What-If 0024: "Model Rockets"

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What-If 0024: "Model Rockets"

Postby rhomboidal » Tue Dec 11, 2012 9:17 am UTC

http://what-if.xkcd.com/24/

I hope there's still enough budget left for some kick-ass decals.

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Re: What-If 0024: Model Rockets

Postby sardia » Tue Dec 11, 2012 9:37 am UTC

What makes a model rocket not a real rocket? Are there rules that differentiate the two?

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Re: What-If 0024: Model Rockets

Postby ijuin » Tue Dec 11, 2012 10:13 am UTC

According to the National Association of Rocketry, the distinction between a model rocket and a high-powered rocket is one of propulsive power. Notably:

A high power rocket must meet at least one of the following criteria:

The rocket weighs more than 1,500 grams
The motor used contains more than 125 grams of propellant
The motor used has an impulse of more than 320 Newton-seconds (is an H-class or above).

Rockets not meeting any of these criteria are classified as model rockets. Additionally, High-power rockets generally require air traffic clearance to launch, as they fly high enough to pass through controlled airspace.

http://en.wikipedia.org/wiki/Model_rocket

***

You can't get into orbit with model rocket engines for two reasons, both of which derive from the fact that model rocket engines are designed to be as safe-to-use as something that flies on a jet of flames can get.

First of all, your typical model rocket engine has a low fuel fraction--i.e. a larger percent of the engine is structural mass than in a spacecraft-grade engine. Not only are the model engines over-engineered with a higher safety factor (thus thicker walls), but they are deliberately constructed of flimsier materials (such as cardboard and clay) that will crumple or disintegrate if your model rocket crashes into something solid such as a building. By comparison, your typical space rocket stage is pretty much built like a beverage can--a thin-walled yet surprisingly strong (at least on the longitudinal axis) container made of metal and filled to the brim. All of this extra structural mass in the model rocket engine cuts into your useful payload capacity.

Second, model rocket engine fuel is made to be relatively safe to handle. Besides being less sensitive to detonation or accidental ignition than the propellants used in say, firearms, it is also selected to emit a minimum of toxic fumes when burnt. This safety however comes at a price--the fuel is much less energetic than the aluminum powder / ammonium perchlorate fuel used in spacecraft boosters (which is legally classified as an explosive and requires an explosives handling permit), producing much less impulse per mass of fuel burnt.

That said, there are a few all-solid-fuel orbiter launchers in existence. Notable for its relatively small size and low cost as space launchers go was the Scout, which could launch 120-140 kg into low orbit with an initial launch mass of about eighteen tonnes and cost about eight million dollars per launch in the 1980s. http://en.wikipedia.org/wiki/Scout_%28rocket_family%29

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Re: What-If 0024: Model Rockets

Postby peewee_RotA » Tue Dec 11, 2012 11:21 am UTC

I have to say that:
"Rockets work best when their thrust is several times greater than the force of gravity."

May be the best quote from what if? ever.


I get what he's trying to say, but it comes across a tad like this
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Re: What-If 0024: Model Rockets

Postby Bernkastel » Tue Dec 11, 2012 11:41 am UTC

Oh well, a big explosion is always good. As long as no-one gets hurt.

peewee_RotA wrote:I have to say that:
"Rockets work best when their thrust is several times greater than the force of gravity."

May be the best quote from what if? ever.

Too bad its ingenuity may not be immediately obvious to everyone.

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Re: What-If 0024: Model Rockets

Postby tryde » Tue Dec 11, 2012 12:43 pm UTC

65000 rockets are going to be hard to assemble in Kerbal Space Program for a test, but the rocket would probably collapse under its own weight.... This would, however, make a very nice explosion!

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Re: What-If 0024: Model Rockets

Postby ImVeryAngryItsNotButter » Tue Dec 11, 2012 1:17 pm UTC

I really liked that callback to Up-Goer Five in the last sentence.

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Re: What-If 0024: Model Rockets

Postby peewee_RotA » Tue Dec 11, 2012 1:36 pm UTC

ImVeryAngryItsNotButter wrote:I really liked that callback to Up-Goer Five in the last sentence.


