Astra 2F Inclination?

[SZGY]

Hello,

I may not be using the right term on this, but let me explain what a friend of mine is reporting.

He has a 4m dish set up at an undisclosed location and for the past two weeks or so, he noticed something strange: signal from 2F dropped significantly so he went out to adjust the dish. A little adjustment on elevation and it was back to normal.

However, by evening the signal dropped again, so it turned out to be a cat and mouse game of some sort until he realized the satellite might actually be moving up and down. He even installed a motor so he could comfortably adjust the elevation angle as required.

Now he has to adjust the elevation maybe twice a day or so. The exact period is currently unknown.

This brings up a few questions:

Is there a malfunction in the satellite's attitude control? Is this all intentional? Is this in preparation of orbital insertion of 2E?

Or perhaps is this just a novel (and very clever) way of locking out "big dish" users? If so, from now on, an AzEl motor might be required for continuous reception, with controlling software.

Interesting times, these are.

SZGY

 

[Analoguesat]

Lets not go down the "is 2F healthy?" route again

2F is completely healthy and will have more tp's fired up in the next 2-3 weeks as SES appropriate 500MHz of spectrum currently held by Eutelsat

2F is currently inclined at 0.1 degrees:

http://www.n2yo.com/satellite/?s=38778

Exactly in line with what we would expect for a 1 year old satellite

 

[timo_w2s]

I may not know what I'm talking about, but wouldn't SES save fuel by not correcting the inclination too much? It's a powerful satellite and the dishes in the UK are so small that a bit of wobble isn't an issue in the intended reception area and they can extend the life a little more.

 

[SZGY]

I may not know what I'm talking about, but wouldn't SES save fuel by not correcting the inclination too much?

Actually I was thinking the same. What baffles me though, why did it start to wobble just now? Sudden decision to save fuel? Hmm

 

[Analoguesat]

Interesting one that timo

The satellite wanders off nominal station due to gravitational effects. The thrusters will fire ever so often just to stop the wander building up. SES cant let the wobble build up toooo much or it'll just cost extra fuel to cancel it out again. No doubt there is a ideal point where inclination is traded against fuel for the operators.

SZGY - if its only just started then its a local effect at your friends house - wobbles dont build up in spacecraft over a few days - its a very slow effect

 

[timo_w2s]

True, it doesn't make sense to just start saving fuel now, assuming it would even save fuel. So how much does a 4m dish need to move to track the satellite? Could something be expanding in the heat of the day or contracting in the cooler nights?

 

[SZGY]

All good questions. I'll try to investigate. AFAIR, friend's dish worked fine without any adjustments up 'till the past two weeks or so. Hence to me it looks like a sudden change, rather than something gradual. I'll talk to him tomorrow and will try to find out.

Also had this idea to photograph the satellite constellation on 28.2E. If Analoguesat's theory is correct, all the satellites should wobble. Question is, do they wobble this much? I have a feeling this would require weeks if not months of observation. Looks like a good winter project... just need to borrow a tripod

 

[timo_w2s]

I seem to remember a timelapse video out there of some of the Astra satellites bobbing about in space from a few years back.

 

[kota]

what's the secrecy of your friend's location all about ???

 

[Analoguesat]

You should certainly be able to identify movement in 2D which is off air at 28.0E and 1.3 degrees inclined.

 

[solly]

the astra 2f was launch end of September 2012
0.1 it not inclication with 4 meter
how are you got astra 2a it also have inclication _
on 2a in tel aviv Israel have problem 3.6m and more

 

[M60]

What's the acceptance angle of a 4m dish, it's got to be about 0.2 deg anyway so the slightest inclination is going to be an issue if we're talking well outside the usable footprint.

 

[Coviello]

Hello,

I may not be using the right term on this, but let me explain what a friend of mine is reporting.

He has a 4m dish set up at an undisclosed location and for the past two weeks or so, he noticed something strange: signal from 2F dropped significantly so he went out to adjust the dish. A little adjustment on elevation and it was back to normal.

However, by evening the signal dropped again, so it turned out to be a cat and mouse game of some sort until he realized the satellite might actually be moving up and down. He even installed a motor so he could comfortably adjust the elevation angle as required.

Now he has to adjust the elevation maybe twice a day or so. The exact period is currently unknown.

This brings up a few questions:

Is there a malfunction in the satellite's attitude control? Is this all intentional? Is this in preparation of orbital insertion of 2E?

Or perhaps is this just a novel (and very clever) way of locking out "big dish" users? If so, from now on, an AzEl motor might be required for continuous reception, with controlling software.

Interesting times, these are.

SZGY

I can confirm what SZGY reported on. Here in Potenza (Basilicata, Italy) with a prime focus Prodelin dish 3.4 m I observed similar variations. Since the signal is good (8.2 dB - 8.8 dB 24/7 on Dr HD. F15 receiver) this is not causing any trouble; any way I have a second actuator for correction in elevation.
Coviello

 

[SZGY]

edit: posted false info due to some misunderstanding

 

[mickwig]

Hi, according to guy I know who works for the SES office in Munich Astra 2F wobbles up and down at about 0.2 degrees at about 20 minutes short of 24 hours. SES knows that but will not do much about it, because in the centre of the footprint it is not noticable at all, even with small antennas. Read also Centre of Box data at ses.lu

 

[Huevos]

wouldn't SES save fuel by not correcting the inclination too much?

No. Inclination builds at linear rate. That means if you allow it to build up for 5x longer you then need to burn the correction motor for 5x longer. The efficiency of the motor is the same in both cases. The only thing that changes is the burn time. Also when there is a corrective burn it doesn't return the satellite to zero inclination, but to the opposite inclination.

But also, diurnal "wobble is not just caused by inclination. The satellite revolves at 1 revolution per day to keep the satellite facing the planet as it revolves around the planet. If the axis that the satellite revolves around is not perfectly parallel with the Earth's axis the beam will wander north/south to some degree over any 24 hour period.

 

[cazhh]

The predominat vector in the north is east/west though. I still believe that these movements are caused by perturbations from gravitational and non-gravitational forces mainly by the sun.
The daily pattern is different in the summer compared with the winter, with a longer transition around the equinox phases.
Compare the daily snr pattern from august:


With oktober and january (january still with my old 100cm dish):





So a dependency on the angle of the attacking forces seems plausible.