peterb@pbear.UUCP (01/31/86)
.... I don't know the exact structure of Voyager, but I'll make a stab at an explanation of the errors in the idea. Voyager does not contain a camera as such, but a scanner that can take a picture of a vertical line, and rotates the scanner to capture the next line. This is much like the principle used in vidicon tubes to scan a picture as it is displayed on its surface. This is highly useful when the object to be viewed is large (such as a planet) since error correction can be applied to aline each and every scan line correctly. also the object that are being scanned are extremely bright (compared to the background). The problem I have is that once you try to scan a point (as a star is to a CCD scanner) is that each line of the scanner "scans" a portion of the sky, not just a vertical line. So at the distance of a few hundred light years, the scanner could not (in one try) distinguish objects closer together than about 1 to 2 light years (I think, plase correct me since I don't have specs). Multiple exposures could reduce this error, but it will still be there affecting calculations. Another problem is the accuracy of the distance between voyager and the sun. We can only determine the distance from voyager to the earth by "pinging" a command to voyager that causes voyager to return a change of state signifying the receipt of that command. So we havce the distance to voager at half the time it takes to return the command. Preferably at that time a plate is taken from a schmidt camera that points at the same star in question. Voyager would retun the "average" picture from multiple exposures of a particular star field, and from that a rough distance can be computed. Another problem to consider is that the percieved angle fromthe scanner to the earth has to be computed. I don;t know if this is possible without introducing oders of magnitude of error into the system. I hope the bbove has explained some of the problems with the idea, but I would hope that JPL can try to give some rough plates in the interim between Uranus and Neptune. In the amount of time in between, Voyager could run up a lot of exposures on a particular porion of the ovservable sky (without burning up a bit of reaction mass). Peter Barada ihnp4!ima!pbear!peterb