nov. 29, 2006mather stsci lunar astrophysics1 science enabled by the exploration architecture (and...

Nov. 29, 2006 Mather STScI Lunar Astrophysics 1

Science Enabled by the Exploration Architecture (and

return to the Moon)

John Mather

NASA Goddard Space Flight Center

STScI, Nov. 29, 3006


Key Strategic Questions• What scientific questions are ripe for the next

few decades?• What scientific questions are worth the

money to do in space? • Site surveys: advantages of the lunar surface

and free space?• Robots or astronauts: which goals need

which systems?• For given requirement, what are cost

differences between sites?• How much does it all cost?


Possible Hardware for Human Space Exploration

• Orion (Crew Exploration Vehicle, CEV, under design/ construction)

• Ares 1 (Crew Launch Vehicle, CLV, under design/ construction)• Ares 5 (Cargo Launch Vehicle, CaLV much larger)• Lunar Surface Access Module (LSAM)• Earth Departure Stage (EDS, cryo upper stage of

Ares 5)• Advanced space suits


Hardware (2)

• Advanced servicing capabilities– Remote robotic– Local astronaut-controlled robots/manipulators– EVAs

• Advanced habitat equipment– Astronaut safety: centrifuges, shields, possibly from local

materials– Life support: food production, recycling– Solar and nuclear power and communication– Service stations at Earth-Moon L1, Sun-Earth L2 (later)


Hardware Enabling New Astrophysics

• CEV and CLV, under design for construction– New sites on Moon– Servicing at new locations not on Moon

• Advanced servicing capabilities - TBD, very important to astrophysics– Very remote robotic (e.g. operated from ground)– Local astronaut-controlled robots/manipulators– EVA - depends on airlocks and many details

• Ares 5 (Cargo Launch Vehicle, CaLV)– Larger payloads, farther away or faster

• Advanced habitat development– Solar and nuclear power and communication– Service stations at Earth-Moon L1, Sun-Earth L2 (later)


Important Astro- & Solar System Physics from the Moon

• Lunar geology: sample recognition, analysis, excavation, return to Earth

• Lunar structure: mapping, gravity, surface and interior chemistry and physics

• Lunar origin• Solar system archeology, by interpretation of

samples• Laser ranging from Earth, to test Einstein


Payload Mass• For JWST, launch vehicle cost ~ 3-4% of life

cycle cost, but launcher imposes strict mass limit

• If same mass were landed on the Moon, would need ~ 3x launcher capability, perhaps rocket cost would scale in proportion?

• Cost estimation algorithms for observatories say cost and mass are ~ proportional, so 6000 kg is about the maximum for a JWST-class telescope anywhere– Does this apply to observatory alone, or including

landing equipment?


Stiffening a Big Telescope for 1/6 g

• No way to make a passively stable system highly precise, ==> need active control loops re-adjusted for each elevation angle

• Like adaptive optics on ground, but much slower - OK but complicated

• Strength not an issue, since launch loads are much larger

• For R. Angel concept of spinning liquid mirror, gravity is required, but there is no possibility of changing its axis from vertical.


Dust

• Lunar dust is hazardous - sharp, small, sticky, covers astronauts, requires cleaning to get vacuum seals on suits

• Lunar dust levitates due to electrostatic forces, seen by astronauts as a haze

• Laser retroreflectors may be contaminated by dust - more info needed

• A serious engineering challenge to manage dust around telescopes


Optical Interferometers

• On Earth or Moon, complicated optical systems with path length equalization systems and huge rooms filled with trolleys and mirrors

• Servicing might be necessary - ground based equipment is hard to adjust

• Free-space version optically much simpler– Path equalization by formation flying– May still need servicing?


Radio Telescopes• Long wavelength (> 30 m) needs space• Very little is known in this band, wide open for

exploration and surprise, but so far not recognized by NAS as top scientific priority– New generation ground-based observatories will allow

extrapolation from higher frequencies

• Need large array of dipoles to image large areas of sky• High angular resolution needs huge array

= /d– 1 arcsec at 30 m means 6000 km span

• Reconfigure array to match required • TBD how quiet the environment must be


Servicing Possibilities• Lunar surface advantages

– Can’t get lost on lunar surface, but must travel by car or on foot

– Tools can’t escape– Astronauts could have permanent safe home (far future),

always available to service complex observatories

• Free space advantages– Can be anywhere the telescope is, or can go

• LEO to EM L1 to SE L2 to …

– Equipment is weightless - no lifting fixtures– No dust to contaminate telescope & tools– Extensive experience with HST, Space Station– Astronauts can come home from EM L1 in a flash if bad

solar weather


Possible Servicing Uses• CEV

– How far can it go to do servicing?– Quick astronaut trip to SE L2? (too risky if EM L1 would be

enough, but maybe later…)

• Robotic servicing, e.g. using astronaut tools and manipulator arms, to reduce risk or enable upgrades– Beyond Einstein probes - servicing probably not needed,

but …?– Interplanetary missions, robot explorers?– Future Great Observatories

• Chandra, LISA, SIM, TPF-C, TPF-I, TPF-Occulter, SAFIR…


Future Large Observatories from Decadal Survey

• Chandra X-ray observatory– Lunar surface bad for very precise optics, free space good,

servicing possibly valuable

• LISA gravity wave observatory– Lunar site impossible, remote servicing possible by replacing a

member of the triangle with a new one (no robot or astronaut visit needed)

