Saturday, September 12, 2009

Satellites flying in formation over Asia

By Peter J Brown
Satellites primarily controlled from the ground have been flying solo and in fixed formations over Asia for years. Now, a smaller and more sophisticated breed of Formation-flying SATellites (FSATs) - especially micro-FSATs, which weigh roughly 35 to 120 kilograms - are making their mark alongside even smaller nano- and pico-FSATs that weigh between 3 and 30 kilograms.Intense micro-FSAT-related research is underway in China, the United States and Europe as well as in Japan and India, while concerns mount about the "dual use" dimensions of FSAT technology in general.Eric Hagt, director of the China Program at the World Security Institute in Washington, DC, is keeping a close watch on the "This is a case of complex and hard to identify dual-use technology and intent. China is certainly working on formation-flying/co-orbital maneuvering for civilian purposes - to make their satellite systems cheaper to maintain, and to make them more robust [and reliable]," said Hagt. "They fit well with accomplishing the same for defense systems as well as acquiring an ASAT [anti-satellite weapons] option. It is the wave of the future."

China's work on micro-FSATs surfaced in the late 1990s with, among other things, the China Brazil Earth Resources Satellite (CBERS) project, and the CBERS spaceflight software that was produced in the process. Although software enhancements for possible cluster formations at an unspecified date were discussed, the primary concern was maintaining mission integrity.Today, leading Chinese FSAT research teams are based at the Chinese National Space Administration's Center for Space Science and Applied Research (CNSA/CSSAR), and DFH Satellite Co Ltd (DFHsat), which is part of the Chinese Academy of Space Technology in Beijing. The Chinese academy is developing a 30 kilogram nano-FSAT called Hummersat-1A with Tsinghua University and the Harbin Institute of Technology (HIT) also on the list.

In July, a new way to regain control of multiple micro-FSATs was presented by a team of researchers from HIT at the International Symposium on Space Technology and Science in Tsukuba, Japan. Achieving a rapid and smooth reconfiguration of any formation in space using autonomous command and control capabilities is essential to successfully sustaining space operations in the event that one or more satellites within the formation fail completely or are unable to function properly. At Beihang University's School of Automation Science and Electrical Engineering, a project has also been underway to explore new switched control systems for micro-FSATs. Additional work in China on micro-FSATs is underway at the Shanghai Academy of Spaceflight Technology, Nanjing University of Aeronautics and Astronautics, and the Chinese Academy of Science-Shanghai Satellite Engineering Center (CAS-SSEC), which was heavily involved in China's launch in late 2008 of the BanXing-1 (BX-1), a micro-FSAT which was released from the manned Shenzhou-7 spacecraft. (See China gets a jump on US in space Asia Times Online, October 25, 2008.)

Last year, Shen Xuemin, director of the CAS-SSEC, described the BX-1 mission as a small satellite technology demonstration of docking procedures and processes, and detailed in-flight inspection of cooperative adjacent spacecraft. China has yet to demonstrate a micro-FSAT maneuver involving a proximity of closer than 1 kilometer in distance because, "this requires pretty autonomous mission processing capability", according to Hagt. For the immediate future, it appears unlikely that China will engage in any close approaches and even co-orbital dockings unless they are guided by a "space-ground communication loop" augmented by Chinese data relay satellites. "There are no known experimental satellites [in China] that are on-orbit or planned that have fully autonomous command and control capabilities. That is not to say it is not being tested. The technology is certainly being discussed," said Hagt.

"All the programs so far involve close proximity using ground-controlled differential GPS [Global Positioning System] command and control, and at best, semi-autonomous control with a cooperative orbiting object as with the Hummersat-1. This is the first step in [so-called] proximity maneuvers and co-orbital approach to non-cooperative [orbiting objects]. The technology is far more difficult for the latter, but the philosophy is same." According to Hagt, China's Huangjing (HJ) series of surveillance satellites and the Shijian-9 test satellite represent tangible evidence of China's steady progress in building this specific type of satellite. "The Huangjing series [of remote sensing satellites] is a program where formation flying is discussed under the rubric of virtual detection technology. HJ-1a and b were launched in 2008 and HJ-1c is supposed to be launched this year with HJ-2, the next series, soon after," said Hagt.

