ok, thanks... I'll make enquiries about "blind scanning"

Cheers

It doesn't work like that. The satellites orbital velocity is either speeded up or slowed down slightly (depending which way you want it go) with a short propellant burst. This moves it to a slightly higher or lower orbit so it's no longer geosynchronous. The satellite only accelerates/deacellerates during the short burn. You then wait till it gets to 28.2E and apply an equal and opposite burn to drop it back to the geosynchonous orbital height. All the satellites at 28.2 are constantly having there orbits adjusted to stop them banging into each other.

At 26199mls the velocity to maintain a stable circular orbit matches the earths rotational period so if orbited above the equator in the same direction as the earth spins it appears stationary from an observer on the Earth

You learn something new every day. Thanks for the explanation

"Constantly" makes it seem more drastic than it is! There are tricks to minimise fuel consumption at 28.2E. Firstly the satellites are in an, AFAIR, 80km "cube" - each with well defined movement patterns which both avoid the slight risk of collisions and make steering adjustments very infrequent.

I believe the latest TeVii cards have details of nearly 200 existing satellites pre-installed so it looks like they have fixed frequency lists and any new frequencies/satellites have to be added manually. It doesn't seem like they are blind scan enabled. In one review I read it said that the original MyTeVii software did a better job at scanning than using WMC mainly due to the availability of more adjustable parameters. Good luck next month.

There is plenty of space in space. In geostationary orbit there is roughly 265790 km of space or about 735,5 km per degree.

In other words: Our precious new satellite has to travel 15800 kms from now before it reaches 28,2.

That is: If my calculations are correct

The N2YO site is now showing 1N at 7.2º - so about 1.3º in 2 days. At a rough guess travelling at this rate it will be at 28º in around 33 days so more like October 24 plus a couple of days to ease it into its final position so maybe by October 26/7.

Do they rely on a single burn to speed it up or would they be doing multiple burns to accelerate it?

I presume that it has then to be slowed and returned to geostationary orbit which would also mean that the current speed of travel between degrees cannot be assumed to be a constant. That would rather put off calculations based on that assumption.

Almost certainly a single burn - a satellites time in orbit critically depends on fuel (hydrazine?) useage.

The faster you make it go the more fuel you need to stop it again!

The speed will be constant until corrected by a further burn as there is no friction to be accounted for.

There is however gravity!

In addition, the retroburn will not cause it to immediately slow to its final speed necessary to maintain a geostationary orbit.

Both would mean surely that a graph of the speed would describe either a bell curve or inverted "bath tub" curve as it increased in speed and then slowed?

Gravity pulls it towards the earth. Gravity is the essential force that keeps an orbiting object in orbit, without gravity, it would continue on a straight line and leave orbit.

In space there is a vacuum so nothing to cause friction. Thus when you burn the thruster, that will apply a force, and the speed will increase as long as the force is maintained (F=M*A) As soon as the burn stops, the acceleration stops and the satellite continues at that speed indefinitely.

The burn in the opposite direction to "stop" it needs to be the same force for the same duration. As soon as the burn stops, it stops decellerating and maintains it's speed. Of course it does not "stop" it, but merely slows it so that the orbit becomes "stationary" as viewed from earth.

Newtons first law of motion

The velocity of a body remains constant unless the body is acted upon by an external force

The burn acts at right angles to gravity so as long as the force is applied the object will accelerate linearly (or the reverse). Once the force is removed the velocity will then remain constant. If the speed is increased the satellite will move to a higher orbit so that it's tendency to fly straight on is matched by gravity (it assumes a stable orbit but at a slightly higher altitude). A reverse but identical burn will restore it's original velocity and hence it geosynchronous altitude.

