CNSA Extraterrestrial Body Landing Comprehensive Test Field

China Aerospace Science and Technology Corporation.

The Extraterrestrial Body Landing Comprehensive Test Field at Huailai County, Hebei (Chinese name 地外天体着陆综合试验场) is described by CNSA as the largest of its kind in Asia [2]. The English form used here is the one carried in the reporting of the 2019 test and has no operator-published equivalent.

The problem

A lander or ascent vehicle has to be tested in its last phase of flight: hover, hazard avoidance, slow descent, touchdown, and on the ascent side ignition and lift-off. On Earth the vehicle weighs three to six times what it will weigh on the Moon or Mars, and the engines and guidance loops are sized for the lower weight. A test field therefore has to remove part of the weight without adding inertia, friction or lateral force to a vehicle that moves in three dimensions.

Huailai does this with a three-dimensional follow-up system. The vehicle hangs from a cable that pulls upward with a constant force so the net downward force matches the target body, while the support tracks the vehicle in three dimensions so the cable stays vertical [1]. The tradeoff is general to suspension offload: the support hardware has mass, friction and stiffness of its own, and those do not shrink because the cable carries less than the full weight [1][5]. The Apollo answer, the Lunar Landing Research Facility at Langley (1965), hung a lander simulator from a gantry on cables carrying five sixths of its weight so astronauts could practice descent [5].

What has flown

The field has not flown; it qualified vehicles that did. The campaigns below are the public record, and the operator sources are press items that state dates and scope but no measured result [2][3][4].

Chang’e-3. The spacecraft hovers at 100 m above the surface to select a site, translates to it, descends slowly, and below 4 m shuts down the main engine and free-falls [1]. The follow-up system reproduced the hover, avoidance and slow-descent segments with rope tension balancing part of the vehicle weight. Chang’e-3 landed at 19.51 W, 44.12 N in northern Mare Imbrium on 14 December 2013 and deployed the Yutu rover on 15 December [14].

Chang’e-5. The campaign added take-off testing, which drove the addition of upper and lower stay cable drives [1]. Test masses were 1.5 t for landing and 0.8 t for take-off on a 20 t platform. The flight drill recovered about 1 m of core against a goal of about 2 m, with no analysis of why [17]. See chang-e-5-sampler.

Tianwen-1. On 14 November 2019 the lander ran hovering, obstacle avoidance and slow descent under a simulated gravity of about one third of Earth’s, as a check of design correctness [3]. It was the Mars program’s first public appearance, observed by envoys from 19 countries and by representatives of the EU, the African Union and APSCO [2][3]. Zhurong’s designers state a landing-site rock coverage about twice that of the Moon as a terrain driver and describe an active rocker-arm suspension with three self-extraction modes, as design statements with no test result [15]. See zhurong.

Lanyue, 6 August 2025. The comprehensive landing and take-off verification of the crewed lunar lander was completed at Huailai, the first such test of a crewed spacecraft in China [4]. It covered the landing and take-off system scheme, the control scheme, the touchdown engine cutoff scheme and the guidance, navigation and control to propulsion interfaces. Lanyue has a lunar module and a propulsion module and carries two astronauts [4]. It has not flown.

None of the flight outcomes is traced to a Huailai measurement in the sources held, so the field’s predictive accuracy against flight is not established. Yutu-2 later operated under a relay loop in which the first telemetry frame arrives 80 to 100 s after a command and execution is confirmed after 3 to 4 minutes, at a nominal 3.3 m/min [16]. A descent test does not reproduce that constraint.

What is being tried now

Cable-parallel drive at Huailai (ground tested, used for flight qualification). The Mars lander system replaced the gantry crane form with cable-parallel drive: 18 drive units and 36 wire ropes connect to the platform, driven by 24 AC servo motors [2][3]. The main hoist has six ground units with parallelogram stays from 133 m, the upper stay system six units at 84 m, and the lower stay six ground units at about 7 m. On the platform, three motors form the fast horizontal follow-up and three the tension fine-adjustment device [1]. The 36 rope tensions are planned by minimum-variance optimization, and rope length error is calibrated on a grid with bilinear interpolation. Measured cable inclination was at most 0.17 degrees, about 12 mm at a 4 m cable length [1].

Other suspension rigs (ground tested). NASA’s ARGOS holds a constant upward force on a suspended subject through a gantry robot over more than 340 cubic meters, at up to 3.3 m/s, detecting faults in under 20 ms [8]. Its three active and three passive degrees of freedom address the limits of POGO, parabolic flight and neutral buoyancy [7]. Across 14 subjects and 68 pivot configurations, a gimbal pivot at the payload center of gravity left the subject unstable; the usable zone was 2.5 to 6.4 cm above and 1.3 to 2.5 cm aft of it [6]. Halving the suspended gimbal mass from 105 lb to 53 lb improved subject ratings [7]. DLR’s LAMA, built for the Philae lander, showed that the suspension perturbs the touchdown it measures: a tilt limiter specified for plus or minus 3 degrees permitted at least 9 degrees, and touchdown detection triggered at 0.5 m/s on soft ground but 0.2 m/s on hard ground [9]. A retest found the suspension stiffness, 4080 N/m, more than sixteen times the pendulum rig’s 242 N/m, a difference corrected against 1996 to 2002 baseline data [10]. At small scale, IRGO, a Michigan Tech two-axis trolley tracking an infrared beacon over 3800 kg of simulant with a passive counterweight, has a stationary error of 0.3 mm and an untested control loop; it is laboratory only [13].

