One of the most amazing endeavors man has ever undertaken is the exploration of space. A big p art of the amazement is the complexity. Space exploration is complicated because there are so many problems to solve and obstacles to overcome. You have things like:
The vacuum of space
Heat management problems
The difficulty of re-entry
Orbital mechanics
Micrometeorites and space debris
Cosmic and solar radiation
The logistics of having restroom facilities in a weightless environment
But the biggest problem of all is harnessing enough energy simply to get a spaceship off the ground. That is where rocket engines come in.
Rocket engines are, on the one hand, so simple that you can build and fly your own model rockets very inexpensively (see the links on the last page of the article for details). On the other hand, rocket engines (and their fuel systems) are so complicated that only three countries have actually ever put people in orbit. In this article, we will look at rocket engines to understand how they work, as well as to understand some of the complexity surrounding them.
Wh en most people think about motors or engines, they think about rotation. For example, a reciprocating gasoline engine in a car produces rotational energy to drive the wheels. An electric motor produces rotational energy to drive a fan or spin a disk. A steam engine is used to do the same thing, as is a steam turbine and most gas turbines.
Rocket engines are fundamentally different. Rocket engines are reaction engines. The basic principle driving a rocket engine is the famous Newtonian principle that "to every action there is an equal and opposite reaction." A rocket engine is throwing mass in one direction and benefiting from the reaction that occurs in the other direction as a result.
This concept of "throwing mass and benefiting from the reaction" can be hard to grasp at first, because that does not seem to be what is happening. Rocket engines seem to be about flames and noise and pressure, not "throwing things." Let's look at a few examples to get a better picture of reality:
If you have ever shot a shotgun, especially a big 12-gauge shotgun, then you know that it has a lot of "kick." That is, when you shoot the gun it "kicks" your shoulder back with a great deal of force. That kick is a reaction. A shotgun is shooting about an ounce of metal in one direction at about 700 miles per hour, and your shoulder gets hit with the reaction. If you were wearing roller skates or standing on a skateboard when you shot the gun, then the gun would be acting like a rocket engine and you would react by rolling in the opposite direction.
If you have ever seen a big fire hose spraying water, you may have noticed that it takes a lot of strength to hold the hose (sometimes you will see two or three firefighters holding the hose). The hose is acting like a rocket engine. The hose is throwing water in one direction, and the firefighters are using their strength and weight to counteract the reaction. If they were to let go of the hose, it would thrash around with tremendous force. If the firefighters were all standing on skateboards, the hose would propel them backward at great speed!
When you blow up a balloon and let it go so that it flies all over the room before running out of air, you have created a rocket engine. In this case, what is being thrown is the air molecules inside the balloon. Many people believe that air molecules don't weigh anything, but they do (see the page on helium to get a better picture of the weight of air). When you throw them out the nozzle of a balloon, the rest of the balloon reacts in the opposite direction.
Action and Reaction: The Space Baseball Scenario
Imagine the following situation: You are wearing a space suit and you are floating in space beside the space shuttle; you happen to have a baseball in your hand.
If you throw the baseball, your body will react by moving in the opposite direction of the ball. The thing that controls the speed at which your body moves away is the weight of the baseball that you throw and the amount of acceleration that you apply to it. Mass multiplied by acceleration is force (f = m * a). Whatever force you apply to the baseball will be equalized by an identical reaction force applied to your body (m * a = m * a). So let's say that the baseball weighs 1 pound, and your body plus the space suit weighs 100 pounds. You throw the baseball away at a speed of 32 feet per second (21 mph). That is to say, you accelerate the 1-pound baseball with your arm so that it obtains a velocity of 21 mph. Your body reacts, but it weighs 100 times more than the baseball. Therefore, it moves away at one-hundredth the velocity of the baseball, or 0.32 feet per second (0.21 mph).
If you want to generate more thrust from your baseball, you have two options: increase the mass or increase the acceleration. You can throw a heavier baseball or throw a number of baseballs one after another (increasing the mass), or you can throw the baseball faster (increasing the acceleration on it). But that is all that you can do.
