopic data to facilitate asteroseismology of pulsating massive stars. Aims. In this first paper, we aim to search for pulsating massive stars suitable for the CubeSpec mission, specifically β Cep stars, which typically require time-series spectroscopy to identify the geometry of their pulsation modes. Methods. Based on the science requirements needed to enable asteroseismology of massive stars with the capabilities of CubeSpec’s spectrograph, ...
CubeSats are increasingly used for Earth observation and astronomy missions. One of the requireme... more CubeSats are increasingly used for Earth observation and astronomy missions. One of the requirements on the payloads in these missions is to gather as much light as possible. Given the small dimensions of CubeSats, the obtainable dimensions of the payload optics are reduced. A potential solution, which is examined in this paper is to use deployable optics. We have investigated different methods to deploy the secondary mirror of a Cassegrain telescope in a 6U CubeSat. One of the designs was developed into a prototype. Its performance was simulated and tested. The requirements of an example astronomy mission are used to verify if the deployable telescope could be used in such a mission.
In this paper, a star tracker attitude estimation procedure with increased robustness and efficie... more In this paper, a star tracker attitude estimation procedure with increased robustness and efficiency, using the AIM (Attitude Estimation using optimal Image Matching) al-gorithm, is presented and validated. The unique approach of the AIM algorithm allows us to introduce a reliable quality check which can be efficiently calculated. Unlike ex-isting validation methods, this quality check not only detects that some of the data is unreliable, it also determines which star measurements are unreliable. These unreli-able measurements can be removed from the data set and a new attitude quaternion can be calculated without having to repeat the entire AIM algorithm. This greatly improves the robustness of the attitude estimation, while limiting the computational expense. Furthermore, the structure of AIM allows us to reuse previously calculated data when the change in attitude between subsequent measurements is small. This way, the efficiency of the entire attitude estimation cycle can be inc...
This paper presents a novel centroiding algorithm for star trackers. The proposed algorithm, whic... more This paper presents a novel centroiding algorithm for star trackers. The proposed algorithm, which is referred to as the Gaussian Grid algorithm, fits an elliptical Gaussian function to the measured pixel data and derives explicit expressions to determine the centroids of the stars. In tests, the algorithm proved to yield accuracy comparable to that of the most accurate existing algorithms, while being significantly less computationally intensive. Hence, the Gaussian Grid algorithm can deliver high centroiding accuracy to spacecraft with limited computational power. Furthermore, a hybrid algorithm is proposed in which the Gaussian Grid algorithm yields an accurate initial estimate for a least squares fitting method, resulting in a reduced number of iterations and hence reduced computational cost. The low computational cost allows to improve performance by acquiring the attitude estimates at a higher rate or use more stars in the estimation algorithms. It is also a valuable contribut...
9th National Congress on Theoretical and Applied Mechanics, Brussels, 9-10-11 May 2012 An Invariant Representation to Facilitate Recognition of Rigid Body Motion Trajectories
— This paper presents the experimental validation of an approach based on a coordinate-free repre... more — This paper presents the experimental validation of an approach based on a coordinate-free representation to recognize six DOF rigid body motion trajectories. In this approach, the three dimensional measured position trajectories of arbitrary and uncalibrated points attached to the rigid body are transformed to an invariant, coordinatefree representation of the rigid body motion trajectory. This representation is theoretically independent of the reference frame in which the motion is observed, the chosen marker positions, the linear scale (magnitude) of the motion, the time scale, and the motion profile. To experimentally validate this approach, a large set of motions was recorded with different camera viewpoints, different time scales, motion profiles, and linear or angular scales. The obtained results clearly show that the invariant representation eliminates the dependency on the effects mentioned above, and yields high recognition rates even when motions were recorded under very...
Optimization of a 3D Printed Cubesat Baffle Using Ray Tracing
Star Tracker Algorithms and a Low-Cost Attitude Determination and Control System for Space Missions
CubeSat technology is evolving rapidly. With the increased performance of these small spacecraft ... more CubeSat technology is evolving rapidly. With the increased performance of these small spacecraft platforms, astronomical missions on CubeSats will be flown in the near future. These types of missions have very demanding requirements in terms of spacecraft pointing. At the KU Leuven university, we have developed a compact, highaccuracy attitude determination and control system for CubeSats. The system uses three reaction wheels and a star tracker to deliver high agility and accuracy. In this paper, we will discuss the test and calibration campaign that was carried out. This campaign was instrumental in achieving the performance required by astronomical missions.
