BepiColombo – Navigation Study of a Low-Thrust Interplanetary Mission

Paper number

IAC-05-C1.7.05

Author

Mr. Daniel Garcia Yarnoz, GMV S.A. at ESA/ESOC, Germany

Coauthor

Mr. Michael Croon, European Space Agency/ESOC, Germany

Coauthor

Mr. Rudiger Jehn, European Space Agency/ESOC, Germany

Year

2005

Abstract

BepiColombo is ESA’s Cornerstone Mission to Mercury, aiming at placing two spacecraft, the Magnetospheric Orbiter (JAXA) and the Planetary Orbiter (ESA), in orbit around the planet. In its five-year journey into the inner solar system, a combination of low-thrust arcs and five planetary flybys (Earth, two at Venus and two at Mercury) will be used to reach Mercury with low relative velocity. The approach adopted for the arrival at the planet also adds complexity to the problem: instead of the traditional hyperbolic approach, the flexibility of the solar electric propulsion allows for a gravitational capture, in which the Sun perturbation is exploited to get weakly captured around Mercury for a number of orbits. A navigation assessment analysis becomes necessary to study the feasibility of the current interplanetary trajectory design.
The particularities of the BepiColombo trajectory impose severe constraints from the navigational point of view. Very precise navigation is required due to the low flyby altitudes planned for Venus and Mercury and the level of accuracy desired for the final approach through the vicinity of the Sun-Mercury L1 point. And even though the solar electric propulsion provides the capability of partially redesigning the trajectory at very low propellant costs, it also introduces noise in the spacecraft dynamics than can negatively affect the orbit determination from Earth. Besides that, the solar plasma effect severely degrades the quality of the radiometric measurements near superior solar conjunctions, which are more common for missions to the inner solar system. Moreover, additional perturbations, as the ones introduced by momentum wheel desaturation burns, entry into safe modes and solar radiation pressure, must be also taken into account. The possible arrival dates at Mercury are also restricted by constraints of coverage and orbit determination quality, and the availability of recovery options after a failed insertion.
Results are obtained through covariance analysis for the overall trajectory, including low-thrust arcs navigation analysis, as well as Monte-Carlo simulations for the critical phases and orbit insertion. Delta-Differential One-way Range (ΔDOR) measurements are found to be required in periods of poor orbit determination and prior to some gravity assists. Also the introduction of 30-day clean arcs (without low-thrust propulsion) is proposed prior to all flybys. Furthermore, it is considered to raise the altitude of the second Venus gravity assist, which takes place during a superior solar conjunction in the current baseline trajectory (launch in April 2012), for safety reasons in case a safe mode is triggered. Finally, a possible multiple burn orbit insertion strategy is discussed, trying to minimise the propellant costs and at the same time providing enough time for precise orbit determination.

Abstract document

IAC-05-C1.7.05.pdf

Manuscript document

IAC-05-C1.7.05.pdf (🔒 authorized access only).

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