Environments

Six operating environments, each set out as the engineering literature defines it: the design values hardware is built against, the model or measurement document each value comes from, and the conditions the value was taken under. Where a quantity is a property of the destination rather than of a vehicle, it is settled on one of these pages, and the robot, software, avionics and testing pages cite it rather than restate it.

The specifications and reference models that span more than one destination are listed under environment references. What a ground rig reproduces of any of these, and where its fidelity stops, is under test facilities.

What separates them

• Microgravity and Orbital. Free fall is not zero acceleration. The residual field is treated as three bands separated by frequency: a quasi-steady band below 0.01 Hz, predictable anywhere in the vehicle from one measurement and the rigid-body kinematics, and vibratory content from 0.01 to 300 Hz and transient content, both of which have to be measured near the point of interest [2]. Surface exposure is set by orientation rather than by altitude, and atomic oxygen fluence on LDEF was 8.81e21 atoms/cm2 on the ram face against 1.13e3 on the wake face, through 34,000 thermal cycles in 5.8 years [3].
• Lunar Surface. The equatorial surface runs between a mean maximum of 391 K at local noon and a mean minimum of 96 K before sunrise, and polar illumination follows no latitude rule, because local topography decides it [1]. The equatorial night lasts about 350 h, and warming a 70 kg rover back to its 243 K minimum operating temperature at dawn costs 452 to 493 W h of battery energy [4], so the unpowered interval sizes the thermal and power design. Round-trip communication is short enough to drive against: VIPER was designed around 6 to 10 s [5].
• Martian Surface. Surface gravity is 3.712 m/s2, and the engineering atmosphere model is parameterized on solar longitude, latitude, longitude and local time rather than on calendar date, with dust storm intensity carried to an optical depth of 3 [6]. Round-trip light time runs 5 to 40 min over the synodic cycle, which precludes real-time monitoring and is why the operations cycle is sol-based [7].
• Small Bodies. Weight is not the dominant term in the surface mechanics. The grain radius at which van der Waals cohesion equals a grain’s own weight is 6.5e-4 m at 1 g and 0.65 m at micro-gravity, which makes the terrestrial analog a cohesive powder rather than a cohesionless soil, and net surface acceleration at Itokawa is 6 to 9 micro-G [8]. What a touch-and-go sampler meets changes character across an assumed regolith cohesive strength of about 50 to 300 Pa, between cratering with no spring engagement and a strength cone that stops the assembly at the surface [9].
• Outer Planets. Solar flux and communication rate fall as the inverse square of heliocentric distance, and round-trip light time runs to hours, so fault response cannot be supervised from Earth [10]. The two reachable surfaces are a giant planet entry corridor, where the Galileo probe met about 30 kW/cm2 of peak heating and 250 g of deceleration [11], and Titan, whose 1.35 m/s2 and dense cold atmosphere put rotorcraft flight power per unit mass at about a fortieth of the Earth value [10].
• Venus Surface. About 460 C at roughly 90 bar of supercritical carbon dioxide with a sulfuric acid aerosol above it [12], which admits two design responses: a sealed and thermally isolated volume with a fixed lifetime, or electronics that operate at ambient temperature. A packaged alumina assembly has been held at 460 C and 92 bar in a simulated Venus atmosphere for 60 Earth days [13], and a silicon carbide JFET RAM has run 10,100 h at 500 C [14].