Nasa has said it will send a new rover to Mars in 2020 as the next stepping-stone to a manned mission.
The new robot will be partially based on the same technology that built and successfully landed the $2.5 billion Mars rover Curiosity earlier this year.
It will be launched in 2020, and will reuse the 'Sky Crane' landing system which saw Curiosity lowered on wires safely to the surface, from a levitating platform.
Nasa said basing the new, $1.5 billion robot on Curiosity's "architecture" would help keep costs low.
"The Obama administration is committed to a robust Mars exploration program," NASA Administrator Charles Bolden said. "With this next mission, we're ensuring America remains the world leader in the exploration of the Red Planet, while taking another significant step toward sending humans there in the 2030s."
In total Nasa said it is participating in seven Mars missions.
- The Curiosity and Opportunity rovers
- The 2013 launch of the Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter to study the Martian upper atmosphere
- The Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) Participation in ESA's 2016 and 2018 ExoMars missions
- The new rover to launch in 2020
It is currently thought that humans might be sent to orbit Mars in the 2030s, but that manned exploration of the surface might be decades further away.
"The challenge to restructure the Mars Exploration Program has turned from the seven minutes of terror for the Curiosity landing to the start of seven years of innovation," NASA's associate administrator for science, and astronaut John Grunsfeld said in a statement.
"This mission concept fits within the current and projected Mars exploration budget, builds on the exciting discoveries of Curiosity, and takes advantage of a favourable launch opportunity."
Nasa has come under strict budget pressure in recent years, and is increasingly turning to private companies to supply its International Space Station and other key mission requirements.