Computer Science
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002iaf..confe.675t&link_type=abstract
IAF abstracts, 34th COSPAR Scientific Assembly, The Second World Space Congress, held 10-19 October, 2002 in Houston, TX, USA.,
Computer Science
Scientific paper
(1) transponders, used for both range and range-rate estimation. These devices are characterized by a frequency stability (measured by the Allan deviation) whose typical value never falls below the limit of 10-13, which broadly reflects in a range rate accuracy of about 15.10-4 cm/s. Moreover, for missions in the ecliptic plane, a critical phase is represented by the solar conjunctions which, depending on the spacecraft trajectory, can last up to two weeks. In such conditions the radio data are inherently corrupted by solar plasma noise, which causes a dramatic decay of the obtainable navigation accuracy. As a matter of fact, in the orbit determination process, radio data collected when the line of sight falls within 40 solar radii are usually discarded, leading to long time spans during which navigation cannot rely on actual data. and 2001 solar conjunctions were removed for navigation purposes. While this strategy is widely acceptable and proven during the cruise flight, it is not recommended during critical mission phases, when frequent ground-commanded maneuvers are executed. maneuver, scheduled on July 1st 2004, a few days before a solar conjunction. A significant improvement of the navigation accuracy would be achieved using, for the Orbit Determination process, all radio data collected up to the SOI. science experiments (RSE). The on-board configuration is based on a X/X transponder, which generates a reference signal to the Ka-Band Exciter (KEX) for the X/Ka link; furthermore a coherent frequency translator (KaT) is used for the Ka/Ka link. With this configuration, the sky frequencies in the three bands (X/X, X/Ka, Ka/Ka) can be coherently combined to remove the effects of the solar plasma, the major noise source in the Doppler observable. plasma calibration scheme, has shown an improvement of a factor of 8 over the noise of the bare Ka/Ka observable and a factor of 100 over X/X data. At an impact parameter of about 25 solar radii, the Allan deviation is as low as 2.10-14 at integration times of 1000 s, offering a range rates accuracy of about 0.003 mm/s. An immediate consequence of such results is the dramatic navigation accuracy improvement which can be obtained calibrating for solar plasma the Doppler observable used by the Orbit Determination Program (ODP). discussed in detail. First, the algorithm to reconstruct the sky frequencies from wideband open loop data is illustrated and, using a simple model of the orbital dynamics, the obtained residuals are characterized in terms of Allan deviations and power spectra. We then show how the plasma calibration scheme, used to generate plasma free observable for each band, leads to a much improved signal stability and to a reduced spectral density. Using the raw and calibrated sky frequencies in the ODP, a thorough comparison is performed among the Doppler frequency residuals obtained from 1) uncalibrated X-band data, 2) uncalibrated Ka-band data, and 3) calibrated X and Ka-band data. Our results show that the plasma free observable generation allows the use of actual data in the orbit determination process, even when the S/C has an impact parameter of about 5 solar radii, well into a superior conjunction.
Ekelund John E.
Iess Luciano
Tortora Paolo
No associations
LandOfFree
Accurate Navigation of Deep Space Probes using Multifrequency Links: the Cassini Breakthrough during Solar Conjunction Experiments does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Accurate Navigation of Deep Space Probes using Multifrequency Links: the Cassini Breakthrough during Solar Conjunction Experiments, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Accurate Navigation of Deep Space Probes using Multifrequency Links: the Cassini Breakthrough during Solar Conjunction Experiments will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1332380