Space

Hypersonic and Ballistic Tracking Space Sensor (HBTSS)
Missile Defense Tracking System Space Sensor Layer (SSL)

The Missile Defense Agency (MDA) continues to build components of the Missile Defense System (MDS), test its capabilities, and plan for countering evolving threats. MDA’s efforts to address hypersonic threats include the Glide Phase Interceptor (GPI) and Hypersonic and Ballistic Tracking Space Sensor (HBTSS). These efforts represent technologies that have considerable risks, but MDA has not taken necessary steps to reduce risks and ensure appropriate oversight from the Department of Defense (DOD) or stakeholder involvement.

The Hypersonic and Ballistic Tracking Space Sensor [HBTSS] program has existed in some form since 2018. In its current iteration, the program is developing an infrared sensor and algorithm that, when mounted to a satellite, will be able to detect a hypersonic weapon against the cluttered background of the surface of the earth and provide intercept-quality data to the GPI, among other systems.

In March 2018, as Breaking Defense reported, MDA Director Lt. Gen. Samuel A. Greaves outlined the central challenge of defeating hypersonic weapons. “If you can’t see it, you can’t shoot it,” he told the source. Recognizing that we can’t build enough ground-based radars to detect and track high-speed, low-flying threats soon enough to intercept them, Greaves argued that tracking the threats from space would make more sense. This is why MDA has been conducting a competition to design and build such a network of sensors, known as the Hypersonic and Ballistic Tracking Space Sensor (HBTSS).

The combination of high speed, maneuverability, and relatively low altitude of some of the emerging advanced missile threats makes them challenging targets for our current missile defense systems. HBTSS is needed, since we cannot populate the earth and the oceans with terrestrial radars to meet this need. The ‘birth to death’ tracking that HBTSS can provide when integrated with terrestrial sensors will make it possible to maintain custody of missile threats from launch through intercept regardless of location. DA is developing HBTSS in collaboration with the U.S. Space Force under the leadership of the Chief of Space Operations and the Space Development Agency. The goal is to implement HBTSS as an element of a unified Overhead Persistent Infrared (OPIR) enterprise solution in order to meet critical Missile Warning/Missile Defense requirements. HBTSS will provide low-latency critical data to the Missile Defense System and support Combatant Command needs associated with advanced threats. Ultimately, this data is critical to enabling engagement by missile defense weapons, including engagement by hypersonic glide-phase weapons.

Military and civilian leaders have issued a steady stream of warnings over the past two years over the growing imbalance between US investments and those being made by Russia and China in hypersonics. The 2018 Missile Defense Review, while thin on details and vague about both the threat and efforts to counter hypersonic glide vehicles, calls for a Space Sensor Layer as a necessary countermeasure. HBTSS will deliver a schedule-focused, cost-constrained missile defense capability with sensitivity and quality of service to address advanced threats. MDA will continue to develop HBTSS as a unique OPIR sensor providing fire-control quality tracking data on hypersonic threats and ballistic missile defense threats. The goal is to deploy an operational prototype system that will provide a rapid capability using mature technology and operate as an element within the larger OPIR Enterprise architecture to meet the Warfighter’s evolving requirements.

MDA is working with the Space Development Agency (SDA), DARPA, and the U.S. Air Force to conduct prototype concept design activities for a space-based missile tracking sensor system known as Hypersonic and Ballistic Tracking Space Sensor (HBTSS). HBTSS is one of several proposed missions within the DoD’s Proliferated Low Earth Orbit (P-LEO) space architecture led by SDA. As part of an integrated multi-tier OPIR enterprise architecture, HBTSS would detect and track additional and emerging threats using persistent infrared sensors. MDA and the SDA are partnering with DARPA and Air Force Space Command (AFSPC) to ensure our nation's ability to detect and track evolving threats. MDA will coordinate and leverage DARPA's Blackjack program for advances in the areas of production-line satellite buses and spacecraft autonomy approaches in parallel with the HBTSS risk-reduction efforts.

MDA is partnering with AFSPC on integrated missile warning and missile defense requirements definition and will explore opportunities to partner with the Air Force on ground services, integration, launch, and operations. MDA is using STSS as a testbed for HBTSS, and MDA will continue to leverage the Enterprise Capabilities developed collaboratively within other Department and federal agencies. MDA will work with SDA to ensure that HBTSS is compatible with a potential P-LEO data and communications transport layer.

