Measuring the Earth's Gravity Field with Cold Atom Interferometers
19/09/2016 | 17:00 | Session 1: Current and future satellite gravity missions
Author(s): Olivier Carraz, Christian Siemes, Luca Massotti, Roger Haagmans and Pierluigi Silvestrin
Olivier Carraz, Christian Siemes, Luca Massotti, Roger Haagmans and Pierluigi Silvestrin
In the past decades, it has been shown that atomic quantum sensors are a newly emerging technology that can be used for measuring the Earth’s gravity field. There are two ways of making use of that technology: One is a gravity gradiometer concept and the other is in a low-low satellite-to-satellite ranging concept. Whereas classical accelerometers typically suffer from high noise at low frequencies, Cold Atom Interferometers are highly accurate over the entire frequency range. Recent results in different labs show that it is possible to build a reliable system for using atom interferometry on vehicles and for space applications. These last developments prove that this technology, which is already suitable on ground vehicles, is competitive with classic inertial sensors. Some developments already worked in zero-g environment in the drop tower facility in Bremen, Germany, or in a 0g plane and are the state-of-the-art of compact setups aiming for spaceborne platform.
We recently proposed a concept using cold atom interferometers for measuring all diagonal elements of the gravity gradient tensor and the full spacecraft angular velocity in order to achieve better performance than the GOCE gradiometer over a larger part of the spectrum, with the ultimate goals of determining the fine structures in the gravity field better than today. This concept relies on a high common mode rejection, which relaxes the drag free control, and benefits from a long interaction time with the free falling clouds of atoms due to the micro gravity environment in space as opposed to the 1-g environment on-ground.
This instrument allows reaching sensitivity of 4.5 mE/Hz^1/2, with the promise of a flat noise power spectral density also at low frequency, and a very high accuracy on rotation rates (below 35 prad/s/Hz^1/2). Thanks to high common mode rejection, drag free constraints will be relaxed compare to GOCE mission and non-gravitational forces will be measured by combining the different measurements from the cold atom interferometers.
An other concept is also being studied in the frame of NGGM, which relies on the hybridization between quantum and classical techniques to improve the performance of accelerometers. This could be achieved as it is realized in frequency measurements where quartz oscillators are phase locked on atomic or optical clocks. This technique could correct the spectrally colored noise of the electrostatic accelerometers in the lower frequencies.
In both cases, estimation of the Earth gravity field model from the instruments has to be evaluated taking into account different system parameters such as attitude control, altitude of the satellite, time duration of the mission, etc.
Miniaturization, lower consumptions and upgrading Technical Readiness Level are the key engineering challenges that have to be faced for these space quantum technologies.