On 12/18/12, Trevor . [email protected] 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