Astrogate Labs GNC Engineer Interview: Rounds, Questions and Preparation

What the job involves

A GNC (Guidance, Navigation and Control) engineer in space and defence tech designs and tests the systems that determine where a satellite or vehicle is, where it needs to go, and how to steer it there. Day to day work includes building and tuning control loops, running simulations of orbital mechanics and attitude dynamics, processing sensor data, and validating algorithms against hardware-in-the-loop test benches. At smaller or fast-growing companies, you may also support mission design, integration testing, and on-orbit anomaly investigation.

Role and Technical Knowledge

1. 1

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

   A strong answer separates navigation (estimating state from sensors), guidance (computing the desired path or attitude), and control (actuating to track that path). Use a concrete example like orbit raising or attitude slew.

2. 2

   What is a Kalman filter and why is it used in satellite navigation?

   Cover the predict-update cycle, handling noisy sensor data, and fusing inputs like star trackers, gyros, and GPS. Mention process and measurement noise covariance tuning.

3. 3

   Describe how you would design a PID controller for satellite attitude control.

   Discuss plant modelling, choosing gains for rise time and overshoot, and practical limits like actuator saturation and sensor noise. Mention simulation and iterative tuning.

4. 4

   What are Euler angles, quaternions, and rotation matrices, and when would you use each?

   Explain that Euler angles are intuitive but suffer gimbal lock, quaternions avoid singularities and are preferred for onboard attitude, and rotation matrices are useful for frame transformations.

Practical Scenarios and Problem Solving

1. 5

   Your satellite's attitude is drifting slowly despite the controller commanding zero rate. How would you debug this?

   A strong answer checks sensor bias or misalignment, actuator disturbance torques, control loop integrator windup, and frame conversion errors. Suggest isolating each subsystem with test data or simulation.

2. 6

   How would you simulate a reaction wheel failure and assess its impact on a small satellite mission?

   Describe modelling the wheel as a torque source, removing it in simulation, and checking controllability with remaining actuators. Discuss safe modes, desaturation options, and mission timeline effects.

3. 7

   You need to validate a GNC algorithm before launch. What steps would you take?

   Cover model-in-the-loop, software-in-the-loop, and hardware-in-the-loop testing, plus Monte Carlo runs for robustness. Mention regression tests and verification against analytical cases.

4. 8

   Given a ground station pass of only 10 minutes, how would you plan a navigation filter update?

   Discuss prioritizing measurements, using a robust filter update, and handling latency and data gaps. Mention pre-pass preparation and post-pass covariance checks.

Behavioural and Teamwork

1. 9

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

   Use a specific story with the situation, action, and result. Highlight self-learning, resourcefulness, and how you applied the new skill to deliver.

2. 10

   Describe a situation where your analysis or simulation result was challenged by a teammate.

   Show openness to feedback, how you verified assumptions or data, and how you resolved the disagreement with evidence rather than ego.

3. 11

   How do you handle tight deadlines when a test campaign is delayed?

   Focus on prioritization, clear communication, and risk-based trade-offs. Mention keeping stakeholders informed and documenting decisions.

4. 12

   Why do you want to work in a small, fast-growing space and defence company rather than a large organisation?

   Connect to broad ownership, fast iteration, and direct mission impact. Show awareness of the sector's constraints like export controls and reliability demands.

HR and Sector Motivation

1. 13

   What do you know about the current Indian space and defence tech ecosystem?

   Mention private launch and satellite companies, IN-SPACe reforms, and demand for indigenous GNC solutions. Show genuine curiosity about the sector's growth.

2. 14

   Where do you see yourself in three years in a GNC role?

   Align growth with deeper technical ownership, leading a subsystem, or mentoring. Keep it realistic and tied to the company's mission.

3. 15

   Are you comfortable with the documentation and review processes common in defence and space projects?

   Acknowledge the need for rigour, traceability, and peer reviews. Give an example of following a process carefully without slowing the team down.

4. 16

   What are your salary expectations for this role?

   Research typical fresher GNC salaries in Indian space tech, give a reasonable range, and express flexibility based on learning and growth opportunities.