Mission-critical communications must happen as micro-FSATs move through space in a single formation. Another desirable characteristic is intelligence rather than total dependence on remote or external command and control. In effect, micro-FSATs are fast becoming robots in space that constantly know what to do, where they are, and what is going on around them at all times. And they must remain aware of the other micro-FSATs in the pack as well.The micro-FSATs described here are not to be confused with navigation/global positioning satellites, and the global phone service satellites deployed by Globalstar and Iridium. These micro-FSATs operate in enormous global constellations and are more closely related to the spacecraft that make up long "caravans in space" such as the US National Aeronautics and Space Administration (NASA's) so-called "A-Train", which consists of five environmental monitoring satellites, the German "RapidEye" fleet of Earth observation satellites, and the multinational Disaster Monitoring Constellation (DMC) satellites which fly in a staggered orbit, and can scan disaster sites on a daily basis on relatively short notice.

Micro-FSATs for ballistic missile launch detection are starting to appear. In February, for example, France launched a pair of demonstration micro-FSATs known as Spirale to detect missile launches using infrared sensors, and next month, the US will do the same thing with its Space Tracking and Surveillance System (STSS) demonstration.The important role of micro-FSATs in so-called "battlespace" and "counterspace" operations is obvious. They can simply accompany larger military communications and surveillance satellites to maintain "situational awareness" because what might be looming nearby is another hostile satellite ready to attack. The US nano-FSAT project, known as Autonomous Nanosatellite Guardian for Evaluating Local Space (ANGELS), is a good example.

At the German Aerospace Center's (DLR) Institute of Space Systems (ISS) in Bremen - one of the world's major research and development centers for FSATs - among other things, researchers can simulate FSAT fleet operations. They can do this by propelling air-cushion vehicles over a so-called "dynamics simulator" at ISS consisting of a pair of finely polished granite surfaces weighing roughly 16 tons. In 2009, the 500 kilogram-plus FSATs which make up the joint DLR-NASA Gravity Recovery and Climate Experiment (GRACE) mission - now in its eighth year of operation - brought unwelcome news about India's underground water supply. The GRACE FSATs, which identify slight variations in gravitational pull triggered by the motion of water and air, confirmed that groundwater losses in northern India amounted to over 100 cubic kilometers of water in this decade.

A joint European-Chinese project underway since late 2007 involves Tsinghua University and the Delft University of Technology in the Netherlands. The Formation for Atmospheric Science and Technology (FAST) involves a pair of micro-FSATs being built in both countries which will be launched by China in 2011. Asia Times Online contacted Jian Guo, a microsatellite engineer in the space systems engineering department at TU Delft who is involved with the FAST project, but he did not respond to questions by press time. 

As for the Indian Space Research Organization's (ISRO) plans for future micro-FSATs, one Canadian researcher indicated that it is quite possible that an ISRO launch vehicle might be used to launch an upcoming Canadian dual micro-FSAT research mission known as CanX-4&5. Otherwise, ISRO did not respond to questions.

The Japan Aerospace Exploration Agency (JAXA) reports that no concrete FSAT plans of any kind have emerged since the ETS-VII project (1997 to 2002) which involved space robotics and spacecraft docking. Still, a JAXA space science project involving five micro-FSATs known as SCOPE is in a preliminary planning stage, and also underway is JC2Sat, a joint JAXA and Canadian Space Agency (CSA) project involving 2 revolutionary nano-FSATs. By varying their cross-sectional dimensions, operators of JC2SAT can altogether bypass the need for a propulsion system - using a so-called differential drag technique instead.However, despite JAXA's comments to the contrary, during JAXA's launch last January of the Greenhouse Gases Observing Satellite or Go-Sat, a group of very small experimental missions went up on the same Japanese launch vehicle, and the majority of these experimental missions consisted of payloads that seem to support ongoing micro-FSAT-related research in Japan.

