The emergence of the international space station as a go-to host platform for Earth observing sensors is testimony to the resourcefulness of NASA and the Earth science community during a time of scarcity.
The massive orbiting outpost already hosts a handful of downward-looking sensors, both government and commercially owned. Examples include the U.S. government-developed Hyperspectral Imager for the Coastal Environment and a pair of commercial imaging cameras — one for taking full-motion video — operated by UrtheCast, a for-profit company.
NASA plans to install at least five more environmental instruments during the next four years. Among them are space-based versions of sensors previously flown only on aircraft and instruments that will build on existing records of satellite-collected environmental data.
The push to utilize station for Earth science can be viewed from one of two different perspectives. As a readily available platform with ample onboard space and power resources, the station is an ideal, low-cost test bed for new technologies and measurements that are candidates for future dedicated satellite missions. Alternatively, but for the same reasons, the station might be seen as an option of last resort for NASA’s Earth Science Division, whose ability to build and launch dedicated satellites, even to collect measurements of proven scientific value, is severely limited by budget pressures. As Michael Freilich, the division’s director, recently noted, the launch — and in some cases the development — costs for station-hosted instruments are covered by that program’s budget.
It’s true that the station is in many ways less than ideal as a platform for Earth observation, especially if the objective is scientific research, as opposed to technology demonstration. Station’s orbit is inclined at 56 degrees relative to the equator, whereas most Earth observing satellites operate in polar, sun-synchronous orbits that provide global coverage and pass over a given point on Earth at the same time each day. In addition, the altitude of the station’s orbit varies widely, and data collection is frequently interrupted during events such as orbit raising maneuvers and the arrival of crew- and cargo-carrying spacecraft.
On the brighter side, some research applications are best suited to relatively low-inclination orbits. Moreover, station-hosted sensors, because they pass over the same spots on Earth at different times of day, can complement the data collected from sun-synchronous orbit.
Given its estimated $100 billion-plus price tag, the international space station could never be justified on the basis of its ability to support environmental or climate-change research. But the station is available, underutilized and has a logistics and research budget that can support any number of NASA science activities. Station managers are doing all the right things to encourage potential users, government and commercial, to take advantage. That the Earth Science Division is taking that offer to heart, in much the same way as it is making the most of hosted payload opportunities aboard commercial telecommunications spacecraft, is to its credit.