Ettore Perozzi

Basic targeting strategies for rendezvous and flyby missions to the near-Earth asteroids

Abstract Missions to asteroids and comets are becoming increasingly feasible both from a technical and a financial point of view. In particular, those directed towards the Near-Earth Asteroids have proven suitable for a low-cost approach, thus attracting the major space agencies as well as private companies. The choice of a suitable target involves both scientific relevance and mission design considerations, being often a difficult task to accomplish due to the limited energy budget at disposal. The aim of this paper is to provide an approach to basic trajectory design which allows to account for both aspects of the problem, taking into account scientific and technical information. A global characterization of the Near-Earth Asteroids population carried out on the basis of their dynamics, physical properties and flight dynamics considerations, allows to identify a group of candidates which satisfy both, the scientific and engineering requirements. The feasibility of rendezvous and flyby missions towards them is then discussed and the possibility of repeated encounters with the same object is investigated, as an intermediate scenario. Within this framework, the capability of present and near future launch and propulsion systems for interplanetary missions is also addressed.

Significant high number commensurabilities in the main lunar problem. I : The Saros as a near-periodicity of the Moon's orbit

A description is given of certain historically known cycles associated with high-number near commensurabilities among the synodic, anomalistic and nodical lunar months and the anomalistic year. Using eclipse records, the JPL ephemeris and results from three-body numerical integrations, any dynamical configuration of the Earth-Moon-Sun system (within the framework of the main lunar problem) is shown to repeat itself closely after a period of time equal in length to the classical Saros cycle of 18 years and 10 or 11 days. The role played by mirror configurations in reversing solar perturbations on the lunar orbit is examined and it is shown that the Earth-Moon-Sun system moves in a nearly periodic orbit of period equivalent to the Saros. The Saros cycle is therefore the natural averaging period of time by which solar perturbations can be most effectively removed in any search into the long term evolution of the lunar orbit.

Resonant Fly-by Missions to Near Earth Asteroids

The authors here propose a mission scenario, aimed at close exploration of a Near-Earth Asteroid, exploiting low-ΔV resonant trajectories. These trajectories allow repeated fly-bys of a chosen target. A selection procedure, which has been used to find some interesting mission opportunities in the 2005-2015 time frame, is described and the corresponding detailed mission profiles are derived, using an indirect optimization method.

On the Past Orbital History of Comet P/Halley

In recent papers (Carusi et al.; 1986, 1987) the authors reported the discovery of temporary librating behaviours about high order mean motion resonances with Jupiter of a number of short-period comets of Halley type, taking place in the period 1585 – 2406 AD. These comets are: P/Brorsen-Metcalf, P/Pons-Brooks and P/O1bers, all librating about the 6∶1 resonance, P/Dubiago, about the 5∶1, and P/Vaisala 2, about the 7∶1.

Small satellite missions to Long-Period Comets: The Hale-Bopp opportunity

Abstract Long-Period Comets are possibly the best preserved primitive bodies of the Solar System because of the limited number, if not any, of passages close to the Sun, thus minimizing the consequences following the onset of cometary activity. The unpredictability of their appearance and the short time spent inside the inner planetary region impose heavy constraints (e.g. limited time from comet discovery to launch) when trying to plan a space mission toward a long-period comet. The reduced cost and overall complexity introduced by studying small satellite missions allowed to draw realistic scenarios. The appearance of comet Hale-Bopp in July 1995 is therefore used to investigate in a real case the feasibility of the proposed LOCO (Long Period Comet Observer) mission. It is found that if all preliminary studies are already carried out at the time of comet appearance, a sufficient timespan is left to prepare and launch a small spacecraft to encounter Hale-Bopp at the descending node of its orbit. A preliminary spacecraft design is presented, some general considerations on the problem of having to wait for a long-period comet to appear are discussed and alternative scenarios are proposed.

Nucleus of the active Centaur C/2011 P2 (PANSTARRS)

Aims. In this paper we present observations of the active Centaur C/2011 P2 (PANSTARRS), showing a compact comet-like coma at the heliocentric distance of r h = 9 au. The observations were obtained in the framework of a wider program on Centaurs aimed at searching for comet-like activity in several targets outside Jupiter’s aphelion. Methods. We analysed visible images of the Centaur taken at the TNG telescope in the R filter to investigate the level of coma contributing to the target brightness and to derive information on its nucleus size. Results. Centaur C/2011 P2 (PANSTARRS) shows a faint but still detectable comet-like activity, which accounts for more than 50% to the observed brightness. The coma contribution has been subtracted in order to derive an estimate for the Centaur’s diameter of D ~ 16 km, assuming an albedo of A = 0.07 (average of albedo measured within the Centaur group). The results for Centaur C/2011 P2 (PANSTARRS) fit in the general picture of the group: Centaurs with smaller perihelion distance q and semi-major axis a are smaller than those remaining farther from the Sun during their orbital path, thus reinforcing the idea that active Centaurs are “comets in fieri ”.

NEO follow-up, recovery and precovery campaigns at the ESA NEO Coordination Centre

The NEO Coordination Centre (NEOCC) has been established within the framework of the ESA Space Situational Awareness (SSA) Programme. Among its tasks are the coordination of observational activities and the distribution of up-to-date information on NEOs through its web portal. The Centre is directly involved in observational campaigns with various telescopes, including ESOs VLT and ESAs OGS telescope. We are also developing a network of collaborating observatories, with a variety of capabilities, which are alerted when an important observational opportunity arises. From a service perspective, the system hosted at the NEOCC collects information on NEOs produced by European services and makes it available to users, with a focus on objects with possible collisions with the Earth. Among the tools provided via our portal are the Risk List of all known NEOs with impact solutions, and the Priority List, which allows observers to identify NEOs in most urgent need of observations.

EXPLOITING EARTH HORSESHOE ORBITS FOR SPACE MISSIONS

Abstract We discuss the usefulness of unstable Earth horseshoe orbits to access interplanetary space, and in particular when low-velocity escape from Earth is involved. The application to a solar stereoscopic mission is described.

The arrangement in mean elements space of the periodic orbits close to that of the Moon

A peculiar feature of the Earth-Moon-Sun system is the existence of the Saros, a cycle of 6585 d ,21 (about 18 years), widely used for eclipse prediction since the time of the ancient Chaldeans who discovered it. After one Saros the type of eclipse repeats itself, implying that the geometry of the Earth-Moon-Sun system also repeats. It has recently been shown that this repetition after one Saros occurs not only at eclipses but also at any phase of the cycle, indicating that the Moon moves in a nearly periodic orbit. This has led us to investigate the possible existence of a periodic orbit in the restricted circular 3-dimensional 3-body problem of period equal to one Saros, with mean semimajor axis a, eccentricity e and inclination i very close to those of the Moon

On the Accessibility of the Moon

The large mass fraction of the Moon with respect to the Earth implies an extended sphere of influence which can be exploited in planning exploration missions either directed to our satellite or to other solar system bodies. The dynamical systems approach to mission design has shown the existence of novel trajectories in the Earth-Moon system, which can respond to widely different exploration goals such as low-energy lunar orbit insertion, reaching Mars from the Moon or bringing lunar resources to Earth. Within this framework the general topic of the accessibility of our satellite is discussed and examples of actual mission profiles are given.