When the second Orbiting Carbon Observatory (OCO) blasted off from Vandenberg Air Force Base July 2 and traveled into orbit aboard a2 rocket, David Crisp, the mission’s science team leader, says he felt “immeasurable relief.” Crisp began work more than 17 years ago on the instrument concept, which initially was included in NASA’s CloudSat mission, then dropped when that satellite’s primary instrument, a radar, overshot its budget. He later led a team that proposed an expanded version of the spectrometer as the primary instrument on the original OCO, only to see it destroyed in a 2009 launch failure. Since 2000, Crisp has shepherded OCO and its replacement, OCO-2, through numerous competitions and budget battles.
He is quick to point out that while the original concept was his, the OCO mission benefited from the contributions of a talented team, including original instrument builder Hamilton Sundstrand, spacecraft manufacturer Orbital Sciences Corp. and scientists around the world eager to obtain data on atmospheric carbon dioxide to help pinpoint the places on Earth where the gas is produced and absorbed.
With the OCO-2 spacecraft in orbit and initial checkout running smoothly, Crisp says he is looking forward to returning to his role as a scientist, analyzing data and contributing to greater understanding of Earth and its climate. Crisp, a senior research scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, has served on the science teams of the Soviet-French-U.S. Venus Vega balloon mission, NASA’s Hubble Space Telescope Wide Field and Planetary Camera 2, NASA’s Mars Pathfinder Lander Atmospheric Structure Instrument and the European Space Agency’s Venus Express. Crisp also was OCO principal investigator, chief scientist for NASA’s New Millennium program and science lead for NASA’s Atmospheric Carbon Observations from Space, a partnership with the Japan Aerospace Exploration Agency’s Greenhouse Gas Observing Satellite (Gosat) mission. Crisp spoke recently with SpaceNews correspondent Debra Werner.
How is OCO-2 performing?
Everything has been working very well. The spacecraft checkouts have been going as expected. We are making very good progress. We validated two of the three science observing modes. We did a quick plumbing check on the propulsion system. It seems to be working properly. Everything is going very smoothly.
How long will it take to move OCO-2 into the constellation of Earth observing satellites, known as the A-train?
If everything works perfectly, which would take some real luck, we would move into the A-train as early as the first week of August. It could take quite a bit longer. We are trying to sync up into a traffic lane moving at 7 kilometers per second. If we miss a burn, or something performs differently than we expect, we may have to wait weeks.
What happens after you join the A-train?
We will cool down the instrument to operating temperatures. The body of the instrument is designed to operate at about 6 degrees below zero Celsius. The detectors have to be cooled to a very low temperature, around 120 degrees Kelvin. Between now and the time we finish our orbit-raising maneuvers, we will leave the instrument at a fairly high temperature to shake off any water or gas before we turn it on.
We will start taking data right away. Our first effort will be to ensure data flow. We will then analyze the performance of the instrument based on targets. Once we’ve done that, we will plan a series of specific observations to further refine the calibration. On the time frame of mid-November, we will start delivering the actual measurements to the NASA Goddard Space Flight Center data archive, where they will be available to the entire science community.
How is the OCO-2 mission different from the OCO mission?
When we built OCO, we were looking at a rapid buildup of carbon dioxide in our atmosphere, primarily driven by the developed world. We knew that natural processes at the surface of the Earth, what we call sinks, were absorbing about half of all the carbon dioxide that human beings were emitting into the atmosphere every year. We knew that the oceans were responsible for absorbing about one-quarter of the carbon dioxide we were emitting and that somewhere on land, something was absorbing another quarter of the carbon dioxide. We knew we had those sinks, we just didn’t know where they were.
Are you still looking for them?
Yes. But the sources have changed too. The developing world, China and India primarily, are contributing 57 percent of the carbon dioxide that’s being pumped into the atmosphere every year by human activities. Unlike the United States, Europe and Japan, they have been unable to track the rapid increase in their emissions. We don’t know how much carbon dioxide is being put into the atmosphere and from where.
So you now are looking for sources and sinks?
Yes. We also want to understand why it is that regardless of how much faster we put carbon dioxide into the atmosphere, the ocean and the land biomass has been able to keep up. We measure the amount that goes into the ocean by measuring the acidification of the ocean. The other quarter is going into the land. We don’t know where. We know that the growing season is longer. Greenhouse-gas-induced warming has increased so much now that the growing season up in the boreal forests in Northern Canada, Northern Europe and across Siberia is much longer than it used to be and that’s absorbing some of it. But those regions are emitting as well as absorbing more.
Why is it important to figure that out?
If we want to control this stuff, we would like to understand what processes are operating, where they’re operating and how much longer they might continue to operate. A constant concern is that important carbon dioxide sinks like the ocean might be becoming saturated.
NASA pegs OCO-2’s cost at $465 million. What does that include?
The launch vehicle, spacecraft, instrument and all the science activities through the nominal two-year mission.
How has your work on Gosat contributed to OCO-2?
A month before the failed launch of OCO, the Japanese launched Gosat. The Gosat project manager and members of the staff were my guests at the OCO launch. Before the sun came up the morning after we lost OCO, the project manager invited us to work with him. We have been working with him ever since. We learned how to make an accurate carbon dioxide measurement from space.
How is OCO-2 different from Gosat?
Gosat was designed to measure carbon dioxide and methane. It takes Gosat four seconds to make a single measurement. In that time, OCO-2 makes 96 measurements of carbon dioxide.
Is OCO-2 designed to make 1 million daily measurements?
Yes. Many won’t be useful primarily because of clouds. Of the million measurements we’re going to make every day, over the sunlit hemisphere of the Earth, probably between 100,000 and 200,000 will be cloud-free enough for us to pull carbon dioxide data out.
How is OCO-2 different from OCO?
To recover the science as fast as possible, OCO-2 was intended to be a carbon copy of OCO. We planned to rebuild the original design. It didn’t quite turn out that way. A lot of the hardware was obsolete and unobtainable. There are discrete pieces of new hardware in the spacecraft and instrument. They weren’t intended to improve the performance but to match the performance of the parts they replaced.
What is new?
The most significant piece of new hardware is the cryocooler, which keeps detectors at very low temperature to maximize their sensitivity. The cryocooler we flew on OCO was a flight spare from the Tropospheric Emission Spectrometer on the Aura Earth Observation System launched in 2004. It was the last of its kind. So we used a new slightly smaller model that did the same job.