IV. A TAXONOMY FOR LASERS IN SPACE

This section develops a taxonomy for space-based laser systems that is connected with the warfighter’s terminology. A number of recently conducted strategic studies, which highlighted various laser applications, are summarized so that the relevant space-based laser concepts can be organized with the taxonomy.

Subsequent sections will explore the concepts in more depth, and provide relative scores for each concept based on its technical merit and operational value. The technical assessment considers both feasibility and maturity. The operational appraisal considers the operational enhancement and the cost, which includes funding, operations and maintenance support, and personnel. The most feasible near-term concepts will be developed further in order to accelerate the process of putting the technology into the hands of the operational commands. This process uses a variety of paths, such as Advanced Technology Demonstrations, Advanced Concept Technology Demonstrations, the new Battlelabs which are chartered to provide operational MAJCOMs with innovative ideas, and other informal avenues.
 

A Taxonomy of Concepts

A functional taxonomy is more useful for technologists who map various laser concepts onto operational applications than other possible taxonomies that are based on laser parameters. Letting ‘form fit function’ gives technologists the greatest flexibility in finding a variety of lasers to implement the concepts, and it also keeps the operators from getting bogged down in technical details. Space-based laser concepts will be grouped into four classes: enabling systems, information-gathering systems, information-relaying systems, and energy-delivery systems. The discussion below elaborates on each class, and numerous examples of concepts within each class will be discussed in subsequent sections.

Enabling Systems.

The effectiveness of some current weapon systems can be enhanced substantially by specific applications of lasers, thus suggesting the term “enabling systems” for this class of concepts. A further breakdown of this area could include three sub-classes of systems, including those that: provide an optical signal for guidance of other systems, provide illumination for other optical sensing systems, and provide information that would normally be provided by non-laser systems. Laser target designators are an example of the first sub-class that uses laser radiation to enhance the accuracy of conventional munitions. An example of the second sub-class would be the illumination of a target area with laser radiation from a carbon dioxide (CO²) laser for improved imaging with forward looking infrared (FLIR) systems.

Laser altimeters and laser velocimeters fall into the third sub-class. However, lasers that are used solely as internal components in a system and do not emit the laser beam outside of the unit, such as ring laser gyroscopes for inertial reference units, will not be included in this study, although they offer substantial improvement in capability. The enhancement of the laser systems that fall into the “enabling” class reflects the incremental improvement that is provided to weapon systems.

Information-Gathering Systems.

Optical sensing systems gather information through the collection of optical energy. This energy may be emitted by the source, as in the case of an aircraft engine’s infrared emission, or may be scattered off or reflected from the source, as occurs when a photograph is taken of a target site for battle damage assessment (BDA) after it is attacked. Currently, such optical systems are passive systems that do not emit any radiation in order to make their measurements. Examples include reconnaissance satellites, infrared missile tracking sensors, and weather satellites. In many cases, active illumination with a laser source can improve the information gathered or provide new information that could not be obtained without the laser radiation.

The class of “information gathering systems” can be further broken into two sub-classes: those that use active illumination to image the target with optical systems on the same platform, and those that use the laser as a probe to gather ‘non-image’ information. The first sub-class is exemplified by the AF’s Starfire Optical Range at Kirtland AFB in New Mexico in which a laser beam illuminates space objects and uses the scattered radiation collected at the same site to form an image.³⁶ An example of this second sub-class is remote sensing using differential absorption laser radar (DIAL) technology to measure effluents from targets that were just bombed or that is engaged in manufacturing questionable substances.

Information-Relaying Systems.

Communication and data-relay systems abound in the space environment, including both military and commercial satellites that relay data, voice, television, and other information across the globe. All of the current systems use microwave frequency transmissions that propagate fairly well through the atmosphere, although both clouds and the ionosphere can interfere with these frequencies. Two attributes of microwave frequencies are important when compared with optical frequencies. First, the amount of information that can potentially be carried on a given frequency (called the carrier) depends on that frequency, so that the higher the carrier frequency, the more information that can be potentially transmitted. Of course, suitable modulation schemes need developing to take advantage of this information bandwidth.

