totm nov 2023 SpaceX Discussion Thread

[kerbiloid]

1 minute ago, SOXBLOX said:

Four flights. The Soviets were too cheap to build a test stand.

A lot of cute rocket explosions have been seen in this thread, even with a stand.

Currently Starship is just an early prototype, even not close to the real aim.

[Nothalogh]

6 hours ago, kerbiloid said:

lifting bodies with flat bottoms

Those were chosen specifically for their LD ratio at super and subsonic speeds, due to the aforementioned requirement of cross range capability with full payload.

[kerbiloid]

16 minutes ago, Nothalogh said:

Those were chosen specifically for their LD ratio at super and subsonic speeds, due to the aforementioned requirement of cross range capability with full payload.

All capsules except Vostok/Voskhod are flat-bottommed, and that's not due to subsonic speed, but exactly to make the aerobraking controlled, unlike the rounded ones.

Aerobrake too vertically - and your capsule dives too fast and reaches the dense air at too high speed, so both heating and overloads get critical.
Aerobrake too horizontally - and your capsule is being heated too long, so it will receive critical amount of heat.

The flat bottom makes the angle of attack manageable to keep the proper angle of descent to prevent overheating and overloading.
Also the flat bottom doesn't concentrate heating at the round lowest point, the heat is distributed more uniformly.

All known spaceplane project have their shape for reasons.

In 1960s they were thinking that even a simple cone has enough L/D to manage the descent properly.
Then they had to slice it first from top, then from bottom. Then attached the fins which became winglets, and look at BOR/Spiral/Dreamchaser and Shuttle/Buran, where they had come to.

There is X-37, of course, but it's much smaller than Starship, and it's still not cylindric below.

Edited April 21, 2021 by kerbiloid

[Beccab]

4 minutes ago, kerbiloid said:

All known spaceplane project have their shape for reasons.

This is true. It is also true Starship is not a spaceplane, nor lands like one

[kerbiloid]

Just now, Beccab said:

This is true. It is also true Starship is not a spaceplane, nor lands like one

The spaceplanes are spaceplanes for reasons, too.

The landing method plays no role for aerobraking.

[RCgothic]

9 minutes ago, kerbiloid said:

All capsules except Vostok/Voskhod are flat-bottommed, 

Except for the craft that are round, no craft are round.

[kerbiloid]

3 minutes ago, RCgothic said:

Except for the craft that are round, no craft are round.

All re-entry vehicles but spherical are lifting bodies. Capsules or planes, doesn't matter. It's to aerobrake nicely.

***

Btw. @tater
If attach winglets to the SLS central core, will it then become reusable?
If yes, maybe SLS makes sense?

Edited April 21, 2021 by kerbiloid

[HvP]

I understand that you're skeptical about the design. You've made that point very plainly.

The proof of the pudding is in the eating, as they say. Starship is still in the prototyping test stage. Will you still be so adamant if Starship is successful at reentry over the next year or two? Or will you still be unconvinced?

Edited April 22, 2021 by HvP

[tater]

27 minutes ago, kerbiloid said:

If attach winglets to the SLS central core, will it then become reusable?

needs huge wings since RS-25 can't restart

 

[JcoolTheShipbuilder]

4 minutes ago, tater said:

needs huge wings since RS-25 can't restart

 

*imagines the SLS with giant flapping wings landing*
 

hmmm.... it’s plausible, but not feasible

[RCgothic]

47 minutes ago, kerbiloid said:

All re-entry vehicles but spherical are lifting bodies. Capsules or planes, doesn't matter. It's to aerobrake nicely.

***

Btw. @tater
If attach winglets to the SLS central core, will it then become reusable?
If yes, maybe SLS makes sense?

Cylinders are also lifting bodies.

[Silavite]

6 hours ago, tater said:

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

True, though STS-1 did have a bit of a close call during reentry due to issues with real gas modeling not matching the actual dynamics of reentry.

