Pointy vs spherical space capsule

[InsaneDruid]

Oh cool.

[magnemoe]

2 hours ago, Nibb31 said:

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.

Cool, but hard to find a place for the hatch inside the cramped capsule. 

One possible place would be between the seats if they removed the box between their heads. 
Another idea would be if you could fold down one of the seats.
 

[Nibb31]

That's where it was.

Edited June 9, 2016 by Nibb31

[magnemoe]

7 hours ago, kerbiloid said:

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

Shuttle had landing leg hatches trough heat shield. Granted they only opened after reentry.

[Nibb31]

1 minute ago, magnemoe said:

Shuttle had landing leg hatches trough heat shield. Granted they only opened after reentry.

It also had hatches for the ET umbilicals and attachment points that closed after the ET was jettisoned.

[kerbiloid]

As most of them have several crew hatches (VA TKS had three) and technological hatches, it's possible to say: they are made from hatches in heatshields, some of them from the bottom side.

[DDE]

19 hours ago, Nibb31 said:

It also had hatches for the ET umbilicals and attachment points that closed after the ET was jettisoned.

Yeah, but I think the Shuttle would have a slightly lower aerodynamic load than a simple capsule, wouldn't it?

[YNM]

59 minutes ago, DDE said:

Yeah, but I think the Shuttle would have a slightly lower aerodynamic load than a simple capsule, wouldn't it?

Uh, Columbia ?

[N_Molson]

I can only sum up what has been said above :

Spherical shape : no lift which means high-G Low Earth Orbit reentry, pure ballistic reentry. Invalid design for a lunar reentry : the crew would endure 15-20 G long enough to be killed. Valid for an uncrewed interplanetary spacecraft (small sample return capsule). Best possible shape in terms of available internal room and living space. Also, a ballistic reentry is easy to predict and doesn't require to master the complex issues of aerodynamics at transsonic speeds. Flown : Vostok, Voskhod (second one is a hasty 2-crew modification of the first one). No controls are required : if the mass is distributed smartly, the capsule will settle itself in the adequate attitude. A fairing is required, as a sphere isn't aerodynamic at all. Vostok fairing had a hole for ejection seat clearance. Voskhod had no Launch Escape System at all (it was too heavy and Khrutchev was in a hurry).

Conical shape : generates lift, depending of the angle of the cone and the shape of the heatshield. Lifting body concept : at supersonic speeds, the capsule works as a wing, provided you can control the Angle of Attack (pitch/yaw control by RCS thrusters). That way you can play with the airflow pressure differential between the "below" and the "above" of the body. Flown : Gemini, Apollo. Recent US concepts share a lot of characteristics with Apollo. Mercury is a bit a special case, because it was conical, but did not generate lift or wasn't really designed to. Mercury reentries were ballistic (8-9 G). This approach makes a computer almost necessary to efficiently manage the AoA and the gliding slope. If the capsule isn't controlled, it will stabilize straight in the airflow, which means no lift at all : you get a ballistic reentry. The shape of the capsule limits internal space a lot, so the only way to improve that is to scale up, which makes the diameter larger, which in turns extends the cross-section (which is bad during launch and especially Max-Q). However, you can save mass as you don't need a fairing, only a cover for some parts like the forward docking part if any. It is then quite convenient to strap a needle-shaped Escape Tower atop of it.

Headlight-shaped : an interesting tradeoff between spherical and conical. It generates nearly as much lift as a conical design, while providing more internal space, which also allows to reduce the diameter of the spacecraft. Flown : Soyuz (all versions). The issue is that it isn't aerodynamic enough to be put on top of a rocket. So you need a fairing anyways, and that means a more complicated Launch Escape System, especially in the Soyuz modular design case, and extra dead mass. An AoA close from 0° (or 180°, from the crew point of view) means a ballistic reentry. Actually this happened quite a few times on crewed Soyuz flight : if the computer controlling the AoA through the RCS fails, the RCS is instructed to make the capsule spin rapidly (roll channel). It proved to be an extremely efficient way to stabilize the spacecraft straight into the airflow. Well, it probably isn't very funny for the crew, taking high Gs + spinning on itself, but it works !

[p1t1o]

1 hour ago, DDE said:

Yeah, but I think the Shuttle would have a slightly lower aerodynamic load than a simple capsule, wouldn't it?

 

7 minutes ago, YNM said:

Uh, Columbia ?

Yes? What about it?

[YNM]

Well, in the way the OP mention it, it's equally "dangerous"... Unless one engineer and operate it right of course. Like all the things posted later in this thread, which certainly have derailed quite far off.

[YNM]

8 hours ago, N_Molson said:

... The issue is that it isn't aerodynamic enough to be put on top of a rocket. So you need a fairing anyways, and that means a more complicated Launch Escape System, especially in the Soyuz modular design case, and extra dead mass.

For Soyuz, I thought the reason why it was having a fairing is because of the orbital module and delicate radar/PVs on it ? I mean, Dragon isn't that pointy too either. Nor is Orion. (For what I refer as pointy, look at Gemini / Mercury).