Thus, laser communication systems have inherently far greater information capacity than microwave systems. The second attribute is the spreading of the beam. As discussed more fully in Appendix A, the physical phenomenon of diffraction causes all EM radiation to spread out whose spreading is inversely proportional to the frequency.³⁷ Thus, for a given beam diameter or antenna size, a microwave beam will spread out much faster than a laser beam, due to the factor of 104 to 105 increase in frequency. Thus, laser communication systems can more efficiently put the signal on the receiver and require less output energy.

In order to transmit information, the space-based laser concepts in the information-relaying class must include some method of temporally varying (or modulating) some output characteristic of the beam. Pulsing the output power exploits the well-developed digital communication technology which uses semiconductor lasers to send information through fiber optic networks. However, other modulation schemes that vary the polarization, phase, and wavelength all offer unique advantages.

Energy-Delivery Systems.

There are some cases in which the only requirement is delivering energy to the target using either a CW or pulsed laser beam. High-energy laser weapons destroy or degrade the target by causing structural damage or blinding sensors. Power beaming recharges a satellite’s batteries or delivers energy to a remote location on the earth. Using high-energy pulses, a laser system could also generate thrust on a distant spacecraft by blowing off an ablative material on the base of a spacecraft, which provides an alternative to chemical rockets for spacecraft propulsion.

Figure 1 summarizes this taxonomy and further refines these four functional categories into possible sub-classes. Some representative concepts are provided for the purposes of illustrating the taxonomy.
 

Figure 1. A Functional Taxonomy for Lasers in Space
Mapping Space-Based Lasers onto Operational Taxonomy
 

One of the most important goals of this study is to show how space-based laser systems can enhance the ability to accomplish various military missions. As we consider specific concepts, it is useful to discuss how these systems relate to the taxonomy used by the Air Force.

The Air Force recently identified six core competencies as it moves beyond the Global Reach-Global Power concept to the new strategic vision of Global Engagement. A “core competency” is the “combination of professional knowledge, specific air power expertise, and technological capabilities that produce superior military outcomes.”³⁸ The core competencies provide one means for expressing the Air Force’s “unique form of military power” and “understanding how the various aspects fit together.”³⁹

The six core competencies are:

• air and space superiority

• global attack

• rapid global mobility

• precision engagement

• information superiority

• agile combat support

The first core competency integrates air and space in order to control the entire expanse from ground to outer space, and thus give “freedom from attack and freedom to attack.”⁴⁰ The ability to designate targets from space platforms, provide high capacity information channels to operators in theater, and, in the long term, directly negate targets on or near the surface of the earth means that space-based lasers have the potential to support this core competency. Other concepts, such as space-based lasers for BDA, that also support achieving air and space superiority will be discussed later.

The concept of global attack involves the ability to rapidly deploy expeditionary forces to a theater of operations where the United States may not have existing bases. Space-based laser systems can improve the knowledge of the theater by directly measuring winds and improve low-light navigation by battlefield illumination with infrared laser radiation, to highlight just two possible roles. Not only does the pervasiveness of space systems translate into global coverage, but the high speed of orbiting systems could be exploited to put laser systems over the area of operations very rapidly, both for weapons and support applications.

Rapid global mobility is essential for all military operations as the United States retains a growing portion of its forces within the US. Missions such as peacekeeping and humanitarian support will likely increase, given that combat operations could always occur. Space-based laser communication systems can provide secure, high capacity connection with command and control facilities in CONUS, while battlefield illumination from space can aid the initial insertion of forces into an undeveloped region, as discussed later in this study.

The ability to achieve precision engagement as a proven core competency has relied largely on laser systems to designate targets from the air or ground. Advances in space systems coupled with improvements in laser technology will give the capability of designating targets, including mobile ones, from space. It is conceivable that laser-guided weapons could be launched from beyond visual range of the target and guided to targets using space-based laser designators in real time. This improved stand-off capability reduces the risk to US forces and increases the vulnerability of the adversary. As a support system, the high capacity laser communication system could relay massive amounts of information to the next generation combat aircraft (which may be uninhabited) to give the pilot or the aircraft the very latest information on the target, the weather, and military threats.

Military operations demand secure, relevant, and timely information. For this reason, information superiority on the battlefield is one of the first objectives. Laser communication systems have the potential of being more jam-resistant given the narrow beam and the optical frequencies. The narrow beam also makes these systems less likely to be intercepted by the adversary. A number of other concepts using space-based laser systems could improve offensive and defensive information warfare activities.

