The engineers, scientists and astronauts at NASA are working on an endless list of fascinating experiments, projects and missions. But one target looms above all: putting a human on Mars.

A manned mission to Mars remains some time off, but much of NASA's current workload is executed with this ultimate goal in mind. On Thursday, NASA detailed the ways in which its current work will pave a path to Mars.

"NASA is closer to sending American astronauts to Mars than at any point in our history," NASA Administrator Charles Bolden said at a press conference on Thursday. "Today, we are publishing additional details about our journey to Mars plan and how we are aligning all of our work in support of this goal."

NASA says its journey to Mars is comprised of three types of work: Earth reliant, proving ground and Earth independent. Earth reliant work includes all the Mars-related science experiments being conducted on the International Space Station -- much of it focused on astronaut health. Proving ground work includes the engineering and logistics work that will enable complex missions to be carried out in deep space.

Earth independent work looks ahead to the future, when the culmination of lessons learned during Earth reliant and proving ground work are demonstrated and perfected on missions to locations within the vicinity of Mars -- perhaps sending a manned spacecraft to orbit Mars, landing a probe on a Martian moon or using rovers to harvest Martian resources for fuel, water and food.

"NASA's strategy connects near-term activities and capability development to the journey to Mars and a future with a sustainable human presence in deep space," explained NASA official William Gerstenmaier, associate administrator for Human Exploration and Operations. "This strategy charts a course toward horizon goals, while delivering near-term benefits, and defining a resilient architecture that can accommodate budgetary changes, political priorities, new scientific discoveries, technological breakthroughs, and evolving partnerships."

NASA's new plan also organizes the types of challenges they're facing into three main categories: transportation, working in space and staying healthy.

Ongoing health experiments on ISS apply most directly the category of staying healthy. While NASA's Space Launch System, Orion crewed spacecraft, and revitalized space launch complex all are focused on the challenges of transportation. A variety of other science projects are working to improve NASA's deep space communications systems and other in-flight capabilities.

NASA has sent a host of orbiters, probes and landers to Mars, advancing its robotic capabilities and understanding of the Red Planet. But sending humans adds many more layers of complexity.

The space agency says each new mission gets them closer to their goal -- each mission offering "successively more capable technologies and partnerships."