Envisioning the world of 2100

[gturner]

sojourner wrote:

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but it has everything to do with the size of the fuel container. Not enough fuel, no orbit. Try to build a tank big enough and strong enough to ly on it's side fully loaded AND deal with the stress of a vertical liftoff and you have 2 outcomes. a vehicle that splits in half or a vehicle that doesn't have the mass fraction to achieve orbit. Because>>>>

Because, apparently, you don't understand basic engineering, even at a child's level. I could discuss loading of a fluid column, tensile stress on a uniformly loaded simply supported cylinder, the varying section modulus of a vertical tank optimized for a given G load and fuel height, and some other things, but you can't even grasp that the horizontally carried liquid fueled rockets for the Stratolaunch are designed to achieve orbit, and survive far more than 1G of horizontal loading for the aircraft to be certified for flight. Try to wrap your tiny little brain around this: Horizontal launch orbital vehicles are being built. You claim it's impossible. Call the Air Force, the NRO, and Burt Rutan and demand they stop building a vehicle whose possible existence you've disproved.

When you start looking at very large rockets, one of the only ways to avoid severe hydrostatic pressure problems is to spread it out horizontally, to avoid tank bottom pressures that would crush a nuclear submarine, and which must be contained by massive increases to the wall thickness, dropping the mass ratio.

Even if you only support a horizontal rocket from the ends, the key factors in determining the maximum tensile stress is the wall thickness and tank fineness, and the wall thickness was already heavily determined by the tank height and pressurization. For most existing rockets, you're probably looking at a 10 to 15 ksi stress increase, consentrated along the bottom, if you don't try to distribute the forces along with load.

not while on it's sideon it's side?not while on it's side

It's actually easier on its side. If you asked the navy to lift an aircraft carrier out of the water using rockets, the last thing they would do is stand it on its end. Basic engineering and common sense tells you thise things.

seriously? I'd like to see you terminate the thrust of a solid before it runs out.

Earth to Sojourner. We've been terminating the thrust of solids on command since before I was born. It's critical for precisely targeted ballistic missiles. It's also trivially simple.

Hmmm, I was gonna comment on your "came up with an idea that improved a conjectural LEM design", but you seem to have retracted it. Oh wait, here it is:

POST PROOF OR RETRACT. Oh, that's right, you already did. nevermind.

proof.

Not my blog, and a throwaway comment, but still nice. I decided it wasn't worth mentioning here, as the people here can't even figure out how use a rocket, much less optimize one, much less running through mass ratios and structures.

When I blogged heavily, for a while I got a couple of dozen multi-hour visits a day that traced back to the Air Force, who were reading my posts explaining the math of missile engagements at extremely long ranges. There were some fundamental things they hadn't seen explained before, with equations.

You need to learn to think outside your tiny little box to see what's possible with rockets, otherwise the life's work of Walter Dornberger (who developed the RASCAL, a horizontally launched liquid fueled rocket), Wily Ley, and the Navy Resarch folks will have been wasted, having shown that all sorts of things that were once thought impossible were trivially easy with a rocket engine and some thinking.

Now, not only is anything they didn't think to do claimed to be impossible, half the stuff they did is claimed to be impossible. They would weep at the breathtaking ignorance, and think their efforts wasted.

[Byeman]

gturner wrote:

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Y

1. The X-1 had a horizontal rocket-fuel tank stressed for 20 G's. The Air Force has hung iiquid fueled intercept missiles on aircraft, where they experience severe sideward G-loads as a part of normal operations.

2. . Elon Musk must've recruited on of these engineers to check the Falcon 4 for Stratolaunch operations,pt in a locked vault next to the Arc of the Covenant.

3. There's dense, and then there's black-hole dense.

4. If an Air Force general got a bee in his bonnet and decided his new ballistic missile should be stored horizontally for easier mobile deployment, leap in the air horizontally, and then transition to vertical flight to cut several minutes off the response time,

5. To NASA types it's apparently more baffling than a warp drive and they think it simply can't be done.

1. Those are vehicles than need to reach orbital velocity

2. The Statolaunch Falcon is not going to be anything like the standard falcon. It will heavily modified. Also, it will not be loaded with propellant during takeoff and it is being dropped, which is the opposite of your idea.

3. That explains you exactly. You don't what you are talking about.

4. Learn some history. They were first horizional but went to vertical because it was better. Also, a general is not going to make such a stupid request.

5. Now you are being an asshole along with being stupid.

Your idiotic idea has no engineering merit.