Haha, I totally missed that the first read through.
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Re: What-If 0024: Model Rockets

Postby cellocgw » Tue Dec 11, 2012 2:34 pm UTC

tryde wrote:65000 rockets are going to be hard to assemble in Kerbal Space Program for a test, but the rocket would probably collapse under its own weight.... This would, however, make a very nice explosion!


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Re: What-If 0024: Model Rockets

Postby Adam H » Tue Dec 11, 2012 4:27 pm UTC

Huh, I never considered that you want the acceleration to start slow and increase. I kind of figured that you just want to get out of atmosphere as quick as possible.

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Re: What-If 0024: Model Rockets

Postby keithl » Tue Dec 11, 2012 7:42 pm UTC

(1) Oh, come now, all you need is a hellaciously strong and thick pusher plate, a taste for very high accelerations, and one model rocket engine moving into the bottom of the pusher plate at 0.9C . Assuming you have the same what-if machine that got a baseball up to 0.9C, you (or the thin smear of slime that used to be you) should be on your way to Jupiter in no time.

(2) Not everyone understands that
Rockets work best when their thrust is several times greater than the force of gravity
See the "interesting" J P Aerospace design, two weeks to orbit on a hydrogen-filled wing. Given my understanding of hypersonic lift-to-drag ratios (about 4 near orbital velocity), this will require system ISPs far greater than 20,000 seconds. The LH/LOX space shuttle main engine was about 360(sea level) to 450(vacuum) seconds, and NERVA was 850(SL) to 1000(Vac) seconds. Ion thrusters have ISPs around 2500(Vac) seconds, but at thrust to weight ratios in the micro-gees. But hey, perhaps there is a what-if machine for balloon wings, too.

(3) As a teenager, my family moved from Oregon to a place in California which did not permit model rockets. So on my last day before the move, I taped all my Estes boosters end to end, put a nosecone on them, and launched the stack. I lost sight of it after the second staging, but by some miracle it was still climbing straight up. I know the math says otherwise, but I like to dream that the top engine and nosecone kept going and never came down.

All my dreams are like that, I suppose.

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Re: What-If 0024: Model Rockets

Postby JunkBox » Tue Dec 11, 2012 9:59 pm UTC

I've been reading xkcd for a while, and this topic finally egged me into signing up. :P

The mission, as described, sounds like the typical flight for a sounding rocket or research rocket. It's way out of reach for model rockets, but amateur rocketeers have done it.

Amateur, in this case, means "as a hobby, or an unpaid volunteer", e.g. Amateur Radio. That does not mean low budget, low tech, or low power.

The Qu8k (or "Quake") rocket was built and launched by amateurs, although they did get help from the pros. The Qu8k used ammonium perchlorate composite propellant - much the same stuff used in the Space Shuttle's boosters. Boundary of space, no problem.

Going even more amateur, using materials that are far more readily available to people working in their sheds, the Sugar Shot To Space project uses a propellant recipe that is far more stable and easier to make - sugar, mixed with potassium nitrate as the oxidizer, is an easy recipe for "rocket candy". (Forum won't let me give links. Google and Wikipedia for definitions.)

Could rocket candy be used to launch a rocket payload to the 100km official boundary of space? The Sugar Shot team aim to answer that question. Most of what they've determined so far says yes, but it'll be a challenge to design.
Could rocket candy be used to launch a payload to orbit? I doubt it.

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Re: What-If 0024: Model Rockets

Postby bmonk » Tue Dec 11, 2012 10:07 pm UTC

ijuin wrote:... That said, there are a few all-solid-fuel orbiter launchers in existence. Notable for its relatively small size and low cost as space launchers go was the Scout, which could launch 120-140 kg into low orbit with an initial launch mass of about eighteen tonnes and cost about eight million dollars per launch in the 1980s. http://en.wikipedia.org/wiki/Scout_%28rocket_family%29


Another solid-fuel rocket (used to provide thrust, but not as the only source) were the two solid fuel rockets attached for each Space Shuttle flight.
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Re: What-If 0024: Model Rockets

Postby wagner » Tue Dec 11, 2012 11:58 pm UTC

Adam H wrote:Huh, I never considered that you want the acceleration to start slow and increase. I kind of figured that you just want to get out of atmosphere as quick as possible.