Shortfalls in the current BMDS include limitations with kill vehicle reliability and gaps in sensor coverage, most notably with the absence of a space-based sensor layer for persistent birth to death tracking and discrimination. Such overhead persistent coverage would close current gaps in terrestrial radar coverage, currently highly dependent on a handful of forward deployed TPY-2s and upgraded early warning radars. A spacebased sensor layer has been a feature of every missile defense architecture for the past five administrations, but none have been fielded, with the exception of two STSS demonstration satellites.

General John E. Hyten, Commander of U.S. Strategic Command (USSTRATCOM) said 01 August 2018: "The most important thing to me, though, is not the interceptor technology, it’s the sensor technology. I’ve testified before that, I think Mike Griffin has also testified, and our common message is that if you can’t see a threat, you can’t deal with a threat. So, the first thing that you have to do is see the threat. So, before we decide on how to respond to it, how to defend against it, et cetera, we have to make sure we can see and characterize not only the threat but where it comes from, who it comes from, and where it comes from. All of those things have to be characterized. That will create a new requirement. On the requirement side of the question that you asked, the mission need has been clearly stated. So there’s a broad-based approach for how we do requirements in the Department of Defense, and you start with a mission need, and our mission need is clear and that’s out there. Now, we’ll go through a detailed analysis process to define the real requirements that we have to go build to, and I hope to do that very rapidly with the other combatant commands, and with the services, to define where we have to go so we can quickly achieve what Congress has asked for, what the department has asked for, what I’ve asked for, and that is building a capability to see and assess the threat. That’s the mid-course tracking system or whatever system is built according to that. But we have very good mission needs required. Now we have to just break out the detailed requirements."

General Terrence J. O’Shaughnessy, USAF, Commander, United States Northern Command and North American Aerospace Defense Command, testified April 3, 2019 before the Senate Armed Services Subcommittee on Strategic Forces : "We must take prudent steps now to ensure our next generation defense capabilities to include a space-based sensing layer are not late to need. That effort cannot start too soon given that our adversaries are already developing and testing advanced weapons specifically intended to avoid detection in order to hold targets in the homeland at constant risk.... obviously with our adversaries, continuing to make more complex weapons systems that we have to be able to respond to. An example is the hypersonics, where our current sensing capability just doesn’t have the ability to watch it from birth, from the time it launches, all the way to the time that it would impact. The space-based sensing layer gives us the ability to see it from the time that it launches, and because of the unique fashion in which the trajectory is, where it starts out very high but then it will come down low, it will not be seen by our current sensors."

Lieutenant General Sam Greaves, Director of the Missile Defense Agency, testified April 3, 2019 before the Senate Armed Services Subcommittee on Strategic Forces : "The major change this year has been the movement from the medium earth orbit deployment of an architecture to a low earth orbit deployment of an architecture.... What has changed within the last year -- and the last year has been a year of transition within the Department -- is that Dr. Griffin is now approaching space capability from a Department-wide perspective. So what has changed is that with industries’ progress in actually developing the capabilities to proliferate multiple small satellites in low earth orbit, very significant potential to deploy a low earth orbit architecture that can do multiple missions, one of which is missile defense. So the vision from Dr. Griffin is to deploy that architecture, multi-hundred satellites, very small, together with a communications transport layer to move the information around between satellites and to the ground and to the warfighters where it needs to be, and to have mission areas plug in as required.... The difference also between what our original government reference architecture was and what Dr. Griffin is proposing has to do with resiliency, the ability while under attack to gracefully degrade your capability and not have it shut off immediately. The way I try to explain it is if you’ve got six big targets up at medium earth orbit, that’s a lot easier to go against and have a bigger effect than a few hundred down at a lower orbit that we have shown through analysis and study that can gracefully degrade and still maintain capability. "

The Pentagon included the Space Sensor Layer, formerly the Missile Defense Tracking System, in its fiscal 2020 unfunded requirements list. After several years of consistent testimony from senior Department of Defense officials regarding the importance of space-based sensors for a missile defense capability, the Congress has strongly supported MDA’s space-based sensor program. Both the John S. McCain National Defense Authorization Act for Fiscal Year 2019 (Public Law 115–232) and the Department of Defense Appropriations Act for Fiscal Year 2019 (Public Law 115– 245) increased funding for the Space Sensor Layer program from $0.0 to $73.0 million. This program, now called the Hypersonic and Ballistic Tracking Space Sensor, was included in the unfunded requirements lists of the MDA Director and the Commander of U.S. Strategic Command.

