The Integrated Science Instrument Module (ISIM) of the James Webb Space Telescope (JWST) is discussed from a
systems perspective with emphasis on development status and advanced technology aspects. The ISIM is one of
three elements that comprise the JWST space vehicle and is the science instrument payload of the JWST. The major
subsystems of this flight element and their build status are described.
One of the goals of the operations system being developed at the Space Telescope Science Institute for the
James Webb Space Telescope (JWST) is to produce the most efficient use of the observatory that is scientifically
justified. To first order, this means maximizing the amount of time spent collecting photons on science targets
while ensuring the health and safety of the observatory and obtaining the necessary calibration data. We present
recent efforts by the JWST EfficiencyWorking Group at STScI to quantify the expected observing efficiency based
on current plans for the operations system. These include collecting the expected observatory and instrument
overheads and updating a set of prototypical observing programs that will approximate over one full year of
JWST observations. The combination of these two efforts is being used to investigate the expected observing
efficiency and determine revised strategies to minimize overheads and maximize this efficiency.
KEYWORDS: Cryogenics, Interfaces, James Webb Space Telescope, Space telescopes, Sensors, Data acquisition, Telescopes, Composites, Space operations, Image processing
The Integrated Science Instrument Module (ISIM) of the James Webb Space Telescope (JWST) is discussed from a
systems perspective with emphasis on development status and advanced technology aspects. The ISIM is one of three
elements that comprise the JWST space vehicle and is the science instrument payload of the JWST. The major
subsystems of this flight element and their build status are described.
KEYWORDS: James Webb Space Telescope, Observatories, Calibration, Space operations, Mirrors, Computing systems, Stars, Space telescopes, Telescopes, Computer architecture
The software architecture of the James Webb Space Telescope (JWST) includes an operational layer implemented by
on-board JavaScripts that orchestrate event-driven operations. Request files specifying up to ten days of high-level
science and engineering tasks and a time-ordered execution list are uploaded periodically to the on-board event-driven
system. The processing of these files is dictated by on-board events. The tasks execute within their specified windows or
could be skipped due to an isolated anomaly, such as a guide star locate failure. For each high-level task, the necessary
flight software commands are constructed on-board according to operational rules, and positive completion confirmation
is required before proceeding to the next flight software command.
The event-driven nature of JWST operations presents challenges to the Science and Operations Center being constructed
at the Space Telescope Science Institute. This paper will outline the design implications on science and engineering
operations planning, flight real-time operations, and post-observation data management. Included will be descriptions of
how the Operations Center 1) plans time-windowed tasks to ensure that the event-driven system will remain
scientifically productive even when anomalies occur, 2) interfaces with and monitors JWST event-driven operations, and
3) records Observatory status information for each science image.
KEYWORDS: Stars, James Webb Space Telescope, Solar system, Observatories, Sensors, Target acquisition, Space operations, Space telescopes, Planets, Comets
The James Webb Space Telescope will provide a unique capability to observe Solar System objects such as Kuiper Belt
Objects, comets, asteroids, and the outer planets and their moons in the near and mid-infrared. A recent study developed
the conceptual design for a capability to track and observe these objects. In this paper, we describe how the requirements
and operations concept were derived from the scientific goals and were distributed among the Observatory and Ground
Segment components in order to remain consistent with the current event-driven operations concept of JWST. In the
event-driven operations concept, the Ground Segment produces a high-level Observation Plan that is interpreted by on-board
scripts to generate commands and monitor telemetry responses. This approach allows efficient and flexible
execution of planned observations; precise or conservative timing models are not required, and observations may be
skipped if guide star or target acquisition fails. The efficiency of this approach depends upon most observations having
large time intervals in which they can execute. Solar System objects require a specification of how to track the object
with the Observatory, and a guide star that remains within the field of view of the guider during the observation. We
describe how tracking and guiding will be handled with JWST to retain the efficient and flexible execution
characteristics of event-driven operations. We also describe how the implementation is distributed between the
Spacecraft, Fine Guidance Sensor, On-board Scripts, and Proposal Planning Subsystem, preserving the JWST operations
concept.
KEYWORDS: James Webb Space Telescope, Observatories, Software development, Mid-IR, Space telescopes, Stars, Space operations, Prototyping, Hubble Space Telescope, Commercial off the shelf technology
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.
NGST ground software and flight software will enable exciting scientific research programs that will address fundamental questions about the structure of the universe and the evolution of galaxies, stars and planets. The design of the spacecraft and instrument command system architecture acknowledges from project start that the ground software and flight software are parts of a single integrated system. A layered architecture is presented where the ground system software provides descriptions of "what to do" with the spacecraft and science instruments, while the flight software provides the detailed "how to do" rules required to execute these requests. All specific knowledge about onboard computer memory structures, hardware device communication rules, and spacecraft/science instrument operational sequences will be encapsulated onboard the spacecraft. The ground system will simply supply high-level alphanumeric requests that the flight software knows how to interpret and perform.
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