totm nov 2023 SpaceX Discussion Thread

[kerbiloid]

3 minutes ago, RCgothic said:

Wings are heavy and useless in space. They're not needed 

Gears and legs, too.

1 minute ago, tomf said:

SS is significantly larger than any capsule

And shuttle was.

[Lewie]

53 minutes ago, kerbiloid said:

 

They should split the tasks into
a partially reusable superheavy of 500+ t payload, to make the Martian ships and the lunar bases reasonable;
an Orion-like ship for the Moon and the Mars (though, it's already claimed by Orion, so not viable)
a CST-100 (but already claimed by CST-100)
scrap the Dragon before it killed somebody (and anyway it can't get lunar), as CST-100 is enough for ISS and Bigelows
develop a standard set of lunar/Martian base modules
develop heavy orbital platforms for low-class customers

Concentrate on large scale cargo fargo, leaving the rare and political crewed flights for CST-100 and Orion which anyway unlikely will get gone.

Why make it a 500+ ton partiality reusable craft? Elon has already said an expendable version would get only 250 tons to LEO, to double that would make SS/SH much more complicated+expensive (which at that point you WANT to make it fully reusable)

Why scarp Dragon? It works well, it’s cheap...

Starliner has yet to fly successfully. Don’t forget the first flight or the problems surrounding the second.

[kerbiloid]

2 minutes ago, Lewie said:

Why make it a 500+ ton partiality reusable craft?

Not exactly, just an ISS or Mir equivalent in one launch, to avoid the orbital assembling.

But also 500+ means 100+ on the Moon, so a lunar base without building.

4 minutes ago, Lewie said:

Why scarp Dragon? It works well, it’s cheap...

The crew Dragon competes with CST-100, and the hypergolic fuel tank inside the crew capsule is weird.

(CST-100 will probably exist anyway, due to political resource.)

[Deddly]

8 minutes ago, kerbiloid said:

Gears and legs, too.

Shuttle had some pretty hefty landing gear, too, Kerbiloid.

As for the point you keep making about wings, Shuttle did not need all of its lift for reentry, it needed that lift for landing on a runway horizontally. If it didn't need to land on a runway, its wings would have been much smaller, maybe even non-existent.

[sevenperforce]

Ignoring this ongoing war and back to the main topic...

I’ve been discussing the catching arm structure with the folks at NSF and this looks fairly promising.

Also, here’s a solution for precise positioning.

 

[tomf]

8 minutes ago, kerbiloid said:

Gears and legs, too.

And shuttle was.

The shuttle had the requirement for the enormous cross range capability, and lacked the  processing to do the flip and propulsive landing which would have been significant drivers in choosing a winged design

[kerbiloid]

4 minutes ago, Deddly said:

Shuttle had some pretty hefty landing gear, too, Kerbiloid.

I'm aware. Also I don't think that everything not needed in vacuum is not needed in flight. Say, the wings.

4 minutes ago, Deddly said:

Shuttle did not need all of its lift for reentry, it needed that lift for landing on a runway horizontally.

I'm afraid the only attempt of the Shuttle to do without a wing finished bad.

Of course, it was asymmetrical, but the lifting force suffered.

Anyway, Shuttle was not a rounded cylinder, it was a flat-bottomed cylinder.

And another one. Wingless but flat and triangular in cross-section.

Spoiler

 

Edited August 9, 2021 by kerbiloid

[sevenperforce]

4 minutes ago, kerbiloid said:

The crew Dragon competes with CST-100, and the hypergolic fuel tank inside the crew capsule is weird.

Heaven forbid that a crew capsule would have hypergolic fuel tanks inside of it!!

That has only ever been done with Mercury, Gemini, Apollo, Orion, and Soyuz! 

4 minutes ago, Deddly said:

As for the point you keep making about wings, Shuttle did not need all of its lift for reentry, it needed that lift for landing on a runway horizontally. If it didn't need to land on a runway, its wings would have been much smaller, maybe even non-existent.

Indeed. In fact, the Shuttle specifically had too much lift for reentry and had to do lengthy and complex S-curve maneuvers to survive. 

[Beccab]

2 minutes ago, kerbiloid said:

Anyway, Shuttle was not a rounded cylinder, it was a flat-bottomed cylinder.

Sounds like shuttle would be an awful comparison to starship

[kerbiloid]

3 minutes ago, sevenperforce said:

That has only ever been done with Mercury, Gemini, Apollo, Orion, and Soyuz! 

Mercury - on top, outside, small, almost spent, and that was the first jump.

Gemini- the same.

Soyuz - never. Only peroxide vented before landing.

Apollo, Orion - much smaller amounts than 1+ t, and true cowboys love the risk.

Edited August 9, 2021 by kerbiloid

[southernplain]

3 minutes ago, kerbiloid said:

to avoid the orbital assembling.

