# Why do spaceships not burn during atmospheric entry like in Star Trek and Star Wars?

#### Sword7

##### Member
I watched Star Trek and Star Wars series and movies for many years. I have a question for you. I noticed that spaceships do not burn through atmospheric entry. One episode in Mandalorian series showed that his broken ship attempted to enter atomsphere but did burn through. I believe that spaceships uses anti-gravity brakes to slow down before enter atomsphere.

Does anyone have know any formula to minimum velocity for avoiding atimospheric entry burn? I think that they have to reduce velocity to a few hundred miles per hour prior entrry to avoid burning.

#### N_Molson

Donator
My idea is more that they use deflector magnetic shields to keep the plasma flow away from the hull. After a bad encounter it is likely the shields will be weakened or worse the shield generator can be destroyed beyond repair.

#### Urwumpe

##### Not funny anymore
Donator
Didn't this large cruiser get some (minimal) scorching during reentry in one of the later Star Wars movies?

Generally: The slower you are, the less heating you produce, its all about the aerodynamic heatflux, which is dynamic pressure multiplied by velocity. Which means in consequence, it is proportional to v³.

For most satellites, the limit for this heatflux is specified to about 1500W/m², which defines the moment, when the payload fairing of a launch vehicle can be safely jettisoned. Using the known density function of Earths atmosphere for example, you can calculate the maximum speed you can travel for staying below a heatflux limit.

#### 4throck

##### Enthusiast !
Real spacecraft do burn. Usually, they use thermal shielding because of that. The shield burns, protecting the actual spacecraft behind it.

Just look at Crew Dragon after landing. Crew Dragon reenters with the bottom facing the atmosphere, and that part is shielded. Looks completly black on the photo below.
The sides of the capsule don't need shielding, but they do look scorched.

So they do burn and look burned, and they use special materials as heat shield in some areas.

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#### Kyle

##### Armchair Astronaut
Didn't this large cruiser get some (minimal) scorching during reentry in one of the later Star Wars movies?

Generally: The slower you are, the less heating you produce, its all about the aerodynamic heatflux, which is dynamic pressure multiplied by velocity. Which means in consequence, it is proportional to v³.

For most satellites, the limit for this heatflux is specified to about 1500W/m², which defines the moment, when the payload fairing of a launch vehicle can be safely jettisoned. Using the known density function of Earths atmosphere for example, you can calculate the maximum speed you can travel for staying below a heatflux limit.

Yeah, Star Wars Episode 3.

#### jedidia

##### shoemaker without legs
Does anyone have know any formula to minimum velocity for avoiding atimospheric entry burn?
It depends on a lot of factors, most importantly the mass and velocity of the object, atmospheric density, and angle of reentry. The density gradient can also matter a lot depending on the reentry angle. And after that, details like angle of attack, surface area of the object, heatflux, heat capacity and ablation of the hull material come into play, and after that even atmospheric composition may start to matter, as that will change the heat flux.
So, no, there's no simple calculation for minimum velocity for reentry. It's a rather complex calculation requiring a lot of known factors.

In my experience, trying to apply math to star wars is a sure-fire way to go insane...

#### Face

##### Well-known member
Orbiter Contributor
Beta Tester
I don't think that there is much sense in comparing science-fiction movies with reality. Especially if it comes to the more fantasy-like sci-fi like Star Wars.

Regarding the OP's question, I think the Mach-number is relevant for reentry plasma to occur, presumably around 5 or so. The Mach number depends on gas properties, though, therefore you can't nail it down to a single velocity. At mean sea level, it would be around 3800mph, at 10km height around 3300mph, at 80km or so about 3000mph. Probably it is save to say that if you reduce your speed to 1000mph, you won't get that toasty feeling during reentry. But who's doing a MK1 eyeball reentry these days, anyway (besides Anakin).

#### Sword7

##### Member
Ok I now got it. We tried to fly darkstar plane on MSFS and noticed that it got some atomspheric heating at mach 10.

I watched some launch videos. Many rockets do not burn through atomsphere when they left earth here. When they left atomsphere, they jettisoned fairings to expose satellites outside.

Does anyone have any aerodynamics book explaining about atmospheric heating?

Tim

#### Matias Saibene

##### Orbiter Linux Beta Tester
In Star Trek Into Darkness they make a little justice to the physics laws and the Enterprise burn a little.
Watch at 2:09
But in mi experience burning and destroying ships in Orbiter I think that would be a massive plasma/fireball.

#### Urwumpe

##### Not funny anymore
Donator
Does anyone have any aerodynamics book explaining about atmospheric heating?

The university subject term is "Reentry aerodynamics", which is just a more specialized high-energy version of "satellite aerodynamics" (yes, that exists).

