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LLM (google/gemini-3.1-flash-lite-preview-20260303) summary:
- Design goals: starship seeks full reusability with short turnaround times for orbital travel
- Physical challenge: reentry requires dissipating massive kinetic energy stored as potential energy during launch
- Velocity factors: spacecraft endure extreme speeds reaching mach 25 or seventeen thousand miles per hour
- Thermal extremes: air impact during atmospheric descent generates temperatures between five thousand and seven thousand degrees celsius
- Heat management: protection methods include thermal storage via insulating tiles and material ablation through phase changes
- Space shuttle history: early tile technology relied on fragile silica materials that required intensive refurbishment after each flight
- Payload tradeoffs: fuel consumption for controlled landings reduces the total cargo capacity available for orbital delivery
- Future outlook: reliable full reusability for rocket systems is estimated to require a thirty year development timeline
Like the space shuttle before it, SpaceX’s giant reusable rocket Starship is built around the idea that a spacecraft should fly, land, and fly again. But Starship—whose newest version, Starship V3, is expected to launch for the first time as soon as next month—is designed from the outset for full reusability, with far shorter turnaround times than the shuttle. If the ambitious rocket works as intended, its launch and return could mark a turning point in how engineers think about getting to and from orbit, just as the shuttle once did.
Both vehicles, though, come with the same catch: the extreme conditions of atmospheric reentry while descending back to Earth. To understand why this phase of flight is so difficult and what it takes to shield reusable rockets, Science spoke with Stephen Whitmore, an aerospace engineer and director of the Propulsion Research Laboratory at Utah State University.
This interview has been edited for clarity and length.
Q: Why is atmospheric reentry often described as the hardest part of reusable spaceflight?
A: The conservation of energy—it doesn’t have anywhere to go. Look at a rocket and think of all the energy that’s stored in that rocket on the launch pad: all of that propellant, all that fire, everything else. All of that gets put into the spacecraft. When it’s up there in orbit, it has stored all of it as potential energy. When it comes back, it’s got to be released somewhere.
It ends up being recaptured by the impact of the high-velocity air. It’s entering the atmosphere at Mach 25, which is a little over 17,000 miles per hour [or nearly 30,000 kilometers per hour] from low-Earth orbit.
That’s basically the issue with atmospheric reentry: You’re taking all of that energy that was stored and getting you into orbit, and now you’ve got to return it. And it all happens in a very short period of time. From when they hit the atmospheric interface until they land is only about 15 minutes.
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As a way to demonstrate how much energy is in a rocket plume, we’ll put a steel bar in the plume so people can watch that steel bar vaporize in about two-tenths of a second.
Q: How hot does reentry get?
A: The actual impact temperature of the air on the main leading edge is going to be on the order of 5000 to 7000°C, nearly 10,000°F. Nothing can survive those temperatures.
Q: What are the main approaches to countering the intense heat of reentry?
A: One way is energy storage. You basically store it and release it slowly so that it doesn’t get into the crew area. That’s what the space shuttle did. They had tiles all over the impact areas, and those tiles had a very large heat capacity. The tiles brought a lot of heat in but very slowly released it.
When the shuttle landed, that heat would all still be in there and then it would get released. That’s why when you saw the shuttle land, [NASA] would send all those trucks with refrigerants and that kind of stuff to pump energy back out of the shuttle. Otherwise, the frame would have actually melted.
The other approach is ablation. You can think of it as being a material that, as hot air impacts it, acts as the heat shield and burns away. It’s just like when you’re melting ice—that latent heat of evaporation pulls heat away from the system. It’s a phase change going from a solid directly to a gas. It’s a very energy-intensive process, so that pulls a lot of the heat away.
And obviously no one knows exactly what the Starship uses for its heat shield because Elon [Musk, SpaceX’s CEO] keeps that very close to the vest, but it’s a combination of heat storage and ablation.
Q: So, in hindsight, where did the space shuttle go wrong?
A: The problem is that they had to make up the materials as they went. In the early days of building the shuttle tiles, it was guys with silica fiber using, believe it or not, commercial dryers—closed and tumbling—to actually make the stuff. And although they’re very, very resistant to heat, those tiles are very fragile. You pick up a shuttle tile and it weighs almost nothing, and so that was one of the issues.
The problem with the shuttle is it was such a new thing, and probably about 4 decades ahead of its time. There were enough flaws in it that it operationally became too expensive to maintain. It became such a valuable asset, especially after the Challenger accident back in 1986, that they could not even remotely have any potential issue.
So, every time it came back, they essentially had to rebuild the thing. Other than the airframe, they rebuilt a good portion of it.
Q: What concerns do you have about fully reusable rockets, versus only partially reusable rockets like SpaceX’s Falcon 9?
A: Commercially, it makes a lot of sense. But also remember the way that Starship does this—they have to use fuel to come down and put it into a controlled landing. That fuel takes away from the payload that will be delivered to orbit. Reusability is sacrificing the lift capacity of the rocket. There’s a trade space in there. SpaceX is a commercial venture, and their trade is to sacrifice payload in order to have full reusability. It’s more profitable.
And with reusability, you’ve got to salvage components, so they become extraordinarily valuable. And that does constrain your mission; it constrains what you can do in terms of operational risk. I think we’re looking at, probably, a 30-year timeline until fully reusable rockets become reliable.
