Extreme Environments in NASA Planetary Exploration

One of the biggest challenges of solar system exploration is the variety of extreme environments that orbiters, landers, and probes must encounter and survive. For example, exploration of the Venus surface requires engineering systems and science instruments that can withstand intense heat (480°C) and pressure (92 bar). A spacecraft that dwells in the equatorial plane of Jupiter, or that orbits any of the inner Galilean satellites, must be designed to handle an extremely harsh radiation environment. Table 2.1 [1] summarizes planetary extreme environments. The planetary environments are organized by extremes in temperature; however, it is evident that missions will often encounter multiple extremes simultaneously. An adequate technical solution for coping with only one or the other of these environments may not work when they are presented simultaneously. For example, at Venus and Jupiter, high temperatures are typically coupled with high pressures, requiring technical developments that integrate solutions for both extreme conditions. Europa’s surface couples low temperatures and high radiation levels, requiring radiation-hard electronics that also function at low temperatures. In general, an important consideration is also the timing of the encounter with the extreme environment. This varies with the target. Examples include the following:

Venus: The temperature and pressure increase steadily during descent until extremes are reached at the surface. The surface exploration platform (lander, probe, etc.) may have to pass through sulfuric acid clouds (Figure 2.1).

Jupiter: Extreme temperatures and pressures increase during the descent phase into the atmosphere.

Europa: High radiation is experienced as the spacecraft enters the Jovian radiation environment, with a substantial fraction received prior to entering orbit. A combination of high radiation and low temperature characterize Europa’s surface.

Figure 2.1 Profile for Venus atmospheric temperature and pressure. https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9781315216911/9fc10d54-04ca-4e8b-af21-9892cbc5b25d/content/fig2_1.tif"/> (From Hall, J.L. et al., Venus Flagship Mission Study: Report of the Venus Science and Technology Definition Team, NASA, Washington, DC, 2009.) Table 2.1 Extreme Environments in the Solar System

Mission Stage

Space

Entry

In Situ

Target

Radiation (krad/Day)

Heat Flux at Atmospheric Entry (kW/cm²)

Deceleration (g)

High Pressure (bar)

Low Temperatures (°C)

High Temperatures (°C)

Day Length (Earth Days)

Chemical Corrosion

Physical Corrosion

High temperatures and high pressures

Venus surface

30

400

92

500

400

H₂SO₄

Jupiter (gas giants)

42

100

450

Low temperatures

Lunar permanently shadowed regions

−230

Comet nucleus

0.5 ^a

−270

Titan surface

−185

CH₄

Low temperatures and high radiation

Europa orbit

40

Europa surface

20

−180

Europa subsurface

0.3 at 10 cm

Thermal cycling

Moon

−180

120

27

Dust

Mars

−120

+20

Dust

a

This heat flux describes the heat flux at Earth for returned missions. A returned sample mission from a cometary surface is discussed further in Chapter 3. However, this heat flux will apply to any returned sample mission.