Like the Orteig prize that spurred Charles Lindbergh's 1927 transatlantic solo flight, the $30 million Google Lunar X Prize (GLXP) is an unprecedented competition both in terms of potential reward and technical challenge.

As with its illustrious forebear, the GLXP is also proving a tough nut to crack. To win the prize, a privately funded team must place on the Moon's surface a robot that will then explore over a distance of at least 500 meters (1,640 ft.) and transmit high-definition video and images back to Earth. When the contest was first announced in 2007, the deadline for winning it was December 2012. However, with no team even close to launching by then, the organizers extended the deadline three years.

The first team will claim a $20 million grand prize, while the second team will earn $5 million. In addition, teams can also win a $1 million award for stimulating diversity in the field of space exploration and up to $4 million in bonus prizes for accomplishing additional technical tasks. These range from traveling up to 10 times as far as the basic stipulated distance to visiting the site of a previous lunar mission.

“Aside from the different prize purses, winning would effectively launch the commercial lunar economy much like Ansari did for commercial space,” says GLXP's Leo Camacho. “The teams will have effectively created commercial means and technology to get to the Moon, and this will ideally spread into more industry that is looking to do the same for various reasons. This is the first step to commercializing the Moon.”

As the GLXP enters its sixth year, the lineup of contestants is going through its biggest shake-up yet. Team SpaceIL of Israel merged with Isle of Man-based Odyssey Moon in November 2012, one of several new pairings that has seen the number of active contestants drop to 23 from 33. Since 2008, seven teams have withdrawn, including Mystical Moon, Team Selene, C-Base Open Moon, Quantum3, SCSG, Micro-Space and Advaeros. Two other groups, Rocket City Space Pioneers (RCSP) and Next Giant Leap, have also been acquired by Moon Express to create one of the most formidable teams in the lunar competition.

Based in NASA's Research Park in Moffett Field, Calif., Moon Express is led by Bob Richards and was already widely considered as a leading contender to win the GLXP before its acquisitions. Prior to the teams combining, Moon Express, RCSP and Next Giant Leap (NGL) bolstered their credentials by being awarded commercial lunar data contracts worth up to $10 million each. As part of the teaming agreement with leading RCSP partner Dynetics, based in Huntsville, Ala., Moon Express also acquired the services of RCSP team leader Tim Pickens as chief propulsion engineer. Pickens was lead propulsion designer for SpaceShipOne.

The acquisition of NGL in May 2012 was the first such event in the Lunar X Prize and brought with it a substantial body of work already undertaken by NGL and its corporate partners, which included Sierra Nevada Corp., Charles Stark Draper Laboratory, the Massachusetts Institute of Technology's Space Systems Laboratory, Aurora Flight Services, Jolted Media Group, The Center for Space Entrepreneurship (eSpace) and the Challenger Center for Space Science Education. Along with Dynetics, the December teaming with RCSP then added Teledyne Brown Engineering, Andrews Space, Spaceflight Services, Pratt & Whitney Rocketdyne, Moog, the University of Alabama-Huntsville and the Von Braun Center for Science and Innovation.

Moon Express plans to use a modified version of NASA's Common Modular Spacecraft Bus (CMSB) for its lunar lander, currently targeted for a mid-2015 launch. NASA originally designed the bus in 2008 and developed the Hover Test Vehicle (HTV) as a CSMB test and demonstration platform. However, this effort was shelved when the Lunar Atmosphere and Dust Environment Explorer (Ladee) program was later awarded to NASA Ames.

Moon Express subsequently entered into commercial partnership with NASA through a Reimbursable Space Act Agreement in 2010 to recommission the HTV and facilities and use it as a test and development platform for the company's lander design. New avionics and hardware have been added as part of Moon Express's investment in the HTV, which became its Lander Test Vehicle (LTV).

“The LTV in its current incarnation is a collaborative effort between Moon Express and NASA. We wouldn't be able to do what we're doing without NASA, and the LTV and facility wouldn't be operating today without our investments,” says Richards.

Outside the U.S., one of the most ambitious teams is the Aeronautics and Cosmonautics Romanian Association (ARCA), a former contender for the Ansari X Prize. ARCA is building a test facility to run the 21-ton-thrust liquid oxygen/kerosene Executor engine for the Haas 2C rocket that will launch the European Lunar Explorer (ELE) vehicle to the Moon. Pending successful tests, ARCA plans to launch the Hass 2C for its first test flight later this year.

Its predecessor, the 2B demonstrator, was powered by what ARCA describes as the world's first composite, reusable, monopropellant engine ever to fly. The 2B was successfully launched in 2004 from the Cape Midia AFB on the Black Sea.

The Executor is also designed to power the IAR-111 Excelsior carrier aircraft, a supersonic platform in development to air-launch the Haas 2C. The carrier concept, which resembles a modified version of the Northrop YF-23 fighter design, was hatched following numerous problems and delays experienced by ARCA during earlier attempts to launch rockets from high-altitude balloons. ARCA has also tested a version of the Helen rocket that would be used for the lunar landing, in which the ELE would descend on a cable to the surface. The Helen 2B rocket, which can also be used for launching, was tested in October 2010, following a balloon launch at 40,000 meters (131,000 ft.) over the Black Sea.

