NASA’s James Webb Space Telescope (JWST) is a 6.5m diameter, segmented, deployable telescope for cryogenic IR space astronomy. The JWST Observatory architecture includes the Primary Mirror Backplane Support Structure (PMBSS) and Integrated Science Instrument Module (ISIM) Electronics Compartment (IEC) which is designed to integrate to the spacecraft bus via six cup/cone interfaces. Prior to integration to the spacecraft bus, the JWST observatory must undergo environmental testing, handling, and transportation. Multiple fixtures were developed to support these tasks including the vibration fixture and handling and integration fixture (HIF). This work reports on the development of the nominal alignment of the six interfaces and metrology operations performed for the JWST observatory to safely integrate them for successful environmental testing.
KEYWORDS: Exoplanets, Distortion, Thermography, Space telescopes, Finite element methods, Thermal effects, Sun, Thermal modeling, Telescopes, Control systems
Starshades are an exoplanet direct-imaging architecture that uses a precisely-shaped screen to block the light from a star
in order to achieve high-contrast imaging of exoplanets. The shape of the deployable starshade structure must precisely
match the design shape in order to maintain the high level of starlight suppression. In this paper, we discuss analysis of
error sources from the starshade structure including manufacturing, dynamics, and thermal distortion to show that the
starshade can achieve the needed optical performance.
A Starshade is a sunflower-shaped satellite with a large inner disk structure surrounded by petals. A Starshade flies in formation with a space-borne telescope, creating a deep shadow around the telescope over a broad spectral band to permit nearby exoplanets to be viewed. Removing extraneous starlight before it enters the observatory optics greatly loosens the tolerances on the telescope and instrument that comprise the optical system, but the nature of the Starshade dictates a large deployable structure capable of deploying to a very precise shape. These shape requirements break down into key mechanical requirements which include the rigid-body position and orientation of each of the petals that ring the periphery of the Starshade. To verify our capability to meet these requirements, we modified an existing flight-like Astromesh reflector, provided by Northrup Grumman, as the base ring to which the petals attach. The integrated system, including 4 of the 30 flight-like subscale petals, truss, connecting spokes and central hub, was deployed tens of times in a flight-like manner using a gravity compensation system. After each deployment, discrete points in prescribed locations covering the petals and truss were measured using a highly-accurate laser tracker system. These measurements were then compared against the mechanical requirements, and the as-measured data shows deployment accuracy well within our milestone requirements and resulting in a contrast ratio consistent with exoplanet detection and characterization.
An external occulter is a satellite employing a large screen, or starshade, that flies in formation with a spaceborne telescope to provide the starlight suppression needed for detecting and characterizing exoplanets. Among the advantages of using an occulter are the broadband allowed for characterization and the removal of light before entering the observatory, greatly relaxing the requirements on the telescope and instrument. In support of NASA's Exoplanet Exploration Program and the Technology Development for Exoplanet Missions (TDEM), we recently completed a 2 year study of the manufacturability and metrology of starshade petals. In this paper we review the results of that successful first TDEM which demonstrated an occulter petal could be built and measured to an accuracy consistent with close to 10-10 contrast. We then present the results of our second TDEM to demonstrate the next critical technology milestone: precision deployment of the central truss and petals to the necessary accuracy. We show the deployment of an existing deployable truss outfitted with four sub-scale petals and a custom designed central hub.
The use of an external occulter, or starshade, has been proposed as one method for the direct detection and spectral
characterization of terrestrial planets around other stars, a key goal identified in ASTRO2010. Because of the
observational geometry, one of the concerns is stray light from the edge of the starshade that is scattered into the line of
sight of the telescope. We have developed a stray light model using physical properties of a realizable starshade edge
geometry and material to calculate the resulting stray light. The background signal due to stray light has been calculated
for the two telescope architectures adopted for study by the Exoplanet Exploration Program Analysis Group (ExoPAG),
a 4 m monolithic and an 8 m segmented mirror design. Using these results, we have developed a set of design
requirements and structure features that will result in a buildable system with stray light levels that meet the overall
system sensitivity requirements.
