Super Telescopes in Space and on the Moon

NASA's sweeping Moon, Mars and beyond agenda demands a sustained ability to build, deploy, rescue, repair, support and upgrade large and complex systems. In mounting this exploration assault, both human and robot can work together to anchor super-optical systems far from Earth, as well as on that nearby celestial mountaintop - the Moon.

Already looming large in the astronomical world is the James Webb Space Telescope (JWST). It is to be launched in 2011. This powerful observatory features a 20-foot (6.5-meter) mirror made up of 18 hexagonal-shaped segments. The large-sized mirror could fit seven Hubble Space Telescope mirrors within its surface area.

JWST will be an infrared observatory, deployed for duty with a large sunshade attached at the second Lagrange point (L2) of the Sun-Earth system, a semi-stable point in the gravitational potential around the Sun and Earth. It will be positioned some 1 million miles (1.5 million kilometers) from the Earth and enable astronomers to observe the formation of the first stars and galaxies in the universe billions of years ago.

Even before JWST is up and operating, interest is growing for larger next generation space telescopes.

These very large optical systems could be assembled and maintained by robot and human attendants - part of an evolving "in-space capability" now being marshaled by NASA in response to President George Bush's visionary space agenda outlined over a year ago.

Hunger for acreage

"Astronomers are greedy for surface area. They want to make even bigger mirrors which will mean, in turn, even more complicated structures to support them," said Harley Thronson, Assistant Associate Administrator (Technology) within the Science Mission Directorate at NASA Headquarters in Washington, D.C.

Thronson said it's not just a hunger for acreage by astronomers. The laws of physics tell you certain apertures, probably multiple apertures in formation flying mode, are needed for future astronomical quests, he suggested.

"This is a problem in astronomy. Most of the universe is far away," Thronson told SPACE.com.

Despite the distance, large space optics offer great promise, Thronson added. "I wouldn't be surprised if school children of 2050 were learning the names of continents on Earth-like worlds around other stars."

New science

Last month, Thronson convened scientists, engineers, astronomers, and astronauts in Boulder, Colorado to evaluate future in-space capabilities and as input to NASA's long-range planning processes.

"What was striking to many of the participants was the breadth of interest in extending in-space capabilities necessary to achieve national objectives in scientific and human exploration," Thronson said. The meeting bridged major goals in bioastronautics, space operations, robotic and telerobotic systems, astronomy, astronaut space walking skills, and large space structures, he said.

Those tools can enable new science, said Dan Lester, a research scientist in the astronomy department at the University of Texas at Austin. He also served on the organizing committee for the February meeting.

Although the humans versus robots picture for science has been debated for years, Lester said, the new picture has "agents" working closely together. Those agents are humans, robots, as well as software, the latter being what we mostly use now as an active agent, he pointed out.

One of the very large telescopes proposed for the 2015-2020 time period is the Single Aperture Far-infrared (SAFIR) telescope. Lester said that SAFIR is now being evaluated in light of projected in-space human and robotic skills for servicing the facility, to make it more scientifically productive over a longer lifetime.

"We can build the kind of telescopes that we never thought we would be able to build. It's pretty simple. In order to do great astronomy, we need to have big telescopes. And the best place to have big telescopes is in space," Lester said.

Spinning liquid

There are niches for telescopes not only here on Earth and in free space, but on the Moon too.

One concept under assessment is a deep field infrared observatory situated near the Moon's south pole. The idea is championed by Roger Angel of the University of Arizona in Tucson and has been funded by the NASA Institute for Advanced Concepts (NIAC).

Angel foresees the prospect of lunar telescopes using liquid primary mirrors that are some 60-feet to nearly 330-feet (20-meter to 100-meter) in diameter. "There is a trick to making very large, very accurate mirrors...which is to spin liquid," he said.

On Earth, liquid mirrors are limited to roughly 20-feet (6-meter) in size, but subject to atmospheric absorption and distortion, even the wind kicked up by spinning the liquid, usually mercury. The Moon, though, provides the required gravity field with no such limitations.

"Because of the unique advantages on the Moon even a 100-meter liquid mirror ain't that scary," Angel said. "The Moon is the absolute ideal place to make an inexpensive, very big spinning liquid mirror."

Tall tent poles

However, such a liquid mirror system in position at one of the Moon's poles would basically stare at the same view continuously. Nevertheless, the result would be a super ultra deep field observational capability, Angel said.

Lunar-based liquid mirror telescopes, equipped with imaging and multiplexed spectroscopic instruments for a deep infrared survey, would be revolutionary in their power to study the distant universe, including the formation of the first stars and their assembly into galaxies.

The goal of the NIAC-funded work is to better appreciate the scientific promise of the concept, as well as explore the "tall tent poles" that must be overcome to make such a telescope practical, Angel said.