If you've ever heard the term "max Q", that's the point in a rocket's flight of maximum dynamic pressure, or aerodynamic drag. The rocket accelerates from a velocity of zero, so dynamic pressure is zero. It increases for the first couple dozen seconds with velocity, until the rocket has gained sufficient altitude that the drop in air density brings it back down. Your rocket has to withstand thrust from the motor at the bottom, drag from dense air at the top, and a ton of vibration. Having low atmospheric acceleration is just as much to keep your structural loading down and allow a lighter craft, as it is to keep your drag losses down.

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Re: What-If 0024: Model Rockets

Postby wagner » Wed Dec 12, 2012 12:31 am UTC

ijuin wrote:This safety however comes at a price--the fuel is much less energetic than the aluminum powder / ammonium perchlorate fuel used in spacecraft boosters (which is legally classified as an explosive and requires an explosives handling permit), producing much less impulse per mass of fuel burnt.


By that you mean the fuels used in "model rocketry" are truly awful. These small rockets use black powder fuel, which is typically good for around 80s specific impulse. By comparison, "real" solid rockets are going to be using some composite propellant in the 200-300s range, petroleum rockets are in the 300-350s range, and hydrogen rockets in the 400-450s range.

The velocity achievable by a single stage rocket is proportional to the specific impulse times the natural log of the mass fraction, or the vehicle/payload mass divided by the fuel mass. Following that formula, for a given payload and velocity, your fuel requirement is going to grow exponentially as your specific impulse drops.

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Re: What-If 0024: Model Rockets

Postby The Synologist » Wed Dec 12, 2012 1:00 am UTC

Taking into account atmospheric drag, to get into space, you need a rocket capable of accelerating (in a vacuum) to about 2 kilometers per second. To get to orbit, you need a rocket capable of accelerating to about 10 kilometers per second.


I'm confused by this part. If you're in a vacuum, wouldn't ANY rocket eventually take you to 2/10/1000 kilometers per second, regardless of how weak it is?

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Re: What-If 0024: Model Rockets

Postby MahouShoujoMaruin » Wed Dec 12, 2012 3:04 am UTC

The Synologist wrote:
Taking into account atmospheric drag, to get into space, you need a rocket capable of accelerating (in a vacuum) to about 2 kilometers per second. To get to orbit, you need a rocket capable of accelerating to about 10 kilometers per second.


I'm confused by this part. If you're in a vacuum, wouldn't ANY rocket eventually take you to 2/10/1000 kilometers per second, regardless of how weak it is?


Not an expert, but I think there are various definitions of the edge of space, and at 100km, there is still some drag, though very little. Also, you need to achieve a certain velocity "sideways" to achieve orbit, which means taking a longer path through the atmosphere, because I don't think the rocket can do a sharp 90 degrees turn at the edge of space, and even if it could, you would need to use some force to stay at the edge of space until you achieve the speed needed for orbit.

Edit: The latter part is the significant one, I think, but the fact that low-earth orbit is not a perfect vacuum does cause orbit decay.

If you instead of going into orbit want to keep going away from earth, you will still be fighting earth's gravity for quite some time, it is only marginally weaker at the edge of space than at the surface. I'm fairly certain it remains significant at the very least until you reach a point of balance where the gravity from other celestial bodies outweighs it. For example, if you wish to go to the moon, you need enough thrust that you have a non-zero velocity when you reach the point between the earth and the moon where the force of the gravity of the moon and earth are equally strong, which is closer to the moon than the earth due to the larger size of the earth.

Edit2: Completely misunderstood the question. See the post below for the answer("eventually" is limited by the amount of fuel carried).
Last edited by MahouShoujoMaruin on Wed Dec 12, 2012 5:14 am UTC, edited 1 time in total.

