Thread: ISS - worse than a construction mishap?

Hello!

My question was if someone has information on how the space station was kept on it's path,
following the moving earth. There was little known about, or also no information were being
published.

Lately there have been so many articles about malfunctioning German made - Russian
computer glitches, effecting also engines being used for that task.

I visualize a scenario, the space station was not be able still to alter it's position while earth
is saying good bye heading towards summer. :-)

Tons of jet engine fuel would have to be taken to the station and, an other question, wasn't
the IS a space ship than a stationary, furthermore, due to that fact?

Maybe even worse than a construction mishap? Is one better to be dumping the whole thing?

Does anyone have any knowledge? Thanks for your replies!

Steve

If you mean the International Space Station, it's in orbit around the earth, it's not following the earth as the earth orbits the sun.

The main reason ISS needs fuel is because there is actually still a tiny little bit of ultra-rarified gases (atmosphere) up to the altitude it orbits at (low enough so that Space shuttles can get to it with heavy loads) that the ISS slowly looses speed over time, and I'm talking like 30 km/hr over a period of a month kind of thing. Also because of the way it's shaped, tidal forces tend to try to make it rotate around at random, and the solar panels need to face the sun to generate the best amount of electricity. So they use Gyroscopes to stabilize the spin and the small attitude rockets to change the way the station points. They can also change the speed it orbits. When you speed up in orbit, the orbit will lengthen and effectivley the orbit will climb higher.

If you increased it's altitude to a few thousand kilometers high, firstly the Shuttle wouldn't be able to get there, but the other effect is that it would loose that last tiny bit of drag, and without any engine power at all, would remain in orbit around earth for hundreds if not thousands of years to come without any further acceleration power. Just like Geostationary satelites, just like the Moon. It would likley however develop spin from tidal forces.

Originally Posted by StarMountainKid

If you mean the International Space Station, it's in orbit around the earth, it's not following the earth as the earth orbits the sun.

1. Yes that ISS I do mean.
2. No? Not following the sun? Sorry, not following earth orbiting around the sun? It's quite a distance for space missions to the station. Summer to winter... summer to win....

Originally Posted by musicalaviator

The main reason ISS needs fuel is because there is actually still a tiny little bit of ultra-rarified gases (atmosphere) up to the altitude it orbits at (low enough so that Space shuttles can get to it with heavy loads) that the ISS slowly looses speed over time, and I'm talking like 30 km/hr over a period of a month kind of thing. Also because of the way it's shaped, tidal forces tend to try to make it rotate around at random, and the solar panels need to face the sun to generate the best amount of electricity. So they use Gyroscopes to stabilize the spin and the small attitude rockets to change the way the station points. They can also change the speed it orbits. When you speed up in orbit, the orbit will lengthen and effectivley the orbit will climb higher.

If you increased it's altitude to a few thousand kilometers high, firstly the Shuttle wouldn't be able to get there, but the other effect is that it would loose that last tiny bit of drag, and without any engine power at all, would remain in orbit around earth for hundreds if not thousands of years to come without any further acceleration power. Just like Geostationary satelites, just like the Moon. It would likley however develop spin from tidal forces.

Thanks for your reply. Seems there isn't being much known about that fact?

You can learn in a hands-on way about orbital mechanics with the freeware orbit simulator

"Orbiter", which is free and downloadable at

http://orbit.medphys.ucl.ac.uk/


You will see there how that accelerating causes your orbit to gain altitude/distance from the body you orbit (ie earth). and how the atmosphere doesn't really have a "Start" point rather it just gets less and less dense as you go further away from Earth.

Originally Posted by Steve Miller

2. No? Not following the sun? Sorry, not following earth orbiting around the sun? It's quite a distance for space missions to the station. Summer to winter... summer to win....

I can't tell if you fully understand yet. The ISS is in orbit around the Earth much like the Moon is. As the Earth moves around the sun it carries the ISS with it - still circling just as the Moon.

The distance to the ISS is pretty much the same at any time of the year at launch points. And they always plot the firing time of the Shuttles to take the shortest path each time they launch. It's much more precise than just "point and shoot."

