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Webb Update #17, Summer 2014 -- attachment This issue online: http://jwst.nasa.gov/resources/WebbUpdate_Summer2014.pdf Newsletters page:
http://www.jwst.nasa.gov/newsletters.html Cryo-Verification Test of the Complete ISIM Begins! By Randy Kimble During this summer of 2014, a milestone event in the JWST test program is underway: the first of two cryo-verification tests of the complete Integrated Science Instrument Module (ISIM). Pumpdown for this critical test began a few weeks ago in Goddard’s largest thermal-vacuum chamber, the Space Environment Simulator (SES). We expect the test will continue for about 110 days. As described in the December 2013 Newsletter, last year the ISIM team successfully executed a “risk-reduction” cryo-vacuum test, termed CV1-RR. CV1-RR demonstrated the capability of the extremely complex test configuration to support all the necessary thermal, optical, electrical, and operational functionality required for verification of ISIM performance against its requirements. It also provided the team with invaluable logistical experience developing and executing a wide array of test procedures. That initial test incorporated only two of JWST’s four Science Instruments (SI’s), however, and so did not constitute a formal verification test for the complete ISIM system. The current test, designated CV2, examines the full flight ISIM assembly: all four Science Instruments (FGS/NIRISS, MIRI, NIRCam, and NIRSpec) along with their associated warm electronics boxes in the ISIM Electronics Compartment (IEC), connected with the flight harnesses across the flight Harness Radiator. The MIRI is cooled to its 6K operating temperature with a non-flight Cryocooler mounted outside the SES chamber, but all of the cold-region cooling hardware is flight or flight-like. CV2 is one of two formal verification cryo-vacuum tests for the complete ISIM element. The final cryo- vacuum test, CV3, scheduled for 2015, will occur after the rest of the ISIM-level environmental test program—gravity sag, vibration and acoustics, and Electromagnetic Interference/Electromagnetic Compatibility testing. One of the key objectives of the ISIM verification program is to demonstrate the stability of the optical and thermal system across the vibration and acoustics environment of launch, so optical measurements of focus, pupil alignment, and wavefront error made during CV2 will provide crucial pre- vibration data for comparison with the post-vibration data to be collected in CV3. CV2 is the first opportunity to assess the health and functionality of the ISIM as a whole at its cryogenic operating temperature. As such, CV2 has a rich array of thermal, electrical, and operational test goals, in addition to the detailed suite of optical tests that will be executed using the OSIM telescope simulator. CV2 will provide critical data for validating the thermal, optical, and structural models used to predict JWST’s overall in-flight performance. In addition, CV2 will gather data to investigate and close out Problem Reports or Problem Failure Reports from earlier tests and provide final verification of some instrument-level requirements that we decided would be more easily addressed in ISIM-level testing than in instrument-level testing. Pre-test preparations for CV2 in Goddard’s JWST clean room culminated in lifting the ISIM into the SES chamber on May 29th, 2014 (see Figures 1 and 2). After closeout operations and a brief elec- trical functional and continuity check, pumpdown for CV2 began in the early morning of June 17th. The first week of vacuum operations saw the completion of a warm System Functional Test of the various ISIM and SI systems as well as a preliminary outgassing measurement for the full-up ISIM. Cooldown then began on June 23rd. The cooldown of the ISIM to its flight operating temperature is a carefully controlled process that manages the temperature of all the various systems against a complex set of rate-of- change, temperature-delta, and temperature gradient requirements. During cooldown, the team began accomplishing CV2 test goals that did not require stable operating temperatures. At the time of this writing (July 9,
2014), the cooldown
process is nearly complete, with stabilization of the
instruments at their flight temperatures expected
within the next few days. Next, the team will begin
roughly two months of testing of all aspects of ISIM
performance at temperature, followed by an equally
carefully controlled warmup procedure. An exciting
summer is expected for all!
By Charles Beichman The JWST Transit Workshop brought
approximately 50 experts to Caltech in March to discuss
observations of transiting exoplanets with JWST.