Why though? Orbital assembly works and we are going to have to do more of it if we want to become a spacefaring civilization.

Engineering and building a 500t LV is much harder than a 150t LV.

2 minutes ago, sevenperforce said:

Indeed. In fact, the Shuttle specifically had too much lift for reentry and had to do lengthy and complex S-curve maneuvers to survive. 

Its almost as if Shuttle's design stems from a combination of requirements that Starship is not bound by. The DOD isn't going to require absurd cross range from Starship and it doesn't have to land like an airplane.

[sevenperforce]

1 hour ago, kerbiloid said:

A primitive cylinder, round in cross-section, like the Starship is like a sphere. Its L/D is very low, it tends to descent ballistically like Vostok.

You are correct that a primitive cylinder moving with its axis at 90° to the direction of flight will have the same L/D ratio as a sphere—zero—and will descend ballistically.

You are incorrect in supposing that Starship will perform re-entry with its long axis at 90° to the direction of flight. Starship will fly with a significant angle of attack and have an L/D ratio significantly greater than a capsule like Apollo.

[Elthy]

8 minutes ago, sevenperforce said:

Ignoring this ongoing war and back to the main topic...

I’ve been discussing the catching arm structure with the folks at NSF and this looks fairly promising.

Also, here’s a solution for precise positioning.

 

I feel realy unconfortable seeing those large levers on which a rocket with >200t drymass is going to land. They surely did the math and it works out, it just seems so wrong...

Also i want to kindly remind some folks here that there is an ignore-function available in the forum: https://forum.kerbalspaceprogram.com/index.php?/ignore/

[sevenperforce]

5 minutes ago, kerbiloid said:

Mercury - on top, outside, small, almost spent, and that was the first jump.

Gemini- the same.

Soyuz - never. Only peroxide vented before landing.

Peroxide is, incidentally, hyperbolic. It is also what the Mercury capsule used.

And of course Dragon 2 vents its residuals while descending under chute  as well. All capsules do.

5 minutes ago, kerbiloid said:

Apollo, Orion - much smaller amounts than 1+ t, and true cowboys love the risk.

Less than 1 tonne or more than 1 tonne, it doesn’t matter how much. Any hypergolic propellant tank breach in a capsule’s RCS or propulsion system, even a modest one, is a catastrophic LOCV. Always.

Besides, while we are talking about hypergolic fuel tanks on a crew vehicle, what about the Shuttle?

4 minutes ago, Elthy said:

I feel realy unconfortable seeing those large levers on which a rocket with >200t drymass is going to land. They surely did the math and it works out, it just seems so wrong...

Well, this is still just hypothetical in terms of configuration. We don’t know anything for sure yet.

One advantage of the design I’ve put together above is that the lift block interfaces directly with the hinge points on the arms, so the cantilever moment is provided by interface with the carriage in tention.

[MKI]

8 minutes ago, southernplain said:

Its almost as if Shuttle's design stems from a combination of requirements that Starship is not bound by. The DOD isn't going to require absurd cross range from Starship and it doesn't have to land like an airplane.

I think Starship could still have the awesome James-Bond level capability of hijacking a Satellite in orbit right? 

 

Actually if propulsive landing was a thing that was "figured out" and used for a Shuttle system, I wonder what the shuttle would look like today . Not saying it would be Starship, but maybe it would of been more re-usable and successful (and safer)

[Deddly]

25 minutes ago, kerbiloid said:

And another one. Wingless but flat and triangular in cross-section.

And designed to land horizontally.

[southernplain]

3 minutes ago, MKI said:

Actually if propulsive landing was a thing that was "figured out" and used for a Shuttle system, I wonder what the shuttle would look like today . Not saying it would be Starship, but maybe it would of been more re-usable and successful (and safer)

Something like the DC-X or the Chrysler SERV maybe: http://www.astronautix.com/s/serv.html

There were lots of wacky alt-shuttle designs floating around in the 60's-70's although I don't know of too many VL variants.

Shuttle is honestly a terrible thing to benchmark your design program around though. So many political decisions fed into the requirements that the end product was seriously compromised. I got the sense in the Everyday Astronaut video, in the parts on Shuttle, that Elon was trying not to trash NASA's history there. However, it is really hard to call the Shuttle anything other than a cautionary tale.

Step 1: Make requirements less dumb. If NASA/DOD had followed that, we wouldn't have got Shuttle as we did.

[Beccab]

3 minutes ago, southernplain said:

Step 1: Make requirements less dumb. If NASA/DOD had followed that, we wouldn't have got Shuttle as we did.

But if it can't launch bombs from orbit over the soviet union and land without passing over it again then what's the point of a low cost reusable NASA shuttle made for station assembly?

