As Webb points to various targets around the sky, the angle of the Sun on the sunshade changes, which alters the thermal profile of the observatory. These variations in temperature can induce small changes in the observatory, and impact Webbs optical quality, pointing, observed backgrounds, and other parameters.
” The thermal stability exercise will measure these changes by moving between the extremes of Webbs field of view, from the hot to the cold mindset, spending multiple days in the cold attitude, then slewing back to the hot attitude.” To start the thermal stability test, the Webb group will point the observatory in the hot mindset at about 0 degrees pitch, and keep it there for a 5 days while it thermally supports. Webb will multitude back to the hot attitude, and the team will take high-cadence pointing stability data using both the FGS/NIRISS and NIRCam instruments.
Artist conception of the James Webb Space Telescope. Credit: NASA GSFC/CIL/Adriana Manrique Gutierrez
Completion of NASAs James Webb Space Telescopes optical alignment has actually moved us into the final phase of commissioning the Science Instruments. Throughout this final stage the Webb team and instrument scientists will check all the modes and operations for the 4 science instruments in order to assess their performance, calibration, and general observatory operations.
While the mirrors of the Webb Telescope are gradually cooling to their last operating temperature levels, the Webb group is preparing for the thermal stability test. We asked Erin Smith, the Webb deputy observatory job scientist, to tell us about the cold and hot of this test.
” Webbs five-layer sunshield keeps the telescope and science instruments cool and protected from the Sun, Earth and moon. This defense permits Webb to make measurements of the infrared universe, which needs a cold telescope and cold instrument optics. As Webb points to various targets around the sky, the angle of the Sun on the sunshade modifications, which alters the thermal profile of the observatory. These variations in temperature can cause little modifications in the observatory, and impact Webbs optical quality, pointing, observed backgrounds, and other parameters.
Webb has 2 sides, divided by its sunshield: a hot side facing the Sun and Earth, and a cold side dealing with out into space, away from the Sun and Earth. The solar panels, interactions antenna, navigation system, and electronic systems live on the hot side facing the Sun and Earth. The mirrors and scientific instruments, which are very conscious infrared radiation, are housed on the cold side, where they are safeguarded by the sunshield. Credit: STScI
” The thermal stability exercise will determine these changes by moving in between the extremes of Webbs field of view, from the hot to the cold attitude, spending several days in the cold mindset, then slewing back to the hot attitude. Throughout this time, the Webb group will determine the thermal stability, pointing efficiency and optical wavefront drift. In addition to determining the performance of the observatory, the team will likewise examine the thermal modeling utilized to anticipate observatory habits.
” With the telescope protected from the Sun, Webb observes an annulus, or donut, on the sky at any given time, called the “field of regard”. Webb points in between pitches of -5 and +45 degrees. The “cold” mindset is +45 degrees, with the sunlight lowered by an element of cosine( 45 degrees), about 0.7.
Top: Webb at the hot mindset, pointed near the continuous viewing zone (CVZ); bottom: Webb at the cold attitude. Credit: NASA/STScI
” To begin the thermal stability test, the Webb group will point the observatory in the hot attitude at about 0 degrees pitch, and keep it there for a 5 days while it thermally supports. Once this baseline has actually been developed, the team will slew the observatory to the cold mindset, about +40 degrees pitch.
” The observatory will spend more than a week at the cold attitude, until the temperature levels stabilize. Webb will slew back to the hot mindset, and the team will take high-cadence pointing stability data using both the FGS/NIRISS and NIRCam instruments.
” When assembled together, the data from the thermal stability tests will permit the observatory group to better comprehend how the observatory acts thermally. Although the changes are expected to be really small, Webb is so delicate that they could make a distinction as we optimize the telescopes efficiency. This real-world calibration of the complicated thermal models used by Webbs developers will assist to notify future observing methods and proposals.”
— Erin Smith, Webb deputy observatory task scientist, NASA Goddard
Composed by Jonathan Gardner, Webb deputy senior task scientist, NASA Goddard and Stefanie Milam, Webb deputy project scientist for planetary science, NASA Goddard.