Benjamin Männel
Type of contribution: oral
Session: 2

Co-location of VLBI with other techniques in space: a simulation study

Benjamin M\"annel, ETH Zurich Markus Rothacher, ETH Zurich

The quality of the links between the different space geodetic techniques (VLBI, SLR, GNSS and DORIS) is still one of the major limiting factors for the realization of a unique global terrestrial reference frame that is accurate enough to allow the monitoring of the Earth's system. Typically the local ties between the techniques are estimated during terrestrial surveyings, unfortunately for many fundamental sites the offset values are inaccurate, incomplete or even missing. A good alternative arises by additional co-locations in space, where the different space geodetic techniques are combined on board a satellite using eccentricities measured before launch. While quite a few scientific satellites provide GPS and SLR data in good quality for such co-locations in space (e.g. JASON1, CHAMP, GRACE, GOCE, TerraSar-X, TanDEM-X), the NanoGEM and GRASP missions, specifically dedicated to co-location, will also integrate a VLBI transmitter (and a DORIS receiver). The optimal use of VLBI signals transmitted by a satellite requires some special mission characteristics especially concerning the orbital parameters. Based on orbit simulations with various values for the orbital elements, in particular for the satellite altitude, the observability of the co-location satellite, depending on the VLBI baseline configurations and the elevation cutoff angle, will be discussed. In addition, a realistic scenario has to take into account the slew rates of the telescope and the available observation time. First results of a variance-covariance study concerning the estimates of the orbit, the station coordinates and tropospheric delays will be presented.