And there was no atmosphere in space. Hence, orbiting round the earth was quite fuel efficient.

As I said in my post, the energy loss from friction with the atmosphere is the equivelent to only around 30km/hr per month, compared to a similar rate per second with things like aircraft in the atmosphere.


Also for all intents and purposes, the ISS is in a constant fall toward earth. The Earth is literally making the ISS fall toward it simply through the gravitational laws. no energy is being expended here. The only reason the ISS doesn't hit the ground is that it is going forwards so fast (remember only loosing a few km/hr every month) that it is effectivley sidestepping the earth through it's fall...


imagine you were walking around a person. Every 3 seconds in this game you have to step once toward this person. so you step toward them one step, then quickly shuffle 3 steps sideways, you are now the same distance away from them compared to that 1 step you took toward them. This is like an orbit. The Gravity is the force pulling toward the middle, but the speed acts sideways.

The Earth is 350km away from ISS, and the sun is a few million km away. Thus the Gravity from Earth is for all intents, the only force acting on the ISS's orbit. The ISS falls toward the Earth, but it's pre-existing speed pulls it away from the earth through inertial force.

Gravity wants to change the direction the ISS goes (curving toward the surface of the ground) but Inertia resists this motion, preferring instead to remain in a straight line. at 28,000km/hr or so, these 2 forces balance out, and the "straight line" becomes bent, by gravity, into a closed loop. an orbit, a circular path. The earth is a sphere, and at 28,000km/hr, the path of the orbit happens to maintain around 350km above the earth at all points of the orbit.

Assuming the friction of Air is gone, you could abandon the ISS today and shut it down, never to fire it's rockets or turn on it's electrics again, and it would stay in the current orbit for thousands of years.

Of course air friction isn't completley gone, but it's small enough so that the energy expenditure to keep it in orbit for a year is far less than it takes for a 747 to fly from London to New York on a sunday morning.

Of coruse last week they just tacked an extra bit onto it so the biggest expenditure is getting space shuttles up to it to 1: add pieces to it and 2: give the people living on it food and other expendables.

I don't get the sample and the person.The person is standing on the ground and gravity is pulling you
to some direction causing you to step back and forth and sideways also?

Gravity pulls you toward the other person

speed allows you to sidestep.


You fall inwards at a specific rate at all times and this is unavioadable that you will always fall toward the centre of the other object (earth).

The thing that you can change is the speed you go sideways. so as you fall down, you also move sideways and if you move sideways enough you always miss hitting the gravity source.


This is why when the space shuttle launches it doesn't go Straight up for the entire launch sequence. If it did, it would go up to around 800km high... then fall straight back down. Instead it noses over (tail down) after just a minute of going straight up, and accelerates horizontally, crossing the Atlantic Ocean in just a few minutes. at orbital velocity (roughly 28,000km/hr) the engines turn off and without using the 3 large booster rockets ever again, sits in orbit for 2 weeks.


A really good demo is using that Orbiter Program, and with the Space Shuttle Autopilot turned off, just launch straight up, and you will find the orbiter is in space for about 5 minutes before it comes hurtling straight down into the ground just off the coast of florida at enormous velocities. With the autopilot launcher on, you end up flying over Europe just 20 mins after takeoff, your speed steady without any engines on. You can then have a look at what happens when you fire your OMS rockets in the direction you are travelling (Prograde rocket firing). your speed becomes greater, but your orbit also gets higher on the opposite side of the orbit compared to your current location. (ie if you fire your OMS Prograde when over Europe, the portion of the orbit centred over Australia gets higher... as you get higher over that location your speed reduces as you climb "uphill" in your orbit, which reduces the energy available and you start to decend "Downhill" in your orbit which increases your speed...)

If you were in a circular orbit at 38,000km high, instead of just 300 like the ISS, there would be absolutley no air... and no power at all would be required to remain in orbit around earth for thousands of years.