Finally, the core competency of agile combat support makes forces more responsive while leaving a smaller “support footprint” in theater. The support includes logistics, airbase security, civil engineering, and other administrative and medical functions. This core competency probably has the least direct connection to space-based laser systems than the others, but there is a role nonetheless.

In addition to the potential for high-capacity communication systems that use space-based lasers, one possible concept is to use space-based laser illumination aimed at corner cube reflectors mounted on terrestrial vehicles as an “identification-friend-or-foe” (IFF) system to reduce the risk of fratricide and improve the detection of infiltrators into the airbase area. By vibrating the corner cubes in a coded pattern that can be varied daily, this IFF system could be made more secure.

To summarize, the four functional classes of laser systems connect to the six core competencies, as shown in Figure 2. The information-relaying systems apply to all the core competencies given the increasingly central role of information in military operations. Enabling systems may have the next widest applicability, while space-based target designation will affect the first, second, and fourth core competencies, and battlefield illumination will aid the third and sixth core competencies, as discussed above. Information-gathering and energy-delivery systems appear, at first cut, to be somewhat more narrowly applicable, but these systems are likely to provide unique capabilities such as improved weather monitoring, remote BDA, and negation of counterforce targets. Clearly, lasers in space are relevant to achieving the AF mission.
 

Figure 2. Mapping Laser Taxonomy to AF Core Competencies
 

In the current doctrine of the Air Force, the four roles are aerospace control, force application, force enhancement, and force support.⁴¹ Aerospace control encompasses those operations that are intended to “control the combat environment”, while force application roles “apply combat power”, force enhancement roles “multiply combat effectiveness” and force support activities “sustain forces”.⁴²

In each role, there are various missions, many of which relate to space operations. There is no unique approach to map the missions to the roles. For example, a bombing mission that destroys an enemy air defense site falls into both “force application” and “aerospace control” roles. Table 2 lists the roles, possible space missions, and the relevant core competencies. Further, the Space Handbook gives a detailed discussion of many of these space missions as related to these roles.⁴³
 

Table 2. Roles and Missions for Space Power
 

As the various concepts for lasers in space are developed later in this report, they will be connected back to these roles and missions to help those who advocate space-based laser systems from either the technological or operational perspective. For example, active imaging of space objects from space platforms aids space control through the space surveillance mission. Laser propulsion systems could aid the spacelift mission in transferring payloads from LEO to GEO.

It is clear that laser communication systems and space-based laser weapons aid the force enhancement and force application roles, respectively. The reason for putting the technical concepts into the proper roles and missions is to bridge the gap between the technological and operational worlds.

The taxonomy developed here for space-based laser systems emphasizes the functional aspects of these systems, which helps relate the concepts to operational roles and missions as well as compare the concepts to existing systems and other non-laser alternatives. This taxonomy will be used in the following sections to discuss specific concepts for lasers in space.

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V. PAST STRATEGIC PLANNING STUDIES

In recent years, a number of long range studies conducted by the Air Force are directly relevant to the use of lasers in space. The reason for looking ahead is that laser technology is maturing and access to space is increasingly easy. At the same time, the end of the Cold War provides the opportunity for the senior leadership of the Air Force to search for the proper vision and strategy for the 21st century. In this section, various concepts for “lasers in space” are extracted from the more relevant strategic studies. It should be noted that some concepts that are being studied by NASA and the commercial sector are included in a final compilation of the concepts.

There undoubtedly are other planning documents, such as Mission Area Plans at AF Space Command, that contain concepts for using lasers in space. These strategic studies describe a reasonable number of concepts of space-based laser systems that fit in the four classes described earlier, and identify several high-payoff concepts with near-term technology demonstrations. The apparent consensus in these strategic studies is that the major concepts are known, but it is likely that some specific applications have been missed.
 

Laser Mission Study

Beginning at the end of 1991 and ending in October, 1992, a comprehensive study of laser applications to military missions, called the Laser Mission Study (LMS), was conducted at the direction of Major General Robert R. Rankine and under the leadership of Lieutenant General Bruce K. Brown (USAF, then retired). The basic objective of the study was to “find applications that the operators could support.”⁴⁴ A number of laser application studies were conducted in the past, but this more comprehensive study considered a wider variety of missions.

