Guidance

Statement of Work

Published 24 October 2024

Positioning, Navigation and Timing (PNT) services are critical to the UK’s economy and society, mainly provided by GNSS, primarily GPS. The dependence on GNSS poses risks due to potential disruptions. To enhance PNT resilience, the National PNT Office aims to develop a two-way satellite time and frequency transfer (TWSTFT) system via a NAVISP Element 3 project. Technical requirements involve using a geostationary communication satellite for high accuracy timing synchronization, seamless time source switching, and service monitoring. This document provides background information, the requirements the project will need to meet to be considered a success, and the criteria the outline proposals will be evaluated against.

1. General

1.1 Glossary of terms

Acronym / Abbreviation	Definition
CDR	Critical Design Review
GNSS	Global Navigation Satellite System
GPS	Global Positioning System
KO	Kick Off
NPL	National Physical Laboratory
PNT	Position Navigation and Timing
SoW	Statement of Work
SRD	System Requirements Document
SRR	System Requirements Review
TBC/D	To Be Confirmed/Decided
TRL	Technology Readiness Level
UTC	Universal Coordinated Time

Table 1: Glossary of Terms

2. Introduction

2.1 Background and UK National Framework for Greater PNT Resilience

Positioning, Navigation and Timing (PNT) services play a critical and growing role for the UK’s economy and society. The UK’s PNT is almost completely provided through global navigation satellite systems (GNSS), primarily the US owned Global Positioning System (GPS). PNT services from GNSS are susceptible to incidental and intentional disruptions, with detrimental effects on Critical National Infrastructure (CNI) and wider society.

The loss of PNT services from GNSS was identified as a significant risk to the UK in the 2023 National Risk Register. To address this risk, the Department of Science, Innovation and Technology (DSIT) published a National Framework for Greater PNT Resilience in October 2023. This Framework outlines 10 Actions to be taken forward to improve the resilience of PNT services upon which the UK relies, and to promote economic growth through PNT. The 10 Actions are listed below:

1. National PNT Office: establish a National PNT Office in the Department of Science, Innovation and Technology – to improve resilience and drive growth with responsibility for PNT policy, coordination, and delivery
2. PNT Crisis Plan: retain and update a cross-government PNT Crisis Plan to be activated if Global Navigation Satellite Systems provided PNT is lost and identify and implement short term mitigations
3. National Timing Centre: develop a proposal for a National Timing Centre – to provide resilient, terrestrial, sovereign, and high-quality timing for the UK (UTC(NPL)), including sovereign components and optical clocks
4. ‘MOD Time’: develop a proposal for ‘Ministry of Defence Time’ creating deeper resilience through a system of last resort and use National Timing Centre provided timing to support the Ministry of Defence
5. eLoran: develop a proposal for a resilient, terrestrial, and sovereign Enhanced Long-Range Navigation system to provide backup Position and Navigation (and Timing)
6. Infrastructure Resilience: rollout resilient GNSS receiver chips, develop holdover clocks, and consider options for legislation on CNI sectors to require minimum resilient PNT
7. UK SBAS: develop a proposal for a UK Precise Point Positioning Satellite-Based Augmentation System to replace the UK’s use of the European Geostationary Navigation Overlay Service, monitor GNSS and enable GNSS dependent high accuracy Position for autonomous and precision uses
8. PNT Skills: explore options for Centres for Doctoral Training in timing and PNT and review PNT skills, education, and training for long term sovereign PNT capability
9. Growth Policy: develop a PNT growth policy, including R&D programmes, standards and testing, to drive innovation for PNT based productivity
10. Next Generation PNT: deploy existing R&D funding into a UK Quantum Navigator and investigate possible options for a UK sovereign regional satellite system

Figure 1. Graphic from the UK National Framework for Greater PNT Resilience

Image description:

PNT (Positioning, Navigation and Timing) is a technology vital to the functioning of Critical National Infrastructure and underpins many everyday activities in modern society.

PNT is:

• positioning, the ability to determine location and orientation
• navigation, the ability to determine current and desire position
• timing, the ability to acquire and maintain accurate and precise time from a standard anywhere in the world

HMG will stregnthen the resilience of the PNTservice on which our Critical National Infrastructure and economy depend by scoping a new Government Policy Framework for Greater PNT Resilience.