Quote

During STS-1, the body flap deflection was twice the amount than had been predicted would be required and was uncomfortably close to the body flap’s deployment limit of 22.5 degrees. NASA determined that the cause was “real gas effects”— a phenomenon rooted in high-temperature gas dynamics.

 

[kerbiloid]

42 minutes ago, HvP said:

Will you still be so adamant if Starship is successful at reentry over the next year or two? Or will you still be unconvinced?

I appreciate any ending of the Starship efforts, just to know if it's possible. I don't have payload to launch.

But the euphoria around it looks so optimistic, when it never tested a prototype of any of its two stages (30-engine 1st and aerobraking 2nd)...

And all previous projects finished in spaceplane-like shapes, so I doubt very much if this cylindric shape can ever be viable.

P.S.
@Kerbaloid stopped visiting the forum probably because he is always referred instead of me.

20 minutes ago, RCgothic said:

Cylinders are also lifting bodies.

Their L/D is much lesser than a plane-like lifting body shape.
So, they have never been used to aerobrake from orbit.

Notice:  Starship is a proper, exact, cylindric cylinder. Round as a sausage. Symmetric.
While even  the wingless spaceplanes are nearly but not exactly cylindric, flattened from bottom.
And if Starship gets non-ideally cylindric, it stops matching the first stage shape, so then there is no reason to have it cylindric. And if so, it would evolve into a spaceplane.

Edited April 21, 2021 by kerbiloid

[tater]

4 minutes ago, kerbiloid said:

But the euphoria around it looks so optimistic, when it never tested a prototype of any of its two stages (30-engine 1st and aerobraking 2nd)...

I think it's been tempered by SpaceX just plodding on its own. Knowing that NASA has looked at the nuts and bolts and thinks it's plausible makes me more convinced they can make it work.

If any sort of cost effective reuse can become a thing, it really is game changing.

[RCgothic]

12 minutes ago, kerbiloid said:

Their L/D is much lesser than a plane-like lifting body shape.

So, they have never been used to aerobrake from orbit.

Notice:  Starship is a proper, exact, cylindric cylinder. Round as a sausage. Symmetric.
While even  the wingless spaceplanes are nearly but not exactly cylindric, flattened from bottom.
And if Starship gets non-ideally cylindric, it stops matching the first stage shape, so then there is no reason to have it cylindric. And if so, it would evolve into a spaceplane.

Starship is not a spaceplane. It doesn't need high L/D. Re-entry vehicles don't *need* any lift. Vostok and Voskhod don't have any. All re-entry vehicles need is stability (Starship is actively stable) and a TPS (which Starship has).

Also it's not a pure cylinder. It has fins.

SpaceX are not idiots. I guarantee if it had to be another shape it would be another shape. 

[kerbiloid]

12 minutes ago, RCgothic said:

Starship is not a spaceplane. It doesn't need high L/D. Re-entry vehicles don't *need* any lift. Vostok and Voskhod don't have any. All re-entry vehicles need is stability (Starship is actively stable) and a TPS (which Starship has).

If it dives, it burns. If it flies too long, it burns. Regardless of the fact if it's called "spaceplane" or not.

Everything need either L/D to pass between two burns, or very thick and heavy skin (like Vostok had).

14 minutes ago, RCgothic said:

Also it's not a pure cylinder. It has fins.

The hull is cylindric. The fins are to small to take them into account.

14 minutes ago, RCgothic said:

SpaceX are not idiots. I guarantee if it had to be another shape it would be another shape. 

This makes to stop worry about the aerodynamic forces.

[sevenperforce]

Just now, kerbiloid said:

The hull is cylindric. The fins are to small to take them into account.

They are decidedly not too small to take into account. They have a dramatic effect. 

[RCgothic]

I guarantee you're not saying anything SpaceX haven't already thought of. This isn't their first re-entry.

