Ariane 5 discontinued - to be replaced by Ariane 6

[scaesare]

I was looking at rocket dimensions as they relate to BIG ROCKETS, like the Ariane which is the subject of the thread.

It is not a pissing match with Starship over what it can do for what price with a refuel aka TWO rockets.

Simply batting around big payload to LEO capacity and what is possible.

Saturn V was near as powerful as the new kid nearly on the block. You have to wonder what they could have done with 3D printed parts.

So you mention "dimensions"... Starship is larger than Saturn V in just about every dimension, except diameter, where I think the engine skirt of the Saturn sticks out a bit past the Starship's straight body, which in turn is wider than Saturn as it tapers down the higher up you go. Starship is also heavier, which is kind of in the "dimension" category.

You then talk about lift capability, which is a specification. SpaceX lists Starship at up to 150K Kg's to LEO, whereas Saturn V is noted as doing 141K Kg.

So again, I'm not sure how Saturn V is the "biggest" in any spec?

 

[scaesare]

I think you mean Starship. The original material was going to be carbon fiber. The idea was to make it as light as possible, improving on Apollo in every way. Then Elon saw how expensive and slow carbon fiber was going to be to work with, and he started thinking about materials from scratch, and came up with the idea of stainless steel. It has every good property you would want, including low cost, ease of use, the right thermal properties, and so on. One of its unfortunate properties is mass.

And I don't think it was all just ease/expense of construction... while steel is heavier per unit area than carbon fiber or other composites, Elon has said that the additional heat shielding required for composites made steel less of a tradeoff in terms of overall mass. I suspect that has changed somewhat, as I think that was in the days of the transpirational cooling idea, which Elon has since recently said requires more internal mass than tiles... so I wonder what the mass tradeoff for steel+tiles for composites+shielding is....

Elon quotes LEO payloads all the time, but we don't know what the actual capability is. It may be around 50 tons right now, but SpaceX is just trying to get the vehicle to work right now. Optimization will come later. The goal is to get to 200 tons to LEO, or even more. As Elon says, for now the payload is data. Even if Starship's final mass to LEO is "only" the same as the Saturn V, it would be a massive step forward because of the system's capability over time. Apollo launched every couple months at best, and each rocket cost $1.6 billion in 2024 dollars. The Starship design has the potential to launch daily at perhaps 1% of the cost, and Elon aspires to do better than that.


They didn't need anything larger than they built, and there was plenty of room onboard Skylab as it was. A larger station would have cost more. The astronauts had two hours of free time, but they normally worked during that time. That, or enjoyed the views. This was the early days, and they weren't thinking about playing games in space. Private space stations can figure out entertainment.

Part II - Life on Skylab - NASA

Originally Published Nov. 10, 2003

www.nasa.gov

And Skylab was a repurposed Saturn V tank/structure when the program was cancelled, I believe... so it's dimensions were set.

 

[TunaBug]

Why not have a nice roomy space station with a rec lounge wing and pool table if you can?

They didn't need anything larger than they built, and there was plenty of room onboard Skylab as it was. A larger station would have cost more. The astronauts had two hours of free time, but they normally worked during that time. That, or enjoyed the views. This was the early days, and they weren't thinking about playing games in space. Private space stations can figure out entertainment.

Somebody suggests putting a pool table into zero-g and and you worry about whether they'll have time to play? I'm wondering what zero-g pool would be like, but I'm guessing there's no need for a table since the balls won't stay down...there is no down (queue the Ender jokes). Although it might be a fun exercise to ponder what billiards in space might look like. Put the pockets in random places on the walls? Special room where the walls are the bumpers? Do we need queue sticks, or shall we just throw the queue ball? We'd need pads!

Apologies for not being on topic, but none of this is

 

[QtownTaxiGreg]

launch daily at perhaps 1% of the cost, and Elon aspires to do better than that.

that's great, but they haven't built anything suoerhravy lifting yet so in the meantime it is vaporware. Not saying it won't get done although 1% seems a stretch.

I guess if you take out the development cost and the cost of building spaceships, the cost of turning one around could get down pretty low as most of the rest is fueling up. But overheads would eat you alive.

150K Kg's to LEO

not actually specific on orbit on the Starhip site. In Elonspeak he could be talking about a 150k kg sub orbital science experiment.

Someone is going to have to explain how a rocket that is 150k Kg or thereabouts heavier dry can lift more without being significantly larger and even having smaller fuel capacity iirc.

I think it will have some chemistry involved. Is liquid methane much more energetic for volume than liquid hydrogen or kerosene?

How come Saturn V used two kinds of fuel anyway? Cost, and simple ability to deal with a large quantity of kero being off the chart easier than H², is a couple of possibilities.

Big fat dirt cheap kero machine to get the real H² rocket moving?

Time to remind myself how a rocket generates thrust. It's the material being chucked out the back at tremendous speed, action and reaction.

