— NASA is considering replacing the Orbital Carbon Observatory (OCO) destroyed during a Feb. 24 launch failure with a larger spacecraft that would include the OCO instrument and a thermal infrared sensor some scientists have hoped would be added to the next Landsat mission.

NASA has begun preliminary design work on the thermal infrared sensor, known as TIRS, with an eye toward including it on the Landsat Data Continuity Mission in development for a December 2012 launch. Congress allocated $10 million in the space agency’s 2009 budget for preliminary design work and to “identify the earliest and least expensive approach and flight opportunity.”

Mike Freilich, NASA’s Earth science division director, said building an OCO replacement could provide NASA an alternative platform for TIRS, which collects remote sensing data used to monitor volcanic activity and measure water consumption.
Western U.S.
states rely on thermal infrared data to determine water rights and monitor interstate water compacts.

The concept of flying TIRS and the OCO instrument on a common spacecraft is one of two options being considered by NASA. The second is to fly a near copy of the first OCO, with the exception of some obsolete components being upgraded.

Dulles, Va.-based Orbital Sciences Corp. designed and built OCO, under the guidance of NASA’s Jet Propulsion Laboratory (JPL) in
, to spend two years mapping Earth’s carbon dioxide concentrations to help scientists understand the impact of human activity on global climate change. The loss of OCO after its protective shroud failed to separate from the Orbital-built Taurus XL rocket after launch sent NASA back to the drawing board to consider how to collect the carbon measurements.

NASA expects to make a decision between the two options in late spring or early summer, NASA Acting Administrator Chris Scolese said during an April 29 House Appropriations commerce, justice, science and related agencies subcommittee hearing.

A duplicate of the first OCO would likely cost about the same amount as the original $273.4 million spacecraft and likely would be ready for launch in about three years, Freilich said.

The option to integrate the OCO instrument and TIRS on one spacecraft is a more expensive undertaking that Freilich said would not be ready for launch until mid-2013. The advantage is the Landsat mission could move forward without any delays that integrating TIRS onto the mission late in development might have caused, he said.

“The [spacecraft] would fly in formation in close constellation with the Landsat Data Continuity Mission,” Freilich said. “But it would not have to hold up the mission.”

NASA also is continuing to evaluate the effects of adding TIRS to the Landsat mission, with a preliminary design review scheduled for late May.

In tandem with that review, a NASA team is working out compatibility issues with TIRS and OCO. For example, the first OCO was designed to take measurements as the entire spacecraft moved, which would not provide the stability needed for thermal infrared measurements.

“The team has come up with some clever ideas to solve this,” Freilich said. “They are not complete but they are being developed right now.”

Under that plan, OCO would fly in Landsat’s near-polar orbit, rather than the near-polar orbit planned for the first OCO. Freilich said the OCO team at JPL approved of the change in orbit.

“The Landsat orbit gives you the measurements you need,” Freilich said.

The disadvantage, Freilich said, is the spacecraft would not join NASA’s so-called A-Train of Earth observing spacecraft, which across the equator within a few minutes of one another. OCO was to be the sixth of the A-Train satellites, but that was “an added positive that wasn’t a Tier 1 requirement,” Freilich said.