Pointy vs spherical space capsule

[Pawelk198604]

I noticed that all Soviets/Russians from Vostok 1 onward are spherical while American one from Mercury project are pointy.

 

So i wonder what design are better spherical or conical one?  

Edited May 1, 2016 by Pawelk198604

[Camacha]

Rounded designs are a compromise, but a healthy one. If you have a pointy design, it means any change in direction or less-than-ideal airflow means that the airflow encounters a sudden change in shape, which in turn means turbulent air. By rounding a nose cone or part, you make the effect of an off-angle much less distinct. You need to point a rocket sideways to cause problems with airflow and you would be having other, more significant problems if that occurs.

Long story short, rounded shapes are less critical and less prone to stalling when it comes to airflow and therefore much more forgiving.

Edited May 1, 2016 by Camacha

[Spaceception]

With Conical spacecraft, it's easier to put a nose cone on, and it makes the rocket look more complete without having to put a faring on it, and it's better to reenter with a conical spacecraft.

For sphere shaped ones, idk.

[Camacha]

Just now, Spaceception said:

makes the rocket look

I am pretty sure they would send rockets into space with a donkey strapped to the top, if that would make them fly better. Looks are not an argument.

[PB666]

18 minutes ago, Camacha said:

Rounded designs are a compromise, but a healthy one. If you have a pointy design, it means any change in direction or less-than-ideal airflow means that the airflow encounters a sudden change in shape, which in turn means turbulent air. By rounding a nose cone or part, you make the effect of an off-angle much less distinct. You need to point a rocket sideways to cause problems with airflow and you would be having other, more significant problems if that occurs.

Long story short, rounded shapes are less critical and less prone to stalling when it comes to airflow and therefore much more fore forgiving.

Yeah but they create a caveot in sears-haack shape, its sort of a moot point anyway, all of them are creating a boundary layer separation and are not very efficient. For most rockets the angle of attack is so low relative to the axis it don't make much of a difference. The stall effect is only for lift. at the Mach you have a build up of gas in front of the leading edge, its sort of a concretization if air, the boundary layer moves forward and the out the side of the vessel making the leading edge appear heavier that it is, but the weight limit is related to pressure, and at 10000 feet its only ~4 PSI and is dropping fast for every meter traveled by  20000 it will ~1.5. At just mach the rocket travels that distance in 20 seconds and thereafter is pretty much free of the effect. In addition the critical zone is only to about mach 1.3 and after this the CoD decreases. 

The goal of the sears haack shape is to keep the boundary layer annealled to the surface, structures that do this well minimize what the wind sees, as they travel up. As you see with CRS-8 there is quite a separation and exhaust is rolling up the sides of the launch. All that is scarey until you realize that at 30,000 meters and beyond there simply is not much gas to matter. 

When we think of Mach effect we think of it generally below 15000 m, if your rocket is traveling strait into the wind and going almost strait up above then there is prolly some other concern......the cone shape has some advantages on the rentry, you can tilt it more for aerobraking purposes inducing lift and keeping the craft high until the speed cools down, with the cone you can add more of the weight under the partial sphere that sits on the heat shield. The sphere shape is a better pressure hull, but alas soviets had a failure of the oxygen feed lines between the service module and the capsule at te interconnect on rentry, so pressure hull is not everything in that regard.  If your craft luanches from a place that sees alot of upper level winds, then it might be best to have a ballistic nosecone, if not and it launches strait up the the added weight of a perfect sears haack has be balanced against the aerodynamic gain and lower max Q. 

[Nibb31]

A sphere is the most efficient ratio between volume and mass, which was the most important criteria for early space craft. The closer you are to a sphere, the lighter your capsule is for a given volume. If your capsule is light, it needs lighter parachutes.

On the other hand, a sphere is not passively stable in the airflow, so it will tend to tumble. You can counter this by ballasting the weight on the bottom so that it remains upright. It will also have practically no lift, so your trajectory will be purely ballistic, which gets you a very high-g descent.

A conical configuration, on the other hand, is inherently stable and provides lift. You can direct the blunt end towards the flow and tilt the capsule to obtain lift. A short cone shape (like Apollo or Orion) can be oriented more obliquely towards the airflow than than a taller cone (like Dragon), which means that you can get more lift. Lift provides a more gentler reentry and more cross-range.

 

[RainDreamer]

5 hours ago, Camacha said:

I am pretty sure they would send rockets into space with a donkey strapped to the top, if that would make them fly better. Looks are not an argument.

You are making me imagining a world where the donkey gods decreed that anything that approaches the heaven must have a donkey on the very top of it, and thus all attempt to space has been using donkeys strapped on rockets.