A rocket engine is generally throwing mass in the form of a high-pressure gas. The engine throws the mass of gas out in one direction in order to get a reaction in the opposite direction. The mass comes from the weight of the fuel that the rocket engine burns. The burning process accelerates the mass of fuel so that it comes out of the rocket nozzle at high speed. The fact that the fuel turns from a solid or liquid into a gas when it burns does not change its mass. If you burn a pound of rocket fuel, a pound of exhaust comes out the nozzle in the form of a high-temperature, high-velocity gas. The form changes, but the mass does not. The burning process accelerates the mass.
Thrust
The "strength" of a rocket engine is called its thrust. Thrust is measured in "pounds of thrust" in the U.S. and in Newtons under the metric system (4.45 Newtons of thrust equals 1 pound of thrust). A pound of thrust is the amount of thrust it would take to keep a 1-pound object stationary against the force of gravity on Earth. So on Earth, the acceleration of gravity is 32 feet per second per second (21 mph per second). If you were floating in space with a bag of baseballs and you threw one baseball per second away from you at 21 mph, your baseballs would be generating the equivalent of 1 pound of thrust. If you were to throw the baseballs instead at 42 mph, then you would be generating 2 pounds of thrust. If you throw them at 2,100 mph (perhaps by shooting them out of some sort of baseball gun), then you are generating 100 pounds of thrust, and so on.
One of the funny problems rockets have is that the objects that the engine wants to throw actually weigh something, and the rocket has to carry that weight around. So let's say that you want to generate 100 pounds of thrust for an hour by throwing one baseball every second at a speed of 2,100 mph. That means that you have to start with 3,600 1-pound baseballs (there are 3,600 seconds in an hour), or 3,600 pounds of baseballs. Since you only weigh 100 pounds in your spacesuit, you can see that the weight of your "fuel" dwarfs the weight of the payload (you). In fact, the fuel weights 36 times more than the payload. And that is very common. That is why you have to have a huge rocket to get a tiny person into space right now -- you have to carry a lot of fuel.
You can see the weight equation very clearly on the Space Shuttle. If you have ever seen the Space Shuttle launch, you know that there are three parts:
The Orbiter
The big external tank
The two solid rocket boosters (SRBs)
The Orbiter weighs 165,000 pounds empty. The external tank weighs 78,100 pounds empty. The two solid rocket boosters weigh 185,000 pounds empty each. But then you have to load in the fuel. Each SRB holds 1.1 million pounds of fuel. The external tank holds 143,000 gallons of liquid oxygen (1,359,000 pounds) and 383,000 gallons of liquid hydrogen (226,000 pounds). The whole vehicle -- shuttle, external tank, solid rocket booster casings and all the fuel -- has a total weight of 4.4 million pounds at launch. 4.4 million pounds to get 165,000 pounds in orbit is a pretty big difference! To be fair, the orbiter can also carry a 65,000-pound payload (up to 15 x 60 feet in size), but it is still a big difference. The fuel weighs almost 20 times more than the Orbiter [source: The Space Shuttle Operator's Manual].
All of that fuel is being thrown out the back of the Space Shuttle at a speed of perhaps 6,000 mph (typical rocket exhaust velocities for chemical rockets range between 5,000 and 10,000 mph). The SRBs burn for about two minutes and generate about 3.3 million pounds of thrust each at launch (2.65 million pounds average over the burn). The three main engines (which use the fuel in the external tank) burn for about eight minutes, generating 375,000 pounds of thrust each during the burn.
Friday, April 16, 2010
Monday, April 5, 2010
Manufacturing Process
Chapter 1
Manufacturing - def - to convert raw material into useful articles with the help of labour or machining.
