Other
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p41b1614m&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P41B-1614
Other
[1221] Geodesy And Gravity / Lunar And Planetary Geodesy And Gravity, [5430] Planetary Sciences: Solid Surface Planets / Interiors
Scientific paper
In the Japanese lunar exploration mission SELENE (Sept. 2007 - June 2009), new types of satellite tracking data were collected and used for precision orbit determination. One of them is differential VLBI (Very Long Baseline Interferometry). The VLBI radio sources (called VRAD) were on board the SELENE two sub-satellites, Rstar and Vstar. The differential VLBI data, when both the radio sources were within the beam-width of the ground antennas, were of particular importance because they are highly accurate with atmospheric and ionospheric disturbances almost cancelled out by the simultaneous observation. Such tracking data, i.e. "same-beam differential VLBI data" were useful for precision orbit determination [1] and also used to develop an improved lunar gravity field model SGM100i [2]. SELENE will be followed by the future lunar mission SELENE-2 which will carry both a lander and an orbiter. We propose to put the VRAD-type radio sources on these spacecraft in order to accurately estimate second-degree potential Love number k2 and low-degree gravity coefficients. By using the same-beam VLBI tracking technique, these parameters will be retrieved through precision orbit determination of the orbiter with respect to the lander which serves as a reference. The VLBI mission with the radio sources is currently one of the mission candidates for SELENE-2. We also propose a new type of observation called inverse VLBI [3] in order to further improve the k2 estimate, but this is regarded as an option instrument because it requires additional resources (electric power and mass). We have conducted a preliminary simulation study on the anticipated k2 accuracy. With the assumed mission duration of about 3 months (84 days) and the arc length of 14 days, the k2 accuracy is estimated to be better than 1 %, where the uncertainty is evaluated as 10 times the formal error considering the errors in the non-conservative force modeling and in the lander position. Through forward model calculation, we will show that the k2 error as small as 1 % is sensitive enough to the change in the liquid core radius of about ±40 km. We will also show that the k2 accuracy has sensitivity to possible partial melt layer and contribute to narrow the range of the plausible internal structure models. Although k2 by itself can not distinguish the effect of core size from that of partial melt layer, it is expected that the combination with other geophysical data such as seismic data as well as geochemical data will establish a realistic lunar interior model. References [1] Goossens et al. (2011), J. Geod.,85, 487-504, doi:10.1007/s00190-011-0446-2 [2] Goossens et al. (2011), J. Geod., 85, 205-228, doi:10.1007/s00190-010-0430-2 [3] Kawano et al. (1999), J. Geod. Soc. Japan, 45, 181-203.
Goossens S. J.
Hanada Hideo
Ishihara Yasuhide
Iwata Takahiro
Kamata Syo
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