Autonomous and Autonomic Swarms Michael G. Hinchey, James L. Rash, Walter E Truszkowski Information Systems Division NASA Goddard Space Flight Center Greenbelt, MD 2077 1, USA michael.g.hinchey, [email protected], [email protected] Christopher A. Rouff Roy Sterritt SAIC Faculty of Engineering Advanced Concepts Business Unit University of Ulster McLean, VA 22102 Northern Ireland rouffc @saic.com r. sterritt @ ulster.ac.uk Abstract packs of wolves, etc. These groupings behave like swarms in many ways. With wolves, for example, the elder male and A watershed in systems engineering is represented by female (alpha male and alpha female) are accepted as iead- the advent of swarm-based systems that accomplish mis- ers who communicate with the pack via body language and sions through cooperative action by a (large) group of au- facial expressions. Moreover, the alpha male marks the ter- tonomous individuals each having simple capabilities and ritory of the pack, and excludes wolves that are not mem- no global knowledge of the group’s objective. Such systems, bers of the pack. with individuals capable qf surviving in hostile environ- The idea that swxmns can he IJSPA to solve complex ph- ments, pose unprecedented challenges to system develop- lems has been taken up in several areas of computer sci- ers. Design and testing and verification at much higher lev- ence, which we will briefly introduce in Section 2. The term els will be required, together with the corresponding tools, “swarm” in this paper refers to a large grouping of simple to bring such systems to fruition. Concepts for possible fu- components working together to achieve some goal and pro- ture NASA space exploration missions include autonomous, duce significant results. The term should not be taken to im- autonomic swarms. Engineering swarm-based missions be- ply that these components fly (or are airborne); they may gins with understanding autonomy and autonomicity and equally well be on the surface of the Earth, under the sur- how to design, test, and verify systems that have those prop- face, under water, or indeed operating on other planets. erties and, simultaneously, the capability to accomplish pre- We will describe NASA’s motivation for using swarms scribed mission goals. Fonnal methods-based technologies, in future exploration missions. We will describe one par- both projected and in development, are described in terms ticular mission, currently in the concept stage, and exam- of their potential utility to swarm-based system developers. ine why this (and similar systems) must exhibit autonomic properties. 1. Introduction 2. Swarms and Intelligence We are all familiar with swarms in nature. The mere Swarms consist of a large number of simple entities that mention of the word “swarm” conjures up images of large have local interactions (including interactions with the en- groupings of small insects, such as bees (apiidae) or locusts vironment) [2]. The result of the combination of simple (acridiidae), each insect having a simple role, but with the behaviors (the microscopic behavior) is the emergence of swarm as a whole producing complex behavior. complex behavior (the macroscopic behavior) and the abil- Strictly speaking, such emergence of complex behavior ity to achieve significant results as a “team” [4]. is not limited to swarms, and we see similar complex social Intelligent swarm technology is based on swarm tech- structures occurring with higher order animals and insects nology where the individual members of the swann also ex- that don’t swarm per se: colonies of ants, flocks of birds, hibit independent intelligence [3]. With intelligent swarms, members of the swarm may be heterogeneous or homoge- which will cover as much of the surface of Mars in three neous. Even if members start as homogeneous, due to their seconds as the now famous Mars rovers &d in their en- differing environments they may learn different things, de- tire time on the planet; the use of armies of tetrahedral velop different goals, and therefore become a heterogeneous walkers to explore the Martian and Lunar surface; con- swarm. Intelligent swarms may also be made up of hetero- stellations of satellites flying in formation; and the use geneous elements from the outset, reflecting different capa- of miniaturized pico-class spacecraft to explore the aster- bilities as well as a possible social structure. oid belt. Agent swam are being used as a computer modeling These new approaches to exploration missions simulta- technique and have also been used as a tool to study com- neously pose many challenges. The missions will be un- plex systems [12]. Examples of simulations that have been manned and necessarily highly autonomous. They will also undertaken include swarms of birds [5, 161, as well as busi- exhibit the classic properties of autonomic systems, be- ness and economics [15] and ecological systems [20]. ing self-protecting, self-healing, self-configuring, and self- In swarm simulations, each of the agents is given cer- optimizing. Many of these