The Space Reviewin association with SpaceNews

space radar illustration
Getting sufficient power to proposed Space Radar spacecraft is a minor concern compared to the bigger issues associated with this effort. (credit: Northrop Grumman)

Letter: solar power satellites and space radar

Taylor Dinerman’s article about developing solar power satellites to power space radar satellites (“Solar power satellites and space radar”, The Space Review, July 16, 2007) represents a solution in search of a problem. To date, the most detailed unclassified discussion of the technology and funding choices concerning Space Radar is a January 2007 report from the Congressional Budget Office (CBO). That report discussed the power issue for Space Radar and although it acknowledged that better solar panels are required, it stated (page 14): “The total power required for the solar arrays in CBO’s notional satellite designs should not present a technical challenge. However, those arrays are smaller and lighter than arrays with similar power output on current generation satellites.” The CBO report identified several other technologies as being greater challenges for Space Radar. These include radar bandwidth, Ground Moving Target Indicator processing, and communications bandwidth. It would be a better approach to devote attention to these existing technology challenges than to try and create new ones by pursuing beamed solar power.

It also seems odd to refer to 2010 as “long term” for any space platform. That is only two and a half years away, much less than the typical development time for even a small satellite using existing technology.

The stated goal of developing this beamed solar power technology in order to make Space Radar “more stealthy” is also puzzling. Space Radar is an active emitter. Active emitters can be made stealthy through complex and classified methods such as narrow beam actively-scanned frequency-hopping arrays (witness the F-22 Raptor’s radar). However, it is unclear if any progress has been made at doing this for the kind of radar being envisioned for Space Radar, or if that is even possible. This is presumably a significant technological challenge and eliminating the need for solar panels on the satellite may have no real effect on the satellite’s stealthiness. Stealth for radar satellites—and the systems needed to achieve it—seems to be the kind of subject best left to satellite systems engineers.

The article also states that an initial test satellite could be launched immediately and an even more sophisticated one can be launched by 2010. Considering that the modern incarnation of Space Radar was initiated about a decade ago and has yet to result in a launch, this schedule seems optimistic. It also seems odd to refer to 2010 as “long term” for any space platform. That is only two and a half years away, much less than the typical development time for even a small satellite using existing technology, not technology that has not been developed yet, like a space-based Airborne Moving Target Indicator. The rule of thumb is: large satellites with new technology take at least seven to ten years to develop (the James Webb Space Telescope will take at least 15 or more), while small satellites with current technology take three to five years to develop. NASA has stated that building even a small satellite in three years increases risk and four years is better. We apparently do not even have the less challenging Ground Moving Target Indicator technology yet, and it therefore seems prudent to walk before we skip.

Finally, it is worth noting that Space Radar has experienced significant programmatic upheaval in past years not because of a “power problem,” but because the Air Force and the intelligence community have been at odds about what it should actually do and how different requirements drive the design and the cost. In addition, the Air Force has done a poor job of explaining why such a maddeningly expensive system is necessary.

The CBO report is fascinating reading and recommended for anybody interested in the subject.