KEYWORDS: Stars, James Webb Space Telescope, Planets, Telescopes, Solar system, Space operations, Astronomy, Space telescopes, Planetary systems, Light scattering
Direct detection and imaging of Exo-Earths is a prime candidate for the next Astrophysics flagship mission. Much effort
is focused on developing the mission concept and technology to enable the direct imaging of an Exo-Earth. However,
several key astronomical unknowns stand in the way of a fully optimized Exo-Earth imaging mission, the primary of
which is the uncertainty in the Exo-Zodi brightness. By analogy to our own Zodiacal dust, Exo-Zodiacal dust is
predicted to exist in the habitable zones of other stars, exactly in the locations where Exo-Earths would reside. Reflected
light from this dust could be a primary background contribution to measurements of the Exo-Earth.
We propose a mission concept called the Exo-Zodi Mapper (EZM) to obtain definitive measurements of the brightness
of the Exo-Zodi dust around target stars which are the prime targets for a future mission aimed at the direct detection of
Exo-Earths. Our mission concept uses a medium sized starshade that works with the James Webb Space Telescope to
image and characterize the brightness and distribution of Exo-Zodiacal dust around ~40 primary target stars. This
measurement would provide more precise requirements for the eventual Exo-Earth flagship mission, which may translate
into significant savings. In addition, EZM can provide a host of ancillary science information on these important targets,
including detailed maps of their dust distribution, studies of outer, giant planets, and exploration of the overall
architecture of these planetary systems. The EZM starshade can also be used to enable high-contrast imaging of other
targets of value to the astronomical community such as debris disks around young stars. We present an overview of the
science that motivated the mission concept, the driving requirements, and the top level mission architecture.
The New Worlds Observer enables high-contrast imaging by placing a space telescope in the dark shadow cast by an
apodized starshade. This starshade is fully opaque and its performance is determined by the precise shape of the petal-like
structure. In this paper, we describe our preliminary efforts to determine the tolerance of the starshade performance
to errors in this shape.
The New Worlds Observer is a flagship-scale terrestrial planet finding and characterizing mission using an external
occulter known as a starshade. The starshade is a separate space vehicle from the observing telescope; the starshade
performs all the necessary starlight suppression to enable high contrast imaging of terrestrial exo-planets. While effective
as a flagship-scale mission designed to fulfill and exceed the requirements of the Terrestrial Planet Finder (TPF) mission,
the starshade architecture is flexible and can accommodate a variety of design and cost categories, including working
with an existing telescope. We present in this paper an architecture using a starshade with the James Web Space
Telescope (JWST), a mission concept we call New Worlds Probe, which can deliver many of the TPF mission
requirements for significantly lower mission cost. We give an overview of the science capabilities, the starshade design
and technical maturity, and concepts for starshade-JWST cooperative operation.
KEYWORDS: Telescopes, James Webb Space Telescope, Space telescopes, Planets, Solar system, Device simulation, Diffraction, Spectroscopy, Jupiter, Image resolution
Starshades have been shown to hold the potential to reveal Earth-like planets around nearby stars and to allow detailed
follow-up study including spectroscopy. Ideally this would be performed with a starshade in excess of 50m diameter and
a telescope over 4m in diameter. However, such a flagship-class mission is unlikely to be realized in under fifteen years.
But much can be accomplished in substantially less expensive missions. I will review the alternatives and provide an
assessment of various architectures and what they can accomplish. These alternatives will include using JWST as the
telescope, using small dedicated telescopes, and using smaller starshades.