While you feel "Weightless" in orbit, Gravity is still the major effect on the vehicles trajectory. An Orbit cannot happen without Gravity. Gravity can be thought of as an acceleration force on a vehicle also... falling toward a body will increase speed, climbing away will reduce speed. Increasing speed will cause a body to Climb away from the Centre of gravity when there is enough horizontal motion, and visaversa


Speed Increases Altitude
Altitude decreases speed
Altitude is defined as distance from centre of gravity, ie Earth.
Rocket power can change speed directly.
Friction will always reduce speed

In space Friction is almost entirely removed


When you are close to the earth (ie closer to earth than the moon) then the forces from other bodies such as the Sun or Other Planets are for all intents so week in comparison to the earth that they are irrelevant to any calculations except theoretical ones. Thus a space shuttle in orbit for a week, or a space station in orbit for years, (or geostaionary sattelites in orbit for decades) needs no power to remain in it's orbit around earth once the initial power has been imparted during the launch. The motion of Earth around the Sun has no bearing on this any more than the motion around the sun has any danger of ripping you off the earth's surface and into the black void of space as it "pushes around into summer".

Just like a very high altitude airplane, the ISS is as firmly gravitationally linked to Earth as your own body is. It cannot increase the distance between the surface of earth and itself without imparting large amounts of rocket energy into it's speed. It's trapped in a circle around the earth, held there by gravity. If one was to strap some solid rocket boosters (those things on the side of the Space Shuttle when it launches) onto the ISS and turn them on, you would increase the altitude at which the ISS orbits (you would more likley just make the orbit elongate into an elipse shape with a "Far point" a few thousand km high and a "Close point" of the same point as when you turned the rockets on)

You would literally need enough energy to get to the moon to make the ISS leave earth's orbit and start wondering around with the Sun as it's Centre of Gravity.

ISS is not "flying in formation" with earth any more than a Jumbo Jet is... any more than a Big Mac Truck is.


Do you know how GPS works?

i decided to do a picture visualization instead



Lets just say a vehicle (Shuttle or something) is in the Red Orbit... The only way it can leave this circle is by imparting energy into it's speed by either colliding with something that has more energy, or by using a rocket to drive itself forward using the "Equal and Opposite reaction" principle.

Say now they want to do that for some reason so, as they pass the asterisk with the yellow circle around it, they turn their rockets on for a few moments. say, 2 or 3 minutes of rocket power.

Their speed now increases and the rocket climbs away, but as it does so the speed decreases due to gravity trying to accelerate them toward the surface of Earth. As their speed decreases their climb rate also decreases until they are actually decending, as they decend they increase speed and as they do that, their decent speed decreases.

Their orbit is now an Elipse...


The earth is trying to make them fall straight toward the middle of the earth. Their Speed-induced inertia is trying to make them fly off in a straight line. When these 2 forces are within certain areas (Speed not too slow or too fast) their track will be a closed track, either Circular or Eliptical.)

The ISS would concieve of the earth as being Still in space, just the same as we do. The earth's passage on it's orbit around the sun does not make the ISS (gravitaionally) feel like it has to "Chase after" the earth, any more than it feels like the ground is moving to a person standing on earth.

Earth's Gravity reigns suprime even in Orbit. There is a misconception that gravity stops in orbit/space... however an Orbit is actually defined and ruled totally by gravity. The reason astronauts 'float' is because the vehicle they are in is actually constantly 'falling' toward earth.

If a space ship were to leave the earth's gravity (ie going to Mars) then at a certain distance away, they would stop 'falling' toward Earth, and instead 'fall' toward the sun. You could then replace the representation of the above picture and put "Sun" in the middle (instead of my surprizingly good represenation of the Atlantic ocean drawn in 2 minutes using MS paint) with "Earth" as the red circle and "Space ship going to mars" as the Green circle.

There are a few actual contradictions in your post. When your saying orbit can not happen
without gravity on the one hand, and on the other, you are talking about weightlessness in
orbit.

Gravity should end where the atmosphere does, shouldn't it? Than, you expose the speed
of the spacecraft replacing gravity, as I got it right. How does that work?

Earth going by the sun, and earths motion regardless it's path would also want to have
some energetic source seen by the time for which this has gone on and continuing, don't
you think?

