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| Titel |
Laser Interferometer for a spaceborne mapping of the Earth |
| VerfasserIn |
M. Dehne, B. Sheard, F. Guzmán Cervantes, Gerhard Heinzel, K. Danzmann |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250026935
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| Zusammenfassung |
| The Gravity Recovery and Climate Experiment (GRACE) is one of the present
missions to map the Earth’s gravity field. The aim of a GRACE follow-on mission is
to map the gravitational field of the Earth with higher resolution over at least 6
years. This should lead to a deeper insight into geophysical processes of the Earth’s
system.
One suggested detector for this purpose consists of two identical spacecraft carrying
drag-free test masses in a low Earth orbit at an altitude of the order of 300 km, following each
other with a distance of about 10 to 100 km. Changes in the Earth’s gravity field will induce
distance fluctuations between two test masses on separate spacecraft. These variations are to
be monitored by a laser interferometer with nanometer precision in the frequency range
between 1 mHz and 100 mHz. The relative velocity between the spacecraft induces a Doppler
shift in the interferometer beatnote. This effect together with the large variations in the
inter-spacecraft separation make heterodyne interferometry ideally suitable as the
pathlength readout scheme. The round-trip Doppler shift introduces variations in the
interferometer beatnote up to a few 100 kHz. A suitable heterodyne frequency is therefore
between several hundred kHz and a few MHz, with the lower limit given by the
maximal Doppler shift and the required control bandwidth of the offset phase lock. The
upper limit is given by technical considerations concerning the photodiodes and the
phasemeter.
We benefit a lot from the current developments for the joint ESA-NASA space-based
gravitational-wave detector "Laser Interferometer Space Antenna" (LISA) and its precursor
mission LISA Pathfinder, such as a precise drag-free technology and the interferometric
readout.
We present preliminary results of an interferometric readout using a heterodyne
configuration with polarising optics, demonstrating the required phase sensitivity. |
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