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Analysis of Various Concepts of the Reusable Space Transport Systems

Dr. Dudar E.N.

The development of techniques and software for design-ballistic researches on advanced aerospace launch systems at NPO MOLNIYA together with TsAGI is described in the paper. The features of different RSTS projects, most complicated problems and the ways of their solution are considered.

On the eve of the 20^th year’s anniversary of NPO MOLNIYA, it is necessary to note that within many years in parallel with the works on BURAN, our team accomplished researches and experimental development in a wide spectrum of winged space transport systems. We considered the systems, operating with the use of aerodynamic lift not only at returning of a reusable orbiter to the Earth, but also at the launch into orbit. This direction was developed practically from the very beginning of NPO existence, as a continuation of works on SPIRAL space system with a hypersonic booster-plane.

In 1976, in Aerodynamics Division the Dynamics of Flight Department was created. That time it was difficult to assume that except for primal problems of BURAN descent and landing, there will be a necessity in researches on the phase of launch into an orbit for a wide range of Reusable Space Transport Systems (RSTS). These systems were distinguishing in a level of aerodynamic lift capacities, number of stages, kind of start and type of propulsion unit.

Methodical and Software Development for Design-Ballistic Researches

At the end of 1977, the Deputy General Designer, Head of Division Dr. Samsonov Ye.A. set the task to develop, in the shortest terms, the program for calculations on BESM-6 computer of injection trajectories for the space systems of different types, including horizontally launched systems with the subsonic carrier-plane.

At the initial stage of works a certain aid was collected due to studying the experience of NPO ENERGIA, however, it was necessary to create a completely new technique for horizontally launched systems and to develop a computer program starting ‘from zero’.

It was decided to engage in this task 15 Division of TsAGI. In this division, responsible for dynamics of flight, the researches on phase of launch were already carried out at that time. It is necessary to note the great contribution of senior scientist of a TsAGI Dr. Filatiev A.S. to development of the methods and software.

In 1977, in three months after the work beginning, the first tested program for BESM-6 named STARTV has appeared as a result of efforts of joint team working together with TsAGI. The elementary methods of parameter optimization were used in it alongside with some classical solutions, such as, for example, the widely known Okhotsimsky-Loaden’s law, were used. Good convergence of iterative procedures and simplicity of the optimization method have allowed further on to fast update the program for different particular projects. It allowed to take into account any constraints: on conditions of longitudinal balancing, on aerodynamic loads on the Space Flying Vehicle (SFV) construction, on conditions of safe separation with the Carrier-Plane (CP) and other constraints, which number increased during particular system’s designing. Practically at once, the program started to be intensively used in mass calculations accompanying design-engineering works in NPO MOLNIYA.

It was right at the beginning of researches that the principled distinctions in mechanics of optimal flight of horizontally launched systems and conventional systems of vertical start have come to light. The physical nature of these distinctions was poorly studied. Therefore the need for development of more serious methodical support and software was felt. The work on creation of the ASTER new program started, in which the classic methods of optimization were used, in particular, L.S. Pontryagin’s Maximum Principle in classical statement. This program allowed to receive the following interesting results: the analysis of influence of the aerodynamic characteristics, thrust/weight ratio and other the SFV design parameters on the structure of optimum control and on mass of payload injected into an orbit.

The results of study on optimum injection trajectories of SFV having aerodynamic lift capacity, were reported on different conferences and published in scientific journals [1]. In 1991, a team from TsAGI and NPO MOLNIYA for the cycle of works on creation methodical support and software was awarded with the Premium named after Prof. N.Ye. Zhukovsky.

In parallel with researches under the STARTV and ASTER programs, by forces of employees of NPO MOLNIYA and TsAGI program was also developed for calculation of through injection trajectories of space systems including the stage of pre-launch CP maneuver of ‘pull-up’ type. This maneuver is executed before separation with the purpose of creation of the optimum initial state for the SFV launch. The ‘through’ program has been created by Mr. V.M. Sumachev under direction of Prof. V.A. Yaroshevskiy. The idea of combining the aircraft and rocket flight legs within the framework of the unified optimization task has appeared very fruitful. Later on, the leg of CP pre-launch maneuver was also added to STARTV and ASTER programs. Further on, all the main design-ballistic calculations were conducted only on through models of the Aerospace System (ASS) motion.

The mentioned above three programs (and their authors) competed with each other to some extent, but as was proved later on, for each of these programs the huge volume of calculation researches was coming. The program of Mr. Sumachev V.M. was mainly used for the launching systems with straight-flow air-breathing engines (ramjet and scramjet), in particular, in works on KHOLOD theme. The STARTV and ASTER programs were applied more often at selection of main design parameters and formation of launching systems configuration with Liquid Rocket Engines (LRE).

Practically all the information on similar researches, carried out in different civil and military scientific and educational institutions, came to NPO MOLNIYA. It enabled to compare methods and results of calculations and to implement in practice all new interesting methodical solutions.

