Article

Event-driven James Webb Space Telescope operations using on-board JavaScripts - art. no. 62740A

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Abstract

The James Webb Space Telescope (JWST) will use an event-driven system architecture to provide efficient and flexible operations as initiated by a simplified, high-level ground command interface. Event-driven operations is provided through the use of an on-board COTS JavaScript engine hosted within the payload flight software. After presenting the overall software architecture, we summarize the trade study that led to the selection of a commercial JavaScript interpreter and review our experiences developing scripts over the past year. Our script development approach is based upon the process successfully used at Space Telescope Science Institute for the last six Hubble Space Telescope science instruments. The major characteristics of our process are 1) coordinated development of the operational scripts and the flight software, 2) an incremental buildup of the operational requirements, and 3) recurring integrated testing. Our iterative script implementation process addresses how to gather requirements from a geographically dispersed team, and then how to design, build, and test the script software to accommodate the changes that are inevitable as flight hardware is built and tested. The concurrent development of the operational scripts and the flight software enables early and frequent "test-as-you-will-fly" verification, thus reducing the risk of on-orbit software problems.

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... In the absolute time commanding design, similar events will consume valuable telescope time, since the onboard software will wait until the affected observation time has elapsed before proceeding to the next observation. For further discussion regarding the JWST event-driven commanding concept and operations, see Balzano and Isaacs (2006). ...
... The process for the on-board script development applies a " test-as-you-will-fly " philosophy (Balzano & Isaacs, 2006). The " test-as-you-will-fly " approach involves early and frequent testing of the on-board scripts, which includes realistic flight scenarios and failure cases. ...
... Based on the Visit parameters, the on-board scripts will generate the associated commands in real-time, which are issued to the flight software for execution. (Balzano and Zak, 2006) In the Visit file (refer to Figure 4), observation parameters are specified in a layered fashion: ...
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