# Presentation: 517479

## Adaptive Structures and Scientific Missions

- John Mather
- Senior NGST Project Scientist
- May 23, 2002

- John Mather, NGST

- May 23, 2002

## The Challenge

- Extreme image quality demands
- Enormous structures 106 - 1010  across
- Extreme environments (dark, cold, huge thermal gradient, difficult to repair)
- Instability of structures
- Imperfections of optics

- John Mather, NGST

- May 23, 2002

## The Approach

- Rigidize and point the instrument on short time scales with feedback loops from vibration sensors, laser metrology, gyros, coarse stars sensors, fine star sensors, etc.
- Sense image quality from a guide star or other reference
- Correct for long term errors (mirror shapes, mechanical instability, changes of thermal environment) by feedback from scientific sensors (may be the only ones with enough sensitivity to know if there’s a problem)

- John Mather, NGST

- May 23, 2002

## NGST Sees the First Stars and Galaxies

**Time in Years**

**300,000**

**100 Million**

**1 Billion**

**5 Billion**

**12 Billion**

**Big**
**Bang**

**COBE**

**Ground-Based**
**Observatories**

**Present**
**Day**

**NGST will probe this era, when stars and galaxies started to form, as well as the present day universe**

**NGST**

**HST**

- John Mather, NGST

- May 23, 2002

## NGST’s Place in Space Astronomy

**Plot of detector integration time  on the sky for NGST relative to the other existing observatories as a function of wavelength**
- NGST is at least an order of magnitude higher performance in every relevant wavelength band
- Large aperture and sensitive detectors lead the telescope to photon counting in the infrared

- Fig 001

- John Mather, NGST

- May 23, 2002

## Top NGST Goal - Find the First Light after the Big Bang

- How and from what were galaxies assembled?
- What is the history of star birth, heavy element production, and the enrichment of the intergalactic material?
- How were giant black holes created and what is their role in the universe?
- When could planets first form?

-  as seen by COBE

- Galaxies,
- stars,
- planets,
- life

- Galaxy
- assembly

- ?

- ?

- John Mather, NGST

- May 23, 2002

**Notes:**
The original goal that got the most public support for NGST was this one: looking back in time to the very first things that happened in the history of stars and galaxies.  We have a map of the universe made by the Cosmic Background Explorer satellite (COBE), showing the initial conditions when the universe was 300,000 years old.  We have lots of theoretical simulations that purport to explain how galaxies were formed from primordial seeds, as illustrated in the second panel here.  The idea is that small objects formed first, and then merged together in collisions to form larger objects, much as small streams merge to form great rivers.  Obviously we have not seen this happen yet, so one of the top NGST goals is to find these first little objects and find out how and when they started to make big ones.  Some of the specific things NGST is after are listed here in the bullets:

## NGST Deep Imaging: 0.5–10 m

- Depth:        AB ~ 34 in 106 s
- Redshifts:   Lyman  to *z* = 40 (?)
-                      4000 Å to *z* = 10

- 4’x4’ deep survey field

- NGST will detect 1 M yr-1 for 106 yrs to z  20 and 108 M at 1 Gyr to z  10 (conservatively assuming  = 0.2)

- 5000 galaxies to AB ~ 28,          105 galaxies to AB ~ 34   photometry, morphology & z's

*ASWG: Simon Lilly*

- John Mather, NGST

- May 23, 2002

**Notes:**
Given that one of the toughest goals to reach is to see back towards the beginning of time, we need to have the greatest possible sensitivity.  With an aperture of 6 m or so, and a protected deep space envirionment, we expect to reach about 34th magnitude in a 10 day exposure, well below a nanoJansky sensitivity.  This is good enough to see many thousands of galaxies at high redshifts.  The original simulation on the left showed easily recognized images at redshifts of 13.  The right hand panel shows that we have plenty of sensitivity to see the Lyman break in the spectrum of a galaxy out to a redshift of 40, beyond what theorists claim is the beginning of galaxy formation.  

More detailed predictions of galaxy evolution show we can see protogalaxies where stars are forming at the rate of 1 solar mass per year out to a redshift of 20.  We can even see individual supernovae to redshifts of order 5 or 10.

## Evolution of Planetary Systems

- _   ____       __Flux*   Contrast _m)    (Jy)   Star/Disk
- 11m    2.4       1.5x107
- 22m    400      2x104
- 33m    1300    3x103
- Reflected & emitted light detected with a simple coronograph.