It is necessary also to note the cycle of works on research of full motion CP and SFV on the legs of pre-launch maneuver and separation. These researches were conducted on more complicated mathematical models, including the angular motion relative to the mass center and dynamics of drives. The greatest contribution to this direction was made by Mr. Leutin A.P. (TsAGI), Sergeev I.V. (NPO MOLNIYA), Dr. Serdyuk I.I. and Mr. Karpov A.S. (ANTK Antonov).

In parallel with creation of the software for design ballistics of aerospace systems, the direction of works on guidance and navigating methods was also developed. Together with VIKI named after A.F.Mozhaiskiy (St.-Petersburg) within several years the researches on formation of onboard algorithms of the trajectory Guidance System (GS) for the task of injection into an orbit of horizontally launched SFV were conducted. KVVAIU Kiev Military Academy, Moscow Mars Design Bureau, TsAGI and MAI were engaged in this work later on. Three main methods of construction of onboard GS algorithms were completed:

• numerical prognosis of terminal state on the reference trajectory;

• analytical prognosis of terminal state with the help of approximated formulas;

• solution of the variation problem with allowance for aerodynamic forces.

The most promising the method with the analytical prognosis was recognized which was worked out in Mars Design Bureau (Dr. Sokolov V.N., Mrs. Koloskova Ye.B.).

Besides the injection into an orbit, the researches and design-construction works on space systems has demanded the creation of other programs for computer modeling of system elements motion on the following flight legs:

• elliptic ascent transfer including injection of the space vehicle into geo-stationary orbit;

• dropping on the ground of expendable non-recoverable system components;

• maneuvering of winged SFV with diving into high layers of atmosphere with the purpose of changing the orbit parameters;

• de-orbiting, descent in atmosphere, pre-landing maneuvering, landing approach and landing of the winged SFV.

The programs for calculation of flight performance (FP) and takeoff and landing performance (TLP) of subsonic airplanes were developed. These programs were used for long range flight, in particular, using of the subsonic airplane as the carrier of ASS. These programs and the appropriate techniques were also applied at calculation researches on the BURAN orbiter, space launching systems and on airplanes of ‘tri-plane’ scheme.

Up to the end of 80s NPO MOLNIYA and TsAGI possessed a sufficient arsenal of techniques and programs for design-ballistic calculations of the launching systems of any type. The programs were realized both on large computers like BESM-6, ES-1040 and ELBRUS, and on PCs with high performances.

In the process of researches of the systems with aerodynamic lift capacity, the very important new results were obtained on the influence of lift-to-drag ratio of a horizontally launched spacecraft on the features of launch and structure of optimal control. The estimations of gain were obtained for winged vertically takeoff launchers when using the flat trajectory with a lift as compared to the conventional launch scheme with gravitational turn. It is possible to consider the established good business contacts of specialists from NPO MOLNIYA with scientists and specialists of different research institutes, design bureaus, civil and military high educational institutions as one of results of huge efforts on creation of methodical support and software.

Design-ballistic Researches on Different RSTS Projects

Alongside with the works on BURAN and project of Multipurpose Aerospace System (MAKS) on the basis of AN-225 subsonic carrier-plane, the researches on a wide range of projects of reusable space transport systems at NPO MOLNIYA, in particular, within the frameworks of OPTIMUM, Rocket-MAP, ОRYOL R&DW were conducted. Many operating calculation and design works on verifying the characteristics of different RSTS versions, offered both by domestic and foreign corporations were executed. From all diversity of RSTS versions researched in different countries, it is possible to select the following main types and the most known projects:

Launch Systems of Vertical Start

1. Launchers with a reusable orbital stage: Arian-5/Hermes (France), Н-2/Hope (Japan).

2. Reusable two-stage RSTS with a winged recoverable booster of the 1 stage: Shuttle-2 (USA) and similar projects of NPO MOLNIYA and NPO ENERGIA.

3. Reusable single-stage launchers (SSTO):

• SSTO with vertical rocket landing - Delta Clipper (USA), Beta-2 (Western Europe);

• SSTO with horizontal landing - winged SSTO (USA), winged ASS (NPO MOLNIYA), lifting body SSTO (USA).

Launch Systems of Horizontal Start

1. Two-stage aerospace systems with subsonic carrier-plane: MAKS (CIS), AN-225/HOTOL-Interim (CIS, Great Britain).

2. Two-stage aerospace systems with a hypersonic booster-plane: Sanger (Germany), KHOLOD (Russia).

3. Single-stage aerospace airplanes (ASP) with LRE, launched from the ground-based accelerating device: ASP (NPO MOLNIYA), similar American and West-European projects.

4. Single-stage ASP with combined propulsion system: NASP (USA), HOTOL (Great Britain), TU-2000 (Russia).

The basic performances of some of the indicated projects are shown in Table 1.

The researches on practically all the indicated concepts were conducted at NPO MOLNIYA. The most deeply (at a level of draft design) MAKS project including two basic designs of the second stage (Fig. 1, 2) is worked out:

• reusable orbital plane (OP or Orbiter) and external fuel tank (ET);

• expendable launch unit (cargo version MAKS-T).

RSTS versions developed in different countries Table 1

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