The teflon plasma rocket for sending probes on their way is a nifty thing at the other end of the scale. 'Ignite' ptfe into a plasma stream that quirts out the back to get maximum thrust from minimum fuel weight. Plasma might be the wrong word. Fully shredded atomic soup???

Still shaking my head at how Starship can get going with the structural weight handicap of the order of the entire payload capacity of a Saturn V. Something is going on here.

 

[scaesare]

that's great, but they haven't built anything suoerhravy lifting yet so in the meantime it is vaporware. Not saying it won't get done although 1% seems a stretch.

I guess if you take out the development cost and the cost of building spaceships, the cost of turning one around could get down pretty low as most of the rest is fueling up. But overheads would eat you alive.

not actually specific on orbit on the Starhip site. In Elonspeak he could be talking about a 150k kg sub orbital science experiment.

Someone is going to have to explain how a rocket that is 150k Kg or thereabouts heavier dry can lift more without being significantly larger and even having smaller fuel capacity iirc.

I think it will have some chemistry involved. Is liquid methane much more energetic for volume than liquid hydrogen or kerosene?

How come Saturn V used two kinds of fuel anyway? Cost, and simple ability to deal with a large quantity of kero being off the chart easier than H², is a couple of possibilities.

Big fat dirt cheap kero machine to get the real H² rocket moving?

Time to remind myself how a rocket generates thrust. It's the material being chucked out the back at tremendous speed, action and reaction.

The teflon plasma rocket for sending probes on their way is a nifty thing at the other end of the scale. 'Ignite' ptfe into a plasma stream that quirts out the back to get maximum thrust from minimum fuel weight. Plasma might be the wrong word. Fully shredded atomic soup???

Still shaking my head at how Starship can get going with the structural weight handicap of the order of the entire payload capacity of a Saturn V. Something is going on here.

Well, if the argument boils down to "I don't believe the published spec", I think that unless you can provide your calcs that they can't meet that number, I'm going to assume the folks that have been actually doing the things within the limits of physics know what they're talking about.

Even if they are off by a bit, they are still in the same ballpark as the ~140 tons that Saturn V could lift to LEO, and exceeds it in all other areas, as I mentioned, so again I'm unsure you suggest Saturn V is the "biggest" rocket ever made.

 

[JB47394]

Something is going on here.

Full-flow staged combustion cycle Raptors. They're more efficient than the F-1 engine (327s vs 264s Isp) and SpaceX has put so many of them on the booster that it lifts off at 1.5g versus the Saturn V's 1.2g. Saturn V wastes more propellant getting out of the gravity well because it leaves it so slowly. So Starship will loft not only the same payload as Apollo, but an extra 100 tons of structure, plus propellant enough to return and land.

How come Saturn V used two kinds of fuel anyway?

RP-1 generates a lot of thrust, but is comparatively inefficient. The thrust is required for a booster stage. Liquid hydrogen produces less thrust, but is comparatively more efficient. The efficiency is required for upper stages.

 

[QtownTaxiGreg]

RP-1 generates a lot of thrust, but is comparatively inefficient. The thrust is required for a booster stage. Liquid hydrogen produces less thrust, but is comparatively more efficient. The efficiency is required for upper stages.

Can you expand on that please? I would have thought efficiency would be the sole criterion in order to get the payload up and cost be damned.

The kind of efficiency
I recognize for a rocket is to able to lift its own weight fast enough to get to LEO and have spare thrust to do the same for some payload. The rocket has to be 100++% efficient. Staging lets you lose dead weight to improve the efficiency of the remainder.

The first satellite was Russian and about the size of a grapefruit. We have moved on aways.

LEO is well inside Earth's gravitational well! It's a speed thing. You have to get up to speed and that's easier with less air around but the gravity is much the same. The moon isn't going anywhere soon.

Hence LEO is the minimum height you need that your orbit won't decay too quickly from the tiny little bit of air left out there. You could 'orbit' after a fashion at 10,000m, as opposed to flying on wings, but you would have to keep putting in massive power. And watch out for commercial jets.

Along with your height you need the speed that you fall towards Earth due to gravity at the same rate as you your trajectory is taking you away.

Speed up and fly out to higher and higher orbit until they again match or you exceed gravity and you are off other places. Speeding up from LEO takes a tiny fraction of the power that getting to orbit takes. This ultimate 'staging' is what Elon wants to solve big time. Then getting away places with a heap of stuff is easy.

 

[JB47394]

Can you expand on that please? I would have thought efficiency would be the sole criterion in order to get the payload up and cost be damned.

There are lots of different factors that must be balanced. In this case, the size of the tanks. A Saturn V first stage that contained liquid hydrogen would be much larger than the one they built. Just going by the density of the two fuels, the hydrogen tank would be ten times that of the RP-1 tank. That would increase the mass of the rocket, and it would never get off the ground. So they needed RP-1 to keep the size of the tank down while providing lots of power.

