Prepared by:
MORE Team
MORE Relativity Meeting
February 16-17, 2009
Rome
Simulation of the solar conjunction experiment with BepiColombo
MORE Relativity Meeting, February 16-17 2009, Rome
Introduction
being r1 and r2, respectively, the Sun-S/C and Sun-Earth distances, and b the
impact parameter.
221
3
4ln)1(
b
rr
c
GMt SUN
A solar conjunction experiment in cruise is foreseen for April 2016.
In principle, the accuracy of the measurement of the post-Newtonian
parameter γ should be higher in cruise rather than in orbit, due to the absence of
gravity gradient
An electromagnetic wave passing near the Sun is affected by a relativistic
delay, expressed as:
MORE Relativity Meeting, February 16-17 2009, Rome
Goals of the simulation
Goals:
Simulating the solar conjunction experiment occurring in 2016; a best case will be presented (upper limit to the accuracy in the estimation of γ);
Comparing the results to what we can achieve doing the experiment in 2017; Determining the effect of uncalibrated non-gravitational acceleration noise on the
measurement.
S/C
SEP
Geometry:
b
Sun
Earth
MORE Relativity Meeting, February 16-17 2009, Rome
Relativistic delay variation
Sun–Earth–Probe angle variation
Relativistic delay variation
MORE Relativity Meeting, February 16-17 2009, Rome
Simulation setup
Dynamic model:
Model for solar pressure: flat plate of 55 m2 area, average thermo-optical coefficients, always pointing toward the Sun (in order to maintain a constant sun-aspect-angle)
Absence of orbital and attitude maneuvers
Observables:
Observables: range, one measurement every 20 sec (the range rate does not give a significant contribution), for 20 days
Two DSN stations, providing a coverage of 15 hours per day Observables under 8 solar radii have not been considered Gaussian noise added (we have supposed to cancel the plasma noise, by
using the multi-frequency link), with a standard deviation of 20 cm
MORE Relativity Meeting, February 16-17 2009, Rome
Estimation - 2016
Estimation:
Estimation of the state vector of BepiColombo and γ The starting value of γ has been set to that obtained with the Cassini
mission γ = 1 + (2.1 ± 2.3)x10-5
γ = 1 – (8.5 ± 8.7)x10-6
Above the goal of the experiment!
MORE Relativity Meeting, February 16-17 2009, Rome
Estimation - 2017
γ = 1 + (1.5 ± 2.6)x10-6
Compatible with the goal of the experiment
MORE Relativity Meeting, February 16-17 2009, Rome
Conclusions
In conclusion:
The geometry of the solar conjunction in 2016 seems not to meet the scientific objective of MORE. In particular, the accuracy is more than 3 times worse wrt what we would like to achieve;
On the contrary, the solar conjunction in 2017 could allow a very precise measurement.