Zhurong

CNSA, via China News Service.

Overview

Zhurong is China’s first Mars rover, delivered to Utopia Planitia by the Tianwen-1 entry module and released onto the surface on 22 May 2021 [1]. Rock coverage at the Martian surface is about twice that of the Moon, which set the obstacle-clearing requirement the rover’s designers worked against. Its answer, unlike the passive rocker-bogie carried by every American Mars rover, is an active suspension that can change its own geometry on command: a main and auxiliary rocker arm linkage with a clutch that, once released, lifts a sunk wheel or contracts the whole chassis rather than relying only on wheel torque to climb out of trouble [1]. The rover operated about a year against a 90 day planned life and entered hibernation on 18 May 2022 without waking again [11].

Specifications

Parameter	Value
Dimensions	approximately 3.3 x 3.2 x 1.85 m
Power source	solar, four deployable panels
Suspension	active, main and auxiliary rocker arms with a releasable clutch
Payload	six instruments

Specifications from [1]. Rover mass is not published.

Mission profile

Parameter	Value	Source
Landing	15 May 2021, Utopia Planitia
Rover egress from the platform	22 May 2021
Planned mission	90 Martian days, completed 15 August 2021	[11]
Odometer traverse to 5 May 2022	1921 m over 347 Martian days	[11]
Reconstructed true-path traverse	2009 m over 206 site operations, 360 sols	[2]
Data returned by rover and orbiter to 5 May 2022	about 940 gigabytes	[11]
Relay test with ESA Mars Express	November 2021	[11]
First solar conjunction outage	mid September to late October 2021	[11]
Status	did not wake from hibernation, 18 May 2022

Landing, egress and status from [1]. The 88 m gap between the 2009 m of true path reconstructed from site imagery and the 1921 m odometer reading is attributed to forward wheel slip on a generally downslope, southward traverse [2].

Mobility

The suspension’s clutch, once released, converts a normally passive linkage into a commandable mechanism with four functions: controlled lifting, controlled lowering, wheel lifting, and suspension contraction [1]. That is a deliberate departure from the JPL rocker-bogie lineage, which excludes springs and active joints altogether because an elastic or actuated link raises the normal force on a climbing wheel while unloading the others, exactly wrong for obstacle climbing on a passive chassis [12]. That design was tuned against six or seven modeled obstacle positions, where six wheels climb an axle-high vertical face at a friction coefficient near 0.8 against 0.78 to 1.4 for four wheels depending on which end meets the wall, a fixed-geometry optimum Zhurong’s clutch trades away [12]. Zhurong trades that climbing optimality for a self-extraction capability the passive linkage cannot offer.

Failure condition	Recovery action
Single wheel sunk	lift that wheel
All wheels caught	contract the suspension
Body in contact with a rock	raise the suspension to clear it

Recovery actions from [1].

Suspension contraction with sequential wheel lifting produces a walking gait that extracts the vehicle from soft ground by changing which wheels carry load rather than by increasing drawbar pull. That addresses slip-sinkage directly: a wheel that is unloaded and repositioned does not have to develop thrust against soil whose shear strength has already been exceeded, the same failure mode a rigid rocker-bogie has no recourse against beyond driving through it [12]. Terrain along the traverse at Utopia Planitia is flat, covered by reddish soils and dust, with dark-toned material exposed where wheels or wind removed the dust layer [3].

Localization during the traverse combined onboard dead reckoning with cross-site visual matching: dead reckoning against a HiRISE-visible rover track carried an error of 3.11 percent of traverse length, cross-site Affine-SIFT visual localization reduced that to 1.75 percent, and matching site imagery to orbital imagery at four waypoints reduced it further to 0.50 percent [2]. Site digital elevation and orthophoto models were built at 0.02 m grid spacing out to 15 m range, with total stereo measurement error of 0.108 m at that range [2].

Power and energy

Solar radiation intensity at Mars orbit is approximately 43 percent of that near Earth [1]. Atmospheric dust adds to that deficit: background column optical depth over the aphelion half of the year sits below 1, and dust storm activity recurs seasonally, so array output carries a seasonal floor independent of surface deposition on the panels themselves [7], [8]. Two measures respond to the combined problem. Maximum power point tracking improves conversion efficiency from the cells, and an ultra-thin solar film with an anti-dust coating gives a dust removal efficiency over 86 percent, addressing deposition rather than the seasonal atmospheric floor [1].