[PB666]

10 minutes ago, RainDreamer said:

You are making me imagining a world where the donkey gods decreed that anything that approaches the heaven must have a donkey on the very top of it, and thus all attempt to space has been using donkeys strapped on rockets.

Donkey shaped maybe, donkeys have a high mass to surface area ratio. You could, theoretically, a nose cone with golf ball dimples. There are things that are absolute no-nos that will weigh up parts of the rocket. One have a payload that is much wider than a rocket and have the fairings diameter collapse rapdly as it goes down the rocket, this makes the boudary layer grip into the rocket like a claw, lots  of side friction. If the width does retract quickly dont place a structure such as a tail fin or winglet, if you do this you need to add a volume that then slowly reduces the total crosssectional area. 

I have put up some pretty hideous structures in the game, the key is don't go above Mach until maximu possible unbound forward load is so low it wouldn't break your forward facing parts. Yes its wasteful of fuel and you turn slower you are hoovering long, not a problem though, if you spam stagger the sfbs parachute the little suckers and keep as much fuel in you main as possible. 

[OhioBob]

3 hours ago, Nibb31 said:

On the other hand, a sphere is not passively stable in the airflow, so it will tend to tumble. You can counter this by ballasting the weight on the bottom so that it remains upright. It will also have practically no lift, so your trajectory will be purely ballistic, which gets you a very high-g descent.

A conical configuration, on the other hand, is inherently stable and provides lift. You can direct the blunt end towards the flow and tilt the capsule to obtain lift. A short cone shape (like Apollo or Orion) can be oriented more obliquely towards the airflow than than a taller cone (like Dragon), which means that you can get more lift. Lift provides a more gentler reentry and more cross-range.

Vostok/Voskhod managed to achieve monostability by offsetting the center of gravity.  (Monstability means that a spacecraft will eventually reach a single stable trim point where the heat shield points toward the velocity vector.)  This needed to be the case because once the equipment module was jettisoned, Vostok/Voskhod had no active attitude control.

Although some conical reentry vehicles are monostable, Soyuz for instance (and I think Gemini), not all are.  Apollo, for example, had two stable positions - heat shield forward and nose forward.  This is because the engineers couldn't get the CoM close enough to the heat shield to produce monostability.

The Mercury spacecraft also performed a purely ballistic reentry.  Gemini was the first spacecraft to perform a lifting reentry.  A ballistic reentry from Earth orbit generally produces a peak acceleration of about 8-9g.  With a lifting reentry this can be gotten down to near 3g.

[cantab]

7 hours ago, Pawelk198604 said:

I noticed that all Soviets/Russians from Vostok 1 onward are spherical while American one from Mercury project are pointy.

You noticed incorrectly. The first Soviet space capsules were indeed spherical, but the part of the Soyuz that re-enters the atmosphere is somewhat conical. Only the Red bit on this mockup re-enters the atmosphere:

It's not as "pointy" as the American designs, but it offers some of the same advantages - such a capsule has a preferred direction to travel in and can be somewhat steered and even generate lift to reduce g-forces. A spherical re-entry capsule does work, and has the advantage that it offers maximum interior volume for minimum hull mass which is why the Soviets originally chose it and still use it for the Soyuz Orbital Module that doesn't survive re-entry, but it gives no control or lift during re-entry, increasing g-forces and reducing landing precision.

[insert_name]

The first consonants must have been pretty balsy to get in the Vostok and voshkod capsules

[Bill Phil]

Spherical designs let you reenter at any attitude. But that attitudeay not be good for the cosmonaut. 

Conical designs give you more control, and can be designed to naturally turn to the correct attitude. 

[Nibb31]

9 hours ago, insert_name said:

The first consonants must have been pretty balsy to get in the Vostok and voshkod capsules

Especially Voskhod. It was considered a death trap, even by the Russian cosmonauts, which is why it only flew manned twice.

Edited May 2, 2016 by Nibb31

[shynung]

When manned spacecrafts were first designed, it was thought that the entire outer surface of the craft must be covered in heatshield material. For this purpose, a spherical design, which has the least surface area for a given volume, was used to reduce the needed heatshield coverage to a minimum.

Later on, conical designs were found to be able to hold a certain stable attitude at reentry, which is blunt end first. Now, the heatshield has to cover only the blunt end instead of the entire outer surface of the spacecraft, saving mass by reducing the required heatshield material.

[wumpus]

On 5/1/2016 at 7:12 AM, Camacha said:

I am pretty sure they would send rockets into space with a donkey strapped to the top, if that would make them fly better. Looks are not an argument.

