ABSTRACT
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.
