Mercury Orbit Insertion Research Articles

BepiColombo Ground Segment and Mission Operations

The ESA/JAXA BepiColombo mission to Mercury was launched in October 2018. It includes two scientific Mercury orbiters, flying as a single stack during the seven years interplanetary transfer, and as individual spacecraft operated by their respective space Agencies ESA and JAXA once deployed in their respective scientific orbit around Mercury. Three ground segments are closely collaborating on this mission. The European Space Operations Center of the European Space Agency, in Darmstadt, Germany, responsible for mission operations of the composite stack during the interplanetary transfer and of the Mercury Planetary Orbiter (MPO) once at Mercury, the JAXA Sagamihara Space Operation Center (SSOC) in Sagamihara, Japan, responsible for Mercury Magnetospheric Orbiter (MMO) operations throughout the mission, and the European Space Astronomy Center of the European Space Agency, in Villanueva de la Canada, Spain, responsible for MPO scientific archiving and Mercury science operations. The mission benefits from infrastructure and concepts developed on previous interplanetary missions of ESA and JAXA. However, it also includes specific operational challenges, such as electric propulsion, and a complex Mercury Orbit Insertion sequence, exploiting weak stability boundaries, and interleaving three module separations with 15 chemical propulsion manoeuvers to deliver MPO and MMO in their respective science orbits, requiring specific developments and operational approaches. In view of the nominal mission duration of 8.5 years, the mission also requires the adoption of specific measures for knowledge preservation and long-term maintenance.

Measurements of Magnetic Field Fluctuations for Plasma Wave Investigation by the Search Coil Magnetometers (SCM) Onboard Bepicolombo Mio (Mercury Magnetospheric Orbiter)

This paper describes the design and performance of the search coil magnetometers (SCM), which are part of the Plasma Wave Investigation (PWI) instrument onboard the BepiColombo/Mio spacecraft (Mercury Magnetospheric Orbiter), which will measure the electric field, plasma waves and radio waves for the first time in Mercury’s plasma environment. The SCM consists of two low-frequency orthogonal search coil sensors (LF-SC) measuring two components of the magnetic field (0.1 Hz – 20 kHz) in the spacecraft spin plane, and a dual-band search coil sensor (DB-SC) picking up the third component along the spin axis at both low-frequencies (LF: 0.1 Hz – 20 kHz) and high-frequencies (HF: 10 kHz – 640 kHz). The DB-SC and the two LF-SC sensors form a tri-axial configuration at the tip of a 4.6-m coilable mast (MAST-SC) extending from the spacecraft body, to minimize artificial magnetic field contamination emitted by the spacecraft electronics. After the successful launch of the spacecraft on 20 October 2018, an initial function check for the SCM was conducted. The nominal function and performance of the sensors and preamplifiers were confirmed, even with the MAST-SC being retracted and stowed in the spacecraft body, resulting in the detection of large interference signals likely from spacecraft electronics. The MAST-SC is scheduled for deployment after the Mercury orbit insertion of Mio in 2025, allowing the SCM to make the first higher frequency measurements of magnetic fluctuations in the Hermean magnetosphere and exosphere, and the local solar wind. These measurements will contribute to the investigation of fundamental problems in the Hermean plasma environment, including turbulence, magnetic reconnection, wave-particle interactions and particle acceleration.

Influence of the Mercury gravity field on the orbit insertion strategy of BepiColombo

In this paper the Mercury orbit insertion (MOI) in January 2022 of the ESA mission BepiColombo consisting of 15 manoeuvres is optimised. To maximise the mass in the target orbit, the gravity losses of the 15 burns are minimised by distributing the burns as evenly as possible. However, severe Sun aspect angle constraints make the optimisation problem difficult to solve. The NLP-solver SNOPT is used for the optimisation.The uncertainty in Mercury's gravity field is still high, such that its influence on the MOI was evaluated in several simulations of Mercury's gravity field. Since the target orbital parameters are still discussed their influence on the MOI ΔV-budget is investigated. The results indicate that the reference case was selected adequately. Since changes in arrival date, scientific orbit, instruments and strategies until BepiColombo's launch in 2015 are possible, this paper covers a wide range of possible future arrival options.

