By now, the detailed system design has been finalized. Some elements of the system have been prototyped and subjected to some tests as part of the iterative development process. In this phase, the fabrication of the flight model of the system is carried out. Followed by this, the system is integrated and then subjected to system-level tests before clearing it for launch.
Procurement of Materials
The best materials would have been decided as per the requirements but it is essential to have a look at the ease of procuring them. While choosing vendors for procuring them, one may realize that everything is not available in the vicinity. Some common materials like aluminium or stainless steel can be easily bought from a local vendor. But as materials become more and more exclusive for space usage, it might be difficult to get a certain material. For example, if one wants to procure good quality solar panels for CubeSats, one might have to import them. In this case, one has to look at any restrictions while importing them. There might be some import duties, large shipping costs or any special permissions which should be taken care of.
There will always be a tradeoff associated with quality and cost. It is up to the team to make decisions. But as the margin of error is very less in space systems, quality is given higher priority almost all the time.
Since a manufacturing plan is ready, one can start looking out for manufacturers parallelly while procuring materials. To manufacture different parts, different processes need to be employed. So, manufacturers should be chosen accordingly as there is a low possibility that a single manufacturer can cater to all our requirements. The tolerances must be decided, and a check should be performed with the manufacturers whether the manufacturing can be done in accordance with it or not. Further, manufacturability of all the parts needs to be checked with the manufacturer. The design files need to be verified with manufacturers. Certain recommendations might be received from the manufacturer like the addition of fillet or chamfers at the edges to the parts. Once the things mentioned above have been completed, the parts of the system are manufactured. Post manufacturing, a check should be done to see if the parts are manufactured as per the requirements.
For space systems, usually, two models are manufactured -
- Flight Model - This is the model which is launched into space and implements the mission. The flight model is subjected to specific tests before the launch.
- Qualification Model - It is a replica of the flight model, which is used for qualifying the space system before the actual flight model is made. The qualification model is passed through more rigorous tests than the flight model to check if the system design is appropriate to be launched into space. If not, the faults in the system are identified and the required changes are made.
Integration is one of the main aspects of satellite design and engineering. It’s quite complex as numerous electrical, mechanical components work together to achieve a challenging objective. Understanding of the system plays a key role in designing an efficient and easier way to integrate the components, functions, subsystems into a full-fledged system and to ensure functional integrity. Functional tests are done prior to integration to check that the components work when assembled together. Documentation is necessary to show that every single component, nut, bolt, wire is compatible with space flight and assembled using proper procedures. Integration and testing often go simultaneously. It is very necessary to draft an integration sequence based on various integration practices. Real or prototyped hardware must be used for practicing the integration.
The integration of a satellite depends on various factors, one of them being configuration or system design. While drafting the integration of the system, mechanical ground support is another important aspect. Design and manufacturing of numerous assembly fixtures needs to be done for the same. Fixtures assist in the integration process and are majorly used to hold or rotate some parts so that contact is prevented. Some of the general fixtures include subsystem integration fixtures, system integration fixtures, handling fixtures, clamps, transportation box.
Testing is a sequential process to verify whether the components, subsystem and the system function and meet the mission requirements. It is done to identify unanticipated interactions of various components and between subsystems, failure modes and recovery procedures for the same, human errors. The main objective of testing is to try and create the actual environment the system will experience in space or during launch.
Various terminology used in testing:
- Component level testing- Tests performed on individual components which assemble together to form parts of the subsystem. (E.g: Solar panel)
- Subsystem level testing- Tests performed on subsystems which are formed by assembly of components. (E.g: Communication subsystem)
- System level testing- Tests conducted on the entire satellite/ space system which is formed after integration of all subsystems.
- Qualification testing- Tests are performed to show that the design, manufacturing, testing, functions, meet the mission requirements. These tests are performed on the Qualification Model (QM). The boundary conditions applied in these tests are severe and do exceed the design safety parameters than the actual scenario to check the sustainability of the system.
- Acceptance testing- These tests are performed on the complete integrated system to be sent in orbit. The objective of these tests is for quality assurance of materials, parts and possible errors in integration along with the specific requirements of the system. However, these test limits are moderate and do not exceed the design safety parameters causing failures in the system.
Once the various tests have been performed on the QM and FM, celebrate! Because your satellite is now ready to be launched.
If you are done reading this page, you can go back to Starting a Student Satellite Project.