Getting on Track:
The Department of Defense is racing to build a constellation of satellites for tracking elusive hypersonic missiles. As these first satellites enter orbit, how should policymakers measure success? In a new report, CSIS unpacks the tradeoffs involved and pitfalls to avoid.
The conflict in Ukraine has made it clear that missiles “are foundational to adversaries’ way of war.” Future missile threats, however, increasingly stress existing missile defenses, flying lower, faster, and on unpredictable trajectories. Most importantly, they are difficult to detect—defeating them will require elevated sensors, on aircraft or satellites, to track them at range. As the Department of Defense begins to deploy a space-based sensor constellation, Getting on Track unpacks the design tradeoffs involved and key pitfalls to avoid. Using advanced simulation tools, the authors underscore the necessity of diversifying satellite orbits, designing constellations for early, persistent coverage, and retaining requirements for fire-control-capable sensors.
This report is made possible with support from General Atomics, L3Harris, Leidos, Lockheed Martin, and general support to CSIS.
Called “Getting on Track: Space and Airborne Sensors for Hypersonic Missile Defense” and authored by CSIS Fellow Masao Dahlgren, the study is designed to help policy-makers understand the tradeoffs that need to be weighed as technical and schedule decisions about missile warning/tracking sensor networks are being made.
The report, which provides in-depth models of different architecture options, “elaborates these tradeoffs, identifies principles to inform future architectures, and highlights temptations to avoid,” CSIS says in its introduction.
Dahlgren told Breaking Defense in an interview that the report identifies three major requirements for sensors as part of a an effective anti-hypersonic defense network: a diverse architecture, with satellites in multiple orbits and consideration given to new airborne sensors; fire-control capability matched to interceptors across the services; and the rapid ramping up of “persistent” coverage of the Pacific theater to keep eyes on China’s evolving missile capabilities.
“We’re not going to prescribe any architectures, but we identify places that require more attention,” he said.
Report: Multi-orbit sensing architectures optimal for hypersonic missile defense
In the near term, the study suggests prioritizing coverage in the Indo-Pacific as quickly as possible. Constellations in MEO might be better suited to cover these mid-latitude regions, while satellites situated in LEO would offer persistent coverage of higher latitudes and the polar region, according to the report.
An airborne underlay of sensors could also provide immediate coverage to the Indo-Pacific, it notes.
“For nearer-term coverage, especially for the lower latitudes relevant to the Indo-Pacific and other theaters, policymakers should be attentive to the pacing of sensor fielding, not only the final product—graceful deployment as well as graceful degradation,” the report says.
Getting on Track:
This report is made possible with support from General Atomics, L3Harris, Leidos, Lockheed Martin, and general support to CSIS.
Key Findings (Insightful)
- The deployment phasing of a sensor architecture is as critical as its final delivery date. Choices over orbital configurations not only affect final sensor coverage but how coverage develops over time. Sensor constellations optimized purely for coverage efficiencies do not necessarily generate persistent coverage until most elements are deployed. For nearer-term coverage, especially for the lower latitudes relevant to the Indo-Pacific and other theaters, policymakers should be attentive to the pacing of sensor fielding, not only the final product—graceful deployment as well as graceful degradation.
- While a space-based sensor architecture is necessary for global missile tracking coverage, a suborbital underlay of airborne sensors could improve point or regional coverage, hedge against schedule or capability gaps of orbiting sensors, and enhance overall system-level survivability. Airborne sensors offer unique detection modalities and could support persistent, localized coverage unbounded by the predictability and rigidity of orbital mechanics.
- Sensor fusion is a major and underappreciated source of schedule risk. Delays in developing sensor fusion software and infrastructure contributed significantly to past space program cost and schedule overruns. Further steps are needed to prioritize command and control and fusion algorithm development for larger satellite constellations and multiple sensor types.
- Fire control-quality tracking must be a fundamental requirement for the emergent elevated sensing architecture. The technical requirements for fire control tracks are relative measures, contingent on the performance of other elements in the missile defense kill chain. Less stringent track data requirements would require interceptors with costlier, more capable seekers or more ability to maneuver to compensate for positional uncertainties. Conversely, more accurate sensor data would both improve the performance of existing systems and ease design requirements for future interceptors.
Key Findings (obvious)
- A new, elevated sensor architecture is required to detect, identify, and track a spectrum of maneuvering missile threats with sufficient quality to support missile defense fire control. These threats combine high speeds, unpredictable, non-ballistic trajectories, and large raid sizes to stress legacy defense designs.▪
- The
future of missile defense and missile defeat will be contingent on the
development, characteristics, and fielding timeline of this
architecture. One cannot defend against what one cannot see. [This Mine
warfare is designed to counter the unseen enemy]
- There is no such thing as a perfect sensor architecture design. Designing an elevated sensor architecture is rather an exercise in tradeoffs. Given this multiplicity of trades, architecture design is as much an art as a science. The application of this art to specific designs reflects various institutional and policy assumptions.
- Unpacking these tradeoffs and assumptions—making them explicit—can help policymakers, budgeteers, and system architects, and better inform the public discussion related to missile tracking and missile defense. Doing so is the purpose of this report. This report does not advocate a particular architecture, but instead elaborates these tradeoffs, identifies principles to inform future architectures, and highlights temptations to avoid.
