Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/institute/atlast/documents/ATLAST-16-m_Telescope_AAS_Poster.pdf Дата изменения: Thu Jun 10 17:43:02 2010 Дата индексирования: Sat Jun 26 02:03:17 2010 Кодировка: Поисковые слова: agn

National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology

A 16-m Telescope for the Advanced Technology Large Aperture Telescope (ATLAST) Mission
Charles F. Lillie, Dean R. Dailey and Ronald S. Polidan (Northrop Grumman Space Technology) and the ATLAST Concept Study Team
Abstract Telescope Performance
17-m

ADDITIONAL / OPTIONAL LOGOS CAN GO HERE

The segmented mirror and deployable optics technologies developed for the James Webb Space Telescope enable a 6.5 meter diameter telescope to be folded for launch in the 5-meter diameter Ariane 5 payload fairing, and deployed autonomously after reaching orbit. Late in the next decade, when the Lunar Program's Ares V Cargo Launch Vehicle payload fairing becomes operational, even larger telescope can be placed in orbit.
H ST 2.4-m JWST 6.5-m ATLAST 8-m ATLAST 16-m

Key Technologies to Enable the Next Generation Space Telescopes
Since Galileo's first telescope 400 years ago, new technologies have enabled the development of increasingly large telescopes. JWST's segmented, deployable optics enable space telescopes with apertures larger than their launch vehicle's fairing diameter, and its chord-fold architecture provides a simple, roust deployment approach. When combined with the large lift capability and fairing volume of the Ares V launch vehicle, the new technologies shown below will enable the ATLAST 16-m telescope to be developed at an affordable cost.
· Rapid, low cost fabrication of ultra-light weight primary mirror segments
­ Eliminates time consuming grinding and polishing ­ Several approaches including vapor deposition of nanolaminates bonded to actuated substrates
Nonolaminate on Mandrel

In this paper we present our concept for a 16.8-meter JWST derivative, chord-fold telescope which could be stowed in the 10-m diameter Ares V fairing, plus a description of the new technologies that enable ATLAST to be developed at an affordable price.

With 36 mirror segments (2.4-m flat-to-flat) and a maximum tip-to-tip distance of ~17-m, the ATLAST 16-m telescope has a collecting area ~40 times greater than Hubble's (180 m2), angular resolution ~7 times better than Hubble's (9.4 milli-arcsec at 0.63 microns) and a limiting magnitude (for point sources) ~8.5 magnitudes fainter than Hubble's.

· Active figure control of primary mirror segments
­ High precision actuators ­ Surface parallel actuation eliminates need for stiff reaction structure (SMD)

Mission Concept
Our ATLAST 16-meter telescope Mission Concept will utilize the capabilities of the Ares V Cargo Launch Vehicle to place a JWST-derivative UV-Optical telescope in a halo orbit around the Sun-Earth L2 point in the post-2020 time frame. The primary mirror (PM) of the telescope consists of thirty-six 2.4-meter hexagonal (flat-to-flat). Candidate mirror materials include ULE glass and SiC, including adaptive mirror segments with replicated nanolaminate mirror surfaces that are currently under development. The segments are attached to the three sections of a backing structure with a hexapod of linear actuators which allow each segment to be placed on the PM's ideal parabolic surface. A tripod of tubular struts forms the secondary mirror support structure (SMSS). In preparation for launch, the SMSS is folded against the face of the PM center section, and the PM "wings" fold back against a cylindrical instrument compartment which is attached to a spacecraft bus which provides power, attitude control and communications for the telescope and its instruments. Solar array panels, an antenna and a solar sail are also folded up against the spacecraft bus, and a sunshade is folded around the instrument compartment. After ATLAST reaches orbit and is separated from the launch vehicle, its solar arrays and high gain antenna will be deployed, and the instrument compartment will be detached from the spacecraft bus and held by an articulated "positioning and isolating boom" while the SMSS and PM are deployed. Following this, a sunshade if erected around the deployed telescope to provide a light baffle and a thermal enclosure, and a solar sail is deployed to align the center of (solar radiation) pressure of the deployed structure with it's center of mass in order to minimize solar torque effects on the attitude control system.
"Sugar Scoop" Stray Light Baffle Ares V Notional Fairing

Telescope Dimensions
As shown above and in the following figure, when fully deployed the 16-m telescope has a maximum width of ~19.4-m (~64 feet) and length of 103-m (~338 feet, i.e.: it's roughly the size of the international space station (~108 x 74 x 45 meters ­ LWH when completed), but has only ~10% of the station's mass (45,000 kg). . . which is well within the Ares V lift capability (~69,000 kg to L2). Providing Integration and test facilities for the 16-m telescope will require some upgrades to existing facilities, but it testing the telescope and verifying its performance is not beyond the current state-of-the art.
36, 2.4 Meter Hex Mirror Petals (3 Ring) Deployable Stray Light Baffle