PNT matters because it underpins the safe operation of Critical National Infrastructure and many everyday activities in modern society including:

• travel - cars, trains and planes
• telecommunications - phones and TV
• computers and internet
• emergency services - ambulance, police and fire
• personal navigation - maps on mobile phoines
• finaces - touch payments and mobile banking

The UK’s PNT is at risk because it is almost completely provided through Global Navigation Satellite Systems (GNSS), primarily the US Global Positioning System (GPS), which is operated by the US Space Force.

There are many potential major disruptions to GNSS-provided PNT, including hazards like severe space weather and catastrophic technical failure, and threats like cyber and physical attacks.

Government Policy Framework for Greater PNT Resilience will scope the following proposals:

• National PNT Office
• PNT Crisis Plan
• National Timing Centre
• MoD Time
• Enhanced Long Range Navigation (eLORAN)
• Next Generation PNT
• PNT Growth Policy
• PNT Skills
• Satellite Based Augmentation System (SBAS)
• Infrastructure Resilience

2.2 The project

The National PNT Office (the Authority) has identified the opportunity to progress some of the Actions outlined above via a NAVISP Element 3 project focussing on two-way satellite time and frequency transfer (TWSTFT). These actions are 2) PNT Crisis Plan, 3) National Timing Centre, 5) eLoran. More detail on each is below (Sections 2.2.1 - 2.2.3).

The Project must deliver a TWSTFT link between three nodes 1) UTC(NPL) currently sourced from the National Timing Centre at NPL Teddington; 2) the eLoran transmitter at Anthorn as the current eLoran infrastructure in the UK and a method of disseminating time; 3) the timing laboratory at Porton Down as the secondary government timing capability after the National Timing Centre. More information is available in further Sections.

2.2.1 How the Project will support the National Timing Centre

The National Timing Centre is looking to provide resilient UTC(NPL) referenced and traceable time to users via a resilient terrestrial network of high-performance clocks and terrestrial timing dissemination nodes. A TWSTFT capability would allow further dissemination of the resilient time signal in a manner that is not dependent on GNSS.

2.2.2 How the Project will support UK eLoran

The UK currently has one eLoran transmitter at Anthorn in northwest England. This transmitter is currently steered to UTC(NPL) using GPS common view, so therefore is not resilient to GNSS outages. A TWSTFT link from the National Timing Centre to this transmitter would remove the reliance on GPS and increase the resilience of the system, allowing it to be used as an effective backup to GNSS in providing timing to users. A proposal for a larger UK eLoran system is currently being developed and this Project will inform any TWSTFT capability within this.

2.2.3 How the Project will support the UK PNT Crisis Plan

The PNT Crisis Plan will help prepare for and effectively act during a period of GNSS outage. This Project will enable resilient time to be broadcast via eLoran. As eLoran has been identified as a suitable backup to GNSS, this will provide the first step to a resilient backup PNT system in the UK which can function in the event of a GNSS outage.

2.3 Overarching objectives

2.3.1 Remove the GNSS dependence from the eLoran transmitter at MoD Anthorn

The eLoran transmitter at MoD Anthorn currently uses GNSS for timing provision. The National PNT Office is currently developing a proposal to extend this eLoran system, focussing on resilience. Therefore, removing the GNSS dependence from the current eLoran assets using TWSTFT will increase the resilience of the current system. This will potentially be further extended within the wider eLoran proposal, therefore this Project will act as a proof of concept, as outlined below.

2.3.2 Proof of concept to inform future UK TWSTFT projects

TWSTFT has been identified around UK government as a potential technique for future time transfer projects. For example, it is being included in the UK eLoran system proposal as one method of linking potential new transmitters to the National Timing Centre and UTC(NPL). Therefore, this Project must inform future UK TWSTFT projects and have the capacity to be extended if successful. The following required elements of this project will help inform future projects:

• testing TWSTFT over X-band and Ka/Ku band and comparing the performance
• assessing the feasibility of TWSTFT over the long-term using a satellite with a digital transponder
• testing of assured components, for example assured modems. The Authority can advise on specific models
• providing an indication of how scalable this capability may be. For example, maximum TWSTFT nodes and maximum geographic separation
• production of a detailed report of findings and recommendations