Also to be investigated by Angel and his colleagues is the value of human presence on the Moon for erecting the telescope and for occasional instrument upgrades. Study findings are expected to be of value in shaping scientific exploration goals for NASA's planned return to the Moon.

Moon: stable, vast platform

Another lunar observatory idea has been evaluated by SpaceDev, Inc. of Poway, California. Dubbed the International Lunar Observatory (ILO), this robotic multi-wavelength observatory is envisioned as conducting astronomy and astrophysics from the Moon.

SpaceDev engineering studies of the idea suggest that a modest $35 million to $50 million is required to spot land ILO on the Moon in just a few years time.

SpaceDev's work on the initiative was done under contract with the Lunar Enterprise Corporation, an arm of Space Age Publishing Company with offices in Kamuela, Hawaii and Palo Alto, California.

"We see the Moon as the next frontier of astronomy, after those of Earth and space. Observatories in space have been successfully operating for more than three decades," said Steve Durst, head of the Lunar Enterprise Corporation.

"It's not so much a question of space-based or lunar-based...or Earth-based. Each has its own advantages," Durst said.

Toe-hold, then foot-hold

Durst said that on Earth, proximity and access means dramatically lower costs compared to space.

On the Moon, the real estate available there provides a stable, vast platform for astrophysics observations, Durst noted. "It's not a question of observatories at which location, but what observatories at each location. There will of course be observatories on Earth, in space, on the Moon...and beyond."

What makes a lunar observatory so compelling and attractive, Durst continued, is its compelling logical necessity. In survey after survey the past 20 years, "observation" and "power" consistently top the list of imperative first steps upon arrival on the Moon...a toe-hold, then foot-hold for lunar base build out, he said.

"On any scouting mission or expedition -- Boy Scouts, Army, Marines, astronauts -- the very first things to do upon arrival at a site is 'to post a look-out' and 'build a fire'...and for the Moon that means observation and power or energy," Durst said. With a human expedition on the Moon, also primary is having a habitat or shelter, which is like "pitching a tent", he said.

Radical and exciting departure

For S. Pete Worden, a research professor of astronomy at the University of Arizona's Steward Observatory, there is a bottom line to his thinking about where best to place future observatories.

"NASA must be open to using the moon for astronomy and be willing to fund the analyses and precursor work needed to determine if the Moon holds advantages over other locations."

The Moon is the first target in President Bush's vision, and that is "a radical and exciting departure considering that our next-door neighbor world has been largely off NASA's radar screen for the past 15 years," Worden said.

However, Worden said, what is lacking is even the basic knowledge about lunar topography and resources to plan for a sustained human presence on the Moon. He contends that NASA should undertake lunar robotic missions to characterize polar landing sites and to quantify the presence of volatile elements critical to life such as hydrogen and carbon. The Moon's poles have more consistent temperature, solar power and variety of chemical resources than the equatorial zones visited by U.S. Apollo crews and the Soviet Union's robotic Luna missions.

"The Moon may also prove to be an ideal location for advanced scientific laboratories in biology and astronomy...but we must fully understand the pluses and minuses of the Moon for such laboratories and not be driven to costly compromises between science and human exploration," Worden explained.

Free space locales

The case for lunar-based astronomy is a case nowhere near as strong as it used to be. That's the appraisal of Lester at the University of Texas at Austin. He is a strong backer of free-space locales such as Earth orbit or Lagrange points over what could be achieved on the Moon.

Lester suggested that an interesting strategic metamorphosis has occurred. "It isn't that we were wrong before, but just that we've gotten much more talented in our free space capabilities."

"With respect to free space, the Moon provides dirt and gravity, and neither are of great value to astronomy, at least of the ultraviolet, optical, infrared variety", Lester said.

There's the claim that telescopes could take advantage of the "stable" surface of the Moon. "But we've known for many, many years," Lester responded, "that free space is a marvelously stable place, and you don't need pylons or concrete!" 

Pointing and stabilization systems for spacecraft are straightforward, off-the-shelf items. The low temperature that would be found in lunar polar craters is attractive, Lester added, but carrying out construction in such cold places is likely to be very hard. "We'll have such low and controllable temperatures in free space in just few years anyway with the James Webb Space Telescope, he said.

"There is an assumption that you need to put telescopes where people can get to
them, in order to derive maximum value. This is probably true, but the assumption that the lunar surface is where such agents will soon congregate is probably naive. Free-space is a fine place for humans, and it has worked well for many years now," Lester said.

"Unless...and this is a big caveat...we find a lot of resources on the Moon that are useful for space travel, long-term human presence on the Moon offers us little as we look toward Mars, and that understanding is reflected in NASA's planning. For most telescopes, free space is the right place. Let's go back to the Moon, but let's go there for good reasons."