Dramatic changes are occurring in the Navy's roles and missions. New ships, planes, and weapons are being procured for the Chief of Naval Operations missions of sea strike, sea shield, and sea basing—delivering ordnance on target, providing a shield for forces against anti-access weapons, providing and protecting logistics, and conducting expeditionary warfare. There is great interest in using Navy ships for ballistic missile defense. A new capability can provide invaluable information for these and other Navy responsibilities: maritime continuous global awareness, made possible by moving-target radars in space.
The Promise
Space-based radar could provide a level of awareness that is hundreds of times faster, clearer, and more complete than today's intelligence, surveillance, and reconnaissance (ISR) toolbox. A group, or constellation, of radar spacecraft could sweep with very high area rates and link the data directly into the theater. The battle group commander, expeditionary warfare commander, and joint forces commander could receive an unprecedented level of battle space information. The types and quality of information provided will make the Navy/Marine Corps team dominant in a far wider variety of engagements and environments than ever before. Space-based radar can provide heretofore unavailable, even unimagined, products:
- Continuous worldwide surface contact tracking. The naval order of battle of every nation could be monitored continuously in real time, something not possible with existing sensors or combinations of sensors. No ship will move for more than a few minutes before it is looked at again. Monitoring all the world's shipping lanes would require a small fraction of constellation resources.
- Direct downlink to the battle group. U.S. forces will have a common operating picture without requiring a link to shore and without delays.
- Cueing and boost phase tracking for theater ballistic missile defense. Some ballistic missile launch sites (if not concealed by terrain or foliage) could be monitored for indications of impending launch. Warnings and partial missile tracking data could be sent instantly to theater missile defense platforms such as Aegis cruisers. Further technology development is required for post-launch missile tracking.
- Feature-aided recognition of high-interest contacts. Threat vessels, such as missile patrol boats, in crowded littorals could be detected and discriminated from fishing and commercial vessels with ease. Once identified through intelligence reports, ships carrying weapons of mass destruction, mines, or contraband would be unable to avoid being tracked continuously.
- Surface search and classification in denied or contested waters. A reliable surface picture would be available immediately to the battle group commander. No longer would he be forced to rely on intermittent searches by vulnerable maritime patrol aircraft or scarce tactical aircraft.
- Real-time targeting updates for strikes on time-critical targets. Depending on the number of satellites in the constellation, dangerous mobile land targets could be watched as strike packages are inbound, with real-time position updates being passed to the strike aircraft. This would be accomplished from the sanctuary of space without placing air-breathing platforms at risk. Targets under foliage, however, would not be detected.
- Surface picture in the vicinity of each underway U.S. Navy vessel, including submarines and special operations craft. Ships with limited or damaged sensor suites, or in radar-emissions-limited conditions for operations security, still could have the safety and security that come from a complete, accurate, timely surface contact picture provided continuously, on a global basis. Because the radar emission comes from space, not from a ship, the location of U.S. naval forces is not compromised.
The Technology
How will such information be obtained? The key is to operate radars in space in the moving-target-indication mode, a technique that proved invaluable during the Gulf War from the Air Force's E-8 Joint STARS aircraft. In the maritime environment, moving-target-indication radar will be remarkably effective. The information is very timely, because all defections are automated, and image interpretation is not required. Advances in technology mean all of the processing required to develop these data can be done on the spacecraft rather than at a shore facility. This allows track icons (rather than raw radar data) to be transmitted directly to ships in theater.
To understand the power of space-based radar, consider the maritime patrol aircraft search capability. At 10,000 feet altitude, its radar horizon extends about 100 nautical miles to either side of its track. So in one ten-hour patrol at 300 knots, the maritime patrol aircraft searches 600,000 square nautical miles. A space-based moving-target-- indication radar could search the same area in less than a minute; a constellation of ten such spacecraft could search all the world's oceans in about ten minutes. Nothing exists today that can approach this rate of surveillance.
A new space-based radar technology that would represent a significant advance in the state of the art was developed by the Discoverer II joint program office, comprised of the Defense Advanced Research Projects Agency (DARPA), the Air Force, and the National Reconnaissance Office. The radars are active, electronically scanned arrays consisting of numerous individual transmit-receive elements operating together to provide gain, clutter discrimination, and beam steering. DARPA-sponsored work led to subscale arrays that are far lighter, cheaper, and more effective than ever before. The radar technology is being perfected and capabilities enhanced by ongoing congressionally mandated research at the National Reconnaissance Office.
Perhaps the most important aspect is that awareness be continuous—if not globally, then at least in a conflict area. Under Discoverer II, it was clear that to obtain this continuity, the globe would have to be circled by a large number of satellites. Discoverer II followed the practice of some commercial satellite projects by concentrating on mass-produced, low-cost spacecraft.
The Littoral Battle Space
To obtain the promise of space-based radar technology, the U.S. Navy and Marine Corps must commit to total involvement in system requirements and concept-of-operation development, with the littoral environment in mind. The Navy will face every conceivable anti-access weapon when taking the fight into an adversary's littoral waters. There will be cruise missiles and ballistic missiles launched from shore; cruise missiles launched by missile patrol boats; torpedoes from diesel, nuclear, and air-independent-- propulsion submarines; mines; attacks by shore-based aircraft; and perhaps even suicide boats. The battle-force position will be reported by dedicated intelligence platforms (AGIs) as well as by noncombatants, such as fishing and merchant vessels. The force must deal effectively with every one of these threats.
