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<P><FONT SIZE=2>Mike,<BR>
<BR>
It's Keith's table. I agree, it's a nice table to have and would be great to include in the Green Book.<BR>
<BR>
I think you are right about the L1/L2 definitions. Those are Sun/Earth distances in the table.<BR>
<BR>
Probably a dumb question, but can you have a halo orbit at L2 with a large enough radius that it can be seen from Earth? <BR>
<BR>
Chris<BR>
<BR>
<BR>
-----Original Message-----<BR>
From: sis-csi-bounces@mailman.ccsds.org on behalf of Kearney, Mike<BR>
Sent: Sun 10/9/2005 9:18 AM<BR>
To: sis-csi@mailman.ccsds.org<BR>
Subject: RE: [Sis-csi] Limit of Cislunar domain<BR>
<BR>
I was thinking the implication was that if L2 is on the far side, it's<BR>
not in line-of-sight of earth. I think that's the reason radio<BR>
telescope projects have been talked about for L2, because the moon<BR>
shields them from earth's RF noise. And if the comm relay at L2 is not<BR>
in RF line-of-sight, then another relay would be needed anyway. But I'm<BR>
not a celestial mechanics guy, I'm just going from diagrams I've seen. <BR>
<BR>
<BR>
<BR>
In any case, I think it's safe to say that lunar missions could have<BR>
some TBD elements at L2, hence extending our definition of Cislunar to<BR>
that point. <BR>
<BR>
<BR>
<BR>
But another source says that L2 is 92,000 Km past the moon.<BR>
<BR>
<A HREF="http://www.projectpluto.com/interest.htm">http://www.projectpluto.com/interest.htm</A><BR>
<BR>
<BR>
<BR>
The earth-moon distance is 385,000 Km, and the round trip time delay for<BR>
earth-moon is 2.5 sec, I would think that the L2 round trip time would<BR>
be only 3.5 sec or so. Not the 10 sec in your table. <BR>
<BR>
<BR>
<BR>
385+92= 477,000 Km for earth-moon L2, not the 1,500,000 Km that you<BR>
listed. I wonder if you got the distance for earth-sun L2 instead of<BR>
earth-moon L2? <BR>
<BR>
<BR>
<BR>
I'm still confused about who wrote this table up to begin with. Was it<BR>
Chris or Keith (Hogie)? It's a great way to define the cislunar domain,<BR>
IMHO, anyway. <BR>
<BR>
<BR>
<BR>
-=- Mike<BR>
<BR>
<BR>
<BR>
Mike Kearney<BR>
<BR>
NASA MSFC EO-01<BR>
<BR>
256-544-2029<BR>
<BR>
________________________________<BR>
<BR>
From: Krupiarz, Christopher [<A HREF="mailto:Christopher.Krupiarz@jhuapl.edu">mailto:Christopher.Krupiarz@jhuapl.edu</A>]<BR>
Sent: Saturday, October 08, 2005 10:15 PM<BR>
To: Kearney, Mike; sis-csi@mailman.ccsds.org<BR>
Subject: RE: [Sis-csi] Limit of Cislunar domain<BR>
<BR>
<BR>
<BR>
Mike,<BR>
<BR>
L2 being on the far side of the Moon is what makes it nice as a comm<BR>
relay for assets that are also on the far side. I'm not sure about L4<BR>
and L5, but I'm with you about not being confident in my knowledge of<BR>
how these points could be used. Off-hand if you're using relays to save<BR>
power/mass on a lander, it would seem using L4 & L5 wouldn't help much.<BR>
However, L4 & L5 would give some coverage of the far side.<BR>
<BR>
Chris<BR>
<BR>
<BR>
-----Original Message-----<BR>
From: sis-csi-bounces@mailman.ccsds.org on behalf of Kearney, Mike<BR>
Sent: Sat 10/8/2005 10:10 PM<BR>
To: sis-csi@mailman.ccsds.org<BR>
Subject: RE: [Sis-csi] Limit of Cislunar domain<BR>
<BR>
Keith (Hogie): I was plugging your table below into section 2...<BR>
<BR>
<BR>
<BR>
0000.1 sec - Interaction between rovers, landers, (e.g. local<BR>
environment)<BR>
0000.1 sec - Low-Earth orbit ( a few hundred kilometers one-way)<BR>
0000.1 sec - Low-Lunar orbit ( a few hundred kilometers one-way)<BR>
0000.1 sec - Low-Mars orbit ( a few hundred kilometers one-way)<BR>
