he uncertainty now surrounding Europe’s plans to build and launch three successive, virtually identical rounds of Sentinel Earth observation satellites to ensure long-term data continuity rings familiar to anyone who has followed NASA’s environmental monitoring efforts over the last two decades or so.

NASA’s Earth Observing System program, hatched under the administration of then-U.S. President George H.W. Bush amid the early rumblings from scientists about global warming, originally featured a similar plan: three successive rounds of spacecraft — each satellite similar to its predecessor — to ensure a continuous 15-year record of climate and environmental data. But budgetary reality set in, forcing NASA to abandon that scheme well before the first satellite was launched. Almost by default, a new strategy emerged under which the measurements after the initial round of satellites would be shifted to a planned series of operational weather satellites jointly owned by the U.S. Air Force and National Oceanic and Atmospheric Administration, with NASA to fill in any gaps with dedicated spacecraft.

Development problems with the civil-military National Polar-orbiting Operational Environmental Satellite System have complicated that plan, however. Several instruments dedicated to climate research were removed from the weather satellite system to help contain its ballooning costs, although some have since been restored. Meanwhile, lengthy delays on the program have raised the specter of a break in the data record begun with the initial-round of Earth Observing System satellites — Terra, Aqua and Aura —which began launching a decade ago.

A similar scenario could be unfolding on the other side of the Atlantic, where the European Space Agency (ESA) and European Commission have mapped out an ambitious satellite-based Earth-observing effort known as Global Monitoring for Environment and Security, or GMES. Sentinel is the GMES core program; the first three Sentinel optical and radar Earth observation satellites are under construction, with a duplicate round of so-called B-unit satellites also under contract. In agreeing to help fund the B-unit satellites, slated to start launching in 2014, ESA broke with its longstanding practice of developing only one-of-a-kind satellites.

In order to avoid a costly Sentinel production gap, and to have backups ready in case any of the B-unit satellites are lost in launch failures, GMES managers need to have the C-unit satellites ready by around 2014, which means they need to be under contract soon. But the European Commission doesn’t have the necessary funding available under its current budget cycle, and the next one doesn’t begin until 2014. ESA, meanwhile, is adamantly opposed to providing its own funding for the C-unit craft. “There is no way,” ESA’s

director of Earth observation, Volker Liebig, said recently of the C-unit funding question, leaving no doubt as to the agency’s position.

While the European Commission may yet find a way to secure the needed funds — as it did a few years ago when it rescued the floundering Galileo satellite navigation program — there is another way: international collaboration. The United States and Europe share not only a common interest in global environmental monitoring from space — as manifested in Europe’s investments and in statements by the administration of U.S. President Barack Obama — but also the problem of sustaining long-term efforts in this area. Now is a good time to begin discussions that could lead to a cooperative strategy whose elements would include common data standards and data sharing, hosted payload arrangements, and joint missions.

The United States and Europe have a track record of collaboration on weather and environmental research satellite programs. The U.S.-French Jason series of ocean-altimetry satellites, to cite one example, has been so successful that the measurements, once considered experimental

, are now considered indispensable by scientists and operational weather forecasters alike.

Earth observation obviously isn’t the only activity where budgetary pressures are driving collaboration. In robotic Mars exploration, for example, ESA and NASA are close to an accord on a two-step program structured in a way that allows both sides to retain or develop key technical competencies on missions that otherwise might not be feasible from a budgetary standpoint. This same cooperative approach could be applied to environmental monitoring, where other nations, notably India and Japan, have plenty to contribute as well. The scientific urgency and long-term nature of space-based climate research will provide ample economic benefits and technology development opportunities for everyone involved.