Jump to content

SpaceX Discussion Thread


Skylon
 Share

Recommended Posts

Just now, SOXBLOX said:

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

Well, both. NASA's view on things can be used in a discussion, I am just cautioning to avoid treating it like the gospel (as a source). Whereas a Congressman's view on a rocket should be ignored for a number of reasons.

For me, rather than any organization or person said so, I would like to "see the numbers".

Link to comment
Share on other sites

15 minutes ago, kerbiloid said:

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

Pretty sure they had discussed recovering the second stage with a propulsive landing, but dropped the concept, because it had no major benefit. In case you hadn't noticed, the second stage is a perfect cylinder, minus the rocket nozzle. And how about Electron reuse? It has no wings. It survived reentry with just thrusters.

13 minutes ago, SunlitZelkova said:

Well, both.

Yeah, but I would like to point out that the Shuttle and Ares 1 were camels, a horse designed by committee. Starship is designed with a specific, constant mission set in mind, and that's a huge difference.

Edited by SOXBLOX
Link to comment
Share on other sites

1 minute ago, SOXBLOX said:

Pretty sure they had discussed recovering the second stage with a propulsive landing, but dropped the concept, because it had no major benefit. In case you hadn't noticed, the second stage is a perfect cylinder, minus the rocket nozzle. And how about Electron reuse? It has no wings. 

Yeah, but I would like to point out that the Shuttle and Ares 1 were camels, a horse designed by committee. Starship is designed with a specific, constant mission set in mind, and that's a huge difference.

Yes. Also, don't insult camels!

I should have been more clear. NASA's interest is not an indicator of viability, but at the same time, that is not to say NASA's interest means it is somehow non-viable.

Link to comment
Share on other sites

3 hours ago, kerbiloid said:

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.

The Shuttle wasn't exactly an "upper stage". More like a sustainer stage. Although, the OMS engines acted kind of like what some upper stages act like.

Anyway, the Shuttle was clearly designed around a very different mission and with different technology. Some comparisons with the Shuttle are valid, but others are pretty questionable.

It's also pretty clear that most of what drives Starship design is not actually the LEO mission or even the Lunar mission.  A lot of the design was clearly driven by a desire to develop a Mars lander.

I think it's actually pretty clear that if you just want to ferry people up to orbit then small capsules are fine. And there are now many examples of spaceplanes that show that the spaceplane concept also works just fine -- if you have a runway to land on. What drives the Starship design is the desire to land on Mars where runways are not available and the atmosphere is too thin for planes or parachutes to be practical.

Edited by mikegarrison
Link to comment
Share on other sites

5 hours ago, SOXBLOX said:

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?

Funny since most planes has an cylindrical body.  Exceptions tend to be modern fighter jets and stuff like the B2.  However here the hull is not pressurized and its reasons why hull is not an cylinder like having to fit two huge engines or stealth. 

Link to comment
Share on other sites

Previous reentry vehicles were not shaped like cylinders because there was no need to do so. The capsules did not have a cylindrical shape because that was not the optimum shape for their missions. SpaceX now wants to bring a vehicle with a cylindrical hull back to Earth intact (because that shape is optimal  for a  launch vehicle body), so they will attempt to do so. I don't know of any Physics reasons saying that it's impossible, so I expect they can do the engineering. We'll see.

The only cylindrical object that I know of that was designed to reenter Earth's atmosphere and land intact (and which actually DID so) was the Apollo Lunar Module SNAP Plutonium cask. On Apollo 13, that cylindrical object entered Earth's atmosphere at lunar speeds and successfully survived the entry and ocean impact without loss of structural integrity (since none of the plutonium was detected in the atmosphere or ocean). Engineering success.

Link to comment
Share on other sites

4 hours ago, mikegarrison said:

The Shuttle wasn't exactly an "upper stage". More like a sustainer stage. Although, the OMS engines acted kind of like what some upper stages act like.

Anyway, the Shuttle was clearly designed around a very different mission and with different technology. Some comparisons with the Shuttle are valid, but others are pretty questionable.

It's also pretty clear that most of what drives Starship design is not actually the LEO mission or even the Lunar mission.  A lot of the design was clearly driven by a desire to develop a Mars lander.

