Section 1.6 - Engineering Tools< Space Transport and Engineering Methods
Space system engineers use a wide variety of tools to do their work. The most important of these is their own knowledge and experience, which we hope this book helps upgrade. The work includes producing designs for a project; then recording the designs and other information in formats that can be shared with other people, or for use by computers and machines as input. For simple or early stage work, some reference books, a scientific calculator, and a pad of graph paper may be all that is needed. For the bulk of the work as done today they typically require a variety of data sources, computer workstations and more powerful supercomputers or networks, and specialized software. When the work gets past design into R&D, prototyping, manufacturing, and test, they often use physical tools and specialized test equipment to measure performance and collect data.
No engineering design can be done without input data of some form. It can be determined internally, but more usually obtained from outside sources. Types of data include:
- Engineering Codes and Standards - These are documents that specify required or accepted methods and features for a design. For example, Building Codes embody accumulated experience in how to design and build safe and sound buildings. Adoption of building codes by governments gives them the force of law - they must be followed. Technical Standards are formal documents that establish uniform and accepted engineering criteria to be followed. For example ASTM Standards for the composition and strength of steel do not have the force of law of themselves, but allow steel suppliers and engineers to work together because both know what is expected from a given alloy grade. Standards may be incorporated by reference in laws, regulations, or contracts. Large engineering organizations may develop their own internal design standards based on their experience, so that more consistent results are obtained and new staff can be trained.
- Handbooks, Textbooks, Monographs, and Journals - Handbooks are compilations of useful information in a particular engineering field. They are often written by multiple contributors and updated periodically. An example is the Handbook of Space Technology. For students, handbooks are often quite expensive, so it is suggested to find them used or in a library collection. Textbooks are intended to teach a subject, like this Wikibook. Monograph means "one writer", books written by one or a few authors. They are typically about advanced topics, primary research, or original scholarship. Journals are periodical publications containing shorter articles than monographs, reporting new research or reviewing the state of the art. There are a vast number of books and journals covering every engineering topic, so it is impractical for an individual to collect them unless for a very narrow specialty. A good technical library can provide access to all these works.
- Supplier Data - One of the basic rules of efficient design is to not repeat a design if someone else already has. Many designs will incorporate parts or subsystems that already exist and are made by someone else. The suppliers of such items have literature and documentation about what they supply, and often will consult about the use of their products.
- Online Data Sources - A huge amount of data is online these days, but the quality is variable. Since incorrect data can lead to space systems failing, these data sources should be carefully selected for quality. Online data also changes quickly, so any links we give would soon be out of date. A good approach is to use a search engine, and understand how to define the search terms to get a specific result.
Historically engineers worked at large drawing tables or desks where they could produce the drawings and documents that represented a design. Such methods have been largely replaced by computer workstations for several reasons. Computer systems can communicate changes much faster than paper-based methods. They can represent designs in three dimensions, which was difficult on two-dimensional paper. And finally, computers can perform analysis and simulation of a design vastly better than hand methods. At one point mainframes and engineering workstations were specialized and expensive equipment. Today a basic workstation may be no different in hardware than an ordinary desktop computer, although more powerful computers are still used for intensive calculations. Just as important as the workstation hardware is the specialized software which runs on them, and the networks which connect them to each other, to production and test areas, and the outside world.
- Workstations - Today an engineering workstation is merely an ordinary computer of sufficient specifications to run engineering software or to remotely access higher performance clusters. The higher end ones may have two or more processor chips, each with 6 or more CPU cores each. They can also include up to 4 graphics or parallel compute add-on cards based on graphics technology. These are used for massively parallel calculations. Typically multiple large monitors are used, and relatively large amounts of memory and hard drive storage. More moderate workstations will have specifications similar to modern gaming systems, because game graphics and engineering computations both rely on making large numbers of calculations. Even relatively powerful workstations are not expensive relative to an engineer's salary (the software they run is a different matter), so the choice of hardware will be driven more by ability to run the needed software than by cost.
- Storage Servers - When working on complex projects, the amount of data involved can exceed what can be stored on individual workstations, and backups should be made in case of accidental deletion or hardware failure. A storage server's main job is store the extra data where it can be accessed by anyone on the project team who needs it. That would include a history of older versions of the design, and test and simulation data, which can be voluminous.
- High Performance Clusters - Some types of engineering calculations require more speed than can be reasonably installed in an individual workstation. High performance clusters, or Supercomputers as they are also called, group many computer chips into racks with high speed data connections between them. They run specialized software designed to make use of this hardware, and the fastest such clusters represent the most powerful single computers in existence. When the the need for high speed transfer between cores is not as great, the Distributed Computing method can be used. This harnesses a network larger single computers, or the excess computing power of a number of workstations, either off-shift or by using whatever extra processing ability is not needed by the primary user of the workstation.