2.3.3 Proof of concept to link the two government timing assets at NPL Teddington and Dstl Porton Down

NPL Teddington houses the current National Timing Centre capability. This is the primary source of UK time (UTC(NPL)). The timing laboratory at Dstl Porton Down is the prototype secondary source of UK time. The two need to be able to compare against each other and provide compatibility in the event of an outage at either site. This Project must integrate the two sites via TWSTFT, with UTC(NPL) as the primary time source, and Dstl Porton Down as prototype secondary time source, and devise and test a method to switch these roles within this Project’s network only. The bidder should test the switchover from using UTC(NPL) as the reference clock for the eLoran signal at Anthorn to using Porton Down as the reference. This switch should aim to have maximum achievable continuity in the phase, frequency or pulse timing delivered by the eLoran signal upon switchover.

3. Two Way Satellite Time and Frequency Transfer

3.1 Scope

The successful bidder is required to design, procure, implement and monitor a TWSTFT capability between three primary nodes:

• UTC(NPL) from NPL Teddington
• eLoran transmitter at Anthorn
• timing laboratory at Dstl Porton Down

The successful bidder must include in their proposal activity to cover an orderly transition at the end of the project. This could be the closedown of the project and handover of equipment to the authority, or to plan for a follow-on activity to change or extend the capability. Hence the transition activity needs to allow time and resource to deal with either scenario.

The Project may be phased, for example, a design phase, procurement and installation phase, testing phase etc. This must be clearly laid out in the proposal and meet the deadline in Section 5.1.9

The successful bidder must design the overall architecture of the solution. This may include choice of satellite provider, selection and configuration of all ground equipment (modem, down/upconversion, clock and steering system etc.), at each end of the transfer, configuration of the ground equipment and any bespoke management software. Note that the authority reserves the right to mandate the use of a preferred TWSTFT modem. If the authority chooses to exercise this right, then the decision will be made prior to contract with appropriate adjustment to the agreed contract funding.

The successful bidder is responsible for relevant permissions needed to transmit the signal, with help from the Authority.

The successful bidder is responsible for procuring and installing equipment needed. The Authority can aid with procurement of assured modems if they are required and installation on secure sites. After the conclusion of the Project, equipment will remain property of UK government.

The successful bidder is responsible for overseeing the TWSTFT capability and the timing control of the eLoran signal throughout the duration of the project.

The successful bidder must regularly report on progress and performance to the Authority, UK Space Agency, and ESA. Clear communication channels are needed between the successful bidder, NPL, Dstl and the Authority around outages. Any planned outages require a pre-defined notice period (length to be confirmed with the Authority). Any unexpected outages must be reported immediately.

3.2 General considerations

3.2.1 The eLoran Site at Anthorn

The installation of the equipment at Anthorn to facilitate the transfer of time from NPL via TWSTFT will require a site survey. In particular, the installation of the TWSTFT antenna will need to be agreed with the authority and the contractor responsible for the management of the facility. Access can be facilitated by the authority.

Figure 2. eLoran Transmitter architecture

Image description:

The UK eLoran station has two Caesium 5071a atomic clocks steered by qUTC Caesium Tuning units currently using GNSS as an input. The clocks each provide an input to separate Loran Timer Units which can be controlled by a control PC via a Remote controller Unit. The Loran timer units provide input to the Pulse Amplitude and Timing Control Units which provide redundant inputs to the Common Control Console which drives the eLoran transmitter. The Caesium Clocks have been recently repaired and replaced and the Caesium tuning units were recently provided and installed by Chronos Technology UK.

The successful bidder must identify and implement a functioning interface with the existing eLoran infrastructure at MoD Anthorn, the architecture of which is illustrated in Figure 2. The transmitter architecture is comprised of 2 separate Caesium 5071a frequency sources (recently repaired), linked to individual qUTC Caesium tuning units. Both of these feed into individual Loran Timer Units, which then lead to individual Pulse Amplitude and Timing Controllers (PATCOs), which are then combined in the Control Console Common, before having the signal passed to the transmitter. The Loran Timer Units are controlled by an existing control PC which has the commands passed by remote control unit (RCU). This control PC is fed an eLoran data channel by internet VPN. The Caesium Tuning is controlled by a new remote dashboard also transmitted over the internet. Note that the existing clock tuning units (green units in Figure 2) may need to be replaced with new equipment as they are currently configured to steer the Caesium clocks using GNSS or common view time transfer. Throughout the project, the successful bidder is responsible for the link from TWSTFT infrastructure to the eLoran transmitter. Any further work or maintenance needed on the existing eLoran transmitter equipment will be discussed with the Authority to identify a suitable implementation plan and if the work extends beyond the scope agreed in the contract for this project an appropriate CCN will be put in place, or another supplier will be engaged to carry out the required maintenance.

