Iridium Will Host Science Payloads

New satellites will give space and wattage for Earth-sensing experiments

Image: Irridium

Last February, in what seems an extraordinary stroke of bad luck, an Iridium communications satellite collided with a Kosmos-2251, a defunct Russian satellite, blowing both to pieces. Fortunately, Iridium was able to swap in one of the backups it maintains in orbit, swiftly restoring global coverage. But that freak event underscores the fact that the once maligned but now resurgent company needs some new satellites. Its quest to acquire them could make the company an important player in the geoscience community.

”At some point in time, if we didn’t do anything, we’d have less than 66 satellites,” says Don Thoma, Iridium’s executive vice president for marketing, referring to the minimum number of satellites needed to complete the company’s constellation. So Iridium, which has gained more than 300 000 subscribers since it emerged from bankruptcy in 2001, has embarked on an ambitious plan to begin launching a new generation of satellites, called NEXT, in 2014.

The new hardware will boost Iridium’s communications capabilities substantially, improving the maximum data rate subscribers can obtain at least fourfold, to 1 megabit per second or more. And the new network will be entirely based on the Internet Protocol, unlike the old voice-based communications infrastructure, which was built on the fleeting premise that enough customers would be willing to pay up to US $7 per minute for voice calls placed from $3300 mobile phones.

That Iridium’s NEXT satellites will provide an Internet in the sky comes as no great surprise. What’s rather amazing about the new satellites is that, in addition to providing globe-spanning communications, the Iridium fleet will also host scientific payloads, likely ones designed to monitor Earth. With the exception of some crude early experiments that involved putting special cameras on geosynchronous communications satellites, this will be a first.

The amount of scientific instrumentation on each satellite will be modest: Iridium’s allotment is 50 kilograms and 50 watts of power on average. ”We wanted to be sure we didn’t lose focus,” says Thoma.

Jan-Peter Muller, a professor at University College London’s department of space and climate physics, doesn’t see these weight or power limits as a big impediment. ”It’s a very cool idea to have it on a communications satellite because you have the communications infrastructure built in,” he adds.

One problem with using Iridium satellites to monitor the surface is that their orbits are optimized for communications, not for viewing. For the latter, a satellite is usually placed in a polar sun-synchronous orbit, so that it passes overhead everywhere at the same time of day, providing consistent illumination. This means that Earth-viewing instruments carried on Iridium satellites would have to cope with a changing sun angle.

Sun angle doesn’t affect all kinds of investigations, though. Radar and thermal-infrared observations, and measurements of the attenuation or reflection of GPS signals, for example, are all insensitive to it. Some visiblelight instruments on Iridium satellites could work perfectly well, too, such as those designed for tracking clouds as a means to measure winds.

However its hosting services are used, Iridium will not be providing them free of charge. Rather, it’ll be selling the space on its satellites, most likely to government customers. The U.S. National Oceanic and Atmospheric Administration has shown interest in that possibility, as has NASA. European researchers have expressed enthusiasm, too, but the chances are slim that European funding agencies will be able to move swiftly enough to meet the Iridium launch schedule. Muller, for one, is frustrated that European governments move too slowly to take advantage. ”For me, it’s so obvious why this is a really good idea and why we should jump on it.”

This article originally appeared in print as "Room for Rent, Stellar View".

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