– The Pentagon’s Defense Advanced Research Projects Agency (DARPA) has scrapped plans to demonstrate a huge radar antenna in space, and closed down the associated research program after spending $156 million, a DARPA official said.


DARPA started the Innovative Space-based Radar Antenna Technology program four-years ago in response to calls from
military commanders for technology that would help them track moving ground targets, especially missiles on trucks. They wanted continuous surveillance anywhere in the world, through clouds and with enough accuracy to fire precision weapons at targets. Calculations showed that radar antennas capable of isolating the movement of such targets against the Earth’s backdrop, with the accuracy required for targeting, would need to be about the size and shape of one face of the
, said Michael Zatman, DARPA’s ISAT program manager.


The challenge would be stowing these huge antennas inside the payload shrouds of the rockets that would be used to launch them and then deploying them on orbit. DARPA planned to test one of two competing antenna approaches in space in 2010. If all went well, the technology would have been transferred to engineers at the Air Force’s Space and
Los Angeles
, who design operational military satellites, and also to engineers at the National Reconnaissance Office outside
, who do the same for spy satellites.


DARPA decided to end the program last month because “these transition partners” – the Space and
and the National Reconnaissance Office – “were not ready … to move into fielding this technology,” Zatman said.


Zatman said the decision was not a reflection on the performance of the antenna technologies in ground testing, nor a sign that the Air Force and intelligence communities are losing interest in large antennas. “Having larger and larger antennas in space will not only improve radar performance but for example enhance communications system performance. So it’s definitely a technology they’re interested in. They’re just not quite ready to pick it up at this time,” Zatman added.


DARPA funded the initial research on its own, but then turned to SMC and NRO for funds for the demonstration. They said no. “With no transition partner willing to co-fund an on-orbit experiment, we were unable to continue with the on-orbit demonstration as planned,” DARPA spokeswoman Jan Walker said in an e-mail Jan. 19.


Zatman said the ISAT technology was always envisioned as a longer-term successor to the Space Radar constellation, a U.S. Air Force program now in the early research phase. The Air Force announced Dec. 18 that it had awarded separate $50 million study contracts to Northrop Grumman and Lockheed Martin for work on Space Radar concepts. As currently envisioned, the Space Radar satellites would provide finely detailed imagery, but something short of continuous tracking. It also would not have the tracking accuracy for global targeting of weapons, Zatman said.


The ISAT effort was born from the Air Force’s post-Sept. 11 Global Strike initiative which called for the ability to destroy weapons of mass destruction anywhere on the globe on short notice.


Mobile ground targets posed a special challenge. Trucks loaded with missiles might roam deep within a nation’s borders and beyond the field of view of the U.S. Joint Surveillance Target Attack Radar System (JSTARS), a Boeing 700 jet equipped with a radar.


Experts at the Air Force Research Laboratory in
, and the Mitre Corp. in
, explored the idea of building something like JSTARS in space, Zatman said. They looked at a notional constellation of radar satellites placed in medium Earth orbits instead of low Earth orbit to minimize the number of spacecraft required for global coverage, a la the Global Positioning System satellites. Calculations showed that the radar antennas would need to be 300 meters long and up to 10 meters wide.


“The technology was not ready to do that, which is why DARPA ran the ISAT program,” Zatman said.


Contractors explored two competing antenna concepts for packing the antennas for launch and deploying them in orbit.


Boeing and its subcontractor, Raytheon of El Segundo, Calif., proposed warming a flexible antenna material and folding it up inside the rocket, then inflating it in the cold of space which would cause the structure to turn rigid.


Lockheed Martin and its subcontractor, Harris Corp., of
, proposed unfolding the antenna mechanically.


“Both of these teams did ground demonstrations where they deployed multiple, repeating modules of these antennas on the ground,” Zatman said.


The stowing and deployment concepts showed promise but there was another test that needed to be done. Large antennas would inevitably arc or bend slightly in orbit as they were turned, or slewed to look at targets, and as they crossed in and out of the Earth’s shadow. The contractors installed sections of their antennas inside experimental chambers to show they could measure distortions and electronically compensate for them to keep the radar beams focused.


“Technically, the ISAT program has been a tremendous success and we’ve learned an awful lot from the contractors and from the work that the government’s done itself in terms of what you need in order to make this system work, what the technology issues are, and what the best path forward in terms of going further with this,” Zatman said.


DARPA officials plan to draft a report, parts of which will be classified, to summarize the technical approaches and the lessons learned should military officials decide to renew their interest in the technology. That report will be completed by August or September, Zatman said.