The successful bidder must collaborate closely with others currently working at or overseeing the eLoran transmitter. Performance must be regularly reported on to the Authority and any problems promptly shared with the Authority and will be addressed accordingly by the responsible party.

Access to the site is closely monitored and all visitors must be escorted by site personnel. Visitor must meet certain security constraints and will be security checked prior to admission to the site. The Authority can aid with site access. Furthermore, all systems used on the Anthorn must comply with site security requirements. More information can be provided by the Authority at the Full proposal stage.

The Authority can provide bidders with contact details relating to the eLoran transmitter.

3.2.2 The NPL Site at Teddington

The successful bidder must identify and implement a suitable TWSTFT link between UTC(NPL) and the two other nodes that will meet the objectives outlined in Section 2.3. This may include conducting site surveys at NPL Teddington and their existing time transfer links and obtaining necessary permissions for installation of antennas on the roof of the building. Any new equipment installed at the NPL site must not interfere with the existing time transfer links or any other radio frequency equipment in regular use by NPL at the site.

The successful bidder is not responsible for the existing timing infrastructure at NPL Teddington and must work with experts at NPL on how this project links to the current National Timing Centre assets.

The bidder will be responsible for supply and installation of the TWSTFT modem, and all equipment related to transmitting the satellite signals including the antenna, down and upconverters cabling and any other components on related to the satellite link. NPL will be responsible for the connection to NPL timing infrastructure. Note that NPL cost will be provided as a fixed cost service which will be included in the overall funding provided by ESA but is not included in the budget envelope for this call for proposals. Access to the NPL facilities is closely monitored. All visitors to site must be escorted by site personnel. If required to visit secure aspects of the time scale infrastructure, visitors will require a minimum UK government security vetting of SC.

3.2.3 The Dstl Porton Down Site

The successful bidder must identify and implement a suitable TWSTFT link between Dstl Porton Down and the other two nodes that will meet the strategic objectives outlined in Section 2.3. The successful bidder is not required to conduct full site surveys, but this work must involve close collaboration with Dstl to ensure suitability.

The successful bidder is not responsible for the current timing infrastructure at Dstl Porton Down and must work with experts at Dstl on how this project links to the current assets.

The Project must include an eLoran monitoring capability at Dstl to ensure timing quality and traceability can be monitored and assured.

Access to the Porton Down site is closely monitored and all visitors must be escorted by site personnel. All systems used must comply with Dstl security requirements. More information can be provided by the Authority if required.

The Authority can provide bidders with contact details at Dstl.

4. Technical requirements

This section lists the technical requirements for the project.

4.1.1 The system shall achieve a minimum (threshold) time difference between the output of one of the Caesium frequency standards at Anthorn eLoran transmitter and UTC(NPL) of less than 100ns (95% confidence interval) with a target (objective) time difference of less than 10ns (95% confidence interval).

Note: The Loran Timing Unit which generates the triggers for Loran pulses to be generated uses the reference frequency from the Caesium standard. Hence the measurement of time difference between the Anthorn Caesium frequency standard is likely to be by means of a phase comparator comparing the output of the Caesium standard to portable frequency standard recently calibrated to UTC(NPL). This comparison will be conducted by NPL as part of the fixed price service they provide for the project.

4.1.2 The system shall achieve the performance target for time transfer to the Anthorn site 95% of time.

Note: It is not necessary to maintain the TWSTFT link continuously or even for 95% or more of time as long as the output of the Caesium standard at Anthorn remains within the bounds specified.

4.1.3 In the case that the time reference at Dstl Porton Down becomes the master source, the system shall achieve a minimum (threshold) time difference between the output of one of the Caesium frequency standards at Anthorn eLoran transmitter and MOD Time of less than 100ns (95% confidence interval) with a target (objective) time difference of less than 10ns (95% confidence interval).

