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Old 08 August 2008, 03:05   #11
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Originally Posted by captnjack View Post
-snip-
The chartplotter is not your biggest problem here IMHO. Its actually generating, propogating and receiving a useful signal.
Ah - but luckily that is not my problem :-) I have radio people doing that. My job is to get hold of a means to handle the data when they are acquired.

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Old 08 August 2008, 03:11   #12
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Is the rib a little small to go 20 miles offshore
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Old 08 August 2008, 06:10   #13
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Size matters

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Originally Posted by bedajim View Post
Is the rib a little small to go 20 miles offshore
Thank you for your concern. Well, you could be right. The rib is the product of our current experience and knowledge divided with our funds...

The 20 miles is an absolute maximum. I presume that most of the time we will not be going further than 5-8 miles offshore but that is also a fair distance, especially in the North Sea.

Luckily we will never sail out in harsh weather because high winds rule out rocket launches. Besides we will be wearing flotation suits and vests and will carry a ship to shore radio, mobile phones, gps chartplotter, flares, fire extinguisher, compass off course and a spare engine. I realize that one should never make plans that include the use of the safety devices, I just point out that we are careful.

In reality it is impossible to know if the boat is large enough because we do not know the exact curcumstances of its use. We just think it is and will test it with recovery after the first launches. They will be to a lower altitude which means splashdown is closer to shore. Then we will know if sailing in this size boat feels safe and if it is too small we will have to change it.

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Old 08 August 2008, 10:14   #14
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Most chart plotters can now receive a position input on an NMEA channel. This is commonly used for receiving a position from a DSC radio. I'm not familiar with the NMEA sentence used but I don't imagine it will be difficult to find. If your transmitter is sending its position frequently, it may be a nuisance dealing with the plotter receiving constant data. But, if the transmitter sent its data less frequently, say every 30sec, then you could know its landing position, manually switch off the NMEA data connection, navigate close to the landing position, switch on the data stream again and receive an update on the transmitter position. Providing, of course, that you are able to receive it as per Captnjack's comments.

If you wish to use the same plotter on land, you will need to make sure to choose a unit which is capable of reading both land based maps and marine charts. A marine only unit will be able to give you a position on land on its chart but the chart will have limited features for you to identify accurately where the transmitter is. It will, however, show you your position in relation to your waypoint (rocket transmitter). It will also give you co-ordinates of the transmitter which you can transfer to a traditional paper land map.
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Old 08 August 2008, 10:32   #15
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i beleive you can "hack" your own charts for mapsource format, ie: suitable to upload into a garmin plotter. here is one article i bookmarked when i was looking into it http://habari.co.tz/pipermail/tzgisu...ne/000271.html
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Old 09 August 2008, 17:12   #16
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I used to do some of this sort of thing when we recovered autonomous seabed landers mid ocean.
There was generally a combination of methods used to back each other up from satellite tracking methods (ARGOS and sat phone lashups) to direction finding (on yagi type aerials and visual methods like strobes and flags).
All of which were large and bulky due to being pressure resistant to 6km or so but you won't need that.
In your position I reckon I would be looking at popping a small GPS receiver behind a radio transparent part of the rocket that would point up and use the output sentence from the GPS to either a sat phone transmitting its position every few minutes or to the ARGOS system.
The satellite phone system is likely to be usable and cost less but still effective.
I don't really know of any way of getting a position signal from that low in the water to a small boat reliably other than up and back down again from the satellites although it has been a few years since working in that field.
The simplest and most reliable way that you can afford is likely to be DF'ing and this doesn't always work.......
What I can say other than expect to lose them now and again no matter what system you use for recovery?
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Old 11 August 2008, 15:31   #17
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What about a large helium filled mylar ballon? Deploy a few seconds before impact. Even just 20m high gives you a horizon of 16+km. Skip all this coordinate signal transmitting etc. and find it by radar. A radar transponder would be even more distinctive but probably too heavy.
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Old 11 August 2008, 19:50   #18
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Quote:
Originally Posted by jwalker View Post
Most chart plotters can now receive a position input on an NMEA channel. This is commonly used for receiving a position from a DSC radio. I'm not familiar with the NMEA sentence used but I don't imagine it will be difficult to find. If your transmitter is sending its position frequently, it may be a nuisance dealing with the plotter receiving constant data. But, if the transmitter sent its data less frequently, say every 30sec, then you could know its landing position, manually switch off the NMEA data connection, navigate close to the landing position, switch on the data stream again and receive an update on the transmitter position. Providing, of course, that you are able to receive it as per Captnjack's comments.
I think the NMEA sentence you want the chart plotter to recieve is "DSE" (the enhanced DSC sentence - the standard sentence will only give you approx 1nm "accuracy"). JW is right MOST chart plotters accept this but not all (some Lowrance definitely do not).

This is normally used to either show on the chartplotter the location of a boat transmitting an incoming distress message or using the "position request" feature to show the location of your "buddy" (as the americans would say!)

I am sure there are some electronics "geeks" in your team who can relatively take the 433 MHz data stream and output this in NMEA 0183 format (effectively RS232), which the plotter will display and (as I understand it) will "refresh" by itself. Assuming your rocket continually transmits you will get a GPS position updating itself until splashdown and then pick up the GPS position again when you start to get closer to pick it up and are back in range.

Unfortunately I think to get all the correct DSE formatting you may need to buy the NMEA standard. This might provide some general info - but not the DSE sentence info unfortunately: http://www.actisense.com/Downloads/T...on%20Sheet.pdf
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Old 12 August 2008, 10:14   #19
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But can we use the serial port to input GPS-data this way? I would presume that the input was for the antenna, ie the chartplotters own position.
To clarify, the GPS antenna is one input, the input/output data cable is separate.
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Unfortunately I think to get all the correct DSE formatting you may need to buy the NMEA standard. This might provide some general info - but not the DSE sentence info unfortunately: http://www.actisense.com/Downloads/T...on%20Sheet.pdf
I think with a bit of looking around, it can probably be worked out. They have the opportunity to test first so should be able to see if the data is doing the right things. I'd assume that any incorrectly formatted sentences would just be ignored.
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Old 12 August 2008, 12:46   #20
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...They have the opportunity to test first so should be able to see if the data is doing the right things. I'd assume that any incorrectly formatted sentences would just be ignored.
At a push, a DSC radio could be connected to an RS232 port on a computer, a position request made and Hyperterminal could be used to read the data and find the structure of the sentence required.
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