[Byeman]

gturner wrote:

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Solids are very precise, because they're used in a control loop with feedback. Liquids are somewhat more precise, but only somewhat. You can gimbal the thrust of both, and you can measure the thrust of both, and you can terminate the thrust of both. You only need the throttle control if you can't predetermine how much thrust you'll need, which is not the case during a launch, otherwise we'd have never launched a single Space Shuttle mission.

Keep in mind that you're arguing that small solids are useless for a 20 second imprecise launch application while advocating that we build entire launch systems to rely on them for precision performance, such as the Shuttle, SLS, and Delta IV.
.

This just shows you do not know what you are talking. Solids are open loop, there is no feedback. The thrust is not terminated in the solids used by the shuttle, Delta IV, Atlas V or SLS. They go until they burn out. Nor is the thrust measured and used in the guidance.

The solids have burn profile that can and does have variations from flight to flight. The shuttle flew an open loop profile during SRB burn and then went to close loop after to correct for dispersions. The same applies for the other vehicles.

[Robert Maxwell]

Byeman, two things:

1. Please avoid making so many posts in a row. Use the Multi-Quote feature if you want to quote multiple posts.
2. Do not call names (e.g. "asshole," "stupid," "idiotic.") This will earn you an infraction the next time.

Everyone: cool your rockets. This thread has some interesting discussion but the sniping is going to stop, or I'll close the thread.

I've been watching this thread for a while and it just keeps escalating. You all need to calm down.

[Crazy Eddie]

Byeman wrote:

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That is totally wrong. Spacex and SNC don't do anything different or use different techiques than the existing contractors at the launch site.

If you say so.

[Crazy Eddie]

sojourner wrote:

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You really need to stop conflating aircraft with rockets. It's embarrassing.

That's not really the issue, actually. Some smaller rockets can (and sometimes are) launched this way and there's been interest in scaling it up for a number of years. Concepts for exactly this sort of launch system date back to at least the 1970s with exactly this same logic behind them. Without exception, they all ran into the wall of the feasibility issue, getting a small enough rocket or cluster of rockets to actually lift the main booster with enough time for the thing to orient vertically for the ascent phase. The best concept I ever saw involved using a two pairs of very large SRBs with 90-degree angled nozzles for a rapid ascent to about 600 feet before the engines separate and the rocket ascends. The real problem with the design proposal, ironically, was that the physical structure of the rocket would have trouble standing up to the lateral forces of the launch; rockets are usually designed for strength along their long axis, and designing along two axises is going to cost you in terms of weight.

[sojourner]

gturner wrote:

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Horizontal launch orbital vehicles are being built. You claim it's impossible. Call the Air Force, the NRO, and Burt Rutan and demand they stop building a vehicle whose possible existence you've disproved.

Last I checked, Stratolaunch doesn't take off vertically from a resting horizontal position, which has been your argument all along. watch those goal posts.

When you start looking at very large rockets, one of the only ways to avoid severe hydrostatic pressure problems is to spread it out horizontally, to avoid tank bottom pressures that would crush a nuclear submarine, and which must be contained by massive increases to the wall thickness, dropping the mass ratio.

Even if you only support a horizontal rocket from the ends, the key factors in determining the maximum tensile stress is the wall thickness and tank fineness, and the wall thickness was already heavily determined by the tank height and pressurization. For most existing rockets, you're probably looking at a 10 to 15 ksi stress increase, consentrated along the bottom, if you don't try to distribute the forces along with load.

Yet despite all this, you want to build a tank that has to endure max loads in 2 orientations and all of the mass penalties that go along with it. On a vehicle that has to reach orbit with a useful payload and be reusable.

It's actually easier on its side. If you asked the navy to lift an aircraft carrier out of the water using rockets, the last thing they would do is stand it on its end. Basic engineering and common sense tells you thise things.

straw man. an aircraft carrier is not a rocket, but, to better fit the analogy, you want them to lift it out of the water with rockets, then while in flight, stand it on end before continuing to move it.

Earth to Sojourner. We've been terminating the thrust of solids on command since before I was born. It's critical for precisely targeted ballistic missiles. It's also trivially simple.

I think Byeman has already answered this

proof.

Nice post there and not a bad observation regarding the Dracos. I would be fascinated about how your idea of a horizontally oriented, vertical liftoff rocket would be received there.

Not my blog, and a throwaway comment, but still nice. I decided it wasn't worth mentioning here, as the people here can't even figure out how use a rocket, much less optimize one, much less running through mass ratios and structures.

