Uranus and Neptune atmospheric-entry probe study

Entry trajectories, decelerations, and heating and heat shielding requirements of probes entering the atmospheres of Uranus and Neptune at velocities up to 26.5 km/s were studied. Much of the Galileo Jupiter probe technology was applicable to these outer-planet probes; therefore, the same configuration was used. Steep (ballistic) entry flight-path angles were needed to facilitate communication from the probes to the spacecraft during atmospheric descent. The Galileo probe's 400 g maximum deceleration structural design was used to define the maximum entry angles for the Uranus and Neptune probes. The carbon phenolic heat shield material used on the Galileo and the successful Pioneer-Venus probes was selected. Turbulent boundary-layer convection dominated the heating of the Uranus and Neptune probes; radiative heating was negligible by comparison. The peak heating rates were found to be about 6 kW/cm, or approximately 25% of the Galileo probe's expected maximum value. The forebody heat shield mass fractions for these outer-planet probes were found to vary from about 0.08 to 0.16 for entry velocities from 22 to 26.5 km/s. By comparison, the Pioneer-Venus probes' heat shield mass fractions ranged from 0.10 to 0.13, and the Galileo probe's forebody value is 0.43.