A flower-like starshade positioned between a star and a space telescope is an attractive option for blocking the starlight
to reveal the faint reflected light of an orbiting Earth-like planet. Planet light passes around the petals and directly enters
the telescope where it is seen along with a background of scattered light due to starshade imperfections. We list the
major perturbations that are expected to impact the performance of a starshade system and show that independent models
at NGAS and JPL yield nearly identical optical sensitivities. We give the major sensitivities in the image plane for a
design consisting of a 34-m diameter starshade, and a 2-m diameter telescope separated by 39,000 km, operating
between 0.25 and 0.55 um. These sensitivities include individual petal and global shape terms evaluated at the inner
working angle. Following a discussion of the combination of individual perturbation terms, we then present an error
budget that is consistent with detection of an Earth-like planet 26 magnitudes fainter than its host star.
We present the results of the Astrophysics Strategic Mission Concept Study for the New Worlds Observer (NWO). We show that the
use of starshades is the most effective and affordable path to mapping and understanding our neighboring planetary systems, to opening
the search for life outside our solar system, while serving the needs of the greater astronomy community. A starshade-based mission
can be implemented immediately with a near term program of technology demonstration.
The New Worlds Observer enables high-contrast imaging by placing a space telescope in the dark shadow cast by an
apodized starshade. Depending on the science requirements, we consider starshades that provide a wide range of
contrast (from ~10-4 to more than 10-15) over an octave of wavelength (from UV to Visible) at a variety of inner working
angles (from a few milliarcseconds to several arcseconds). The starshade-telescope system is described by many
parameters, including starshade diameter, telescope diameter, starshade-telescope separation, and wavelength range, that
interact non-linearly. In this paper, we show how the different parameters contribute to the starshade's performance and
discuss the selection process for different science requirements.
The James Webb Space Telescope will be an extraordinary observatory, providing a huge range of exciting new
astrophysical results. However, by itself it will not be capable of directly imaging planets in the habitable zone of
nearby stars, one of the most fascinating goals of astronomy for the coming decade. In this paper we discuss the
New Worlds Probe (NWP) concept whereby we use an external occulter (or starshade) to cast a shadow from
the star onto the telescope, therefore canceling the direct star light while the light from a planet is not affected.
This concept enables JWST to take images and spectra of extrasolar planets with sufficient contrast and inner
working angle to be able to discover planets down to the size of the Earth in the habitable zone around nearby
stars. JWST's instruments are appropriate to achieve low resolution spectroscopy (R ≅ 40) of these planets, and
address a series of fundamental questions: are there planets in the habitable zone around nearby stars? What
is the composition of their atmosphere? What are the brightness and structures of exozodiacal disks around
nearby stars? What is the mass and composition of currently known giant planets? In this paper we study the
starshade optimization for JWST given the instrumental constraints, and show that the modest optical quality
of the telescope at short wavelength does not impact the possibility of using a starshade. We propose a solution
to enable imaging and spectroscopy using target acquisition filters. We discuss possible time allocation among
science goals based on exposure time estimates and total available observing time. The starshade can be launched
up to 3 years after JWST and rendezvous with the telescope in orbit around L2.
KEYWORDS: Space telescopes, Telescopes, Planets, James Webb Space Telescope, Space operations, Stars, Interferometers, Antennas, Tolerancing, Coronagraphy
The detection and characterization of exo-solar planets, which are 25 to 30 magnitudes fainter than their (5th to 6th visual magnitude) central stars, requires large aperture telescopes that must be folded to fit within the payload fairings of existing launch vehicles, and then deployed after reaching orbit. Many other elements of the various terrestrial planet finding observatories which have been proposed also must be deployed on orbit, including sunshades, solar arrays, high gain antennas and the external occulters ("starshades") that we have been designing for a "New Worlds Observer" mission. In this paper we discuss the requirements, tolerances, design options and technology readiness levels for deployment technologies for TPF-Coronagraph, -Interferometer, and -Occulter missions and describe our strawman design concepts.
