Time for me to be stoopid...

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el chubbo

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O.k.

So I am talking with a 7th grader about Space Ship One... she asks a simple question..."after the ship breaks through the upper atmosphere and weightlessness occurs why doesn't it just float off into space?".

I look at her and say "blaaaaaggghhhhh....I dont know"

I look at the scaled composites website and they indicate that the pilot has no additional control beyond hitting the "fire" button... nothing about additional thrusters, magic, the use of alien technology....

O.K. brain people. I haven't had my coffee yet so I am missing something pretty simple here. Someone explain the obvious to me. So I can explain the obvious to her.

And look like just a LITTLE moron.

Thanks!

Matt C.
 
Just because it broke through the upper atmosphere doesn’t mean it’s out of the pull of the earth's gravity. Of course it uses a few ohm burns to position itself for reentry gravity will pull it back by itself.

Dan
 
if you are weightless are you not beyond the earths' gravitational field?

I understand that they only made it 400 ft. into space (bbc science).. at what point do you just "float"?

Thanks... I'm going to drink my coffee via I.V.

mc
 
Im presuming that it hybrid motors like some of the Nasa ships do . They are used in space to rotate/turn ect as the main boosters fall off. ( Hey I was supprised that the main boosters are just likea GIANT BP motor. )

They use hybrids because they can controll how fast they want to turn by changing the rate of mixture going into the combustion chamber , and because they can turn them off when they like unlike the main boosters.
 
Well, I'll try to give you a simple answer, and let someone that acts smart to give you the long complicated answer...:

Whenever there is a body in space, it creates a gravitational field. On planets and stars, they are big enough to creat a huge dip in space-time. This is because of the gravitational field. It is pretty dang big, encompassing the moon and some space beyond it. Everything in this circle is in effect of the gravity of the planet. On something like a star, it's big enough to encompass the entire solar system. Only when you exit that dip in space-time are you truly out of the gravitational field.

The reason you experience weightlessness is because you are always falling, in orbit. You just have enough forward momentum to not smack into the ground. The shuttle goes 17000+ mph, so it has enough velocity to go around and around. It's not true weightlessness, as far as I know, until you have enough velocity to escape the gravitational field.

That might be the "I watch too much Star Trek" response, but I don't really care.

Jason
 
OK, this is kinda complicated so hang on.

The pilot was weightless not because he left the earth's gravitational field, he was weightless becauce he was at the top of his flight path and was about to start falling back down...sortof like an elevator the just starts to go down only more so.

The earth's gravity field extends for millions of mile, if it didn't the moon would float away.

In order to escape the earth's gravity you have to go very very fast.

Imagine a man firing a gun parralel to the earth's surface...the bullet travels in an arc until it hits the ground.

If his gun could shoot a bullet faster the arc curve becomes longer and longer the faster the bullet goes.

Eventually the bullet goes so fast that it's curve will match the curve of the earth...this is an orbit! and the bullet's curve will follow the earth's curve and hit the guy in the back.

Eventually the bullet will be slowed down enough by air friction and fall down but if he could fire it out of the atmosphere it would stay in orbit.

This orbital speed is about 5 miles per sec or a little over mach 24.

5 miles a sec is "Orbital Velocity".

Now if he could go even faster say...7 miles a sec, mach 34, his orbit would become larger and larger in an ever increasing spiral until he eventually would leave the earth's gravity.

This speed (7 miles a sec.) is called "Escape Velocity".

Now answer me this...why to spacecraft launch toward the east from Florida?

NOBODY HELP HIM!!!

sandman
 
Sandman,

Your explaination makes perfect sense... did you make that graphic just now or did you just have that "on hand" for when the subject came up :)

On to your question...

Looking at a standard map of florida it would seem that if they launched west from florida the earth would move east underneath them and they would end up in the ocean (or at least with a very long glide path). Launching east allows them to follow the rotation of the earth and thus puts them back on solid ground...

yes?

I may have to have a doughnut now.....

mc :)
 
I just made the drawing...just now...I'm fast! Actually I have to thank Willey Ley and Walt Disney for first showing me that about 1955!

Some things you just remember.

Your answer is close...very close...

Think about the earth's rotation...25,000 miles around at the surface...more or less and it takes 24 hours for a complete rotation.

How fast is the surface of the earth moving?

Now say you have to accelerate a satelite to 17,500mph (orbital velocity) if you go east you only have to accelerate to 16,500mph 'cause the satelite is already going about 1,000mph in that direction as it sits on the pad.

sandman
 
You could try the ball on a string experiment. Whirl a ball on a lenth of string aroud your head. The ball is the space craft, your head is the planet (mines as thick as ) and the string is the force of gravity.

Now if you swing too fast the string breaks and the ball kies off (into space).

If you swing too slow you hit yourself in the head(spacecraft lands)

If you swing just right the ball flies around your head (in orbit).

Very much over simplified but a valid demo.

David
 
Going east from Florida adds the Earth's own rotational velocity to that of the spacecraft, so that less delta V (change in velocity) is required by the spacecraft to reach orbital velocity.

I don't remember the exact value of Earth's rotational speed, so I'm just going to use 1000 mph as an example. Sitting here in my chair writing this post, I am moving over a thousand miles an hour, due to the speed of Earth's rotation (which is maximum at the equator).

An object must be moving at 17,200 miles an hour tangentally to the surface of the earth in order for an object to reach minimum orbit. Add in the Earth's own rotational speed, and that means a spacecraft moving east around the earth at the equator only needs to move at something less than 16,200 miles per hour. However, a spacecraft moving WEST would be fighting AGAINST Earth's rotation, and would therefore have to move over 18000 miles per hour (relative to its starting point) in order to achieve low Earth orbit!
 
