Multiple Spacecraft Observatories for 2020 and Beyond: Breaking a Tradition of Four Centuries

Webster Cash

University of Colorado

Telescope

Large Telescope

Multiple Telescopes

Radio Telescope

Large Radio Telescope

Multiple Radio Telescopes

Space Telescope

Large Space Telescopes

• ATLAST 8-16m Visible light

• Gen-X 1000x area, 10x res (vs Chandra)

• SAFIR 100x Spitzer area

These represent the largest affordable telescopes.They are being proposed right now.

Multiple Space Telescopes

• Stable - not rotating like Earth surface

• No Gravity – Large Lightweight Structures

• Large Diameters -- formation flying

• Very Long Baselines – formation flying

• Reduces pointing problem -- formation flying

Natural Evolution, because space has major advantages

Thin Lens Behavior

As a thin lens wobbles, the image in space does not movePosition on the detector changes only because the detector moves

Formation Flying

If detector is on a separate craft, then a wobble in the lens has no effect on the image.

But motion of detector relative to Line of Sight (red) does!

Much easier than stabilizing array.

Let’s Look at Some Multiple Craft Observatories

Constellation-X

Grouping of similar craft to increase area.Can only be of use in a low noise application like x-ray astronomy.

New Worlds Observer

External OcculterLarge Distance but Loose Formation

Stellar Imager

Dilute Aperture Telescope

MAXIM

Dilute aperture telescope

TPF-I

Dilute aperture (nulling) telescope

LISA

Complete break with telescope traditionBut gee! It’s gravity waves. What do you expect?

Trend in Multiples• Gang together

– Save some money

• Dilute aperture telescopes– Driven by resolution– Formation fly to optical tolerances– They’re gonna be expensive!

• Special Applications– LISA for gravity waves– New Worlds for contrast enhancement

New Worlds Observer

Occulter Diagram

• Telescope big enough to collect enough light from planet• Occulter big enough to block star

– Want low transmission on axis and high transmission off axis

• Telescope far enough back to have a properly small IWA• No outer working angle: View entire system at once

NWD Starshade JWSTTarget Star

Planet

Big Sheet of Specially Shaped Plastic can suppress diffraction

Performance

(with circularly symmetric apodization)A 50m diameter occulter at 50,000km will reveal Earths at 10pc

a=b=12.5mn=6F=50,000km

Shadow of 16 Petal Mask

Linear Log

Simulated Solar System

Image of Solar System with 4m Telescope

JupiterSaturn

Uranus

Neptune

Zodiacal Light

Galaxies

10 arcseconds

Spectroscopy• R > 100 spectroscopy will distinguish terrestrial

atmospheres from Jovian with modeling

O2

H2O

CH4

NH3

Photometry

Calculated Photometry ofCloudless Earth as itRotates

It Should Be Possible to Detect Oceans and Continents!

1.5m Telescope

2.4m Telescope

4m Telescope

10m Telescope

1.5m Telescope

2.4m Telescope

4m Telescope

Conclusion

Multiple Spacecraft Observatories are inevitable

They uniquely enable fundamental new science.

They are being developed now. 2020 Observatories

Simpler applications likely to go first while the astronomy community completes its large telescope imperative.