Bailey, Natalya

spacecraft propulsion engineer; former MIT researcher; founder and CTO of Accion Systems

Natalya Bailey: Rocket Engines and Electric Spacecraft Propulsion

Lex Fridman Podcast · Feb 1, 2021

• Natalya Bailey
• Accion Systems
• ion propulsion
• colloid electrospray thrusters
• chemical versus electric propulsion
• Drake equation
• small satellites and space debris
• nuclear propulsion
• EM Drive debunking
• Breakthrough Starshot
• startup culture and vision
• meaning as pursuit of knowledge

Core ideas

Bailey opens with reflections on the Drake equation and the likelihood of extraterrestrial life, expressing more confidence in the existence of basic life than intelligent life, and entertaining Lex's speculative idea that a sufficiently advanced civilization's "signal" might not be a broadcast at all but something structural, like the very tendency of intelligent life to ask whether it's alone. She is candid about an unusual view within her field: she questions whether humans, as "finicky biological things," are actually well-suited to deep space exploration compared to robotic or AI-driven missions (potentially carrying only preserved DNA or stem cells rather than living crews), framing this less as pessimism than as a recognition that removing the human-survival constraint could let exploration go much farther, though she personally once wanted to be an astronaut specifically to do research aboard the ISS.

The technical core of the conversation is a detailed explanation of rocket propulsion. Bailey distinguishes chemical propulsion (well-understood since antiquity in principle, used for launch, high instantaneous thrust but fuel-inefficient, with remaining open questions mainly around modeling the exact products of combustion) from electric propulsion (much more fuel-efficient but comparatively poorly understood, used once a spacecraft is already in orbit for station-keeping, collision avoidance, and maneuvering). Within electric propulsion, she details ion engines (which ionize a neutral gas like xenon via collision with high-energy electrons, then accelerate the resulting ions through a grid-generated electric field, requiring an external electron source to neutralize the beam and keep the spacecraft charge-neutral) and Hall thrusters, before explaining her own specialty: colloid (ion-electrospray) thrusters. These extract ions directly from an ionic liquid rather than a gas, by applying a strong electric field that first shapes the liquid into a cone (balancing electric field pressure against surface tension) and then, at the cone's tip — where the radius of curvature approaches zero and field strength spikes — pulls a jet of pure ions directly from the liquid at a scale of roughly 20 nanometers. She describes Accion's engineering approach: manufacturing chip-sized arrays (currently around 500 micro-emitters per square centimeter, with plans to roughly quadruple the density) using silicon MEMS fabrication techniques borrowed from the semiconductor industry, which lowered costs enough to make this decades-old theoretical concept (first proposed mid-20th century but unmanufacturable until modern lithography) commercially viable — contrasting this batch-manufacturable approach with the historical norm of a single expert hand-building "bespoke" ion engines over decades.

Bailey discusses genuine open scientific questions in her field, particularly the gap between molecular-scale ion behavior (how individual large ions absorb energy from the field, sometimes fragmenting) and observed beam-level performance, noting Accion's focus as a startup is building and characterizing rather than resolving underlying theory. She is drawn to how deeply engineering problems in her domain — capillary action moving liquid to emitter tips, wetting and surface energies — repeatedly lead back to unresolved material science questions at nanometer and quantum scales, and finds a kind of Platonic delight in mathematical connections across unrelated domains (citing the shared use of the same partial differential equation in airfoil aerodynamics and the Black-Scholes options-pricing model). She covers practical space-industry topics: the tradeoffs and cluttering risks of "geo" graveyard orbits versus low-Earth-orbit deorbiting, the rise of small and even shoebox/softball-sized satellites enabled by Moore's-law-driven miniaturization (though optical imaging satellites are constrained by aperture size, which does not shrink the same way), the growing collision-avoidance burden facing large satellite constellations (several planned maneuvers per year for some small satellites, still largely non-autonomous), and her skepticism about near-term nuclear-powered rocket propulsion given both technical bulk constraints and political/safety concerns, despite the efficiency gains it could unlock (contrasting this with battery and solar power limitations she considers a genuine long-term bottleneck for higher-power electric propulsion).

On more speculative propulsion, Bailey discusses the appeal of hypothetical "propellantless" propulsion (mentioning the Casimir effect as one legitimate-seeming physical phenomenon that might someday be harnessed) and recounts the recent (as of the interview) debunking of the "EM Drive," where a NASA researcher discovered thrust readings persisted even when the device was physically reversed, revealing the effect was an artifact of the test setup rather than genuine thrust. She discusses Breakthrough Starshot's laser-accelerated nanocraft concept for reaching Proxima Centauri as legitimately exciting despite the current infeasibility of most of its components, and is candid that traveling near light speed for crewed missions runs into the hard wall of relativistic mass increase, while allowing — in a more speculative, "childlike" register — that missing physics (dark matter, extra dimensions) might eventually change that picture.

On entrepreneurship, Bailey describes the early-stage relative ease of raising money and recruiting talent around an exciting technical vision (crediting this vision as essential fuel for enduring startup hardship), the importance of genuine, high-quality professional relationships built through direct, non-transactional conversations (rather than networking small talk) as a primary channel for building a strong team, and the necessity of staying close to first-principles understanding of the underlying problem and customer needs rather than relying on generic entrepreneurship training. She reflects candidly on culture-building as a founder — initially assuming company culture could be authored separately from founders' personal behavior, then realizing culture inevitably "oozes out" from founders' actual conduct, requiring active self-work (she describes coaching herself out of reflexively "snapping" at underperforming colleagues) — and on competitive strategy, noting she considers SpaceX a future customer rather than a competitor, and that Accion's edge came from applying semiconductor-style mass manufacturing to a field that had never industrialized ion engine production. She closes on personal reflections: favorite books (Fitzgerald's Tender Is the Night, David Deutsch's The Beginning of Infinity — which she credits with introducing her, formally, to ideas like memes and objective beauty, and even to her husband — and Harry Potter, from which Accion's name derives via the "Accio" summoning charm) and her view of life's meaning as centered not on survival and reproduction but on the pursuit and preservation of knowledge, expressing comfort with the idea that even a civilization-ending catastrophe would be redeemed if humanity's accumulated knowledge (she cites Wikipedia as a model) survived and reached whatever comes next.

Excerpts