mission control and web technology Use of WWW Technology for Mission Control Systems S. Haag, J. Gallego & M. Jones Mission Control Systems Division, ESA Directorate for Technical and Operational Support, ESOC, Darmstadt, Germany What is a mission control system? temperatures of particular components, or Descriptions of mission control systems are binary values, such as an on/off indication for often obscured in layers of jargon and tedious, an on-board experiment. irrelevant detail that conceal the relative simplicity of their principles. We will try here to The practice during the Launch and Early Orbit give a simple explanation of a mission control Phase of a mission has been to operate system’s basic functions, and then make an mission control from control rooms at ESOC, analogy with systems more familiar to the either the Main Control Room (MCR) or layman to help reinforce this. Dedicated Control Rooms (DCRs). These control rooms are equipped with work stations The remarkable increase in the popularity of the Internet, fed by rapid supporting the various displays. It is important expansion of its supporting technology, has led to new ways of doing to note that in this traditional approach, business, as well as revolutionising the entertainment industry. In spacecraft operations activities have always particular, people are beginning to use the Internet for many daily been localised in the MCR or the DCR at ESOC. tasks, such as on-line shopping, on-line banking, booking travel, etc. This simplifies security (i.e. authentication and authorisation of users of the control system). Until recently the world of mission control was a closed one, carried out from control rooms equipped with expensive custom-built Analogies between MCS and other systems. Providing access to mission data from outside this hermetic systems environment was difficult and expensive. The Internet and its From the point of view of the interactive user, a technologies – especially those associated with World Wide Web mission control system has many features in (WWW) browsers – are beginning to change all that. common with commercial Information Technology (IT) systems, such as those for banking, stockbroking and e-commerce. In essence, a Mission Control System (MCS) is Typically these systems have a certain number responsible for monitoring the health of a of ‘screens’ falling into two categories: spacecraft and for controlling it. It may also – Various views of the data the system deals monitor and control elements of the supporting with (e.g. for banking, the statement of ground equipment. It comprises a computer recent transactions on an account; for system connected to one or more ground stockbroking, the current price of a selection stations, which are responsible for com- of shares). These screens correspond to the munication with the spacecraft. Via the ground telemetry displays and telecommand history stations, the MCS receives telemetry data from displays of mission control. the spacecraft, which it uses to monitor the – Those which allow the user to give spacecraft’s health. The MCS controls the instructions to the system (e.g. for banking, spacecraft by sending it telecommands, which to initiate a transfer from an account). These are in effect instructions to the spacecraft. An screens correspond to the interface for MCS thus operates on the same principles as a sending telecommands to a spacecraft (in process control system, in which the process is ESOC terminology, the ‘manual-stack’). monitored via readouts of sensors and controlled via commands to the process. The On-line or Internet banking allows account telemetry data will contain so-called holders to manage their accounts via the World ‘housekeeping’ parameters; typically these are Wide Web (WWW). They need a simple PC with regularly sampled on board to acquire Internet access and a suitable WWW browser. information about the spacecraft’s subsystems. Typically they start the browser, key in the These parameters can contain analogue values, Internet address (Unified Resource Locator: such as battery charges and currents, URL) for their on-line banking service. The user r bulletin 97 — march 1999 bull will have to give security information (e.g. to do this is to automate them, thus reducing account number and password or Personal the amount of manual control needed. Identification Number: PIN) – this corresponds However, it is unlikely that all situations can be to the ‘roles and privileges’ facilities of an MCS. dealt with automatically and spacecraft He/she will then get the on-line banking home specialists may still need to be called out. page that will have hyperlinks in the form of Traditionally the engineer would physically desktop icons to the various services provided. travel to the control centre. Remote access to Each such service will typically have a ‘screen’ mission control data via Internet technology associated with it. The user may then have to could allow more responsive on-call support provide further security information (e.g. to without the engineer having to leave home. Of carry out a cash transfer) and the screen may course, automation technology is also required be a form. The analogy can be carried further. (not the subject of this article). After making cash transfers the user can ask for a list of completed transfers, the analogue of The technologies a telecommand history. In some forms of e- Object orientation commerce, the response to say a purchase Until the early 1990s, most software request, will be provided in the form of an e- engineering (i.e. building of software) was mail. In MCS terms, this is the analogue of a based on the techniques of structural analysis, telecommand report, a feature of ESA’s Packet involving the analysis of data-processing Utilisation Standard (PUS). problems by functional decomposition. In such analyses, data was treated separately from The question is then, if such services can be function. provided to the public at large for such a security-sensitive service as banking, can a Object-oriented methods originated in the similar service be provided to the space data or Simula67 and Smalltalk programming operations community by mission control languages, and the techniques of structured systems? This article sets out to demonstrate analysis, particularly data modelling. Although that the answer is definitely yes. Because of the the approach dates back some 20 years, it has high cost of space missions, it is natural that in only recently become mature to the extent that the past a closed, conservative approach has it is the mainstream paradigm for the 1990s. been taken to the implementation of control Object-oriented methods differ from structured systems. However, the pressures to reduce methods by: costs and the increasing demands of users are – starting development with the identification changing this. Remote access to mission of the objects in the problem domain with control systems is now really needed and we which the software will deal can cite three reasons: – building an object model (rather than a functional model) 1. During certain phases of a mission, support – integrating functions and data into objects, is needed from the spacecraft manufacturer or instead of separating them between the data from payload providers. Traditionally, they have model and the functional model. come to the mission control centre and used facilities there, but it would be cheaper for them Object-oriented methods are supported by a to work from their home bases. number of object-oriented languages, of which C++ and Java are the most well-known. 2. Payload providers need to access the data provided by their on-board experiments and to For reasons for which we do not have space be able to control them. Typically this has been here, object-oriented methods have proved to done via expensive special-to-project Payload have many advantages over the earlier Operations Control Centres (POCCs) or structural ones. In particular, software with rich Science Operations Centres (SOCs), with functionality is made easier to implement dedicated communications links to the mission because of the ability to inherit code. This control centre. The idea of having remote inheritance property also permits easier re- access to payload control from the useability, which can be realised using object experimenter’s home base has been around for libraries (analogous to subroutine libraries in the a long time under the name of ‘telescience’. As older technology) and application frameworks, the number of low-cost missions which cannot which are in effect reusable object-based afford expensive POCCs/SOCs grows, the architectures. pressure to provide genuine telescience increases. The object-oriented paradigm is now leading to a new discipline of component-based software 3. There are great pressures to reduce the cost engineering in association with technologies of operations. For routine operations, one way such as CORBA and DCOM (discussed later). mission control and web technology Client/server work stations and written in different There is no precise consensus in the IT Industry programming languages. It provides location on the meaning of the term ‘client/server’, but transparency in that a client located on any the following ‘definition’ probably captures the work station can access objects located on a most common understanding. In the client/ server, over a network. CORBA is based on server approach, an application is split into a two main concepts: server and a client process. The server process – An Interface Definition Language (IDL) to provides services and the client consumes define object interfaces; these can be them. A server can service many clients at once invoked from any language providing and regulates their access to resources. This CORBA bindings (this includes C, C++ and also means that client/server systems are some versions of Java; see below) usually distributed. However, it is also possible – The Object Request Broker, which is the to localise server and client(s) on one machine.