SAN FRANCISCO — News that a team of judges selected Astrobotic Technology Inc. and Moon Express Inc. as finalists in all three categories of a contest related to the Google Lunar X Prize is feeding speculation that the two U.S. teams are leading the pack of international competitors racing to the Moon.

However, Andrew Barton, Google Lunar X Prize technical operations director, said it is too soon to identify likely winners in the $30 million race to send the first commercial spacecraft to the Moon by the end of 2015. “There are still 18 teams left from all over the world with a whole diversity of approaches,” Barton said. “It would be premature to say which teams are still in the running.”

The Google Lunar X Prize announced Feb. 19 that an independent panel of eight judges selected Astrobotic, Moon Express, Japan’s Hakuto, Germany’s Part-Time Scientists and India’s Team Indus to compete in the final phase of three separate competitions to win milestone prizes totaling $6 million. The milestone awards were added to the Google Lunar X Prize in November as a way to spur on competitors facing the daunting technical and financial challenge of sending a privately funded spacecraft to the Moon.

Milestone prizes are designed to provide an infusion of cash at a critical time for competitors. “One to 1.5 years out from launch, you really need to be making down payments on your launch vehicle,” Barton said.

In addition, milestone prizes may help teams attract investors and customers seeking to send payloads to the Moon. “Having the judging panel, a panel of international experts, say you’re on the right path and you’ve made solid progress in a certain subsystem area is a big boost for those teams in terms of technical credibility,” Barton said.

Astrobotic, Moon Express and Team Indus are finalists for prizes of $1 million per team for hardware and software systems to enable a soft landing on the Moon. Astrobotic, Moon Express, Hakuto and Part-Time Scientists are finalists for prizes of $500,000 per team related to the mobility systems that allow a team’s lunar craft to travel 500 meters across the lunar surface after landing. Astrobotic, Moon Express, Part-Time Scientists and Team Indus are finalists for prizes of $250,000 per team for technology designed to produce high-quality images and video on the Moon.

Each of those tasks is an important component of the overall race. The Google Lunar X Prize promises a $20 million grand prize to the first team that succeeds before the end of 2015 in landing a commercial spacecraft on the Moon, traveling 500 meters and sending high-definition images and video back to Earth. The second team to achieve those goals stands to win $5 million. Additional $1 million bonus prizes will be awarded to teams that complete various tasks including detecting water and conducting operations at night. An earlier plan to reduce the first-place award to $15 million if a government beat the first Google Lunar X Prize team to the Moon was dropped last year in anticipation of China’s Chang’e lunar landing.

Participation in the milestone prize competition was optional and not all Google Lunar X Prize teams entered. Teams that win one or more milestone prizes and later go on to finish first or second in the overall race will have their final award reduced by the amount of the milestone award.

Judges selected milestone prize finalists after entrants defined their primary technical challenges in the various categories and plans to overcome those challenges. Whenever the judging panel declares that a team has met its objectives, that team will be awarded its milestone prize, Barton said. If all teams meet their objectives, each one could be awarded one or more prizes.

Being selected as a finalist in all three milestone prize categories will help Astrobotic attract paying customers, said Chief Executive John Thornton. “It indicates we are out in front,” Thornton said. “All our customers can see that. Once you get momentum going it starts to snowball.”

Pittsburgh-based Astrobotic, which spun off from Carnegie Mellon University in 2008, is financing its Google Lunar X Prize mission on a dedicated Space Exploration Technologies Falcon 9 rocket scheduled for launch in October 2015 by delivering secondary payloads at prices starting at $1.2 million per kilogram. Astrobotic announced Feb. 17 its latest agreement with Singapore-based Astroscale to deliver a time capsule containing a Japanese sports drink. Astrobotic previously revealed agreements to carry cremated remains to the Moon for Celestis Inc. of Houston and to provide NASA with mission-related data through the space agency’s Innovative Lunar Data Demonstrations program.

Additional Astrobotic customers will be announced later this year. “We are currently talking to upwards of two dozen customers around the world who want to fly with us,” Thornton said. “It’s more payload than we need for the first mission.”

Moon Express officials also greeted news of the milestone finals with enthusiasm. “We are thrilled we were selected to compete in the milestone prizes,” said Bob Richards, co-founder and chief executive of Mountain View, Calif.-based Moon Express. “The prize goals align very well with the things a competitor needs to do to reach the Moon next year. We are rocketing forward with our plans to open the Moon as the eighth continent.”

Moon Express, a company with plans for lunar prospecting and mining, has not yet revealed its launch plans, except to say its spacecraft is designed to fly as a secondary payload on a commercial rocket such as the SpaceX Falcon 9. In December Moon Express unveiled its MX-1 lunar lander, a single stage spacecraft designed to travel to the Moon’s surface from geosynchronous transfer orbit.

Germany’s Part-Time Scientists were extremely excited and relieved to be chosen to participate in two of the three milestone prize competitions, said Chief Executive Robert Boehme. “The preparations of our applications took us literally months and many sleepless nights,” Boehme said by email.

“For us, the milestone prizes are first of all a recognition for the great work our team managed to accomplish in the past five years without the additional financial and governmental support most other teams managed to acquire,” Boehme said. “Now it’s up to us to show that our technology is really as good as it looks. The milestone prizes may not fully mark out all the teams with a chance to win but they surely show you which teams have the right technology foundation to pull off the first private mission to the Moon.”

The Part-Time Scientists plan to launch their rocket in the fall of 2015 on a Russian Dnepr rocket. The team’s planned use of Dnepr, which has far less payload capacity than the Falcon 9, underlines a key element of the mission. “We try to achieve more with less using the existing satellite industry infrastructure to build the foundation for off-world exploration and continuing operations,” Boehme said. “It’s important to understand that the Google Lunar X Prize can be won many different ways but to open up space exploration to private entities you need to get the costs down and the technology on a stable foundation.”