- NGST resolution at 24m = 5 AU at Vega, > 10 pixels
- 			   across the inner hole

*ASWG: Marcia Rieke*

- **per Airy disk*

- John Mather, NGST

- May 23, 2002

## Beyond NGST

- SAFIR (Single Aperture Far IR) and SUVO (Space UV Optical) telescopes
- SPIRIT and SPECS (Far IR interferometers)
- TPF (Terrestrial Planet Finder) interferometer or coronagraph
- Stellar Imager (visible interferometer)
- MAXIM (X-ray interferometer)
- LISA (Laser Interferometer Space Array) gravity wave antenna

- John Mather, NGST

- May 23, 2002

## SAFIR: Far IR Successor to NGST

- Like NGST but larger and colder (~ 5 K) and 10x less accurate
- Challenge: stability and adjustment when cold

- John Mather, NGST

- May 23, 2002

## Far IR Interferometry

- Half the luminosity of the Universe in far IR
- Cryogenic Imaging interferometer, < 1 μm measurement, 1 cm control over spans of 1 km to achieve 0.05 arcsec resolution
- Formation flying to sweep out a 1 km aperture in 1 day using small mirrors, with tethers to keep down fuel consumption

- John Mather, NGST

- May 23, 2002

## Planet Finding Requirements

- Suppress starlight by 10_x001d__x001d_7 - 1010 to see planet
- Coronagraph needs /104 optical surfaces at UV
- Infrared interferometer needs /105 short term position control to null starlight (intensity is quadratic)
- Catch a lot of stellar photons to tell when we’re out of adjustment
- Be stable long enough to compensate to desired tolerance

- John Mather, NGST

- May 23, 2002

## TPF Interferometer - 9 m baseline on-Orbit Configuration

- SIRTF Mirror

- CRYOSTAT

- Lockheed Martin team concept for a Terrestrial Planet Finder, 12/01 San Diego review meeting, for nulling interferometer, small version before much larger instrument

- John Mather, NGST

- May 23, 2002

## TPF IR Coronagraph Design Concept - TRW team

- 28-meter filled aperture telescope
- Three-mirror anastigmat
- 36 segments, 4-meter flat-flat
- Composite replica optics
- Gold mirror coatings
- Multi-layer sunshade
- Passive cooling to ~30K
- IR Coronagraph for planetary detection/characterization
- 107 contrast at 100 mas
- IR camera and spectrograph for general imaging/spectroscopy
- 2 x 2 arcmin FOV
- Launched with EELV heavy to L2
- On-orbit assembly option

- 35 x 50-m Sunshield

- 28-m Telescope

- 6-DOF Secondary

- John Mather, NGST

- May 23, 2002

## UV Telescope Requirements

- 6 m diffraction limited telescope at 0.2 μm --> surface accuracy of 6 nm, angular resolution of 0.008 arcsec (5-10x < HST and NGST)
- Stability after launch --> adjustment to 6 nm precision and stability between adjustments
- Pointing control to 1/20 beamwidth rms = 0.4 milliarcsec
- Obtain image quality from star images and feed back to adjusters

- John Mather, NGST

- May 23, 2002

## Is this the UV astronomers’ dream telescope too?

- Coronagraphic TPF concept, off-axis elliptical telescope, Ball Aerospace, 12/01, San Diego review meeting

- John Mather, NGST

- May 23, 2002

- 30 small (1 m) telescopes on 1 km baseline
- Micro-arcsec knowledge of position of entire constellation of telescopes using bright guide stars and laser interferometers
- Vibration and instability suppressed by active feedback

- John Mather, NGST

- May 23, 2002

## X-ray requirements

- Formation flying X-ray interferometer
- Wavefront knowledge to x/20, made possible by grazing incidence optics - forgiveness of sins in proportion to sin()
- Use bright guide stars and laser interferometer sensors to get μarcsec resolution and feedback control relative to sky coordinates and other spacecraft

- John Mather, NGST

- May 23, 2002

## Gravity wave detection

-  /105 laser interferometry across 5 x 106 km (LISA) from 0.1 mHz to 0.1 Hz to see death spirals of black hole and neutron star pairs
- Acceleration noise < 3x10-15 m sec-2 Hz-1/2
- μN spacecraft thrusters
- GREAT (Gravitational Echoes Across Time) mission to see gravitational waves from the Big Bang needs < 10-17 m sec-2 Hz-1/2 acceleration noise, 100 W lasers, 8 m telescopes

- John Mather, NGST

- May 23, 2002