How to Get a Spacecraft to Mercury

Mercury’s heavily cratered surface can help scientists piece together its 4.6 billion year history, but its fragile atmosphere provides little protection from UV radiation or micrometeoroids striking its surface.

Spacecraft bound for Mercury must be constructed using heat-resistant materials and feature sophisticated navigation and communication systems, in addition to gravity assists and advanced propulsion systems.

The Early History

Spacecraft travelling to Mercury must gain speed quickly in order to catch up; due to Mercury’s faster orbital motion around the Sun than Earth, without some energy reduction from their orbital energy, they will simply fly past Mercury without stopping or returning home.

Spacecraft must withstand extreme temperatures and atmospheric conditions, intense solar radiation, high velocity orbital dynamics and challenging orbital dynamics. Therefore, mission design calls for advanced thermal control systems and robust shielding solutions.

MESSENGER has observed that Mercury shares our magnetic field. This finding supports the theory that its iron core formed during some early process that enriched it relative to silicate in its protoplanetary disk origin, giving rise to our solar system.

The spacecraft also confirmed that ice, likely brought by cometary collisions, persisted at the bottom of polar craters even though they remain shaded from direct Sunlight. This finding could enable future astronauts to survive on Earth.

The MESSENGER Mission

MESSENGER, or Mercury Surface, Space Environment, Geochemistry and Ranging mission, began its 10-year orbital investigation of Mercury in March 2011 and made impactful observations on April 30, 2015. Since then, its data have continued to revolutionize our understanding of both Mercury and its inner solar system surroundings.

MESSENGER was developed and built at APL as the first orbiter since Mariner 10’s flybys in 1974 to study Mercury. A squat box, it featured an innovative ceramic-fabric sunshade to shield itself from Mercury’s intense heat while permitting its instruments to operate efficiently.

MESSENGER was initially scheduled to end its mission in March 2012; however, two extensions were approved during its time. MESSENGER answered fundamental questions about Mercury’s composition and history during that period, such as its unusually dense core. Furthermore, it mapped the planet’s entire surface and discovered evidence of polar water ice. Notable discoveries included Rembrandt Crater with its 440 mile-wide diameter as well as perpendicular chains of cliffs in Caloris basin containing lavas that has permanently obscured northern pole from sunlight.

The BepiColombo Mission

BepiColombo, launched jointly between Europe and Japan in 2018, will investigate the role of water ice at Mercury’s poles and abnormally large core, plasma and particle environments around this unique planet, Einstein’s theory of general relativity, as well as test it. Insertion into Mercury orbit can be tricky due to close proximity with Sun and having to avoid being “sucked in” by gravitational pull, so careful mission planning was required as well as development of innovative technologies like high efficiency electric propulsion engines that allowed significant savings of propellant.

bepiColombo will also help answer many of the new questions raised by MESSENGER discoveries, for instance its low eccentricity MPO orbit will allow global mapping of volatile-rich regions on Mercury to establish their source (Salazar et al. 2019), thus clarifying whether volatiles were delivered during formation of Mercury’s surface or not.

The Future

Since NASA’s Messenger mission ended in 2015, scientists have been studying Mercury’s data and dreaming of sending a robot down its surface one day – though doing so requires powerful rockets and advanced technologies.

Mercury orbits the Sun with staggering speed, its thin atmosphere making it hard for it to slow down or decelerate. Solar interference also poses challenges to navigation systems as transmissions may fail or force changes to positioning sensors.

A lander must be equipped with instruments designed to function under these extreme conditions, as well as high-capacity memory for recording data and robust transmitters capable of relaying it back home. Furthermore, wheels or tracks would need to be in place in order to navigate around obstacles like craters and obstacles as well as suspension systems that can handle landing on hard surfaces with sufficient suspension systems absorbing impact upon impact landing. Furthermore, power will need to last through long nights while producing energy independent of sunlight production.