In a multi-hour February 2021 interview with Elon Musk himself, Joe Rogan inexplicably told the famous engineer and CEO that he had never seen a SpaceX rocket landing.

Of course, the 200+ minute conversation did produce a few minor tidbits of interesting information about SpaceX (and much more about Tesla projects), but Rogan’s statement that he’d never seen a SpaceX rocket landing before stole the limelight by a long shot.

SpaceX landed its first Falcon 9 booster – to an extraordinary amount of fanfare – in December 2015. In the five years since that breakthrough, SpaceX has successfully landed Falcon boosters 73 more times. A full 26 of those landings occurred in just the last 12 months. Falcon Heavy – responsible for spectacular, crowd-favorite performances – completed three dual-booster landings and one triple-booster landing between February 2018 and June 2019.

It’s not unimaginable that almost every single human on Earth with some level of access to the internet or social media is at least vaguely aware of or has watched videos of SpaceX landing rockets. To be clear, it is an unequivocal fact – including past comments on landings from Rogan himself – that Rogan has watched SpaceX land Falcon boosters at least once, if not several times. The only real takeaway, fellow readers, is that heavy, long-term drug use is inadvisable.

Cringeworthy moments aside, the interview did produce a select few minor details that weren’t explicitly known before. Most notably, Musk briefly discussed the challenge of developing a heat shield capable of safely returning orbital Starships back to Earth and revealed the main issue that SpaceX is currently working on.

Over the last six or so months, SpaceX has been gradually expanding small installations of heat shield tiles on Starship prototypes, ranging from vehicles that never left the ground to high-altitude Starships SN8 and SN9. Those tile installations have grown from a handful (4-8 on Starhopper in 2019) to literal hundreds on the most recent Starship completed by SpaceX.

During earlier ground testing and more recent hop tests with Starships SN5 and SN6, some of those ceramic composite tiles actually fell off or shattered, perhaps due to vibrations from Raptor engines or mechanical stress caused by Starship shrinking and contracting from thermal expansion. According to Musk, what SpaceX is trying to determine with those coupon-style tests is how to install a heat shield with tiles that are neither too close together or too far apart.

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According to Musk, ceramic heat shield tiles placed too close together will ultimately shatter, break, or fall off when subjected to the stresses of Starship operations. Those stresses include the violent vibrations created by rocket propulsion supersonic to hypersonic travel, as well as airframe expansion and contraction that occurs when Starship’s steel hull is cyclically heated and cooled by Raptor burns and cryogenic propellant. In other words, assuming fragile, ceramic tiles are a necessity, they need to be placed far enough apart to avoid all of those possible pitfalls.

On the opposite hand, though, the entire point of Starship’s heat shield is to insulate it from extreme thermal stress during atmospheric reentry. If individual tiles are situated too far apart, superheated gas (plasma) produced during reentry will find its way between those tiles, heating up the structure they’re meant to keep cool. In the case of Starship, its steel hull is more than twice as resilient to reentry heating than comparable vehicles (like the Space Shuttle) with common aluminum frames, but a few millimeters of steel is still not enough to prevent weakening, damage, or outright burn-through in the face of orbital reentry.

In essence, SpaceX has to “get the gaps just right” – not too far apart to protect the airframe from plasma intrusion but not so close together that tiles impact or damage their neighbors as Starship cools and warms.