CAPE CANAVERAL, Fla. — NASA intends to expand the scope of research hosted on the international space station by adding at least five Earth science instruments over the next four years. 

Two instruments are slated for launch in 2014: a next-generation RapidScat, designed to monitor the oceans’ winds, and the laser-scanning Cloud-Aerosol Transport System, a technology that previously has only flown aboard aircraft. 

“It’s a new candidate technology that would be great for a free-flier in the future,” NASA space station chief scientist Julie Robinson said. 

Those instruments will be followed in 2015-2017 by third versions of the Stratospheric Aerosol and Gas Experiment (SAGE 3) and the Orbital Carbon Observatory (OCO)-3 instruments, and by a second-generation Lightning Imaging Sensor, which would supplement and eventually replace one now flying aboard the 16-year-old Tropical Rainfall Measuring Mission spacecraft, a joint project of NASA and the Japan Aerospace Exploration Agency. 

The space station already is host to a handful of Earth science instruments, including the Hyperspectral Imager for the Coastal Ocean instrument, which was developed and used by the Naval Research Laboratory before being turned over to NASA and the space station’s national laboratory manager, the Center for the Advancement of Science in Space, for use by a broader community. 

Like the Hyperspectral Imager for the Coastal Ocean, some of the impetus for the new missions is to test technologies before instruments are built for free-flying satellites. But the space station also offers Earth scientists the ability to compile complementary data sets from those made with traditional remote-sensing satellites, which typically fly in polar or sun-synchronous orbits about 800 kilometers above Earth.

The station flies over the planet’s mid-latitudes at an altitude of about 400 kilometers.

“What we’re finding is that it can make a lot of sense to get that ISS orbit because you get different times of day,” Robinson said. 

“In a polar orbit you’re going to pass the equator at 2 o’clock or at 1:50 and it’s going to be the same every day. Because the ISS orbits precess” — shift position relative to Earth’s rotation — “you can take advantage of that and start understanding the diurnal cycles of things.

“The Earth scientists have a good sense of the daily climatology for the different things they’re measuring and they’re realizing that sometimes you’re missing something huge. If you’re not seeing the buildup of clouds in the tropics across the morning, you’re not really understanding the process of clouds,” she said. 

Earth scientists are finding an even more practical reason to join the space station community: money. 

“Where it makes sense — and it does at the moment make exceptional sense for us — we can actually launch more or less bare instruments to the ISS,” NASA’s Earth Science Division director, Michael Freilich, said at the American Geophysical Union conference in December. 

“The launch costs are covered by the space station program. The [instrument] installation and operation are similarly covered. And in some cases, actual instrument development is covered by the space station program and we here in science division pay for the scientific exploitation,” Freilich said. 

The Cloud-Aerosol Transport System payload, for example, cost about $14 million to develop; RapidScat was about $26 million, Robinson said. 

The OCO-2, a free-flying satellite to replace one lost in 2009 and precede OCO-3 on the space station, will cost about $372 million, including the launch vehicle, the spacecraft and two years of operations, Freilich said.

Being a station-hosted payload, however, has its drawbacks. The outpost’s altitude varies, pointing can be challenging and instruments may be shut down for operational issues, such as the arrival and departure of visiting spacecraft. 

Some instruments may be vulnerable to the station’s orbital environment and at times have to cover sensitive optics, preventing their use. Engineers also have to deal with NASA’s extensive human spaceflight safety protocols for any equipment coming aboard station. 

“There are always are going to be challenges going to space and these are the ones we have,” said Jack Kaye, NASA’s associate director for Earth science research.

“I’m really excited about seeing Earth science instruments that add missing data that isn’t available any other way,” Robinson added. “That’s an important aspect of getting the most out of ISS.”