[vsnet-chat 3736] Re: why is Galileo looking at delta Vel?

[Fraser Farrell <fraser@trilobytes.com.au>]

Bish,

> For the latest interplanetary missions, NASA (or its PI institution
> elects to) use at least two functionary attitude and articulation
> control systems: Sun sensor is one to lock on the Sun's coordinate,
> and star scanner is the other. The latter namely tracks not only
> Canopus but a number of other stars at the same time. 

The latter is often described as a "Canopus sensor" on the older 
spacecraft but I guess NASA use a better version nowadays. So it seems 
we're getting the delta Vel observations as a bonus.

(Note to those who asked me "why Canopus?" Two reasons: (1) it's very 
bright and easy to distinguish, and (2) it is close to the ecliptic south 
pole. For the early interplanetary missions it was fairly easy to program 
them "if radio signal from Earth is lost, then aim at the Sun, roll 
slowly until Canopus appears, stop, and point my antenna here...")

> I speak based on educated guesses gained from other space missions,
> not as a fact. Please take the comments with a grain of salt.
> But if you need me to find out more explicitly, then you will have
> to tell me your address where I can send a bill for my consultation fee 
;-).

Thanks for the explanation and I have sent you the cheque via sea-mail. 
With the way our dollar is dropping at the moment the cheque should be 
totally worthless when you receive it - so I won't owe you anything 
;-))))

cheers,
Fraser Farrell

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