If you need an old, expensive text book to get started, there it is:

#### Sword7

##### Member
The university subject term is "Reentry aerodynamics", which is just a more specialized high-energy version of "satellite aerodynamics" (yes, that exists).

If you need an old, expensive text book to get started, there it is:

I now got it. Thanks for providing a link to a book about re-entry atomsphere that I am looking for. Thanks for repies.

#### steph

##### Well-known member
Well ,we all know the real reason. They're life-size props made of cardboard and styrofoam; so they decelerate really fast when they reenter and only get a very high G load, but not too much heat

#### Thunder Chicken

Donator
In Star Trek Into Darkness they make a little justice to the physics laws and the Enterprise burn a little.
Middle of the 22th century and they still need to use percussive maintenance.

Well ,we all know the real reason. They're life-size props made of cardboard and styrofoam; so they decelerate really fast when they reenter and only get a very high G load, but not too much heat
And all of the rocks on the planets of the original Star Trek were styrofoam too, so gravitational acceleration on those planets wasn't so bad.

#### Thunder Chicken

Donator
Does anyone have any aerodynamics book explaining about atmospheric heating?
Fundamentally re-entry heating involves basic thermodynamics processes, particularly compression of gases and frictional losses, and heat transfer. These are fundamental physics and engineering topics. Aerospace is one of many applications of these ideas.

### Why do spaceships not burn during atmospheric entry like in Star Trek and Star Wars?​

Maybe because you're not in Star wars ...
Just my 2 cents

#### N_Molson

Donator
A very nominal Soyuz recovery (Expedition 37/1) :

#### APDAF

##### Well-known member
Well in Star Wars the ships aren't moving that fast when they are close to a planet, repulsers work upto something like six planetary radii.

#### steph

##### Well-known member
Well in Star Wars the ships aren't moving that fast when they are close to a planet, repulsers work upto something like six planetary radii.
Yeah , but that would just mean a 'normal' reentry. Would still mean a lot of heat, which may or may not soak through and fry the habitat even if the hull holds

#### steph

##### Well-known member
I watched Star Trek and Star Wars series and movies for many years. I have a question for you. I noticed that spaceships do not burn through atmospheric entry. One episode in Mandalorian series showed that his broken ship attempted to enter atomsphere but did burn through. I believe that spaceships uses anti-gravity brakes to slow down before enter atomsphere.

Does anyone have know any formula to minimum velocity for avoiding atimospheric entry burn? I think that they have to reduce velocity to a few hundred miles per hour prior entrry to avoid burning.

Well, what they mean is powered descent. More or less what Falcon9 does at a lower altitude. I guess there is no set speed limit, as 'burn' doesn't really happen, it's just ionized gases. More like a speed at which ionization doesn't happen, but that might still mean it gets hot. If you have unlimited engines etc, you can absolutely plop it down at 300m/s or something and no burn would happen. Like, it may not even be in a classical orbit, but just hovering in space. It may not even have much energy to bleed

In real life, it's always a trade-off between heat and G force and time. The centrifugal force keeping you up decreases in theory gradually, but in reality this doesn't help you much below, say, 6500m/s. Gravity works as a vector pointing down, as if it were just the core of the planet as a source. Technically speaking, you start decreasing your perigee slowly , a few dozens km is nothing compared to the planet radius, but suddenly you have the issue of now having the planet in your way, so to speak. And density variation means the lower you go, the more you decelerate and heat up etc, and so you need lift and/or proper thermal protection to survive. And even if you have movie-grade thermal, a bad trajectory might mean you end up too fast in the lower atmosphere and then the G loads when it decelerates there are not human-compatible, even if the ship holds, or you don't decelerate enough and then you sort of 'decelerate by using the ground'

Then again, if they used warp drive, the ship wouldn't technically be moving so there'd be no energy to lose. Even if , say , they fell from a hover above the atmosphere , we'd be talking of something like 1000m/s vs at least 7200. It would heat up lower down, but it's mostly Mach3-4 coming straight down and decelerating hard in the troposphere.

The only way to avoid (much) heating IRL would be to have a huge surface to weight ratio, either by design or by having a huge parabolic heat shield/airbrake structure deployed. Perhaps a big empty SSTO might need less thermal shielding, but anything that goes for a re-entry like that must be unmanned, since it would be pulling hundreds of Gs

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#### APDAF

##### Well-known member
Yeah , but that would just mean a 'normal' reentry. Would still mean a lot of heat, which may or may not soak through and fry the habitat even if the hull holds
No it wouldn't, the tech in Star Wars allows ships to hover over a point on the ground and still be in low orbital altitudes. Meaning they can go up and down without needing to do any normal orbital manouvers

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