- Computer Networks - Networks are almost universally used in modern engineering to transfer data both within a project and with the rest of the world. Since installing a network is like adding new utilities to a building, forethought should be given to making it easy to upgrade, and putting in enough network capacity that it does not need to be upgraded too often. Networking protocols and hardware change constantly like most computer-related things. Currently the most common method uses the Internet Protocol and routers. The protocol defines how addresses for each destination and data packets to be sent are constructed. Routers are the devices which look at the address on a packet, and send it towards the destination. There are many methods of transmitting the data between locations, ranging from Ethernet, to fiber, to wireless. In some cases it is faster and cheaper to send large amounts of data in the form of tapes or hard drives, because of their enormous storage capacity in a small package.
As mentioned above, engineers typically use specialized software to help with their work. The particular software will vary according the task being done. Software usually evolves rapidly, so we will discuss it in terms of categories and give some examples. If working on an actual project, a designer should find out what is the best software and most up-to-date versions available at the time. In some cases, no existing software is completely suitable, and modified or completely new software would be needed.
Analysis and Simulation SoftwareEdit
Historically numerical analysis relied on manual methods with devices like slide rules and tables of performance. With the advent of digital computers, special purpose programs were written in mathematically oriented languages such as FORTRAN. These performed calculations much faster than by hand, but were still limited. The processing speed and memory capacity of early computers limited the complexity of the mathematical models and how many calculations could be performed in a reasonable time. The fastest available processors in 2016, which have evolved from mainframes to supercomputers with many parallel cores, are up to a 30 billion times faster than mainframes from 50 years earlier. Desktop workstations are millions times faster than 50 year old mainframes. So the mathematical models of a design can be much more detailed and smaller time steps or more iterations of the analysis can be run. Parametric analysis allows varying parameters of the design or simulated conditions over a range of values. Since this requires multiple runs of the calculations, they have become more feasible with faster computers.
What started as individual special purpose programs is evolving into integrated general purpose suites. This reduces the need for re-entry of model data. Often the data can be used directly from the original design software, or the analysis results can be fed back to the design program directly. For some projects, custom software may still be needed where general purpose software is not adequate.
- Numerical Analysis - This category includes spreadsheets (for simpler analysis), general numerical calculators, such as Mathworks MATLAB for more complex analysis, computer algebra software, such as Wolfram Software's Mathematica or Maplesoft's Maple for symbolic problems, and more specialized programs written for particular fields. A more detailed list of Numerical Analysis Software can be found on Wikipedia.
- Simulation - This software category analyzes the behavior of a design with respect to time or changing conditions. They can cover a single type of behavior, such as mechanical stress, or multiple ones, which are called Multiphysics tools. These can do multiple analyses in series from the same source model, or in some cases a combined effects analysis all at once. A detailed list of Simulation Software can also be found on Wikipedia.
- Multiple Programs
NASA Open Source Software - Repository of 240 software projects.
Public Domain Aeronautical Software - Website with many downloads of programs, source code, and documentation.
Aerospace Software Tool Library - A list of links to commercial, government, and free software, sorted by category.
- Aircraft Design
CEASIOM - Software package for airplane design. Download with registration.
- Space Simulators
Space Engine 0.9.7.2 - Space simulation software.
Celestia 1.6.1 - A 3D space simulator which can be used as a planetarium or for mission visualization.
- - Celestia Motherlode - A collection of add-ons for Celestia.
- - Celestia Wikibook - An online guide to the Celestia software.
Design and Manufacturing SoftwareEdit
These are the modern replacement for drafting tables. They include 2D and 3D drafting, 3D modeling, and illustration programs, and software to feed manufacturing data direct to factory machines or to vendors. Modern graphics cards and processors allow direct visualization and manipulation of the design in real or near real time. As noted above, the design and analysis software categories are becoming more integrated. Design category is also called Computer-Aided Design (CAD). When use of computer workstations and mainframes was new, the phrase distinguished it from the traditional drafting on paper type of design. Today design on paper is a rarity, so saying it is done with computers is mostly redundant. We group the types of software below in terms of function: drawing, modeling, and production.
2D and 3D DraftingEdit
This category produces a set of drawings, which in turn consist of a set of lines, curves, and text or attached notes. They are distinguished from 3D models by the drawing elements existing independent of each other, and not forming more complex entities with attached non-drawing properties. Nowadays only lower-tier software such as AutoCAD LT or [Solid Edge 2D is restricted to 2D.
This category defines the three dimensional shape of an object in terms of a linked set of points, lines, curves, surfaces, or volumes. In addition to the shape, a wide range of other parameters may be associated with the object. Primitives, basic shapes such as boxes, cylinders, or spheres, often are used as starting points, and then various operations are performed to modify or join them into more complex shapes. Wikipedia has an extensive list of 3D Modeling Software A few examples are:
- Autodesk Products - Originally developer of Autocad, a 2D drawing program, this company, through acquisitions and development of new software, now has a vast range of overlapping and linked products. The tendency is to offer more integrated suites of compatible programs rather than individual ones.