Reduced vehicle mass with Earth-gravity soil (ground practice, known bias). Coupled granular-dynamics simulation shows this practice gives optimistic trafficability: a 73 kg test rover climbing 30 degrees at about 42 percent slip corresponds to a 440 kg lunar-mass rover at about 85 percent slip, above the roughly 80 percent dig-in threshold, and at 10 degrees slip goes from 18 to about 75 percent [11][12]. Parabolic flight with soil and wheel both at lunar gravity measured drawbar pull to weight falling 20 percent or more and sinkage rising up to 40 percent against reduced-weight testing; granular scaling laws came within 8.5 percent on drawbar pull and erred conservatively [19]. Huailai holds the vehicle at flight mass and adjusts only net force, so it does not import this error, but its terrain field is undocumented.

Magnetic levitation of soil (laboratory only). A magnetic-gravity rig at 1/6 g, 1 g and 2 g measured cone penetration resistance 29.1 percent lower at 1/6 g than at 1 g at 40 percent relative density but only 8.8 percent lower at 76 percent, in a 95 mm by 160 mm chamber with a magnetite simulant [18]. It measures soil strength, not vehicle landing.

Consolidated practice (review, not data). NASA’s 2025 mobility test guide states that no known facility reproduces the inertial and dynamic effects of a fast vehicle specified to 15 km/h, and that cone index gradient as a lunar strength match is of uncertain validity under lunar gravity [20].

The numbers

Laboratory data

Parameter	Value
Operator	Not established in open sources [2][3]
Location	Huailai County, Hebei Province, China [2][3]
Commissioned	Chang’e-3 era, upgraded for Chang’e-5, rebuilt for the Mars lander [1]
Type	Outdoor gravity-offload landing and take-off test field
Floor area	Not published. Ground drive units sit on a 60 m radius circle [1]
Simulant or terrain	Not published
Ground truth	Suspension-point encoder and gyroscope for rope inclination; rope tension from motor torque [1]
Access	National program facility. No external user route published [2]
Cited by	zhurong, chang-e-5-sampler

Three-dimensional follow-up system

Parameter	Value
Working volume	20 x 20 x 80 m [1]
Tension range	0 to 20 kN, continuously adjustable; dynamic capacity 3x static [1]
Offload accuracy	Constant tension, 3 parts per thousand or better; tension error below 20 N [1]
Moving mass of platform	Over 20 t
Maximum cable inclination	0.17 deg, about 12 mm at 4 m [1]
Carriage tracking error	7.1 mm, upper carriage rise time 0.72 s
Coupled sway, limit case	Under 5 cm measured; 8 to 9 cm simulated at 60 m height [1]
Horizontal stiffness	Above 1.8 x 10^6 N/m, about 1.4 x 10^6 N/m above 80 m [1]
Vacuum, temperature	Outdoors at ambient pressure, not controlled [2]

Earlier builds

Parameter	Value
Chang’e-3	Three levels: 100 m coarse travel on rails, 16 x 16 m servo gear and rack, and the fast follow-up platform on six wire ropes [1]
Chang’e-5	18 ropes: six upper stay from 80 m height and 70 m radius, six lower stay from 5 m and 60 m, six main hoist; 60 degree spacing [1]
Chang’e-5 drives	Main hoist two 845 kW motors at 1250 rpm; upper stay six 540 kW; lower stay six 359 kW
Wire rope	22 mm diameter, 217 mm2 effective section

Average set tensions by platform height [1]:

Rope set	80 m	50 m	10 m
Upper stay	2.17 t	2.18 t	1.36 t
Lower stay	1.80 t	2.10 t	2.10 t
Main hoist	10.00 t	9.00 t	6.60 t

Comparison rigs

Rig	Figure
ARGOS	More than 340 m3, 3.3 m/s, fault detection under 20 ms [8]
Langley LLRF	240 ft high, 400 ft long, 265 ft wide, drop height about 200 ft, bridge crane 65,000 lb [5]
LAMA suspension stiffness	4080 N/m against 242 N/m for the pendulum [10]
IRGO	0.3 mm stationary error, 3800 kg simulant [13]

What is not established

The operator of the field is not named in open sources, and no source gives the terrain field’s composition, depth, grain size or whether it is a simulant [1]. The official items give no measured quantity: no offload accuracy achieved, hover altitude, descent rate or pass criterion [2][3][4]. The published system paper gives no residual vertical force and no control bandwidth, and its 8 to 9 cm sway figures are simulation. The designers chose suspension over other methods because it follows actively, not because it is exact [1].

Gravity is compensated, not changed. Internal masses, propellant slosh and any gravity-dependent behavior inside the vehicle still see 1 g. Suspension compensation must overcome the friction and inertia of the hardware, horizontal following is vulnerable to rope vibration, and the two couple and can destabilize the system [1]. Stiffness is bought with pretension, which costs motor power: the target is the smallest pretension that meets the requirement [1].

The envelope is the last 100 m: hover, avoidance, slow descent and touchdown, and for take-off the constant-tension hold before unlock and constant-force following after ignition [1]. The rest of the descent and the Mars entry phases are outside the field.

Whether 1 g and reduced-gravity soil tests agree is itself disputed [19][20]. Parabolic flight data and magnetic-gravity data on cone resistance differ in simulant, density and method, and the penetration resistance measured in the latter is not the cone index gradient the former reports [18][19]. Fast-vehicle dynamics have no known facility [20].

References