A first performance assessment of two new concepts of satellite gravitational gradiometers
19/09/2016 | 15:30 | Session 1: New missions and concept performance
Author(s): Karim Douch, Hu Wu, Akbar Shabanloui, Phillip Brieden, Jürgen Müller and Gerhard Heinzel
Karim Douch, Hu Wu, Akbar Shabanloui, Phillip Brieden, Jürgen Müller and Gerhard Heinzel
The ESA mission GOCE has been instrumental in mapping the Earth static gravitational field with an unprecedented spatial resolution and precision. One reason for this success is the performance of the onboard electrostatic gradiometer. The need for more accurate and continuous mapping of the gravitational field led us to examine whether it is possible to go beyond GOCE performance (e.g. observing the time-variable component of the field) and to what extent. To answer this question we introduce two promising concepts of gravitational gradiometers. The first one is based on cold-atom interferometry while the second is based on laser interferometry:
- The cold atom interferometer concept envisioned here is the fruit of a collaborative study led by Observatoire de Paris. Because atom interferometers are highly sensitive to rotations, only 2 operational configurations can be implemented, both requiring a stringent attitude control. The first configuration is the so-called nadir pointing case for which the satellite rotates only along the cross-track axis Y and only Vyy is measured. The second configuration is the inertial pointing for which the satellite attitude remains fixed in the inertial frame but enables to measure Vxx, Vyy and Vzz. In both cases it is estimated that a white noise of 3.5 mE/Hz1/2 would contaminates the gradients measurements.
- The laser interferometry concept is similar to GOCE: pairs of electrostatic accelerometers sense the inertial acceleration gradients in the satellite frame, from which the gravitational gradients are then deduced. Contrary to GOCE, the position of the test-mass in the accelerometer is measured by laser interferometry rather than capacitively, which improves the overall measurement chain. Such a system is expected to benefit from the recently launched LISA Pathfinder mission which opened the way to this kind of inertial sensor techniques.
After a description of the main physical characteristics of both concepts, the results of a performance analysis, carried out thanks to an end-to-end simulator, for various mission scenarios are discussed. It turns out that the cold atom interferometer gradiometer is not able to detect non-tidal time-variable gravitational signals and therefore must be dedicated to the static field mapping. The laser interferometer gradiometer is more sensitive and likely to detect them, however more work is required to optimize the sensor measurement bandwidth.