MDA is eeking technology to eliminate reliance on integrated non-uniformity correction hardware in electro-optical/ infrared (EO/IR) sensors to reduce sensor size, weight, power, and cost (SWaP-C), simplify maintenance and integration, and streamline mission continuity of operations. This seeks to explore two areas of development to address bias drift in infrared Focal Plane Arrays (FPA): 1) Next generation Read-Out Integrated Circuits (ROICs); and 2) Next generation adaptive Non-uniformity Correction (NuC) algorithms for machine vision applications.

EO/IR sensors have become ubiquitous for not just missile defense applications, but across the DoD mission space. One of the main drives of SWaP-C is integrated hardware to address bias drift in thermal infrared (3 microns wavelengths or higher) FPAs caused by both electrical and thermal drift. These effects create both transient and fixed pattern noise that down-stream processing algorithms must contend with if not properly corrected. The need exists to emulate within the thermal infrared sensor domain the long-term stability typical of visible-near infrared FPAs. The gold standard for removing these biases is a flat-field correction which constitutes a signal-interrupt and requires in-line optical calibration hardware. Adaptive NuC algorithms have also demonstrated their utility in scenarios where SWaP is limited and/or signal-interrupts are untenable. However, these algorithms are usually optimized for human consumption and not machine vision applications and/or perform poorly under highly transient temperature conditions.

On 22 January 2021 the Missile Defense Agency (MDA) announced award of Other Transaction Agreements (OTA) with L3Harris Technologies, Inc and Northrop Grumman Systems Cooporation for the Hypersonic and Ballistic Tracking Space Sensor (HBTSS) program’s Phase IIb On-orbit Prototype Demonstration. Phase IIb will continue developing the capability to support Warfighter fire-control quality data requirements. This will result in Launch and Early Orbit Testing of HBTSS prototype satellites that demonstrate the sensitivity and fire-control quality of service necessary to support both the emerging hypersonic threat kill chain and dim upper stage ballistic missiles. These agreements were awarded under MDA’s OTA authority and are the only planned awards for Phase IIb. In Phase I, industry teams developed conceptual end-to-end designs that focused on utilizing mature spacecraft and sensor technology, and in Phase IIa, they held Preliminary Concept Reviews and conducted risk reduction activities to demonstrate the maturity and capability of their designs. Phase IIb will build on the work industry previously completed through design and risk reduction efforts from Phases I and IIa.

HBTSS’s current phase is a prototype, not an operational capability, with two contractors demonstrating their design. The current phase of HBTSS seeks to place two demonstration sensors into orbit by the end of fiscal year 2023. Eventually, HBTSS will be integrated into a broader set of satellite constellations that are being developed by the Space Development Agency (SDA). DOD established SDA in 2019 to lead the development and deployment of new satellite architectures, emphasizing the use of large numbers of smaller, cheaper satellites in lower orbits. This concept is known as proliferated, low earth orbit (pLEO), and at present, SDA is developing multiple constellations (or “layers”) to meet different requirements, including one for missile warning and missile defense. For this layer, SDA is developing satellites with a so-called Wide Field of View (WFOV) sensor.

If deployed in sufficient numbers these WFOV sensors would provide “global persistence,” meaning the ability to view the entire surface of the earth without gaps in coverage. According to MDA officials, the HBTSS sensor will employ a Medium Field of View (MFOV) sensor that lacks the ability to view the entire earth at once but would provide greater sensitivity, and thus better accuracy, than a WFOV sensor. SDA is planning to launch eight WFOV satellites starting in fiscal year 2022. In an operational constellation, both MFOV satellites and WFOV satellites would work together with WFOV satellites initially detecting a hypersonic weapon and providing a cue to the MFOV satellites, that tells them where to look in order to provide missile tracking data. Currently, SDA reports to the OUSD(R&E), but as of the start of fiscal year 2023, the agency will become a branch of the Space Force.

OUSD(R&E) responded to the congressional request with two reports released several months apart (May 2020 and January 2021). While these reports stated that the MFOV sensors developed as part of HBTSS would indeed be integrated into SDA’s architecture, neither report stated which agency would operate the satellites hosting the MFOV sensors in future phases. Thus, it was not specified whether MDA could in the future develop (1) sensors for inclusion on SDA satellites, (2) satellites of its own for inclusion in SDA’s broader tracking layer, or (3) operate an entirely separate constellation.