0000.5 sec - Earth geosync orbit (36,000 kilometers one-way)<BR>
0002.5 sec - Earth-to-Moon (384,000 kilometers one-way)<BR>
0010.0 sec - Earth to L1 or L2 (1,500,000 kilometers one-way)<BR>
------------------Limit of Cislunar domain<BR>
0366.0 sec - Earth to Mars (closest = 55.000.000 kilometers one-way, 6<BR>
minute, RTT)<BR>
2673.0 sec - Earth to Mars (farthest = 401,000,000 kilometers one-way,<BR>
45 minute RTT)<BR>
<BR>
<BR>
<BR>
But I started wondering about the usage of L1 and L2. L1 is closer to<BR>
earth than the moon, so it would really not be a factor in establishing<BR>
the boundary of cislunar missions in terms of time delay. L2 is on the<BR>
far side of the moon and wouldn't have much value for comm relays. Did<BR>
you have some other mission in mind?<BR>
<BR>
<BR>
<BR>
In terms of comm relays, I was wondering if L4 or L5 (preceding or<BR>
following the moon in earth orbit) have more value as comm relays. And<BR>
I started wondering if anyone what Exploration was considering as<BR>
possible uses for those Lagrangian points. I'm not confident in my<BR>
understanding, and I just want whatever text that goes into the Cislunar<BR>
GB to be credible. <BR>
<BR>
<BR>
<BR>
Anyone have any insight into that?<BR>
<BR>
<BR>
<BR>
I ask the question, because a better description of what might be done<BR>
at the Lagrangian points would help the "mission characteristics"<BR>
section.<BR>
<BR>
<BR>
<BR>
-=- Mike<BR>
<BR>
<BR>
<BR>
Mike Kearney<BR>
<BR>
NASA MSFC EO-01<BR>
<BR>
256-544-2029<BR>
<BR>
________________________________<BR>
<BR>
From: sis-csi-bounces@mailman.ccsds.org<BR>
[<A HREF="mailto:sis-csi-bounces@mailman.ccsds.org">mailto:sis-csi-bounces@mailman.ccsds.org</A>] On Behalf Of Keith Hogie<BR>
Sent: Thursday, September 08, 2005 12:55 AM<BR>
Cc: sis-csi@mailman.ccsds.org<BR>
Subject: Re: [Sis-csi] IP Header Compression<BR>
<BR>
<BR>
<BR>
Adrian J. Hooke wrote:<BR>
<BR>
At 01:40 PM 9/6/2005, Keith Hogie wrote:<BR>
<BR>
<BR>
<BR>
I agree we need to consider issues with small packets and low rates,<BR>
but how low do we need to go. In all of the missions I have seen (non<BR>
deep space), the lowest data rates are 125 bps. This is over an order<BR>
of magnitude difference from your 10 bps.<BR>
<BR>
For the Cislunar environment, we need to figure out what some of our<BR>
limits are. Do we really want to burden the Cislunar design with issues<BR>
that only relate to Deep Space?<BR>
<BR>
<BR>
Aren't the Lunar missions supposed to be "training" for going to Mars?<BR>
For critical emergency commanding operations, shouldn't we be developing<BR>
a robust, unified, reliable, tested system that works wherever you go?<BR>
<BR>
<BR>
For emergency commanding I don't see any difference between Cislunar<BR>
or Deep Space. In both cases the solution is to send a string of bits<BR>
that gets decoded by hardware and do not need any protocol. The<BR>
critical hardware commands are their own frame sync, authentication, and<BR>
command all packed into a highly unique string of bits. Most hardware<BR>
decoders pick off the bits they are looking at directly from the<BR>
receiver and don't involve any flight software. This means that there<BR>
is no complex packet processing and the hardware is just looking for<BR>
particular sequence of bits. The length of this sequence is not a<BR>
function of any CCSDS or IP headers. Getting the command to the<BR>
spacecraft just requires radiating the proper string of bits. The<BR>
length of the hardware command is just a function of how many bits you<BR>
