Hadas Porat

Radiometric temperature analysis of the Hayabusa spacecraft re-entry

Hayabusa, an unmanned Japanese spacecraft, was launched to study and collect samples from the surface of the asteroid 25143 Itokawa. In June 2010, the Hayabusa spacecraft completed it’s seven year voyage. The spacecraft and the sample return capsule (SRC) re-entered the Earth’s atmosphere over the central Australian desert at speeds on the order of 12 km/s. This provided a rare opportunity to experimentally investigate the radiative heat transfer from the shock-compressed gases in front of the sample return capsule at true-flight conditions. At these conditions, the total heat transfer to the vehicle has a significant radiative component and this can be estimated by studying the radiation emitted from the shock layer and the hot surface. Such measurements can be compared with numerical simulations of the flow and with results from ground-based testing in shock tunnels and expansion tubes. This in turn leads to a better understanding of the complex thermochemistry occurring within the shock layer and aids in the design of more efficient thermal protection systems for future spacecraft.

Vacuum ultraviolet and ultraviolet emission spectroscopy measurements for Titan and Mars atmospheric entry conditions

Vacuum Ultraviolet (VUV) emission spectroscopy radiation measurements were conducted for Titan and Mars atmospheric entry conditions using the Centre for Hypersonics X2 expansion tube. The VUV measurements were taken while viewing downstream through the shock layer of a scaled model. UV-Visible emission spectroscopy measurements were conducted in parallel, viewing the shock layer through a side window. The spectra was dominated by the CN violet molecular bands and the main atomic lines identified were C, N and Al. For a Titan 8.5km/s condition, sample of the calibrated spectra for the VUV is presented and discussed, alongside uncalibrated continues spectra from the VUV through to the UV-Visable.

Super-Orbital Re-entry in Australia: Laboratory Measurement, Simulation and Flight Observation

There are large uncertainties in the aerothermodynamic modelling of super-orbital re-entry which impact the design of spacecraft thermal protection systems (TPS). Aspects of the thermal environment of super-orbital re-entry flows can be simulated in the laboratory using arc- and plasma jet facilities and these devices are regularly used for TPS certification work [5]. Another laboratory device which is capable of simulating certain critical features of both the aero and thermal environment of super-orbital re-entry is the expansion tube, and three such facilities have been operating at the University of Queensland in recent years[10]. Despite some success, wind tunnel tests do not achieve full simulation, however, a virtually complete physical simulation of particular re-entry conditions can be obtained from dedicated flight testing, and the Apollo era FIRE II flight experiment [2] is the premier example which still forms an important benchmark for modern simulations. Dedicated super-orbital flight testing is generally considered too expensive today, and there is a reluctance to incorporate substantial instrumentation for aerothermal diagnostics into existing missions since it may compromise primary mission objectives. An alternative approach to on-board flight measurements, with demonstrated success particularly in the ‘Stardust’ sample return mission, is remote observation of spectral emissions from the capsule and shock layer [8]. JAXA’s ‘Hayabusa’ sample return capsule provides a recent super-orbital reentry example through which we illustrate contributions in three areas: (1) physical simulation of super-orbital re-entry conditions in the laboratory; (2) computational simulation of such flows; and (3) remote acquisition of optical emissions from a super-orbital re entry event

Radiative Heat flux Measurements for Titan Atmospheric Entry Condition in a Superorbital Expansion Tunnel

Entry into the atmosphere of Titan, a moon of Saturn, was studied using the X2 superorbital expansion tunnel. For Titan atmospheric entry conditions, the radiative heat transfer is expected to be significant even at what is considered to be a relatively low shock speed of 6.5 km/s. To further our understanding of superorbital flows, the experiments presented hereafter use newly developed radiation gauges to measure the radiative heatflux and emission spectroscopy to provide quantitative information about the radiating species in the shock layer for a Titan atmospheric entry condition. The radiative heatflux for a Titan 6.5 km/s entry condition was successfully measured by newly developed CNT-Rad radiation gauges. Radiative heatflux measurements were made using cylindrical and hemispherical models, confirming that scaling the shock standoff has successfully resulted in comparable radiative heatflux measurements. The spectral distribution and radiative intensity was also measured for the cylindrical model along the stagnation streamline. The results show that CN violet bands are dominating the spectra and can be analysed to allow a temperature analysis to further characterise the flow.

Emission Spectroscopy of a Mach Disk at Titan Atmospheric Entry Conditions

The prediction of heat transfer is important for atmospheric entry applications, as it guides the design of a spacecraft thermal protection system (TPS). The radiative heat transfer processes encountered by a spacecraft upon atmospheric entry are more complex in nature than the convective heat transfer and therefore more challenging to predict accurately, resulting in the use of large safety factors.