I think it's actually pretty clear that if you just want to ferry people up to orbit then small capsules are fine. And there are now many examples of spaceplanes that show that the spaceplane concept also works just fine -- if you have a runway to land on. What drives the Starship design is the desire to land on Mars where runways are not available and the atmosphere is too thin for planes or parachutes to be practical.

Yes, space planes has the benefit of having an large cross section then re-entering and they can land like planes. 
Downsides is the weight of the wings and the landing gear and structure letting it land as a plane.  They are also expensive to develop.

Powered landings has the benefit of using the engines you already need and it land upright so forces is a lot like liftoff. 
Now one smart thing about starship is that it does not need to survive reentry to work as an cheap very heavy lift rocket. 
I don't think launching starlinks on SS will be much more expensive than on falcon 9 even if second stage does not survive, and they will learn stuff to improve the next SS.

Who raises an question, there will orbital SS land. I can not imagine they overflying Texas with an very high chance of breaking up. 
It makes more sense to have an landing spot on the west coast next to the ocean. Another idea is to use the oil platform they bought to land SS on. 
This is pretty simple just strip off most of the superstructure and add an landing deck. You can even have facility to refuel it to jump back to base but you want an crane so you can put it on an ship too. 

Link to comment
Share on other sites

6 hours ago, SOXBLOX said:

It also doesn't have a full-surface heat shield.

It doesn't need it, because it's the 1st stage. Its speed is much lower than re-entry speed.

6 hours ago, SOXBLOX said:

Anyway, how about the Falcon second stage?

How what? Its remains have fallen on ground. Is it still intact and reusable? Did it have heavy fragile parts like engines staying intact?

Afaik, no. Just remains.

5 hours ago, mikegarrison said:

The Shuttle wasn't exactly an "upper stage". More like a sustainer stage. Although, the OMS engines acted kind of like what some upper stages act like.

The Shuttle is a part of the splitted second/upper stage. To save the engines, they use a spaceplane which is at the same time the vessel itself.
But they didn't try to land the fuel tank of the second stage, they were saving the most expensive part of it, the engines.

These engines were not used in orbit (as they didn't have fuel onboard), so they are not own engines of the vessel itself, they are exactly launch vehicle's engines.

5 hours ago, mikegarrison said:

Anyway, the Shuttle was clearly designed around a very different mission and with different technology. Some comparisons with the Shuttle are valid, but others are pretty questionable.

The Shuttle is still the only case when some part (let alone - whole) of a second/upper stage has been returned and even reused.
So, currently nobody has implemented something better for that than a winged lifting body.

5 hours ago, mikegarrison said:

It's also pretty clear that most of what drives Starship design is not actually the LEO mission or even the Lunar mission.  A lot of the design was clearly driven by a desire to develop a Mars lander.

But they have to reentry here, long before they can (if ever can) get to Mars.

So, they may be happy on Mars, but first it must be able to aerobrake on the Earth.

5 hours ago, mikegarrison said:

I think it's actually pretty clear that if you just want to ferry people up to orbit then small capsules are fine. And there are now many examples of spaceplanes that show that the spaceplane concept also works just fine -- if you have a runway to land on. What drives the Starship design is the desire to land on Mars where runways are not available and the atmosphere is too thin for planes or parachutes to be practical.

I know four reasons to make spaceplane instead of capsules.

1. (main)
A military craft capable to return to an inhabited place (preferrably - a military base) from an orbit with random inclination. The aim of the side maneuver beloved by the warrior staff.
Was mostly actual in 1960, for a single-orbit-turn fly-by recons and bombers.
Obviously, not about Starship.

2.
Return fragile human material, like civil specialists, not trained for 9-g overloads. Because 2..3 g instead of 3..4+,

3.
Return large and/or heavy cargo, because a conic capsule for that would require a giant capsule of enormous mass.
The Shuttle primary purpose, as it was designed first - to deliver from orbit KH-11 when they scrapped the KH-10 Dorian/MOL project; second - to be the only civil launch vehicle to pay for the whole program.

As KH-11 was the first spysat without photocapsules, so its lifetime was not limited by amount of photofilms and photocapsules, which were never delivered to American spysats.
Originally they were planning to save the film and photocapsules by placing clever crew on the spysat, so they combined Gemini+home-on-wheels+Dorian and got MOL.
But better electronics killed this romantics by providing enough wide radiochannels to transfer images by radio instead of the films.
USSR made Almaz, which was not limited in that sense, because TKS was bringing all that stuff.
So, Pentagon wanted a ferry craft to rotate the expensive KH-11, i.e. a whole fleet of Hubbles yearly or so. But KH-11 appeared to live without repair much longer, and this killed the main purpose of Shuttle, turning it into the overexpensive launch vehicle combined with internal capsule for eight.