- No single orbit or domain represents an optimal approach for missile defense sensing. Low (LEO), medium (MEO), geosynchronous (GEO), and highly elliptical orbits (HEO) each contribute varied advantages for coverage, schedule, cost, and resilience.
- Proliferating space sensors in LEO is one way to improve resilience, assuming large numbers and low-cost replacement. It is not the only way. Reliance on a single orbital regime, or on any single approach to resilience, invites disruption. LEO constellations can be degraded by area- or domain-wide effects, including electronic attack, nuclear or radiological means, and the intentional generation of debris.
- The Department of Defense’s recently updated plan to deploy a mixed-orbit missile tracking constellation is thus a welcome step for enhancing resilience. Sensor architectures should complicate adversary targeting by leveraging the unique benefits and drawbacks of multiple orbits and domains.
- Infrared sensor performance is a function of the target’s signature and the sensor’s resolution, sensitivity, and field of view. Both wide- and medium-field-of-view sensors share promise for fire control-quality tracking. In recent years, Congress has prudently scrutinized and sustained efforts to deploy fire control sensors, including the Hypersonic and Ballistic Tracking Space Sensor (HBTSS), which is slated to transfer from the Missile Defense Agency to the Space Force around 2026. Whatever the sensor configuration and type, it is imperative that fire control efforts cross the valley of death and deploy at scale.
- Many of the technologies and programs to realize an elevated sensor architecture are in place, but a disciplined acquisition and systems engineering authority will be needed to align its many components. Policymakers must exert oversight to ensure schedule discipline, orbital and systems diversity, and continued attention to missile defense fire control requirements.
- Acquiring
this new elevated sensor architecture will be an exercise in avoiding
certain temptations. These include temptations to optimize global
coverage efficiencies at the expense of schedule and resilience, to
consolidate assets into a single orbital regime, and to abdicate fire
control requirements.
Table of Contents
1. The Elevated Sensing Imperative 1
Elevated Sensing Missions 2
Unpacking the Tradeoffs: Art and Science 5
Modeling the Problem 7
2. Sensor Tradeoffs 10
Hypersonic Weapon Signatures 12
Sensors, Field of View, and Architecture 13
Alternative Sensor Types 21
3. Orbital Tradeoffs 24
Low Earth Orbit 24
Effects of Proximity 25
Systemic Threats to Proliferated Low Earth Orbit 31
Medium Earth Orbit 34
Geosynchronous and Highly Elliptical Orbits 38
Airborne Architectures 41
Opportunism or Persistence 41
Sizing a Constellation 43
Finding the Right Mix 45
Addressing LEO Indo-Pacific Coverage 46
Selective Polar Coverage with HEO 47
Combining Layers for Resilience 49
4. Schedule Tradeoffs 52
5. An Emerging Architecture 60
Next Generation OPIR 63
Resilient Missile Warning/Missile Tracking – Low Earth Orbit (Proliferated Warfighter
Space Architecture) 65
Resilient Missile Warning/Missile Tracking – Medium Earth Orbit 71
Hypersonic and Ballistic Tracking Space Sensor 72
Seeking Alignment 73
6. Three Temptations 74
Temptation to Abdicate 74
Temptation to Overoptimize 76
Deploy Gracefully 76
An Airborne Underlay 77
Reducing Integration Risks 79
Temptation to Consolidate 83
7. Staying on Track 86
Appendix 88
Sensor-Level Analysis 88
Constellation-Level Analysis 90
About the Authors 94
Endnotes 95
The authors would like to acknowledge the many peer reviewers who were generous with their time and expertise during the course of this project, including Mark Lewis, Doug Loverro, Todd Harrison, Kari Bingen, Jason Keen, Ken Harmon, and many others who remain anonymous.
Within the CSIS Aerospace Security Project and the Missile Defense Project, Kaitlyn Johnson, Thomas G. Roberts, Shaan Shaikh, Ian Williams, Wes Rumbaugh, Seth Walton, and Marie Dean contributed to the research and production of this report.
This report is made possible with support from General Atomics, L3Harris, Leidos, and Lockheed Martin. The research team leveraged computer simulation tools, including
· SMARTSet, an air and missile defense simulation tool, by Iroquois Systems/Lockheed Martin, and
· Systems Toolkit (STK) Enterprise, by Ansys Government Initiatives (AGI).
North America Is a Region, Too: An Integrated, Phased, and Affordable Approach to Air and Missile Defense for the Homeland, July 14, 2022
A closely related recent report by some of the same authors/reviewers
Tom Karako, Matthew Strohmeyer, Ian Williams, Wes Rumbaugh and Ken Harmon
Tom Karako, Matthew Strohmeyer, Ian Williams, Wes Rumbaugh and Ken Harmon, "North America Is a Region, Too: An Integrated, Phased, and Affordable Approach to Air and Missile Defense for the Homeland," Missile Threat, Center for Strategic and International Studies, July 14, 2022, last modified August 1, 2022, https://missilethreat.csis.org/north-america-is-a-region-too-an-integrated-phased-and-affordable-approach-to-air-and-missile-defense-for-the-homeland/
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