Collective Systems in Space and for Planetary Explorations

In an issue of Wireless World magazine, back in 1945, A. C. Clarke in a letter to the editor wrote, “However, I would like to close by mentioning a possibility of the remote future-perhaps half a century ahead . . . . Three repeater stations, twelve degrees apart in the correct orbit, could give television and microwave coverage to the entire planet.” These words envisioned, before the space era even started, the now overcrowded geostationary orbit, while also introducing one of the most lucrative commercial applications of the space business: telecommunications. It is worth noting in this context, how this early space mission concept made use of multiple satellites to achieve its goal. Twenty years later, the space era actually began with the successful launch of the Russian satellite Sputnik I. In the following years, many missions have been proposed, designed, and realized that make use of multiple satellites, probes, planetary rovers, robots, or, in general, what can be called “space agents” to underline the connection to multiagent systems research. The European Space Agency (ESA) mission named Cluster II, currently orbiting around our planet, is made of four identical satellites that need to accurately fly in a tetrahedron formation during part of their orbit. This particular geometry allows for the determination of three-dimensional and time-varying phenomena related to Earth’s magnetic field. Several satellite constellations, among which the currently active global positioning system (GPS), Globastar, and Iridium and also the planned European Galileo and Swarm constellation are formed of many identical spacecrafts (up to 50) that achieve a common overall objective, thanks to complex orbital and communication strategies. The innovative and ambitious Teledesic project (involving contributions from Bill Gates and Paul Allen but canceled in 2001) considered, at a certain point, to employ 840 active identical satellites orbiting Earth to provide a global Internet service. In the United States, the National Aeronautics and Space Administration (NASA) is working on a mission called Terrestrial Planet Finder (TPF), a mission consisting of five separate spacecrafts working together to function as one single huge telescope-likewise the considered ESA science mission named Darwin (see Fig. 18.1). NASA rovers Spirit and Opportunity are currently performing a collective exploration of the Martian planetary surface [Squyres (2005)] while allowing scientists to test sophisticated intelligent algorithms [Estlin et al. (2007)]. The ESA technology demonstrator Proba 3, currently in its design phase [Borde et al. (2004)], requires two heterogeneous satellites to acquire a quite complex and coordinated orbital movement with one satellite partially “shadowing” the second, allowing a solar coronography experiment. A possible architecture of a human mission to Mars involves an in-orbit assembly of several heterogeneous components launched separately (this scenario was touched upon by the Concurrent Design Facility at the ESA during the early architecture study of the Human Mission to Mars). These are only a few selected examples of space missions that need coordination between two or more satellites to achieve their overall goal and that have been already developed beyond a purely conceptual design. This last criterion partitions the set of all the ever-conceived space missions into quite distinct classes. It is no surprise that interesting missions belong also to the other class, the one often including concepts far fetched in the future, concepts that are typically attracting smaller investments as they currently fail to be economically viable or to have an appropriate technological readiness level. These include the homogeneous in-orbit assembly concept, where several identical spacecrafts assemble a large structure (e.g., a reflective mirror or a gigantic solar panel made of 861 elements placed in an hexagonal lattice [Izzo et al. (2005)]); the fractionated spacecraft [Mathieu and Weigel (2005)], where one whole spacecraft is substituted by independent heterogeneous modules carrying out specialized functions in coordination; the Japanese Petsat project [Nakasuka et al. (2006)], where the spacecraft is essentially made of LEGO-type modules that can assemble in different types of shapes and reconfigure to carry out different tasks; the APIES mission [D’Arrigo and Santandrea (2003)], employing a swarm of spacecrafts to collectively explore the asteroid belt; the early NASA Autonomous NanoTechnology Swarm (ANTS) concept [Curtis et al. (2000)]; and the many concepts on planetary exploration that involve multiple probes and rovers collectively performing tasks on planetary surfaces and atmospheres. It is worth to highlight the work done at the Massachusetts Institute of Technology (MIT) in the framework of the project named SPHERES, which considers, as an objective, to develop and test sophisticated algorithms to achieve precise autonomous coordinated movement of three metal spheres placed in a zero-gravity environment. The three spheres are built (see Fig. 18.2) and, as of 2006, are functioning onboard the International Space Station (ISS). A program to upgrade the hardware with cameras is ongoing, and the SPHERE-Zero-Robotics initiative will soon provide students with access to a microgravity environment for experimentation and analysis. A number of papers [Mohan et al. (2009); Saenz-Otero et al. (2009); Nolet et al. (2007)] published recently report on themost significant advances obtained.