Early manned flight (and most later manned flight for that matter) was all about propaganda.  You better believe looks mattered (but don't let it interfere with getting there first).

[fairytalefox]

18 hours ago, insert_name said:

The first consonants must have been pretty balsy to get in the Vostok and voshkod capsules

Well, it's not like they've got their "Hero of the Soviet Union" titles for their pretty eyes.

22 minutes ago, wumpus said:

Early manned flight (and most later manned flight for that matter) was all about propaganda.  You better believe looks mattered (but don't let it interfere with getting there first).

Wanna know when looks actually matter? Look at the Soyuz-Apollo custom docking module:

 

...as opposed to the original docking module design:

[InsaneDruid]

On 1.5.2016 at 1:01 PM, Pawelk198604 said:

I noticed that all Soviets/Russians from Vostok 1 onward are spherical while American one from Mercury project are pointy.

 

So i wonder what design are better spherical or conical one?  

(voice of the templar knight from the Last Crusade)

You noticed wrongly!

(/voice of the templar knight from the Last Crusade)

Given that there aren't that many russian (and american) manned spaceship designs, only one of them (the vostok/voshod - which I count as one as it was one design, just modded) was spherical.

Sojuz is a combination of spherical heat shield, a (slightly angled) frustum shaped main section and hemispherical top.

The VA capsule, the first reusable capsule was a frustum which clearly falls under you "pointy" description.

The Federatsiya will be a frustum shaped object, too.

 

[DDE]

On ‎02‎.‎05‎.‎2016 at 7:41 PM, InsaneDruid said:

Sojuz is a combination of spherical heat shield, a (slightly angled) frustum shaped main section and hemispherical top.

The VA capsule, the first reusable capsule was a frustum which clearly falls under you "pointy" description.

The Federatsiya will be a frustum shaped object, too.

And the latter is getting blasted for not having a Soyuz-style orbital module on top!

The former... the former was a very special, Blue Gemini-esque case. Three words: hatch through heatshield.

[Kerbart]

On 5/1/2016 at 7:12 AM, Camacha said:

I am pretty sure they would send rockets into space with a donkey strapped to the top, if that would make them fly better. Looks are not an argument.

It's bad PR. Animal rights organizations would not stop complaining.

[Nibb31]

3 hours ago, DDE said:

And the latter is getting blasted for not having a Soyuz-style orbital module on top!

The former... the former was a very special, Blue Gemini-esque case. Three words: hatch through heatshield.

We've been doing hatches through heatshields for 30 years now. It's proven technology.

[kerbiloid]

I've read that when Vostok was being designed, a sphere was just the only capsule shape enough studied to be used in the short term.

 

On 01.05.2016 at 2:12 PM, Camacha said:

I am pretty sure they would send rockets into space with a donkey strapped to the top,

Btw... Here is an outdated mod with a pony... (Reliant Robin + pony).

[DDE]

8 hours ago, Nibb31 said:

We've been doing hatches through heatshields for 30 years now. It's proven technology.

Yeah, but just like the NSWR,

Quote

Duvalier left Ortiz main engineering and vaulted down the access tube to the reactor room. The tube ran down the ship's spine, surrounded by megaliters of water enriched with uranium salts in highly complex tanks made of neutron absorbing material. In his head, he knew the tube was the safest part of the ship, shielded from the worst the universe could throw at it by dozens of meters of water. In his head, he knew the fuel, so long as it didn't pool into a critical mass somewhere in the thousands of kilometers of pipes on all sides of him, emitted only low intensity alpha rays which couldn't penetrate his own skin, let alone the aluminum skin of the pressure tube. It was all perfectly safe, so far as anything in space could be safe. He knew that in his head.

His balls, however, hadn't gotten the memo. His netherss tried to crawl up into his body every time he climbed through the hatch.

 

[kerbiloid]

Besides Big Gemini and VA, "Soyuz VI" re-entry capsule also had a hatch in the floor and heatshield.

[InsaneDruid]

Did a Gemini actually fly with a heat shield hatch? IMHO only VA did (AND also was reusable, too), which is kinda cool, imho.

[Nibb31]

37 minutes ago, InsaneDruid said:

Did a Gemini actually fly with a heat shield hatch? IMHO only VA did (AND also was reusable, too), which is kinda cool, imho.

Yes, The capsule from Gemini 2 was modified into a Gemini B, with a hatch in the heatshield, for the MOL program. It's the only Gemini capsule to have flown with a USAF insignia instead of NASA and the only Gemini capsule to have ever flown twice (both times unmanned), and the first spacecraft to be reused.

Edited June 9, 2016 by Nibb31