Concerning SOHO's orbit, and its corrections.

[Tasem]

Hi,

I've read that SOHO (SOlar and Heliospheric Observatory) is orbiting around the L1 point. I remember this point being unstable (that is, that something in orbit will diverge from stability). How are the corrections made for this orbit ? Does it really cost a tiny amount of fuel, or is the fuel somehow transferred to SOHO regularly, like it is for the ISS ? Or is there a metastable state in between that I don't know about ?

Thanks.

 

[Bandersnatch]

The spacecraft is in a halo orbit around L1, which reduces the need for orbit corrections. The corrections are made with on-board fuel reserves. SOHO initially had something in the vicinity of 200 kg of hydrazine left after final orbit insertion, which then would be periodically (on the order of every 100 days or so) expelled to correct the drift, allowing for something like 10 years of station keeping (but the probe developed some hardware problems that reduced this time).
The fuel on-board is all there is available, and once it's exhausted, the mission has to end and the probe drifts away. There are no means for refuelling provided, as it is more cost-efficient to just send out a new probe.

 

[davenn]

allowing for something like 10 years of station keeping (but the probe developed some hardware problems that reduced this time).

and amazingly, 20 yrs later, it is still operating well !

From the SOHO site
http://sohowww.nascom.nasa.gov/hotshots/index.html/

Twenty years of operation without a single service or tune-up is no piece of cake for a spacecraft . As anyone who has operated scientific instruments in a lab will know, it's amazing how many things can go wrong, requiring some form of intervention or repair. But that has not been an option for SOHO and its instruments - if it breaks, it's broken, and all you can do is adjust to a new reality. But miraculously, we're doing very well even after all these years.
So, spirits are high at the SOHO operations center at Goddard Space Flight Center and in the instrument teams around the world as SOHO is embarking on its third decade of operations.

I have been following SOHO since it went into operation in the mid 1990's
and have been collecting daily records from it since there ... it has given me a huge database of solar images

Dave

 

[Bandersnatch]

and amazingly, 20 yrs later, it is still operating well !

But... I read its design parameters...
Hold on, let me find it again.

 

[Bandersnatch]

But... I read its design parameters...
Hold on, let me find it again.

All right, I need to consider handing over my badge, since apparently I can't even read properly.
Here's what I read:
http://www.esa.int/gsp/ACT/doc/ARI/...3-4103a-InterplanetaryHighways-Barcellona.pdf
It says that at orbital insertion, due to well-executed manoeuvre, an before reaction wheel troubles, it had enough fuel left to 'complete a 11 year solar cycle', which obviously doesn't mean that it would run out of fuel at that moment.
Not enough eggs for me, today.