According to the white paper, China's Space Activities in 2016, the Mars sample return mission represents one of the main tasks to be implemented in China's deep space exploration field in the next 10 years. As the key technologies to be developed for Mars sample return, the design, analysis, and verification for Mars take-off and ascent can play a very important support role in the engineering design and implementation of the rover.

Moreover, the shape design of Mars ascent vehicles (MAV) is the key link of the Mars take-off and ascent technology.

Currently, countries all over the world mainly adopt two routes for the shape design of Mars ascent vehicles. One is the slender body similar to the missile/rocket, and the other is the short blunt body with a high loading volume ratio. Furthermore, the thickness of Martian atmosphere is about 100km, and although the atmospheric density at the same altitude is only 1%~10% of the earth's atmosphere, its effect on aerodynamic drag in the process of ascent shall also be considered.

In a research paper recently published in Space: Science and Technology, Qi Li from Beijing Institute of Spacecraft System Engineering studied the aerodynamic characteristics of two types of MAV, namely slender body and short blunt cone cylinder, and explored the influence law and efficiency of the change of forebody generatrix parameters on the aerodynamic performance, which can provide design basis and data basis for the aerodynamic selection of future MAV.

The authors first proposed the aerodynamic performance demands of MAV. On one hand, the optimization indicators for the drag performance of ascent vehicles are proposed as follows:(1) When the maximum windward section is taken as the reference area, the zero-attack-angle drag coefficient of an ascent vehicle with a short blunt body shall not be higher than 1.02 at Ma2.0 and 0.8 at Ma4.1, respectively.

When the maximum windward section is taken as the reference area, the zero-attack-angle drag coefficient of an ascent vehicle with a slender body shall not be higher than 0.9 at Ma2.0 and 0.44 at Ma4.1, respectively. On the other hand, the authors identified that the ascent vehicle should be capable of static stability in the atmosphere. The reason behind the fact is that a little disturbance such as crosswinds and asymmetric jets will cause the ascent vehicle to deviate from the designed trimmed attitude and result in large attitude drift, thereby increasing aerodynamic drag and inducing large oscillation.

Afterwards, the method of selecting shape parameters of the forebody of MAV is proposed. During the ascent of an ascent vehicle from the surface of Mars, its aerodynamic drag mainly comes from shock wave drag, wall friction drag and pressure drag and is proportional to the inflow pressure. According to the previous research, the shock wave drag of a flight vehicle in the supersonic region accounts for more than 70% of the total drag. Therefore, reducing the shock wave drag of the ascent vehicle is crucial to the lower energy consumption and system cost. With the aerodynamic configuration design of the warhead as a reference, the shape of the warhead is determined by the generatrix curve type.

Therefore, the authors researched the influences of five common generatrix curve types on the aerodynamic performances of MAV, including spherical-conical, circular arc, parabolic, exponential, and von Karman curves. In detail, the three-dimensional compressible viscous gas dynamics equations are used as the governing equations of flow field and the finite volume method of grid center based on structural grid was used to solve the governing equations. Moreover, Roe's FDS scheme was used to discretize the flow term, and MUSUL interpolation and Min-mod limiter were used to obtain the second-order accuracy. Term was iterated in LU-SGS format. The turbulent model of viscous diffusion term adopts an equation model based on SA.

Finally, according to the Influence analysis of aerodynamic performance of forebody configuration of the slender ascent vehicle as well as the short blunt ascent vehicle, two main conclusions are obtained: For slender ascent vehicle, the shape of conical forebody can play a better role in drag reduction, and the drag performance after drag reduction can meet the demand.

However, the slender body has poor static stability due to its front center of pressure, and the improvement of forebody shape has little effect on static stability. (2) For the short blunt body riser, the exponential forebody with 0.2 Research Report: "Study on Effect of Aerodynamic Configuration on Aerodynamic Performance of Mars Ascent Vehicles"

Related Links
Institute of Spacecraft System Engineering (ISSE)
Mars News and Information at MarsDaily.com
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