Images: NASA's Kepler to seek Earth-like planets

It's one of the oldest questions confronting humankind: Is there life out there beyond the confines of planet Earth? NASA hopes to get some answers from its Kepler spacecraft, which is set to launch Friday evening on a mission into the Milky Way.

Kepler will be in search of orbs like Earth: "rocky planets that orbit sun-like stars in a warm zone where liquid water could be maintained on the surface," according to NASA. In other words, it's looking for places where life might be possible.

But before a spacecraft can fly, there's a lot of work to be done. This view shows the solar array side of the nearly completed Kepler construction.

The business end of Kepler is its photometer, a 0.95-meter telescope with a field of view of 105 square degrees--"comparable," NASA says, "to the area of your hand held at arm's length." Such a relatively large field of view for an astronomical telescope is needed so that Kepler can monitor the brightness of 100,000 stars.

A squad of technicians at a Titusville, Fla., hazardous processing facility check out Kepler on February 3. While work on the spacecraft is all but completed, it didn't happen as quickly as planned. When the spacecraft takes off Friday, the launch will be nine months behind schedule, according to a report from the Government Accountability Office on a number of large-scale NASA projects. The GAO document, released Monday, also puts the Kepler project's total cost (as of December 2008) at $594.8 million, a nearly 20 percent overrun from the baseline cost of $497.5 million established for fiscal year 2007.

This artist's rendering (a portion of a larger portrait of the Milky Way by Jon Lomberg) shows the region of space that Kepler will be observing. Kepler won't be taking close-ups of any planets; rather, it will find them by detecting minute reductions in the brightness of a star when a planet passes between star and spacecraft.

In this rendering, by Carter Roberts of Oakland, Calif.'s Eastbay Astronomical Society, the rectangles show specific regions of the Milky Way that will be targeted by the CCD (charged coupled device) elements in Kepler's photometer. The spacecraft is expected to keep watch on its Milky Way beat for at least three and a half years.

There are 42 CCDs in Kepler's focal plane array. Each CCD measures 2.8 by 3.0 centimeters and has a resolution of 1,024 by 1,100 pixels, and the entire array is rated at 95 megapixels, according to NASA.

Here's a closer look at one of the CCDs, still in its shipping container. A radiator system on Kepler will cool the focal plane array to minus 95 degrees Celsius. (CCDs, albeit smaller ones, are also used in digital cameras.)

Kepler's 1.4-meter primary mirror gets a look-see from a trio of technicians.

The primary mirror has a honeycomb structure that keeps it very lightweight; it's just one-seventh the weight of a solid mirror with the same thickness and diameter.

Kepler stands shrouded by part of the fairing atop the Delta II rocket that will lift it into space from Launch Pad 17-B at Cape Canaveral Air Force Station in Florida. The fairing creates an aerodynamic nose cone over the spacecraft during its transit through the atmosphere and will break away after that. (Not to jinx anything for Kepler, but a fairing that failed to separate properly spelled doom in late February for NASA's Orbiting Carbon Observatory satellite.)

Liftoff for Kepler is scheduled for 10:49 p.m. EST on Friday.