There have been numerous technological advances, including the maturing of semiconductor lasers, the development of adaptive optics, and the integration of various technologies necessary for laser-based remote sensing. The Laser Mission Study objectives were:

• Unite users and technology developers in search for militarily useful laser applications, some as yet undiscovered, by (1) exposing users to laser technology and technologists to user missions and (2) identifying technology shortfalls or mission capability enhancements, considering the potential of laser technology

• Gain user understanding of, and support for, laser technology development

• Present game plan (methodology) for early injection of study results into S&T investment process⁴⁵

More than 100 people from all four military services as well as other government agencies participated, including a specific “space panel” comprised of over 14 members from AF Space Command, Phillips Laboratory, program offices and support contractors. Of the 94 applications identified in the overall study, 22 made the final cut as concepts of high value to the operational community. Seven of these relate directly to space:

• Illuminator/Imager for Space Surveillance

• Ground-Based Laser ASAT Weapon

• Laser Satellite Communications/Mission Data Relay

• Weather Monitoring and Characterization

• Remote Earth Sensing and Characterization

• Space Debris Cataloging

• Space Track Accuracy Improvement⁴⁶

Each of these seven concepts is discussed in some detail in the LMS, including a technical description, an operational concept, key enabling technologies, and technical challenges. These discussions are particularly useful for evaluating the concepts in terms of technical feasibility and operational enhancement. The LMS also includes a brief analysis of space-based active sensing for weather monitoring and remote sensing.

Additional concepts were identified by the space panel as “worth keeping in the database” and are included in the final compilation at the end of this section. However, the Laser Mission Study did not elaborate on these concepts because either the mission was of low interest to the operational users or the technology was not sufficiently mature. But most of the titles of the concepts are sufficiently descriptive to permit a first-order discussion.
 

New World Vistas

During the summer of 1995, the Air Force Scientific Advisory Board (SAB) was tasked by the Secretary of the Air Force and the Chief of Staff to “identify those technologies that will guarantee the air and space superiority of the United States in the 21st century.”⁴⁷ The SAB undertook an intensive study that resulted in a 15 volume report called New World Vistas (NWV) that covers a wide range of technologies, including a host of concepts for lasers in space. (The NWV report consists of 14 unclassified volumes and one classified volume, including an ancillary volume of interviews and speeches related to NWV. All of the information discussed in this report related to NWV came from the unclassified volumes.)

The SAB study team was composed of many leaders in the R&D area who collected information from AF laboratories, Department of Energy laboratories, operational AF organizations, and industry. While some of the ideas contained in NWV are evolutionary, some have revolutionary implications, there is a blend of technical and operational perspectives. And NWV is broader than the LMS given the greater breadth of the charter and the diversity of its participants.

Throughout the NWV report, lasers in space appear as concepts that will be of great value to the Air Force in the 21st century. The table at the end of this section consolidates these concepts. The NWV report discusses a number of weapons and non-weapons concepts for lasers in space, although the technical depth of the discussion varies from brief comments to extensive descriptions of systems. Not surprisingly, there is considerable overlap in the concepts between the LMS and NWV. Nevertheless, these two studies represent the best technical assessment of the strategic studies that include space-based laser concepts.

The Air Force scientific and technical community has taken the recommendations of the SAB as stated in the New World Vistas quite seriously. The senior leadership not only has redirected budgetary resources, but also is reorganizing the R&D laboratories into one AF research laboratory that will not report through the Product Centers as the four current laboratories do.⁴⁸ Anyone interested in understanding where the AF will be heading in the early 21st century is well advised to consider the NWV report in great detail. The weapon systems of tomorrow’s air and space forces will emerge from the technologies that are examined in NWV.
 

Spacecast 2020

One strength of in-residence officer professional military education (PME) is giving a select group of officers the opportunity to focus their intellect and expertise on academic topics of interest to the Air Force, and to do so without the normal daily distractions. Thus, the Chief of Staff has used Air University (AU) on two recent occasions to study the effects of emerging technology on the future operational capabilities of the AF. The participants were primarily the students of Air War College (AWC) and Air Command and Staff College (ACSC), with oversight and contributions from the faculty. These studies typically have greater operational depth and less technical strength as compared to NWV and LMS. Though not intended as criticism, this distinction serves as a highly useful balance to the other reports. Since many AWC and ACSC students have operational experience, including combat in various recent engagements, they focus on what really works and what will be useful.

