| Date: | 2014-08-06 15:44:04 | |
| Sender: | ”Prof. Schreiber Ulrich” <schreiber@fs.wettzell.de> | |
| Subject: | [SLR-Mail] No.2266: Introduction of the ELT project | |
| Author: | unknown | |
| Content: | The European Laser Timing (ELT) experiment, in preparation for the Columbus module on the international space station represents an optical time transfer technique, similar to T2L2 on Jason 2. The major difference is the integral combination with the microwave two-way-time-and-frequency-transfer technique and the atomic clock ensemble in space (ACES), a Cs standard and a H-maser. A GNSS receiver attached to the ACES package provides a continuous orbit for the atomic clocks at high resolution. This offers a unique opportunity to transfer time over intercontinental distances and to synchronize distant clocks with an unprecedented accuracy. A fuller description of ACES and ELT can de found at (Hess et al. ”The ACES mission: System Development and test status; Acta Astronautica 69, 929 - 938 (2011) doi:10.1016/j.actaastro.2011.07.002) In order to utilize ACES and ELT for accurate time transfer and to study the potential of optical time transfer, a number of SLR facilities with access to accurate atomic clocks (Cs secondary standards, H-masers or optical clocks) on different continents are needed to support this activity. The goal is a single shot precision of less than 50 ps for the laser link to the ELT module. In order to achieve this and to reduce power and weight requirements on the flight hardware, the detector on the Columbus module is operated in single photon mode. Furthermore the wide acceptance angle detector is automatically gated relative to the spacecraft clock. There are a number of requirements for the SLR stations to fullfill in order to achieve the science goals. These are: control capability of the laser fire epoch to about 100 ns shot by shot operation on the second harmonic of 532 nm +/- 1 nm (spectral filter) eye safe laser operation (with respect to the ISS) fast tracking in order to point at the ISS capability of timing the laser fire epoch to no worse than 5 ps in the local timescale capability to send fullrate data (including all laser fire epochs) to the ELT data center rapid data transfer to EDC to allow the ELT data center to update predictions within one orbital period adjustable energy density control in order to meet the single photon space segment response and SLR ground segment operation simultaneously capability to use the ILRS Go/NoGo flag Prior to the ELT participation a calibration with the ELT calibration tool has to be performed in order to establish the SLR system delay for time transfer We encourage ILRS stations to consider participation in this project. Details of these requirements are being discussed at the Washington ILRS workshop within the transponder working group. Kind regards, Ulrich Schreiber, Ivan Prochazka and Anja Schlicht ------------------------------------------------------------------------------- Prof. Ulrich Schreiber Forschungseinrichtung Satellitengeodaesie Technische Universitaet Muenchen - Fundamentalstation Wettzell - D-93444 Bad Koetzting Tel.: +49 9941 603113 Fax.: +49 9941 603222 schreiber@fs.wettzell.de ulrich.schreiber@bv.tum.de ----------------------------------- Prof. Ulrich Schreiber Depart. of Physics & Astronomy University of Canterbury Private Bag 4800 Christchurch, 8020 New Zealand Fax: +64 3 3642469 ulrich.schreiber@canterbury.ac.nz The European Laser Timing (ELT) experiment, in preparation for the Columbus module on the international space station represents an optical time transfer technique, similar to T2L2 on Jason 2. The major difference is the integral combination with the microwave two-way-time-and-frequency-transfer technique and the atomic clock ensemble in space (ACES), a Cs standard and a H-maser. A GNSS receiver attached to the ACES package provides a continuous orbit for the atomic clocks at high resolution. This offers a unique opportunity to transfer time over intercontinental distances and to synchronize distant clocks with an unprecedented accuracy. A fuller description of ACES and ELT can de found at (Hess et al. ”The ACES mission: System Development and test status; Acta Astronautica 69, 929 - 938 (2011) doi:10.1016/j.actaastro.2011.07.002) In order to utilize ACES and ELT for accurate time transfer and to study the potential of optical time transfer, a number of SLR facilities with access to accurate atomic clocks (Cs secondary standards, H-masers or optical clocks) on different continents are needed to support this activity. The goal is a single shot precision of less than 50 ps for the laser link to the ELT module. In order to achieve this and to reduce power and weight requirements on the flight hardware, the detector on the Columbus module is operated in single photon mode. Furthermore the wide acceptance angle detector is automatically gated relative to the spacecraft clock. There are a number of requirements for the SLR stations to fullfill in order to achieve the science goals. These are:
We encourage ILRS stations to consider participation in this project. Details of these requirements are being discussed at the Washington ILRS workshop within the transponder working group. Kind regards, Ulrich Schreiber, Ivan Prochazka and Anja Schlicht ------------------------------------------------------------------------------- Prof. Ulrich Schreiber Forschungseinrichtung Satellitengeodaesie Technische Universitaet Muenchen - Fundamentalstation Wettzell - D-93444 Bad Koetzting Tel.: +49 9941 603113 Fax.: +49 9941 603222 schreiber@fs.wettzell.de ulrich.schreiber@bv.tum.de ----------------------------------- Prof. Ulrich Schreiber Depart. of Physics & Astronomy University of Canterbury Private Bag 4800 Christchurch, 8020 New Zealand Fax: +64 3 3642469 ulrich.schreiber@canterbury.ac.nz |