“It’s really being done for safety,” spaceport spokesman David Wilson said. “It was a guess until they started dropping it and simulating and doing different scenarios, how this thing was going to behave on the runway. This is all a product of the testing and the characteristics of the vehicle.”

Backed by British billionaire Richard Branson, the commercial space line has been developing its craft and rocket engines in California’s Mojave Desert. The company plans to begin moving into the hangar and terminal facility later this year, and the runway extension is not expected to cause delays.

The runway was dedicated by Branson and other officials in October 2010 with much fanfare.

Stretching across a flat dusty plain 45 miles north of Las Cruces, the runway is designed to support almost every aircraft in the world, day-to-day space tourism flights and payload launch operations. It is 42 inches thick and includes a 14-inch layer of concrete.

The extension will cost $7 million, Wilson said. Money will be reassigned within the spaceport’s $209 million taxpayer-financed budget to absorb the cost of the change.

Designing the extension will take six to eight months.

Virgin Galactic has said rocket testing is continuing and commercial flights are at least a year away.

Wilson said the extension did not come as a surprise to spaceport board members. As part of the agreement Virgin Galactic had with New Mexico to build the spaceport, any technical changes that resulted from development of the spaceship technology would have to be accommodated by the state.

One scenario considered was if the rocket ship’s engines did not fire. That would require the craft to glide back to the spaceport, loaded with unburned fuel. That would mean the craft would be heavier and would require more room to land.

Other factors involve New Mexico’s altitude and high temperatures, which make the air thinner.

“That dictates longer runways,” Wilson said.

Branson and Virgin Galactic officials have said repeatedly that everything possible will be done to ensure safety once commercial flights begin.

Unlike experimental programs run by NASA, Wilson said Spaceport America and Virgin Galactic are based on business models and investments.

“Obviously safety has to be at the highest level, especially when you’re talking about commercial passenger service,” he said.

Branson announced last week that Virgin Galactic had netted its 500th customer, actor Ashton Kutcher. Others include Hollywood types, international entrepreneurs, scientists and space buffs.

At $200,000 a ticket, the space tourists get a 2 1/2-hour flight with about five minutes of weightlessness and views of Earth that until now only astronauts have been able to experience.

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“There’s massive excitement about it,” Harris said Wednesday, following one of his meetings. More meetings were planned Thursday and again next month.

Harris said there is international interest in the success of a U.S. hub that would allow electricity to flow more freely between grids, and in the development of a trading system that could work seamlessly in a global market.

“With the technology that we have today, the communications we have and the environmental issues we need solved … you’ve got to have a way to trade on all the derivatives and all of the other environmental constraints. There’s definitely a huge need for us to find a worldwide platform,” he said.

First announced in 2009, the Tres Amigas project includes building a hub across 22 square miles of rangeland near Clovis. It would serve as the meeting point for interconnections that serve the eastern and western halves of the U.S. and a separate grid that supplies Texas.

Such a hub would create a bigger market for buying and selling electricity and help ease the bottleneck for renewable energy developers who have been unable to access a share of transmission to get their power to markets outside the Southwest.

While developers see Tres Amigas as a step toward making the nation’s power system more reliable, experts say avoiding massive power outages like the one that hit Southern California and parts of Arizona and Mexico last year will require a combination of modernization and more smart-grid technology throughout each of the three interconnections, especially given the scale of the grids involved.

The eastern U.S., for example, depends on about 150,000 megawatts of generation to meet its load. Tres Amigas will initially be capable of transferring 750 megawatts between the eastern and western grids.

“In the grand scheme of things, even a project like this is dwarfed by the need of each of these interconnections to continue to pursue modernization and expansion of their grids,” said Abraham Ellis, a Sandia National Laboratories scientist who works on renewable energy grid integration.

In addition to infrastructure, Tres Amigas is planning for its own power exchange that would allow for the buying, selling and trading of power across all three U.S. interconnections and potentially beyond, Harris said.

Mitsui has agreed to invest $12 million in exchange for an equity interest in the project. The European exchange plans to share the expertise it has gained while coupling power markets in France, Germany, Austria and Switzerland. That exchange operates spot markets that account for more than one-third of Europe’s electricity consumption.

With construction only months away, Tres Amigas is grappling a location for its trading operations.

“Ultimately what it’s boiling down to is taxes,” Harris said. “It looks like it’s going to be a pretty heavy tax penalty to locate in New Mexico and that very well could be a deal-killer for the state.”

Tres Amigas officials said they would pay 4 to 6 percent higher taxes in New Mexico than if they were to locate in neighboring Texas, which has a number of power exchanges already in operation.

Former Gov. Toney Anaya is working with Tres Amigas to develop legislation that would offer an abatement of the gross receipts taxes related to the trading.

Supporters of the project are facing a time crunch. The Legislature begins its 30-day budget session on Tuesday and Tres Amigas plans on making a decision on where to locate its headquarters and trading floor by March.

Anaya and Harris said there’s a possibility the Legislature will address the issue since the spin-off opportunities of having both the hub and power exchange in New Mexico are so great.

“This is a way for New Mexico to get into the energy game in a big way,” Harris said. “It’s hard to estimate the peripheral and derivative businesses that will come in as a result of where it’s located.”

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Follow Susan Montoya Bryan on Twitter: http://www.twitter.com/susanmbryanNM