think you need to make sure your command doesn't occur in normal data<BR>
transfers.<BR>
<BR>
My main concern is for all the other operational modes there is a very<BR>
large disconnect between things that will work in a Cislunar environment<BR>
and a long haul link to Mars. If you consider the following round trip<BR>
times (RTT):<BR>
<BR>
0000.1 sec - Interaction between rovers, landers, (e.g. local<BR>
environment)<BR>
0000.1 sec - Low-Earth orbit ( a few hundred kilometers one-way)<BR>
0000.1 sec - Low-Lunar orbit ( a few hundred kilometers one-way)<BR>
0000.1 sec - Low-Mars orbit ( a few hundred kilometers one-way)<BR>
0000.5 sec - Earth geosync orbit (36,000 kilometers one-way)<BR>
0002.5 sec - Earth-to-Moon (384,000 kilometers one-way)<BR>
0010.0 sec - Earth to L1 or L2 (1,500,000 kilometers one-way)<BR>
------------------Limit of Cislunar domain<BR>
0366.0 sec - Earth to Mars (closest = 55.000.000 kilometers one-way, 6<BR>
minute, RTT)<BR>
2673.0 sec - Earth to Mars (farthest = 401,000,000 kilometers one-way,<BR>
45 minute RTT)<BR>
<BR>
When you look at distances like these there is a huge break between<BR>
Cislunar ones and Mars. In the Cislunar area it is actually possible<BR>
to do interactive things like interactive audio, video, and data access.<BR>
You can consider security protocols that negotiate security details. At<BR>
L1 and L2 things get a bit uncomfortable at 10 seconds RTT but that is<BR>
still manageable. At Lunar distances you can do most anything you do on<BR>
Earth. A 2.5 second delay is a bit long for some interactive operations<BR>
but it is not really any longer than what happens when you surf the open<BR>
Internet and hit a bit of congestion. The main point is that out to L1<BR>
and L2 you can actually do interactive operations This also applies to<BR>
systems on Mars and orbiting around Mars.<BR>
<BR>
However, when you move to the long haul link between Earth and Mars,<BR>
the RTT jumps up to over 100 or 1,000 times that of the Earth and Moon.<BR>
With a 6 to 45 minute RTT, you can't carry on an interactive voice or<BR>
video conversation and lots of interactive data access just doesn't<BR>
work. On a Earth-to-Mars link you are forced to shift to an operations<BR>
concept of two one-way links. Operations must shift into email-like<BR>
file store-and-forward or one-way streaming of data.<BR>
<BR>
So I don't see any real problem with using the same hardware<BR>
commanding solution in Cislunar or Earth-to-Mars scenarios. Some file<BR>
store-and-forward and one-way streaming operations will also work for<BR>
both environments. Of course any acknowledgments on the file-store-and<BR>
forward will take lots longer.<BR>
<BR>
My concern is that other there are lots of protocols and applications<BR>
that will work fine in an interactive Cislunar environment but just<BR>
don't work for Earth-to-Mars. We don't want to limit our Cislunar<BR>
solutions to only those that will also work for Earth-to-Mars. I think<BR>
we need to develop our Cislunar solutions and then see if any of them<BR>
will also work in a Earth-to-Mars scenario.<BR>
<BR>
<BR>
<BR>
----------------------------------------------------------------------<BR>
Keith Hogie e-mail: Keith.Hogie@gsfc.nasa.gov<BR>
Computer Sciences Corp. office: 301-794-2999 fax: 301-794-9480<BR>
7700 Hubble Dr.<BR>
Lanham-Seabrook, MD 20706 USA 301-286-3203 @ NASA/Goddard<BR>
----------------------------------------------------------------------<BR>
<BR>
<BR>
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