In 2015, NASA explored the expanse of our solar system and beyond, and the complex processes of our home planet, while also advancing the technologies for our journey to Mars, and new aviation systems as the agency reached new milestones aboard the International Space Station.

"It was a fantastic year that brought us even closer to Mars," said NASA Administrator Charles Bolden. "Our space program welcomed advances from commercial partners who will soon launch astronauts from the United States to the International Space Station, and progress on new technologies and missions to take us into deep space, improve aviation and explore our universe and home planet."

Solar System and Beyond
NASA is exploring our solar system and beyond to unravel the mysteries of our universe. After a decade-long journey, the agency's New Horizons spacecraft completed a historic flyby of Pluto in July, making it the first-ever space mission to explore a world so far from Earth. New Horizons captured never-before-seen views of the distant dwarf planet and its moons, and collected data that will keep scientists busy for years to come, returning the data and images to Earth using NASA's Space Network.

NASA's Dawn spacecraft made history in March with another dwarf planet, Ceres, when it became the first spacecraft to orbit such a celestial body. In October, NASA's Cassini spacecraft made the closest-ever flyby of Saturn's moon Enceladus - capturing valuable scientific data from the plume of icy spray coming from the moon's subsurface ocean.

In the search for a twin of our home world, NASA's Kepler spacecraft confirmed in July the first near-Earth-size planet in the habitable zone around a sun-like star 1,400 light-years away. Back on Earth, NASA managers working the early stages of the agency's Europa mission selected nine science instruments to investigate whether Jupiter's mysterious icy moon could harbor conditions suitable for life.

The first of 18 flight mirrors for NASA's James Webb Space Telescope were installed in November, beginning a critical piece of the observatory's construction ahead of its 2018 launch.

In April, NASA's Hubble Space Telescope, a Great Observatory that forever transformed our understanding of the universe, celebrated 25 years of scientific discovery. After its last astronaut servicing mission in 2009, Hubble is better than ever and expected to continue to provide valuable data into the next decade.

The agency's Solar and Heliospheric Observatory (SOHO) celebrated its 20th anniversary as the longest-running solar observatory, as well as the discovery of its 3,000th comet, the study of which can shed light on how our solar system was formed.

In March, the four Magnetospheric Multiscale spacecraft were launched and positioned in Earth's orbit to study magnetic reconnection, the interaction between our sun and Earth's magnetic field that can disrupt modern technological systems such as communications networks, GPS navigation, and electrical power grids.

Journey to Mars
NASA's journey to Mars was advanced in 2015 by valuable science findings from current missions traversing and orbiting the Red Planet. In September, NASA announced its Mars Reconnaissance Orbiter provided the strongest evidence yet that liquid water flows intermittently on present-day Mars.

NASA's Mars Atmosphere and Volatile Evolution (MAVEN) mission identified the process that appears to have played a key role in the transition of the Martian climate from an early, warm and wet environment that might have supported surface life to the cold, arid planet Mars is today. MAVEN findings also showed how space weather near Mars affected its potential to support life.

The Opportunity and Curiosity rovers continued to explore the surface of the Red Planet this year, with data from Curiosity showing signs of a form of nitrogen - further evidence that conditions on ancient Mars may have been able to support life

Development of the core capabilities required to send astronauts to Mars in the 2030s continued this year with significant progress on NASA's Orion crewed spacecraft, Space Launch System (SLS) rocket, Asteroid Redirect Mission, and revitalized space launch complex at the agency's Kennedy Space Center in Florida. And in October, NASA held its first workshop to brainstorm with the science community to identify the best Martian landing sites for astronauts to carry out scientific exploration.

In 2015, the agency moved ahead toward the first integrated Orion and SLS flight test, designated Exploration Mission 1. In a report released in October, NASA's Journey to Mars: Pioneering Next Steps in Space Exploration, the agency provided a detailed outline of its plan to send the first humans to the Red Planet.

Building on the success of Orion's first flight test in 2014, agency officials completed their rigorous technical and programmatic review of Orion to establish NASA's commitment to the program's technical, cost and schedule baseline.

