R V Ramanan
Articles written in Journal of Earth System Science
Volume 114 Issue 6 December 2005 pp 619-626
Numerical investigations have been carried out to analyse the evolution of lunar circular orbits and the influence of the higher order harmonics of the lunar gravity field. The aim is to select the appropriate near-circular orbit characteristics, which extend orbit life through passive orbit maintenance. The spherical harmonic terms that make major contributions to the orbital behaviour are identified through many case studies. It is found that for low circular orbits, the 7th and the 9th zonal harmonics have predominant effect in the case of orbits for which the evolution is stable and the life is longer, and also in the case of orbits for which the evolution is unstable and a crash takes place in a short duration. By analysing the contribution of the harmonic terms to the orbit behaviour, the appropriate near-circular orbit characteristics are identified.
Volume 114 Issue 6 December 2005 pp 711-716
The Indian lunar mission Chandrayaan-1 will have a mass of 523 kg in a 100 km circular polar orbit around the Moon. The main factors that dictate the design of the Indian Moon mission are to use the present capability of launch vehicles and to achieve the scientific objectives in the minimum development time and cost. The detailed mission planning involves trade-off studies in payload optimization and the transfer trajectory determination that accomplishes these requirements. Recent studies indicate that for an optimal use of the existing launch vehicle and space-craft systems, highly elliptical inclined orbits are preferable. This indeed is true for the Indian Moon mission Chandrayaan-1. The proposed launch scenario of the Indian Moon mission program and capabilities of this mission are described in this paper, highlighting the design challenges and innovations. Further, to reach the target accurately, appropriate initial transfer trajectory characteristics must be chosen. A numerical search for the initial conditions combined with numerical integration produces the near accurate solution for this problem. The design of such transfer trajectories is discussed in this paper.
Volume 114 Issue 6 December 2005 pp 807-813
Optimal trajectory design of a probe for soft landing on the Moon from a lunar parking orbit by minimizing the fuel required is obtained. The problem is formulated as an optimal control problem with the thrust direction being the control variable. Using the maximum principle of Pontryagin, the control variable is expressed as a function of co-state variables and the problem is converted into a two-point boundary value problem. The two-point boundary value problem is solved using an optimization technique, i.e., controlled random search. The strategies such as
• direct landing from a lunar parking orbit using powered braking
• direct landing from an intermediate orbit using powered braking
• by executing powered braking in two phases: through horizontal braking and vertical landing
are analyzed and an optimal strategy that achieves the goals is suggested. Also, appropriate design parameters are selected using this analysis