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To use aerodynamics for control you need to be moving fast. Planes achieve this by moving horizontally, but they need a runway (or arrestor cables). Helicopters achieve this by moving just their wings (the rotors) fast. Starship (or Falcon) basically has no aerodynamic control at touchdown, so it relies entirely on thrust vectoring.

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2 hours ago, Silavite said:

Somewhat offsetting this disadvantage is the fact that Starship has the ability to maintain flight at a higher angle of attack, thus the component of area seen by the flow is larger. (That said, while we all know that the AoA tends to 90 deg for the terminal descent, I'm unsure what AoA Starship is supposed to reenter at.)

This was for a return from Mars, not sure if that changes anything about the angle you fly it at, but we’ve had an approximate number on that before. 
“... & hypersonic angle of attack is ~70 degrees” -Elon Musk

But then again, seeing as that’s a return from Mars your heatshield is going to need to be significantly better than the Shuttle’s, almost certainly beyond the point where increasing AoA gets you to.

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5 hours ago, JoeSchmuckatelli said:

My question is a bit different - having looked at wind loads and turbulence on rectangular vs cylindrical buildings - the cylinders have the least turbulence (and, hence drag??) of the two.  If the concept extends to a reentry vehicle - Won't that make it more difficult to slow? 

It's not all that simple. One thing to understand is that sharp edges are very important in fluid dynamics. Sometimes you want them (trailing edges of wings) and sometimes you don't (leading edges of wings).

Re-entry is more about controlling heating and deceleration than anything else. You don't *want* to slow down too quickly, because that is too much g-load for your structure (and people, if crewed). But you don't want to slow down too slowly either, because you don't want to sit there for a long time in a superheated plasma oven.

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20 hours ago, kerbiloid said:

Any known aerobraked cylinder?

No. Any known spacecraft comparable to Starship in any way? No. Any significant advances in manned spaceflight in last 40 years? Very little.

Sometimes you must invent new things if you want to go further.

 

20 hours ago, kerbiloid said:

And I believe that aerodynamics hasn't changed since 1960s.

Physics is the same but technology is much more developed. Abilities to simulate things, plan optimal structures, new materials and fabrication methods etc. Many severe restrictions in 60s are simple problems now.

But this is the thing we will very probably see in relatively short future. I think this summer is too aspirational schedule but in next summer we may see how cylindrical Starship handles hypersonic reentry.

If I remember correctly there was debate like this before first Falcon 9 landings. Some prediction from 60's was that rocket engine can not work if you try to brake at supersonic speed. I do not know was it theoretical prediction or based on some tests with actual engines.

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26 minutes ago, Hannu2 said:

Any known spacecraft comparable to Starship in any way?

The biggest known are Shuttle and Buran. Both are winged lifting bodies with flat bottoms.

26 minutes ago, Hannu2 said:

No. Any significant advances in manned spaceflight in last 40 years? Very little.

Any significant changes in aerodynamics or metallurgy in last 60 years?

26 minutes ago, Hannu2 said:

Sometimes you must invent new things if you want to go further.

Yes, and what new is invented in the idea, old like rockets, "let the rocket just reenter".

Why did they have to put thr 2nd stage engines of Shuttle into the orbiter, rather than deorbit them together with the whole tank as a full-featured stage?

26 minutes ago, Hannu2 said:

Physics is the same but technology is much more developed. Abilities to simulate things, plan optimal structures, new materials and fabrication methods etc. Many severe restrictions in 60s are simple problems now.

Yes. And where is a test deorbit of, say, Falcon 2nd stage?
Without landing, just to aerobrake.

26 minutes ago, Hannu2 said:

But this is the thing we will very probably see in relatively short future.

Or won't, if the Starship structure is not enough tough.

26 minutes ago, Hannu2 said:

If I remember correctly there was debate like this before first Falcon 9 landings.

Falcon 9 re-enters at almost plane speed, and the discussion was (and is) mostly about its actual (not the declared) price/cost ratio, which is still unknown.
Nothing even close to 8 km/s.

 

Edited by kerbiloid
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1 hour ago, kerbiloid said:

Yes. And where is a test deorbit of, say, Falcon 2nd stage?
Without landing, just to aerobrake.

