10,981 research outputs found
Safety verification of a fault tolerant reconfigurable autonomous goal-based robotic control system
Fault tolerance and safety verification of control
systems are essential for the success of autonomous robotic
systems. A control architecture called Mission Data System
(MDS), developed at the Jet Propulsion Laboratory, takes
a goal-based control approach. In this paper, a method for
converting goal network control programs into linear hybrid
systems is developed. The linear hybrid system can then be
verified for safety in the presence of failures using existing
symbolic model checkers. An example task is simulated in
MDS and successfully verified using HyTech, a symbolic model
checking software for linear hybrid systems
Unattended network operations technology assessment study. Technical support for defining advanced satellite systems concepts
The results are summarized of an unattended network operations technology assessment study for the Space Exploration Initiative (SEI). The scope of the work included: (1) identified possible enhancements due to the proposed Mars communications network; (2) identified network operations on Mars; (3) performed a technology assessment of possible supporting technologies based on current and future approaches to network operations; and (4) developed a plan for the testing and development of these technologies. The most important results obtained are as follows: (1) addition of a third Mars Relay Satellite (MRS) and MRS cross link capabilities will enhance the network's fault tolerance capabilities through improved connectivity; (2) network functions can be divided into the six basic ISO network functional groups; (3) distributed artificial intelligence technologies will augment more traditional network management technologies to form the technological infrastructure of a virtually unattended network; and (4) a great effort is required to bring the current network technology levels for manned space communications up to the level needed for an automated fault tolerance Mars communications network
Design for validation: An approach to systems validation
Every complex system built is validated in some manner. Computer validation begins with review of the system design. As systems became too complicated for one person to review, validation began to rely on the application of adhoc methods by many individuals. As the cost of the changes mounted and the expense of failure increased, more organized procedures became essential. Attempts at devising and carrying out those procedures showed that validation is indeed a difficult technical problem. The successful transformation of the validation process into a systematic series of formally sound, integrated steps is necessary if the liability inherent in the future digita-system-based avionic and space systems is to be minimized. A suggested framework and timetable for the transformtion are presented. Basic working definitions of two pivotal ideas (validation and system life-cyle) are provided and show how the two concepts interact. Many examples are given of past and present validation activities by NASA and others. A conceptual framework is presented for the validation process. Finally, important areas are listed for ongoing development of the validation process at NASA Langley Research Center
Online Scheduled Execution of Quantum Circuits Protected by Surface Codes
Quantum circuits are the preferred formalism for expressing quantum
information processing tasks. Quantum circuit design automation methods mostly
use a waterfall approach and consider that high level circuit descriptions are
hardware agnostic. This assumption has lead to a static circuit perspective:
the number of quantum bits and quantum gates is determined before circuit
execution and everything is considered reliable with zero probability of
failure. Many different schemes for achieving reliable fault-tolerant quantum
computation exist, with different schemes suitable for different architectures.
A number of large experimental groups are developing architectures well suited
to being protected by surface quantum error correcting codes. Such circuits
could include unreliable logical elements, such as state distillation, whose
failure can be determined only after their actual execution. Therefore,
practical logical circuits, as envisaged by many groups, are likely to have a
dynamic structure. This requires an online scheduling of their execution: one
knows for sure what needs to be executed only after previous elements have
finished executing. This work shows that scheduling shares similarities with
place and route methods. The work also introduces the first online schedulers
of quantum circuits protected by surface codes. The work also highlights
scheduling efficiency by comparing the new methods with state of the art static
scheduling of surface code protected fault-tolerant circuits.Comment: accepted in QI
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