Comparison of Super-Heavy Launchers

[jwenting]

1) kerosene is heavier per unit volume than is LH2. that's probably the main reason

2) no, they have not. Saturn V was the pinnacle of rocket design, everything since has just been accomplished by strapping boosters on even older rockets (mostly Atlas and Titan). Other nations' designs are at a similar level.

What advances have been made have been in the guidance systems and materials used, enabling things to be made less heavy and/or more reliable to some degree, with reliability often taking center stage as the legal cost of a launch failure can break a company.

[Kerbface]

Then wouldn't remaking the Saturn V with better materials, guidance systems and other minor manufacturing improvements give us the best rocket ever? Why don't they just do that and then work on improvements on there. It'd probably be able to be completed much faster than designing the SLS from scratch, right?

[tek_604]

Then wouldn't remaking the Saturn V with better materials, guidance systems and other minor manufacturing improvements give us the best rocket ever? Why don't they just do that and then work on improvements on there. It'd probably be able to be completed much faster than designing the SLS from scratch, right?

Well, NASA already looked at starting up production of the engines again, and decided the cost wasn't actually worth it. Theres so much redesign to be done, you might as well start with a blank piece of paper and design the whole thing anew at this point.

I agree with improving things as time goes on, but when talking about something as old as Saturn, theres really no point.

[Kerbface]

If only they had improved gradually on existing rockets instead of dumping them for the space shuttle... sigh...

[tek_604]

If only they had improved gradually on existing rockets instead of dumping them for the space shuttle... sigh...

I agree. Blame it on Nixon. If only they'd continued Apollo... one of the great "what if's" of history.

[philly_idle]

2. I thought our rocket building capabilities were supposed to have improved since Saturn V, so why is it still the most powerful launcher percentage-of-mass-that-gets-to-space-wise? According to this chart at least.

Well no actually it didn't. What was used in the 1960s is still state-of-the-art technology. Computers obviously are much smaller these days, and we have fancy new lightweight alloys, carbon fiber, and machining techniques. But really there's not much you can do to improve upon the Saturn V. If you use these super-lightweight materials, cost is skyrocketing. Increasing engine performance of the F-1 means a lot more mass (since pressure and temperature go up), a hell of a lot of testing, and high manufacturing cost. And all that gives - maybe - 10% more payload capability.

Then wouldn't remaking the Saturn V with better materials, guidance systems and other minor manufacturing improvements give us the best rocket ever? Why don't they just do that and then work on improvements on there. It'd probably be able to be completed much faster than designing the SLS from scratch, right?

The problem is, that all the knowledge how to manufacture the parts is lost. All the tools and machines they built for building that rocket are gone. It is actually easier to build one from scratch than trying to rebuild the Saturn V. There is not a single case in rocketry where reverse-engineering led to a usable result (and no, North Korea didn't do it. Seriousely, they didn't).

So all in all yes, the overall design of the Saturn V is very good and could be used for SLS. Minor improvments can be done to the structural mass and building cost if done right. But nothing major. This rocket already is one of the - if not the - most efficient (with a payload ratio of about 4-5% to LEO) I know of.

[jwenting]

I agree. Blame it on Nixon. If only they'd continued Apollo... one of the great "what if's" of history.

Not sure who ordered the production rigs and tooling for the Saturn series rockets and their components destroyed, I doubt the president himself made that decision.

The reason behind it was people at NASA wanting to make it imperative that the STS went ahead, had no competition from Saturn for manned orbital launches (it was the only human rated rocket in NASA's inventory, and thus a major threat to the STS which was hailed as the future of manned spaceflight even as cost was skyrocketing, and to this date there is none).

[Fuzzy Dunlop]

Some questions.

1. Why are the Spacex rockets so very heavy for their size? Eg. the Falcon Heavy is much smaller than the Delta IV but nearly twice as heavy.

2. I thought our rocket building capabilities were supposed to have improved since Saturn V, so why is it still the most powerful launcher percentage-of-mass-that-gets-to-space-wise? According to this chart at least.

1) The SpaceX rockets use only kerosene/liquid oxygen, which is a lot more dense than liquid hydrogen.

2) Saturn V uses 3 stages, 2 of which are liquid hydrogen. More stages tends to give a better payload fraction, as does using liquid hydrogen. Most rockets are only 2 stage because thats cheaper.