The first study, Spacecast 2020, resulted from a tasking from the AF Chief of Staff to “identify capabilities for the period of 2020 and beyond and the technologies to enable them”⁴⁹ that equate with US space superiority. The study uses an “alternate futures” approach to help the participants develop new concepts. Those concepts scored by an operational analysis and the highest scoring concepts were developed in a series of white papers. Scattered throughout the report are various concepts that involve lasers in space.

While there is some overlap with the LMS and NWV concepts, the participants were less constrained by preconceived notions of technology and hence identified some concepts that stretch the limits of technology. For example, Spacecast 2020 includes holographic projection from space, planetary defense weapons, and weather modification systems that would involve lasers in space in ways or at power levels that stagger the imagination. The table at the end of the section consolidates more important concepts for space-based lasers from Spacecast 2020.
 

Air Force 2025

The second AU contribution to strategic studies is the recently completed Air Force 2025 study, which was directed by the AF Chief of Staff. The study was designed to be the capstone of a series of long-range studies that had been directed by the CSAF, including NWV and Spacecast 2020. The objective of AF2025 was to address the question: “What capabilities should the USAF have in 2025 to help defend the nation?”⁵⁰ The study examined both technical ideas and operational concepts, soliciting worldwide input through the World Wide Web. The final product consists of 3,300 pages in ten volumes with 40 white papers that address a wide range of topics by focusing on innovative ideas rather than defining new roles and missions.

This study was undertaken just as New World Vistas was being completed. This timing allowed the AF2025 participants (as with Spacecast 2020, composed of AWC and ACSC students and faculty) to interact with the NWV team. That overlap, however, meant that the AF2025 study did not benefit from a careful consideration of the ideas in NWV. The primary value of AF2025 is the operational perspective brought by the officers in the study, even though a significant amount of technical detail is contained in some of the white papers.⁵¹

A number of concepts were generated, both internally and externally, and operations analyses were used to rank those concepts in terms of the competitive edge offered in alternative scenarios. The best concepts were more fully developed into white papers. As with Spacecast 2020, the number of space-based laser concepts included in the study included varying amounts of technical detail. Most of the laser concepts involved high-energy laser weapons rather than the other three classes of laser systems. The laser concepts examined in AF2025 are included at the end of the section.
 

NASA and Commercial Applications

The value of using lasers in space has been clear to the non-military users. The National Aeronautics and Space Administration (NASA) recently orbited a laser-based remote sensing experiment called LITE (that is described in more detail later). Both NASA and the commercial sector are interested in laser satellite communications for very-high data rates. Further, NASA is exploring the use of lasers for improved instrumentation onboard spacecraft, such as a deep space altimeter that uses laser pulses for accurate ranging off distant objects.

The International Society for Optical Engineering 1993 conference on “Space Guidance, Control and Tracking” examined technologies to improve spacecraft performance through enhanced attitude control.⁵² For example, one of the concepts explored using a charged-coupled-device (CCD) detector to improve spatial acquisition and tracking for laser satellite communications. The interest of NASA and the commercial sector in technologies that enable space-based applications helps the military to be “smart buyers” in some of these technologies and to focus on areas that are militarily unique.

It is critical that DOD collaborate with NASA, the Department of Energy, and commercial companies in order to get the optimal use of dwindling R&D resources in the development of space-based laser applications. Although this type of cooperation is time-consuming and difficult, the payoffs should include improved interoperability, more rapid fielding of experiments, and improved understanding through data sharing. While all of the participants will benefit, the Air Force is best positioned to take the leadership through AF Space Command and the Phillips Laboratory.
 

Summary of Concepts from Strategic Studies

A variety of concepts discussed in the strategic studies use lasers positioned in space to accomplish various missions. In several concepts, the laser may be based on the ground and the beam sent to the intended target, possibly with the use of relay mirrors. The ground-based laser (GBL) ASAT weapon and power beaming from earth to space are examples of such concepts; these are also included in the table below for completeness because the beams transit the space environment. Table 3 is a compilation of the concepts grouped into the taxonomy described above. Additional concepts from other sources are included in the table to provide a comprehensive summary.