This paper presents analysis showing the sensitivity of the hypergaussian starshade to various types of
errors. These errors are defined and classified. Using a single exemplar of the starshade the sensitivity to
various kinds of errors, the kind now envisioned for the New Worlds Observer mission. After review of
the basics of starshade diffraction, the error classes are defined. The errors include, static errors in global
shape, correlated errors, being the same on all petals, and uncorrelated errors, the errors being unique to
each petal edge. The effects of the first two classes of errors are evaluated using computerized numerical
solutions to the diffraction problem. In the case of uncorrelated errors, a statistical approach is taken.
The New Worlds Observer (NWO) is a mission concept for the detection and characterization of extra-solar
planets. It employs an external starshade and a space telescope. The starshade suppressed the parent star's
light making detection of the extra-solar planet possible. This paper formulates system performance based
on fundamental systems parameters and explores their interaction.
Perhaps the most compelling piece of science and exploration now under discussion for future space missions is the
direct study of planets circling other stars. Indirect means have established planets as common in the universe but have
given us a limited view of their actual characteristics. Direct observation holds the potential to map entire planetary
systems, view newly forming planets, find Earth-like planets and perform photometry to search for major surface
features. Direct observations will also enable spectroscopy of exoplanets and the search for evidence of simple life in
the universe. Recent advances in the design of external occulters - starshades that block the light from the star while
passing exoplanet light - have lowered their cost and improved their performance to the point where we can now
envision a New Worlds Observer that is both buildable and affordable with today's technology. In this paper we explore
the comparison of scientific capability of external occulters relative to indirect means and to internal coronagraph
missions. We conclude that external occulters logically provide the architecture for the next space mission for exoplanet
studies.
As currently envisioned, New Worlds Observer is a NASA flagship class mission, designed to fulfill the
Terrestrial Planet Finding mission objectives with a much more flexible architecture than the current TPF
design concepts. In this paper, we discuss the scalability of NWO for a variety of telescope sizes and briefly
discuss the associated science capability. In particular, the paper will address in detail three mission categories:
medium, large, and future mission concepts. Medium missions are missions with life cycle costs under $600
million dollars, including a version of NWO that may potentially fit within a MIDEX budget. Large missions
are flagship missions that involve significant science returns on a Observatory class level; this is our current
realization of NWO for the TPF mission. Future concepts use the NWO architecture, in conjunction with
enabling technologies such as in-space servicing, to solve long-term NASA missions such as Lifefinder and
Planet Imager. We present a multi-starshade NWO architecture designed for launch on an Ares V launch
vehicle as an example of a future concept.
A multitude of coronagraphic techniques for the space-based direct detection and characterization of exo-solar terrestrial
planets are actively being pursued by the astronomical community. Typical coronagraphs have internal shaped focal
plane and/or pupil plane occulting masks which block and/or diffract starlight thereby increasing the planet's contrast
with respect to its parent star. Past studies have shown that any internal technique is limited by the ability to sense and
control amplitude, phase (wavefront) and polarization to exquisite levels - necessitating stressing optical requirements.
An alternative and promising technique is to place a starshade, i.e. external occulter, at some distance in front of the
telescope. This starshade suppresses most of the starlight before entering the telescope - relaxing optical requirements to
that of a more conventional telescope. While an old technique it has been recently been advanced by the recognition that
circularly symmetric graded apodizers can be well approximated by shaped binary occulting masks. Indeed optimal
shapes have been designed that can achieve smaller inner working angles than conventional coronagraphs and yet have
high effective throughput allowing smaller aperture telescopes to achieve the same coronagraphic resolution and similar
sensitivity as larger ones.
Herein we report on our ongoing modeling, simulation and optimization of external occulters and show sensitivity
results with respect to number and shape errors of petals, spectral passband, accuracy of Fresnel propagation, and show
results for both filled and segmented aperture telescopes and discuss acquisition and sensing of the occulter's location
relative to the telescope.
This article was originally published online on 20 September 2007.
The following errors were discovered by the authors after publication: missing author (Park J. McGraw) and missing references.