Note: The same measurement process will be used as for the comparison with UTC(NPL) as maintained at NPL Teddington, but with the portable clock calibrated against the time source at Dstl Porton Down.

4.1.4 The system shall achieve a time difference between the master frequency reference at MOD Porton Down and UTC(NPL) of less than 10ns (95% confidence interval). 

4.1.5 The system shall be capable of switching the time source used to transfer time to the Anthorn eLoran facility from UTC(NPL) to MOD Time.

Note: MOD Time is used throughout to refer to the timescale maintained at MOD Porton Down. This is defined as the output of the frequency reference at Porton Down that is designated as the master reference.

4.1.6 The system shall be capable of switching the time source used to transfer time to the Anthorn eLoran facility from MOD Time to UTC(NPL).

4.1.7 When switching between time sources the system shall ensure there are no discontinuities in phase in the frequency references used to provide timing for the eLoran transmissions or any other anomaly that would cause disruption to, or errors in, the signals broadcast from the eLoran transmitter.

4.1.8 The system shall be capable of re-synchronising MOD Time to UTC(NPL) after there has been a break in the link between MOD Time and UTC(NPL).

4.1.9 When re-synchronising MOD Time to UTC(NPL) there shall be no discontinuities in phase or any other anomaly that would disrupt the provision of MOD Time to end users.

4.1.10 The system shall use a geostationary communications satellite as the means to transfer time between sites.

4.1.11 The system shall use two way time and frequency transfer methodology whereby both ends of the link receiver and transmit signals for the purpose of measuring delays time difference data is exchanged between the two sites.

4.1.12 The system shall provide an eLoran monitoring capability at NPL Teddington to enable comparison of time delivered by eLoran with UTC(NPL).

4.1.13 The system shall provide an eLoran monitoring capability at Dstl Porton Down to enable comparison of time delivered by eLoran to MOD Time.

4.1.14 The system shall provide fault monitoring capability to detect and provide timely reports of faults likely to disrupt the eLoran service.

Note: The time between a fault occurring and an alert being provided will be negotiated with the authority as part of the system requirements definition phase of the work.

4.1.15 Although the intention is for non-GNSS dependent timing synchronisation as a primary method for steering the clocks at the Anthorn eLoran transmitter, the currently installed capability to synchronise via GNSS should be retained as a viable alternative. 

5. Project requirements

5.1.1 The contractor shall hand over all equipment installed at Anthorn, NPL and Dstl Porton Down to the Authority at the end of the project.

5.1.2 The contractor shall provide user manuals shall for all equipment supplied including bespoke software applications. The manuals shall be adequately detailed to allow a competent engineer to operate the system.

5.1.3 The contractor shall provide training on the use of any equipment supplied to those nominated by the Authority.

5.1.4 The contractor shall provide an analysis comparing the performance of TWSTFT over Ku/Ka band with the performance of TWSTFT over X band links.

Note: This analysis can be conducted by testing or by modelling the links. Any models used must have been validated for the purpose.

5.1.5 The contractor shall provide an analysis of the potential to use communications satellites with digital regenerative payloads for TWSTFT. The analysis shall examine the challenges to delivering TWSTFT over such links and any proposed means of overcoming those challenges.

Note: It is recognised that it may simply be impossible to deliver TWSTFT over such links with anything approaching the performance of TWSTFT using bent pipe Satcom systems, but the analysis should make recommendations as to what provisions in the design of a Satcom system that uses a regenerative payload are required to enable high performance TWSTFT.

5.1.6 The contractor shall test the performance of any modem used in the project, both in laboratory conditions and using live Satcom links. The supplier should assume that the Authority will provide examples of an assured modem which should be tested even if not used in the final TWSTFT links between the three sites. 

5.1.7 The supplier should provide an analysis of the scalability of the TWSTFT solution developed for this demonstrator. The analysis should examine the number of nodes that could be accommodated as a function of key parameters such as Satcom bandwidth used, number of channels required at each node (and particularly the master node) etc.

5.1.8 The contractor shall provide a final report listing all key findings and recommendations.

Note: the list of deliverables in Section 8 includes all documentation that must be delivered as part of this project

5.1.9 The contractor shall deliver an initial operating capability with links between the three sites by December 2025.

5.1.10 The contractor shall ensure that all personnel required to work at Anthorn, NPL and Dstl Porton Down have UK government security vetting SC clearance and are fully aware of the security requirements for operating at each site.