4.
Return the main engines of the upper stage, because they can stick out backwards, and they are heavy.
The secondary purpose of shuttle. It delivers the 2nd stage engines, balanced with the crew capsule at the opposite end.

For Spaceship as a spaceplane-like craft only #2 and #4 are actual.

1 hour ago, Brotoro said:

Previous reentry vehicles were not shaped like cylinders because there was no need to do so. The capsules did not have a cylindrical shape because that was not the optimum shape for their missions

Capsules appeared later. All original plans, US and SU, were about spaceplanes of various shapes.
Capsules were treated as something doubtful. Just when they realized that spaceplanes wouldn't be a thing in the near future, they accepted the capsules.

1 hour ago, Brotoro said:

SpaceX now wants to bring a vehicle with a cylindrical hull back to Earth intact (because that shape is optimal  for a  launch vehicle body),

It's optimal for launch, but not fo re-entry.
And normally the last stage is much smaller than the first one, so it plays no role how optimal is it for launch.

1 hour ago, Brotoro said:

I don't know of any Physics reasons saying that it's impossible, so I expect they can do the engineering. We'll see.

Suboptimal shape results in greater strength at heat capacity requirement, in greater mass of the launch vehicle payload.

P.S.
Got an analogy.
Current Starship upper shape is like Cybertruck, an ugly prototype of actual design.

Edited by kerbiloid
Link to comment
Share on other sites

48 minutes ago, kerbiloid said:

Suboptimal shape results in greater strength at heat capacity requirement, in greater mass of the launch vehicle payload.

Mass doesn't matter.

Cost/kg is all that matters.

If expendable vehicles (or spaceplanes) can get us to 10s of dollars per kg, great. I suppose as Musk said to the Boeing CEO:

 

Link to comment
Share on other sites

If I'm understanding the argument correctly:

  • There have been plenty of reentry vehicles, yet none are cylindrical.
  • The cylinder would have been used it were a viable shape.
  • The cylinder hasn't been used historically, ergo it is likely unsound.

I think that arguing from the perspective of historical trends isn't necessarily sound in this case. I would argue that capsules have been predominant due to their stability without active control surfaces (only a CG shift and RCS are necessary). Among reentry vehicles with active control surfaces, all thus far have utilized lift to glide to a horizontal landing (X-15, Dyna-soar, MiG-105, Buran, STS, X-37B). Therefore, Starship's rather unique method of landing (descent at 90 degrees AoA and then vertical propulsive landing) makes the comparison to other vehicles (which utilize lift during the terminal phase) invalid.

If I may flip this conversation for a moment: Does @kerbiloid have a dynamical or thermal reason as to why the cylindrical body is unsound?

Link to comment
Share on other sites

Starship doesn't claim to be stable like a capsule—like Shuttle it will need to be controlled, presumably their models (they've shown simulations (not glossy renders)) show that the flaps provide enough control combined with RCS to maintain the desired nose up attitude.

Seems like a very long argument for something we may literally watch live in a few months. Does anyone think it will fail so badly that Elon slaps his forehead and say, "Wings, we need to add wings!"

3 minutes ago, kerbiloid said:

The thicker the hull - the lighter the cargo,

True, but SpaceX just bid against smallsat launchers to launch 5 cubesats using Starship. Presumably the extra 100,000kg will be packed with Starlinks.

Spoiler

Mars, but they've been working Earth as well (since it's obviously a required aspect of the mission plan).