Pittsburgh-based Astrobotic Technology Inc. is on track to launch its “Icebreaker” mission to the Moon in late 2015. The company, which emerged as an offshoot of Carnegie Mellon University's Robotics Institute in 2008, is aimed at developing space robotic products, services and missions for commercial space markets and will launch on a Space X Falcon 9. The Icebreaker mission will consist of two spacecraft: a lander and a robotic rover called Polaris. Once safely on the surface, Polaris will prospect for water at the lunar poles using a drill, oven and suite of instruments that will be delivered on the lander.

Dubbed Red Rover, for CEO and robotics specialist William (Red) Whittaker, the vehicle will be configured with vertical solar panels to generate 250 watts of power, as well as heat-rejecting radiators. Laser and stereo cameras will generate a 3-D image of the lunar surface and help guide the rover, which will be capable of autonomously driving and avoiding obstacles. The rover will communicate with Earth using an S-band antenna and is designed to explore for 10 days until the 14-day lunar night begins, after which it will hibernate, recover and continue with the mission.

With development of the rover and its systems progressing, Astrobotics is testing devices that could be used to explore inside a lunar cave. A trolley with a pulley and winch capable of lowering monitors into a skylight opening in a cave, was tested in a quarry in late February.

Team Stellar, led by Stjepan Bedic, is proposing a vehicle called the Stellar Eagle. Sponsored by KGo Aerospace Inc., Stellar has partnered with George Washington University on development of a plasma propulsion system for the cruise vehicle. Another company, Flightline Films, has aligned with Stellar in developing the space-rated, 3-D stereoscopic camera system on the cruise, decent and rover vehicles.

Other contenders include the Juxtopia Urban Robotics Brilliant Application National (Jurban) challenge. It aims to develop a vehicle that will be launched by a conventional rocket and then powered by an electrostatic-ion-propulsion system for a flight to the Moon that could take up to 10 days. Jurban says chemical rockets will perform course corrections closer to the lunar surface while the actual landing will be cushioned using inflatable air bags.

Independence-X Aerospace is a Malaysian team led by Mohd Izmir Yamin. Few details of the team's ILR-1 lunar rover design are available, though the group says a key goal is to transform Malaysia into a “developed space country” by 2020.

Florida-based Earthrise Space Inc. (ESI) is developing a lunar rover called Sagan as part of its Omega Envoy commercial lunar delivery service. ESI, which also received a NASA Innovative Lunar Demonstrations Data contract, recently added rapid-prototyping company Rapid Machining to its growing list of sponsors and partners. In December 2012, ESI also announced it had obtained U.S. government approval to work with Chile-based Team Angelicvm.

Under the agreement, Angelicvm has become ESI's “first lunar payload delivery customer.” Angelicvm's “Dandelion” rover will travel with ESI's Sagan rover to the Moon following a launch currently slated to take place in the second half of 2014. Both rovers will be attached to ESI's lunar descent vehicle, although ESI adds that “Sagan will get the first crack at roving the Moon's dusty plains, followed a few days after by Dandelion.”

The Denmark-based European Lunar Exploration Association (Euroluna) team includes Swiss and Italian members and is proposing a rover called Romit. Another broadly international team, White Label, formerly based in the Netherlands, announced in January it is moving its base of operations to Japan. “The team will now focus its efforts on furthering the development of its Japanese Moon rover, benefiting from the advice of its academic partner, the Space Robotics Laboratory at Tohoku University,” says White Label.

Based in Berlin, Part-Time Scientists is developing a rover called Asimov 1 and, as part of its project, plans to contribute to the development of a new global communications network called Comray. This is designed to link together radio dishes around the world to enable 24/7 communications with in-space assets. Part-Time Scientists says that “utilizing amateur radio frequencies, this network could potentially provide a cheaper alternative to the currently existing government and proprietary commercial networks.”

Representing Russia, Selenokhod derives its name from Lunokhod, the Soviet-era vehicles that in 1970 and 1973 became the first remote-controlled rovers to travel on the surface of the Moon. Unlike other wheeled-rover concepts, Selenokhod has adopted an unusual solar-powered craft that pushes itself along with two movable ski-like legs. The vehicle incorporates cameras and a low-gain, omnidirectional antenna, and it will be delivered by a Dnepr or Rokot launcher.

Other teams include the Barcelona Moon Team from Spain, Puli from Hungary and SpaceMETA of Brazil. “Team B” is a concept from a privately funded Canadian company, Adobri Solutions, while a team from Pennsylvania State University is developing a single vehicle, the Lunar Lion, that will serve as spacecraft, lander and rover.

Team Indus, based in New Delhi, is targeting a potential launch in 2014 on the Indian Space Research Organization's Polar Satellite Launch Vehicle. The team plans to attempt the Endurance and Distance bonus prizes.

Finally, another U.S.-based team called Phoenicia aims to launch its lander/rover as a hosted payload on a communications satellite launch to geosynchronous orbit. From there, the lander will separate from the parent craft and insert itself into a transit orbit to a direct landing on the lunar South Pole. The rocket-braked descent will end with an airbag-assisted landing.