In particular, Doppler data have been the primary data type for this application (e.g. The key difference between SLR/LLR and ILR is that ILR requires a transponder on both the ground and space segments, as opposed to the purely passive space segment in SLR/LLR (retroreflectors).Ĭurrently, deep-space missions largely rely on the use of radio tracking for their orbit determination and the associated parameter estimation. 2002), Lunar Laser Ranging (LLR Murphy 2013) as well as Laser Time Transfer (LTT Prochazka et al. The technology for such a system derives strongly from Satellite Laser Ranging (SLR Pearlman et al. A tracking data type that will become available for future planetary missions is Interplanetary Laser Ranging (ILR) (Degnan 2002). Similarly, laser ranging data will be superior for the construction of planetary ephemerides and the improvement of solar system tests of gravitation, both for orbiter and for lander missions.įor both Earth-orbiting and planetary missions, a variety of tracking observables is available from which the trajectory of the spacecraft can be reconstructed. Laser ranging data, however, are shown to have a significant advantage for the retrieval of rotational and tidal characteristics from landers. ILR data will be able to supplement the orbiter tracking data used for the estimation of parameters with a once-per-orbit signal. This indicates that Doppler tracking will typically remain the method of choice for gravity field determination and spacecraft orbit determination in planetary missions. We find that ILR has the potential for superior performance in observing signatures in the data with a characteristic period of greater than 0.33–1.65 hours (assuming 2–10 mm uncertainty for range and 10 \(\upmu \)m/s at 60 s for Doppler). We show that mm-precise range normal points are feasible for ILR, but mm-level accuracy and stability in the full analysis chain are unlikely to be attained, due to a combination of instrumental and model errors. We use both an analytical approximation and numerical analyses of the relative sensitivity of ILR and radio Doppler observables for more general cases. Subsequently, we analyse the sensitivity of radio Doppler and laser range measurements in representative mission scenarios for parameters of interest. We first provide an overview of the near-term attainable quality of ILR, in terms of both the realization of the observable and the models used to process the measurements. In this article, we compare the relative strength of radio Doppler and laser range data for the retrieval of parameters of interest in planetary missions, to clarify and quantify the science case of ILR, with a focus on geodetic observables. ILR does not produce Doppler data, however. Two-way ILR will provide range data that are about 2 orders of magnitude more accurate than radio-based range data. Future planetary missions may use Interplanetary Laser Ranging (ILR) as a tracking observable. At present, tracking data for planetary missions largely consists of radio observables: range-rate (Doppler), range and angular position (VLBI/ \(\Delta \)DOR).
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