Structureless Space Telescope Could Look For Life Around Other Stars

A big aspiration for astronomers is to identify life on planets orbiting other stars. Thanks to NASA's Kepler mission we will know about the statistical abundance of Earthlike worlds in our galaxy in just a few years.

But confirming that other worlds are actually inhabited (not just inhabitable) could take decades.

And, finding just one such planet won't be enough. We'll need to survey at least several nearby exo-Earths to convince ourselves we are actually seeing the biosignatures of life.

Accomplishing this will be a Herculean task. Huge space telescopes are needed to harvest the feeble glow of an exo-Earth. That's because the light needs to be dissected into a spectrum that yields the chemical fingerprint of life processes.

Probably nothing smaller than a 16-meter space telescope would be needed. Just such a telescope is under study. But whether NASA could someday afford it is another story. The observatory would cost at least $5 billion. And, the development of the heavy lift rocket boosters needed to place the telescope far from Earth could be indefinitely delayed in NASA's exploration timetable.

But keep in mind that the Hubble Space Telescope only exists because it has cousins up there. I don't mean the other working pair of NASA Great Observatories, the Chandra and Spitzer space telescopes. I mean the KH-11 Earth reconnaissance satellites built in the 1970s and 80s. Hubble is from the same assembly line as these spy satellites. The only difference is that it looks up instead of down. In theory (but not in practicality) Hubble could resolve an object on Earth's surface as small as Apple's new iPad.

The Defense Department is exploring the possibility of placing our nation's spy satellites into much higher orbits than used today. One reason is that such eyes-in-the-sky cannot be so easily destroyed by anti-satellite weapons.

The high ground is geostationary Earth orbit (GEO) at approximately 24,000 miles, where telecommunications and weather satellites are parked. At this altitude a satellite hovers over the same hemisphere of Earth all the time because it has the same orbital period as Earth's rotation rate.

A 30-meter mirror in GEO would image an area the size of metropolitan Washington with a resolution down to one meter. Three super-spy-eyes -- located 120 degrees apart on the sky -- would cover all of Earth all the time. The message to terrorists: you can run but you can't hide.

If you aimed the mirror array out to the stars, it would be ten times sharper than Hubble and 60 times as sensitive.

An elegant "thinking outside the box" concept is to assemble the telescope from a constellation of 88 separate mirrors that are only 2-meters across. They would be precisely position to formation-fly and make a 30-meter diameter shallow bowl that would bring all of their light to a spacecraft located at a central focus.

They would be kept in place inside a "virtual cube" with the corners staked-out by free-floating lasers. Pulses of light from the lasers would nudge each mirror back into place should they drift. The laser beams  pulsed by a master control platform would be located at the focus of the super-segmented mirror. The mirrors would be initially deployed by magnetic force from small "assembly spacecraft" (sorry, no "tractor beams").

What makes this concept promising, albeit technically challenging, is that the super-mirror is very fault tolerant. If any component of it fails it could easily be replaced. It could even work despite the loss of mirror segments to meteoroid hits.

Most importantly, today's rockets have the payload capacity to launch the components for the super-telescope piecemeal. A launch failure on a package of mirrors would not be catastrophic to the program.

Best of all, we're again talking about an assembly-line telescope. If you are building several of these telescopes for national security, then the cost drops significantly per telescope rather than if you were building just one from scratch purely for astronomy. And, to get the public onboard, this observatory needs a name that inspires. My first choice would be "Hubble-2." But how about, "Life Finder?"