Chapter 2
Metal casting
Def- of casting- the flow of molten metal into the mould where it solidifies the shape of the mold cavity
Advantage
- Complex shape
- Net shape ability
- very large part
- Variety of metal
- Mass production
Disadvantage
- Poor accuracy
- Poor surface
- Internal defects
- mechanical properties
- environmental impact
Casting technology
Sand casting
Fluilidity
The measure of the capability of a molten metal to flow into the mold cavity before freezing.
Factors effecting fluilidity
1. Pouring temperature
2. Heat transfer
3. Viscosity
4. Metal composition
Riser design
Solidification of metal ( graph)
Solidification of the volume shrinkage (graph)
Shrinkage
Sand casting benefits
1. Cheap casting process
2. Can go up to several tons
3. Cheap machining shapes from bar stock
4. Can be used with most pourable metal and alloy
5. Can intricate shape
The sand casting process
The sand
1. FLOWABILITY
2. PLASTIC DEFORMATION
3. GREEN STRENGTH
4. PERMABILITY
Metal casting
- Shell moulding
- Investment casting process
- Die casting
Molten metal is injected into a closed metal die under high pressure
Pressure maintained during solidification
Die separated and casting ejected
- cold chamber
- hot chamber
Hot chamber
Advantage
- No transfer of molten metal
- Offer fast cycling time
- Good strength product
- Excellent dimensional
Disadvantage
- expensive
- requires high production rates to justify the usage
- cannot be used for high melting point metals
Cold chamber
Advantage
- Good advantage
- Excellent dimensional
- Excellent surface
Disadvantage
- Expensive
- requires high production rates to justify the usage
- The need to transport molten metals
Centrifugal casting
Utilize inertial force by rotation to distribute molten metal into mold cavities.
Process :
Pour molten metal into rotating mould
Metal is held against the mould wall by centrifugal force until it is solidifies
3 types of centrifugal casting
1. True centrifugal casting
2. Semi centrifugal casting
3. Centrifuging
Continuous casting
Fundamental of Metal Cutting
- Plastic deformation in cutting
- Type's of cutting
- Orthogonal cutting => the cutting edge is straight and is set in a position perpendicular to the direction of the primary motion.
- Oblique cutting => the cutting edge is set as an angle, the tool of the cutting edge is inclined , λs.
- Cutting condition
cutting velocity, v
Depth of cut, d
Feed,f
- Chip formation
3 types of chip produced in casting.
1. Discontinuous chip
2. Continuous chip
3. Continuous chip with BUE (build up edge)
Manufacturing - def - to convert raw material into useful articles with the help of labour or machining.
Chapter 2
Metal casting
Def- of casting- the flow of molten metal into the mould where it solidifies the shape of the mold cavity
Advantage
- Complex shape
- Net shape ability
- very large part
- Variety of metal
- Mass production
Disadvantage
- Poor accuracy
- Poor surface
- Internal defects
- mechanical properties
- environmental impact
Casting technology
Sand casting
Fluilidity
The measure of the capability of a molten metal to flow into the mold cavity before freezing.
Factors effecting fluilidity
1. Pouring temperature
2. Heat transfer
3. Viscosity
4. Metal composition
Riser design
Solidification of metal ( graph)
Solidification of the volume shrinkage (graph)
Shrinkage
Sand casting benefits
1. Cheap casting process
2. Can go up to several tons
3. Cheap machining shapes from bar stock
4. Can be used with most pourable metal and alloy
5. Can intricate shape
The sand casting process
The sand
1. FLOWABILITY
2. PLASTIC DEFORMATION
3. GREEN STRENGTH
4. PERMABILITY
Metal casting
- Shell moulding
- Investment casting process
- Die casting
Molten metal is injected into a closed metal die under high pressure
Pressure maintained during solidification
Die separated and casting ejected
- cold chamber
- hot chamber
Hot chamber
Advantage
- No transfer of molten metal
- Offer fast cycling time
- Good strength product
- Excellent dimensional
Disadvantage
- expensive
- requires high production rates to justify the usage
- cannot be used for high melting point metals
Cold chamber
Advantage
- Good advantage
- Excellent dimensional
- Excellent surface
Disadvantage
- Expensive
- requires high production rates to justify the usage
- The need to transport molten metals
Centrifugal casting
Utilize inertial force by rotation to distribute molten metal into mold cavities.
