James Webb Telescope Issue - 12

Feature
A pictorial representation of JWST, with images on mirror segments representing various kinds of observations performed by the telescope, including direct
imaging, coronagraphy, spectroscopy, and much more. Credit: STScI
Commanding the James Webb Space
Telescope: OSS and Event-Driven
Operations
Kyle Elliott, Senior Software Engineer, Space Telescope Science Institute (STScI)
I. Introduction
The James Webb Space Telescope (JWST) is a spacebased,
near- to mid-infrared observatory that follows a
novel engineering design. Unlike its infrared predecessors
such as the Spitzer Space Telescope and Herschel Space
Observatory, JWST employs a segmented primary mirror
and a sunshield the size of a tennis court. The 6.5-meter
diameter primary mirror renders a light gathering power
that is about 6.25 times greater than that of the Hubble
Space Telescope (HST) and, coupled with the fact that
it reflects infrared light, enables us to see as far back as
about 250 million years following the Big Bang. Orbiting
around the second Lagrange Point (L2), roughly 1.5 million
kilometers from Earth, JWST enjoys a space environment
that imposes fewer constraints on activities than low-Earth
orbit. For instance, there is no South Atlantic Anomaly
bombarding spacecraft electronics with high-energy protons
or terminator transitions causing changes in the electrical
and thermal environments. These features enable JWST to
address fundamental questions in astronomy ranging from
the evolution of protoplanetary systems, stars, and galaxies
to extrasolar planetary atmospheres and the origins of life.
THE BRIDGE
Given the many years spent developing this mission and
the amount of ground-breaking science we stand to gain,
it is crucial to note that JWST is planned for only 5.5 to10
years of mission lifetime. We must get the most out of
this mission as possible. To maximize the efficiency of
science observations that will address varied questions in
astronomy, JWST implements an event-driven operations
architecture that is predicated on the idea that each
planned command should be issued as soon after the
previous one as possible, even when the ground system is
out-of-contact with the spacecraft or when an activity fails in
a non-critical manner.
II. Absolute Time Commanding vs. EventDriven
Commanding
HST is a technological marvel that has provided the
astronomy community with over three decades of data
(read more in the third feature). HST is operated in
a manner that befits a steady stream of observations
whereby onboard activities, such as slews and filter wheel
moves, are modeled and broken down into individual
time-stamped commands to be uplinked to the spacecraft.

James Webb Telescope Issue

Table of Contents for the Digital Edition of James Webb Telescope Issue