Sky and Telescope - November 2018 - 28

Oct 2020
Dec 2024

Arrival
Dec 2025

Launch
Oct 2018
June 2023
Sep 2024

Sun
Mercury
Transfer
Module
(MTM)

Mercury
Planetary
Orbiter
(MPO)

Jan 2025

Oct 2021
June 2022

Aug 2021
Apr 2020

p COMBO SPACECRAFT Top: Artist's impression of BepiColombo in
cruise configuration. Bottom: An expanded view of BepiColombo's components. The Mercury Planetary Orbiter and Mercury Magnetospheric
Orbiter (nested in the sunshield) will ride to the innermost planet with the
ion-powered thrust of the Mercury Transfer Module.

Earth flyby
Venus flyby
Mercury flyby/capture

Coast phase
Ion-propulsion phase

p SCENIC ROUTE? To reach the innermost planet, BepiColombo has
to lose orbital energy - a lot of it. The spacecraft will use gravity assists
with Earth, Venus (twice), and Mercury itself (six times) to slow down
enough to gently enter orbit around the iron planet in 2025.

thrust direction and solar-panel orientation dictate the direcSpacecraft propulsion alone won't be enough. BepiCotion that the spacecraft points, so there's no possibility of
lombo will perform one flyby of Earth, two of Venus, and six
pointing instruments to do observations - except when the
of Mercury to tweak the shape, size, and orientation of its
engine is off and the craft is coasting (see diagram above).
heliocentric orbit before settling in at Mercury in DecemThe next seven years will not just be a waiting game,
ber 2025. The MTM will be dropped two months before the
though. BepiColombo's science teams are particularly eager
combination craft enters orbit. On arrival, MPO will hit the
to test their instruments at Venus. MPO's remote-sensing
brakes so that Mercury can capture the paired craft. After
instruments mostly have their eyes pressed firmly against
many smaller maneuvers, the duo will reach MMO's desired
the transfer module, but a couple of instruments (notably
orbit. MMO will separate, and MPO will drop to its own lowMERTIS) have sideways-pointed chanaltitude circuit of the planet in March
nels that will be able to take some data.
2026. The science mission is planned to
And measurements of fields and parbegin shortly thereafter.
ticles - by the magnetometer, neutral
Unfortunately, the stacked spacecraft
and ion spectrometers, radio science
structure limits BepiColombo's science
experiment, accelerometer, and others
capability during the long cruise. MMO
- can be made even while the spacecraft
in particular will be hidden beneath a
remain stacked. Perhaps, when BepiCoEuropean-built heat shield and unable
lombo passes Venus, it will be able to do
to employ its instruments. It won't be
coordinated observations with another
able to do any science at all until it's
Japanese mission, Akatsuki, training its
been captured by Mercury, where it
senses on one enigmatic world en route
will jettison the shield and spin up to a
to another.
4-second rotation period, using that spin
to deploy its booms and redistribute heat
so that it can bear the high temperatures p HOLLOWS Strange pits pockmark Mercu- ¢ S&T Contributing Editor EMILY LAKry's surface, sometimes appearing in clumps
close to the Sun.
DAWALLA is Senior Editor and Planetary
several kilometers across. Individual hollows
The use of ion propulsion also conEvangelist for The Planetary Society, and
can be as small as a couple of hundred mestrains science observations during the
author of the recent book The Design and
ters wide. Scientists think that the vaporizavoyage. The engine has to operate nearly
Engineering of Curiosity: How the Mars
tion and escape of volatile compounds in the
continuously for months on end. The
Rover Performs Its Job.
surface might explain the marks.
28

N OV E M B E R 2 018 * SK Y & TELESCOPE

BEPICOLO MBO AT MERCURY: ESA / ATG MEDIA L A B; TR A JECTORY
DIAG R A M: LE A H TISCIONE / S&T, SOURCE: BEPICOLO MBO TE A M;
HOLLOWS: N ASA / JHU A PL / CA R NEGIE INSTIT U TION FOR SCIENCE

Sun
Shield

Mercury
Magnetospheric
Orbiter
(MMO)



Sky and Telescope - November 2018

Table of Contents for the Digital Edition of Sky and Telescope - November 2018

Contents
Sky and Telescope - November 2018 - Cover1
Sky and Telescope - November 2018 - Cover2
Sky and Telescope - November 2018 - 1
Sky and Telescope - November 2018 - Contents
Sky and Telescope - November 2018 - 3
Sky and Telescope - November 2018 - 4
Sky and Telescope - November 2018 - 5
Sky and Telescope - November 2018 - 6
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