Process :
Pour molten metal into rotating mould
Metal is held against the mould wall by centrifugal force until it is solidifies
3 types of centrifugal casting
1. True centrifugal casting
2. Semi centrifugal casting
3. Centrifuging
Continuous casting
Fundamental of Metal Cutting
- Plastic deformation in cutting
- Type's of cutting
- Orthogonal cutting => the cutting edge is straight and is set in a position perpendicular to the direction of the primary motion.
- Oblique cutting => the cutting edge is set as an angle, the tool of the cutting edge is inclined , λs.
- Cutting condition
cutting velocity, v
Depth of cut, d
Feed,f
- Chip formation
3 types of chip produced in casting.
1. Discontinuous chip
2. Continuous chip
3. Continuous chip with BUE (build up edge)
Sunday, April 4, 2010
Awesome =)
Life is so interesting now. Nothing much to complain about besides MONEY!
So excited! Finally after ages, now I am catching up with all my old friends. We are planning to meet up and I believe there's allot to catch up about all these years. Few of them are already in the verge of marriage. Best wishes and congratulations.
Easter was an awesome one this year. Baked cake for the orphanage. Satisfied!The kids were so adorable!
Preparing for the small test this Wednesday! Hope I'll give my best shot!ere
America here I come =)
So excited! Finally after ages, now I am catching up with all my old friends. We are planning to meet up and I believe there's allot to catch up about all these years. Few of them are already in the verge of marriage. Best wishes and congratulations.
Easter was an awesome one this year. Baked cake for the orphanage. Satisfied!The kids were so adorable!
Preparing for the small test this Wednesday! Hope I'll give my best shot!ere
America here I come =)
Thursday, April 1, 2010
Seven Steps to Better Presentations
I find this tips really effective, I personally tried these tricks on better presentations during my Presentation on power plants generations. Thank you @Prakash Chandran.
Hope this will also help my fellow friends as well.
Here they are:
Seven Steps to Better Presentations
“I’ve noticed a lot of talk about Powerpoint lately. About how it’s so terrible and how it enables awful presentations. But the problem isn’t Powerpoint, of course. The problem is bad content delivered poorly.
I speak for a living, and hear lots and lots of presentations at the conferences I attend. Here are some notes I wrote up for someone who is about to give his first ever public presentation.”
1. Tell stories. Seriously. People could care less about the five ways some XML vocabulary will enable enterprise whatever. Rather, put a screenshot of your project up, tell people what you learned while doing it, then give them a slide that reiterates those ideas in easy to digest bullets. That’s interesting. Even more interesting are before-and-after screenshots. Better yet: a step-by-step evolution. Just do not go from bullet-point slide to bullet-point slide trying to tell people what to think.
2. Show pictures. Got a good metaphor? Use it. “The Web is like a school of fish.” But go to images.google.com and type in “sardines” or “school of fish” or whatever. Make it a slide. Then say the Web is like that. Much more powerful and memorable.
3. Don’t apologize. Ever. If something is out of order, or if something occurs to you as a mistake during the presentation, keep it to yourself. They’ll never know. Besides, nobody cares about the presentation itself. This is really hard, because you know the whole backstory, and you’ll be tempted to explain why something isn’t quite perfect. Skip it. Also, you don’t need to apologize about the color on the projector, or the fact that your mic just popped off your lapel, or that a staff person spilled a pitcher of water. Commiserating is fine, however. “If it gets another 5 degrees colder in here, I’ll be able to see my breath!”
4. Start strong. I can’t believe how many presenters forget this. Do not get up there and say, “Um, well, I guess we should probably get started.” Instead, say, “Hi, I’m Jeff. It’s really great to be here, and thank you so much for coming to my session. Today, we’re going to talk about….” Make sure those are the absolute first words you say out loud. No need for a joke or an opening or any of that. Just start strong and confident.