KEYWORDS: Space telescopes, Telescopes, James Webb Space Telescope, Planets, Stars, Mirrors, Exoplanets, Visible radiation, Optical instrument design, Sun
The New Worlds Observer (NWO) mission uses a large external occulter, or "starshade," to block the light from
nearby stars and cast a deep shadow over the entrance aperture of a space telescope, enabling it to detect and characterize
Exo-Solar Planets. Since these planets are intrinsically faint (30th to 32nd magnitude), the telescope must have a large
aperture (2.4 to 4 meters) and the starshade must be large enough (25 to 50 meters) to create a shadow that is deep
enough (108 to 1010 starlight suppression) and large enough (5 to 10 meters in diameter) to envelop the telescope. The
telescope must also be far enough from the starshade (30,000 to 80,000 kilometers) that planets close to the star (50 to 65
milli-arc-seconds) are not occulted. Since the starshade's performance is inversely proportional to the wavelength of the
starlight, the telescope must operate in the visible and near infrared. The telescope should also have a significant capability
for general astrophysics observations, since it will have more than half its time available for other observations while
the starshade is moving from one target to the next.
This paper describes our conceptual design for the NWO telescope, including its instrument suite and operations concept.
We note that in addition to comparative planetology studies and the detection and characterization of terrestrial
planets, the telescope could provide a UV/Optical observing capability for the general astronomical community in the
post-HST era.
A new mission concept for direct imaging of exo-solar planets called New Worlds Observer (NWO) has been proposed. It involves flying a meter-class space telescope in formation with a newly-conceived, specially-shaped, deployable star-occulting shade several meters across at a separation of some tens of thousands of kilometers. The telescope would make its observations from behind the starshade in a volume of high suppression of incident irradiance from the star around which planets orbit. For an efficacious mission, the required level of irradiance suppression by the starshade is of order 0.1 to 10 parts per billion in broadband light. We discuss an experiment to accurately measure the irradiance suppression ratio at the null position behind candidate starshade forms to these levels. We also present results of broadband measurements which demonstrated suppression levels of less than 100 parts per billion in air using the Sun as a light source. A simulated spatial irradiance distribution surrounding the null from an analytical model developed for starshades is compared with a photograph of actual irradiance captured in situ behind a candidate starshade.
New Worlds Observer (NWO) is a formation flying mission that combines a starshade with a telescope to study Earthlike
exoplanets around neighboring stars. The general architecture consists of a telescope and detector that share one
spacecraft platform pointed toward a nearby solar system. Planets in the solar system are revealed by blocking the bright
star with a starshade, on its own spacecraft, positioned between the telescope and its target. Questions arise regarding the
type of precision, tolerances, and diffraction control required when considering the practicality of such an endeavor. We
address the generalities here by presenting an overview of requirements necessary for this type of system. Basic
tolerances are described at both the mission and starshade level.
Perhaps the most compelling piece of science and exploration now under discussion for future space missions is the direct
study of planets circling other stars. Indirect means have established planets as common in the universe but have given us
a limited view of their actual characteristics. Direct observation holds the potential to map entire planetary systems, view
newly forming planets, find Earth-like planets and perform photometry to search for major surface features. Direct
observations will also enable spectroscopy of exoplanets and the search for evidence of simple life in the universe. Recent
advances in the design of external occulters - starshades that block the light from the star while passing exoplanet light -
have lowered their cost and improved their performance to the point where we can now envision a New Worlds Observer
that is both buildable and affordable with today's technology. We will summarize recent studies of such missions and
show they provide a very attractive alternative near term mission.
This paper explores and quantifies the sources and effects of light scattering from the
New Worlds Observer Starshade into the observing telescope. We will discuss the
calculation of the scattered light level and its effect on
extra-solar planet detection. We
consider light scattered off the starshade from the Sun, the Earth, the Moon, the solarsystem
planets, zodiacal dust, and the galactic background. We will treat holes caused by
micrometeorites and other orbital debris as a separated case.
