Tamper-proof GPS receivers installed in smart weapons.

Precision-guided munitions coming off the assembly line this fall will have new satellite receivers that deny access to unauthorized users. There are concerns, however, that this technology is expensive and will drive up the cost of satellite-guided weapons.

Four years ago, the Joint Chiefs of Staff mandated that all military devices relying on the Global Positioning System satellite constellation be equipped with a security chip called SAASM (selective availability anti-spoofing). The directive is scheduled to take effect on October 1. It bans military buyers from purchasing GPS receivers that are not SAASM compliant, unless they request a special waiver.

The SAASM technology was meant to ensure that receivers would not be easily compromised should they fall into enemy hands. The SAASM module replaces the existing security chips that are installed in military GPS receivers to decrypt a classified access code. Cornerstone technologies that have helped move the SAASM program forward, experts said, are advances in cryptography and the development of tamper-proof peripheries for the receiver's sensitive electronics and software.

The GPS Joint Program Office, in Los Angeles, is responsible for the implementation of the SAASM program. The National Security Agency helped the JPO set up the security architectures. Manufacturers of GPS receivers have been working on their own SAASM-compliant designs, which had to be approved both by the JPO and the NSA.

The security procedures used with current GPS receivers are based on a crypto-key architecture (black keys are unclassified, red are classified), which requires a user to have a key-code, issued by the NSA. With SAASM receivers, there will be no need for red keys, because the classification protection is embedded in the SAASM tamper-resistant coding. JPO officials predict this will simplify logistics and lower the security risks. According to one source, "the distribution of red keys is a logistical nightmare."

The SAASM module only is mandatory for new receivers. Existing systems do not have to be upgraded, unless someone chooses to do so.

Users of SPASM-based receivers can directly acquire the military P(Y) code signal from the GPS satellites. The P(Y) code has more robust anti-jamming defenses than the civilian code, which anyone can access with a commercial receiver. The SAASM, per se, doesn't provide jamming immunity. It's only a security device that enables access to the P(Y) code.

The tamper-resistant coding has been the most challenging hurdle in this program, said Larry Wells, chief technical fellow at L-3 Communications, in Anaheim, Calif. The company recently began delivering SPASM-based receivers to military customers.

Wells explained that making the receivers was not difficult, but the program nevertheless was behind by about two years, as a result of "setbacks and difficulties" in achieving a tamper-resistant coding that met the strict NSA standards.

The concept of tamper-resistant coding is simple, Wells said. The coding is applied on top of the SPASM module. If anyone tried to break through the coding to investigate the electronics inside the receiver, the system disables itself. The coding essentially aims to prevent any successful attempt to reverse engineer the design inside the module, Wells explained.

To get their designs approved, the manufacturers had to apply the tamperproof coding in ways that were acceptable to NSA.

L-3 is now supplying SPASM-based receivers to the Raytheon Co., for the Navy's extended-range guided munition (ERGM) and the Army's Excalibur round. Both are GPS-guided projectiles. The 5-inch ERGM is fired from a naval gun and the 155 mm Excalibur from a howitzer.

But even though Raytheon--the company responsible for developing both weapons--selected the L-3 receiver, it is investing corporate research dollars in its own guidance system.

David G. Martin, vice president for guided projectiles at Raytheon, said the company is funding a so-called "projectile common guidance" that eventually could be used in Excalibur, ERGM or other artillery-type munitions.

During a briefing to reporters, Martin said that Raytheon is concerned about the high prices of GPS receivers and is betting that the projectile common guidance could help lower those costs. Compared to other GPS-guidance systems, he said, it has 35 percent fewer parts and a simpler assembly process. He speculated that the Raytheon system eventually could compete against L-3 and other firms, such as Rockwell Collins.

Excalibur program manager John Halvey told National Defense that the Raytheon system is unlikely to replace L-3's in the foreseeable future. But, in the meantime, "We want to keep their feet in the fire."

Industry sources estimated that each GPS receiver for a guided projectile costs about $2,000, assuming it's a large order. For small orders--of a few hundred--prices can shoot up to $5,000 or higher. GPS guidance kits for gun projectiles are expensive, industry officials said, because they must be hardened to withstand up to 16,000 gravity forces when they are launched out of the gun tube. A single Excalibur round is expected to cost at least $15,000.

The market for munitions-based GPS receivers is expected to grow in the years ahead. Precision-guided munitions that employ GPS receivers currently or will do so in the future include missiles, rockets bombs, in addition to artillery and mortar rounds.

The military services also buy thousands of GPS receivers to embed in radios, land navigation systems or other vehicular applications. There is also a huge demand for stand-alone handheld receivers used for navigation and location purposes.

Manufacturing Changes

Most GPS-guided munitions programs today use receivers made by Rockwell Collins, in Cedar Rapids, Iowa. Last year, the company's SAASM design was approved for full-rate production, said David West, director of business development at Rockwell.

Like L-3, Rockwell experienced some "growing pains" associated with the SAASM technology, largely because these systems require new manufacturing procedures, said West.

Even though there are multiple SAASM-based receiver designs, some elements are common across all vendors, explained Dan Ellsworth, a Rockwell engineer. The JPO and NSA, for example, specified the security architecture, which is the same for all receivers.

Rockwell manufactures between 30,000 and 50,000 GPS receivers per year, many of which are used in U.S. missiles and smart bombs. The company currently has more than 37,000 SAASM-based receivers on order. That number is expected to rise, said West. "We sold more than 300,000 receivers so far. We expect the SAASM market to be at least that large over time, especially given the potential for growth in the artillery market."

Although the Defense Department does not mandate that current receivers be retrofit with the SAASM module, some U.S. Army customers are expressing interest in possibly upgrading, said West. "There are advantages to retrofitting," he said. "Users are looking at the benefits not only of going to black keys, but also the benefits of having a higher-performance GPS receiver."

The SAASM receivers are more expensive than the conventional ones, Ellsworth said. But that may change in the future. "Over time, the cost will go down as we implement more miniaturization. At some point, they will become less expensive than the receivers being made today without SAASM."

Rockwell officials predict that foreign sales of SAASM will expand, once the U.S. government authorizes more allied nations to purchase this technology. The U.K. Bowman digital radio program has a SAASM-based receiver.

"Other programs internationally have accepted the fact that they should jump on the bandwagon with SAASM, so they can avoid obsolescence and take advantage of new features," Ellsworth said.

Competing for the SAASM business as well is Trimble Corp., in Sunnyvale, Calif. The firm specializes in commercial GPS. Its military business makes up less than 4 percent of the company's GPS sales, but the firm is bullish about the Defense Department market, said Bill Walters, Trimble's business development manager.

Trimble's SAASM design was approved in 1999, he said. The company already is shipping products to undisclosed military customers and expects to increase production of SAASM receivers for applications in secure telecommunications, unmanned aircraft and munitions.

"The military has adopted a more commercial-like position on how to incorporate GPS into things that they've never done before," said John Kahle, director of marketing at Trimble. "GPS munitions get a lot of attention. But increasingly, they are using it for asset-tracking applications, embedding it into radios for individual soldiers, for situational awareness," he said. "The commercial industry has been doing that for many years.

GPS receivers, said Kahle, "used to be large and consumed a lot of power. As we build smaller and lower power requirements, the GPS can be embedded in more applications. "--Sandra I. Erwin