• SAFIR far IR telescope– Lunar surface much too hot except possibly in dark crater - don’t

know this yet, need ~ 4 K cooling for ~ 10 m telescope

• SPECS and SPIRIT, far IR interferometers– ~ 4 K telescopes at all possible spacings in (u,v) plane– Lunar surface not possible - too hot, telescopes not mobile


Planet Finders• Kepler: transit search, 2008 launch

– Continuous monitoring of Cygnus region, declination ~ 40o +/- 23o

– Dark crater at North lunar pole? target elevation ~ 40o +/- 23.5o

• Microlensing Planet Finder (Discovery proposal)– Requires continuous monitoring of Galactic Center– GC is in Ecliptic Plane, ~ on horizon from Lunar poles

• Nearest Star Planet Transit Survey (extends ground-based surveys with better photometry)

– Like Kepler, but all-sky survey, to find nearest and brightest, best candidates for follow-up by JWST, etc.

– Lunar pole locations possible; need 2 for all-sky


Planet Finders (2)

• SIM– Requires complete thermal stability and wide sky view– Dark crater potential site, but loses > half of targets

• TPF-Coronagraph– Lunar surface probably impossible - optical system must be /3000 and

perfectly stable, and extremely clean (no dust at all!)

• TPF-Interferometer– Lunar surface probably impossible - but worth some study– Filling (u,v) plane much easier in space than on surface of Moon

• New Worlds Observer - remote occulter– Lunar surface impossible - formation flight configuration with ~25,000 km

spacing


Site Survey: the Moon and Free Space (e.g. L2)Item Lunar Surface Free Space (e.g. Sun -Earth L2)Delivered payload mass per launch (implies launch cost difference)

~ 1/3 (depends on Isp of propulsion, many details) 1

Gravity g/6, causes sag of optical system vs. pointing, needs stiff structures, added mass. Enables spin-formed parabolic mirror with vertical axis (R. Angel, P. Worden)

0

Servicing, repair, upgrade Six Apollo missions; 1969 -- 1972; few days trip each way, limited radiation exposure to astronauts.

Shuttle missions for HST, ISS, CGRO; robotic arms; numerous robotic designs. Sun-Earth L2 much farther from Earth than Moon. Possible service center at Earth-Moon L1.

Dust Sticky, small, charged, naturally levitated above surface; activated by astronauts, rovers, and retrojets; seen by astronauts; evidence of accumulation on retroreflectors

0

Solar power duty cycle 14 days/29, except polar peaks (1) or dark craters (0), may require storage for lunar night

1

Communications duty cycle 1 on front, needs relay on backside or deep crater 1

Temperature variation of environment Variable solar direction (except in dark craters) requires complex sunshield designs

Constant solar direction permits simple sunshield designs.

Observing duty cycle Depending on stray light shields, power, thermal protection and stability, and comm

1

Field of Regard Depends on lunar latitude and horizon shape inside thermal shields

Whole sky

Interferometer baseline maintenance Passive, can’t get lost. Fixed positions, or movement across challenging terrain

Active servos, full (u,v) coverage. Requires station keeping and propulsion.

Path length compensation Long range (comparable to spacing of collectors), to obtain field of view and (u,v) coverage

Short range (few cm), as part of formation flying servo control loop

Maximum baseline Size of flat region on Moon Optics limited, huge

Radio quiet Far from Earth; back side is protected for now Can be much farther from Earth


What would I do?• Coordinate with manned program to assess capabilities needed

by both manned program and science• Understand approach of manned program to manage dust, and

what equipment and infrastructure they will develop and when• Study how much dust contaminates lunar optics, and how to

mitigate it• Study how to design astronomical equipment ON Moon

– AFTER manned program is defined, lunar sites and habitats are selected, and infrastructure is known

– Lunar Astronomy is NOT a driver for the manned program - plenty of other ways, currently easier, to do science

• Present to NAS review for comparison to other sites• Offer new observing sites and infrastructure in competitive AO’s

for science• Astronomers are ingenious: they’ll find a way to use the

infrastructure or the lunar surface!


In the meantime• Assess possible augmentations to Exploration

Architecture with joint benefits to science and manned program

• Study potential radio astronomy at > 30 m: does it justify space equipment?

• Study (with AAAC) what equipment matches the scientific goals for exoplanets - if very complex or risky, servicing may be appropriate

• Study (with NAS) what has priority in next decade for space and ground-based astronomy– If top priorities could benefit from the VSE infrastructure, do

needed studies


Summary and Conclusions• Exploration Architecture & infrastructure (heavy lift vehicles, CEV,

robotic servicing) could enable much more powerful large observatories, in free space, with much longer useful lifetimes, than are possible today

• Since we’re going to the Moon, then study the Moon itself• Lunar surface not best use of money for most telescopic

astronomy, but when manned program is defined, then offer lunar sites and infrastructure in AO’s

• Astronomy is NOT a driver for manned program requirements - too many other ways to do most science, and conflicting program requirements drive up costs

• For specific science, e.g. gravity studies by laser retroreflector, lunar placement is very important

• Need to know whether (expensive, fragile) human presence is required on-site for astrophysics missions

nov. 29, 2006mather stsci lunar astrophysics1 science enabled by the exploration architecture (and...

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