- Solidworks suite by Dassault Systemes. - This is a high end commercial software set for design, simulation, and data management.
- FreeCAD is an open source 3D modeling program.
Modern factories use extensive computer control for their operation, which in turn requires software to control the equipment. As each factory is different, the software is often customized for a given application. Computer Numerical Control (CNC) is the name for the machine category controlled this way. This was to distinguish it from the earlier manual control of factory equipment, and the intermediate numerical control, via stored commands, but without a computer. Computer-aided Manufacturing (CAM) is the process of using these kinds of machines, and the software category for producing commands and controlling the machines. Wikipedia has a very large list of Computer-aided Technology companies and software projects.
Software Development SoftwareEdit
These are tools to help make software. Many end products today require sensors, data transfer, and internal decision making and control which requires custom software to operate. Naturally enough, such software is developed on computers, using Integrated Development Environments (IDE) such as the Microsoft Visual Studio suite. When such software runs inside hardware other than computers, special test rigs and test software may be required to test the target software, and how it functions with the intended hardware. For example, a surface rover being sent to Mars is a unique item. So extensive testing would be done with software simulation and prototypes before installing it on the flight unit.
Planning and Management SoftwareEdit
Complex projects have to track more than just the engineering design. They have to coordinate the work of many people, do advance planning, track production and costs, etc. Project Management Software is designed to help with these tasks. Both project management and documentation tasks can use general office software suites, such as Microsoft Office, which has a compatible Project program. A given project can also use specialized programs for accounting, scheduling, inventory tracking, etc. Wikipedia has a very extensive list comparing various Project Management Software packages. There are very many other pieces of business software available. Strong consideration should be given to compatibility between programs, so that data may be moved easily between them, rather than having to convert or re-enter data.
This category is used to record all the data created in a project so it can be found, shared, updated, and used.
Instrumentation and Test HardwareEdit
Physical instruments and test equipment can be grouped into two categories: Those used in common with other industries, and those unique to space systems
Common Instrumentation and Test EquipmentEdit
Space systems projects use many of the same items as other industries to test, measure, and inspect during manufacturing, assembly, and test. Amazon's website has a large listing in that category, but there are many other sources for instrumentation and test equipment. Categories include calibration, dimensional measurements, electrical, electronics, and software testing; motion, speed, and forces; pressure and temperature, airflow and air quality, inspection and testing, light, network and cables, recording and data acquisition, weight, sound, and surface and hardness. The modern trend is to use equipment that directly feeds computer data storage, so that manual recording of data isn't necessary. Common tools, such as wrenches to remove an inspection panel, are also used, but normally those are available from production areas and don't need to be specially provided.
Special Test EquipmentEdit
Space hardware is typically exposed to two special environments. The first is launch on a rocket, followed by the conditions in space. To make sure the hardware will work properly, the hardware is subjected to a number of tests to simulate these environments. These tests require special test chambers to reproduce the conditions. Commonly used ones include:
- Acoustic Chamber - Rocket engines emit high pressure gas through a constriction, the engine throat, and therefore function like a whistle or organ pipe, generating huge amounts of sound and vibration. The sound portion is tested in an acoustic chamber with powerful speakers, which play a noise spectrum matched to the launch vehicle the hardware will ride on.
- Shaker Table - The high speed flow from the rocket engines, and air flowing past the rocket in flight is turbulent, generating physical vibration in the vehicle. This is distinguished from sound that travels through air. Vibration is simulated by a table that holds the hardware the same way it is held for launch. The table is moved in all directions with powerful pistons, springs, and unbalanced masses, to reproduce the levels the space hardware will experience.
- Zero-G Deployment - Spacecraft often have solar panels, antennas, and other items that are folded to fit in the payload space of a rocket, then unfolded once in space. The unfolding happens in zero gravity, and this is simulated by doing it sideways, with counterweights to remove the weight from the joints and mechanisms.
- RF Chamber - Most spacecraft communicate through radio frequencies (RF) and antennae. Antenna operation and links to the rest of the spacecraft are tested in am RF-shielded chamber and separate transmitters that simulate ground stations.
- Thermal-Vacuum Chamber - The space environment is usually in vacuum. Hardware is subjected to cold from the cosmic background near absolute zero, and heat from the Sun, which is more intense above the atmosphere, or if the mission goes closer than Earth to the Sun. Since vacuum does not allow heat transfer by conduction through the air, different sides of a spacecraft can be hot and cold at the same time. These conditions are tested in a large vacuum chamber, which is provided with cooled walls and intense lamps to simulate the cold and heat conditions.
Beyond these devices, which are commonly used for whole spacecraft, special purpose equipment may be needed for particular instruments. For example, the Chandra X-Ray Telescope needed a 300 meter vacuum tunnel to test the X-Ray optics from an optically distant source.