[amsat-bb] Re: Kwangyongsong-3

[B J]

On 12/18/12, Trevor . <m5aka at yahoo.co.uk> wrote:
> The BBC quotes an SSTL engineer as saying It was too early to say that the
> satellite was dead. He stressed that any spacecraft would be unstable
> immediately after launch, and that North Korea could be trying to rectify
> the problem.

But that would depend upon what its rotational geometry is.  If it's
rotating in a stable mode, then there may be a chance.  But if it's
marginally stable, the slightest perturbation could make the satellite
unmanageable.

Shortly after I started grad studies many years ago, I saw a video
recording of a satellite made using a ground-based camera.  One could
see the sunlight reflecting off the photovoltaic arrays and, thereby,
determine both its spin rate and its axis of rotation.

As I recall, the ground station had lost control of the bird and it
started rotating about an axis parallel to the length of the arrays.
Over a period of days or weeks, that configuration had become
unstable.  The satellite slowly moved through about 90 degrees,
possibly because the angle of libration became too large .  It
eventually settled into its new orientation with the rotational axis
being through the main body.

>
> "We take typically two or three days to get a satellite stable, and we know
> what we're doing - whereas this is the North Koreans' first try.

But if the tumbling is such that the North Koreans can't establish
communications, the satellite's a write-off.

>
> "It would be prudent to wait a little longer and monitor the tumble rate to
> see whether there's any attempt to stabilise it."

The satellite's been in orbit for several days now.  They might not
have much time left.

>
> See http://www.bbc.co.uk/news/world-asia-20769324
>
> A Google English Korean newspaper report is at
> http://tinyurl.com/cjhpa79


73s

Bernhard VA6BMJ @ DO33FL