5.1.11 The supplier be responsible for obtaining any permissions and/or licenses required to broadcast the signals used in the project.

5.1.12 The contractor shall ensure that all equipment installations for which they are responsible are safe, compliant with relevant standards and within the scope of any planning restrictions.

5.1.13 The contractor shall be responsible for the health and safety of its personnel when working at any of the sites used in the project.

5.1.14 The contractor shall include a roadmap to providing an extensible operational service including rough order of magnitude annual costs and an indication of how those costs will vary with the number of nodes requiring time synchronisation to UTC(NPL) using the TWSTFT system.

6. Project management

This section of this SoW covers the requirements for Management, Reporting, Meetings and Deliverables. 

6.1 Management requirements 

The contractor is expected to implement effective management of the project. The following requirements cover the plans expected to support the project delivery. 

6.2 Management planning requirements 

6.2.1 The contractor shall document its Project Management activities, organisation roles and responsibilities, reporting and interfaces, and general governance in the Project Management Plan. 

6.2.2 The contractor shall document its Quality Management activities, project team roles and responsibilities, reporting and interfaces, and general governance, including methodology and support use of tools in the Quality Management Plan. 

6.2.3 The contractor shall document is System Engineering approach, team, organisation, reporting and general governance. Particular focus on Engineering tasks and supporting tools. This shall be documented in the System Engineering Management Plan.  

6.2.4 The contractor shall document its approach to managing risks associated with the project, its schedule, tasks and deliverables or outputs, as well as mitigation actions and reporting process. This shall be documented in the Risk Management Plan. 

6.3 Meetings 

6.3.1 The contractor shall arrange quarterly Executive Steering Board meetings with representatives of the Authority and other stakeholders the Authority may nominate. 

6.3.2 The contractor shall organise other meetings in accordance with the requirements of ESA NAVISP terms and conditions. This will include review meetings for each of the key deliverables listed in Section 8.

7. Milestones

The significant programme milestones and reviews are: 

Milestone	Description	Date
KO	Kick-Off	T0
SRR	System Requirements Review	To be agreed
PDR	Preliminary Design Review	To be agreed
CDR	Critical Design Review	To be agreed
EOC	End of Contract	To be agreed
ESB	Executive Steering Board	Quarterly

Table 2: Milestones and reviews 

8. Deliverables

Deliverable	Description	Date
PMP	Project Management Plan	T0 + 4 weeks
QMP	Quality Management Plan	T0 + 4 weeks
RMP	Risk Management Plan	T0 + 4 weeks
SEMP	Systems Engineering Management Plan	T0 + 4 weeks
SRD	System Requirements Document	To be agreed
PDR Data Pack	Preliminary Design Review Data Pack	To be agreed
CDR Data Pack	Critical Design Review Data Pack	To be agreed
Final Report	Final report summarising the findings of the project and recommendations	To be agreed
TWSTFT Equipment	All equipment installed at Anthorn, NPL sites and Dstl Porton Down to deliver the TWSTFT capability	End of project
Equipment documentation	User manuals and instructions for all supplier equipment.	End of project

Table 3: List of deliverables and suggested timeline

9. Budget

The target budget for the project is €1,800,000. This does not include the costs of support provided by NPL which will be covered by a separate service contract element of the project.

10. Evaluation criteria

The proposal will be evaluated in four areas:

1. track record: contractor’s track record in delivering similar projects and understanding of the requirements. 20% of evaluation score
2. compliance against the technical requirements: the degree to which the contractor’s proposed solution meets the technical requirements as specified in this document. 30% of evaluation score
3. compliance against project requirements: the degree to which the contractor’s proposal complies with the project requirements. 25% of evaluation score
4. price: 25% of evaluation score. Bids over the stated budget of €1,800,000 will receive a score of zero for price. Those bids received within the budget 1 point out of a maximum of 25 will be awarded for every €10,000 below the stated budget of €1,800,000 will be awarded

The outline proposal shall include specific sections covering:

• relevant track record of the partners
• the technical solution
• the proposed programme of work and breakdown between partners
• the price and breakdown of costs between the partners
• a compliance matrix covering the requirements in sections 4 and 5