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Re: What-If 0024: Model Rockets

Postby ijuin » Wed Dec 12, 2012 3:56 am UTC

bmonk wrote:
ijuin wrote:... That said, there are a few all-solid-fuel orbiter launchers in existence. Notable for its relatively small size and low cost as space launchers go was the Scout, which could launch 120-140 kg into low orbit with an initial launch mass of about eighteen tonnes and cost about eight million dollars per launch in the 1980s. http://en.wikipedia.org/wiki/Scout_%28rocket_family%29


Another solid-fuel rocket (used to provide thrust, but not as the only source) were the two solid fuel rockets attached for each Space Shuttle flight.


True--and the Shuttle boosters were the largest solid rocket motors ever to fly until the 5/5.5/6 segment derivatives of the 4-segment Shuttle booster were developed for the new Ares/SLS rockets. I cited the Scout mainly to demonstrate that yes, it is practical to achieve Earth Orbit using exclusively solid-fueled rocket stages, despite the best solid rocket fuel having only 50-60% of the specific impulse of hydrogen/oxygen liquid fuel.

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Re: What-If 0024: Model Rockets

Postby Pfhorrest » Wed Dec 12, 2012 4:09 am UTC

MahouShoujoMaruin wrote:
The Synologist wrote:
Taking into account atmospheric drag, to get into space, you need a rocket capable of accelerating (in a vacuum) to about 2 kilometers per second. To get to orbit, you need a rocket capable of accelerating to about 10 kilometers per second.


I'm confused by this part. If you're in a vacuum, wouldn't ANY rocket eventually take you to 2/10/1000 kilometers per second, regardless of how weak it is?


Not an expert, but I think there are various definitions of the edge of space...


I think that wasn't the point of Synologist's question. I believe he was taking the phrase "capable accelerating in a vacuum to 2km/s" and asking "wouldn't any amount of acceleration eventually get you to 2km/s if you had no atmosphere slowing you down?"

If that is indeed his question, then the answer is yes, but the variable in question is not the amount of force the rocket is capable of exerting (how hard it can accelerate something of a given mass), but the amount of impulse: force times time, how hard it can accelerate something of a given mass for how long, and thus how much it can change its velocity on the whole. If your rocket would burn out before it could get you up to 2km/s in a vacuum, you are not going to the edge of space today. If your rocket would burn out before it could get you up to 10km/s in a vacuum, you are not going into orbit today. And that's taking into account that in reality there's air in the way and you're not getting up to those speeds anyway: you'd need a rocket that could get you to those speeds in a vacuum in order to get up enough speed in the atmosphere to reach those objectives.
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Re: What-If 0024: Model Rockets

Postby MahouShoujoMaruin » Wed Dec 12, 2012 5:13 am UTC

Pfhorrest wrote:
MahouShoujoMaruin wrote:
The Synologist wrote:
Taking into account atmospheric drag, to get into space, you need a rocket capable of accelerating (in a vacuum) to about 2 kilometers per second. To get to orbit, you need a rocket capable of accelerating to about 10 kilometers per second.


I'm confused by this part. If you're in a vacuum, wouldn't ANY rocket eventually take you to 2/10/1000 kilometers per second, regardless of how weak it is?


Not an expert, but I think there are various definitions of the edge of space...


I think that wasn't the point of Synologist's question. I believe he was taking the phrase "capable accelerating in a vacuum to 2km/s" and asking "wouldn't any amount of acceleration eventually get you to 2km/s if you had no atmosphere slowing you down?"

If that is indeed his question, then the answer is yes, but the variable in question is not the amount of force the rocket is capable of exerting (how hard it can accelerate something of a given mass), but the amount of impulse: force times time, how hard it can accelerate something of a given mass for how long, and thus how much it can change its velocity on the whole. If your rocket would burn out before it could get you up to 2km/s in a vacuum, you are not going to the edge of space today. If your rocket would burn out before it could get you up to 10km/s in a vacuum, you are not going into orbit today. And that's taking into account that in reality there's air in the way and you're not getting up to those speeds anyway: you'd need a rocket that could get you to those speeds in a vacuum in order to get up enough speed in the atmosphere to reach those objectives.


Ah, this makes a lot more sense. Sorry for misunderstanding.

