Dirt, Gravity, and Lunar-Based Telescopes:

1. Dirt, Gravity, and Lunar-Based Telescopes: The Value Proposition for Astronomy ? Dan Lester University of Texas Astrophysics Enabled by The Return to the Moon Space Telescope Science Center 29 November 2006 Astrophysics & Return to Moon

2. Genesis of the lunar astronomy vision “So many factors favor the Moon as a site for future large-scale space astronomy that planning an observatory there deserves the closest attention in the years ahead.” William Tifft, Steward Observatory Aeronautics and Astronautics December 1966 The world in 1966: Earth-based sites (1” seeing) emulsions , photomultipliers post-Gemini, pre-Apollo OAO-2 (point/track 1’/1”) and also … we were actively headed to the Moon Hale 5m OAO-2 Astrophysics & Return to Moon

3. Advantages of the Moon for astronomy c.1966 • Vacuum (compared to Earth) multiwavelength not seeing-limited • Radiation isolation (compared to Earth orbit) no damage to sensitive emulsions • Stable surface (compared to free space) proven tracking technologies no human perturbations • Thermal control (compared to low Earth orbit) long diurnal cycle & lunar polar craters • Accessibility (if near an outpost) service, maintenance This vision was smart, both scientifically and technologically! Astrophysics & Return to Moon

4. Lunar telescopes were a bold answer to our needs! Innovative optical, mechanical, thermal, and civil engineering. Astrophysics & Return to Moon

5. But then something changed … … we came to understand that telescopes in free-space could meet our needs, offering advantages previously seen only for the lunar surface. Astrophysics & Return to Moon

6. HST gave technology leap - free-space potential • demonstrated precise pointing and tracking (0.003”) • demonstrated widefield diffraction-limited performance • demonstrated precise thermal control in tough environment • demonstrated high observational efficiency • demonstrated long timescale survivability in space and, in particular • demonstrated accessibility for servicing and maintenance Space performance with ground-based reconfigurability All this with what is now 25 year old technology … Astrophysics & Return to Moon

7. Strategic Planning 101 (part 1) Relationship of astronomy and lunar exploration needs to be couched in a strategic context. • Can we deploy and service telescopes on the lunar surface? Yes, but possible doesn’t make optimal. • Does lunar surface offer uniquely enabling opportunities to priority astronomical research? • Does Exploration architecture offer uniquely enabling opportunities to this research? • Cost offsets to sweeten the deal? e.g “50% performance for 10% of the cost”? destination versus architecture Astrophysics & Return to Moon

8. Strategic Planning 101 (part 2) What the lunar surface offers: • gravity (and reaction mass) • rocks (grit, dust & regolith) • possibly sustained human presence • possibly useful ISRU materials Are either of these conspicuously enabling to astronomy? In many respects, no. NO QUESTION that lunar siting is VASTLY better for astronomy than terrestrial siting. But free space is too! In a full-cost picture, NO QUESTION that lunar siting is more expensive than free-space siting. Astrophysics & Return to Moon

9. What astronomy needs Astronomical needs based on real mission concepts made to meet established science priorities. Of course, these UVOIR needs not developed with expectation of lunar surface capabilities. • Precise alignment • Precision acquisition and tracking • Large field of regard • Low natural background • Large baselines/collecting areas • Low temperatures • Quality optical surfaces • Assured comm & power • Upgrade/repair opportunities Astrophysics & Return to Moon

10. Potential problems for lunar surface siting - 1 •Precise alignment: thermal stability, low flexure 1/6 Earth gravity - bending modes. Changing illumination - temperature changes. TPF-C needs 10mK temperature stability! •Precision acquisition and tracking Slow-moving moving coordinate system, but need very high precision. Natural seismic activity low, but induced activity may be a risk. •Large field of regard One hemisphere FOR, significantly less if in crater. Supernovae and NEOs monitoring? Astrophysics & Return to Moon

11. Potential problems for lunar surface siting - 2 •Large baselines and collecting areas Gravity disadvantageous for assembly. Delivery to surface adds risk. Non-uniform surface complicates optical linkage and UV plane-filling. •Low natural background emission “Horizon glow” may add to background emission. IR shielding challenging. Sun & Earth not blockable simultaneously. •Low temperatures Cosmic background-limited IR telescopes will need T <10K. Probably unachievable passively in sunlit parts of the Moon. Astrophysics & Return to Moon

12. Potential problems for lunar surface siting - 3 •Low scatter, high reflectivity optical surfaces Dust: natural – electrostatically levitated and meteoritic, and activity-driven – surface ops, etc., can compromise performance. •Assured communications and power Solar power assured only 1/2 time except in very limited areas (Malapert, etc.). Direct comm convenient only on nearside. •Upgrade/repair opportunities by humans Risk and propulsion requirements to both agents and their tools. Mitigation of problems like these translates to COST. Astrophysics & Return to Moon

13. Where we find humans in space Surprising that accessibility by humans is often cited as an advantage somehow unique to the lunar surface! Astrophysics & Return to Moon