[JoeSchmuckatelli]

6 minutes ago, southernplain said:

Make requirements less

...amended on by a committee. 

 

The Govt has a real hard time with that. 

[southernplain]

8 minutes ago, Beccab said:

But if it can't launch bombs from orbit over the soviet union and land without passing over it again then what's the point of a low cost reusable NASA shuttle made for station assembly?

Its obviously of no use at all! I'll be darned if those NASA hippies get a shuttle while the Soviets are the only ones to militarize space! Uncle Sam can do it better, why our military space program will have card games and women of ill-repute! Yee-haw! - Cold War USAF planners.

11 minutes ago, JoeSchmuckatelli said:

...amended on by a committee. 

 

The Govt has a real hard time with that. 

I think a comparatively huge advantage SpaceX has in the pursuit of a reusable launch system is they are basically only beholden to Musk and small number of hand-picked investors. As long as Musk stays in the picture, SpaceX can pursue whatever design they need to fulfill the mission without being beholden to dozens or hundreds of government stakeholders. Congress has a tendency to lose sight of the big picture end goal when the pork gets rolling.

[Meecrob]

2 hours ago, kerbiloid said:

A cross-section is a rounded triangle with extended aside flat bottom.

Like the cross-section of Apollo, too.

  Reveal hidden contents

 

Dude, its a spaceplane, not a capsule. Like its got wings and landing gear. Please tell me you aren't gonna be so obtuse to argue this?

[Meecrob]

~please delete~

Edited August 9, 2021 by Meecrob

[sevenperforce]

27 minutes ago, Meecrob said:

Dude, its a spaceplane, not a capsule. Like its got wings and landing gear. Please tell me you aren't gonna be so obtuse to argue this?

It is true that for a blunt body experiencing re-entry with 0° angle of attack, the body cross-section is the only thing that has any effect on drag and heat distribution. A sphere functions the same way as a cylinder (assuming the cylinder’s axis is perpendicular to the airflow). A delta-wing aircraft with a flat bottom and rounded fuselage functions the same way as a capsule with a flat bottom and a rounded top.

But this is only if there is no angle of attack (or, depending on your frame of reference, a 90° AoA). With a nonzero angle of attack, lots of things start changing. And that is what someone seems intent on ignoring.

[Jacke]

2 hours ago, Deddly said:

As for the point you keep making about wings, Shuttle did not need all of its lift for reentry, it needed that lift for landing on a runway horizontally. If it didn't need to land on a runway, its wings would have been much smaller, maybe even non-existent.

The Shuttle had its large wings because it needed large cross-range landing ability to satisfy U.S.A.F. requirements for a Vandenberg launch south for a single orbit to deploy a payload, then re-enter to land at Vandenberg.  Earlier designs had smaller straight wings (because they were within the supersonic shockwave of the nose) that weren't final design, but without that large cross-range landing requirement the wings would likely have been smaller.

2 hours ago, southernplain said:

However, it is really hard to call the Shuttle anything other than a cautionary tale.

Somewhat true.  What was wrong was considering the Shuttle to be an "operational space truck" when it was a first and very experimental design put into production that flew and pushed so much so far.  There was a lot of poor design, especially for crew safety considering its abort modes (and Starship has those same safety lackings and should never launch with crew).  Its supply and maintenance chain and handling were far from optimal, partly due to politics.  And there wasn't sufficient safety-over-operations attitude at the start, which led to Challenger.  That it flew so many flights with so low a failure and incident rate was partly luck and a lot of hard work, especially considering the faults.  Its replacement should have been started in design no later than the early 1990's.

Edited August 9, 2021 by Jacke

[Jacke]

2 hours ago, southernplain said:

Orbital assembly works and we are going to have to do more of it if we want to become a spacefaring civilization.

Trying to run, either a sprint or worse a marathon, while still working on walking is fraught with risks.

Straight out of Zubrin's The Case for Mars and his Mars Direct design: ground checkout and assembly is cheaper and much more reliable than orbital assembly and will be so for a long time.

Which is why Mars Direct used 2x Saturn V sized launch vehicles.  To first send the uncrewed Earth Return Vehicle to autonomously create the methane and oxygen using hydrogen feedstock and carbon dioxide from the Martian Atmosphere.  Then the Mars Habitat Vehicle to take out the crew.  And lands near the Earth Return Vehicle for on-surface rendezvous.

https://en.wikipedia.org/wiki/Mars_Direct

Jumping right to orbital assembly and refueling is making a similar mistake to what was done with the Space Shuttle: trying to make an operational vehicle and process when there's not been enough experimental vehicles and process testing.  Look at what went wrong with changing the modules on the ISS just now.  And how easily that could have turned out so much worse.  This is an area that needs more research, development, testing, and practice.