In the next section, a semi-quantitative scoring scheme is developed and then applied to the concepts listed in Table 3. In subsequent sections, a brief synopsis of each concept is presented as part of this scoring. The discussion briefly identifies the operational concept, operational enhancement, key enabling technologies, and primary challenges. (It is impossible in this report, due both to space limitations and the author’s expertise, to cover all the concepts in depth.) Subsequent sections will focus on a few of the concepts that have the greatest near-term potential and discuss ways to bring these concepts to fruition. The plethora of concepts and the emphasis given to space-based laser applications in the strategic studies strengthens the drive to put this technology into the operational community.
 

Table 3. Summary of Concepts from Strategic Studies
 

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VI. CRITERIA FOR EVALUATING THE CONCEPTS

A simple set of criteria that covers both technical and operational perspectives is used to rank the twenty-eight concepts identified in the previous section. Although somewhat qualitative, the assessment moves the discussion from purely descriptive reviews of concepts to critical evaluations of concepts that are most likely to strengthen operational capabilities in the near term. A five-point scoring system is used to evaluate proposals during a source selection and permit a semi-quantitative ranking of concepts.
 

Technical Criteria

Feasibility

This criterion measures whether the concept is theoretically possible by assessing the potential of the concept rather than its implementation. In some cases, the path to fielding a system is relatively straightforward even if the process has not proceeded very far, while in other cases, despite years of intensive study, significant challenges remain. In still other cases, the basic laws of physics may limit the likelihood that the concept will ever achieve fruition.

The following five-point scale measures the technical feasibility of the concept:

1- concept unlikely to succeed, due to current understanding of basic laws of nature
2- multiple new breakthroughs required to make concept work
3- only a few major technical challenges or breakthroughs remain
4- no major breakthroughs required; multiple engineering issues remain
5- only minor technical issues remain to be resolved

Maturity

Technical maturity measures how far the concept has moved toward realization. The score assesses demonstrated progress in the process of developing the maturing of a concept, using the following five-point scale:

1- nothing has been demonstrated to support this concept
2- multiple major components remain to be demonstrated or developed
3- a few major components remain to be demonstrated or developed
4- major components exist but multiple, minor components remain to be developed
5- components exist; a complete system may have been demonstrated

Operational Criteria
Assuming that the concept would meet its technical objectives, the operational questions are whether the concept would substantially enhance operational capabilities, and whether the “cost” of the concept would prohibit the development or purchase of other military systems. The idea of enhancement and cost are distinct but related. A concept may be expensive in terms of funds and manpower but worth the investment if it adds unique capability. Although not addressed in detail here, there are alternative methods of achieving the same mission, many of which influence the assessment of new concepts.

Enhancement

This measurement qualitatively assesses how much the deployment of the proposed system would aid operational capabilities. In some cases, it adds a new way of operating that already exists, and thus provides an incremental improvement in capability. In other cases, the capability offered by a concept revolutionizes the operational capabilities, and thereby permits radical changes in the conduct of military operations. The following five-point scale assesses the enhancement of the various concepts:

1- limited enhancement; military requirement adequately met by existing systems
2- minimal improvement in military capability
3- some significant improvement, permitting increased flexibility or responsiveness
4- substantial new capability or greatly enhancing existing capability
5- revolutionary capability, giving decisive military edge to warfighter

Cost

Here, “cost” is meant to estimate the required funds and manpower in the current resource-constrained environment where procuring system A may mean system B will not be procured or modernized. These alternative costs are inherently subjective, because they are based on a prediction of which system delivers the most “bang for the buck.” The following five-point scale measures the cost of the particular concept of a space-based laser system:

1- extremely expensive, requiring substantial delay or canceling of other systems
2- very expensive, requiring entirely new support system and multiple platforms
3- expensive, requiring a few platforms and using existing support system
4- inexpensive, using a single platform with multiple capabilities
5- relatively inexpensive, readily adaptable to existing systems

Although careful thought underlies the application of these criteria to the concepts described in the next sections, other evaluators might give different scores based on their knowledge of technology or operational requirements. There is no “correct” answer to this evaluation, rather it is a considered assessment. If the scoring motivates others to develop their own ranking, then one of the objectives of this study will have been achieved.
 

Table 4. Scoring Criteria

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