It we had no atmosphere you could orbit a satellite at any height provided there was not a mountain in the way

Exactly. The gravity is merely a constant downward acting force for a given orbital radius as measured from the Earth's centre of mass (which decreases by the inverse square law the higher the orbit)

However, depending on whether the satellite is moving faster or slower than the earth, if it's moved out of geosynchronous orbit, it'll have to change altitude.
Since it's moving easterly, it'll have to travel faster than the earth's rotation, and hence move to a lower altitude to maintain a stable orbit, so there's another dimension to consider, rather than just a burst of propellant east or west.

Surely an increase in speed would require a lower altitude orbit, not higher?

An orbit is effectively constantly in freefall, but going fast enough to miss the horizon before you hit the ground. If we had no atmosphere or mountains, as you say, and wanted to orbit the planet from an altitude of only 1 metre, the velocity would have to be pretty hight in order to reach the horizon before you reached the ground, and maintained that 1 metre altitude. Surely more than the earth's geostationary speed of 3.07 km/s, where there's consequentially less gravitational force. Or am I confusing myself?

Why

The increase or decrease in final velocity is directly proportional to the force produced by the thruster and the time it's applied for and inversely proportional to the satellites mass. Any change in orbital height is entirely automatic. Take a satellite outside the earths atmosphere and accelerate it to 1.91 miles/sec at right angles to the Earths surface in any direction it will assume an altitude of 26199mls from the Earths centre and complete an orbit in 1 sidereal day. It won't be geosynchronous purely because of it's path (It could be pole to pole).

The velocity along its orbit is the only variable in this instance.

An equal and opposite burn will restore it's original velocity of about 1.91 miles/sec so it will return to the Clarke Belt altitude.

All you need to do to bring a satellite down is to speed it up sufficiently so it assumes a lower orbit and clips the Earths atmosphere, the force of friction then slows it down

Hopefully 5 HD will follow ITV 3,4,2 HD and remain encrypted.

We're not talking about clipping the earth's atmosphere to slow it down though.

Your earlier posts states that to speed it up, it will move to a higher orbit, you contradict that in the next post though, by concurring that it's actually a lower altitude.

I think the confusion (on my part here) is that I'm mixing up angular velocity of the body, with speed relative to a fixed point on the earth's surface.
By that I mean, for a given speed relative to a fixed point on the earth, a body at a higher altitude would have a longer arc, and thus would be covering a greater distance, and require more angular velocity, just to maintain the same speed relative to that fixed point.

However, what's really throwing me is the fact that the height of the orbit is automatic. If (as you now accept) a faster speed with respect to a fixed point on the earth requires a lower orbit, how exactly would it happen automatically? This is a genuine question, I'd really like to know.

An object happily orbiting a body is accelerated in a direction at a rightangle to its orbit, such that its angular velocity is increased (ignoring what happens to its relative velocity to a fixed point on the body's surface, since we don't even care whether or not it's traveling in the same direction as the body's rotation). What force would cause it to drop its altitude? Surely its altitude would increase?
Hmmm, and thinking about this point, its relative velocity to a fixed point on the surface would consequently reduce too. *head explodes*

Er, why? Channel 5 gain nothing from encryption, it's not part of the HD sub like ITV2 etc is.

I know the feeling. Thinking about it the, burn needs to be up or down not along the orbital path. This adjusts the altitude and the speed follows. Lower it speeds up and higher it slows down. For an object at Geosynch height in a polar orbit it would pass over the same point on the earth on each pass at the same time but of course it won't be above the same point at any different time.

Hes got sky, most of their posts dont make sense on here.

Been trying n2yo.com all afternoon but the servers are choca due to people tracking the crashing UARS bird http://www.foxnews.com/scitech/2011/...-in-real-time/

Such a childish comment to make, i see you fit with the Sky brigade on here that loves to piss on everything and everyone else when it comes to either Freeview or Freesat...

Channel5HD is something i think would be of huge benefit to Freesat and Channel5 broadcasting as a whole!
Then ad 5USA and 5* to the mix, and it looks better...

I took it that he lives outside of the UK and relies on the encrypted wide-beam broadcasts in order to receive the HD channels.

but why