NASA still has not received approval for a replacement carbon-observing satellite that could provide baseline data for monitoring compliance with a new climate treaty being negotiated this week in Copenhagen.
The new satellite would replace the Orbiting Carbon Observatory doomed by a rocket mishap during launch in February.
Since OCO crashed back to Earth, scientists and policymakers have set plans to build a new spacecraft.
Sources close to the mission say the internal discussion has "changed from if to when" an OCO replacement would be approved and funded. But officials are still waiting on formal authorization to proceed with the reflight.
"I really can't confirm anything for sure, and I'm not sure when such confirmation would be possible, although one might look for some indication when the president's budget is released in early February," said Michael Freilich, director of the Earth Science division at NASA headquarters.
The $209 million mission lost in February was designed to pinpoint carbon sources and sinks, regions where carbon is emitted and absorbed into and from the atmosphere.
The push for an OCO reflight comes as world leaders meet in Copenhagen to negotiate a new deal to restrict emissions of heat-trapping carbon dioxide, a contributor to climate change.
The National Research Council sent a letter to NASA Administrator Charlie Bolden in July saying OCO measurements could monitor emissions from human sources like cities and power plants. Although OCO was designed to detect larger natural sources and sinks, the mission could provide key baseline data during the first few years of a new climate treaty, the letter said.
A demonstration of the OCO platform could also lead to more advanced and accurate systems to gather better data in the future, the NRC report said.
The letter sparked more urgency in the effort to authorize an OCO reflight, officials said.
Freilich said NASA got the message. The space agency sought input from a broad range of scientists in a study of the value of a new OCO mission, compared to upgraded sensors and different observation methods.
"It came to the conclusion that OCO-type measurements were indeed still the valuable measurements that both the science and the policy community needed," Freilich said.
Japan launched a satellite named Ibuki in January to also keep tabs on carbon dioxide in the atmosphere, but OCO's three-channel spectrometer instrument is designed to collect data with greater sensitivity.
When NASA releases funds for the new mission, a satellite could be built and launched in about 28 months, according to David Crisp, the OCO principal investigator at the Jet Propulsion Laboratory.
Officials assessed options to mount a new OCO spectrometer on the International Space Station or fly the instrument with a thermal infrared sensor on a dedicated platform.
NASA ultimately decided a clone of the original OCO mission, using a nearly identical instrument, spacecraft and launch vehicle, would be the best option.
"The carbon copy of OCO did come out to be the most rapid and, given the state of maturity of the estimates, the least costly approach for the nation," Freilich said.
NASA presented the options to the White House's Office of Science and Technology Policy in early September. According to Freilich, the Obama administration has not yet notified NASA on any decision.
The agency's Earth science program would have to receive extra funding or some future missions could face delays to pay for another OCO satellite, Freilich said.
Earth observation missions are primarily selected based on the NRC's decadal survey, a broad set of recommended missions based on the input of scientists.
"The decadal survey recommendations oversubscribe the budget that we have, and the budget that we have did not include, and does not include, an OCO replacement," Freilich said. "So either we would have to change priorities were the decision made to fly an OCO replacement, or there would have to be additional resources put into the system."
Freilich would not discuss specific missions that could be in jeopardy.
Ed Weiler, NASA's associate administator for science, singled out in September the SMAP soil moisture monitoring satellite and the ICESat 2 mission to study Earth's ice sheet. Both missions are part of NRC's decadal survey recommendations.
Freilich said it was too early to determine what, if any, missions could fall victim in a reshuffling of funding for another OCO satellite.