totm nov 2023 SpaceX Discussion Thread

[kerbiloid]

3 minutes ago, Beccab said:

Those aren't cylindrical

They are asymmetric cylinders with internal spatial support structure and the nadir surface combined together with wing into a lifting body, and ogive nose.
With fins, rudder, and elevons.

The starship mockup is a cylinder with ogive nose, with winglets.

The capsules are just capsules.

Edited August 9, 2021 by kerbiloid

[CatastrophicFailure]

4 minutes ago, kerbiloid said:

Aerodynamics

Yes, and..?

One went up, came down, landed. The other went up, came down, landed. Neither could have gone to space (without major work). I fail to see the difference…

[kerbiloid]

Just now, CatastrophicFailure said:

Yes, and..?

Anything like a gliding?

[Beccab]

2 minutes ago, kerbiloid said:

They are asymmetric cylinders with internal spatial support structure and the nadir surface combined together with wing into a lifting body, and ogive nose.
With fins, rudder, and elevons.

The starship mockup is a cylinder with ogive nose, with winglets.

The capsules are just capsules.

"It is different so it can't work", again, for the fourth or fifth time. Just because you can't find a decent comparison it doesn't invalidate anything

[kerbiloid]

It has to pass through the atmosphere from 8 km/s, btw, not just land vertically.

Just now, Beccab said:

"It is different so it can't work", again, for the fourth or fifth time.

No.
"It began working when become the shuttle."

[Beccab]

Just now, kerbiloid said:

It has to pass through the atmosphere from 8 km/s, btw, not just land vertically.

Because the enterprise definitely did that

[RealKerbal3x]

I don't really understand the argument here. If it's 'Starship doesn't exist' again then you're going to find yourself running out of excuses pretty soon.

[kerbiloid]

1 minute ago, Beccab said:

Because the enterprise definitely did that

Do you think the shuttle developers would not make it a simple cylinder if it worked?

Do you doubt that "they know better than you?" (as I always hear here).

As they had to make the shuttle shuttlish, they were forced  to complicate this this way.

Edited August 9, 2021 by kerbiloid

[Beccab]

1 minute ago, kerbiloid said:

Do you think the shuttle developers would not make it a simple cylinder if it worked?

Do you think that the shuttle developers wouldn't make it a capsule if it worked?


Different vehicles have different shapes and different functions. Stop trying to compare it to the shuttle, it isn't trying to be a shuttle. Do you remember when the Shuttle made the bellyflop manuevere and landed on its back using the SSME? The shuttle lands like a plane and has the shape to make it land like a plane. Starship doesn't land like a plane and has the shape to make it not land like a plane

[kerbiloid]

The "new materials" argument doesn't work here, as as it was stated earlier (not by me) they replaced the 12 m composite with old style 9 m steel.

1 minute ago, Beccab said:

Do you think that the shuttle developers wouldn't make it a capsule if it worked?

With 10 m round cargo bay?

And 20 wide booster?

Probably, they thought, no.

Edited August 9, 2021 by kerbiloid

[CatastrophicFailure]

4 minutes ago, kerbiloid said:

Do you think the shuttle developers would not make it a simple cylinder if it worked?

Do you doubt that "they know better than you?" (as I always hear here).

As they had to make the shuttle shuttlish, they were forced  to complicate this this way.

So, again, your whole argument is, “it’s never been done like that before so it can’t work?”

[kerbiloid]

  

1 minute ago, CatastrophicFailure said:

So, again, your whole argument is, “it’s never been done like that before so it can’t work?”

No. My whole argument is "the best of the best aviation engineers tried do to that, and look how it worked"

The elementary physics says the same.

A simple cylinder is a harsh way to aerobrake from both aerodynamics and thermodynamics pov.

Edited August 9, 2021 by kerbiloid

[James Kerman]

Thread temporarily locked for moderator review.

[Vanamonde]

Thread re-opened. Please keep it polite and avoid sarcasm. Belittling the other side's position just makes people mad and isn't persuasive. 

[CatastrophicFailure]

8 hours ago, kerbiloid said:

  

No. My whole argument is "the best of the best aviation engineers tried do to that, and look how it worked"

The elementary physics says the same.

A simple cylinder is a harsh way to aerobrake from both aerodynamics and thermodynamics pov.

The best aviation engineers of the time tried to make a highly complex vehicle to a meet a very specific set of conditions, including massive cross-range capability. They got much right, and much wrong. 
 

Now, 40 years later, the best rocket engineers are trying to make as simple a vehicle as possible to meet an entirely different set of conditions, having learned from those 40 years of others’ experience much of what to do and what not to do. The technology available has radically changed in that time too. 
 

They believe it can be done. Not just Musk, not just Shotwell, but a whole bunch of really really smart talented people arguably at the top of their industry who’ve done the math and done the physics and done the simulations. 

[kerbiloid]

Two letters. L/D

For planes = 4 .. 60
For conical capsules = 0.3 .. 0.5
For non-rotating spheres and cylinders along the flow ~0.

***

Heat concentration.

Flat bottom (incl. lifting bodies) = distributed across total cross-section.

Spheres and cylinders = concentrated at the convex spot.

Edited August 9, 2021 by kerbiloid

[Rakaydos]

15 minutes ago, kerbiloid said:

Two letters. L/D

For planes = 4 .. 60
For conical capsules = 0.3 .. 0.5
For non-rotating spheres and cylinders along the flow ~0.

