نشریه فناوری در مهندسی هوافضا
پیاپی 1 (تابستان 1396)

Most space missions fall in the hypersonic reentry regime. There are several open questions and unknown phenomena in aerothermodynamics around vehicles at flow regimes exceeding Mach 4 due to its inherent complexities. Strong entropy gradients, thick shock layers, dissociated high temperature flows, chemically reacting boundary layers, and viscous interactions are some of the unique flow features dominating the hypersonic flight regimes. It is possible to carry out a detailed analysis on spacecraft aerodynamics leading to an optimized design. Considering the complexity of the problem, desired accuracy of the analysis, and restrictions of numerical methods such as CFD, the experimental approach is preferred in most real-world projects. Due to the increasing importance of Hypersonic Aerodynamicsin modern aerospace studies, this paper reviews the recent advances, technical achievements as well asindustrial and scientific trends subsequent topresenting a brief introduction to the field.

Due to the complex nonlinear nature of Navier Stokes equations, theyhave not yet been fully solved ad hencethe role of classical CFD methods have become more highlighted. Using numerical methods, we can discretise nonlinear partial differential equations and change them into linear algebraic equations thatcan be solved via classical methods in a very straight forward manner. In these approaches, also each method suffers some limitations which areimposed on it during its derivation, so inorder to cover the weaknesses and shortcomings of these methods, many scientists and researchers try to improvethem or invent new methods. Continuum assumption,being created during NavierStokes equations derivation, is an extreme limitation for classical CFD methods which puts them in the macro-scale category. The goal of this paper is to introduce the strengths of a modern CFD method which is a mesoscale method that can easily cover most shortcomingsof the macroscale approachesand can handle a wide range of problems satisfactorily.

The major purpose of this paper is presentation of the technology development phase (modernization or technology management) in space systems and also the review of technology development in space launch system of propulsion system. To this end, firstly, the technology areas in both propulsion systems and space launch systems and technology development are introduced. In this study, technology development and achievement trend in all propulsion subsystems are common. Propulsion system used the technology of kerosene and Nitric Acid in the first the step. Then the Hydrazine fuel, N2O4, L(O2), Kerosene and finally L(O2) and (H2) are achieved. As a conclusion, a new SLS in space transportation is considered and the reason for technology development is clarified so as to find a reduced cost (in both space launch system technology development approaches) and enhance the performance (thrust chamber low cost concepts and reduction of engine components in Expandable Launch Vehicle (ELV) and thrust chamber enhanced life concepts and reliability improvemments in Reusable Launch Vehicle (RLV)).

In the present study, the evolution of using TVC as a novel technology in gas turbine combustors is investigated. The reported data suggest that different types of TVCs (AFRL and GE products) have the potential to provide low lean-blow out (LBO) and a wide range of dynamic operations. Also, in some types of TVCs, the NOx emission is in the range of 40% to 60% of ICAO standard and combustion efficiency is maintained at 99%. Moreover, TVC technology has passed the technology readiness level 6 but to the date, its use has not been reported in any kind of commercial gas turbine engines.

Today, in order to reduce costs, the use of small satellites in LEO orbit has been considered and byincrease of observation missions in this orbit, which requires high orbital precision satellites,orbital control of  LEO satellites beside attitude control has been especially important. Recent researches have tried toincrease system’s accuracy and on the other hand, reduce costsmore than before by offering autonomous orbit control system. This system hasreduced human intervention in the ground stationby maintaining all or some of satellite orbital elements via satellite itselfand thus has eliminated need of multiple ground stations; also in addition to costreduction andaccuracy increase, it adds abilities to space missions that did not exist before. This researchwill analysis approaches of using autonomous orbit control by expressing  features of this system and reviewing theoretical and practical researches in this regard.

First, the history of space explorations is reviewed briefly in this paper alongside with current successful and future missions in this field. Then,missions with landing on celestial bodies, especiallyMoon and Mars landings, and their technical problems and mission challenges are reviewed. Then, as one of the requirements for landing missions, the soft landing problem is introduced in details. As a specialcase, the soft landing on the Moon with mission phases and other system requirements is presented. Due to the importance of fuel saving in the space, the soft landing problem on Moon is modeled as a minimum fuel optimal control problem with nonlinear ordinary differential equations. The governing equations, initial and final conditions in various cases and common performance index formulations are also given based on the recentreferences. Finally, the results of a numerical simulation in a test case problem of Moon landing arereviewed.