Thermal Protection System
The thermal design of the QARMAN CubeSat, with special attention to the re-entry phase, is a major topic. In fact during the atmospheric re-entry, the CubeSat will interact with the atmosphere at hypersonic velocity and, due to aerodynamic heating and exothermic chemical reactions, it will face temperatures which can go over 2000 K.
Protecting the CubeSat components from those heat fluxes is one of the most critical aspects of the mission: designing a TPS capable to protect the satellite within the standard dimensions of a 3U CubeSat, is a challenging and delicate task. After a preliminary study, the QARMAN team efforts were oriented to protect only those components necessary to complete the re-entry phase of the mission, designing a “Survival Unit” capable to keep the electronic components within the operative limits for the entire re-entry phase. Nevertheless this design shall be thermally compatible with the orbital thermal environment as well.
Front Thermal Protection System (TPS)
An ablative cork TPS is protecting the front part of the satellite during re-entry.
The material selected after a detailed TPS selection campaign is the P50.
Plasmatron Testing of the Front Cork insulation
Side and Back TPS
A ceramic layer of SiC constitutes the side panels of QARMAN. This protective shell will cover all the lateral sides of the satellite, protecting from the reentry heat fluxes. Moreover, a thin layer of FiberFrax insulation is placed between the side TPS walls and the internal structure, providing further insulation and protecting the CubeSat structure.
Survival Unit (SU) Concept
The idea is to collect all the components needed to complete the re-entry phase on one single PCB board, surrounded by a dedicated TPS. The thermal protection will be achieved with a layer of Aerogel, a lightweight and low-conductance material which will protect the electronic components from overheating. The aerogel is a brittle and structurally weak material, so a Titanium box is used to cover the entire SU and to connect the Survival Unit to the rest of the structure. The part of the Cover Box surrounding the Iridium Antenna, has been designed in ceramic material, to reduce EMI. The SU walls are also coated with a low emissivity/low absorptivity material, to reduce the radiated heat flux effects on the SU.
The components needed to be functional up to end of re-entry (ground impact) are: the OBC, the Iriudium modem, the batteries, the IMU, all the needed regulators. All this components are placed on a unique PCB, which is glued to a thick plate of aluminum, which serves as heat sink. Everything inside the SU.
Also the XPL DAQ board shall keep on functioning up to 45-50 km of altitude. For that board is foresee a dedicated Survival Unit placed just behind the cork TPS.
Design of the Survival Units: main SU (left) and XPL DAQ SU (right)