***

Heat concentration.

Flat bottom (incl. lifting bodies) = distributed across total cross-section.

Spheres and cylinders = concentrated at the convex spot.

This is literally why Starship has a heat shield at all- before they ran the numbers, they thought they might be able to get away with bare steel.

The heat shield they have now is at the "might work" level- not because they CANT build a "guaranteed to work" heat shield, but because they'll never know how little they can get away with unless they try... And because they dont want to recover this obsolete ship anyway, because it would just take up museum space.

Edited August 9, 2021 by Rakaydos

[RCgothic]

There's nothing about that that is correctly applicable to Starship.

Starship isn't coming in flat, has an angle of attack (and has large fins). It has plenty of lift. (And even with a poor L/D, drag is desirable. It doesn't take very much lift to stay aloft at very high speeds).

Heating is inversely proportional to bluntness. Bluntness is the inverse of radius of curvature. Because of its size and high AoO, Starship is the bluntest body that will ever have re-entered. It's much blunter than shuttle or X37B in absolute terms.

Edited August 9, 2021 by RCgothic

[Deddly]

I don't think there is any argument regarding the greater lift of a spaceplane. The Shuttle had vastly superior lift than anything SpaceX has presented with Starship. This, I think, is indisputable.

What I can't personally understand with your argument, @kerbiloid, is why does that matter for Starship? If I understand you correctly, you feel that changing Starship into a Shuttle-style spaceplane would be much superior and that their current design will not work well (or at all). As far as I understand things, all they need is some attitude control to keep Starship side-on to the airstream on re-entry in order to maximise drag and give them some level of control over the landing location. They have already demonstrated cross-range capability and are apparently satisfied that they have good control, since they did not make any significant changes to that part of the design from the first three flights until now. They don't believe they need wings because they are planning a powered landing on a launch pad/catching gantry, not a glide onto a runway. The problem with putting a spaceplane on top of the stack - as those of us who have tried it in KSP know all too well - is that the centre of pressure/lift is moved way too far forward, causing a very unstable configuration. It's not insurmountable, but it is certainly a big consideration.

Now, all of that aside, Elon would be the first to say that he and anyone else could be wrong, and that includes me. Maybe you are right, Kerbiloid. I can see some benefits of a spaceplane. For one, there's no need to include any fuel margin for landing. The header tanks and additional plumbing would be unnecessary, etc. - it could land with zero fuel on-board. Whether the added weight of the wings and strengthened airframe would make that a good trade-off is debatable, though. But the main killer is: what benefit is a spaceplane on the Moon and Mars? If you were given the task to design the craft(s) given the following criteria, what would it look like?

• As inexpensive as possible
• High payload capacity
• Fully reusable with rapid turnaround
• Can be scaled up to rapid production
• R&D must go quickly
• Capable of landing on Earth and Mars
• As few parts as possible, to avoid points of failure

I'm confident that the current Starship design is not the only option here. How could it be improved?

[magnemoe]

20 minutes ago, CatastrophicFailure said:

The best aviation engineers of the time tried to make a highly complex vehicle to a meet a very specific set of conditions, including massive cross-range capability. They got much right, and much wrong. 

Now, 40 years later, the best rocket engineers are trying to make as simple a vehicle as possible to meet an entirely different set of conditions, having learned from those 40 years of others’ experience much of what to do and what not to do. The technology available has radically changed in that time too. 

They believe it can be done. Not just Musk, not just Shotwell, but a whole bunch of really really smart talented people arguably at the top of their industry who’ve done the math and done the physics and done the simulations. 

This, also the shuttle worked and had lots of capabilities we don't have to day, it was just dangerous and very expensive to operate. 
Starship is in many ways an simpler system and as you say technology has advanced, its no way they would go with tiles if they expected as many problem as the shuttle had for one. 

 

[Beccab]

28 minutes ago, Deddly said:

are apparently satisfied that they have good control, since they did not make any significant changes to that part of the design from the first three flights until now

Not only that, but they made the aft flaps on S20 *smaller* compared to the previous ships

[mikegarrison]

1 hour ago, Deddly said:

But the main killer is: what benefit is a spaceplane on the Moon and Mars?

But Earth is not Luna or Mars.

This is what makes the whole idea somewhat questionable. On the one hand, Luna and Mars are very difficult to practice on, while Earth is where we live. So perfecting the technology for these kinds of landings on Earth makes sense. But on the other hand, *using* the technology on Earth doesn't make as much sense, if the only advantage is that it works better on Luna or Mars.

I guess we'll see how it all works out. Propulsively landing the boosters does seem to look like it is working.

[Meecrob]

I find this argument hilarious...So many people want to say Elon is some out of touch crazy person with no ability to make a timeline, but he consistently creates things on time and under budget...I mean  Vegas would gladly take your money to bet against him to say the least.

[Beccab]

 

[mikegarrison]

1 minute ago, Meecrob said:

I find this argument hilarious...So many people want to say Elon is some out of touch crazy person with no ability to make a timeline, but he consistently creates things on time and under budget...I mean  Vegas would gladly take your money to bet against him to say the least.

Wasn't he already supposed to be landing ships on Mars by now?

How "on-time and under budget" was the Tesla Model 3?

There is a vast gulf between "out of touch crazy person" and "perfect record for being on-time and under-budget", and I argue that Musk is somewhere in that vast gulf rather than being either of the extremes.