A dormancy and wake-up mode covers the range of surface lighting conditions. On the onset of a dust storm the rover powers off to prevent battery drain and remains asleep until generated power and temperature reach their thresholds simultaneously, a coupling that makes the mode a survival state rather than a low-power state [1]. During a global dust storm, column optical depth reaches a global mean near 4 with local values of 5 to 10, so a storm subtracts from generation at the same time as it adds to deposition on the arrays [8]. The dust climatology behind that figure was itself validated against independent measurements from CRISM in orbit and from PanCam and Mini-TES on the ground, which is why it is used as the dust forcing in the Mars Climate Database [8].

Thermal

Surface temperature below -100 C sets the design case [1]. Measured air temperature at landed Mars sites spans roughly 140 to 300 K depending on season and latitude, with a diurnal range large enough that a surface vehicle crosses most of that span every sol [7]. At Gale crater, the diurnal amplitude of the ground temperature cycle runs on a thermal inertia of roughly 170 to 550 SI units depending on terrain, the same site-dependence that makes any fixed thermal design a compromise across a traverse [7]. The architecture combines active and passive control.

Element	Function
Solar window	collects heat during the day, raises cabin temperature at night
Aerogel plus CO2 isolation	passive insulation: reduces conduction, isolates radiative leakage, eliminates in-cabin convection
Active heating at night	brings in-cabin equipment to its required ambient temperature
Active control on external equipment	navigation and obstacle avoidance cameras, multispectral cameras

Thermal elements and their functions from [1].

The passive layer is what makes the active budget affordable: with limited active thermal resources, leakage is attacked on all three transfer paths at once rather than compensated by heater power [1]. That approach to the cold is not the only one flown to Mars: the InSight HP3 mole, a hammering probe rather than a thermally isolated cabin, failed to reach its planned depth because the cohesive duricrust at its site gave no lateral soil pressure and therefore no hull friction to react the hammer’s recoil, a soil-mechanical failure mode with no counterpart in Zhurong’s cabin-insulation design [9].

Communications

Link	Parameter	Value
X-band direct	Rover-to-Earth visible arc	approximately M04:30 to M16:00 each sol
X-band direct	Uplink rate to the omnidirectional antenna	as low as 7.8125 bps
UHF relay	Architecture	loop relay mode, two-way, through the Tianwen-1 orbiter
UHF relay	Near-Mars arc pass around noon	approximately 10 min
UHF relay	Martian night pass	approximately 5 h
UHF relay	Near-Mars arc rate	Mbps class

Link parameters from [1]. The 7.8125 bps direct uplink is a command channel, not a data path, so the relay carries everything of volume: telemetry, images and instrument data, all within the same near-Mars pass. The orbiter’s own magnetometer, MOMAG, continued returning solar wind and interplanetary magnetic field data through the relay period, cataloging two coronal mass ejections and three stream interaction regions at Mars between November and December 2021 in coordination with NASA’s MAVEN [10]. Each event’s magnetic field measurements were compared directly between the two spacecraft rather than merged, since Tianwen-1 orbits Mars while MAVEN samples the solar wind further out, and the two records agree on timing even where local field magnitude differs [10].

Modes of operation

The rover is in standby by default, with computers on and other equipment operating intermittently against a mission cycle template run onboard [1]. Standby rather than sleep is affordable because the passive thermal stack holds cabin temperature without continuous heater draw.

Interval	Action
Martian afternoon, approx 10 h	X-band omnidirectional receiver on, holding a basic uplink channel
Martian noon, approx 1 h	UHF receiver on for the near-Mars arc
Martian night, approx 5 h	UHF receiver on for the remote arc
M11:00 to M15:00	primary work period, ambient temperature highest and no additional heating needed

Daily template from [1].

Scheduling the work period against temperature rather than against illumination is a direct consequence of the thermal budget: heating an actuator costs energy the arrays would otherwise deliver to the activity itself.

Ground operations

Delayed instructions are uplinked each Martian morning via the orbiter, relayed to the rover by UHF around noon for execution, and telemetry is returned through the orbiter by UHF during the Martian night [1]. The cycle is therefore one command load per sol with a single execution window and a single return window, rather than the multiple tactical passes available to the NASA rovers through the Mars Relay Network [2].

