The European Space Agency’s Planck satellite was launched on 14 May 2009, and surveyed the sky stably and continuously between August 2009 and October 2013. The scientific analysis of the Planck data ...requires understanding the optical response of its detectors, which originates partly from a physical model of the optical system. In this paper, we use in-flight measurements of planets within ∼1° of boresight to estimate the geometrical properties of the telescope and focal plane. First, we use observed grating lobes to measure the amplitude of mechanical dimpling of the reflectors, which is caused by the hexagonal honeycomb structure of the carbon fibre reflectors. We find that the dimpling amplitude on the two reflectors is larger than expected from the ground, by 20% on the secondary and at least a factor of 2 on the primary. Second, we use the main beam shapes of 26 detectors to investigate the alignment of the various elements of the optical system, as well as the large-scale deformations of the reflectors. We develop a metric to guide an iterative fitting scheme, and are able to determine a new geometric model that fits the in-flight measurements better than the pre-flight prediction according to this metric. The new alignment model is within the mechanical tolerances expected from the ground, with some specific but minor exceptions. We find that the reflectors contain large-scale sinusoidal deformations most probably related to the mechanical supports. In spite of the better overall fit, the new model still does not fit the beam measurements at a level compatible with the needs of cosmological analysis. Nonetheless, future analysis of the Planck data would benefit from taking into account some of the features of the new model. The analysis described here exemplifies some of the limitations of in-flight retrieval of the geometry of an optical system similar to that of Planck, and provides useful information for similar efforts in future experiments.
Planck pre-launch status: The optical system Tauber, J. A.; Norgaard-Nielsen, H. U.; Ade, P. A. R. ...
Astronomy and astrophysics (Berlin),
09/2010, Letnik:
520
Journal Article
Recenzirano
Planck is a scientific satellite that represents the next milestone in space-based research related to the cosmic microwave background, and in many other astrophysical fields. Planck was launched on ...14 May of 2009 and is now operational. The uncertainty in the optical response of its detectors is a key factor allowing Planck to achieve its scientific objectives. More than a decade of analysis and measurements have gone into achieving the required performances. In this paper, we describe the main aspects of the Planck optics that are relevant to science, and the estimated in-flight performance, based on the knowledge available at the time of launch. We also briefly describe the impact of the major systematic effects of optical origin, and the concept of in-flight optical calibration. Detailed discussions of related areas are provided in accompanying papers.
Polarimetric mode of MIRAS Martin-Neira, M.; Ribo, S.; Martin-Polegre, A.J.
IEEE transactions on geoscience and remote sensing,
08/2002, Letnik:
40, Številka:
8
Journal Article
Recenzirano
The L-band Microwave Imaging Radiometer with Aperture Synthesis (MIRAS), scheduled to be flown as single payload on board the European Soil Moisture and Ocean Salinity (SMOS) mission, has a very wide ...field of view and synthesizes narrow beams by means of two-dimensional (2-D) interferometry, the same concept used in radio astronomy. Wide field of view is indeed a key feature of this radiometer, which leads naturally to the measurement of the full vector of brightness temperatures of the image. This paper analyzes the theory of polarimetry in the 2-D wide-field-of-view microwave interferometry and describes the way MIRAS will measure the polarimetric brightness temperatures.
The Planck mission Polegre, A. Martin; Tauber, J.; Crone, G. ...
Proceedings of the Fourth European Conference on Antennas and Propagation,
2010-April
Conference Proceeding
This paper describes the main characteristics of the latest medium-sized mission launched by ESA as part of its science programme. An overview of the telescope and cryogenic system is given.
This paper summarises the work done over the last few years on the prediction of the RF performance of the Planck telescope, which was done initially to support the design phase, and later to assess ...compliance to specifications and to infer the in-flight performance of the telescope once in its operational orbit.
GAIA is one of the cornerstone space science missions of the European Space Agency (ESA). It is scheduled for launch in 2012, and will improve the accuracy in the knowledge of the position, velocity, ...and magnitude of stars provided by its predecessor, Hipparcos. The dynamics of the GAIA spacecraft in orbit, together with the high volume of scientific data to downlink to Earth, impose very demanding requirements on the design of the antenna for the science telemetry link. Additionally, the antenna must not make use of any sort of moving parts, in order to avoid any perturbation to the attitude of the platform that would degrade the scientific output. The selected baseline concept for the GAIA science and telemetry link antenna is a conformal phased array, with radiating elements located on the surface of a truncated cone. This antenna makes use of a semi-active excitation scheme, so that a smooth steering of the beam is guaranteed, avoiding any risk of losing the receiver lock on the ground station while transmitting. Feeding the subarrays through Butler matrices allows for the amplifiers to work at a constant operating point, where they are most efficient; it also insures a graceful performance degradation, should any of the amplifiers fail. The work reported on in this paper is a result of various contracts awarded by ESA to Alcatel Space, within the framework of the Agency's technological research program. These contracts have provided the framework for the design, manufacturing and testing of the antenna, in order to guarantee that all the required technology will be timely available for the antenna flight model. A partial elegant breadboard (EBB) of the antenna has been manufactured, allowing representative radiation tests. The predicted performance of the complete antenna, based on the partial EBB measurements, is fully compliant to specifications. Additionally, some environmental tests have also been carried out to verify the performance of the antenna in the predicted space flight environment.
The Planck mission and its optical system Tauber, Jan A.; Nielsen, P.; Martin-Polegre, A.
The 8th European Conference on Antennas and Propagation (EuCAP 2014),
2014-April
Conference Proceeding
This paper will provide a very brief overview of the Planck mission, its scientific objectives, the key elements of its technical design, current status, and recent scientific results. I will also ...give an overview of the optical system of Planck, how it was characterized in flight, and how it affects the science results.
Following several earlier feasibility studies, in 1998 ESA began the MIRAS Demonstrator Pilot Project within the Agency's Technology Research Programme (TRP) and General Support Technology Programme ...(GSTP) in an attempt to provide a technology solution to the inherent challenges of L-band radiometry. The objective was to build a representative element of the MIRAS instrument, which has subsequently been selected as the main payload for the Soil Moisture and Ocean Salinity (SMOS) mission. A second phase was initiated in April 2001 to demonstrate key end-to-end instrument performances, including antenna deployment and image validation, following approval of the SMOS mission Phase-A at the end of 1999.
Accurate fitting of the noisy irregular amplitude only main beam data is essential for the retrieval of the Planck space telescope geometry. Therefore, a novel two-step fitting algorithm which ...focuses on the spatial dependency of the in-flight measurements has been implemented. To reduce both the noise and the size of the dataset a spatial filter is applied, without reducing the amount of pattern information. Thereafter, a Kriging, fitting is performed, providing a smooth model with a significant noise level reduction. As a result, this algorithm provides a much more accurate and smoother result, reasonable error estimates and runtimes several orders of magnitudes faster than the previous algorithms.
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