Ice Cube Tray exercise
Decisions made over the next five years to launch, cancel, or curtail U.S. programs will determine positioning, navigation, and timing (PNT) capabilities over the next twenty years--how the picture will look in 2025. In this context, it's important to take a strategic outlook, to see if a more effective overall system could be had for the same or even perhaps less cost.
Preliminary results of the National PNT Architecture drew some pointed feedback from a group of high-level stakeholders gathered at a Cambridge, Massachusetts, meeting in late April, hosted by the National Security Space Office (NSSO) and the Departent of Transportation's Research and Innovative Technology Administration (RITA).
The purpose of the PNT Architecture is not to design programs, but to gain understanding of higher-level issues and set down principles by which programs may then be designed--and to ensure that decisions on individual programs are not taken piecemeal, but in the context of a larger vision.
The centerpiece of the exercise appears in the PNT User Perspectives 2025, aka the Ice Cube Tray.
For each cube, participants identified current or potential gaps in fulfililng perceived user needs in accuracy, availability, coverage, continuity, integrity, timeliness, and security. For each gap, which cube has that problem, who are the users living there, why do they have that problem, what is their need, what solutions are possible? Which are feasible? What fits within an overall architecture?
The gaps largely fall under the following categories, according to the military's PNT Joint Capabilities Document, with additions and modifications from parallel civil community documents and discussions:
* Physically impeded environments
* Electromagnetically impeded environments
* Higher accuracy with integrity
* Hazardously misleading information (integrity)
* High altitude/space position and orientation
* Geospatial information: access to improved GIS data
* Insufficient modeling capability
PNT architect-participants scored, for each cube, how six representative architectures might bridge or mitigate gaps. These six future combinations of PNT technologies are: evolved baseline (few changes from current); dependent terrestrial; combined GNSS constellations; network aiding of GNSS; aided autonomous sensors and aiding sources; and highly autonomous. Evaluating factors included adaptability, interoperability, robustness, and sustainability.
Many marathon sessions and more than 6,000 stakeholder scores and comments were consolidated to identify insights and features. A three-month assessment period has begun, with a report expected in the July timeframe, with recommendations, guidance, and decision criteria.
Findings. Among the preliminary findings of the analysis and assessment phase of the Architecture study:
* Demand for assured PNT in RF impeded environments (interference and obscuration) will increase;
* Current GPS-centric architecture could be significantly altered by emergence of networked or autonomous PNT systems;
* Higher power is one way to address impeded environment, but must consider implications of raising the noise floor;
* Combined GNSS has the potential to provide improved accuracy and integrity; but the U.S. must maintain sufficient stand-alone global capability to support military operations;
* Low-frequency RF-based systems are not sufficiently accurate to meet most-stressing positioning needs.
Ponderables. Some of the architecture-level questions (27 total) considered in this exercise include:
* What requirements should be apportioned to basic GPS: which to augmentations, and which to user equipment?
* How can terrestrial/augmentation systems best make up GNSS shortfalls?
* What international agreements are most important in protecting U.S. national security and the economy?
* How can we better embrace commercial industry and academia, since they are often a driving force for innovation and change?
* How do we protect the spectrum, nationally and internationally?
Feedback. Stakeholders from both government and industry (Boeing, Lockheed Martin, Navcom Technology, Omnistar, and the U.S. Data Grid) at the April workshop commented:
* The communications world (now fully digital) versus the GPS world (analog): how should we factor in the migration to software-defined (and software-redefineable) radio architecture? Are software-defined receivers a disruptive technology? Do they enable, or limit, because everyone has to have one?
* Some federal agencies' policies inhibit innovation and use of latest technologies. And yet the federal government is one of, if not the biggest user of PNT
* A stable government policy may bring inhibition or stagnation--but it also provides an environment for investment and innovation by industry. Flexibility in public policy is not necessarily good for industry.