14. A digression: advantages of free-space • Panchromatic operation • Zero-g; mass advantage • Contamination free • Low latency for Earth orbits and in particular for Earth-Sun L1&2 … • Extraordinary thermal stability • Very low temps at L2 w/shields • Extraordinarily low torques • Continuous communication link • Continuous solar power • Low energy paths to Earth-Moon L1&2 WMAP Not a big surprise, that Earth-Sun Lagrange points are prime destinations for future telescopes! JWST Astrophysics & Return to Moon

15. Exploration and astronomy - a new vision Exploration architecture - CEV, etc. can make free space an astronomy-enabling place! Build on HST legacy. Construction, maintenance of BIG telescopes. Access at Earth-Moon L1 as part of lunar program, ops at Earth-Sun L2. Teams are actively looking at opportunities here. Future In-Space Operations (FISO) Astrophysics & Return to Moon

16. Build big things in free space … we already do this Astrophysics & Return to Moon

17. The bottom line … Creativity and innovation assure us lunar surface telescopes can be deployed/built/maintained/serviced. We can do it! (But complexity translates into cost.) Lunar surface is vastly better for telescopes than the Earth’s surface, but compared with new free-space opportunities, is no longer as compelling as it used to be. Not at all clear that we need to do it! Astrophysics & Return to Moon

18. The dirt on lunar dust … view from the experts “… one of the most aggravating, restricting facets of lunar surface exploration is the dust and its adherence to everything no matter what kind of material, whether it be skin, suit material, metal, no matter what it be and it’s restrictive friction-like action to everything it gets on.” “There's got to be a point where the dust just overtakes you, and everything mechanical quits moving.“ Gene Cernan; Apollo 17 “The LM was filthy dirty and it has so much dust and debris floating around in it that I took my helmet off and almost blinded myself. I immediately got my eyes full of junk, and I had to put my helmet back on. I told Al to leave his on.” “We tried to vacuum clean each other down, which was a complete farce. In the first place, the vacuum didn’t knock anything off that was already on the suits. It didn’t suck up anything, but we went through the exercise.” Pete Conrad; Apollo 12 “Dust is going to be the environmental problem for future missions, both inside and outside habitats.” Harrison “Jack” Schmitt, Apollo 17 Astrophysics & Return to Moon

19. Dust clouds on the Moon -- not a subtle effect scattered light by naked eye from lunar orbit scattered light by primitive TV camera Astrophysics & Return to Moon

20. Is lunar dust a risk for UVOIR optics? • For ops-driven dust … almost certainly. • For naturally levitated dust … we just don’t know yet. Lessons from lunar laser retroreflectors are neither clear nor clearly applicable. Astrophysics & Return to Moon

21. So what’s so bad about a little dust on optics? • reflectivity (goes as 1-absorptivity) gold coating is 97% reflective (not a really big deal) • scattering (goes as absorptivity) TPF needs CL<100 ; <103/m2 of 10µm particles! (hard!) • emissivity (goes as absorptivity) background emission proportional to emissivity (hard!) SAFIR needs <1% from contamination Performance of low scatter, high MTF, and thermal IR systems strongly dependent on surface cleanliness. Astrophysics & Return to Moon

22. But there could be niches -- using gravity Very large aperture with a rotationally shaped liquid mirror. (Angel et al.) NEED gravity to make it work. Liquid Mirror Telescope for the Moon Technical feasibility? Cost?? Priority science drivers for deep small-field operation? Trade against (pointable!) large telescopes in free-space. Astrophysics & Return to Moon

23. But there could be niches -- using rock (for shielding) Quiet zone of the Moon (QZM) offers potentially low radio background. Deep Radio Surveys from QZM Is QZM protected? Depends on farside development? Trade against active interference rejection techniques. Trade against free-space telescope at larger distance from Earth. Astrophysics & Return to Moon

24. But there could be niches -- using rock (for platform) The Moon offers a platform to deploy an optically linked array of interferometric telescopes. Interferometric Array on the Lunar Surface • Penalty of redeployment to fill UV plane, and limited FOR? • Impact of monthly temp swings, power availability? • Trade against requirements in free space. (As baselined for LISA, TPF-I, DARWIN, etc.) Astrophysics & Return to Moon

25. But there could be niches -- using rock (as a detector) • High energy particle detector • Gravitational wave detector • High energy photon (gamma ray) etc. etc. This is where we should be focusing our attention. Astrophysics & Return to Moon

26. Summary Niche astronomy opportunities should be evaluated with regard to science priorities and other approaches. Lunar surface astronomy conceived by visionaries reaching for enabling opportunities. H. Smith W. Tifft Don’t reject Moon for astronomy, but approach it in a way that is cognizant of science priorities and Exploration capabilities elsewhere in space. Astrophysics & Return to Moon

27. Reexamination of lunar astronomy in the recent literature. A sample of papers. Astrophysics & Return to Moon

28. Space Policy vol 20, p 99-107, 2004 astro-ph/0401274 Astrophysics & Return to Moon

29. Physics Today November 2006 Astrophysics & Return to Moon

30. StarDate Magazine July/August 2006 Astrophysics & Return to Moon