Speaker
Description
Highly Eccentric Orbits (HEO; eccentricities above 0.8 and perigee above the drag regime) are favourable for scientific and observations missions since the satellite is outside of the Earth’s radiation belt for most of the orbital period, avoiding noise and radiation effects which can interfere with Earth and Universe observations. Over the years, more than 30 missions have been operating in this type of orbits (i.e. Chandra, MMS, THEMIS amongst the US missions; ISO, XMM, Cluster, Integral are the ESA ones), and future missions in this type of orbits are planned such as the Plasma Observatory one.
For this particular class of orbits, the re-entry velocity (> 10 km/s) is higher than from a circular orbit, which translates in the radiative heat exchange as the dominant heat transfer mechanism. The strong bow shock wave generated in front of the re-entering body and the consequent temperature rise results in a non-equilibrium flow condition, leading to molecular dissociation. The complexity of this phenomenology implies chemical reactions which are expected to belong to observable spectra.
However, due to the low occurrences, HEO (or super-orbital) re-entries are usually studied in the context of the re-entry of meteorites rather than artificial objects and the gap of knowledge related to the phenomenology for this type of re-entries is still large.
The Cluster II mission is a constellation of 4 identical cylindrical satellites flying in a tetrahedron configuration on HEO. The re-entry of the first of these satellites is expected in early September. Due to the dominant third body perturbation, the re-entry trajectory is very stable and predictable to a large extent, providing the perfect target for an airborne re-entry campaign and a unique opportunity for a repeatable experiment.
The work presented highlights the knowledge gaps that Cluster-II re-entry observations aim to fill in terms of understanding the thermal response of satellite components and predicting breakup events.