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Re: What-If 0024: Model Rockets

Postby The Synologist » Wed Dec 12, 2012 5:16 am UTC

Pfhorrest wrote:
MahouShoujoMaruin wrote:
The Synologist wrote:
Taking into account atmospheric drag, to get into space, you need a rocket capable of accelerating (in a vacuum) to about 2 kilometers per second. To get to orbit, you need a rocket capable of accelerating to about 10 kilometers per second.


I'm confused by this part. If you're in a vacuum, wouldn't ANY rocket eventually take you to 2/10/1000 kilometers per second, regardless of how weak it is?


Not an expert, but I think there are various definitions of the edge of space...


I think that wasn't the point of Synologist's question. I believe he was taking the phrase "capable accelerating in a vacuum to 2km/s" and asking "wouldn't any amount of acceleration eventually get you to 2km/s if you had no atmosphere slowing you down?"

If that is indeed his question, then the answer is yes, but the variable in question is not the amount of force the rocket is capable of exerting (how hard it can accelerate something of a given mass), but the amount of impulse: force times time, how hard it can accelerate something of a given mass for how long, and thus how much it can change its velocity on the whole. If your rocket would burn out before it could get you up to 2km/s in a vacuum, you are not going to the edge of space today. If your rocket would burn out before it could get you up to 10km/s in a vacuum, you are not going into orbit today. And that's taking into account that in reality there's air in the way and you're not getting up to those speeds anyway: you'd need a rocket that could get you to those speeds in a vacuum in order to get up enough speed in the atmosphere to reach those objectives.

Thanks Pfhorrest, I hadn't thought of the whole running out of fuel thing. In light of that, those metrics are pretty cool!

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Re: What-If 0024: Model Rockets

Postby Arancaytar » Wed Dec 12, 2012 7:55 am UTC

you will not go to space today


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Re: What-If 0024: Model Rockets

Postby cantab314 » Wed Dec 12, 2012 11:40 am UTC

I'm skeptical on the N1 explosion being larger than Minor Scale. I've found no source but Wikipedia, which has no citation, for the yield. It appears like it might have been possible, considering the probably mass of the fuel on board, though I can't find any definite figure for that either.

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Re: What-If 0024: Model Rockets

Postby stianhat » Thu Dec 13, 2012 1:32 pm UTC

What I am wondering is...

Is there a critical mass of model rockets where the rockets are unable to escape their own gravity? Not talking if they were built into a directed large rocket, but a small planet sized collection of rockets, all pointing outwards from the center... is there a golden number / mass of model rocket that would actually, when ignited, create a sphere of spent model rockets orbiting themselves?

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Re: What-If 0024: Model Rockets

Postby rmsgrey » Thu Dec 13, 2012 1:48 pm UTC

stianhat wrote:What I am wondering is...

Is there a critical mass of model rockets where the rockets are unable to escape their own gravity? Not talking if they were built into a directed large rocket, but a small planet sized collection of rockets, all pointing outwards from the center... is there a golden number / mass of model rocket that would actually, when ignited, create a sphere of spent model rockets orbiting themselves?


Yes.

No idea what it is, but, obviously, in the absence of other nearby mass, a pair of rockets facing away from each other would accelerate away and never fall back. At the other extreme, the density of a black hole (its mass divided by the volume that would be enclosed by its event horizon if the space inside were flat) decreases as its external diameter increases, so, for a large enough volume occupied by model rockets, the density of the rockets would be greater than that of a black hole of the same size, so the rockets would have to be a black hole, and so unable to escape.

Somewhere in between, you have the situation where the rockets just barely fail to escape and eventually fall back together (barring external influences)

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Re: What-If 0024: Model Rockets

Postby Klear » Thu Dec 13, 2012 1:50 pm UTC

stianhat wrote:What I am wondering is...

Is there a critical mass of model rockets where the rockets are unable to escape their own gravity? Not talking if they were built into a directed large rocket, but a small planet sized collection of rockets, all pointing outwards from the center... is there a golden number / mass of model rocket that would actually, when ignited, create a sphere of spent model rockets orbiting themselves?


Definitely. At the very least, enough rockets would collapse on themselves and create a black hole, so there must be a limit. I'm also guessing that at some point far before that happens the rockets would crush each other under their own weight, thus preventing them from functioning as rockets.