· High speed wavefront sensing and control
­ High density figure control enables very light weight mirror segments ­ High speed, active while imaging WFS&C allows for rapid slew and settle and earth imaging

Image Plane & WFS&C Sensor
Model Sensor Scene Tracker Focal Plane Fine Figure & Phase Sensor Beam Footprint at FPA Plane

Imaging FPA (4096 X 4096 8m pixels)

· Highly-packageable & scalable deployment techniques
­ Deployment architecture should take advantage of light weight mirrors

· Active control for light weight structural elements to supply good stability

19.4 m

2.4 Meter Diameter ISIM Tower

Other technology developments that would facilitate the development of the 16-m telescope include: sunshade materials and deployment systems; Attitude Control system components such as active/passive vibration isolation struts; large reaction wheel; fine pointing/beam steering mirrors; Integration &Test facilities for large aperture telescopes; and robotic on-orbit servicing capabilities.

­ Reduces weight required for vibration and thermal control

16.8 m

Telescope Positioning and Isolation Boom

Deployable Solar Array 4.4 Meter Diameter Primary Central Cylinder Structure Deployable Solar Sail

Conclusions
· Space telescopes with 16-meter and larger apertures are within affordable reach by the mid-2020's · To achieve this we need to initiate a technology development plan that thoroughly explores the trade options and identifies and matures the enabling technology

103 m Preliminary analysis suggests that 16.8 m will fall well within the Ares V lift capacity

· We need the sustained technology development funding to mature the technology · HST servicing missions clearly demonstrated the desirability of onorbit servicing, and further developed NASA's EVA capabilities

On-Orbit Servicing
The Hubble servicing missions have clearly demonstrated astronaut's ability to repair space systems on orbit and to upgrade them with new technology, thus extending their operational lifetime and increasing their performance by orders of magnitude.. As a result, recent congressional legislation directed NASA to design all future space observatories for on-orbit servicing. The feasibility of robotic servicing on-orbit has also by DARPA's Orbital Express miss which performed and docking maneuvers, equipment replacement and activities required for servicing an observatory in an recently been demonstrated the automated rendezvous propellant transfer L2 orbit.

· The Orbital Express robotic servicing mission demonstrated the feasibility of autonomous rendezvous and docking, fluid transfer, and equipment replacement. · Servicing ATLAST at L2 or the Earth-Moon L1 point could extend its operational lifetime and enhance its performance

References
R. Polidan, C. Lillie, G. Segal, D. Dailey, "Large Deployed and Assembled Space Telescopes", Astrophysics 2020 Workshop, November 13-15, 2007 in Baltimore, Maryland http://www.stsci.edu/institute/conference/astro2020 C. Lillie, D. Dailey, R. Polidan, "Future Deployment Systems and Very Large Fairings", Ares V Astronomical Workshop, April 26-27, 2008, Moffett field, CA, http://event.arc.nasa.gov/aresv/ C. Lillie, D. Dailey, R. Polidan, "Large Telescopes for Launch with the Ares V launch Vehicle", 59th International Astronautical Congress, 29 September to 3 October 2008, Glasgow, Scotland. http://www.iac2008.co.uk/sitesia.aspx/page/112/node/112/l/en

16.8 m Primary Solar Sail for Momentum Balance

Scaled JWST Chord Fold Technology

· DARPA demonstration program to advance technologies for satellite serving
­ Rendezvous and Docking ­ Fluid Transfer (propellant resupply) ­ ORU (orbital replacement unit) Transfer

The positioning boom has a natural frequency of 0.3 to 1.0 Hz to avoid transmitting reaction wheel vibrations to the telescope, yet still control the telescope pointing at a lower (0.02 Hz) rate The sunshade shown above is one of two concepts being considered, along with an offers significant packaging advantages. instrument components will be packaged (ORU)'s to facilitate on-orbit servicing. mechanically deployed design inflatable sunshade design which The spacecraft avionics and in orbital replaceable units

· General Program
­ ~5 years from program award to end of flight operations ­ NGST provided the Fluid Transfer and Propulsion Systems for the Boeing/Ball spacecraft ­ Class C+ (limited redundancy)

Self portrait of the two docked vehicles (ASTRO servicing vehicle on left; NextSat client/ commodities spacecraft on right)

"Launching Science: Science Opportunities Provided by NASA's Constellation System", Report of the National Research Council's Committee on Science Opportunities Enabled by NASA's Constellation System, Copyright 2008 by the National Academy of Sciences.