In March, Orion's Launch Abort System (LAS) was tested to prove it can survive the intense temperatures, pressures, noise and vibrations experienced during a launch emergency and get the crew to safety. The spacecraft's heat shield arrived in June at NASA's Langley Research Center in Hampton, Virginia, where it will be readied for water-impact tests in 2016.

Technicians at Michoud also have begun welding the primary structure of Orion's crew module and joined the middle part of the spacecraft to the bottom portion of the crew module, and expect to finish welding in early 2016. Engineers at NASA's Marshall Space Flight Center in Huntsville, Alabama, analyzed core samples from Orion's heat shield, which was used in the 2014 spaceflight test, to better understand its performance and to provide improvements in thermal protection models, as the agency continues to refine Orion's overall design and reduce its mass.

NASA received in November a full-size test version of the Orion European Service Module provided by ESA (European Space Agency), which is being prepared for testing early next year at the Plum Brook Station test facilities in Sandusky, Ohio.

Progress also continues on SLS - the world's most powerful rocket. The booster and engines that will propel SLS and the Orion spacecraft to space passed significant tests this year. The upgraded rocket booster passed a major ground test in March after firing for two minutes, the amount of time it will fire when it lifts SLS off the launch pad. Engineers will conduct a second and final qualification booster firing test in 2016. In August, NASA completed the first series of tests for the upgraded developmental RS-25 engines on the A-1 test stand at NASA's Stennis Space Center near Bay St. Louis, Mississippi. Preparations will continue in 2016 as the flight engines that will power SLS on missions into deep space will be tested for flight.

For the first time in almost 40 years, a NASA human-rated rocket completed all steps needed to clear a critical design review while the hardware is being built: a structural test article of the rocket's propulsion system was finished and numerous other flight and qualification hardware were completed and are ready for welding.

Work also began on infrastructure projects supporting SLS and Orion. Construction began in May on a 215-foot-tall structural test stand for SLS at Marshall. In August, NASA completed modifications to the Pegasus barge, previously used to move space shuttle hardware. For its new mission, transporting the core stage of the SLS, a 165-foot center section was added to the barge, bringing its total length from 260 feet to 310 feet.

In addition, Kennedy continued its transformation into a 21st century, multi-user spaceport for both government and commercial customers. Modifications continue on the ground structures that will launch the next generation of rockets and spacecraft. Several new work platforms that will be used to access, test and process SLS and Orion arrived on site, and the giant steel platforms are being installed in the center's Vehicle Assembly Building.

Testing began at Kennedy on the umbilical system that provides power and ground communications between the mobile launcher tower, rocket and Orion spacecraft. Upgrades and designs in progress were reviewed to ensure they will be ready to support all system and processing requirements for the first launch of SLS and Orion.

NASA's Asteroid Redirect Mission (ARM) passed a pivotal mission milestone in the spring with the successful completion of the agency's mission concept review. After extensive expert and public engagement forums and workshops to gather ideas on how to best meet the president's challenge to redirect an asteroid, NASA refined its robotic capture approach that will achieve the goal of redirecting a large asteroid boulder back to a parked orbit near our moon, allowing astronauts to train and conduct sampling of the space rock.

Having an asteroid parked near the moon also will open up commercial opportunities for American companies interested in learning the challenges of mining asteroids. In October, NASA issued a call to American industry for innovative ideas on how the agency could obtain a core advanced solar electric propulsion-based spacecraft for the robotic boulder retrieval mission.

The agency also took steps to stimulate the development of deep space capabilities in the commercial aerospace sector with the selection of 12 projects on which NASA will partner to advance development of necessary exploration capabilities.

To further prepare for the journey to Mars, the eight candidates from NASA's 2013 astronaut class received their astronaut pins in July, symbolizing the completion of their training. And in December, NASA began a search for its next group of astronaut candidates.

In October, Hollywood and NASA science and technology came to audiences around the world with the premier of "The Martian." The agency collaborated on this journey to Mars film with 20th-Century Fox Entertainment, providing guidance on production design and technical consultants. Across NASA, dozens of people already are working on many of the technologies seen in the movie that astronauts will need when they begin to explore Mars in real life.