The best place to launch a satellite into geostationary orbit is from a launch site near the equator, to take advantage of the rotation of the Earth. But satellites are also launched from the equator into other orbits.

A geostationary orbit is about 36,000 kilometres from the surface of the Earth. In it, a satellite appears to hover over a fixed point on Earth, a location ideal for communications satellites and for some Earth observation satellites.
The easiest way to attain the right speed for orbiting a geostationary satellite is to launch it along the equator in the direction of the Earth’s rotation. The launcher then gets a boost from the Earth which, at the equator, moves at a speed of 1675 kilometres per hour. Thus the rocket can do its job with less propellant.

Space on board a launcher is limited. The load carried divides between the useful payload (satellites) and the propellant. The greater the payload capacity, the lower the cost for orbiting each satellite. First, the launcher orients itself in the satellite’s orbit, and then it releases the satellite. Thereafter, the satellite stays in its orbit, which it can adjust as needed using small on-board thrusters.

French Guyana is a good site for launching satellites into the equatorial plane. Here, ESA’s powerful Ariane 5 rockets are launched. The Ariane 5 has a load capacity of up to eight tons, enough to orbit the heaviest satellites.

Dan
 
Concerning the orbital mechanics and why the object *falls* back to earth, you need to understand that there *is* no real "edge" to the atmosphere. They pick an arbitrary point and call that the beginning of space, but it has little meaning.

So, in addition to gravity pulling them back, there is the effect of air resistance slowing them down.

Even the space shuttle and our old skylab never got high enough to avoid atmospheric friction.

As for the extent of gravities effect, it is actually limitless, though its effect falls off with the square of the distance making it SO small that it can be ignored after a fashion...

jim
 
I feel smarter just reading this stuff from you smart guys!!:cool:

I'm comfortable with my ability to count down and press the launch button. When I click on the Logoff button, I think it erases everything I just read also????:confused:

TRF is a great place because of our great members!!!
 
I feel smarter just reading this stuff from you smart guys!!

Smart:confused: ??

I can't count to twenty one unless I take my shoes and pants off!:D

sandman
 
Originally posted by sandman
Smart:confused: ??

I can't count to twenty one unless I take my shoes and pants off!:D

sandman

Shoes and Pants. I guess your missing a finger or tow? :D :D :D

Dan
 
Originally posted by Karl
Im presuming that it hybrid motors like some of the Nasa ships do . They are used in space to rotate/turn ect as the main boosters fall off. ( Hey I was supprised that the main boosters are just likea GIANT BP motor. )

They use hybrids because they can controll how fast they want to turn by changing the rate of mixture going into the combustion chamber , and because they can turn them off when they like unlike the main boosters.

I am unaware of any hybrids (liquid/solid) used for oms. IIRC the shuttle uses a hypergolic bi-propellant. Some spacecraft have also just used pressurized gas.

The SS1 does have a hybrid main engine.
 
Tell your little friend that she too can be weightless.

All she has to do is jump up in the air.

From the time she leaves the ground, until she lands back on the ground, she'll be just as weightless as the astronauts.

Astronauts on a suborbital trajectory feel weightless from the time they stop accelerating up, until they feel the deceleration of slowing down again on their way down. That's why they said Mike Melville was "weightless" at the top of his trajectory.

The only humans who have ever been almost truly weightless were our Apollo astronauts at the instant they crossed the line between the earth and the moon, when both forces balanced in opposite directions. Unfortunately they couldn't stay there, they were just passing through. And they weren't truly weightless, even there, because the sun's gravity (as well as that produced by every other big and little particle in the universe) was still acting on them.

Best cheap earthbound way to feel how it feels to be weightless?

Rollercoaster! :D

Best site with simple explanations of the realities of cosmic travel?


Warp Drive When
 
Originally posted by el chubbo
O.k.

So I am talking with a 7th grader about Space Ship One... she asks a simple question..."after the ship breaks through the upper atmosphere and weightlessness occurs why doesn't it just float off into space?".

I look at her and say "blaaaaaggghhhhh....I dont know"

I look at the scaled composites website and they indicate that the pilot has no additional control beyond hitting the "fire" button... nothing about additional thrusters, magic, the use of alien technology....

O.K. brain people. I haven't had my coffee yet so I am missing something pretty simple here. Someone explain the obvious to me. So I can explain the obvious to her.

And look like just a LITTLE moron.

Thanks!

Matt C.


Weightlessness is not the same as no gravity.
Weightlessness, as far as SS1 is concerned, is due to falling. The pilot and the ship are falling freely together. With no forces acting on them other than gravity, they have the same velocity as compared to each other, and so inside the craft seems like there's no gravity. But it only seems like that because they're actually falling together.

This is true even when it's still headed upwards. After the engine quits, it might still be heading upwards, but it's falling. That is, gravity is acting on it to slow it down at exactly the same strength it would be if the craft happened to be heading down. The result is the same; the appearance of no gravity.

In cases where there really is no (or very, very little) gravity, out between the stars, things would act exactly like this, but due to lack of gravity rather than the ship and the person inside it falling freely in gravity.
 
Originally posted by rstaff3
the shuttle uses a hypergolic bi-propellant

I think the shuttle uses hydrazine for attitude control. Very nasty stuff---quite poisonous to people (that's why nobody runs right up to the shuttle after it comes to a stop on the runway, the astronauts on-board are still running through their 'purge' procedures to get any trapped hydrazine vapors pumped overboard). But it has the handy property of violently breaking down (chemically speaking) when it touches the catalyst grid inside the head of a thruster motor.
 
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