5. End strong too. “…so that’s why I like social software. I appreciate your attention today. Thank you.” Then stand there and wait. Everyone will clap, because you just told them you were done. When they’ve finished, ask them if they have any questions. If nobody asks anything, break the uncomfortable silence with “Well, I guess I told you everything you need to know then. [heh heh] I’ll be around after if you think of anything. Thanks again!” and start packing up your stuff.
6. Stand. Away from the podium. Out from behind the presenter table. Keep your hands out of your pockets. Take off your conference badge (the lights will catch it and be distracting). I pace a little bit around the stage, timed with my points, saying one thing from over here, and another from over there. But don’t move too much.
7. Pause. When you say something important, leave a gap after it. Let it hang there for a few seconds. Try it when talking to your friends. “You know what I think? (pause…two…three…four…) I think Bush is bankrupting this country for the next twenty years. (pause…two…three…four…) Here’s why…”
Hope this will also help my fellow friends as well.
Here they are:
Seven Steps to Better Presentations
“I’ve noticed a lot of talk about Powerpoint lately. About how it’s so terrible and how it enables awful presentations. But the problem isn’t Powerpoint, of course. The problem is bad content delivered poorly.
I speak for a living, and hear lots and lots of presentations at the conferences I attend. Here are some notes I wrote up for someone who is about to give his first ever public presentation.”
1. Tell stories. Seriously. People could care less about the five ways some XML vocabulary will enable enterprise whatever. Rather, put a screenshot of your project up, tell people what you learned while doing it, then give them a slide that reiterates those ideas in easy to digest bullets. That’s interesting. Even more interesting are before-and-after screenshots. Better yet: a step-by-step evolution. Just do not go from bullet-point slide to bullet-point slide trying to tell people what to think.
2. Show pictures. Got a good metaphor? Use it. “The Web is like a school of fish.” But go to images.google.com and type in “sardines” or “school of fish” or whatever. Make it a slide. Then say the Web is like that. Much more powerful and memorable.
3. Don’t apologize. Ever. If something is out of order, or if something occurs to you as a mistake during the presentation, keep it to yourself. They’ll never know. Besides, nobody cares about the presentation itself. This is really hard, because you know the whole backstory, and you’ll be tempted to explain why something isn’t quite perfect. Skip it. Also, you don’t need to apologize about the color on the projector, or the fact that your mic just popped off your lapel, or that a staff person spilled a pitcher of water. Commiserating is fine, however. “If it gets another 5 degrees colder in here, I’ll be able to see my breath!”
4. Start strong. I can’t believe how many presenters forget this. Do not get up there and say, “Um, well, I guess we should probably get started.” Instead, say, “Hi, I’m Jeff. It’s really great to be here, and thank you so much for coming to my session. Today, we’re going to talk about….” Make sure those are the absolute first words you say out loud. No need for a joke or an opening or any of that. Just start strong and confident.
5. End strong too. “…so that’s why I like social software. I appreciate your attention today. Thank you.” Then stand there and wait. Everyone will clap, because you just told them you were done. When they’ve finished, ask them if they have any questions. If nobody asks anything, break the uncomfortable silence with “Well, I guess I told you everything you need to know then. [heh heh] I’ll be around after if you think of anything. Thanks again!” and start packing up your stuff.
6. Stand. Away from the podium. Out from behind the presenter table. Keep your hands out of your pockets. Take off your conference badge (the lights will catch it and be distracting). I pace a little bit around the stage, timed with my points, saying one thing from over here, and another from over there. But don’t move too much.
7. Pause. When you say something important, leave a gap after it. Let it hang there for a few seconds. Try it when talking to your friends. “You know what I think? (pause…two…three…four…) I think Bush is bankrupting this country for the next twenty years. (pause…two…three…four…) Here’s why…”
Canon PowerShot SD3500 Digital Camera
Canon PowerShot SD3500 Digital Camera
The Canon PowerShot SD3500 digital camera boasts an innovative 3.5" touch screen, optical image stabilization and smart auto mode but Chris Hardwick and Alison Haislip find out if these features are worth the $330 cost.
