Relativity Space Interview Flashcards

What is the Tsiolkovsky rocket equation?

Δv = Isp g0 ln(m0 / mf) — relates a rocket's velocity change to its propellant mass and specific impulse.

Define specific impulse.

Specific impulse (Isp) is thrust per unit mass flow rate of propellant, divided by gravity. Isp = F / (ṁ * g0), in seconds.

Write the rocket thrust equation.

F = ṁ ve + (Pe - Pa) Ae — thrust from momentum and pressure differences.

What are the main differences between pressure-fed and pump-fed systems?

Pressure-fed: simpler, heavier tanks, lower performance. Pump-fed: more complex, higher thrust, lighter tanks.

What is a typical LOX/methane mixture ratio?

Approximately 3.5:1 oxidizer to fuel by mass.

What happens if a nozzle is over-expanded at sea level?

The exit pressure is too low, leading to potential flow separation and instability.

How does increasing chamber pressure affect engine performance?

Increases thrust and Isp, but also increases thermal and structural loads.

What is cavitation in a turbopump?

Formation and collapse of vapor bubbles in low-pressure areas, damaging the pump.

What is blowdown vs. regulated feed?

Blowdown: tank pressure drops over time. Regulated: uses regulators to maintain constant feed pressure.

Why is helium commonly used as a pressurant?

It's inert, light, and remains gaseous over wide temperature/pressure ranges.

What are the benefits of additive manufacturing for propulsion hardware?

Fewer parts, complex geometries, integrated cooling, faster iteration.

What inspection methods are used for 3D printed rocket parts?

CT scanning, dye penetrant, pressure testing, and destructive sample testing.

How do you handle a propellant leak during a test?

Safe the system, evacuate if needed, locate and identify the leak, repair, and retest.

You see signs of combustion instability. What do you check?

Injector pattern, chamber acoustics, pressure data, dampers or baffles.

How would you size an engine for 20 kN sea level thrust, Isp = 330 s?

ṁ = F / (g0 Isp) = 20,000 / (9.81 330) ≈ 6.17 kg/s.

How does 3D printing affect propulsion system design decisions?

Enables integrated components, optimized structures, and faster prototyping.