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Probes communicating over interplanetry distances

Posted by: Ekkehard Augustin - Sun Nov 27, 2005 9:45 am
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Probes communicating over interplanetry distances 
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Post Probes communicating over interplanetry distances   Posted on: Sun Nov 27, 2005 9:45 am
I am wondering about the communication between ground station and probes hundreds of millions of kilometers away - the reason is something special I read regarding the problems with Hayabusa.

It has been reported that there was a problem when Hayabusa was about sending Minerva to the asteroid's surface. The ground station commanded the launch of Minerva but without knopwing the situation of Hayabusa well enough - according to one or a few reports.

The command reached Hayabusa 16 minutes later and has been obeyed to - but the situation had changed then. This had to be expected. Hayabusa was departing from the asteroid already by a velocity higher than the asteroid's escape velocity

Don't probes be have an algorithm to account for the time a command needs to arrive? Don't their computers have a log providing the informations about what has happened or has been done during the time a command needs to arrive from Earth? If they would have then the computer could calculate that time back and look to the log. This could enable the probe to do the required corrections of the command or to ignore it if that would be better for its success.

What about it?



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)


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Post    Posted on: Sun Nov 27, 2005 11:05 am
Normally remote craft have altonomous systems which allow them to work out a situation and respond accordingly, one of these responses might be to await for new orders from Earth.

I can only guess that the problem was something that was not anticipated.

Once moon exploration gets underway it will be an ideal place to test rovers or small craft because the delay is only seconds.

Of course this is all more power to the argument for manned exploration. :)

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Post Re: Probes communicating over interplanetry distances   Posted on: Mon Nov 28, 2005 1:40 pm
Ekkehard Augustin wrote:
This could enable the probe to do the required corrections of the command or to ignore it if that would be better for its success.


Requires some pretty impressive AI to accomplish that sort of thing - and the technology isnt really there yet. Although they can attempt to program for all possible scenarios, that obviously isnt possible - these are the somethings you need the AI for.

I would expect that the probes do log everything they do, and receive. In fact, it would be insane not to do so, just so you can backtrack command and actions if necessary if there are problems.

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Post    Posted on: Mon Nov 28, 2005 2:03 pm
It depends on how the data are logged. For example the software could write one record each second which containes the velocity at that second, the distance to Earth, the distances to close objects and the observed object and the scientific or commercial task to be done that second.

The computer could be enabled to calculate the time the command has gone when it arrives (using the distance to Earth that second) and subtract it from the current time. Then it knows which record to retrieve from the log. The log should use the time as one of possibly several keys.

The retrieved record would tell the probe the situation valid when the Command has been sent.

Now in the example the command had been based on the data the probe has sent to Earth - so the computer should log the times of transmission too and would be able to account for the time his own data needed to arrive at Earth and would go back further to the time of transmission. This would tell him the data the command is based on.

In the example the probe would have known this way that the command had been based on data saying that its velocity was below escape velocity plus the velocity itself. This would allow for a comparison of that velocity to current velocity. So the command could be corrected. the same would be possible regarding distance and so on.

Because of this it seems to me that AI isn't required. Perhaps some DS1-like software could be applied.



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Post    Posted on: Fri Nov 07, 2008 10:29 am
What the article "Space Communications Patent Spans Solar System" ( www.space.com/businesstechnology/081105 ... atent.html ) tells about is a little bit off the focus and reason I initiated this thread for and has more to do with an interplanetary communications network.

But it might be used to solve the problem perhaps. The relay satellites around other planets would be closer and might be applied to store commands related to particular situations. Informations and commands could be exchanged faster if they are closer to the probe. ...
...
...
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What about it?



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Post    Posted on: Sat Nov 29, 2008 5:04 pm
The new technology reported by the article "NASA Tests Interplanetary Internet" ( www.space.com/news/081119-deep-space-internet.html ) might offer building blocks for a solution of the problem I started to think about.

An
Quote:
interplanetary Internet
based on a protocol that handles problems that might occur in space but dön't happen on Earth -
Quote:
Disruption-Tolerant Networking, or DTN
.

The article explicitly mentions that
Quote:
The Interplanetary Internet must be robust enough to withstand delays, disruptions and disconnections in space. Glitches can happen when a spacecraft moves behind a planet, or when solar storms and long communication delays occur. For instance, the delay in sending or receiving data from Mars takes between three-and-a-half to 20 minutes, even at the speed of light.
.

Such delays caused the problem being the subject of my thoughts.

Quote:
If a disruption occurs in the pathway along which the information travels, each node in the network will hang on to its information until it's safe to communicate, unlike our Internet on Earth, which just discards the data packets.


The new network could ease communication with distant spacecraft and enable new kinds of space missions.


"In space today, an operations team must manually schedule each link and generate all the commands to specify which data to send, when to send it, and where to send it," said Leigh Torgerson, manager of the DTN Experiment Operations Center at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "With standardized DTN, this can all be done automatically."


If the nodes would be turned to hang on also at delays then they might be enhanced to default operations designed to assist mission success. Such a default operation could have been not to launch the small robot to the asteroid while moving away from it at a velocity larger than the gravitational acceleration the asteroid provides. This might be one of the automations mentioned.

Regarding the new kind of missions - in The Spaceflight Cafe-section I long ago initiated a thread about the idea of an interstellar internet.

This new technology might be a first germ of that - yet lacking replicating and self-reüairing probes spread over the galaxy at interstellar distances.



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