Natalya Bailey: Rocket Engines and Electric Spacecraft Propulsion | Lex Fridman Podcast #157

Lex Fridman talks with Natalya Bailey about how spacecraft move once they're already in space, contrasting chemical rockets with electric propulsion. She explains her company's colloid (ion electrospray) thrusters, which pull ions from ionic liquids using tiny nanoscale cones formed in strong electric fields. The conversation ranges across the search for alien life, the case for nuclear power in space, satellite size trends and collision avoidance, propellantless propulsion concepts like the debunked EM drive, and Breakthrough Starshot. It closes with startup-building lessons, her favorite books, and reflections on the meaning of life as the pursuit and preservation of knowledge.

• Bailey suggests trees may be more intelligent than humans, operating on a time scale we are too dumb to appreciate.
  00:07:20
• She questions whether humans should even leave Earth, calling us finicky biological things possibly best replaced by robotic or silicon-based exploration.
  00:11:33
• She states the ISS is being decommissioned, expecting it out of use by around 2025.
  00:15:41
• She argues power supplies, not engines, are the real limit, and pushes nuclear power as the key to powerful electric propulsion.
  00:38:44
• She names the EM drive as a propellantless engine that was effectively debunked after a NASA test produced thrust even when flipped backwards.
  00:56:53
• She reveals ion engines historically cost $20-25 million but customers now expect to pay around $10k.
  01:06:48
• Accion's name comes from accio, the Harry Potter summoning charm, with an n added, not just accelerate plus ion.
  01:26:05
• She admits company culture isn't chosen but oozes out of who the founders are, requiring real introspection.
  01:18:46

• All rocket propulsion relies on conservation of momentum: throw mass out the back, spacecraft goes forward.
  00:16:14
• Chemical propulsion is essentially a firework and has been around since roughly 400 BC.
  00:18:51
• Ion engines collide hot electrons with neutral gas like xenon or argon to create plasma, then accelerate ions through charged grids.
  00:23:31
• In a colloid thruster a liquid forms a Taylor-like cone when electric pressure balances surface tension, emitting ions from the tip.
  00:28:14
• The ion-emitting region of a cone is only about 20 nanometers across, which is why the tech only became feasible recently.
  00:29:46
• Accion's thruster chip is one square centimeter holding about 500 emitter cones, with plans to increase density fourfold.
  00:31:51
• Dead geosynchronous satellites at ~40,000 km are pushed to a graveyard orbit where natural deorbit takes about a million years.
  00:44:23
• Some small satellites perform around three collision-avoidance maneuvers per year, mostly planned manually, not autonomously.
  00:45:25
• The same equation describing airflow over an airfoil also prices options via the Black-Scholes equation.
  00:36:38
• Breakthrough Starshot aims to laser-accelerate tiny chip spacecraft to reach Proxima Centauri in about 20 years.
  00:59:30