One of the major goals in astronomy today is the detection and characterization of extra-solar planets. There are
currently many exciting new concepts on the horizon that have the capability to vastly increase our knowledge of extrasolar
planets, particularly, planets like our own. The Terrestrial Planet Finder (TPF) program spans several different
mission concepts that are all capable of detecting and characterizing Earth-like planets. One such concept under study
consists of a telescope spacecraft and separate occulter spacecraft. The external occulters (EO) will be tens of meters in
diameter and will be located thousands of kilometers away. This arrangement allows the mission to observe companion
planets with a ~4 m telescope by extinguishing on-axis starlight. The operational efficiency of external occulters is
constrained by the large separation between the telescope and the occulter spacecraft. Slewing between target stars will
consume maneuvering fuel and time. Thus, the efficiency of any single EO mission may be greatly improved by using
two or more occulters and optimizing the mission scenario. We explore the design of different size occulters for
different objectives in the TPF mission. In one approach, a smaller occulter performs a "survey" function, while a large
occulter performs follow-up searches on prospective planets and fainter celestial objects. The small occulter would have
more maneuverability, but have a large inner working angle. The optimized combination of two such occulters may
provide the best compromise in the mission's ability to search and characterize extra-solar planets. This paper discusses
several potential TPF mission scenarios involving two occulters (one large, one small) and explores the optimization of
different scenarios for detection and characterization of Earth-like planets.
The New Worlds Observer (NWO) is a mission concept for the detection and
characterization of
extra-solar planets. It employs an external starshade and a space
telescope. The starshade suppressed the parent star's light making detection of the extrasolar
planet possible. This paper reviews the proposed requirements for the Terrestrial
Planet Finding (TPF) mission. Using current understanding of the performance and
trades inherent in the NWO architecture it is shown how to construct the allowed design
space for a NWO mission.
We have developed a novel chromatic correction scheme for a large aperture space astronomy telescope, using a Fresnel lens as the primary aperture. Systems built around Fresnel optics hold the possibility of drastically reducing mission costs. The use of a Fresnel optic allows a light weight primary lens which results in lighter systems, which in turn can be flown on smaller, less expensive launchers. Costs are also reduced in the manufacture of the primary lens. The performance of the telescope will be given and the tolerancing of the system discussed. The key issue of the mitigation of the intrinsic chromatic aberration will be discussed in detail, as well as deployment methods of a large monolithic lens. It will be shown that architectures based on Fresnel optics can be considered viable and should be considered in the technology selection for future missions.
We have performed a large trade study of the factors affecting the performance of the New Worlds Observer occulter. This external occulter has a multidimensional requirement space and a multidimensional parameter space. Additional engineering constraints of an external occulter spacecraft makes finding the optimal occulter parameters a complicated problem. We present here the requirements space, specifically, requirements that lead to an exoplanet detection mission. We also present the occulter parameter space, factors that lead to changes in the occulter performance. We find that it is possible in almost all cases to find a solution, meaning a set of occulter parameters, which can meet requirements for an exoplanet hunting program. We present our methodology for defining and finding the solution space.
This paper presents an error budget for the imaging performance of the Generation X telescope. This budget is used to inform the selection of the intrinsic imaging performance of the mirror modules. This calculation is done by forming a budget of top level claims to imaging performance and calculating the intrinsic optic performance, α, needed to meet the top level goal with some margin and contingency. This intrinsic optical performance is quantified by the image half-power diameter of a point source. Different values of telescope misalignment and necessary top level imaging performance is used in a Monte Carlo calculation to determine the imaging half power and the resultant optic performance.
Fresnel lens technology gives the ability to make very large, 10s to 100s meter apertures and enables a whole new regime of science and exploration missions allowing a new look at currently planned missions. Examples of missions that would be enabled or modified by these extremely large aperture sizes will be discussed at a conceptual level. This paper will conclude with a roadmap of technical challenges to be solved that will enable this exciting technology to develop and move into the technological main stream.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.