tagged: , , , , , ,

In the latest Quest

Posted by in Physics & Maths, Science in Society, Space

Systems engineering – how to make a radio telescope work

 

Systems engineering is all about managing complexity. Richard Lord explains how this approach will make SKA work.

The South African SKA organisation is using systems engineering to build the 64-antenna MeerKAT radio telescope.

Managing complexity

What is systems engineering? The International Council on Systems Engineering (INCOSE) defines it as follows:

‘Systems engineering is an interdisciplinary approach to enable the realisation of successful systems. It focuses on defining customer needs and required functionality early in the development cycle, documenting requirements, then proceeding with design synthesis and system validation while considering the complete problem:

  • Operations
  • Performance
  • Testing
  • Manufacturing
  • Cost and schedule
  • Training and support
  • Disposal

Systems engineering integrates all the disciplines and specialty groups into a team effort, forming a structured development process that proceeds from concept to production to operation. Systems engineering considers both the business and the technical needs of all customers with the goal of providing a quality product that meets the user needs.’

Systems engineering techniques are used in complex projects: spacecraft design, computer chip design, robotics, software integration, and bridge building. Systems engineering uses a host of tools that include modeling and simulation, requirements analysis and scheduling to manage complexity.

A systems engineer must understand the entire problem before attempting to solve it. A systems engineer looks at where the system is now, where it is going and what is going to happen once the project is completed. In other words, the system is understood in the context of its environment, and in the context of its entire life cycle, including maintenance, replacement, decommissioning and retirement.

The field of systems engineering is too vast to cover completely in a short article. Instead, we will look at some of the key focus areas of the systems engineering approach.

Definition of a system

A radio telescope system is more than just a collection of antennas and computing hardware.  Operators are needed to control and monitor the telescope and to record data that is given to the scientists. Maintainers are needed to repair faulty equipment and to service the telescope regularly. The telescope, together with its operators and maintainers, is often grouped as belonging to the mission and operations functions. The logistic support functions, which are also needed to operate and maintain the telescope, include items such as supplies, facilities, specialist equipment, as well as data and documents. The systems engineering approach requires proper documentation, so that the system can be maintained and supported long after the design and engineering teams have moved on to other projects. Figure 1 shows that a system consists of far more than imply the equipment that is needed to perform the mission.

Managing requirements

The objective of any system is to satisfy the needs of the end user. For a radio telescope such as MeerKAT, the most important users are the scientists. Capturing user requirements is an essential first step toward building a telescope that allows scientists to perform world-class research.

User requirements are translated by systems engineers into system specifications, i.e. into requirements that engineers and subcontractors can understand. These requirements need to be measurable and verifiable. The requirements analysis process is an iterative process; some requirements are too costly or time-consuming to implement, and trade-offs have to be negotiated.

Requirements nedd to be traceable – an important concept in systems engineering. For example, if a particular requirement shows up lower-level requirements, you need to be able to trace from these lower-level requirements all the way to the top-level requiremnts. If you don’t do this, it is possible that there may be unecessary development work going on at a lower level.

In the same way, all top-level requirements have to have lower-level requirements. Otherwise it is possible that some required functionality is not being implemented at a lower level.

Concept exploration

To arrive at the best solution for a particular problem, it is important to investigate all feasible alternatives before selecting a solution. As part of the systems engineering process, alternative designs are evaluated, based on performance, schedule, cost, risk and figures of merit.

Qualification and acceptance testing

Qualification and acceptance testing is an integral part of the systems engineering process.  Qualification testing verifies that the end-to-end design meets the given requirements, and it needs to be performed before an item is mass produced. Qualification units are not typically used in the final system, since they often undergo extreme testing, such as vibration testing, shock testing, ingress protection testing, etc.

Acceptance testing is performed on all production items, and typically forms a subset of the qualification tests. Acceptance tests are usually performed at the factory, where the item is produced, in the lab, where the item is assembled into the next higher level, and also on-site, after an item has been installed and integrated into the final system.

Before the final system is handed over to the operational user, the systems engineers make sure that it meets the original user requirements.

Commissioning

The objective of engineering verification is to verify that the system meets the system requirements. The commissioning process involves the characterisation and calibration of the instrument. Commissioning is also seen as the process that establishes the user system, i.e. it is the process that takes the engineering deliverable and refines it until it is a system that can be monitored and controlled by the operators.

Risk reduction

Building a radio telescope in the Karoo is not without its challenges. Any system erected in the Karoo must be able to withstand dust, strong winds, lightning, and large variations in temperature. Infrastructure such as roads, power, water, sewage, accommodation, maintenance, support and operating facilities, etc. has to be established. In order to reduce both the project management risks as well as the technical risks, a number of development models were constructed. This is part of the systems engineering approach to developing complex systems.

At the end of 2007, the Experimental Development Model (XDM) was completed at the Hartebeesthoek Radio Astronomy Observatory (HartRAO). XDM is a single-antenna radio telescope with a diameter of 15m.  XDM not only addressed many technical risks, but acquisition of the XDM was allowed the building of a coherent engineering team and was also part of growing the systems engineering maturity of the SKA SA organisation.

KAT-7 was developed immediately after the completion of the XDM, and it is the first interferometric radio telescope built in Africa.  KAT-7 can be regarded as the Engineering Development Model (EDM) for MeerKAT. Its aims were to implement an operational system in the Karoo to learn how to operate and maintain a radio telescope on a remote site.