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Re: What-If 0024: Model Rockets

Postby MahouShoujoMaruin » Thu Dec 13, 2012 5:04 pm UTC

I don't know exactly what the density of model rockets are, but assuming they have roughly the density of water, you would need around 150 million solar masses worth of rockets, or (1.5 * 10^8) * (1.9891 * 10^30 kg), for the mass of model rockets to be smaller than its Schwarzschild radius and thus form a black hole. That's a lot of model rockets..... :shock: (insert mandatory your-mom-so-fat joke here)

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Re: What-If 0024: Model Rockets

Postby Klear » Thu Dec 13, 2012 5:37 pm UTC

MahouShoujoMaruin wrote:I don't know exactly what the density of model rockets are, but assuming they have roughly the density of water, you would need around 150 million solar masses worth of rockets, or (1.5 * 10^8) * (1.9891 * 10^30 kg), for the mass of model rockets to be smaller than its Schwarzschild radius and thus form a black hole. That's a lot of model rockets..... :shock: (insert mandatory your-mom-so-fat joke here)


Yeah, I know I overshoot the actual value big time, but since he was asking "Is there a critical mass...", I established the upper bound and was able to answer "yes". I was kinda hoping someone would step in and answer the question more fully.

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Re: What-If 0024: Model Rockets

Postby Tyris and Cortle » Thu Dec 13, 2012 9:12 pm UTC

Oddly enough, we've been thinking a lot lately about using model rocket engines. Not to reach orbit, though - to give a short burst of additional power to a bicycle.

It would be far more expensive than effective. :(
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Re: What-If 0024: Model Rockets

Postby stianhat » Thu Dec 13, 2012 9:19 pm UTC

Klear wrote:* 10^30 kg), for the mass of model rockets to be smaller than its Schwarzschild radius and thus form a black hole. That's a lot of model rockets..... :shock: (insert mandatory your-mom-so-fat joke here)


Well, not to be overly critic to input to my own idea, but a black hole mass of rockets mean simply rockets that wont go anywhere. I was more thinking rockets that reach the escape velocity but not overshoot it - so the rockets would fly up and not escape, but neither fall back down. It would just be a sphere of spent rockets not collapsing down to become a planet of spent model rockets =P

I am aware that my imagination is probably richer than my ability to explain it fully.

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Re: What-If 0024: Model Rockets

Postby ikrase » Thu Dec 13, 2012 9:59 pm UTC

There is gravitational binding energy. If the enthalpy of all the gunpowder is less than the gravitational binding energy of the rocket mass, they will be unable to escape (this is the same formula used to calculate the lower limit on the energy needed to blow up a planet.
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Re: What-If 0024: Model Rockets

Postby rmsgrey » Fri Dec 14, 2012 6:25 pm UTC

stianhat wrote:
Klear wrote:* 10^30 kg), for the mass of model rockets to be smaller than its Schwarzschild radius and thus form a black hole. That's a lot of model rockets..... :shock: (insert mandatory your-mom-so-fat joke here)


Well, not to be overly critic to input to my own idea, but a black hole mass of rockets mean simply rockets that wont go anywhere. I was more thinking rockets that reach the escape velocity but not overshoot it - so the rockets would fly up and not escape, but neither fall back down. It would just be a sphere of spent rockets not collapsing down to become a planet of spent model rockets =P

I am aware that my imagination is probably richer than my ability to explain it fully.


If they just head straight out, then there are only two possibilities - either they keep going forever, or they fall back. If they have a sideways component, then they'll tend to tumble and end up spending some of the thrust accelerating inward. It'll take someone who's rather more familiar with rocketry than me to get proper answers there...

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Re: What-If 0024: Model Rockets

Postby Fire Brns » Fri Dec 14, 2012 6:38 pm UTC

stianhat wrote:What I am wondering is...

Is there a critical mass of model rockets where the rockets are unable to escape their own gravity? Not talking if they were built into a directed large rocket, but a small planet sized collection of rockets, all pointing outwards from the center... is there a golden number / mass of model rocket that would actually, when ignited, create a sphere of spent model rockets orbiting themselves?

