* NASA plans to send nuclear-powered spacecraft to Mars

* Lunar Gateway space station was largely already built

* NASA to repurpose station components as lunar surface

base

By Joey Roulette

WASHINGTON, March 24 (Reuters) - NASA announced on

Tuesday it has canceled plans to deploy a space station in lunar

orbit and will instead use components from the project to build

a $20 billion base on the moon's surface, while also planning to

send a nuclear-powered spacecraft to Mars.

U.S. space agency chief Jared Isaacman, an appointee of

President Donald Trump who took charge at NASA in December,

announced an unprecedented array of changes to the Artemis moon

program that would expand humanity's footprint in space, as the

U.S. pushes to return to the moon before China sends its

astronauts there around 2030.

The plans for the moon base included an aim to send more

robotic landers, deploy a fleet of drones and lay the groundwork

for using nuclear power on the lunar surface in the next few

years.

"This revised step-by-step approach to learn, build muscle

memory, bring down risk, and gain confidence is exactly how NASA

achieved the near impossible in the 1960s," Isaacman said,

referring to the U.S. Apollo program.

NUCLEAR-POWERED MARS MISSION

NASA also disclosed plans to launch a spacecraft called

Space Reactor 1 Freedom to Mars before the end of 2028 in a

mission it said would demonstrate advanced nuclear electric

propulsion in deep space. NASA called this a major step forward

in bringing nuclear power and propulsion from the laboratory to

space. NASA said the spacecraft, once it reaches Earth's

planetary neighbor, will deploy helicopters for exploring Mars.

The Lunar Gateway station, largely already built with

contractors Northrop Grumman ( NOC ) and Intuitive Machines ( LUNR )

subsidiary Lanteris Space Systems, was meant to be a

space station in a lunar orbit.

"It should not really surprise anyone that we are pausing

Gateway in its current form and focusing on infrastructure that

supports sustained operations on the lunar surface," Isaacman

told a crowd of foreign delegates, companies and members of

Congress at a day-long event at NASA's headquarters in

Washington.

Repurposing Lunar Gateway to create a base on the moon's

surface - a difficult undertaking - leaves uncertain the future

roles of Japan, Canada and the European Space Agency in the

Artemis program, three key NASA partners that had agreed to

provide components for the orbital station.

"Despite some of the very real hardware and schedule

challenges, we can repurpose equipment and international partner

commitments to support surface and other program objectives,"

Isaacman said.

European Space Agency chief Josef Aschbacher, who attended

the event, told Reuters he will study the new plans and continue

talking to NASA about them.

Lunar Gateway was designed to serve as both a research

platform and a transfer station that astronauts would use to

board the moon landers before descending to the lunar surface.

NASA's current plans call for landing astronauts on the moon's

surface in 2028.

The changes made by Isaacman in recent weeks on the flagship

U.S. moon program are reshaping billions of dollars' worth of

contracts under the Artemis umbrella, sending companies

scrambling to accommodate the extra U.S. urgency as China makes

progress toward its own planned 2030 moon landing.

LUNAR LANDER PROJECTS BEHIND SCHEDULE

Central to the Artemis program is its astronaut lunar lander

program, with Elon Musk's SpaceX and Jeff Bezos' Blue Origin

both racing to develop moon landers for NASA. The two companies,

each targeting an initial crewed landing on the moon in 2028,

have fallen behind schedule.

Isaacman and other senior NASA officials on Tuesday made

little mention of the two companies' plans to accelerate

development of their landers to meet a 2028 astronaut landing

deadline. But NASA's acting associate administrator Lori Glaze

suggested the companies want to dock with the Orion astronaut

capsule in a different orbit between Earth and the moon than

planned, before ferrying the astronauts to the surface.

Glaze said "SpaceX has been considering alternatives of

their current Starship design" for the moon lander, "while

implementing a more streamlined approach to try and speed things

up and pull things forward."

NASA's inspector general this month said SpaceX, tapped in

2021 for the first astronaut moon lander under the program, is

two years behind schedule, while the company and Blue Origin

face a list of complex engineering challenges before they can

fly humans.

But as part of the agency's Artemis shakeup, Glaze said it

would use whichever lander is ready first instead of sticking to

a pre-determined order of mission assignments.

The Artemis program, begun in 2017 during Trump's first term

as president, envisions regular lunar missions as NASA's

long-awaited follow-up to its first moon missions in the Apollo

program that ended in 1972.

(Reporting by Joey Roulette; Editing by Andrew Heavens, Jan

Harvey and Lincoln Feast.)