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Phases and Manoeuvres Involved in Orbital Rendezvous Missions

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Phases and Manoeuvres Involved in Orbital Rendezvous Missions INTERNATIONAL JOURNAL FOR RESEARCH & DEVELOPMENT IN Volume-6, Issue-2 (Sep-16) TECHNOLOGY ISSN (O) :- 2349-3585 Phases and Manoeuvres Involved in Orbital Rendezvous Missions __________________________________________________________________________________________ Rafał Duch1 1Department of Avionics and Control Systems 1Rzeszow University of Technology, Rzeszow, Poland Abstract – The information presented in this paper provides measurement. RAAN angle is measured between the points of the reader with an overview of the major techniques used spring equinox and the ascending node [1]. during rendezvous and docking of spacecraft. The whole process is divided into five phases: launch, orbit injection, orbit phasing, rendezvous operations and mating. These phases are required for successive establishment of necessary kinematic and dynamic conditions leading to the connection of target and chaser spacecraft. Each stage of rendezvous mission profile is executed under issues and constraints such as: time of launch window, optimal strategy for orbit phasing, limited communication link availability, Sun illumination conditions for spacecraft powered by solar energy, crew working cycles, safety concerns and general operating issues of target and chaser objects. Figure 1: Orbit Parameters [2] INTRODUCTION Another important orbital element is defined as Eccentricity The aim of the following sections is to describe the main (e), shown below. Its value is used for a visual representation issues of rendezvous phases. The reader will be familiarised of orbit pattern. Existing patterns are: circle (e=0), ellipse (0 < with the basic concepts of each phase. The rendezvous e < 1), Parabola (e=1), hyperbola (e > 1) [7]. mission is initiated during launch and finalised after completion of connection between spacecraft. II. LAUNCH First matter taken into consideration is the launch window. Launch in easterly direction is favoured due to tangential velocity component of the rotation of Earth (approx. 458 m/s at the equator). The time of launch should remain in close vicinity to the moment of target spacecraft orbit plane passage. It is the early launch phase when the most efficient correction Figure 2: Orbit Eccentricity [2] of plane error of desired orbit is possible. Launch window size III. ORBIT INJECTION is also limited by the launcher correction capability [6].The Orbit Injection phase is accomplished when the chaser critical parameters of drawn orbit are: i – inclination angle, Ω spacecraft is inserted into a stable orbit. Chaser‟s orbital plane - right ascension angle of ascending node (RAAN), a – major should be as identical to target orbital plane as possible. Initial axis size, b – minor axis size and υ – true anomaly angle. True orbit of chaser spacecraft is usually situated lower and at an anomaly angle is used for an instantaneous satellite position 265 All rights reserved by www.ijrdt.org Paper Title:- Phases and Manoeuvres Involved in Orbital Rendezvous Missions angle behind the target. Further perigee raising manoeuvres which allow for low fuel consumption during orbit change must be taken into consideration in case of insertion into low process [1]. initial orbit. The case described above is shown in the Fig. below. The angular difference dividing both spacecraft is defined as “phase angle” [2]. Figure 5: Apoapsis Lower and Periapsis Raise [2] Chosen strategy of changing orbit parameters is dependable on the following factors: time limitations, initial phase angle, needed corrections of orbit parameters [1,6]. We can distinguish between five strategies involving different manouevre types: 1 – backward and forward phasing (Fig. 2), Figure 3: Orbital Elements [2] 2 – elliptic or circular phasing orbits, 3 – manipulation of IV. ORBIT PHASING height of circular orbits, 4 – apoapsis and periapsis The process of reducing the phase angle between chaser and modification of elliptical orbits, 5 – corrective manoeuvres in target spacecraft is “orbit phasing”. Its objective is to acquire lateral planes (mostly corrections of inclination and RAAN). aim point located in the vicinity of target spacecraft, which is used for further rendezvous operations. The aiming point margins are dependent on safety concerns [5]. All phasing manoeuvres are using absolute navigation measurements [3]. Figure 6: Forward and Backward Phasing [2] Figure 4: Phase Angle [2] V. FAR RENDEZVOUS OPERATIONS Phasing techniques use the fact that a higher orbit has a longer Far range rendezvous also known as „homing‟ leads to orbital period and lower orbit shorter respectively. There are acquisition of aiming point where close range rendezvous two general ways to achieve new orbit: Hohmann and Bi- operations are initiated. During this phase target orbit is elliptical transfers. They are qualified as low energy transfers, captured, chaser‟s approach velocity is further reduced. Additional aim is to synchronise the mission timeline. The 266 ISSN:-2349-3585 |www.ijrdt.org Paper Title:- Phases and Manoeuvres Involved in Orbital Rendezvous Missions position of aiming point is usually situated at a range of ten to fourty kilometres from the target. Due to safety concerns a special area – approach ellipsoid is established in the vicinity of orbital target. This phase of orbital rendezvous incorporates usage of relative navigation measurements (GPS or RPGS) between both spacecraft. In case of ISS renezvous scenario required measurement accuracy is in the order of 10m [2]. Figure 9: ESA‟s ATV Final Approach Steps [9] CONCLUSIONS The rendezvous or berthing mission consists of several steps which include different orbital manoeuvres. The complexity of described operations results from a huge variety of constraints and conditions which must be fulfilled during the whole mission. Understanding these, requires familiarisation with the Figure 7: Phasing Orbit to Rendezvous Drift Orbit [2] wide variety of topics related to celestial mechanics, dynamics VI. CLOSE RENDEZVOUS OPERATIONS AND and its integration with space technology. SPACECRAFT MATING REFERENCES The close rendezvous phase is divided into two parts: path [1] Curtis H.D. “Orbital Mechanics for Engineering leading to approach corridor and a final approach leading to a Students”. Elsevier, 2014 mating port. There are three means (types of approaches) of [2] Fehse W. “Automated Rendezvous and Docking of acquiring paths leading to final approach corridor: V-bar, R- Spacecraft”. Cambridge University Press, 2003 bar and H-bar (also known as Z-bar). The choice of approach [3] Wertz J.R. “Spacecraft Attitude Determination and method will often depend on safety concerns. The safest Control“. Kluwer Academic Publishers, 1978 approach type is R-bar due to a „natural braking effect‟, which [4] Aldrin B. “Line-of-Sight Guidance Techniques for is a result of orthogonal motion to the orbital velocity of the Manned Orbital Rendezvous“. Massachusetts Institute target spacecraft [2]. of Technology, 1963 [5] Larson W. J., Wertz J. R. “Space Mission Analysis and Design”. Kluwer Academic Publishers, 2006 [6] Hintz G. R. “Orbital Mechanics and Astrodynamics – Techniques and Tools for Space Missions”. Springer, 2015 [7] Taylor J. R. “Mechanika Klasyczna Tom 1”. PWN Warszawa, 2012 [8] Rocket and Space Technology 20.09.2016 http://www.braeunig.us/space/index.htm Figure 8: Target Spacecraft Safety Zones [2] [9] ATV Rendezvous and Docking. ESA, 2008 20.09.2016 When the chaser spacecraft eneters approach corridor, relative http://esamultimedia.esa.int/docs/ATV/infokit/english/ attitude, velocity and angular differences have to be reduced to acceptable minimums required for final transition to docking port or berthing box. Berthing box is a space where spacecraft holds before being captured by the manipulator arm [2]. 267 ISSN:-2349-3585 |www.ijrdt.org .
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