I bet they have data on most reentries. Just because we don't see it doesn't mean they don't have it.

1 hour ago, kerbiloid said:

Falcon 9 re-enters at almost plane speed, and the discussion was (and is) mostly about its actual (not the declared) price/cost ratio, which is still unknown.
Nothing even close to 8 km/s.

Yeah, but they have decent models.

The Shuttle was designed with far less ability to model anything accurately, and worked the very first time.

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2 hours ago, kerbiloid said:

For sure. Until it burns

Given that you said "without landing", what are you suggesting, making a full 15 meters high falcon 9 second stage just crash somewhere without burning, all this from orbital velocity? Doesn't seem safe at all

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10 minutes ago, Beccab said:

Given that you said "without landing", what are you suggesting, making a full 15 meters high falcon 9 second stage just crash somewhere without burning, all this from orbital velocity? Doesn't seem safe at all

The question is, can it aerobrake down to the terminal velocity, let alone the landing.

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If it had a heat sheild and landing guidance, probably. SpaceX is pretty good at doing what they say they are going to do, and doing it faster than any other company or organization.

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10 minutes ago, kerbiloid said:

The question is, can it aerobrake down to the terminal velocity, let alone the landing.

I'm pretty confident that math has been done by all the launch providers, and NASA, ESA, etc. They dispose of upper stages routinely, and presumably they actually design them to intentionally fail, since the goal is for them to burn up.

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3 hours ago, tater said:

The Shuttle was designed with far less ability to model anything accurately, and worked the very first time.

Do not forget all the basic research that NASA and the USAF did in the 60s on lifting bodies.

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1 minute ago, mikegarrison said:

Do not forget all the basic research that NASA and the USAF did in the 60s on lifting bodies.

Yes, and iirc, the original full-steel Starshiphopper has already become aluminium and covered with tiles after first tests.

So, calculations are good, but actual  successful aerobraking is gooder.

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1 minute ago, mikegarrison said:

Do not forget all the basic research that NASA and the USAF did in the 60s on lifting bodies.

True, they absolutely did the math. I specifically mean the computational ability to do CFD at a level that was just not possible in the 60s. (maybe it was possible, but with far, far more human effort and time required).

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11 minutes ago, tater said:

I'm pretty confident that math has been done by all the launch providers, and NASA, ESA, etc. They dispose of upper stages routinely, and presumably they actually design them to intentionally fail, since the goal is for them to burn up.

As far as I can tell, mainly the goal is to make them land in the ocean. "Burning up on re-entry" is sort of a polite fiction.

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Just now, mikegarrison said:

As far as I can tell, mainly the goal is to make them land in the ocean. "Burning up on re-entry" is sort of a polite fiction.

Well, people did get to see one breaking into pieces east of Seattle a few weeks ago, right?

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4 minutes ago, kerbiloid said:

Many cylinders  have aerobraked, but noone without turning into scrap before touching the ground.

I think you're confusing correlation with causation. Many cylindrical objects have burned up on re-entry, but that's because none of them were designed to survive it - they weren't equipped with heat shielding or any method of attitude control. Cylinders aren't a bad re-entry vehicle shape just because a discarded cylindrical stage doesn't survive.

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6 minutes ago, kerbiloid said:

Many cylinders  have aerobraked, but noone without turning into scrap before touching the ground.

Are we sure of that? Seems like some might have only  had a problem with the sudden stop at the end of the flight ;)

Spoiler

thumbnail_image2.jpg

 

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3 minutes ago, tater said:

Seems like some might have only  had a problem with the sudden stop at the end of the flight ;)

Waiting for it with engines and head, made of Starship materials and 9 m wide.

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12 hours ago, kerbiloid said:

Lifting body is not just for terminal velocity (all of them have it ~150 m/s at last). 

Radial acceleration and heat distribution.

Sorry - I meant 'lifting body for aerodynamic landing' - to allow for landing on wheels on a runway.  I intended that to be distinct from terminal velocity - which AFAIK is the best a cylinder can do without the engines kicking in.   

From what I glean from Mike's thread, lifting body + control surfaces allow for a plane-like landing.  Cylinder + control surfaces give you some control over where you crash absent the engine assist 

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