When I blogged heavily, for a while I got a couple of dozen multi-hour visits a day that traced back to the Air Force, who were reading my posts explaining the math of missile engagements at extremely long ranges. There were some fundamental things they hadn't seen explained before, with equations.

You need to learn to think outside your tiny little box to see what's possible with rockets, otherwise the life's work of Walter Dornberger (who developed the RASCAL, a horizontally launched liquid fueled rocket),

You mean this RASCAL? the one that was air launched from a bomber? Yeah, not seeing anything about it being launched vertically from a horizontal orientation.

[gturner]

One simplification you can make is that the thrust vector doesn't need to stay vertical (rotating the nozzle). In free space a side-thrust will pivot the rocket around a fixed point located at the center of percussion relative to the center of the applied thrust (and the thrust can be distributed across multiple engines, which are summed for the calculation), as if the rocket was somewhere along the second hand of a watch. Once in the air, it doesn't need to remain above a fixed point and moving sideways is fine, even helping it clear any ground support equipment. You can also include a significant unpowered free-fall period to allow the completion the rotation, since the powered phase will give you a both vertical velocity and a rotational velocity. The stage will continue the rotation until it's stopped by another motor, either the main engines after ignition or a de-rotate motor, trusting Isaac Newton to once again complete what you've set in motion. But if you've already decided on pivoting half the rear-engines, igniting the remainder as the orientation becomes more vertical, you could improve on this.

I'd been crunching some numbers on the tank's bending stress, and one side may need to be thickened to handle an increased tensile load, but there may be some things you can take advantage of involving the fact that the tank is normally pressurized and already handles large hydrostatic loading. During the horizontal lift-off the hydrostatic pressures aren't very prevalent yet (the pipe is on its side), so you've got some margin, especially lower down toward the tail.

If you were gong for a completely re-usable liquid lift, you could trade off the weight savings of using a common bulkhead between fuel an oxidizer with going back to seperate bulkheads and exploit the empty area between for an engine mounting location, reducing the bending loads on the stage. Of courrse, if you really wanted to get wonky you could run a line of small pressure-fed engines all down the sides (your basic thruster), fed from the main engines' turbopumps, avoid the bending loads altogether and leaving you plenty of redundancy, with only a small fraction of the same thusters firing for landing.

But speaking of side-loadings, what happens to the Shuttle SRB's on SSME ignition is brutal! A beam clamped at one end, swaying to absorb the sudden application of a side-load. That's two feet of deflection in bending. As one of the Shuttle's designers said, if they didn't time the SRB ignition to coincide with the stack swaying back to vertical, and lit them while fully deflected, the SRB's might just blow up. You could say the Shuttle was an experiment to see how many catastrophic failure modes could fly in a single vehicle, which is probably one of the reasons emergency thrust termination on the SRB's was built right in. Wouldn't want one of those running loose!

ETA:

I think Byeman has already answered this.

No, he said we don't use it, not that commanded thrust termination isn't there. Range safeties require the ability to be built in to any really large solid.

Any shortfall in the solid booster's thrust is compensated for by the subsequent stages, but on solid-fueled ballistic missiles (and some final stage applications), you have to terminate the thrust so you don't overshoot the target. To kill the thrust you simply blow open vents at the foward end of the motor, which drops the chamber pressure, and thus exponentially drops the burn rate.

[sojourner]

Yeah, agreed. The STS was an exercise in bad compromises.

[Byeman]

gturner wrote:

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1. Earth to Sojourner. We've been terminating the thrust of solids on command since before I was born. It's critical for precisely targeted ballistic missiles. It's also trivially simple.
2. Range safeties require the ability to be built in to any really large solid.

.

1. Not any more. They use a trajectory optimization maneuvers to use up all the impulse of the motor so that thrust termination systems would not be needed because they were not trivially simple. Or They use liquid in the final stage.

2. It is thrust termination by destruction. They split the whole casing lengthwise.

[Byeman]

newtype_alpha wrote:

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If you say so.

I know so.

[Byeman]

[QUOTE=gturner;7263751]

sojourner wrote:

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Call the Air Force, the NRO, and Burt Rutan and demand they stop building a vehicle whose possible existence you've disproved.

None of them are building a horizontally launched vehicle that don't use wings. And the Air Force and the NRO aren't doing anything horizontal.

[gturner]

Byeman wrote:

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1. Not any more. They use a trajectory optimization maneuvers to use up all the impulse of the motor so that thrust termination systems would not be needed because they were not trivially simple. Or They use liquid in the final stage.

