Robert W. Farquhar

The MESSENGER mission to Mercury: spacecraft and mission design

Abstract A Mercury orbiter mission is challenging from thermal and mass perspectives. The Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) mission overcomes these challenges while avoiding esoteric technologies by using an innovative approach with commonly available materials, minimal moving parts, and maximum heritage. This approach yields a spacecraft with good margins in all categories and low technical risk. The key concepts are a ceramic-cloth sunshade, an integrated lightweight structure and high- performance propulsion system, and a solar array incorporating optical solar reflectors (OSRs). The sunshade maintains the spacecraft at room temperature. The integrated structure and propulsion system provides ample mass margin. The solar array with OSRs, which has already undergone significant testing, provides thermal margin even if the panels are inadvertently pointed directly at the Sun at 0.3 AU. 0.3 AU .

Libration Point Missions, 1978 - 2002

This paper summarizes the six missions to the vicinity of libration points that have been flown up to the time of this conference in June 2002. The first libration-point mission, the third International Sun-Earth Explorer (ISEE-3), is emphasized because it laid the groundwork for so many later missions, most of which are covered more thoroughly in other papers given at this conference. First, the authors present some basic properties of libration-point orbits, and some history of their development for early missions. Only brief information is given here; details can be found in the references.

The indirect launch mode: A new launch technique for interplanetary missions

Abstract An indirect launch technique for interplanetary missions is described. With this scheme, the launch vehicle first places the spacecraft into a high-apogee “phasing orbit.” The spacecraft remains in this orbit until it attains a specified orientation with respect to its escape trajectory. When this occurs, a propulsion stage that is an integral part of the spacecraft is used to inject the spacecraft into the desired interplanetary trajectory. It is shown that the indirect launch technique has a number of important advantages over a conventional direct launch including a significant gain in delivered spacecraft weight, and an unconstrained launch window. For high-C3 missions, the increase in spacecraft weight is substantial.

John Breakwell, the restricted problem, and halo orbits☆

Abstract This Note is based on a presentation made at the special session “Tribute to John Breakwell” of the 42nd IAF Congress (Montreal, 7–11 October 1991) recalling the outstanding achievements of J. V. Breakwell in theoretical Celestial Mechanics. The study of spacecraft oscillating about the Earth-Moon translunar L 2 libration point for a communication satellite to service the backside of the moon led to the concept of halo orbits which gained credibility with the launch of ISEE-3 on 12 August 1978 and subsequent insertion of the vehicle into an orbit about the Sun-Earth libration point L 1 . The investigation was expanded to search for complete families of solutions, in particular also near L 3 . The contribution of the authors (R. W. Farquhar and K. C. Howell) is mentioned.

Fourth John V. Breakwell memorial lecture the use of earth-return trajectories for missions to comets

Abstract The concept of using Earth-return trajectories in connection with missions to comets was originally proposed in 1972. Papers published in the 1970s and 1980s showed that by using multiple Earth-to-Earth transfers, it was possible to construct a trajectory that would encounter several comets. This technique was used for the first time by ESAs Giotto spacecraft. Following its encounter with Halleys comet in March 1986, Giotto used a single Earth gravity-assist maneuver to intercept comet Grigg-Skjellerup in July 1992. Japans Sakigake spacecraft tried to use Earth gravity-assist maneuvers to reach comet Honda-Mrkos-Pajdusakova in 1996, but was not successful. Earth-return trajectories are essential elements of two Discovery-class missions to comets; Stardust, and the Comet Nucleus Tour (CONTOUR). The Stardust mission will be launched in February 1999, and will return dust samples collected from comet Wild-2 to the Earth in 2006. CONTOUR is scheduled for a launch in June 2002, and will use six Earth gravity-assist maneuvers to carry out three comet encounters: Encke in 2003; Schwassmann-Wachmann-3 in 2006; and dArrest in 2008. An extended-mission scenario would allow CONTOUR to accomplish two additional encounters: Tempel-2 in 2015, and Encke for a second time in 2023.

A Voyager-style tour of comets and asteroids 1994-2005

A low cost program that links a dual-comet flyby sample-return mission with a multicomet/asteroid tour is proposed. Two spacecraft are used to carry out this program: a three-axis stabilized Observer-class spacecraft and a smaller spin-stabilized sample-return probe. The Observer spacecraft uses earth-swingby and propulsive maneuvers to accomplish the small-body tour, which includes flybys of three comets (Tempel-1, Tempel-2, and Encke) and two asteroids (46-Hestia and 433-Eros) over a 12-year period. Two of these comets (Tempel-1 and Tempel-2) are also the shared targets, the Observer serves as a navigational aid for the probe, which scoops up dust particles as it flies through the cometary atmosphere. After collecting the cometary dust samples, the probe returns to a low earth orbit where it is recovered by the Space Shuttle.