MESSENGER's use of solar sailing for cost and risk reduction

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission used six planetary gravity assists in order to enable capture into orbit about Mercury. A key element of MESSENGER's successful trajectory was achieving the proper gravity assist from each planetary flyby. The criticality of the MESSENGER gravity assists levied tight accuracy requirements on the planetary-flyby targeting. Major errors could have precluded Mercury orbit insertion or required modifications to the trajectory that increased mission complexity, cost, and risk by requiring additional Mercury flybys and extending mission duration. Throughout the mission, MESSENGER modified its strategy for achieving accurate planetary flybys. By using solar sailing, the MESSENGER team was able to eliminate all of the flyby approach maneuvers without sacrificing flyby accuracy, thereby saving mission ΔV margin. The elimination of these approach maneuvers also markedly reduced mission risk, as these approach maneuvers were nominally planned during a time of heightened sensitivity to errors and precluded unique flyby science opportunities. The paradigm shift used by MESSENGER may be useful for other interplanetary missions, particularly if their trajectories require gravity assists in the inner solar system.

Astrophysical objects observed by the MESSENGER X-ray spectrometer during Mercury flybys

The MESSENGER spacecraft conducted its first flyby of Mercury on 14th January 2008, followed by two subsequent encounters on 6th October 2008 and 29th September 2009, prior to Mercury orbit insertion on 18th March 2011. We have reviewed MESSENGER flight telemetry and X-ray Spectrometer observations from the first two encounters, and correlate several prominent features in the data with the presence of astrophysical X-ray sources in the instrument field of view. We find that two X-ray peaks, attributed in earlier work to the detection of suprathermal electrons from the Mercury magnetosphere, are likely to contain a significant number of events that are of astrophysical origin. The intensities of these two peaks cannot be explained entirely on the basis of astrophysical sources, and we support the previous suprathermal explanation but suggest that the electron fluxes derived in those studies be revised to correct for a significant astrophysical signal.

Solar influence on nuclear decay rates: constraints from the MESSENGER mission

We have analyzed 137Cs decay data, obtained from a small sample onboard the MESSENGER spacecraft en route to Mercury, with the aim of setting limits on a possible correlation between nuclear decay rates and solar activity. Such a correlation has been suggested recently on the basis of data from 54Mn decay during the solar flare of 13 December 2006, and by indications of an annual and other periodic variations in the decay rates of 32Si, 36Cl, and 226Ra. Data from five measurements of the 137Cs count rate over a period of approximately 5.4 years have been fit to a formula which accounts for the usual exponential decrease in count rate over time, along with the addition of a theoretical solar contribution varying with MESSENGER-Sun separation. The indication of solar influence is then characterized by a non-zero value of the calculated parameter ξ, and we find ξ=(2.8±8.1)×10−3 for 137Cs. A simulation of the increased data that can hypothetically be expected following Mercury orbit insertion on 18 March 2011 suggests that the anticipated improvement in the determination of ξ could reveal a non-zero value of ξ if present at a level consistent with other data.

Preliminary ISAS Mercury orbiter mission design

This paper shows the recent results of ISAS Mercury orbiter mission study conducted by ISAS Mercury Exploration Working Group. Two options are under study; 1) A Spacecraft which utilizes Solar Electric Propulsion (SEP) as a primary propulsion system for interplanetary transfer phase as well as Mercury orbit insertion phase and 2) Conventional chemical propulsion spacecraft.

Hermes Global Orbiter spacecraft system design

The Hermes Global Orbiter (HGO) mission was one of the eleven DISCOVERY NASA HQ Code SL projects funded for study in FY’93. It proposes to launch a spacecraft to Mercury in the 1999 launch opportunity, with multiple encounters at Venus and Mercury, to reduce the launch and Mercury Orbit Insertion energy requirements. This mission design strategy results in an interplanetary cruise of 3.44 earth years and with a Mercury orbit lifetime of 1 earth year. The project proposes to maintain total run out to launch plus 30 days cost at less than 150 M$ (1991 FY $) with launch vehicles being excluded from this cap. The spacecraft uses a great deal of heritage from prior TRW spacecraft developments. The key elements are the Lightsat avionics being used for the TRW Advanced Bus, the TRW dual mode Liquid Apogee Engine, TRW graphite fiber wrapped tanks, the JPL/TRW X-band Solid State Power Amplifier, TRW heat pipe technology and the TRW Gallium Arsenide solar array technology.