Big Science with Small Satellites: A Roadmap to the Moon Nov. 30, 2006 Pete Worden, Ames Research Center Director, Michael Bicay, ARC Director of Science, Yvonne Pendleton, ARC Chief of Space Science Division
Overview The goal of this roadmap is to plan for future lunar science by outlining the necessary steps to answering questions with real data. Using the Moon for small sat missions will open the door to both exploration and science, bridging the divide between the two and developing new technologies for subsequent large missions. Our consideration of small spacecraft missions to the Moon falls into three categories: 1) initial site surveys of key locations, 2) a lunar robotics program to provide initial data or infrastructure, and 3) human lunar activities such as suitcase science and/or large telescope deployment. Additionally, we cover three important topics in this roadmap: 1) the role of dust on humans and machines, 2) lessons learned from establishing outposts in remote locations on the earth, and 3) small satellite missions both in orbit and on the surface.
Advantages and Disadvantages of lunar ops Advantages: • Ultra High Vacuum—effectively no atmosphere; Perfect transmittance diffraction limited imaging; Dark sky, day and night observing; Cold sky; No wind • High Lunar Mass— Easier to work in than zero-G; Unlimited Mass Available for Shielding Humans and Sensors From radiation of solar storms and Galactic cosmic rays • Stable real estate—Small-sidereal-rate 500 times smaller than LEO; 14 Day (or more) Availability of source; Uninterrupted observations of variable phenomena; Long integrations on faint sources (adv over LEO, but not libration points); Slowly changing thermal environment; dimensional stability; Giant filledapertures; large interferometers; far-side radio receivers. Disadvantages: • Lack of Solar Power During Lunar Night—or location at or near “peaks of eternal light” at poles. • Requires Enormous batteries, Doubled Solar Array Size, or Radioisotope Thermal Generators for Small Observatories • High Radiation Background— Increased Detector Noise; Meters of Rock needed to for shielding; excavation near science sites problematic; scattered light due to dust? • Dust interference— with machinery operation/ telescope mirrors, toxicity to humans (degree unknown) • Expense— transfer of materials to surface; operation costs for Human Tended Observatories; Unmanned cargo ships needed to relax safety driven costs. Soft lander automated observatories are much cheaper; Free flyers appear to be even more affordable-unless substantial infrastructure is in place for non-astronomical purposes.
Site Surveys The most important first step will be a thorough survey of the proposed lunar location. The ultimate selection of a lunar base location will be driven not by science, but by advantages such as mining potential, accessibility, and availability of power and communications. • Preliminary studies can be made via small satellite missions both in orbit and on the surface. • Selecting the optimal site for a lunar observatory requires a small spacecraft that can evaluate a precision landing and do an analysis of lunar dust during approach, landing and after landing. Also, instruments that analyze the physical and chemical properties of dust would be of value and could be utilized in a small satellite mission to specifically to study dust. • Early establishment of a lunar communication/navigation satellite system that enables contact from Earth with the entire lunar surface at any time would be useful for both the near-term robotic missions and the longer term human establishments.
Lunar Robotics Program Lunar robotic activities could facilitate all "phases" of science experiments: • "Suitcase science"-- similar to the Apollo lunar science. • "Cargo-container science"-- like the AGOs and the AASTO deployed by CARA and JACARA during the 1990 s. Self-contained unit scaled to a single transport load. • “Large-scale experiments” requiring many cargo loads and extensive on-site construction.
Human Lunar Activities • The Moon, unlike any other celestial body, is close enough that Space Tourism and general space travel might be accomplished within the lifetimes of most young adults. • Once initial infrastructure is in place, there are limitless possibilities for entrepreneurs. • The initial phases prepare the lunar surface for human activities. In the final phase, astronauts will complete extensive on-site construction of lunar installations.
Lunar Dust • The lunar dust is potentially detrimental for several reasons including: 1) the small, angular particulates are especially harmful to humans, 2) fine particles are harmful to hardware components, joints, etc. (even on the relatively short stay Apollo missions hardware components were severely compromised by lunar dust contamination), and 3) incoming high velocity particle, thought to be infrequent, could prove fatal if impacting a critical component (such as an astronaut face shield), 4) Lofted dust could scatter sunlight and ruin very low sky background light opportunities. • We simply cannot know whether or not the dust is a serious problem or simply a problem requiring mitigation techniques. Possible mitigation techniques can only move beyond speculation once the data are available.
Using “Lessons Learned” from earth analogue sites • Time scales for lunar development will almost certainly be as long or longer than for development of remote earth-based sites. • It has proven cheaper to deploy small exploratory experiments first at the established South Pole base where scientists and technicians can intervene if things don't quite work as expected. If the human transport system and lunar infrastructure is in place, this will probably also be true for lunar exploration. • Once “lessons learned” from earth analogue sites are coupled with findings of the lunar physical parameters, the answer to the type of astronomy and the best uses for the Moon in terms of astronomy will be more apparent.
Small Satellite Missions • NASA Ames Research Center and Goddard Space Flight Center are formulating a coordinated series of low-cost lunar orbiters and landers • Small 0. 5 - 1. 0 m telescopes and other components would serve as the evolutionary building blocks for a more powerful lunar observatory and could be delivered via small landers carrying a few tens of kgs. • Science with small satellites requires a mission philosophy of rapid development timescales and the use of commercial-off-the-shelf components. • Schedule compression and use of heritage makes it possible to implement a series of low-cost small satellite launches every six months. • Small spacecraft missions using existing capabilities could serve the build-up of lunar installations as a first step after a successful site survey.
