Published online 15 April 2009 | Nature 458, 814-815 (2009) | doi:10.1038/458814a
By: Eric Hand
Since the Orbiting Carbon Observatory (OCO) crashed into the ocean minutes after its 24 February launch, researchers at NASA and elsewhere have been working on how else they might get the data on atmospheric carbon dioxide levels that the mission was meant to collect.
Within a week of losing the satellite, NASA, which spent US$278 million and seven years developing OCO, put together a committee of two dozen climate scientists to weigh up various options. Should they rebuild OCO with existing designs and launch it as quickly as possible? Start a new design that would take longer to develop? Or fund ground and sub-orbital carbon measurements, while working with existing greenhouse-gas monitoring satellites such as Europe's Envisat and Japan's Greenhouse gases Observing Satellite (GOSAT, also known as IBUKI).
Take two? A replacement Orbiting Carbon Observatory could be launched in 2011.NASA/JPL
The case against reincarnating OCO is that the spectroscopy it used to measure carbon levels needed reflected sunlight to work, preventing it from making measurements at dawn, dusk and night. Many scientists, including OCO's principal investigator David Crisp, of the Jet Propulsion Laboratory in Pasadena, California, think that probing the atmosphere with lasers will eventually offer a way to get round-the-clock data and thus see important effects such as those of nocturnal respiration by soil organisms.
But laser-based systems are technologically challenging. In a recent competition to design atmospheric-science satellites the European Space Agency eliminated a laser-based carbon-dioxide-monitoring mission, A-Scope, citing insufficient readiness. The technology for a similar NASA mission called ASCENDS (Active Sensing of CO2 Emissions over Nights, Days and Seasons) is still in development.
Crisp, who chaired the post-OCO working group, says that something like ASCENDS wouldn't launch until at least 2015. Other options - putting OCO-type instruments on weather satellites or on the International Space Station (ISS) - would also take a long time, and in the case of the ISS would miss the polar regions.
So - as expected - the bottom line of the report by Crisp's committee, submitted to NASA on 2 April, was that the agency should build an OCO "Carbon Copy" with the same design and instruments and launch it as soon as possible. Getting the data quickly is "critical to support national policy initiatives", says Crisp. The repeated mission would cost more or less what OCO cost, and could be ready for launch in the autumn of 2011.
Michael Freilich, head of NASA's Earth- science division, has sent the white paper out for review and says he will make a decision "possibly in May". But even if he plumps for a rebuild, paying for it might be difficult. As OCO was lost just six weeks ago, the only money in the budget that might naturally flow to Carbon Copy is the $23 million earmarked for OCO's operating costs. That might be a start - and might hold Crisp's team together after its current budget runs out in June - but if Carbon Copy is to fly it needs either new or diverted money.
"In all our opinions, the need for these data is just as high, if not higher, now as when the observatory was first planned."
It might seem that the $150 million recently added to NASA's fiscal-year 2009 budget for Earth science by Congress, or the $400 million more given to the same end in the stimulus package, would fit the bill. But there is a queue for that windfall. Landsat, a US Geological Survey land-mapping mission that NASA is procuring, and Glory, a mission due to be launched later this year to studyaerosols and clouds, could both use more money if they are to stay on schedule. And other new Earth-science missions recommended as priorities by the National Academies also need to get started. "We have far more to do than the available resources given us," says Freilich.
There are other options. Carbon dioxide can be monitored from the ground. Pieter Tans, who heads ground-based carbon-cycle monitoring for the National Oceanic and Atmospheric Administration from the University of Colorado in Boulder, points out that with his $5-million annual budget, he can monitor 84 spots, mostly in North America, via ground-based sites, aircraft, or ships. That represents approximately half of the world's non-satellite effort to monitor carbon dioxide.
Tans was on the OCO science team, but says he has long worried that excitement about satellites - which are, after all, NASA's stock in trade - leads politicians and policy-makers to neglect ground- and aircraft-based measurements. A more even split in spending between ground and space would allow him to boost his network of sensors by an order of magnitude, he says.
Crisp acknowledges the importance of the ground-based network - OCO needed it to calibrate its indirect measurements - but says there are things only a satellite can do, especially considering the importance of enforcing international climate treaties. "Try putting a CO2 station the middle of China," says Crisp. "Try it in the Congo."
What all concerned agree on is the need to do something soon. Says Ken Jucks, OCO programme manager at NASA, "In all our opinions, the need for these data is just as high, if not higher now [as when OCO was first planned]."