GPS? I have an idea about the functioning of it! GPS proves Einstein being right, right (oh
lord where am I )?

You did draw the earth image yourself? Looks good! I first thought you had taken the pic
from Google Earth or something.

If gravity stops at the earth's atmosphere, why does the Moon orbit the earth?

Answer: Gravity does not stop at the Atmosphere. Instead Gravity gets gradually weaker the further away from the Earth's Centre you get. At a very very high altitude (I'm Talking hundreds of thousands of miles away from the Earth's surface) the gravitational pull from the sun ends up being more dominant than the pull from the earth. However that altitude is further away than the moon is.


GPS works because there are a number (I believe 38) sattelites in an orbit (like that red circle in the picture above) in orbit around the sun.



The Weightlessness is caused by the act of falling. G-Force can be considered a biproduct of acceleration. When you are standing on the earth, the Ground is resisting the force of acceleration caused by Gravity by 1G. When in orbit that 'falling' force is not being resisted, but merely 'sidestepped'. The object is falling just as fast as if you jumped out of a plane... however it is moving forward fast enough that it 'misses the ground' as the earth is a sphere-ish shape. Imagine you had 50 miles to fall... but you went so far toward the horizon that once you had fallen that 50 miles, that the earth's surface was still 50 miles below (but now in a different direction) due to the earth's surface 'curving away' as you raced forwards to the horizon.

If you slow down, part of your orbit would 'touch the ground'... if you speed up enough, the orbit becomes a hyperbola and you end up shooting off into an orbit around the sun. Within the speedrange of 'orbit' (say 27,000km/hr up to 37,000km/hr) you are locked into an orbit which would theoretically remain gravitationally locked with the earth at all times.

Just because you "Float" around inside the spacecraft doesn't mean the spacecraft's motion is not effected by gravity... the only reason you 'float' is because the spacecraft is falling toward the planet with an 'acceleration' force of gravity of 9.8m/s/s not being opposed by either Thrust, Lift or Contact with a solid surface. You can consider laying down in bed on Earth as being an opposition to Gravity being imparted by your bed and the ground below it. Contact with the Ground imparts the same amount of "Thrust" to you as a rocket accelerating at 1G.

For more thought experiments, explain the "Vomit Comet" airplane which does 0 G flights by decending rapidly in the atmosphere.
http://www.youtube.com/watch?v=xrjosOjvlOc

As you can see in the youtube video, it really is Weightlessness, but it is a boeing 727 airplane well inside the atmosphere... The reason for the weightlessness is "Freefall"... Reducing the action against gravity. An orbit is the same thing, except that the speed of orbit is such that the 'ground' is always missed because by the time it's fallen the distance to the ground, the craft has already 'sped' to the horizon.

The Weightlessness is caused by the act of falling. G

There I stopped reading your post. This was not pseudoscience. That station, as well as other space missions,
was real I'm pretty much sure.

Steve

huh? Are you saying you think the ISS needs power to maintain position "With the earth as it moves around the sun".


The action of the Earth orbiting the sun is the same force that keeps the ISS in orbit around earth. It's all to do with Gravity. Orbits are gravity in action. The most important thing about gravity is not just size, but also distance. That's how the Apollo CSM could orbit the moon for the 11 days that Apollo 17 was on the surface. It wasn't under power the whole time. In fact the spacecraft only took enough fuel to fire it's rockets for around 30 minutes all up. The rest of the 14 days they were 'falling'. Either in orbit around Earth, the moon, or coasting uphill from either one of those bodies.


Of course there is the "Langrange" points which are more interesting, points where the gravitational pull from Earth and the Moon are roughly equal. That needs some good Newtonian physics to be understood, but for the standard circular orbit with all sattelites are in, a simpler understanding can suffice.

Understand that to be in the position that the ISS is in, there is no power needed to maintain position compared to the earth. The earth is constantly moving around the sun, and summer/winter is not a place, but just having the north/south hemisphere slightly off centre compared to the trajectory around the sun. This is why in the North hemisphere, summer is in July, but in Australia/Antarctica/South Africa/South America summer is in January.