The force entered the littoral to project power: to influence events ashore decisively, to deter conflict, or to prevail in it. This power projection can take the form of air strikes, cruise or tactical missile strikes, or extended-range naval gunfire. The promise of space-based radar is that it contributes to information dominance against a wide range of threats while supporting power projection-particularly when the information is fused with other ISR assets, such as unmanned aerial vehicles. The information from space-based radar can be downlinked directly to afloat forces in the form of track icons.
How might the warfare commanders use space-based radar information in a littoral operation?
- Battle group commander receives continuous tracking information on the hostile AGI and other surface traffic. Using an evasive maneuver, the strike is launched without alerting the adversary.
- Surface warfare commander uses feature-aided tracking to pinpoint the hostile missile patrol boat among fishing activity; launches weapons to neutralize.
- Antisubmarine warfare commander monitors in-port submarine order of battle continuously; tracks sub from the moment it gets under way; launches SH-60 to neutralize, routing it away from vessels potentially armed with shoulder-fired surface-to-air missiles. Datum error is greatly reduced by tracking the hostile sub to the dive point.
- Strike warfare commander monitors time-critical targets not concealed by terrain or foliage before and after launch of strike package; detects motion of targets; passes target positions to manned and unmanned strike aircraft.
- Mine warfare commander, using continuous surface contact picture, identifies slow-speed, loitering vessel behavior as suspicious. Synthetic aperture radar image of vessel detects presence of mines on deck; minesweeping area is greatly refined.
- Electronic warfare commander maintains restrictive emission controls. Direct downlink of information provides real-time common tactical picture to all units.
- Submarines in direct support have access to the same reliable, continuous surface picture, enhancing sub safety and facilitating attacks against hostile surface combatants.
- Expeditionary warfare obtains clear picture of the littoral battle space through moving-target indication of friendly and hostile ground forces.
Space-based radar could be an adjunct to the emerging mission of sea-based missile defense. It would allow Aegis ships to maintain restrictive emission controls, denying targeting information to hostile forces, as the spacecraft monitor ballistic missile launch sites. For launch sites in the open, launch warning would be nearly instantaneous and unaffected by weather.
The U.S. Navy historically has had a limited role and interest in space. Yet of all the services, the Navy may have the greatest interest in using a space-based radar constellation. The carrier battle group brings strike assets to the crisis early, without the need for forward basing. However, without forward basing, there will be reduced support for expeditionary warfare from Air Force assets such as Joint STARS aircraft. The space-based solution will make early, carrier-launched strikes more effective. As a multipurpose, joint system, space-based radar supports power projection as well as force protection.
The Price
Before it was terminated in 2000, the Discoverer II space-based radar demonstration project had a targeted goal of $100 million per spacecraft. Additional expenses include developing and installing the shipboard user segment and fusing its data with that from other sensors in combat management systems. One major savings would come from using existing satellite communications antennas. To this cost must be added development, the cost of launching the first flight of ten spacecraft (five Delta II launchers at $70 million each), ground infrastructure, and cost growth. This suggests that the initial cost of an objective system focused on maritime surface contact detection could be approximately $5 billion.
Developing and testing space-based radar equipment that evolved from the Discoverer II program must continue so that procurement of a full constellation can proceed with confidence. The Air Force recently began an analysis of alternatives for space-based radar. The Navy and Marine Corps must voice clearly their interest in this system if the system is to be defined to support their needs. The ten-satellite constellation could be a pathfinder to a larger constellation, providing limited data on land and ballistic missile targets in addition to an early, complete global maritime surveillance capability. An advantage of a single constellation supporting all services would be its contribution to joint operations.
Some interesting questions arise about future Navy and Marine Corps acquisitions if space-based radar is included in the force mix. Does the availability of a continuous, worldwide surface picture change the nature and number of future maritime patrol aircraft designs? Can some of the impetus for developing a space-based radar capability be found in the context of developing a sea-based national missile defense capability? Does space-based radar provide a needed balance between weapon systems for the land battle and sensor systems to find the targets? What is the optimum balance between a space-based radar system and air-breathing unmanned platforms for intelligence, surveillance, and reconnaissance?
The Future
A space-based radar system supports 8 of 12 future naval capabilities, the goals set by the Chief of Naval Operations to guide research and development. The Navy and Marine Corps must evaluate the potential of this technology and articulate their requirements. The combination of continuous worldwide awareness, direct information distribution to the theater, and affordability could enhance greatly many Navy and Marine Corps missions by enabling battlefield dominance in the challenging littoral environment, providing targeting information for influencing events ashore, and providing support for the emerging mission of sea-based ballistic missile defense.
Drs. Roesler and Steinhardt are program managers at the Defense Advanced Research Projects Agency. Dr. Roesler’s expertise is in physics and space systems. He has been an attack submarine officer and a battle group tactical action officer. Dr. Steinhardt has expertise in radar and sonar signal processing. He was chief scientist for the Discoverer II spacecraft and program manager for the Distant Thunder asymmetric warfare program.