An Invariant Representation to Facilitate Recognition of Rigid Body Motion Trajectories
This paper presents the experimental validation of an approach based on a coordinate-free represe... more This paper presents the experimental validation of an approach based on a coordinate-free representation to recognize six DOF rigid body motion trajectories. In this approach, the three dimensional measured position trajectories of arbitrary and uncalibrated points attached to the rigid body are transformed to an invariant, coordinatefree representation of the rigid body motion trajectory. This representation is theoretically independent of the reference frame in which the motion is observed, the chosen marker positions, the linear scale (magnitude) of the motion, the time scale, and the motion profile. To experimentally validate this approach, a large set of motions was recorded with different camera viewpoints, different time scales, motion profiles, and linear or angular scales. The obtained results clearly show that the invariant representation eliminates the dependency on the effects mentioned above, and yields high recognition rates even when motions were recorded under very d...
CUBESPEC: stellar spectroscopy on a CubeSat platform
CUBESPEC is an ESA in-orbit demonstration 6U CubeSat mission, currently in phase A/B. CUBESPEC wi... more CUBESPEC is an ESA in-orbit demonstration 6U CubeSat mission, currently in phase A/B. CUBESPEC will deliver months long series of high-resolution spectroscopy to study the structure of massive stars. The payload consists of a Cassegrain telescope with a rectangular primary mirror of 9 x 19 cm2 and a compact high-resolution echelle spectrograph. We aim at a 2023 launch demonstrating the CUBESPEC concept: providing the astronomical community with a generic solution for affordable space-based spectroscopy. The spectrograph design can be configured with minimal hardware changes for low spectral resolution (R = 50) up to high resolution (R ~ 50000) over a over wavelength ranges between 200–1000nm. CUBESPEC will use the KU Leuven ADCS for coarse pointing of the spacecraft, supplemented with a fine-guidance system using a fast steering mirror to center the source on the spectrograph slit. We present the CUBESPEC design and mission analysis, and give an update of the project status.
Low-Cost Attitude Determination and Control System using Reaction Wheels and Star Tracker
Star Tracker Cost Reduction for Small Satellites
Scientific and Technological Payloads Aboard the B3LSat CubeSat of the QB50 Network
CubeSats are currently being involved in more and more ambitious missions. One example is B3LSat ... more CubeSats are currently being involved in more and more ambitious missions. One example is B3LSat (Belgium Leuven Liege Louvain Satellite), a double-unit CubeSat developed in the framework of the QB50 network. B3LSat will be provided with two scientific and two technological payloads. Scientific measurements will be performed using an ultra-low power ionization sensor, which will probe the atmospheric gas composition by fingerprinting the ionization characteristics of distinct gases, and an optical micro-sensor array aimed at monitoring the etching rate of selected polymer materials exposed to space plasmas. The first technological payload will be a low-cost attitude determination and control system, featuring innovative tracking algorithms for star trackers and extremely high-capacity reaction wheels. In addition, B3LSat will demonstrate in-orbit a novel control algorithm for propellantless rendez-vous and formation flying based on the differential aerodynamic drag concept. The obje...
Low-Cost Star Tracker with Highly Effcient Algorithms
Characterization of reaction wheel micro-vibrations
The EGU General Assembly, 2015
It is accepted that the climate on earth is changing due to a radiative energy imbalance at the t... more It is accepted that the climate on earth is changing due to a radiative energy imbalance at the top of the atmosphere, up to now this radiation imbalance has not been measured directly. The measurement is challenging both in terms of space-time sampling of the radiative energy that is leaving the earth and in terms of accuracy. The incoming solar radiation and the outgoing terrestrial radiation are of nearly equal magnitude – of the order of 340 W/m 2 – resulting in a much smaller difference or imbalance of the order of 1 W/m 2 . The only way to measure the imbalance with sufficient accuracy is to measure both the incoming solar and the outgoing terrestrial radiation with the same instrument. Based on our 30 year experience of measuring the Total Solar Irradiance with the Differential Absolute RADiometer (DIARAD) type of instrument and on our 10 year experience of measuring the Earth Radiation Budget with the Geostationary Earth Radiation Budget (GERB) instrument on Meteosat Second ...
CUBESPEC: low-cost space-based astronomical spectroscopy
Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave
The Sun-earth Imbalance radiometer for a direct measurement of the net heating of the earth
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Papers by Tjorven Delabie