Aerothermal Modeling Challenges for Ice Giant Entry Probes

In June 2017, NASA published the Ice Giants Pre-Decadal Survey Mission Study Report which took a fresh look at science priorities and mission concepts for missions to the Uranus and Neptune systems. In addition to science objectives, the team explored the state of required technologies for remote and in-situ science exploration. Notably, three of the four mission architectures considered in the study included an atmospheric probe. More recently, interest has grown within ESA for outer planet exploration. In support of this objective, ESA has performed two CFD studies (January & July 2019) which analyzed the feasibility of stand-alone elements (orbiter and probes) provided by ESA as a part of a NASA led mission to the Uranus or Neptune systems. The first study was carried out by ESA experts with active participation of NASA/JPL. ESA highlighted the necessity to deepen the knowledge characterizing the aerothermal environment of the probes.

 

Entry environments for the NASA study were estimated using an aeroheating correlation that was calibrated to data returned from the Galileo probe entry to Jupiter. For the ESA concept study, aeroheating estimates were made using correlations employed during the design of the Galileo probe. Importantly, these correlations show large discrepancies in predicted total aeroheating (in some cases more than 100%), largely due to differences in the predicted radiative heat load. The magnitude of the disagreement is disconcerting in and of itself, but the problem is made worse by the fact that both correlations are being extrapolated from the extreme Galileo entry conditions to the (relatively) more benign Uranus and Neptune entry. It is likely that neither correlation is providing an accurate assessment of the true aeroheating loads at this time. Given that current NASA predictions are near the limits of existing TPS test capability, and that ESA predictions are more severe, improving the accuracy and associated margins of the prediction is critical to better assess mission feasibility.

 

Recent work in NASA by Cruden (AIAA Paper No. 2015-0380) and Erb (AIAA Paper No. 2019-3360) have substantially improved our fundamental understanding of aerothermodynamics in Hydrogen-Helium atmospheres. Similar work is planned in ESA as well. However, these recent data have not been incorporated into updated design models for Outer Planet probes. In addition, this work does not address the problem of trace atmospheric constituents (such as Methane) that are known to be present in Ice Giant atmospheres and may substantially alter the resulting shock layer radiation signal by providing a ready source of free electrons to initiate excitation processes. The proposed presentation will review the current status of aerothermal modeling for Ice Giant entries and propose a path forward to reduce key uncertainties and enable optimized thermal protection system designs.