Your conception seems to have the earth sitting there still in space with the ISS sitting offside it, then suddenly bursting out and whipping around to the other side of the Sun, leaving the ISS burning gallons of gas to catch up. This concept has no relation to reality in the slightest.

Certain distances, earth - sun, but causing something like summer and winter as well?

Here's a spacecraft above the earth... It is able to travel at different speeds, and the trajectories show where the craft will end up landing.

As you can see at sub-orbital speeds the craft will end up landing (or crashing) on the earth... I have actually put some theoretical "Dotted lines" where the orbit would take the craft if it was able to pass 'through' solid matter and continue on it's orbital trajectory through the earth's rock.


You can see that all the lines are 'falls'... except that at above 28,000km/hr or more the line never touches the ground.

At Escape Velocity, the object actually breaks orbit and never returns to it's original location. Such an object has now started orbiting the sun...

the "Straight line" could only occur at speeds which are a significant fraction of the speed of Light.

The only difference between "Falling to earth" and "Orbiting the earth" is the speed you are moving 'forwards'.

Earth is pushing forward in your sample?

It doesn't matter which direction the earth is going in this sample. There is no air resistance in space, so the only force acting on the space craft is the Gravity of the Earth and the ships own speed. The force of the Suns gravity is such a small fraction of the earth's gravity at this distance that the effect of the Sun could be considered to be close to zero. (in reality it'd be a small fraction of 1 percent - enough to perterb the orbits by a measurable degree in a few years time).

Without taking into account this small effect though, the Earth can be considered as being "the centre" of the orbital motion, in a similar way that the earth can be considered the centre of attraction point to someone standing on the earth's surface/ground.

Motion in space is always Relitave, and when 99.993% of the gravitational forces are coming from earth, then Earth can be considered 'stationary' relitave to the spacecraft. Only once the earth's gravity has reduced (through distance) a large degree (say to 50% compared to another body.. in the case of being close to earth, this can only be either the Moon or the Sun) can another frame of reference become useful. Remember too that the Sun is in orbit around the centre of gravity of the Galaxy Milkyway. The sun itself travels through space at some literal hundreds of miles per second. Every frame of reference is moving in relation to something else. The galaxy is moving toward the andromeda galaxy, the local cluster itself is moving in relation to the galactic clusters near it. The driving force of all of these motions is the balance between Gravity and Inertia. Inertia wants objects to continue in a straight line without changing speed, Gravity wants objects to accelerate toward each other. (Accelerate in this sense can also mean slow down in relitave velocity given the right conditions)

That's a point I'm confused about. Everything was in motion, all the time. In space, one
could not decide what the own actual status was. Would you agree or not?

On earth it's easier I would say.

This is the seasons of Summer and Winter (and everything in between)

The major difference between Summer and Winter is not the distance between the earth and the sun (if it were, then summer and winter would be the same between north and south hemispheres, and this is not the case).

Instead the difference is the amount of sun each hemisphere gets per day. as in the length of time the daylight hours are. For instance where I live, in Southern Australia, the Winter Solstace just occured (summer solstace occured on the same day in Northern hemisphere). This is the (for south) shortest day of daylight hours of the year. In this case the sun rose at about 7:55am and set at 5:02pm. During the summer months the sun rises at about 5:00am and sets at around 8:30pm. The difference is over 6 hours worth of sunlight per day. This extra 6 hours of light warms the earth in the local area, causing summer... indeed at the poles, nearly 3 months of sunlight 24 hours a day occurs (the sun appearing to mearly circle around the horizon)

The earth spins on it's axis at a 23 degree offset relitave to it's motion around it's orbit. This 23 degree offset remains fixed to the same degree and direction throughout the orbit. so at some times the south pole is more toward the sun, and at other times the north is. Between these two times the position graduates closer and closer to the equinox (equality between poles... the tilt crossways according to the sun, roughly as in the diagram above is configured.)