Payload and instruments

Six instruments are carried [1]. Four measure the environment rather than the rover’s own state, and the meteorology package is the Chinese counterpart to REMS and MEDA [7].

Instrument	Measurement	Source
Navigation camera	surface morphology, driving
Multispectral camera	mineral and rock types, material distribution
Subsurface detection radar	soil structure and stratification, water and ice content
Surface composition detector (MarSCoDe)	LIBS for quantitative chemistry, short-wave infrared spectroscopy for mineralogy	[5]
Magnetic field detector	magnetic field intensity, variation, ionospheric current
Meteorological instruments	temperature, pressure, wind speed and direction, sound

Instrument list from [1] unless noted.

MarSCoDe’s laser is a passively Q-switched 1064 nm unit at 23 mJ per 4.5 ns pulse, firing at 1 to 3 Hz with fixed energy, feeding a 106 mm Ritchey-Chretien telescope that both focuses the beam and collects the plasma emission, pointed by a worm-gear mechanism driven by two stepping motors [5]. Emission is dispersed across three LIBS channels covering 240 to 340, 340 to 540 and 540 to 850 nm, while a short-wave infrared channel covers 850 to 2400 nm [5]. Because the rover is solar powered and cannot keep the spectrometer at a constant temperature, its spectra drift with Martian temperature; the instrument carries an onboard titanium calibration target, and an elastic particle swarm optimization algorithm matches the shifted spectral lines against a standard wavelength set established in a Mars simulation chamber before launch, cutting the residual wavelength error after correction to under 0.006 nm at the ultraviolet channel’s coldest tested point of -40 C [6]. That correction was validated in a Mars simulation environment chamber holding Earth-lab pressure near 1 percent of Earth’s own and temperatures from -40 to 30 C, using standard element lamps for the initial calibration and the onboard target for the temperature-shift correction itself [6].

MarSCoDe measured LIBS and short-wave infrared spectra of six Vastitas Borealis Formation targets, soils, an outcrop and a coherent rock, in the rover’s first 300 sols, and the result reads as a low-alteration mix of igneous minerals with clay-like alteration phases formed under limited or ephemeral water and cold conditions [3]. The magnetometer campaign returned vector measurements at 16 sites along a 1089 m track; the field measured, under 10 nT over most of the track, is far weaker than the roughly 81 nT that downward-continued orbital models had predicted for the site, though InSight measured about 2000 nT at Elysium Planitia, so the discrepancy is a local rather than a universal one [4]. Separating that faint ambient field from the roughly 10,000 nT generated by a permanent magnet inside the rover’s own mast-mounted camera required rotating the mast and the whole rover to isolate sensor-frame, rover-frame and Mars-frame components of the reading [4].

End of mission

Zhurong entered hibernation on 18 May 2022 and did not re-establish contact [2]. Dust accumulation on the arrays is the assumed cause, against an 86 percent dust removal efficiency demonstrated for the coating and a wake logic requiring both power and temperature thresholds to be met at once [1]. Removal of deposited dust by wind requires a surface shear stress at or above the saltation threshold, which is not a schedulable event, and the storm conditions that would generate that stress are the same conditions that raise column optical depth and cut array output at the same time [8].

Technologies developed

The active suspension is the one mobility capability on Mars that no NASA rover has carried. Its value is not obstacle clearance, which a passive rocker-bogie already provides by design [12], but a recovery mode that does not depend on developing more thrust: lifting a sunk wheel, or contracting the whole suspension, changes the load distribution instead of demanding more shear from soil that has already failed. The thermal architecture pairs a passive stack that attacks conduction, radiation and convection simultaneously with a solar window that stores daytime heat for night use, converting part of the survival heating load from an electrical draw into a thermal one. MarSCoDe’s onboard particle-swarm wavelength recalibration is a narrower but transferable lesson: an instrument that cannot be thermally stabilized on a solar-powered platform can still hold calibration by matching against a known target rather than by controlling its own temperature [6].

What is not established

Rover mass, the exact panel count beyond what is visible in imagery, and a definitive account of the wake failure, dust accumulation versus a hardware fault, remain unpublished. The magnetometer discrepancy between ground and orbital field estimates is attributed to demagnetization at either the scale of the whole Utopia Basin or of the smaller ghost crater the rover landed in, and neither is ruled out [4].