If all goes as planned, NASA’s campaign to pinpoint sources and sinks of atmospheric carbon dioxide will get a major boost early next year with the launch of the Orbiting Carbon Observatory-3, a leftover satellite instrument modified to attach to the International Space Station.

OCO-3 is an important precursor to the more ambitious Geostationary Carbon Cycle Observatory, or GeoCarb, mission slated to reach orbit on a commercial communications satellite in 2022.

Although the Trump administration and House Appropriations Committee called for an end to the OCO-3 program last year, Senate appropriators backed it. The funding question, however, was not resolved since Congress has yet to enact a budget for 2018. [Editor’s note: The 2019 budget proposal the White House sent Congress Feb. 12 again seeks to cancel OCO-3 and several other science missions]

NASA — like the rest of the federal government — has been operating since Oct. 1 under a series of stop-gap spending measures, the most recent of which expires Feb. 8. As a result, NASA’s Earth Science Division is marching forward with the same funding and programmatic guidance it received when Congress finally passed the 2017 budget late last spring. That means the Jet Propulsion Laboratory’s work on the OCO-3 instrument has continued despite the Trump administration’s desire to shut it down.

NASA spokesman Stephen Cole said by email that OCO-3 “hardware is expected to be completed this spring, at which time the instrument will be placed in storage, as planned, to await launch.”

OCO-3’s launch — as cargo on one of the SpaceX Dragon capsules bound for the ISS late this year or early next —is considered “pending,” Cole said, as NASA awaits direction from “the final fiscal year 2018 NASA appropriations and/or the NASA Administrator’s fiscal year 2019 budget request” due out Feb. 12.

For an Earth-observation program, OCO-3 is a bargain, said Mike Freilich, NASA Earth Science Division director. NASA paired leftover pieces from the free-flying OCO-2 launched in 2014 with some additional hardware to create an instrument capable of monitoring atmospheric carbon dioxide from a perch on the exterior of the International Space Station.

“Using ISS makes a lot of sense,” Freilich said at the American Meteorological Society meeting in Austin, Texas, in January. “We build a bare instrument and it gets flown on a commercial space station resupply mission. We get Earth-observation measurements for a mere fraction of what it would cost to do the spacecraft, the launch and the instrument as well.”

Unlike OCO-2, a free-flyer in sun-synchronous polar orbit that observes locations on Earth at nearly the same time every day, OCO-3 will monitor changes in carbon dioxide concentrations throughout the day due to the space station’s low Earth orbit with an inclination of 51.6 degrees.

“For those of us who are excited about GeoCarb, having something ahead of us looking down at the Earth at different times with different sun angles is very important,” said Berrien Moore, GeoCarb principal investigator and Oklahoma University vice president of weather and climate programs.

GeoCarb will be NASA’s first attempt to monitor greenhouse gases from a staring sensor. NASA plans to launch the instrument to measure carbon dioxide, methane and carbon monoxide over most of North and South America as a hosted payload on a commercial telecommunications satellite. NASA is arranging GeoCarb’s ride through SES Government Solutions, the federal contracting arm of satellite fleet operator SES, which last week launched a satellite hosting a NASA instrument to study the ionosphere. GeoCarb, like NASA’s Global-scale Observations of the Limb and Disk instrument flying on SES-14, will benefit from its perch some 36,000 kilometers above the equator.

“From that vantage point we’ll be able to collect data from dawn to dusk,” said David Crisp, NASA’s OCO-2 science lead, adding that the GeoCarb data will help researchers determine how efficiently plants absorb carbon dioxide.

The GeoCarb instrument is being built by Lockheed Martin’s Advanced Technology Center in Palo Alto, California. Gary Kushner, Lockheed’s GeoCarb program manager, said the mission is blazing a trail that others hopefully will follow. “We’re developing this instrument to look at the Western hemisphere but there is a need for this type of information in other parts of the world,” Kushner said. This would be relatively easy to do with a hosted payload going up on a satellite that is already going to cover an area, he said. “We’re trailblazing and developing this for NASA. If we prove to be successful, more people … will want more of this kind of mission to cover other parts of the Earth.”

Carb loading

While GeoCarb stands to be the first instrument to do this type of monitoring from geosynchronous orbit, the United States is not alone in conducting space-based investigations of atmospheric greenhouse gases.

In October, the European Space Agency received the first signal from Sentinel-5P, part of the European Union’s Copernicus Earth-observation program. Sentinel-5P produces daily high-resolution global images of methane and carbon monoxide. China launched Fengyun-3D, a meteorological satellite with a greenhouse gas spectrometer, in November. Later this year, Japan plans to launch its second Greenhouse gases Observing Satellite-2. The French space agency CNES plans to launch MicroCarb in 2020 to monitor atmospheric carbon dioxide.

“People realize these are extraordinarily important measurements,” Moore, co-chair of the National Academies’ 2007 Earth science decadal committee, told SpaceNews.

The new Earth science decadal survey published Jan. 5, “Thriving on Our Changing Planet: A Decadal Strategy for Earth Observation from Space,” emphasized that point by calling on NASA to “conduct more research on the fluxes of carbon, water, nutrients, and energy between ecosystems and the atmosphere, the ocean and the solid Earth, and how and why are they changing.”

Carbon buildup isn’t controlled entirely by human activities. Fossil fuel burning adds 40 billion tons of carbon dioxide to the atmosphere every year, “but the 800-pound gorilla is the natural carbon cycle,” Crisp said.

Plants and oceans have traditionally absorbed half of the human emissions but researchers don’t know if that trend will continue as the climate changes. The latest ocean-warming El Niño produced some alarming results. Ecosystems did not appear to play their usual part by absorbing all the natural CO2 they emitted plus half the CO2 that humans produced.

“We don’t think the natural carbon cycle will necessarily behave as it has been since the beginning of the industrial age and continue to clean up half of our mess,” Crisp said. “We need to understand those processes far better than we currently do… Otherwise anything we might do to manage our emissions will be negated by what the natural carbon cycle does.”

Since its launch in 2014 as a replacement for the original OCO satellite that was destroyed in a 2009 launch failure, OCO-2 has made key observations and proven its three grating spectrometers could make precise measurements of atmospheric carbon dioxide.

OCO-2 was intended initially as a two-year experiment. In early January, JPL won approval to extend the OCO-2 mission three years. The satellite and instruments are “extremely healthy,” Crisp said.

In addition to helping researchers monitor atmospheric greenhouse gases, OCO-2 and OCO-3 are demonstrating technology needed for GeoCarb. Without those precursors, GeoCarb “would be bridge too far, we wouldn’t try it,” Moore said.

OCO-2 established the algorithms used to measure atmospheric carbon dioxide in addition to calibrating and validating the necessary instruments. OCO-3 will demonstrate ways to make those measurements throughout the day. “That’s going to be very important for us,” Moore said.

Crisp said there is still some uncertainty about the long-term future of NASA’s carbon-monitoring missions beyond OCO-2, OCO-3 and GeoCarb. Budgets are being squeezed across the U.S. government but, he said, NASA remains committed to this effort.