[Nibb31]

Apollo had a fairing, and so does Orion. It's not a big deal.

[N_Molson]

Quote

For Soyuz, I thought the reason why it was having a fairing is because of the orbital module and delicate radar/PVs on it ? I mean, Dragon isn't that pointy too either. Nor is Orion. (For what I refer as pointy, look at Gemini / Mercury).

The pressure on every square centimeter of a spacecraft at MaxQ is really enormous. If you don't have a "pointy" end, the payload simply disintegrates. And the larger the cross-section, the worse the problem of course.

 

Quote

Apollo had a fairing, and so does Orion. It's not a big deal.

Apollo and Orion have a windshield, its a bit different as a full fairing encapsulates the whole spacecraft and makes the cross-section larger. And the extra dead mass has definitively an impact on performance. Of course, the Launch Escape System itself is anyway heavier.

[magnemoe]

13 hours ago, YNM said:

For Soyuz, I thought the reason why it was having a fairing is because of the orbital module and delicate radar/PVs on it ? I mean, Dragon isn't that pointy too either. Nor is Orion. (For what I refer as pointy, look at Gemini / Mercury).

Orion is not very pointy, too me it looks like an flattened Apollo capsule. Dragon looks more like the soyus pod with an flatt top. 
 

[Kerbart]

21 hours ago, YNM said:

Well, in the way the OP mention it, it's equally "dangerous"...

So it's safe, because there were never any issues with it?

[DDE]

21 minutes ago, magnemoe said:

Orion is not very pointy, too me it looks like an flattened Apollo capsule. Dragon looks more like the soyus pod with an flatt top. 
 

What's bizarre about Orion to me is that the LES Boost Protective Cover is rounded and gives it a Soyuz shape!

[YNM]

5 hours ago, N_Molson said:

The pressure on every square centimeter of a spacecraft at MaxQ is really enormous. If you don't have a "pointy" end, the payload simply disintegrates. And the larger the cross-section, the worse the problem of course.

Apollo wasn't that pointy (so it had protective cover). Dragon doesn't use any "pointed" protective cover on it yet the docking/berthing mechanism required (and of course, uses) a cover, which IMHO isn't that pointy at all.

2 hours ago, Kerbart said:

So it's safe, because there were never any issues with it?

As I said, only if you engineer and operate it well... Unlike the major fiasco Challenger and Columbia accident was... Something easily prevented yet left alone un"fixed" by those responsible. (ex. they could've stopped the launch, they could've thickened the panels. But nothing chimes in.)

Edited June 11, 2016 by YNM

[Kerbart]

Just now, YNM said:

Apollo wasn't that pointy (so it had protective cover). Dragon doesn't use any protective cover on it yet the docking/berthing mechanism required a cover, which IMHO isn't that pointy at all.

As I said it, only if you operate and engineer it well... Unlike the major fiasco Challenger and Columbia accident was... Something easily foreshadowed yet let alone by those responsible.

The sub discussion was about hatches in heat shields. I still fail to see what the Columbia accident had to do with that.

[YNM]

2 minutes ago, Kerbart said:

The sub discussion was about hatches in heat shields. I still fail to see what the Columbia accident had to do with that.

It's about "what if it hasn't closed or fails to work during re-entry" which luckily hadn't happened.

[DDE]

14 hours ago, YNM said:

It's about "what if it hasn't closed or fails to work during re-entry" which luckily hadn't happened.

I've seen poorly-sourced references to an experimental Soyuz-VI capsule also having a hatch burn-through situation, which didn't destroy the vehicle, but would have killed the crew if there were one.

[Nibb31]

17 hours ago, DDE said:

What's bizarre about Orion to me is that the LES Boost Protective Cover is rounded and gives it a Soyuz shape!

Because the protective cover is shaped for going up, whereas the Orion capsule is shaped for going down.

Orion's conical shape has nothing to with being aerodynamic on its way up. It's to provide more life during reentry.

Edited June 12, 2016 by Nibb31

[DDE]

23 minutes ago, Nibb31 said:

Because the protective cover is shaped for going up, whereas the Orion capsule is shaped for going down.

Orion's conical shape has nothing to with being aerodynamic on its way up. It's to provide more life during reentry.

As I thought. From what I read, pointiness is of little help at hypersonic velocities.

[N_Molson]

Quote

Apollo wasn't that pointy (so it had protective cover). Dragon doesn't use any "pointed" protective cover on it yet the docking/berthing mechanism required (and of course, uses) a cover, which IMHO isn't that pointy at all.

"Pointy" doesn't exactly mean "aerodynamic". Early rockets had very "pointy" tips and fairings, not unlikely heavy artillery shells. Advances in understanding of the airflow behaviour at high speeds, stronger and lighter materials, engine throttle control during ascent, all made nowadays rocket look more "round" (in fact, they are somehow pointy and round at the same time, that's the trick ).

Edited June 12, 2016 by N_Molson

[SSgt Baloo]

On 5/1/2016 at 1:50 PM, insert_name said:

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

Hey! To be completely fair, vowels have been going into space just as long as consonants have.