Yes, it has to be far less than a black hole as the others quote. The thrust of the rocket is the deciding factor, but assume we had a ball of carbon with the same mass as the sun floating in space. A sphere of carbon in a vacuum (that carbon could be a cow or it could not be do as you will with it); an average model rocket engine would not produce the requisite thrust to overcome the gravity of the sphere before it burned out.

Edit:I'm not talking about reaching escape velocity, I mean lifting off the surface by over a centimeter. Also I'm too lazy to math but my hypothesis is this.
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adanalis
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Re: What-If 0024: Model Rockets

Postby adanalis » Fri Dec 14, 2012 7:30 pm UTC

I would like to disagree with the statement that "you can't use model rockets to dock with the ISS", or any other similar formulation of getting in orbit with model rockets.

Here is how you can achieve it:
The first part of the model rockets story shows how you can use a "ship" made of model rockets to deliver 60Kg to about 100km up and have zero speed upon reaching there. Let's call this ship type A.
Nobody said that can use _only one_ ship in this endeavor, so imagine X ships (of type A) all of them taking off at the same time and all of them meeting at the same region 100Km up from the earth's surface. One ship delivers the 60Kg payload, X-1 ships deliver 60-e Kg worth of model rockets and e Kg worth of machinery to bind these new model rockets into a new ship, of type B. Then you fire the rockets of the B type ship.
Since the B type ship is starting at 100Km up, where the gravity of the earth is weaker and there is practically no atmosphere, it should have an easier time accelerating than the A type ships. If it's still not enough to put ship B in orbit, you build more pyramids of A ships that auto-assemble B ships that make it to the limit of B ships and auto-assemble a C type ship there and so on until eventually the last ship makes it into orbit.

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keithl
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Re: What-If 0024: Model Rockets

Postby keithl » Fri Dec 14, 2012 7:47 pm UTC

cantab314 wrote:I'm skeptical on the N1 explosion being larger than Minor Scale. I've found no source but Wikipedia, which has no citation, for the yield. It appears like it might have been possible, considering the probably mass of the fuel on board, though I can't find any definite figure for that either.


Wikipedia claims Minor Scale was 4 KT TNT equivalent, ammonium nitrate and fuel oil.

Here's a citation on russianspaceweb. The N1 used 680 "tons" of kerosene and 1780 tons of LOX. Presuming metric tons, and 43 MJ/kg, that is 2.93E13 joules. A "kiloton" is defined as 1e12 calories or 4.184E12 Joules. The result is 7 kilotons for the N1 fuel. The story is a bit more complex, though.

There were four N1 launch attempts. The first, third, and fourth exploded in flight, before first stage separation. They were depleted of enough fuel that their explosions were smaller that 4 kilotons, The second attempt, on July 3, 1969, started up on the pad, ate a bolt, and shut down 29 out of 30 engines. One engine kept running for 23 seconds, then the stack exploded, destroying the pad and launch tower. We can presume that the engines used little of the fuel, so almost all 7kT was consumed in the explosion. More N1 details here. Two weeks later, Apollo 11 started for the moon, and succeeded, because our German rocket scientists were better than their German rocket scientists.

A pad explosion of four initially separated RP-1/LOX tanks would not be as "brisant" (shock producing) as Minor Scale, which in turn was not as brisant as the sophisticated explosion that took out the Murrah building in Oklahoma City (and no, I will not provide details on a public forum).

BTW, the main engine for the first stage, the NK-15, became the NK-33, which is still in use. The NK-33 was licensed to Aerojet of Sacramento, and renamed the AJ26-58, and will appear in the Japanese Galaxy and Orbital Sciences Antares launchers. The N1 might have sent cosmonauts to the moon, if it was started a few years earlier, with enough time to fix the problems. The AJ26-58 engines may send payloads to the moon someday, an acquaintance at Aerojet is pushing for this.

