(O)rbiting=(C)arbon=(O)bservatory
Posted: Sun Feb 22, 2009 10:54 pm
Aviation Week and Space Technology wrote:First NASA CO2 Satellite Set for Launch
By Michael Mecham Feb 8, 2009
<<Nature's carbon is far more abundant than what humans produce, but man-made sources are growing. Between 1751 and 2003, 306-626 billion tons of carbon were added to the atmosphere as carbon dioxide, mostly through fossil fuel combustion, cement manufacturing and forest clearing. The range in those numbers underscores the uncertainties of current carbon sampling methods.
Scientists posit that about 60% of human emissions are absorbed. The rest stays in the atmosphere. While they say absorption is split 50:50 between oceans and soil, they are uncertain where the carbon is going when on the land. Clearly, the political drive to battle global warming will be on firmer scientific ground if concrete facts can be given.
To this end, NASA is set to add another satellite to its inventory. About the size of a phone booth, the Orbiting Carbon Observatory isn't even as big as some of the instruments on the space agency's larger Earth-observing fleet.
Built by Orbital Sciences Corp. in Dulles, Va., the 972-lb. OCO will become the newest member of the Afternoon Constellation, or A-Train, of Earth-observing spacecraft funded by NASA, France and Canada.
It is set for a 1:53 a.m. PST launch on Feb. 23 by an Orbital Sciences XL 3110 booster from Vandenberg AFB, Calif. The solid-fueled Taurus will raise OCO into an initial 398-mi.-high orbit for a 10-day systems and instrument checkout. Over the next 20 days, the spacecraft's own propulsion system will raise it to an altitude of 438 mi. where it will be inserted at the front of the A-Train. The observatory will be the train's sixth member, followed, in order, by NASA's Aqua and CloudSat, France's Calipso and Parasol, with Aura as the caboose.
Their Sun-synchronous orbit has a near polar inclination. They circle the Earth every 99 min. and pass the same ground track every 16 days, crossing the equator at 1:30 p.m. local time. The A-Train stretches 3,800 mi. in space, but orbital speeds of 4.7 mps. mean they pass the same ground spot so rapidly their observations can be coordinated. OCO will be only 3.3 min. ahead of Aqua.
The OCO's single instrument was manufactured by Hamilton Sundstrand Sensor Systems of Pomona, Calif., and assembled and tested at JPL with one basic task in mind: measuring atmospheric carbon dioxide globally. Of special note will be the "sinks" that absorb CO2 and the "sources" that release it. These amount to the same thing in different stages. Healthy forests absorb CO2; dying or felled forests emit it. Cold oceans absorb the gas; warmer waters release it.
Vertical atmospheric measurements will draw CO2 profiles as they appear on cloud-free days. Monthly regional-scale concentrations will factor in cloud cover. They will span continents and oceans in surface regions of 386 X 386 mi.
The instrument uses three high-resolution grating spectrometers - two for CO2 measurements and one for molecular oxygen. Viewing is through an f1.8 Casseýýgrain telescope with a resolving power of 20,000. The camera is so powerful its control algorithms have to factor in that it can image individual buildings.
"Ten years ago, it couldn't have been built," Crisp says of the instrument. But new resolving techniques and better focal plane arrays, design and construction methods have made it possible. The detectors have a quantum efficiency close to 90% of perfection, he says.
Carbon dioxide molecules aren't measured directly; the instrument tabulates the absorption of sunlight by CO2 and molecular oxygen molecules before and after the sunlight is reflected off the Earth's surface. Since each molecule has a specific infrared signature, they can be singled out and counted. There are two detectors for CO2 because it is easier to spot near Earth's surface at 1.61 microns and in the atmosphere at 2.06 microns. The molecular oxygen A-band channel acts as a survey control because its presence in the atmosphere is constant.
The observatory will continuously collect 12 soundings per second while over the sunlit hemisphere - approximately 33,500-35,500 individual measurements. It will record 8 million over a 16-day cycle with ground tracks that are separated by less than 100 mi. at the equator.
Pointing the instrument straight down in a nadir mode provides the highest spatial resolution on the surface and is expected to be most useful in cloudy or mountainous regions. But the instrument achieves a stronger signal-to-noise ratio when it is aimed at the bright glint spot where the Sun's reflection is brightest on the Earth's surface. So the camera will alternate between nadir and glint pointing modes over sequential global ground tracks. Periodically, it also will be aimed at ground-based solar-looking spectrometers for calibration checks.
Humans release about 8 billion tons of carbon into the atmosphere annually, says Anna Michalak, an OCO science team member from the University of Michigan at Ann Arbor. About half of that remains in the atmosphere, the rest is absorbed by oceans, plants and soils in carbon sinks.
"But it's difficult to pinpoint where these sinks are," she says. The promise of OCO is that it can better define the sinks and track changes in them, making it easier to predict how the carbon cycle evolves. Crisp notes that the total variation in CO2 between sinks and sources is only about 3%. "So we have to distinguish between very small differences."
OCO is part of NASA's Science Pathfinder program of relatively quick, low-cost and highly focused missions using small- or medium-sized spacecraft. The total mission cost is $273.4 million and it has a nominal two-year life span. Success will encourage climate change scientists to ask for more. But the spacecraft they will pitch is likely to shift technologies. A more advanced instrument might rely on light detection and ranging (Lidar) remote-sensing technology because it is unhampered by clouds and can operate day or night, says Crisp.>>
So I just kept the last post, and it seems it worked out good.
