Facing a lack of rocket options for medium-class robotic missions, NASA's launch czar said the agency will not need another medium-lift rocket until at least 2014, enough time for new boosters to prove themselves.

William Wrobel, NASA's assistant associate administrator for launch services, said future medium-class missions will most likely fly on Falcon 9 or Taurus 2 rockets now being developed for resupply missions to the International Space Station.

NASA hopes the Taurus 2 and Falcon 9 rockets will be ready to launch medium-class science missions. Credit: Orbital Sciences and SpaceX

"About the time we would expect the (Falcon and Taurus) vehicles to be ready is about the next time we would be able to see ourselves picking another vehicle for some of those missions that are out there in the 2014 timeframe," Wrobel said.

NASA is discontinuing its use of the venerable Delta 2 rocket line, a family of boosters that has been the backbone of the country's launch infrastructure for more than 20 years.

After the last NASA Delta 2 mission in late 2011, there are no medium-class spacecraft due for launch until around 2014, according to Wrobel.

Those missions, the SMAP and ICESat 2 Earth observation satellites, would need to be assigned launch vehicles by around 2012.

Designed by SpaceX and Orbital Sciences, respectively, the Falcon and Taurus rockets are being privately developed under a NASA program to procure commercial suppliers for the space station after the space shuttle's retirement.

The Falcon 9 rocket could debut by the end of this year. The Taurus 2 launcher is scheduled for its maiden flight in late 2010 or early 2011.

SpaceX and Orbital Sciences were the winners of NASA's International Space Station Commercial Resupply Services, or ICRS, contract last December. The companies are also building ships to dock with the complex.

"About the time we would expect the ICRS vehicles to be ready is about the next time we would be able to see ourselves picking another vehicle for some of those missions that are out there in the 2014 timeframe," Wrobel said.

Both rockets are designed to be less expensive than current launchers, an important factor for science missions in a tight budget environment. Lower launch costs would allow more missions to be started for less money.

The Falcon 9 is already part of the NASA Launch Services, or NLS, contract, an open-ended agreement that puts the rocket in a pool of launchers the agency can choose from for robotic missions.

Wrobel said the Taurus 2 will likely be added to the NLS contract when it is renewed for launches between 2010 and 2020. The current NLS agreement expires next year.

But observers say NASA should have more medium-lift alternatives available.

"A combination of the current tight funding and the lack of launch vehicles is almost a perfect storm, and it will limit what we can do for medium-sized space missions for the future," said Jack Burns, chairman of the NASA Advisory Council's science committee.

NASA's long-term needs will have to be met by a new rocket. Officials are aware of the risks of counting on vehicles with no flight history.

"It's a tough market out there and I don't see anything on the near-term horizon that makes it appreciably better. So I think we have to evaluate any and all options as they come forward," Wrobel said.

That's why NASA negotiated a deal with the Pentagon to buy an Air Force Minotaur rocket to launch a lunar atmospheric experiment in 2012.

The 287-pound LADEE mission was too large to fit on a smaller booster and a more powerful rocket would have been overkill, according to Wrobel.

"So the decision was made to see if we couldn't get a Minotaur 5, and that's the path we went down and went through the Administrator's office," Wrobel said.

Officials had to get approval to use the Minotaur because NASA prefers commercial launch providers.

"We have to go through a similar evaluation for any new mission we would want to put on a Minotaur going forward. It's not like it opens the door, necessarily, but it's good that it's an option," Wrobel said.

Burns, also a professor at the University of Colorado at Boulder, said his committee recommends looking at the Minotaur family for more launches.

"We want to continue to encourage NASA to pursue other options. One of those options is using the Minotaur rockets from the Department of Defense," Burns said.

The SMAP soil moisture observatory could fit on the smaller Minotaur 4 rocket, a NASA spokesperson said.

The Minotaur 4 rocket stands on its California launch pad. Credit: Orbital Sciences

The Minotaur 5 rocket is made of retired stages of the military's Peacekeeper missile and commercial solid-fueled upper stages. The booster can dispatch almost 1,000 pounds to the moon.

"The Department of Defense has quite a supply of these things, although they will have to negotiated one at a time," Burns said.

Officials are wary of committing to future Minotaur launches because of fears government-backed rockets would compete with private vehicles like Falcon 9 and Taurus 2.

"We have to be careful, too, in that we want to continue to encourage (NASA) not to compete with the private sector in these new emerging rockets that are coming forward," Burns said.

In 2007, NASA decided to end its relationship with the Delta 2 program after the Air Force phases out the launcher in favor of the more versatile Atlas 5 and Delta 4 rockets that can haul a wider variety of satellites.

With the Air Force leaving the Delta 2, NASA would have had to pay to restart production of the rocket and assume fixed costs to support ground facilities and a standing army of workers, according to Wrobel.

The increased costs would have nearly equaled the price tag of the more capable Atlas 5 and Delta 4 rockets.

"It basically makes the bill too large for NASA afford by itself," Wrobel said. "When you compare that to the cost of an EELV, that's kind of where you are."

The Air Force conducted its last Delta 2 mission earlier this month. Seven more Delta 2 launches are planned through 2011 for NASA and commercial customers.

"They'll be around for a few years, at least," Wrobel said. "Even though Delta 2 is going away, we still see a need and we still have five more to fly ourselves."

United Launch Alliance, builder of the Atlas and Delta rockets, says five Delta 2 vehicles are available to sell.

Despite officially moving away from the Delta 2, Wrobel said NASA could purchase some of the remaining rockets if a need arises.

"We're not ruling anything out," Wrobel said. "It might be a good enough deal that we could make something really work there. And it depends on what other needs come up, so it's too hard to say."

ULA only has large "Heavy" 46-inch-wide strap-on boosters in stock right now, according to Wrobel. The company is evaluating acquiring more smaller 40-inch motors to use for lighter missions, Wrobel said.

United Launch Alliance did not respond to requests for information.

The company has also studied putting a less powerful second stage on the Atlas 5 and Delta 4 rockets, making the new workhorse launchers available to carry smaller satellites.

"It would be something we would have to evaluate if it becomes something that is legitimate or real when it comes online," Wrobel said.

"We're in this dry period where there just aren't many choices," Burns said.