11/30/06astrophysics enabled by the return to the moon astrophysics enabled by a permanent lunar...

11/30/06 Astrophysics enabled by the Return to the Moon

Astrophysics Enabled by a Permanent Lunar Facility

Massimo StiavelliSpace Telescope Science Institute

Summary

- Assumptions - Why the Moon?- Building instruments for a lunar facility- Scalable telescopes on the Moon- Conclusions


Assumptions

- Main focus: UVOIR- ignore TPF-C : hard enough as a free flyer- ignore first stars etc : we need to know what JWST finds before we can talk seriously about the next step

-A lunar facility will be built for reasons unrelated to astronomy and will be occupied for extended periods by astronauts.- Transportation cost to the Moon surface will be modest for small payloads able to exploit unused lift capacity.

Similar to the relation between HST and the Shuttle program. Installation of ACS on HST

during SM3B (17 Nov 2004)


Why the Moon?

Is the Moon unique for UV-optical-IR astronomy?

Not in absolute terms but it may allow telescopes or instrumentation that would be impractical elsewhere.

The best site for astronomy on the surface of the Earth might well be Dome C in Antarctica but no major telescope has been built there (yet) because of practical considerations!

Concordia station at Dome C


Why the Moon?

For a similar instrument the Moon is more expensive than LEO:

• additional transportation cost to reach the lunar surface• a new environment with a new set of engineering problems to be solved

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.




Why the Moon?

For a similar instrument the Moon is more expensive than LEO:

• additional transportation cost to reach the lunar surface• a new environment with a new set of engineering problems to be solved

However, the Moon may offer direct cost savings by reducing instrumental complexity and indirect cost

savings by reducing programmatic complexity. It is likely that only projects designed to take advantage of these possibilities will be practical for the lunar surface (cf. Lester’s dirt and gravity).






Why the Moon?

Comparable instruments from the ground and from space differ in cost by a factor of many tens. Why?

- modern ground based instruments are more complex but- cost is driven by people rather than materials

- extensive testing, redundancy (two-sides) more people- delays (often caused by aggressive, “success oriented” schedules) everything needs to be ready when needed, if something is not ready one has the “marching army effect” and major cost overruns

Installation of ISAAC on the VLT


Instruments on ground based observatories:• deployed when ready at no extra observatory cost• mass is not a major driver• testing can be completed at the observatory faster and in more realistic conditions• single side instruments (no redundancy)• less demanding contamination control• no special worries for control and data handling as one relies on observatory facilities (no compression, no work around to fit a given bandwidth)

CFH12K camera with 6 times the pixels of ACS and operational at the CFHT in 1998.

Why the Moon?


An observatory on the Moon must duplicate some of the ground-based benefits in order to be cost effective.

The major advantages could be:- lower development risk (and thus lower final cost) by decoupling development of instruments from that of the observatory- reducing cost/complexity by testing only for likely events- enabling scalable telescope designs- allow for a failure-resistant (descope-resistant) observatory

Why the Moon?

“ESD testing” at Lick Observatory


Building instruments for a lunar facility

Single side: Instruments operated from a lunar facility wouldn’t need redundant sides as long as the design is modular and thus enables simple repairs. Complexity decreases significantly by reducing elements by a factor of two and eliminating cross-strapping. The number of possible configurations to be tested decreases by a factor ~10.

A1

A2

B1 C1

B2 C2Control: instruments could be built without or with minimal internal computer and be controlled from the lunar observatory. Communications: by transferring data to the facility computers data volume issues would be simplified and more sophisticated post-processing of data would be enabled.Power and Cooling: the observatory provides power and cooling. Design without “artificial” limitations.


Building instruments for a lunar facility

Single side: Instruments operated from a lunar facility wouldn’t need redundant sides as long as the design is modular and thus enables simple repairs. Complexity decreases significantly by reducing elements by a factor of two and eliminating cross-strapping. The number of possible configurations to be tested decreases by ~10.

A1

A2

B1 C1

B2 C2Control: instruments could be built without or with minimal internal computer and be controlled from the lunar observatory. Communications: by transfering data to the facility computers data volume issues would be simplified and more sophisticated post-processing of data would be enabled.Power and Cooling: the observatory provides power and cooling. Design without “artificial” limitations.

The poster by Ebbets et al. investigates aspects of design for a lunar facility similar to those discussed here. They find that (ignoring transportation cost) the lunar option has a cost of only ~50 per cent that of the free flyer.


Site choice for a lunar facility

The choice of a site is driven by many sometimes competing factors.

The availability of solar power would drive one to select a polar location. A telescope built within a crater at the lunar poles might enjoy a relatively cold and undisturbed environment while the crater rim might be suitable for installation of solar panels.