2. It is thrust termination by destruction. They split the whole casing lengthwise.

You don't know what all the impulse of the motor is until it's too late to do anything about the error, because once you've found out how big the error is, the motor has quit burning. It's a catch-22. The IUS on the Shuttle does use trajectory optimization, with each flight planned with months of simulations to make sure a satellites own RCS fuel won't be overly consumed to correct a residual error due to the inexact final impulse (which is accurate to about 0.5%)

The Polaris, Minuteman, and other missiles have ports on the forward dome that operate explosively within about 2 milliseconds, providing a net negative thrust for re-entry vehicle seperation, while not directly impinging on the subsequent stage. Lockheed, UTC, and Aerojet were involved in the design, as I recall, and the knowledge that you could precisely terminate a solid's thrust like that was a high-classified secret for a long time, eventually leaking out because we used the same boosters for space flight. The Russians adopted the same system, and our ABM systems have to distinguish between the re-entry vehicle, staging parts (bolts, washers), and warm pieces of fuel blown through the forward thurst termination ports that tend to travel along near the RV, giving off their own infrared signatures.

The Shuttle SRB's thrust termination system comes from the Minuteman research, and sounds very similar, consisting of six shaped charges in the upper dome of the casing. The systems on both engines are tied together, so if the system on one engine is fired the system on the other engine is also fired automatically.

[gturner]

Byeman wrote:

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None of them are building a horizontally launched vehicle that don't use wings. And the Air Force and the NRO aren't doing anything horizontal.

Of course they're not. Notice the thread title you're in. "Envisioning the world of 2100."

The reason they're not is that currently rocket engines are extremely expensive. If you asked someone about lifting something like the SLS horizontally, they'd look at using a dozen RS-25's at probably $120 million a piece, adding about $1.5 billion to the launch, and then throwing them away. You could use a million man hours of pad support and still come out cheaper than adding one engine.

But of course the whole reason you can throw crazy amounts of labor into a launch is that the launch itself is extremely expensive. The SLS is going to throw away four or five RS-25's per launch already. These costs also keep spaceflight from being either routine or affordable.

The horizontal launch becomes preferable only when motor costs drop (and reliability goes up), and SpaceX is making a lot of progress along those lines even while using largely conventional construction. As we start moving to re-usable systems, not just rebuildable or refurbishable systems like the Shuttle, the key to low cost operations is to massively reduce the amount of man-hours needed to operate the system. Once you've got low-cost rocket engines that are as reliable as any Pratt and Whitney or Rolls Royce on a Boeing, you can add extra engines to a rocket to save man-hours.

The performance penalty is quite small. I've just run some numbers on about 30 different rocket stages, adding 33% to the dry tank weight and providing the extra engine weight to accelerate the structure, payload, and fuel at 1.3 G's (generally doubling the engine mass). That's upping the structural coefficient of most stages by 39 to 49%, which isn't a whole lot considering that structural coefficients of existing stages vary by a factor of thee or more. Almost all of the stages retain 91 to 96% of their original delta-V, or for the same delta-V deliver 75 to 96% of the original payload. If half the cost of the rocket still remains the engine, then such a rocket would cost about 150% as much as the vertical version, and the cost per pound to LEO is 54% to 100% higher (which is among the reasons why we don't do this yet).

But the horizontal stage is much easier to reuse, more controllable for re-entry and landing, never needs a VAB or a giant launch tower, and if the engines are truly reliable, it won't need much ground maintenance, either. Its support costs start looking much more like an airliner's than the billion dollar launches we currently employ. Using twice the engines for fifty flights is 25 times cheaper than throwing away one engine every flight. When it comes down to it, eventually the extra manpower in the vertical support (giant crawlers, Guinness Book buldings, $100 million dollar towers) will lose out to a company that has figured out how to launch a rocket over and over with a ground crew of forty instead of a thousand, able to maintain vastly higher flight rates as the designs evolve.

Keep in mind that engineers and aerospace systems analysis comes up with solutions optimized (hopefully) for the current cost environment. When relative costs shift, so should the designs.

(I highly recommend MIT's graduate level course on aerospace system design that was entirely devoted to the Space Shuttle). It's far more fascinating than Star Trek.

[Byeman]

gturner wrote:

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1. The Polaris, Minuteman, and other missiles have ports on the forward dome that operate explosively within about 2 milliseconds,

2, The Shuttle SRB's thrust termination system comes from the Minuteman research, and sounds very similar, consisting of six shaped charges in the upper dome of the casing. .

1. Not the Minuteman III or Tridents. The missile systems using that method have been retired long ago.

2. There is no such system on the shuttle. It never was implemented.