[Kerbface]

1) The SpaceX rockets use only kerosene/liquid oxygen, which is a lot more dense than liquid hydrogen.

2) Saturn V uses 3 stages, 2 of which are liquid hydrogen. More stages tends to give a better payload fraction, as does using liquid hydrogen. Most rockets are only 2 stage because thats cheaper.

Well, cheaper is more important I suppose, no good having an efficient rocket weight-wise if it costs you more money than a less efficient rocket. On another note, I noticed the Falcon Heavy's payload fraction is seemingly quite a bit better than the Delta IV, is Kerosene/Liquid Oxygen more efficient than liquid hydrogen? I always thought Hydrogen/Oxygen was the most efficient fuel (and the main difficulty was keeping it at the right temperature).

[Rune]

Well, cheaper is more important I suppose, no good having an efficient rocket weight-wise if it costs you more money than a less efficient rocket. On another note, I noticed the Falcon Heavy's payload fraction is seemingly quite a bit better than the Delta IV, is Kerosene/Liquid Oxygen more efficient than liquid hydrogen? I always thought Hydrogen/Oxygen was the most efficient fuel (and the main difficulty was keeping it at the right temperature).

H2/LOX engines are indeed the most efficient ones (upwards of 400s vacuum isp, with about 450 theoretical maximum), but they use one of the worst fuels for everything else. Hydrogen is a bitch to keep inside the tanks without evaporating, and it needs HUGE tanks due to it's low density. As a result, the fuel fraction of H2/LOX stages is quite low, relatively speaking, due to the heavy insulation on the big H2 tanks. Crossfeed also plays a part, turning the Falcon 9H into a 3-stage-to-orbit design in practice. That, and F9's first stage has the biggest mass ratio in the history of rocketry. Makes more sense now? Delta IV has one of the lowest takeoff weights on its class of launcher, though, thanks to its first stage H2/LOX propulsion... as if that metric mattered the least bit to anyone.

Rune. Engineering is about how different factors affect a design, and the compromises you make with them.

[Kerbface]

So I guess since the size of the insulation on the fuel tanks limits the amount of liquid hydrogen, this would mean that the larger the rocket, the more efficient it would be, since the thickness of the insulation remains the same (unless it doesn't...) but the tanks get larger. So perhaps liquid hydrogen is a better fuel for large launchers than small ones?

[DerekL1963]

If only they had improved gradually on existing rockets instead of dumping them for the space shuttle... sigh...

Which was pretty much exactly what happened. Despite NASA's best propaganda, the Shuttle never did take over all US space launches (public or private).

I agree. Blame it on Nixon. If only they'd continued Apollo... one of the great "what if's" of history.

This is completely disconnected from reality.

People don't seem to realize that the short stay missions were never intended to continue indefinitely. All Nixon (or more accurately the NASA administrators) did was lop three missions off a program whose end was already in sight. The short stay missions were capped and the ambitious Apollo Applications program essentially cancelled (though the rover and Skylab were salvaged from the wreckage) during the congressional budget battles of FY'65-FY'67. Apollo's fabled blank check only lasted a few years, and only then because LBJ pushed it as a memorial to Kennedy. By the time Apollo 11 landed, the program was running on fumes and had been for some time.

Not sure who ordered the production rigs and tooling for the Saturn series rockets and their components destroyed, I doubt the president himself made that decision.

The reason behind it was people at NASA wanting to make it imperative that the STS went ahead, had no competition from Saturn for manned orbital launches (it was the only human rated rocket in NASA's inventory, and thus a major threat to the STS which was hailed as the future of manned spaceflight even as cost was skyrocketing, and to this date there is none).

Saturn production was capped in 1967, and Congress refused to budget for resumed production - the rigs and tooling were destroyed because they refused to budget money to store them either. Nor was the Saturn V the only human rated launch vehicle - there was also the Saturn Ib (which suffered the same fate as the V). On top of that, this all happened while the Shuttle was still mostly paper and long before it's costs started spiraling out of control.

[tek_604]

I'd just like to make a comment on my Nixon comment. As I understood it, with Apollo running down, the budget couldn't support the final 3 Apollo missions to the moon, and the craft were repurposed for the Soviet linkup, and Skylab.