The LMC : visible from the lunar south pole (a Shackleton observatory)

The Cat’s Eye nebula : visible from the lunar north pole (a Peary observatory). A north polar observatory guarantees a broader target choice JWST CVZ.


Communications and site choice for a lunar facility




Site choice for a lunar facility

Other locations would likely require the use of RTGs to provide power during night time but would allow observations of a broader variety of astronomical targets.

Large thermal excursions might also complicate the design and present challenges to maintain the wavefront accuracy of an optical telescope.

Given the thermal and energy source complexity of a non-polar site it is perhaps best to focus on applications that do not require visibility of the full sky and select the lunar north pole as a site.


Transportation

• Dedicated launches to the Moon are going to be expensive. Thus, hitchhiking opportunities are the best option. • The estimated payload to the lunar surface is 2.7 tons for a mission with a crew and 19 tons for a mission without a crew (de Weck private communication). • With this type of payloads even a 1% unused capacity would be interesting.

As an example a 1-2m-sized telescope unit with a mass below few hundred kg or mirror segments for a larger telescope could be launched as piggy back.


Scalable telescopes on the Moon

A large space telescope is a high risk enterprise. Everything needs to be ready before the facility is launched leading to high risk of delays and cost overruns. Should there be a major cost overrun the telescope is generally not suitable for reasonable descopes and in case of cancellation one has no return on investment (see case of SSC)

These problems may be solved by building scalable telescopes on the Moon.

These telescopes could begin doing interesting or even fundamental science before completion or even if cancelled before development is completed.


Scalable telescopes on the Moon : Large aperture

A 12 m non-filled telescope could focus on the fossil record from local stellar populations where depth is limited by confusion and angular resolution rather than aperture. One could study:

• the oldest stars in the local groups, their location and their properties

• the dependence of the low mass portion of the IMF on environment

• star formation history of nearby galaxies and its relation to their mass assembly history

Stellar High Angular Resolution Probe



A 12 m non-filled telescope could focus on the fossil record from local stellar populations where depth is limited by confusion and angular resolution rather than aperture. One could study:

• the oldest stars in the local groups, their location and their properties

• the dependence of the low mass portion of the IMF on environment

• star formation history of nearby galaxies and its relation to their mass assembly history

Stellar High Angular Resolution Probe

Relevant for The origin and evolution of cosmic structure : Explore the Milky Way and its neighbors and for The origin and evolution of stars : The emergence of stellar systems.



Larger filled apertures would allow us to study the main sequence down to nearby rich clusters of galaxies such as Virgo (for 14m) and Coma (for 35m) so as to enable resolved stellar population studies in all galaxy types.



Larger filled apertures would allow us to study the main sequence down to nearby rich clusters of galaxies such as Virgo (for 14m) and Coma (for 35m) so as to enable resolved stellar population studies in all galaxy types.

Potential promising application: a 25+m telescope or interferometer would be able to rule out the fuzzy nature of spacetime on the Planck scale which would induce blurring on QSO images (e.g. Steinbring and reference therein). The limits from HST are interesting but not definitive.



Larger filled apertures would allow us to study the main sequence down to nearby rich clusters of galaxies such as Virgo (for 14m) and Coma (for 35m) so as to enable resolved stellar population studies in all galaxy types. Resolving the bulge of M31 would a aperture of 100m. A telescope of this class would also allow us to measure the mass of black holes similar to that in M87 essentially anywhere in the Universe and even if quiescent.

Apparent size of 90 physical pc as a function of redshift. This corresponds to M87 seen from the ground.

5 100

5

10

15

Fθ z( )

z

5 100

0.050.06

0

θarcsecz( )

0.01

100.1 z

90 pc h=0.65

m=0.3 =0.7



Larger filled apertures would allow us to study the main sequence down to nearby rich clusters of galaxies such as Virgo (for 14m) and Coma (for 35m) so as to enable resolved stellar population studies in all galaxy types. Resolving the bulge of M31 would a aperture of 100m. A telescope of this class would also allow us to measure the mass of black holes similar to that in M87 essentially anywhere in the Universe and even if quiescent.

Apparent size of 90 physical pc as a function of redshift. This corresponds to M87 seen from the ground.

5 100

5

10

15

Fθ z( )

z

5 100

0.050.06

0

θarcsecz( )

0.01

100.1 z

90 pc h=0.65

m=0.3 =0.7

Relevant for The origin and evolution of cosmic structure : The galaxy-black hole connection and for The origin and evolution of stars : The emergence of stellar systems.



