The U.S. government has taken its first steps toward replacing the old and ailing Landsats 5 and 7 spacecraft with a new land-remote-sensing satellite it expects to put in service in 2011.

NASA, which is buying the satellite on behalf of the U.S. Geological Survey, plans to request bids from industry for the so-called Landsat Data Continuity Mission later this year. NASA intends to award a firm, fixed-price contact for a spacecraft and instrument that sources following the program said could cost on the order of $400 million.

Because the new satellite, already dubbed Landsat 8 by some U.S. government officials and scientists, is not expected to be in service until perhaps a year or longer after Landsats 5 and 7 cease operating, NASA and the U.S. Geological Survey also are considering buying imagery from one or more planned or existing remote sensing satellites to help bridge the anticipated data gap.

Theodore F. Hammer, acting flight program director for NASA’s Earth Sun System Division, said in an e-mail that Landsats 5 and 7 both have enough fuel on board to remain in service until late 2010 assuming, of course, the spacecraft suffer no mission-ending instrument or subsystem failures before then.

Acknowledging that some gap is possible, if not probable, Hammer said NASA and the U.S. Geological Survey “are currently analyzing potential effects of a Landsat data gap and are leading a multi-agency working group to assess what resources could be used to help lessen the impact of such a gap.”

Some of the potential resources include data from the Indian and Chinese-Brazilian remote sensing satellites systems, although diehard Landsat users maintain that these systems offer only partial substitutes for the multispectral imagery Landsat spacecraft have been collecting for more than 30 years.

In order to minimize any gap between the demise of Landsats 5 and 7 and the arrival of the new satellite, Hammer said, NASA intends to offer financial incentives to industry for on-time delivery of the new satellite.

“True we have some initial planning estimates for a Landsat Data Continuity Mission satellite to deliver on orbit early [in calendar year] 2011,” Hammer said. “However, we have come to the understanding that industry could possibly do much better than that, so we will incentivize the contract to minimize if not eliminate the potential of a gap.”

A draft request for proposal for the new Landsat mission is due out before the end of June to be followed before the end of September by the final solicitation.

According to the pre-solicitation notice that NASA’s Greenbelt, Md.-based Goddard Space Flight Center released Feb. 22, NASA also is considering including a thermal band on Landsat 8’s main instrument. Contractors will be asked to bid the thermal band as an option when they submit their proposals.

While Landsats 5 and 7 are both capable of making thermal infrared observations, NASA decided sometime in the 1990s that including a thermal band on the next generation of Landsat cameras then in development would add too much cost and complexity.

Samuel Goward, a geography professor at the University of Maryland, College Park who co-chairs the National Satellite Land Remote Sensing Data Archive Advisory Committee, said recent technological advances should make adding a thermal band a more affordable option for Landsat 8.

Landsat 7, like all previous Landsats, features an optical mechanical camera, old technology that has since given way to solid-state detectors similar to those used in today’s digital cameras.

When NASA was developing Earth Observer 1, an experimental spacecraft launched in 2000 to flight test a prototype solid-state Landsat camera, the technology required to add a thermal infrared band “was very, very expensive and required a lot of onboard power,” Goward said.

Goward said that thinking persisted all the way through NASA’s unsuccessful 2003 bid to commercialize the collection of Landsat imagery and through the writing of technical requirements for the Landsat-type instrument that, up until this past December, the United States intended to add to its next generation of U.S. polar-orbiting weather satellites instead of flying it aboard a dedicated spacecraft.

Goward said NASA’s decision to drop the thermal band from future Landsat missions provoked a “hew and cry” from users who had come to rely on the capability.

He said adding the thermal band to Landsat 8’s instrument should require neither as much expense nor onboard power as previously estimated thanks in part to so-called microbolometer technology developed with the help of the U.S. Defense Department for solid-state cameras.

Hammer said the thermal capability is only an option, not part of the baseline requirements for the next Landsat mission. However, he said NASA decided to at least consider including the thermal band after hearing from members of the Landsat community that such a capability still is desired.

Among those NASA heard from was Richard Allen, a professor of water resources at the University of Idaho. Allen uses Landsat’s thermal band to help Idaho manage agricultural water consumption across a region of the state that is larger than Connecticut, Maryland, Massachusetts and New Jersey combined.

While NASA’s Terra and Aqua satellites have cameras capable of seeing in the thermal infrared, neither spacecraft, Allen said, offer views in high enough resolution to distinguish the fields of one land owner from that of his neighbors. “That is quite troubling to a state water resource department mandated to regulate individual water rights,” Allen said.