 

[QtownTaxiGreg]

There are lots of different factors that must be balanced. In this case, the size of the tanks. A Saturn V first stage that contained liquid hydrogen would be much larger than the one they built. Just going by the density of the two fuels, the hydrogen tank would be ten times that of the RP-1 tank. That would increase the mass of the rocket, and it would never get off the ground. So they needed RP-1 to keep the size of the tank down while providing lots of power.

Ok. But why not carry on with kero in the other stages? Smaller tanks, less to lift for the primary, more payload less rocket??

 

[JB47394]

But why not carry on with kero in the other stages?

Because the size of the tanks is no longer prohibitive for the amount of delta-V that you need. You've got a much lighter vehicle that can do better with higher efficiency, lower thrust engines. It's a bit like the way that ion engines are great when you're free of a gravity well; they are extremely efficient, extremely low output engines that are completely useless on a first stage.

 

[scaesare]

Can you expand on that please? I would have thought efficiency would be the sole criterion in order to get the payload up and cost be damned.

The kind of efficiency
I recognize for a rocket is to able to lift its own weight fast enough to get to LEO and have spare thrust to do the same for some payload. The rocket has to be 100++% efficient.

Efficiency and total thrust are not the same.

Some engines, such as ion thrusters, have very high efficiency/ISP (in the 1000's), but relatively low thrust, (< 1 lb), whereas chemical rockets have high thrust (100,000's of lbs) yet have much less ISP (100's).

So efficiency in not the sole criteria, as if you have to get a 100 tons in the air, you need massive thrust.

And "rocket has to be 100++% efficient" ... you know efficiency greater than 100% isn't possible, right?

 

[QtownTaxiGreg]

"rocket has to be 100++% efficient" ... you know efficiency greater than 100% isn't possible, right?

Yeah, the payload bit on top isn't contributing, so Sputnik got a ride on a rocket that was 100.0000001% efficient is what I was getting at.

Sputnik fell down pretty damn quick so it must have been a bit low to be what we would call LEO these days.

Back to efficiency. I hark back to the original problem of getting a grapefruit into orbit.

Two things needed.
Speed overcomes gravity.
Altitude overcomes air resistance.

Speed comes from thrust being more than your mass over a sustained period of time. Thrust comes from chucking mass out the back at high velocity.

I guess rocket efficiency coming down to how fast you chuck how much mass is indeed dependent on how much mass you are still pushing.

It doesn't explain how one fuel is better for pushing a mighty big load still, while you are still suffering gravity and needing more speed or you fail (but your air resistance has fallen off to insignificant).

 

[scaesare]

I guess rocket efficiency coming down to how fast you chuck how much mass is indeed dependent on how much mass you are still pushing.

This implies that efficiency is related to your total mass. That would mean that a heavier payload somehow made your rocket less efficient. Or that as you burned fuel and therefore had less mass, it became more efficient.

Rockets themselves really don't contribute much to overall efficiency (sure there's some aerodynamic properties, but that's not usually counted as contributing much). It's typically rocket engines that have their efficiency rated in terms of specific impulse (ISP) , which basically boils down to how long an engine can accelerate a given fuel mass at 1G utilizing that amount of fuel. It's measured in seconds, with more being better.

The examples I gave above of ion thrusters versus chemical rockets have an ISP (i.e. - efficiency) range of 100s of to 1000's of seconds.

Of course, that's just engine efficiency, whereas it appears you are talking about the efficiency of getting a specific mass to orbit, which has the penalty of a 1g gravity well to overcome, etc... I don't know of a rating for that.,

 

[QtownTaxiGreg]

Or that as you burned fuel and therefore had less mass, it became more efficient.

that's what I said. They throw Way the tank along the way fir good measure.

specific impulse (ISP) , which basically boils down to how long an engine can accelerate a given fuel mass at 1G utilizing that amount of fuel.

now we are getting into the real stuff. Can you do the cooks version without the immediate distillation?

The fuel has to lift itself is the problem. Efficiency of engine is the solution. What's the maths in between?

Seconds aka Time is a completely weird reduction result but intuitively it makes sense. How long can the engine push the fuel against fresh air and Earth pulling it back transforms to how long it has to do the lift and that has to be longer than the lift will take with the thrust available. Aka 100++% efficient in over educated taxi driver speak.

You keep bringing up the ION engines but they are operating outside of gravity.

How does kero do it better for the first stage? If H² has more hoist time per pound of fuel then have a bigger tank. Bigger tank is more volumetric efficient to weight of tank than smaller tank, less aerodynamic but not much.

Just can't get the thrust out of the H² fast enough? Simple as that?

 

[bxr140]

Yeah, the payload bit on top isn't contributing, so Sputnik got a ride on a rocket that was 100.0000001% efficient is what I was getting at.

Your definition of “efficiency” is quite misleading. It’s more accurate to actually say they’re 0.0000001% efficient (though that’s also a pretty narrow metric).