These telescopes would require significant lifting capacity even if the apertures were only partially filled. The mass below is just for the primary (adopting 15 kg m2)

30% filled Unmanned fractional lift

12m 509 kg 2.7 %

14m 693 kg 3.6%

35m 4.3 ton 22.6%

100m 35.3 ton 186%

A liquid mirror would reduce but not eliminate the heavy lifting needs, e.g., for 100m and 1mm thickness one has 7.5 m3 of liquid plus the support structure. Very large apertures are impractical unless one exploits local materials.


Scalable telescopes on the Moon : an interferometer

One could begin building an interferometer by deploying a number of small size (1-2 m) UV-telescopes with a high resolving power UV spectrograph and photon counting detectors.

While more units are being built these telescopes could tackle the problem of the cosmic web (see talk by Sembach). This problem can be equally well addressed by carrying out many integrations on faint QSOs in parallel with small telescopes as it can be done with a larger telescope operating serially. This is because the best UV detectors are photon counters and have no read-out noise.





Relevant for The origin and evolution of cosmic structure : The intergalactic medium and dark matter and for The origin and evolution of stars : How the elements are made and distributed.





These instruments would also be able to measure changes in predicted by some dark energy models by measuring wavelength differences of doublets and triplets as a function of redshift for z<2.



Installation on the unit telescopes of wide field cameras and low-medium resolution spectrographs would enable a few of these telescopes to detect and identify distant supernovae as well as to study weak lensing. Multi-object spectrographs could enable massive redshift surveys to carry out a study of baryon oscillations. All these methods would allow us to study the nature of dark energy (Riess).




Some of these methods might require full sky coverage and would not be optimal for a polar lunar observatory (see also Shapley).




Relevant for The birth of the Universe : Dark energy and the destiny of the Universe.




Wide field cameras of this nature would also allow one to search for planets using transits or microlensing.




An interferometer on the Moon would enable :

Resolving solar neighborhood-like density in Virgo: 160m

Search for terrestrial planets around nearby stars and characterize their properties and signatures for life: 200m

Resolve stellar accretion disks in Orion: 400m

Geometry of the Universe from AGN broad line region x-t measurements (Elvis-Karovska): 500+m



An interferometer on the Moon would enable :

Resolving solar neighborhood-like density in Virgo: 160m

Search for terrestrial planets around nearby stars and characterize their properties and signatures for life: 200m

Resolve stellar accretion disks in Orion: 400m

Geometry of the Universe from AGN broad line region x-t measurements (Elvis-Karovska): 500+m

Relevant for Exploring new worlds : The search for habitable planets and life




Precision astrometry of faint sources

100 as : 3D kinematics around the Milky Way Mass

10 as : 3D internal kinematics of globular clusters

1 as : planetary masses from light deflection dynamical mass of the Virgo cluster planet discovery by reflex motion




Scalable instruments

An example from another field:•The PS (1959) works as injector for SPS, LEP and LHC.•The SPS is part of the injection process for LEP and LHC.

•SPS was doing proton science while accelerating electrons and positrons for LEP!

•LHC uses the LEP tunnel.

CERN adopted a scalable approach and achieved major successes along the way!


Conclusions

- We need detailed studies! - Full sky access may require more complex engineering.- Preliminary considerations suggest that the most promising opportunities deserving further study are:

- North polar installation- 21cm from the (not too) far side [unique & compelling]- small, cost-effective, briefcase or suitcase-sized experiments that would be transported as piggy back- a scalable interferometer accomplishing TPF-like science when completed but capable of studying dark energy and the cosmic web while being developed.- investigate high energy, gamma and X-ray options.




Communications and site choice for a lunar facility



Conclusions - limitations of a polar observatory

- Drift scan doesn’t work well. One needs some pointing capability perhaps of the Arecibo/HET type. - Hard to cover a large fraction of the sky. Probably it is hard to cover more than ~ 100 square degrees without the complication of a movable primary.- Mid-IR is problematic. Optics at 50-80K will be bright at > 5 m (dust may make it worse).- 21cm tomography might be feasible from the neighborhood of the observatory (how far in the far side does one need to go?)


Requirements for a lunar facility

0. Location (polar or non-polar)1. A simple low maintenance telescope on which

instruments are to be installed.2. Electric power (several kW)3. Uplink and downlink capability (> 8 Mbit/s day average)4. Control and Data Handling5. Computing power for post-processing6. Cooling power7. A simple workshop where instruments can be repaired

(generally by swapping boards/boxes).8. Transportation to site(s) of scalable telescope(s)

11/30/06astrophysics enabled by the return to the moon astrophysics enabled by a permanent lunar...

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