For spacecraft swarms, the multi-agent localization algorithm must scale well with the number of spacecraft and adapt to time-varying communication and relative sensing networks. In this paper, we present a decentralized, scalable algorithm for swarm localization, called the Decentralized Pose Estimation (DPE) algorithm. The DPE considers both communication and relative sensing graphs and defines an observable local formation. Each spacecraft jointly localizes its local subset of spacecraft using direct and communicated measurements. Since the algorithm is local, the algorithm complexity does not grow with the number of spacecraft in the swarm. As part of the DPE, we present the Swarm Reference Frame Estimation (SRFE) algorithm, a distributed consensus algorithm to coestimate a common Local-Vertical, Local-Horizontal (LVLH) frame. The DPE combined with the SRFE provides a scalable, fully-decentralized navigation solution that can be used for swarm control and motion planning. Numerical simulations and experiments using Caltech's robotic spacecraft simulators are presented to validate the effectiveness and scalability of the DPE algorithm.
The Austrian Space Forum OeWF conducts Mars analog missions with varying location, length and complexity, which include analog astronauts using space suit simulators who conduct a variety of experiments. As well as the scientific and technological benefits gained from these missions, the Flight Plan Team (FPT) focuses on testing different planning strategies for planetary (analog) missions. As the missions tend to involve large numbers of participants worldwide and have high demands regarding experiment time and outcome, they provide a suitable training ground for activity planning and scheduling. Over the course of three missions we applied three different strategies in order to study their overall performance: real-time planning, 3-days-in-advance planning and 1-day-in-advance planning for the OeWF analog missions Dachstein 2012, MARS2013 and World Space Week 2013, respectively. For human planetary missions beyond the Moon, delays in crew-ground communications will rule out real-time planning. The described 1-day and 3-day-in-advanceplanning strategies address this difficulty. For robotic missions, decisions in critical circumstances can be postponed and no lives are at risk, whereas human planetary exploration may require short reaction times and cannot await a response. Complete preplanning is not feasible for manned missions due to their complexity. Additionally, health and safety requirements as well as feedback and interactions, e.g. regarding human-based in-situ decisions on mapping or experiment locations, make complete pre-planning not applicable. Instead, the situation requires detailed advance planning that allows for feedback for mission optimization while giving the astronauts the necessary authority and experiment knowledge to apply autonomous, instantaneous changes to the schedule where necessary. To simulate this situation, an artificial time-delay of 10 minutes in each direction was applied after an initial preparation phase for one of the three analog missions, MARS2013. The remaining two missions have no time-delay. We compare the three planning strategies -realtime, 1-day, 3-days-in-advance -and discuss their implementation together with mission specific advantages and disadvantages: real-time planning allows for instantaneous changes authorized by the Flight Director, but also leads to increased unnecessary changes. These are reduced by advance-planning. Because the request for changes in the activity schedule is restricted to 1 (3) days before, the planning process can be made smoother. However, all crew members have to first adjust to this method. A new challenge with advance planning is that the field crew has to be able to make decisions about changing the activity schedule by themselves. This applies to changes in personnel or activities for health and safety reasons or when equipment is unavailable. The decisions regarding activity changes have to be based on knowledge; this increased level of information has to be carefully prepared. If an experiment cannot be carried out and a replac...
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