Find the full review from Gadget Pron on Attack of the Show after the cut.
What You Need To Know
The camera measures about 4" across and is under 1" thick.
It might be bigger than most cameras you are used to.
This camera features a much improved touch screen.
It's much more responsive and acts the way you'd expect it to.
Just tap on your subject to auto-focus.
There are also tactile controls like tapping the camera to start a slide show, and tilting it to move to the next image.
overall, the experience is much better.
They added a few features like Creative Effects and Smart Shutter (which takes a picture when you smile or wink), all of which work well for the most part.
The effects like fish-eye and miniature are fun to have, and really do add value.
Most of the time, effects on digital cameras are worthless.
Smile shutter works like a charm, but the wink timer has trouble detecting whether or not you're closing your eye.
Canon was close to make their pictures look just as good as their previous point-and-shoot cameras.
Normal light pictures have a lot of detail and accurate colors, but they don't pop like we're used to seeing.
Low light pictures look good, too, but occasionally, you might get a little too much noise or soft focus.
Most of the time, images are super clear.
Price
$330
Rating
3 Seals of Approval out of 5 (How do we rate gadgets?)
The camera is good in many respects, but the super high price and barely above average image quality means you'll have to decide for yourself on whether or not this is a buy.
The Canon PowerShot SD3500 digital camera boasts an innovative 3.5" touch screen, optical image stabilization and smart auto mode but Chris Hardwick and Alison Haislip find out if these features are worth the $330 cost.
Find the full review from Gadget Pron on Attack of the Show after the cut.
What You Need To Know
The camera measures about 4" across and is under 1" thick.
It might be bigger than most cameras you are used to.
This camera features a much improved touch screen.
It's much more responsive and acts the way you'd expect it to.
Just tap on your subject to auto-focus.
There are also tactile controls like tapping the camera to start a slide show, and tilting it to move to the next image.
overall, the experience is much better.
They added a few features like Creative Effects and Smart Shutter (which takes a picture when you smile or wink), all of which work well for the most part.
The effects like fish-eye and miniature are fun to have, and really do add value.
Most of the time, effects on digital cameras are worthless.
Smile shutter works like a charm, but the wink timer has trouble detecting whether or not you're closing your eye.
Canon was close to make their pictures look just as good as their previous point-and-shoot cameras.
Normal light pictures have a lot of detail and accurate colors, but they don't pop like we're used to seeing.
Low light pictures look good, too, but occasionally, you might get a little too much noise or soft focus.
Most of the time, images are super clear.
Price
$330
Rating
3 Seals of Approval out of 5 (How do we rate gadgets?)
The camera is good in many respects, but the super high price and barely above average image quality means you'll have to decide for yourself on whether or not this is a buy.
Whats happening!
I know It has been sometime since I last Blogged.
I was happy that I could hunt back my old 'skool' friends.
It has been sometime since I last meet them all up.
Its Easter, great feeling. I'm into fasting, 'oh well it's just for a day'
We're thinking of some charity to carry on this weekend. I and the girl's going to bake cake *back-to-back*
It's going to be an awesome one, because we have decided to bake those cake for the orphan kids. And of coarse Egg painting will be on and following by our all time BBQ party!
Excited though.
At the same time - bloody exams around the corner, many sleepless night.
Will upload more of the current event soon =)
I was happy that I could hunt back my old 'skool' friends.
It has been sometime since I last meet them all up.
Its Easter, great feeling. I'm into fasting, 'oh well it's just for a day'
We're thinking of some charity to carry on this weekend. I and the girl's going to bake cake *back-to-back*
It's going to be an awesome one, because we have decided to bake those cake for the orphan kids. And of coarse Egg painting will be on and following by our all time BBQ party!
Excited though.
At the same time - bloody exams around the corner, many sleepless night.
Will upload more of the current event soon =)
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