Incidently the offset axis is what defines the tropic lines. At the Tropic lines, the sun's rays are directly overhead at the summer solstace, as discribed by Eratosthenes and recounted by Carl Sagan in this video:

http://www.youtube.com/watch?v=0JHEqBLG650

and a shorter version made by someone else
http://www.youtube.com/watch?v=35UQV...elated&search=

Originally Posted by Steve Miller

That's a point I'm confused about. Everything was in motion, all the time. In space, one
could not decide what the own actual status was. Would you agree or not?

On earth it's easier I would say.

This is where the 'frame of reference' idea comes in. If you are just going around the earth in orbits, you can ignore the other motions, and consider "Earth" to be the centre of the frame of reference... temporarily making it the centre of the universe for the simplicity of visualization. If however you need to go to another body, you need to make something else the frame of reference, for instance going to the moon, you have the earth as the frame of reference (acting as a fixed point for calculatons) until you enter the moon's dominant gravity "Sphere of influence" after which you ignore the Earth and calculate based on the Moon being a fixed reference point. If you are going to Mars, you consider Earth the centre of reference until you achieve escape velocity, and then you can consider the Sun to be the centre fixed point of reference... until you approach mars and slow down to orbit that body. The hard points come when you are in the 'transition' zone where the langrange points start happening, and then large newtonian equasions start being needed to work out what's going on.

But unless you want to work for NASA, usually the simplified "Relevant frame of reference" and "Orbit is falling" is good enough for the concepts to work... good enough to even simulate/play with the Orbiter program and get yourself to the moon and back in the simulator.

Wouldn't that mean winter was else here in Europe and in Australia? Have you been to those places?

Originally Posted by musicalaviator

Originally Posted by Steve Miller

That's a point I'm confused about. Everything was in motion, all the time. In space, one
could not decide what the own actual status was. Would you agree or not?

On earth it's easier I would say.

This is where the 'frame of reference' idea comes in. If you are just going around the earth in orbits, you can ignore the other motions, and consider "Earth" to be the centre of the frame of reference... temporarily making it the centre of the universe for the simplicity of visualization. If however you need to go to another body, you need to make something else the frame of reference, for instance going to the moon, you have the earth as the frame of reference (acting as a fixed point for calculatons) until you enter the moon's dominant gravity "Sphere of influence" after which you ignore the Earth and calculate based on the Moon being a fixed reference point. If you are going to Mars, you consider Earth the centre of reference until you achieve escape velocity, and then you can consider the Sun to be the centre fixed point of reference... until you approach mars and slow down to orbit that body. The hard points come when you are in the 'transition' zone where the langrange points start happening, and then large newtonian equasions start being needed to work out what's going on.

But unless you want to work for NASA, usually the simplified "Relevant frame of reference" and "Orbit is falling" is good enough for the concepts to work... good enough to even simulate/play with the Orbiter program and get yourself to the moon and back in the simulator.

Are you going to work for NASA?

I live in Australia. It's winter right now.

A few days ago (June 21) was the shortest day of the year (The day that the sun is above the horizon for the shortest time)

on the northern side of the Tropic of Cancer, June 21 is the longest day of the year ( the day that the sun is above the horizon for the longest time)

If you were at the North pole now, the sun would be above the horizon for another 4 weeks... no night time at all... the last time it was dark there was over 4 weeks ago. South pole is undergoing the reverse. It's dark there now and has been for over 4 weeks, not a peep of sun in 4 weeks. and for another 4 weeks to come... eventually the sun will be making brief appearances of less than an hour at a time. and slowly as the earth continues it's trajectory around the sun, the daylight will become longer and longer through the day, till in 6 months time, it will be Daylight for 8 weeks without stopping.

Have you got snow?

Mountains to the west have snow (Mount Hotham, Mount Kosioskow) but the city I live in (Melbourne) has just been getting fog in the mornings. Temperature right now is 8 degrees Celcius.

Im not intending to do much Space work beyond playing the Orbiter game, I do hold a private pilot license, but my profession so far has been Music Teacher.

Oh, I thought you are much younger!

i'm 25 years old. Still a kid at heart though

I do love you.