The darboux point and the conjugate point on optimal deorbit for reentry trajectories

The concept of the Darboux point at which an extremal loses its global optimality is extended to the case of discontinuous control. Using Contensou's domain of maneuverability, the condition for optimal switching at a corner is derived and the optimality of the trajectory in the neighborhood of a Darboux point is analyzed. The theory is applied to the problems of minimum-fuel planar and noncoplanar deorbit from elliptical orbits for atmospheric entry at a prescribed angle. In each case, the global optimal trajectory is assessed and it is found that in these nonlinear problems the Darboux point and the conjugate point are distinct. The global optimality is always lost before local optimality.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25561/1/0000103.pd

Optimal aeroassisted transfer between coplanar elliptical orbits

This paper presents the solution for minimum-fuel, free-time transfer between coplanar elliptical orbits with the possible use of a planetary atmosphere to generate a decelerative braking force. The optimal pure propulsive two-impulse transfer is first considered. It is shown that the solution is obtained by solving a set of three equations for three unknowns. Reduction of the general equations is made for the case of symmetrical transfer and a complete first-order solution is provided for the case of transfer from nearly circular orbit. In aeroassisted transfer atmospheric braking at the perigee can be used to circularize the orbit, and in the circular configuration the orbit can be arbitrarily rotated without fuel consumption. It is shown that complete circularization of this intermediary orbit is optimal only when the rotation angle is large, and an explicit formula for evaluating this critical angle is provided. A complete solution is presented for the case of optimal rotation of an orbit. Finally, an example of optimal aeroassisted transfer is provided for the case of a transfer from a low-energy orbit to a high-energy orbit.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26152/1/0000229.pd

Explicit guidance of drag-modulated aeroassisted transfer between elliptical orbits

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77072/1/AIAA-20103-582.pd

Launch Period Development for the Juno Mission to Jupiter

The Juno mission to Jupiter is targeted to launch in 2011 and would reach the giant planet about five years later. The interplanetary trajectory is planned to include two large deep space maneuvers and an Earth gravity assist a little more than two years after launch. In this paper, we describe the development of a 21-day launch period for Juno with the objective of keeping overall launch energy and delta-V low while meeting constraints imposed on Earth departure, the deep space maneuvers' timing and geometry, and Jupiter arrival

Europa Planetary Protection for Juno Jupiter Orbiter

NASA's Juno mission launched in 2011 and will explore the Jupiter system starting in 2016. Juno's suite of instruments is designed to investigate the atmosphere, gravitational fields, magnetic fields, and auroral regions. Its low perijove polar orbit will allow it to explore portions of the Jovian environment never before visited. While the Juno mission is not orbiting or flying close to Europa or the other Galilean satellites, planetary protection requirements for avoiding the contamination of Europa have been taken into account in the Juno mission design.The science mission is designed to conclude with a deorbit burn that disposes of the spacecraft in Jupiter's atmosphere. Compliance with planetary protection requirements is verified through a set of analyses including analysis of initial bioburden, analysis of the effect of bioburden reduction due to the space and Jovian radiation environments, probabilistic risk assessment of successful deorbit, Monte-Carlo orbit propagation, and bioburden reduction in the event of impact with an icy body