The Determination of Jupiter's Angular Momentum from the Lense-Thirring Precession of the Juno Spacecraft

Details The Determination of Jupiter's Angular Momentum from the Lense-Thirring Precession of the Juno Spacecraft The Determination of Jupiter's Angular Momentum from the Lense-Thirring Precession of the Juno Spacecraft

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p41b1620f&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P41B-1620

Statistics

Computation

[0520] Computational Geophysics / Data Analysis: Algorithms And Implementation, [5700] Planetary Sciences: Fluid Planets, [6900] Radio Science

Scientific paper

In its one-year mission around Jupiter (Oct. 2016 - Oct. 2017), the Juno spacecraft will carry out a precise determination of the gravity field, with the goal of unveiling the interior structure of the planet. Juno will be inserted in a polar, highly eccentric orbit (e = 0,9466) with a period of nearly 11 days. The very low pericenter (about 5000 km altitude) makes the orbit especially sensitive to the zonal gravity field. In addition to the perturbations due to classical gravity, the spacecraft is also exposed to significant relativistic effects. In particular, the high velocity at pericenter (60 km/s), in combination with Jupiter's fast rotation (T=10 h), induces a significant acceleration due to the Lense-Thirring (LT) precession. In the low-velocity, weak field approximation, the acceleration is proportional to the angular momentum of the central body and to the velocity of the test particle, and orthogonal to them. A measurement of the LT precession would therefore provide also the angular momentum of the planet. As the perturbing field rapidly decreases with the radial distance, by far the largest acceleration occurs during the pericenter pass (about 6 h). This unique opportunity to observe the LT precession on a planet other than the Earth was first pointed out in [1]. However, the suggested approach, used for the LAGEOS satellites orbiting the Earth, cannot be applied to Juno because large longitude-keeping maneuvers destroy the dynamical coherence of the orbit. We have adopted a different approach, based upon the direct estimation of the LT parameter using a multi-arc, least squares filter. During a pericenter pass, the LT acceleration produces a line-of-sight velocity variation of 0.35 mm/s and a displacement of several meters. These variations can be observed as Doppler shifts on the two-way tracking radio signal. The onboard radio system supports a highly stable, two-way, Ka-band radio link (34 GHz uplink, 32.5 GHz downlink), providing two-way range-rate data accurate to 3 micron/s or better over time scales of 1000 s. The excellent stability of the Ka-band radio system enables a very good sensitivity to the LT effect (at SNR~100). The onboard unit, a Ka-band uplink, Ka-band downlink frequency translator, has been manufactured by Thales Alenia Space Italy, under contract from the Italian Space Agency. The measurement has been simulated numerically using JPL's Orbit Determination Program (ODP) using the nominal mission profile. However, the current version of the ODP does not allow the estimation of the LT parameter, so that it had to be complemented by additional software for the integration of the modified state and variational equations. The Jupiter's angular momentum is estimated together with the zonal harmonic coefficients, k2 and k3 Love numbers and the spacecraft state vector. This realistic simulation shows that the specific angular momentum can be estimated with an absolute accuracy of 4.956E3 corresponding to a 2% relative accuracy if the moment of inertia of the planet is 0.26 and the rotation uniform. [1] Iorio L., "Juno, the angular momentum of Jupiter and the Lense-Thirring Effect", New Astron.15: 554-560,2010

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