What's Qarman?

 

QARMAN is the ”QubeSat for Aerothermodynamic Research and Measurements on AblatioN” of  the von Karman Institute, developed in the framework of the QB50 project.

Design

An innovative concept for passive stability is employed for QARMAN based on the aerodynamic forces. Typical satellites are using either passive control via permanent magnets which aligns itself with the magnetic field lines or active control elements like reaction wheels and magnetorquers. These active mechanisms have major drawbacks due to the power consumption of the system during actuation which could be too demanding for small scale satellites like CubeSats. Furthermore they have a strong impact on the mass and volume budget. However the main issue preventing their usage on QARMAN is that the disturbance forces below 150km of altitude are too large to be counteracting with a reasonable sized systems.


Therefore QARMAN employs an Aerodynamic Stability and De-orbiting System which relies completely on the aerodynamic forces acting on the satellite. This passive system has the advantages of no power consumption after deployment and that the restraining forces are increasing with decreasing altitude similar to the perturbations. This makes the system ideally suitable for the QARMAN mission allowing the satellite to perform the complete re-entry with a controlled attitude.

A trade-off campaign was performed to identify the best solution of the AeroSDS used on QARMAN keeping in mind the different requirements on the system like compatibility which orbital and re-entry phase, a reliable and simplified system, the interoperability with other systems like power generation and the target lifetime in orbit from deployment altitude. As an example the effect of different systems on the lifetime is shown in the following picture and gives evidence of the customable design to satisfy the mission needs for faster or slower de-orbiting.

NRLMSISE00 atmospheric model, initial altitude 320km, inclination 79°
NRLMSISE00 atmospheric model, initial altitude 320km, inclination 79°

A design based on four ceramic panels with a length of approximately 30cm and inclination of 15° with respect to the longitudinal axis was chosen due to the good performance in orbit and during the re-entry mission. To ensure a smooth outer surface and transition without gaps from the sidewalls to the panels, a deployment based on two simultaneous motions (rotational and translational) was implemented for the AeroSDS. Sufficient generated power during the first phases in orbit is ensured by the integration of solar cells on both sides of the deployable panels.

AeroSDS in deployed state with solar cells
AeroSDS in deployed state with solar cells

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
Plasmatron Testing of the Front Cork insulation

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.

Sidewalls insulation
Sidewalls insulation



 

Back Plate (Left)
Back Plate Left
AeroSDS Right
AeroSDS Right

 
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
main SU
XPL DAQ SU
XPL DAQ SU


Design of the Survival Units: main SU (left) and XPL DAQ SU (right)

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