Publication: Inflatable aerodynamic decelerator for cubesat reentry and recovery: geometry effects under rarefied conditions
Date
2023-08
Authors
Caqueo Jara, Nicolás Gabriel
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Abstract
In the last decade, a large number of nanosatellites have been placed into Earth’s lower orbits, with the
most common class of nanosatellite being the CubeSat. The long-lasting nature of these objects is causing a
significant number of close encounters between active and decommissioned satellites. An efficient way to
address this problem is the use of inflatable aerodynamic decelerators (IAD) for the deorbit and recovery of
nanosatellites. Furthermore, the application of this technology to CubeSats reentry and recovery missions
could enhance the capabilities of these small satellites in a sustainable and accessible manner.
Inflatable aerodynamic decelerators are devices designed to increase the area of the thermal protection
system of a spacecraft regardless of the diameter constraints of the launch vehicle. These devices can be
stored in a compact stowed configuration and expanded into a high-drag aeroshell for reentry and recovery
applications. In this scenario, the primary objective of this investigation is to evaluate the impact of the
IAD geometry on the flow, surface properties, and aerodynamic forces experienced by the spacecraft during
reentry. In particular, numerical simulations are carried out on three distinct IAD configurations coupled
with a 1U CubeSat during the upper stages of atmospheric reentry. The geometries considered in this study
are assumed to be fully inflated, with a forebody radius of 0.3 m and three different cone angles of 68.8◦
,
45◦
, and fully rounded. Reentry of the IADs coupled with a 1U CubeSat payload was simulated considering
nonreactive flow at 0◦
angle of attack and 105 km of altitude. Due to the high degree of flow rarefaction at
this altitude, the Direct Simulation Monte Carlo method is used for all computations.
The influence of the IAD geometries on the velocity, temperature, density, and pressure profiles and
contours was carefully investigated and discussed. From the results, the formation of a strong diffuse shock
wave can be observed for all geometries considered in this investigation. However, a lower angle of the
inflatable aeroshell is associated with a thinner shock wave and a maximum shock wave temperature closer to
the shield’s surface. These differences subside in the flow expansion over the IAD shoulder. In the rear of the
inflatable shields, a low-temperature and low-velocity region is observed, indicating that the IAD geometries
successfully mitigate the harsh conditions of reentry experienced by the payload. Moreover, it was found that
aerodynamic elongated shapes exhibit larger wake regions when compared to blunt geometries, albeit at the
expense of slightly higher gas temperature closer to the front surface of the shield. No recirculation zone was
observed in any of the simulated IAD configurations considered in this investigation.
The effect of the forebody geometry on the surface aerothermal coefficients and aerodynamic forces
is discussed thoroughly. According to these results, the thermal load experienced by the shields is particularly
severe near the stagnation point, especially for aerodynamically shaped geometries. This kind of geometry
exhibited the highest maximum heat transfer coefficient and total heat transfer of all configurations studied.
However, it also showed a lower heat transfer coefficient on the middle segment of the shield’s surface
compared to the other geometries. In addition, the maximum pressure coefficient and the minimum shear
stress coefficient were also identified at the nose tip, with the shear stress increasing toward the edge of
the shoulder at a rate dependent on the geometry of the aeroshell. Geometries with aerodynamic profiles
exhibited a low drag coefficient and a high ballistic coefficient, while more blunt geometries were found to
have a better mass-to-drag ratio. The results show that thermal and mechanical loads decrease to negligible
values in the rear section of the shield and on the CubeSat surface, further demonstrating the effectiveness of
IAD devices in reducing mechanical loads on the payload.
All simulations were carried out using the dsmcFoam+ code, an open-source Direct Simulation Monte
Carlo solver. A validation and verification process is performed to assess the physical accuracy and numerical
resilience of the dsmcFoam+ code under conditions similar to those employed in the main body of work of this
investigation. For the validation process of one of the test cases, additional continuum-based computational
fluid dynamic computations were performed by researchers from the University of Naples Federico II at the
lowest altitude of analysis. The results of this process demonstrate that the dsmcFoam+ solver is an adequate
tool for the numerical investigation of CubeSat-based IADs in rarefied reentry conditions.
Description
Keywords
AEROTERMODINÁMICA DEL DESEQUILIBRIO , SIMULACIÓN DIRECTA MONTE CARLO