The missions in question included JAXA's 100 kilogram Small Demonstration Satellite-1, the Intelligent Space Systems Laboratory at the University of Tokyo's Pico-satellite for Remote-sensing and Innovative Space Missions, the Tokyo Metropolitan College of Industrial Technology's Kouku-Kosen-Satellite-1, and the Space Tethered Autonomous Robotic Satellite-1, a joint demonstration project of Kagawa University and Takamatsu National College of Technology which was designed to test a tethered space robot system.Besides providing great opportunities for lots of interested space engineering students to gain hands-on experience, these research missions addressed space flight trouble-shooting, micro-thrusters, attitude control using tether tension, and autonomous control systems, to name a few areas of research.

Europe is awaiting the upcoming launch of the Swedish Space Corporation-led twin PRISMA micro-FSAT program. This will be followed by ESA's twin Proba-3 micro-FSATs. PROBA stands for "PRoject for On Board Autonomy".Perhaps the most exciting and yet most challenging potential FSAT applications involve Space Solar Power System technology. Supporters see large FSATs harnessing the energy of the sun by collecting it and then beaming it down to Earth. Another unusual and provocative FSAT application is tied to the longstanding campaign to devise effective ways to deflect asteroids heading towards Earth. In the US, the Defense Advanced Research Projects Agency (DARPA) is working on a radical spin off of FSAT technology. It is rapidly pursuing its "Future, Fast, Flexible, Fractionated, Free-Flying spacecraft" project (F6). Along with DARPA's Fast Access Spacecraft Testbed (FAST) program, and DARPA's Front-end Robotic Enabling Near-term Demonstrations program which is aimed at creating an in-flight robotic refueling capability, F6 will completely transform satellites.

In 2007, at DARPA's 25th Systems and Technology Symposium in California, Dr Owen Brown, program manager in DARPA's Virtual Space Office described F6 as demonstrating that, "we can decompose a large monolithic spacecraft into a group of wirelessly linked elements, or nodes. Each node executes a specific spacecraft function. One node for example might be a computing node. Another, a payload node - like say a transponder, or an intelligence sensor." "These nodes - operating together - create a single 'virtual' spacecraft. F6 offers great flexibility. Let's say for example, you wish to upgrade a spacecraft with a new, faster computer. The solution is to fly a new module that performs 'just' that computing function into the cluster. The virtual spacecraft will then seamlessly integrate this new capability into the network," said Brown.

"By decoupling - or, fractionating - various parts of the spacecraft, we can reduce fragility, and implement new flexible design and acquisition paradigms. For instance, we can physically isolate payloads from the rest of the system. This addresses two major issues plaguing our current generation of large multi-payload space systems. If a payload is late in arriving, we have the flexibility to launch it when it is ready on its own module. Fractionation also alleviates the systems engineering nightmare that results from having multiple, structurally coupled, sensing payloads." DARPA's F6 could extend the length of satellite missions considerably, and rewrite the rulebook for the global satellite launch sector entirely given the emphasis on launching smaller, lighter-weight nodes rather than on launching complete spacecraft.

A hostile variant of F6 could surface. This would involve stealthy attack modules which would trail a potential target, and then be used to carry out extremely stealthy and lethal anti-satellite strikes, too. F6 follows on the heels of several recent micro-FSAT successes in the US including ST5, Orbital Express, Near Field Infrared Experiment, XSS-11 and the string of Tacsat experiments where more successes then failures were recorded. Recent US setbacks include the DART and Techsat21 missions. F6 is also closely tied to a relatively new US Air Force program known as Operationally Responsive Space which addresses flexible, low cost ways to rapidly configure, launch and deploy small spacecraft including micro-FSATs in a variety of scenarios.

An F6 spacecraft might seem like science fiction to some, but DARPA has already started approving F6 contracts. Keep in mind that not so long ago, FSATs and micro-FSATs in particular also seemed like they were quite exotic and a bit far-fetched. The striking success of scientific missions like GRACE in this decade is remarkable, and it underscores the fact that there is no turning back. As micro-FSATs multiply over Asia, one can only hope for the best. 

Peter J Brown is a satellite journalist from the state of Maine, USA.


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