3 hours ago, kerbiloid said:

I just want to see an upper stage stayed structurally intact after aerobraking, according to its telemetry.

Just sit tight and some day (very likely this year) you'll get your wish.

[SOXBLOX]

9 minutes ago, kerbiloid said:

The hull is cylindric. The fins are too small to take them into account.

Um, no. They're called control surfaces for a reason. Look, I figure these people know what they're doing.

And just because a high percentage of the small number of human-carrying return vehicles have had a certain shape does not mean that all future vehicles must have that shape.

What are you worried will happen? Do you think Starship won't be able to control itself properly; or that it will break up on reentry, or something else?

[tater]

16 minutes ago, RCgothic said:

Just sit tight and some day (very likely this year) you'll get your wish.

The beauty of the current iteration of "Elon time" is that we get to watch interesting stuff happen literally in front of us (since we always have screens), and in real time.

If SN15 flies in the next week to 10 days, it will be keeping the pace of around a flight a month.

That's a bunch of flights before the end of the year.

[SunlitZelkova]

53 minutes ago, tater said:

I think it's been tempered by SpaceX just plodding on its own. Knowing that NASA has looked at the nuts and bolts and thinks it's plausible makes me more convinced they can make it work.

If any sort of cost effective reuse can become a thing, it really is game changing.

NASA also went forward with the Space Shuttle despite its major risks and thought that the Ares I was a good idea. These two things happened for different reasons, but NASA's interest should not be an indicator of viability.

We will just need to wait and see. Either the SpaceX engineers will experience the exhilaration of the Apollo engineers following Armstrong's footstep, or the disappointment of the L3 engineers following the third explosion of the N1. No amount of discussion here, either for or against Starship, will change the outcome in the end, or the way reentry works.

Even if it can't reenter, Starship has other uses. Although it would be expensive and become less capable, surely they could redesign the architecture to have less reusability.

[Elthy]

Guys, you are just feeding a troll...

Noone here knows better than SpaceX engineers.

[tater]

It's not a sure thing, but I think it is possible. I'll fully admit that I want fully reusable spacecraft to be a thing. It seems possible WRT the physics, so it's just a matter of when it gets done.

Under the assumption that full reuse is possible, then the sooner it exists, the better.

[SOXBLOX]

6 minutes ago, SunlitZelkova said:

but NASA's interest should not be an indicator of viability.

Can I offer a correction? Fine. "[Congressional representatives'] interests should not be indicators of viability." There.

[kerbiloid]

53 minutes ago, sevenperforce said:

They are decidedly not too small to take into account. They have a dramatic effect. 

1. Are they tested on aerobraking? Do they provide enough L/D and not break?
2. They don't have effect on the hull shape.

44 minutes ago, RCgothic said:

I guarantee you're not saying anything SpaceX haven't already thought of. This isn't their first re-entry.

They didn't have any survived re-entry except the Dragon  capsules.

44 minutes ago, RCgothic said:

Just sit tight and some day (very likely this year) you'll get your wish.

That's exactly what I'm doing, but still nothing.

38 minutes ago, SOXBLOX said:

Um, no. They're called control surfaces for a reason.

They are control surfaces. And it needs lifting ones.

It's not enough to turn a flying iron under proper angle. Enough lifting surface is required, too.

38 minutes ago, SOXBLOX said:

What are you worried will happen? Do you think Starship won't be able to control itself properly; or that it will break up on reentry, or something else?

I'm not worried at all. I expect them redeveloping the 2nd stage into a spaceplane.

13 minutes ago, Elthy said:

Guys, you are just feeding a troll...

Noone here knows better than SpaceX engineers.

No one knew better that Space Shuttle engineers when they made the cylinder expendable and moved the engines into the winged body.
Btw, it's still the only reusable upper stage ever succeeded.

How can one be sure that current knowledge is enough to make a cylinder re-entry stage when this has never been proven yet.

Edited April 21, 2021 by kerbiloid