Lunar Transit Search Using a low-cost lunar probe, the Moon can serve as an ideal location to base a long-lasting extrasolar planet transit search system. • A simple, robust system could be built with no moving parts, simple optics, and a single CCD camera. The data recording and transmission requirements could be minimized with on-board image compression and analysis. • A photometer with a 30 degree field-of-view can observe 20 -40% of the whole sky, or about 7, 500 square degrees, in which there around 5, 000 stars brighter than 7 th magnitude. • Achieve shot-noise limited photometric precision, allowing a small (~10 cm) lens to detect terrestrial planets around 7 th magnitude stars. • lack of scattered light from an atmosphere removes the observing constraints caused by the day-night cycle on the Earth.
Advanced Wavefront Sensing & Control and Lightweight Adaptive Optics: New Tools Enabling Future NASA Science & Exploration • Advances in Wavefront Sensing & Control (WFS&C) and lightweight Adaptive Optics (AO) enable substantial reductions in cost and complexity of large aperture optical science missions – Reduced mechanical specifications and ground alignments via onorbit mirror figure calibration – Reduced effects of rapidly changing optical distortions – Increased field of regard without slewing via reduced off-axis aberrations – Shorter delivery, integration and checkout of the optical payload • Currently studying the application of these advances to the Near Earth Object (NEO) detection mission – Very lightweight AO primary mirror combining an active Si. C substrate and an ultra-thin surface coating – Advanced WFS&C of the telescope primary mirror – Complementary wide area search and acute object imaging via foveated imaging – Basis: 1 to 3 m class optics in a 600 kg class satellite – Technology applicable to a broad range of SMD missions including TPF, solar observations, Tropospheric Wind Lidar, TPF, GEO Lidar, Kuiper Belt observations – A step toward flagship science on a MIDEX budget
Dust Collector • A small orbiter mission concept: collector plates containing substrates that can capture particles entering at both high and low velocities, with the ability to capture the stickiest of particles lofted up from the lunar surface both electrostatically and by movement. • The orbiter concept would combine a highly elliptical lunar orbit (down to 15 -20 km altitude) and a Stardust aerogel-based collector to capture and return lofted dust to Earth. • The lunar dust samples would be analyzed for composition, isotopic anomalies and evidence of extra-lunar matter, such as meteoritic materials and embedded solar wind particles.
LEEAH One mature concept for a low-cost orbiter under study is being adapted from the Lunar Explorer for Elements and Hazards (LEEAH) mission. LEEAH is designed to systematically explore the lunar surface composition using a unique ion mass spectrometer technique capable of detecting the presence of water in all areas, including permanently shadowed regions. It will characterize dynamic processes that cause lifting and transport of lunar dust, and the dependence of this activity on solar illumination and the local space environment. LEEAH will characterize radiation through total integrated dose and solar energetic particle measurements. It will also carry a novel biology experiment that will examine the impact of both radiation and microgravity on living systems. LEEAH is based on high heritage subsystems and sensors, including an existing, qualified spacecraft bus based on NASA’s The History of Events and Macroscale Interactions During Substorms (THEMIS) program. The science sensors are contributed from existing flight spares and the remaining ones are built out of high Technology Readiness Level (TRL) components. Rigorous reviews of the proposal concluded that the rapid development schedule (24 months) and modest cost ($53 million) were credible.
Lunar Ionosphere • Another mission would measure the lunar ionosphere. There are discrepant measurements, with some suggesting ionospheric cut-off frequencies as high as a few megahertz, which would have a significant impact on any possible day-side observations. • One might imagine a couple of possible concepts, either landing an ionosonde directly on the Moon or a lead-follow pair of spacecraft having orbits such that they could transmit between each other and measure the resulting signal delay.
RFI Measurements • This mission consists of Radio Frequency Interference (RFI) measurements. The most ambitious plans for far-side arrays suggest observing as low as a few tens of Hertz. The assumption is that the Moon shields even these frequencies. • The issue is that at these frequencies the radiation diffracts around the Moon, so the extent to which the Moon really serves as a shield depends upon diffraction, which in turn depends upon the lunar sub-surface, which isn't well understood. • This mission concept would probably be simple, one or two dipoles with a receiving system operating between about 10 k. Hz and 500 k. Hz checking to see how much shielding is seen on the lunar far side.
No Pest Strips • Small landed probes can provide in situ measurements of direct relevance to future manned outposts and potential lunar telescopes. Beyond the obvious follow-on to Apollo LEAM experiments (pictured right), these probes could deploy vertical adhesive ‘No Pest Strips’ of various materials to which lunar dust might adhere. • This would allow researchers to obtain vertical profiles of dust lofting and to assess the relative “stickiness” of the lunar dust. Due in part to the changing mass to surface area ratios of different sized particles, it is expected that the adhesion efficiency of lunar particles depend on the particle size. It is also anticipated that different components of lunar fines may preferentially adhere to different types of materials. • Apart from the scientific knowledge gained, these data could be integrated into NASA’s design for next-generation spacesuits to be used by crews on the lunar surface.
Summary The moon could offer great astronomical science opportunities. Lessons learned from other remote sites, such as Antarctica, suggest beginning with site surveys and then small remotely operated facilities before mounting major initiatives. Small robotic spacecraft, both in orbit around the moon and on the surface, offer exciting, affordable near-term opportunities to begin.
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