missions will be sent to parts tain parameters that it tries to maximize. In terms of bird of the solar system where manned missions are simply not swarms, each bird tries to find another bird to fly with, possible, and to where the round-trip delay for communi- and then flies off to one side and slightly higher to reduce cations to spacecraft exceeds 40 minutes, meaning that the its drag. Eventually the birds form flocks. Other types of decisions on responses to problems and undesirable situa- swarm simulations have been developed that exhibit un- tions must be made in situ rather than from ground control likely emergent behavior. These emergent behaviors are the on Earth. The degree of autonomy that such missions will sums of often simple individual behaviors, but, when ag- possess would require a prohibitive amount of testing in or- gregated, form complex and often unexpected behaviors. der to accomplish system verification. Furthermore, learn- Swarm behavior is also being investigated for use in such ing and adaptation towards continual improvements in per- applications as telephone switching, network routing, data formance will mean that emergent behavior patterns simply categorizing, and shortest path optimizations. cannot be fully predicted through the use of traditional sys- Swarm intelligence techniques (note the slight dif- tem development methods. The result is that formal spec- ference in terminology from “intelligent swarms”) are ification techniques and formal verification will play vital population-based stochastic methods used in combinato- roles in the future development of NASA space exploration rial optimization problems. where the collective behavior missions. of relatively simple individuals arises fkom their local inter- actions with their environment to give rise to the emergence 3.1. ANTS: A Concept Mission of functional global patterns. Swarm intelligence repre- sents a metaheuristic approach to solving a wide variety of Automomous Nan0 Technology Swarm (ANTS) is a problems. joint NASA Goddard Space Flight Center and NASA Lang- Swarm robotics refers to the application of swarm intel- ley Research Center collaboration to develop revolutionary ligence techniques to the analysis of swarms where the em- mission architectures and exploit artificial intelligence tech- bodiment of the “agents” is as physical robotic devices. niques and paradigms in future space exploration. The mis- sion will make use of swarm technologies for both space- craft and surface-based rovers. 3. NASA Swarm Technologies ANTS consists of a number of concept missions: Future NASA missions will exploit new paradigms for SARA: The Saturn Autonomous Ring Array will launch space exploration, heavily focused on the (still) emerg- lo00 pico-class spacecraft, organized as ten sub- ing technologies of autonomous and autonomic sys- swarms, each with specialized instruments, to perform tems [25, 261. Traditional mission concepts, reliant on in situ exploration of Saturn’s rings, by which to un- one large spacecraft, are being complemented with mis- derstand their constitution and how they were formed. sion concepts that involve several smaller spacecraft, op- The concept mission will require self-configuring erating in collaboration, analogous to swarms in nature. structures for nuclear propulsion and control, which This offers several advantages: the ability to send space- lies beyond the scope of this paper. Additionally, au- craft to explore regions of space where traditional craft tonomous operation is necessary for both maneu- simply would be impractical, greater redundancy (and, con- vering around Saturn’s rings and collision avoid- sequently, greater protection of assets), and reduced costs ance. and risk, to name but a few. Planned missions entail the PAM: Prospecting Asteroid Mission will also launch lo00 use of several unmanned autonomous vehicles (UAVs) fly- pico-class spacecraft, but here with the aim of explor- ing approximately one meter above the surface of Mars, ing the asteroid belt and collecting data on particular ~~~ - asteroids of interest. PAM is described below in Sec- tion 3.1.1. m: ANTS Application Lunar Base Activities will ex- ploit new NASA-developed technologies in the field of miniaturized robotics, which may form the basis of re- mote landers to be launched to the moon from remote sites, and may exploit innovative techniques (described below in Section 3.1.2) to allow rovers to move in an amoeboid-like fashion over the moon’s uneven terrain. Since SARA and PAM have many issues in common (as regards autonomous operation), we will concentrate on PAM in the following. Section 3.1.2 describes the unique technologies that are planned for the LARA (and other) con- cept missions. 3.1.1. PAM The ANTS PAM (Prospecting Asteroid Mis- sion) concept mission [8,9,25,26] will involve the launch of a swarm of autonomous pico-class (approximately lkg) Figure 1. NASA’s Autonomous Nan0 Technol- spacecraft that will explore the asteroid belt for asteroids ogy Swarm (ANTS) mission scenario.