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Re: What-If 0024: Model Rockets

Postby ijuin » Sat Dec 15, 2012 4:00 am UTC

keithl wrote:BTW, the main engine for the first stage, the NK-15, became the NK-33, which is still in use. The NK-33 was licensed to Aerojet of Sacramento, and renamed the AJ26-58, and will appear in the Japanese Galaxy and Orbital Sciences Antares launchers. The N1 might have sent cosmonauts to the moon, if it was started a few years earlier, with enough time to fix the problems. The AJ26-58 engines may send payloads to the moon someday, an acquaintance at Aerojet is pushing for this.


The good thing about Soviet/Russian technology is that even though it is not necessarily as "bleeding-edge" as some nations, once they work the bugs out of the design, it is robust and reliable. When they care to, Russian engineers build stuff to last. Note that current middle-lift Russian rockets (most famously the Soyuz launcher) still use a modified version of the R-7 rocket stage designed SIXTY years ago. If it ain't broke, don't fix it.

sotanaht
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Re: What-If 0024: Model Rockets

Postby sotanaht » Sat Dec 15, 2012 3:21 pm UTC

I'm having a hard time understanding how something "pancake shaped" wouldn't be able to stand up under it's own weight. The load at any given point would be fairly minimal except near the middle of the center spire which doesn't really sound THAT structurally unstable, being basically a pyramid shape. What I DO see happening though is it breaking apart almost as soon as it's off the ground, if it got that far, due to the aerodynamics putting more force on certain areas than others. I guess if that's what he meant, that it would fall apart as soon as it was off the ground, it makes sense.

webgiant
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Re: What-If 0024: Model Rockets

Postby webgiant » Sun Dec 16, 2012 9:38 am UTC

So if model rocket engines can't manage to stick a rocket into space, how about a boost to get it to the edge of space? I was thinking of a balloon system to get the rocket up most of the way, then fire off the engines while there's still enough atmosphere left to keep the balloons from popping and to allow the solid fuel to burn.

Now given that model rockets are notoriously difficult to get pointed "up" from a launch pad on the ground, and thus a balloon system with no secure flat ground will make it harder to make sure the rocket goes up, but with some sort of stability device this could work. I think that some sort of oxygen tank would be necessary towards the end of the engine stack, but as a consequence of starting higher the engine stack would be smaller and allow for more weight from the tank.

ijuin
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Re: What-If 0024: Model Rockets

Postby ijuin » Tue Dec 18, 2012 12:47 am UTC

No need for an oxygen tank--solid-propellant model rocket engines have the oxidizer pre-mixed with the fuel.

As far as getting the rocket to point upwards goes, a plumb weight on a metal rod ought to do for keeping the launch platform upright (since as long as the whole thing isn't swinging too violently, the weight will be almost at the bottom of its arc). You want to avoid getting the engine flames on the balloon envelope as it rises though, so maybe you want a tube-launch like a bazooka, only emerging from the tube once it is far enough away from the carrier balloon envelope.

taemyr
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Re: What-If 0024: Model Rockets

Postby taemyr » Wed Dec 19, 2012 8:20 am UTC

adanalis wrote:I would like to disagree with the statement that "you can't use model rockets to dock with the ISS", or any other similar formulation of getting in orbit with model rockets.

Here is how you can achieve it:
The first part of the model rockets story shows how you can use a "ship" made of model rockets to deliver 60Kg to about 100km up and have zero speed upon reaching there. Let's call this ship type A.
Nobody said that can use _only one_ ship in this endeavor, so imagine X ships (of type A) all of them taking off at the same time and all of them meeting at the same region 100Km up from the earth's surface. One ship delivers the 60Kg payload, X-1 ships deliver 60-e Kg worth of model rockets and e Kg worth of machinery to bind these new model rockets into a new ship, of type B. Then you fire the rockets of the B type ship.
Since the B type ship is starting at 100Km up, where the gravity of the earth is weaker and there is practically no atmosphere, it should have an easier time accelerating than the A type ships. If it's still not enough to put ship B in orbit, you build more pyramids of A ships that auto-assemble B ships that make it to the limit of B ships and auto-assemble a C type ship there and so on until eventually the last ship makes it into orbit.


That is a truly horrible way of constructing a multi stage rocket. It will not be a better solution that the pancake shaped mountain.


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