However, with Apollo running down, NASA did have plans to extend the Apollo program, at a much reduced rate (I'm pretty sure NASA officials were understanding the budgetry reality). There was also the competing idea for the STS. As I understood it, it was sold better to the powers that be (one would imagine that would be the President then), and the order came to do STS, and abandon the Apollo extensions. Maybe the decision was made by the NASA administrators, but, its always good to blame Nixon for everything anyway, not like he has much of a reputation to be defended

But, I'm glad there have been posts pointing out why my thinking is likely incorrect. Its always nice to learn new things

[Flixxbeatz]

"Washington Monument - Not approved for flight."

The kerbals beg to differ.

EDIT: I find the Saturn V MLV designs to be appropriate for KSP

Edited July 3, 2013 by Flixxbeatz

[jwenting]

Saturn production was capped in 1967, and Congress refused to budget for resumed production - the rigs and tooling were destroyed because they refused to budget money to store them either. Nor was the Saturn V the only human rated launch vehicle - there was also the Saturn Ib (which suffered the same fate as the V). On top of that, this all happened while the Shuttle was still mostly paper and long before it's costs started spiraling out of control.

why do you think I said Saturn, not Saturn V...

Congress ordered that, from all I've heard, based on NASA lobbying that was intended to derail any future capability that was not STS related.

[thorfinn]

That, and F9's first stage has the biggest mass ratio in the history of rocketry.

Better than Atlas balloon tanks? Really? Seems strange to me....

[Fuzzy Dunlop]

Better than Atlas balloon tanks? Really? Seems strange to me....

Higher engine thrust to weight ratio and better ISP

[wronkiew]

Here are some speculative rocket designs from SpaceX from a few years back.

http://www.parabolicarc.com/2010/08/06/15941/

The Falcon Heavy numbers are from before they opted for fuel cross-feed. These designs are realistic and interesting but now they are working towards MCT instead, and no one outside the company knows what its specs are.

Also I agree with tavert and others that Ares I is never built.

[wronkiew]

Buran's payload was about 30t, not 100. If you're not counting the mass of the orbiter, which you aren't for STS. Its weight on pad would have been 2500t.

You have to include Energia by itself, which had a 100t to LEO payload capacity.

[firerider521]

Looking at these, I have to say that I really admire NASA's taste for black stripe placement.

[Kerbface]

Wait, if the Shuttle/Buran are about 100 tons with payload each, the launcher must actually be really powerful. Why is it not possible to adapt that launcher to a payload that's not the shuttle and just cap the tank off at the top?

[Promii]

Energia was launched once without the Buran attached. Look up Energia Polyus. Problem with using the shuttle launcher without the shuttle is that, unlike Buran, the engines on the shuttle are a key component of the stack. Essentially what the upcoming SLS is, is the combining of the shuttle engines and the large tank to make a more conventional rocket.

[jwenting]

There have in fact been proposals in the past to do that with the STS, mate a big orange tank with some SRBs and a large cargo container, then strap some mainsails to that cargo container.

Sounds almost Kerbal, and yes I used Kerbal terms on purpose, but that's essentially the plan NASA had for using the STS infrastructure to create a superheavy launcher.

They might even have had plans to deorbit the engine stack for reuse, don't have the book that mentioned the plan with me here.

[Shuttle]

Energia was so cool looking

[Rune]

Better than Atlas balloon tanks? Really? Seems strange to me....

Yup, close to 30:1 for the whole stage with the new merlins:

Design details of Falcon Heavy, and of Merlin 1D performance, have not been divulged. In order to achieve the payload capability claimed by SpaceX, the new rocket engine will have to provide improved specific impulse and the stages will have to provide very high propellant mass ratios. SpaceX claimed that the two "first stage" strap-on units will achieve a 30 to 1 gross mass to dry mass ratio, implying an unprecedented propellant mass fraction of better than 0.966.

From:

http://www.spacelaunchreport.com/falcon9.html

And yeah, the Atlas' tanks were pretty good, but they were made before material science really took off, and stuff like composites became available. Besides, the engines didn't have such a nice T/W ratio.

Rune. It took a while to find a reference, I wonder where did I read about it the first time.