NASA and the European Space Agency have signed an agreement calling for the Europeans to provide the service module for the Orion space capsule, the U.S. space agency's crew vehicle for exploration beyond Earth orbit.

The hardware would provide the Orion with propulsion, power, thermal control and basic supplies such as water and breathable air. ESA said the design will be based on that of the ATV supply ships that are currently being sent to the International Space Station.

"ATV has proven itself on three flawless missions to the space station, and this agreement is further confirmation that Europe is building advanced, dependable spacecraft," Nico Dettmann, head of the ATV's production program, said in an ESA statement.

The Orion's first test flight is scheduled for 2014, using a test service module built by Lockheed Martin. That unmanned launch would send the Orion to an altitude of 3,600 miles (5,800 kilometers). The European-built service module would get its first in-space tryout along with the Orion capsule and heavy-lift Space Launch System rocket in 2017, during an unmanned test flight that would go around the moon and back.

"This is not a simple system," Orion program manager Mark Geyer said in a NASA statement. "ESA's contribution is going to be critical to the success of Orion's 2017 mission."

The first flight with astronauts aboard would follow a round-the-moon route in 2021, and ESA will provide components for that flight as well.

NASA's current exploration plan calls for the Orion-SLS system to send humans to a near-Earth asteroid in the mid-2020s, and to Mars and its moons in the 2030s. Meanwhile, the task of sending cargo and crew to the International Space Station would be left to commercial spaceship providers.

When the Orion-SLS program was unveiled in 2011, the development cost was estimated at $18 billion through 2017, and roughly that much more for the 2017-2022 time frame.

Under the NASA-ESA agreement, which was signed in December and announced on Wednesday, ESA will provide the design and the hardware for the Orion service module as part of its contribution to the International Space Station project. The BBC reported that without such a contribution, ESA would owe NASA $600 million for the 2017-2020 period.

"Space has long been a frontier for international cooperation as we explore," Dan Dumbacher, NASA's deputy associate administrator for exploration system development, said in the space agency's statement. "This latest chapter builds on NASA's excellent relationship with ESA as a partner in the International Space Station, and helps us move forward in our plans to send humans farther into space than we've ever been before."

Even though ESA will provide the service module, its propulsion system will make use of engines left over from NASA's space shuttle program.

Bill Gerstenmaier, director of spaceflight operations at NASA Headquarters, said the European contribution would help keep the Orion project on track for the 2017 and 2021 flights. "We shouldn't try to go look at what ESA's contributing and then try to subtract that out of our budget," he told reporters. "We're actually getting a better, more robust design by cooperating together."

He acknowledged that the agreement put the Europeans in the "critical path" for future U.S. space exploration.

"I'm a realist, and I know that this won't be easy," he said. "It's not 100 percent comfortable — but I'm never 100 percent comfortable." 

More about Orion:

• Europeans decide to boost NASA's Orion
• Orion project on schedule for 2014 test flight
• The moon looms again as future destination

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.

STScI

NASA and the Space Telescope Science Institute are offering free e-books about space telescopes.

Free books from NASA, the Hubble Space Telescope's science team and the European Space Agency bring Earth and the heavens to life — as long as you have an iPad, and the patience to wait for a longish download.

Even if you have a regular old computer, you can still download the books about Hubble and its successor, the James Webb Space Telescope, as PDF files. But you'll miss out on all the interactive features.

Those two books were unveiled today by the Baltimore-based Space Telescope Science Institute, which takes care of the science programming for the two NASA-funded telescopes. They're joining the ESA's first iBook, "Earth From Space: The Living Beauty," on my iPad bookshelf.

The Hubble book guides you through scores of pictures from the world's most famous space telescope, organized into categories ranging from cosmology to planetary science. There's also a chapter on the telescope itself, with a 3-D model and a diagram you can tap on to learn about all the components. (Our Flash interactive about Hubble takes a similar approach.) When you tally up all the interactives, videos and picture galleries, the content adds up to a lot more than the 84 pages on the screen.

NASA / STScI

The iBooks are crammed with cosmic images.

The 74-page e-book about the Webb telescope uses a similar approach to explain the science behind the $8.8 billion observatory, which is currently scheduled for launch in 2018. There aren't any pictures from the Webb, of course, but the book's interactives, videos and photo galleries explain how the telescope will observe the cosmic frontiers in infrared wavelengths.

"These new e-books from NASA will allow people to discover Hubble and Webb in a whole new way — both the science and the technology behind building them," Amber Straughn, an astrophysicist on the Webb telescope project at NASA's Goddard Space Flight Center, said in today's news release. "They collect all of the amazing resources about these two observatories in an excellent product that I think people will really enjoy."

While the NASA iBooks look outward, ESA's iBook looks back toward Earth, incorporating stunning images from Europe's Earth-observing satellites. The 104 pages cover our planet from the core to the cryosphere, from the oceans to the wilderness. You can set color-coded virtual globes spinning with a brush of your fingertip.

ESA

"Earth From Space" is the European Space Agency's first iBook.

"By turning the virtual pages of this iBook you will discover how some of the latest technology has changed the way we see Earth," Volker Liebig, director of ESA's Earth observation programs, said in the space agency's publication announcement. "So, it was time to bring these ‘scientific voyages’ to you in a dynamic way. I believe that electronic media hold a huge potential, just like satellite technology. They help you to discover the scientific world of spaceflight."

While the Hubble and Webb e-books are downloadable via Apple's iBookstore, you download "Earth From Space" directly from ESA's website and follow the instructions. You'll need to be patient: Each book packs in hundreds of megabytes' worth of data, so the download can take as long as 20 minutes over a home broadband connection. There were times when I wondered whether it'd ever finish. But if you're a fan of space imagery, these books are well worth the wait — especially when you consider that they're free.

More space imagery:

• 2012: The Year in Space
• Space slideshow gallery
• App lets you take the planet's pulse
• 2012 Cosmic Log Space Advent Calendar

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.