PARIS — The European Space Agency on Feb. 18 gave final approval for a $500 million mission to measure the biomass and carbon stored in tropical forests using a satellite in low Earth orbit equipped with a novel P-band-frequency sensor that features a 12-meter-diameter deployable antenna.
The decision by ESA’s Earth Observation Program Board will permit the 21-nation ESA to issue bid requests to the two consortia, led by Airbus Defence and Space and OHB AG of Bremen, Germany, that have been working on the Biomass satellite design.
The bid solicitation will be sent out in March, with responses due by June and an expected decision on a satellite contract, valued at about 220 million euros ($275 million), in September. A launch could occur in late 2020.
The ESA board’s approval came after ESA and NASA concluded a Technical Assistance Agreement (TAA) that will allow NASA’s Jet Propulsion Laboratory to share details of the 6-meter-diameter mesh antenna on NASA’s Soil Moisture Active Passive (SMAP) satellite.
SMAP was launched Jan. 31 and the boom to support the mesh antenna was successfully deployed Feb. 18, NASA said. The antenna itself, built by Northrop Grumman Astro Aerospace of Carpenteria, California, is scheduled for deployment in the coming week.
The deployment will be closely watched by ESA as the agency will be purchasing a 12-meter-diameter mesh antenna either from Northrop Grumman or from Harris Corp. of Melbourne, Florida. The SMAP antenna system has the additional complexity of having to rotate, at 14.6 revolutions per minute, during the mission’s life.
Despite industrial attempts to win government backing, Europe has not developed large-diameter mesh antenna technology — one reason why ESA and Inmarsat of London used U.S. hardware for the Alphasat telecommunications satellite in geostationary orbit.
“I was in Washington two weeks ago for bilateral talks with NASA and it was confirmed that JPL will support us,” ESA Earth Observation Director Volker Liebig said in a Feb. 18 interview. “We have a TAA with them, so we will be able to profit from their experience with SMAP. The ground testing of an antenna like this is not trivial, so we are happy to have NASA as a partner to support us. The thermal loads on the antenna structure are completely different in low Earth orbit, with more shadow-and-sun cycles compared to geostationary orbit 36,000 kilometers in altitude.”
NASA’s own experience with mesh antennas suggests the challenge. In 1991, NASA’s Galileo probe to Jupiter failed to fully deploy its high-gain antenna. The mission was nonetheless a success.
ESA had tentatively approved the Biomass mission in May 2013, but asked that the program be paused before hardware construction began to verify that the required technologies were available and that the cost-at-completion estimate, of as much as 420 million euros, or $505 million, withstood scrutiny. The cost figure includes the satellite, its launch aboard a European Vega rocket, and operations in orbit.
“We are now very confident that the target prices will be met, which is why the board issued the green light today,” Liebig said.
The Biomass mission will use P-band frequency on its synthetic aperture radar. The frequencies, between 420 and 450 megahertz, are in use in North America, Greenland, Britain and Turkey by the United States and its allies as part of a missile warning and space-surveillance system known as the Space Object Tracking Radar network.
Wherever these radars are operating, Biomass will not work. Some Biomass supporters had feared that deployment of ground radars using these frequencies would spread beyond the current zones, compromising Biomass’ scientific harvest.
Liebig said this remains a concern, but that the consensus is that the data produced from tropical rainforests will be of such value that Biomass has retained Earth scientists’ favor despite the radar threat.
The ground radars “were explicitly taken into account in the scientific assessment” of Biomass, Liebig said.
“The conclusion was that the most uncertainties in today’s biomass models are in the tropical rainforests. For the rainforests in North America, Europe and Russia we have relatively good statistics. The goal of Biomass is to bring the modeling error for the tropical rainforests down to 20 percent. It’s around 40 percent now,” Liebig said. “This can be done even after accounting for the ground radars.”
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