Sievert Larsen India GNC Engineer Interview: Rounds, Questions and Preparation

What the job involves

A GNC (Guidance, Navigation and Control) engineer designs and tests algorithms that help spacecraft, launch vehicles or defence systems determine where they are, where they need to go, and how to steer there safely. In a fast-growing space and defence company, you may work on attitude determination, trajectory optimisation, sensor fusion, and simulation-based validation for missions or missile systems. Daily work involves MATLAB/Simulink or Python modelling, hardware-in-the-loop testing, and close coordination with avionics and systems teams.

Role and technical knowledge

1. 1

   Explain the difference between guidance, navigation, and control in a spacecraft mission.

   Guidance computes the desired path or attitude, navigation estimates the current state from sensors, and control generates actuator commands to reduce the error. Use a concrete example like a satellite orbit transfer.

2. 2

   How do you represent attitude, and why are quaternions often preferred over Euler angles?

   Cover Euler angles, rotation matrices, and quaternions. Mention gimbal lock and computational efficiency as reasons for quaternion preference in real-time GNC.

3. 3

   Describe the working of a Kalman filter for a spacecraft attitude estimation problem.

   Explain predict and update steps, process and measurement noise covariance, and how gyro and star tracker data are fused. Mention extended or unscented Kalman filter for nonlinear cases.

4. 4

   What are the key considerations when designing a control law for a launch vehicle during ascent?

   Discuss actuator saturation, flexible body dynamics, wind disturbances, and gain scheduling. Mention stability margins and time-varying plant dynamics.

Practical scenarios

1. 5

   Your simulated spacecraft is drifting away from the target orbit. How would you debug the GNC software?

   Check sensor inputs, estimator convergence, guidance law parameters, and actuator commands in that order. Suggest logging intermediate states and comparing against a reference trajectory.

2. 6

   You need to test a new attitude control algorithm on hardware-in-the-loop. What steps would you follow?

   Outline model-in-the-loop, software-in-the-loop, then HIL with real flight computer and simulated sensors. Mention real-time constraints, interface checks, and failure injection.

3. 7

   How would you handle a star tracker outage during a critical mission phase?

   Propose using gyro propagation and other sensors like sun sensors or magnetometers for a safe mode. Discuss fault detection, isolation, and reversion logic.

4. 8

   A defence customer wants a missile guidance law that is robust to target manoeuvres. What approach would you take?

   Consider proportional navigation or augmented PN, and mention estimation of target acceleration. Discuss trade-offs between agility, accuracy, and control effort.

Behavioural and situational

1. 9

   Tell me about a time you had to learn a new tool or concept quickly for a project.

   Use STAR format. Highlight self-learning, resourcefulness, and how you applied the new skill to deliver a result.

2. 10

   Describe a situation where you found a bug in your own or a teammate's work. How did you handle it?

   Show ownership, systematic debugging, and communication. Emphasise verification and learning from the mistake.

3. 11

   How would you explain a complex GNC concept to a non-technical stakeholder?

   Demonstrate clarity, use analogies, and focus on impact rather than equations. Show you can adapt communication style.

4. 12

   Why do you want to work in space and defence tech, and how do you handle the responsibility that comes with it?

   Connect personal motivation to national or global impact. Mention attention to detail, safety culture, and willingness to follow rigorous processes.

HR and company fit

1. 13

   What do you know about our company and why does it interest you?

   Research the company's projects, technology stack, and recent achievements. Link your skills to their work without claiming inside knowledge.

2. 14

   Where do you see yourself in three to five years in a growing space and defence company?

   Show ambition to deepen technical expertise and take ownership of subsystems. Mention interest in end-to-end mission lifecycles.

3. 15

   Are you comfortable working on defence projects that may require security clearances and strict confidentiality?

   Express willingness to follow security protocols, maintain confidentiality, and undergo clearance processes. Show maturity and integrity.

4. 16

   How do you prioritise when multiple mission-critical tasks are due at the same time?

   Describe a method like impact vs urgency, communication with team leads, and risk mitigation. Give a brief example if possible.