Structural Engineer interview prep

What the job involves

Structural engineers in space and defence tech design and analyse load-bearing structures for satellites, launch vehicles, radar systems, and ground support equipment. They ensure these structures withstand extreme loads such as launch vibrations, thermal cycling, and shock while meeting strict weight and reliability targets. Day to day work includes CAD modelling, finite element analysis, material selection, and preparing qualification test plans.

Role and sector knowledge

1. 1

   What are the typical loads a satellite structure must withstand during launch?

   Cover quasi-static acceleration, random vibration, acoustic, shock, and thermal loads. Mention that these come from the launch vehicle and must be qualified through testing.

2. 2

   Why is weight reduction critical in space structures, and how do you achieve it without compromising strength?

   Explain the cost per kilogram to orbit, use of high specific strength materials like aluminium alloys and composites, and design optimisation such as honeycomb panels and topology optimisation.

3. 3

   What is the difference between a qualification test and an acceptance test for a defence or space component?

   Qualification test proves the design meets requirements and is often destructive or at higher levels. Acceptance test verifies workmanship and is non-destructive, done on every flight unit.

4. 4

   How do thermal loads affect structural design in spacecraft?

   Discuss thermal expansion mismatch, induced stresses, and the need for materials with low coefficient of thermal expansion. Mention thermal cycling causing fatigue and the use of thermal isolators.

Technical fundamentals

1. 5

   Explain the difference between static and dynamic analysis in the context of a launch vehicle adapter.

   Static analysis assumes loads are constant or slowly applied, while dynamic analysis considers time-varying loads, inertia, and damping. For a launch vehicle adapter, dynamic analysis is crucial for vibration and shock response.

2. 6

   What is modal analysis and why is it important for space structures?

   Modal analysis finds natural frequencies and mode shapes. It helps avoid resonance with launch vehicle excitation and ensures the structure does not amplify vibrations excessively.

3. 7

   How do you decide between using aluminium, titanium, or carbon fibre composite for a structural bracket?

   Compare specific strength, stiffness, thermal expansion, cost, manufacturability, and galvanic corrosion risk. Aluminium is common for general use, titanium for high temperature, and composites for high stiffness-to-weight.

4. 8

   What is buckling, and how do you prevent it in thin-walled cylindrical shells?

   Buckling is instability under compressive loads. Prevention includes adding stiffeners, increasing thickness, using sandwich construction, and performing nonlinear buckling analysis.

Practical scenarios and problem solving

1. 9

   Your FEA results show a stress concentration at a bolt hole in a satellite panel. How do you address it?

   Suggest local thickening, adding a doubler, increasing edge distance, using a larger washer, or changing the bolt pattern. Also verify with hand calculations and consider fatigue.

2. 10

   A component fails during vibration testing. What steps do you take to diagnose and fix the issue?

   Review test data to identify the failure mode, check for resonance, inspect the failed part, and propose design changes such as adding damping, stiffening, or changing material. Then re-test.

3. 11

   How would you design a lightweight support structure for a radar antenna on a moving vehicle?

   Consider dynamic loads from vehicle motion, wind, and vibration. Use a stiff, damped structure, possibly a truss, with materials like aluminium or composites. Perform dynamic analysis and ensure pointing accuracy.

4. 12

   You need to reduce the mass of an existing bracket by 20 percent without reducing strength. What is your approach?

   Start with topology optimisation, then size and shape optimisation. Consider replacing material with a higher specific strength one. Validate with FEA and ensure safety factors are met.

Behavioural and HR questions

1. 13

   Why do you want to work in the space and defence sector rather than a commercial automotive or consumer product company?

   Show passion for national security or space exploration, mention the challenge of extreme environments, and highlight the satisfaction of contributing to critical missions.

2. 14

   Describe a time when you worked in a team to complete a complex engineering project. What was your role?

   Use the STAR method. Emphasise collaboration, your specific contribution, and how you overcame a technical or coordination challenge.

3. 15

   How do you handle tight deadlines when you have multiple design iterations to complete?

   Talk about prioritisation, breaking tasks into smaller milestones, using tools like FEA efficiently, and communicating proactively with stakeholders.

4. 16

   Are you comfortable working on projects that require strict confidentiality and may involve defence secrets?

   Answer affirmatively, show understanding of security protocols, and mention your ability to maintain discretion and follow procedures.