Wednesday, February 25, 2009

NASA OCO satellite crashes and burns

Satellite failure clouds future of US climate science


The failure of NASA's Orbiting Carbon Observatory (OCO) is a loss to climate science, but that loss could be doubly compounded if engineers can't correct what went wrong in time for NASA's next climate satellite to fly later this year.

That satellite, known as the Glory mission, is currently set to launch in November, but it's now on hold pending the results of the OCO investigation. Whereas OCO was build to measure greenhouse gases, Glory is designed to study the effects of aerosols on clouds. This has been called the "missing link" of climate science, and it's information that is needed as soon as possible to refine global climate models.

It's well known that clouds reflect sunlight, which has a net effect of making the Earth cooler. It's also known that minute particles called aerosols often become the nuclei around which water droplets form in clouds. But what nobody understands is exactly how much humans are affecting the clouds with all the aerosols we generate through combustion, agriculture and other dust-raising activities.

So a delay in getting Glory off the ground means a delay in filling in this crucial piece of the climate puzzle. But wait - it gets worse.

One of the instruments on Glory is the "Total Irradiance Monitor" (TIM). Its job is to measure the total light output of the Sun to a degree of precision that is simply unachievable on the ground. This is important because sunlight is the key input into global climate and it drives the whole system. The fact that some climate sceptics still site changes in the Sun's energy output as responsible for climate change speaks to the fact that we don't have a good handle on what the Sun is likely to be doing long-term and more data are urgently needed.

Solar irradiance has been measured continuously from space for about the last 30 years. But during the 1980's coverage was insufficient and the calibration is not good between instruments that measured the Sun before and after this period. The deficit has led to disputes and to opposite conclusions about the long-term trend in solar irradiance.

Right now the best instrument for measuring solar irradiance is on the SORCE satellite, which was launched in 2003 and is now well past its nominal mission lifetime.

The TIM instrument on Glory is a descendant of this device and scientists involved with the mission say it's vital for the two instruments to observe the Sun together for at least six months to preserve the continuity of the 30-year solar record. If not, says TIM instrument scientist Greg Kopp of the University of Colorado, "it puts the whole record in jeopardy".

That would mean we might not be sure if the Sun is getting brighter, dimmer or staying the same in the coming decades, which is essential information for climate modelling and policy-making.

Glory will be launched on the same model of Taurus XL rocket that failed to place OCO into orbit today. The likely cause of the failure - a fairing that decided not to separate - has been established. What is not clear is whether this will require changes that could push back the launch of Glory into 2010 or beyond. Obviously scientists are hoping this will not be the case, and that any changes can be made in parallel with their own preparations for launch. On the other hand, another failure would be disastrous.

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