The meeting drew together exoplanet observers
and theoreticians, instrument team experts, JWST
project personnel, and STScI operations experts
for an intense three-day summit and brainstorming
session to generate ideas for observational
programs and to distill lessons from previous
missions. Table 1 (online) provides the meeting
agenda and links to individual presentations. See:
http://nexsci.caltech.edu/committees/JWST/agenda.shtml Transiting exoplanets are planets whose orbits are inclined so that they pass in front of their host stars, blocking the star’s light at regular intervals. Photometry of these events yields a planet’s radius, which combined with radial velocity measurements, yields the planet’s mean density and important constraints on its bulk composition. Carrying out spectroscopic transit observations can provide information on atmospheric composition, vertical structure, and even planetary rotation! Observations of secondary transits, where the star blocks the light from the planet, provide additional information about the planet’s temperature and atmospheric properties. Monitoring a full orbital phase curve can reveal information on planetary winds and global circulation. Among the major conclusions of
the workshop
were the following: • A large sample of exoplanets orbiting bright stars will be available for study with JWST from ground- and space-based surveys, including Kepler, the Transiting Exoplanet Survey Satellite (TESS), and ESA’s CHaracterizing ExOPlanet Satellite (CHEOPS) . • A complete multi-wavelength dataset at spectral resolutions of R>1000 in either primary transit or secondary eclipse will require between 2 and 4 separate observations per object using various JWST instrument modes. Each transit observation will require between 5 and 20 hours. • A survey of 100-200 gas and ice giants with a range masses (0.05-5 MJup) orbiting stars with a broad range of spectral types and metallicity could lead to a breakthrough in our understanding of the formation and evolution of planets (Figure 3a). Transit observations might reveal, for example, an enhanced carbon- oxygen (C/O) ratio compared to the host star’s which might be indicative of a core accretion formation mechanism. Transit signals are strong enough that a single transit/instrument mode should provide adequate sensitivity in almost all cases. • The study of a few 10s of mini-Neptunes or super-Earths (5-15 MEarth) would explore a species of planet not found in our own solar system in a variety of stellar environments. In many cases, observations of these smaller planets could be accomplished in a single transit/per mode for planets orbiting M stars. • Intensive observations of one or two
terrestrial-sized planets (1-5 MEarth) preferably located
in the Habitable Zone of their host stars, might only be
possible with filter photometry and might
require
coadding many tens of transit
observations. But such
observations would offer the promise of characterizing the
atmospheres of a planet much like our own
(Figure 3b).
A white paper summarizing the
workshop’s findings has been submitted to PASP
(Beichman 2014,
submitted) and will be available on astro-ph
shortly.
JWST Status By Eric P. Smith, NASA
Headquarters
The James Webb Space Telescope Program remains on schedule for its October 2018 launch and within its budget guidelines established in 2011. Proactive management within NASA and its industry, international and non-profit partners and stable funding from Congress have enabled the program’s solid performance. The budgets proposed by the U.S. House of Representatives and Senate for the Government fiscal year 2015 are in line with the funding defined in the 2011 replan and will keep JWST on pace for its 2018 launch. This year’s
major new activity has been the
manufacturing of spacecraft components.
The spacecraft
bus is the final major component
undergoing
development.
The bus follows both the telescope
optics and four science instruments, which
are in
storage or undergoing testing at the
Goddard
Space Flight Center (GSFC).
The JWST project has begun its second major cryogenic vacuum testing of the science instruments, the so-called `CV2’ test (figures 4 and 6). This test is designed to complete some instrument verifications, to test instrument fixes deemed necessary following last year’s CV1 test, and to establish the initial measurements needed prior to next years vibration/acoustics/electromagnetic test sequence of the science payload. The instruments will undergo a third `CV3’ test for final science instrument verifications in the late summer of 2015 In July, the
engineering structure representing
the
center section of the primary
mirror backplane and the
deployable
secondary mirror support tower
(figure 5)
arrived at GSFC where it will
serve to refine the
process for
placing mirror segments within the
structure. This delivery sets the
stage for
next year when
the flight integrated backplane
and secondary mirror
support tower
arrive at GSFC and are populated
with
the flight mirror
segments.
The JWST project has begun its second major cryogenic vacuum testing of the science instruments, the so-called `CV2’ test (figures 4 and 6). This test is designed to complete some instrument verifications, to test instrument fixes deemed necessary following last year’s CV1 test, and to establish the initial measurements needed prior to next years vibration/acoustics/electromagnetic test sequence of the science payload. The instruments will undergo a third `CV3’ test for final science instrument verifications in the late summer of 2015. In July,
the engineering structure
representing the
center section of the
primary mirror backplane
and
the deployable secondary
mirror support tower
(figure
5) arrived at GSFC where
it will serve to
refine the process for
placing mirror segments
within the structure. This
delivery sets the stage
for next year when the
flight integrated
backplane
and
secondary mirror support
tower arrive at
GSFC and
are populated with the
flight mirror segments.
The
full five-layer
engineering
sunshield
structure is
currently
undergoing
rigorous
deployment testing
at
Northrop-Grumman
Aerospace Systems
at their
Redondo Beach
Space Park
facility (figure
7). This
“engineering
model” or
prototype
sunshield is full
scale and was
manufactured with
the same material
and
processes that the
flight sunshield
will use. Its
deployment testing
is only a small
part of the extensive
set of reviews and
tests that NGAS
and NASA
conduct. During
the years
2014-2016,
representatives
from other NGAS
organizations
(i.e., not the
JWST
project) , will
conduct at least
three reviews per
year
on the various
deployments of the
mission (e.g.,
tele-
scope,
sunshield, and
spacecraft) with
NASA participation.
These tests
precede major
tests or reviews
to
ensure
that the
deployments in
particular are
ready for
their
next level of
testing and/or
integration into
the
flight system.
Construction of
the flight
sunshield
membranes has
begun; the first
layer is complete
and
the second is
underway.
-- _________________________________________________ Marc J. Kuchner Exoplanets and Stellar Astrophysics Laboratory Goddard Space Flight Center Code 667 Greenbelt, MD 20771 Marc.Kuchner@xxxxxxxx (301)286-5165 http://asd.gsfc.nasa.gov/Marc.Kuchner/home.html Help NASA find new planetary systems! www.diskdetective.org |
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