 

Edited by tater
Link to comment
Share on other sites

Does this Kerbiloid guy really think that he understands re-entry and what is possible during re-entry better than  Elon Musk, all the engineers at spaceX and at NASA? If it was so obvious that re-entry with cylindrical hull was impossible, why [Snip] would spaceX use all this time, effort and money to design and test such a vehicle? They aren't exactly idiots at spaceX

Also many many people called landing falcon core stage on a drone ship a science fiction and impossible until it was done. SpaceX has already proven that it can do amazing stuff that many consider impossible

Edited by James Kerman
Redacted by a moderator
Link to comment
Share on other sites

6 hours ago, tseitsei89 said:

Does this Kerbiloid guy really think that he understands re-entry and what is possible during re-entry better than  Elon Musk, all the engineers at spaceX and at NASA? If it was so obvious that re-entry with cylindrical hull was impossible, why [Snip] would spaceX use all this time, effort and money to design and test such a vehicle? They aren't exactly idiots at spaceX

Also many many people called landing falcon core stage on a drone ship a science fiction and impossible until it was done. SpaceX has already proven that it can do amazing stuff that many consider impossible

It's legitimate to wonder if it will work, and it's not certain it will (though I think it will).

 

Spoiler

We keep him around for his consistently amusing interjections.

Spoiler

Usually posted inside a spoiler.

Spoiler

Burma Shave

 

 

 

Edited by Gargamel
Portions of Quote Redacted by moderator.
Link to comment
Share on other sites

3 minutes ago, tater said:

It's legitimate to wonder if it will work, and it's not certain it will (though I think it will).

 

  Reveal hidden contents

We keep him around for his consistently amusing interjections.

  Reveal hidden contents

Usually posted inside a spoiler.

  Reveal hidden contents

Burma Shave

 

 

 

Yeah, it is of course not guaranteed to work, but the argument he has ("it won't work because hull is cylindrical and previous re-entry vehicles have not been cylindrical") is quite ridiculous. He is basically saying that "it won't work because it hasn't been done before". By that logic nothing new will ever work.

Link to comment
Share on other sites

Yeah indeed this is getting tedious reading the same argument about why it won't work, over and over. It's an interesting argument, point taken, but we ultimately don't know and the answer is still a giant "maybe", no matter how much we keep on beating this dead horse.

On one side we have kerbiloid from the internet, on the other we have SpaceX and to an extent NASA.

I'd be willing to bet money that SpaceX has a better idea about this than keribiloid. I'd be willing to bet billions, in fact. Of course, I'm talking out of my ass since I don't have billions.

However, some people do, and that's exactly what they did with it.

 

Link to comment
Share on other sites

And if somebody pays attention, that's not kerbiloid repeats the same argument,  but kerbiloid is repeatedly quoted with no argument  but "In Musk we trust".

Of course, absence of billions should not make anyone do things he is not used to. 

I hope, SpaceX succeeds with cylindric Starship, so I will be able to treat this as a viable design for KSP, because it would simplify a lot.

Edited by kerbiloid
Link to comment
Share on other sites

Switching topics a bit, I’m cross-posting this from the Perseverance thread.

https://www.bbc.co.uk/news/science-environment-56844601

Why? Because not only has oxygen been made on Mars but carbon monoxide has too. And CO is one possible starting material for synthesising methane on Mars which I believe is relevant to SpaceX’s interests!

More importantly, it’s a practical demonstration that CO2 can be captured in useful quantities from the Martian atmosphere, which is a prerequisite for synthesising methane via the (more direct), Sabatier process.

Link to comment
Share on other sites

32 minutes ago, kerbiloid said:

And if somebody pays attention, that's not kerbiloid repeats the same argument,  but kerbiloid is repeatedly quoted with no argument  but "In Musk we trust".

Of course, absence of billions should not make anyone do things he is not used to. 

I hope, SpaceX succeeds with cylindric Starship, so I will be able to treat this as a viable design for KSP, because it would simplify a lot.

I've presented plenty of arguments:

1) Re-entry vehicles don't need lift.

2) In any case, cylinders have lift and fins have lift.

3) The design of re-entry vehicles is generally dominated by bluntness for heat transfer purposes, not aerodynamics.

4) Being large, Starship is blunt without special shapes.

5) Sure, the other vehicles can benefit from efficiencies of special shape, but they aren't primarily high pressure pressure vessels which are dominated by other requirements.

6) There have been round re-entry vehicles.

7) Starship has active stability and TPS and so will be controllable during re-entry and terminal descent.

Here's a new one:

8) Stainless steel is more robust than normal aerospace alloys and doesn't need to be protected to the same extent.

The counterpoint presented of "re-entry vehicles can't be cylinders because they've never been cylinders before" is pretty easily dismissed by "they haven't needed to be".

Only *after* all of that do I appeal to SpaceX and NASA knowing what they're doing, because they self-evidently do.

Edited by RCgothic
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...