Reports 2007-2008Space Debris ProyectINTRODUCTION:
This document briefly describes how the Geostationary and Transfer Orbits Object Survey has been carried out during the period of time that ranges from January 2007 to May 2008, at the Optical Ground Station (OGS), under subcontracts: 1) Subcontract E/17825-01 of contract 17825/03/D/HK ESOC-ESA “Space Debris Optical Observations and Analysis with ESA 1M Telescope”. 2) Subcontract E/15836-01 of contract 15836/01/DK/HK ESOC-ESA “Extension of Optical Observations Capability for the Zeiss 1M Telescope”, Phase 1 and 2. We present some statistics about the site atmospheric conditions (seeing), the distribution of the observation nights and the different technical problems found during the achievement of the observational campaigns of the year 2007 and beginning of 2008.
THE CAMPAIGNS:The Geostationary and Transfer Orbits Object Survey has been distributed over monthly campaigns, selected, among other criteria, to coincide with as much dark nights as possible around the New Moon, to avoid scattered light. Figure 1 shows a diagram of the distribution of the observation nights during the different campaigns. The number that appears at the end of each row of the diagram indicates the number of observation nights each month (these will be considered as “good nights”, according to the criteria defined in the contracts). Those nights were the astronomer was not at the observatory (due to a prolonged bad weather situation or persistent technical problems) have not been taken into account.
Figure 1. Distribution of the observation nights (“good nights” according to the contract definition) of the 2007-2008 campaign of the Geostationary and Transfer Orbits Object Survey. DISTRIBUTION OF THE OBSERVATION TIME:We have planned a total of 1507,18 hours in the 2007-2007 Space Debris Campaign (finishing in May 2008), spread over 99 effective observation nights (“good nights” according to the contract definition).
Figure 4. Distribution of the observing time during the whole period of the 2007-2008 Space Debris Campaign (finishing in May 2008).
As Figure 4 shows, around 65% of the observing time in all the campaigns, was dedicated to do observations, which is a clear indication of the good weather conditions prevailing over the years. The other two aspects that caused lost time were software problems (mainly at the Level-1 Control System), and problems related to the building itself (dome control and general power down). During the end of 2007 and beginning of 2008, several tests were made to start using the new control system for the camera and the telescope. From February 2008 on, this new system has been used has the definite control system. All in all, we did not lose too much observational time due to these problems (less than 5%), which gives an idea of the efficiency of the overall system.
SEEING CONDITIONS:We have measured seeing values during the observational period of the 2007 Geostationary and Transfer Orbits Object Survey. These measurements include atmospheric seeing and perturbations introduced by dome-telescope system. The technique used to obtain these values is the following. In order to focus the telescope at the beginning of a typical observation night we normally take an unbinned image of 10 secs. Using the IRAF imexam task, we observe radial profiles and note down values of the FWHM of different stars in the field of view. Once we find the appropriate value of the focus, we take the maximum and the minimum FWHM and get the average value. Finally we multiply this value with the CCD resolution : 0,62 arcsec / pixel. We started to use the new control system for the camera systematically from February 2008 on. This new software presents a particular program designed to find the best focus value at the beginning of the night, but does not provide the user with any astronomical package to measure seeing values.
Figure 5. Histogram of seeing values for 2007 Space Debris Campaign.
The great sky quality of the Observatorio del Teide can be seen at Figure 5. It shows the distribution of seeing values during all the effective nights over the 2007 Space Debris campaign. The histogram presents its maximum near 1,0 arcsec. The dome of the Optical Ground Station is quite big and its contribution to the perturbations of the overall system is not negligible. Some simulations and the experience gained in other telescopes led to a typical value of 0,5 arcsec, which has been conveniently subtracted in order to do the histogram.
CONCLUSIONS:The main conclusions that can be derived from this report are: • No significant problems appeared during the execution of the Level-1 Telescope Control System or the On-line Data Processing System, and the ones that appeared were easily solved, as can be seen in Figure 4. The new control system installed, that works normally since February 2008, is quite stable. • Control systems related to the dome and the building had also an excellent behaviour. • Excellent weather conditions contributed to a great extent to increase the number of “operational” observing nights, and the great sky quality of the Observatorio del Teide has been also decisive for the achievement of the whole project. • After having seen the results of the Space Debris campaigns of 2007 and beginning of 2008, we can conclude that they have undoubtedly been good campaigns, regarding the distribution of the observing time and seeing conditions.
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