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Galileo satellite system (merged thread)

But to change the orbit the satellites will have to expend a lot of fuel.

But why change the orbit (significantly)? We’re already using different satellite orbits for the navigation signals, for example the 55 degree inclined orbit of the “normal” GPS satellites and the geostationary WAAS satellites,

Why not manufacture the spares now

I guess the “assembly line” is running at full speed at the moment.

Also, the constellation will continually need new launches to keep it fully operating, and new blocks of satellites likely have an improved navigation payload, so instead of adding capacity now to build two more satellites, it might make more sense to start the next block a few months earlier…

LSZK, Switzerland

Also I wonder if some receivers have hard-coded limits on the orbital parameters, perhaps as a form of sanity check on the received data? If this satellite is at half the altitude, that ought to be regarded as not right.

Can the satellite really boost itself all that way just using its maneuvering thrusters?

Administrator
Shoreham EGKA, United Kingdom

The recivers would need to know that these two satellites are at a different altitude because otherwise the syncronised times will be off by whatever the distance difference is. The orbit angularity may be ok but the height is wrong, therefore they need to be lifted. I guess the need to move it depends on operational constraints of the consumer units and also what is/is planned to be allocated at the altitude where these two are orbiting at the moment.

The satellites are not insured. Unfortunately.

Wow. That is an interesting decision. What if the launch vehicle exploded before insertion?

EGTK Oxford

I am very surprised as well. Each one I have been involved in (non-galileo) so far has had more insurance than a pessimistic pessimist.

According to arianespace, the planned orbit was circular at 29900km semimajor axis, and 55° inclined. The actual orbit is at 26200km semimajor axis and inclined by 49.8°, but with a high eccentricity of 0.23. If I calculate this correctly, this means the perigee is 17554km and the apogee 32226km.

The recivers would need to know that these two satellites are at a different altitude because otherwise the syncronised times will be off by whatever the distance difference is.

In any satellite navigation system, no two satellites will have exactly the same orbit, so there needs to be a way to communicate the exact orbital parameters to the receiver. This is where the navigation message containing the Almanach and the Ephemeris date comes into play.

There is one problem though – it’s the range of encodable values. I don’t know the Galileo message format, but the GPS one (page 32) only allows encoding of eccentricities up to 0.03

Wow. That is an interesting decision. What if the launch vehicle exploded before insertion?

Not to buy insurance is apparently a deliberate decision. And one that makes sense, given that they launch 30 satellites, coupled with the relative unreliability of space launch (and the associated high insurance costs), they have the statistical basis to self insure.

They need 24 satellites for the complete constellation, but ordered 30 satellites, so clearly they’re planning for some failures.

LSZK, Switzerland

Only Europe would self insure for satellite launches….. It isn’t the hardware costs only. The launch costs are far higher than the value of the satellite.

EGTK Oxford

The German federal government doesn’t procure insurance either as a matter of principle. You only need insurance when the possible damage is more than you can cope with. I don’t need insurance to protect me when I lose my mobile phone but I need insurance to protect me in case of disability even though the former is much more likely. The Galileo project partner have the deepest pockets, there is little value in procuring insurance.

It is very unusual to entirely self insure in the space launch business. Sometimes partial self insurance is used or required.

EGTK Oxford

I recall seeing a documentary on this, and the insurance premium was 20% of the satellite value.

So if you are launching 25, self insurance is the obvious way to go. To argue otherwise is to argue that insurers lose money, which is obviously false.

Administrator
Shoreham EGKA, United Kingdom
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