The reports did lay out areas in which MDA and SDA would coordinate their efforts. The May 2020 report stated that OUSD(R&E) would oversee the development of a memorandum of understanding between MDA and SDA to formalize the agencies’ roles and responsibilities in the broader SDA architecture. MDA later stated that Space Force was eventually included in the draft memorandum as well.

The January 2021 report, which described itself as a “roadmap” for the future architecture, further stated that the eight SDA WFOV satellites and the two HBTSS MFOV satellites (slated for launch starting in 2022 and 2023, respectively) would be equipped with optical cross-links. These cross-links enable the ability of the satellites to communicate with each other directly in space. Equipping these satellites with the cross-links would allow them to practice and demonstrate the WFOV-MFOV detection and cueing process described in the January 2021 roadmap. This roadmap further stated that SDA would procure and provide launch services for both HBTSS and SDA.

However, since the 2021 roadmap was presented to Congress, MDA made decisions about HBTSS that run contrary to several aspects of the roadmap’s plan. MDA has declined to equip the HBTSS demonstrators with the optical cross-links needed to communicate with SDA’s satellites. MDA officials stated that they made this decision to avoid becoming unnecessarily involved in SDA’s plans. MDA stated that a technical risk assessment determined it would create an unnecessary risk. However, when we asked for documentation of this assessment, MDA stated that there was no documentation available. MDA also stated that they would consider including cross-links on future iterations of HBTSS, even though HBTSS has not been budgeted funding past the current two-satellite phase.

MDA also declined to procure launch services through SDA, stating that the orbital requirements of the HBTSS demonstrators precluded using the same launch vehicle. MDA officials said that these orbital requirements were not new and predated the roadmap report by several years. Affirming a plan to procure launch services through SDA, when doing so is not technically possible, indicates the need for better coordination.

SDA and MDA officials also said that progress on the memorandum of understanding stalled at some point in 2021. According to SDA officials, the main reason for the lack of progress was that, at present, there were few, if any, areas to coordinate with MDA. Based on MDA’s decisions, their satellites could not communicate in space, they would be launched separately, and MDA had invested considerable sums into its satellite ground control facility, such that the HBTSS satellites would operate independently. Though SDA and MDA would continue to work together in some areas (and indeed, they had worked together in several areas prior to 2020), these areas did not require a memorandum of understanding to execute.

In October 2021, MDA proposed a plan that would continue the HBTSS program past the current phase, expanding it until it provided an operational satellite constellation. DOD has not requested or received funding for this expanded effort, but under this proposed plan, an additional phase of HBTSS would launch six satellites in the fiscal year 2025 time frame. The satellites would be operational demonstrators, meaning they could eventually be used by warfighters for operational purposes, including providing data for GPI. Following this phase would come the production phase, which would involve a production decision and declaration of a formal initial operational capability. MDA’s plan did not assign a target date to the production phase.

These plans pose a significant risk of duplication or overlap with SDA’s tracking layer. If completed, MDA’s MFOV constellation would still depend on the SDA tracking layer for a cue in order to track a hypersonic weapon.55 While the HBTSS sensor is more sensitive than SDA’s, both SDA and MDA officials acknowledged that the SDA’s satellites can meet the requirements for intercept-quality data that MDA determined were necessary for the GPI. Both MDA and SDA officials said that the GPI interceptor’s current requirements for sensor accuracy are equivalent to what is necessary to provide a Launch-on-Remote capability and that the WFOV sensor planned for SDA’s satellites meets or exceeds this threshold. MDA officials did note, that the MFOV HBTSS sensor, if deployed properly, will be able to provide the more difficult Engage-onRemote capability; however, this was not the original GPI requirement.

This set of advantages and disadvantages is not static. Because of the short operational life of satellites in pLEO architectures, SDA plans also provide for improvements over time, adding new capabilities every 2 to 4 years. SDA’s near-term plans include the deployment of MFOV sensors capable of supporting engage on remote in future iterations of the tracking layer. Further, even if an HBTSS constellation could provide this added capability sooner than SDA, it may not be useful. As noted above, GPI will most likely not be completed until sometime in the 2030s and even then will not be available for operational use. If MDA pursues its plans to expand HBTSS, it risks constructing a separate and independent satellite constellation, for which the current requirements are already being met by SDA’s constellations, and whose additional capabilities may exist without a system ready to take advantage of them.