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<title>RE: [Sis-csi] Limit of Cislunar domain</title>
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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>I was thinking the implication was that if
L2 is on the far side, it’s not in line-of-sight of earth. I think
that’s the reason radio telescope projects have been talked about for L2,
because the moon shields them from earth’s RF noise. And if the
comm relay at L2 is not in RF line-of-sight, then another relay would be needed
anyway. But I’m not a celestial mechanics guy, I’m just going
from diagrams I’ve seen. </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>In any case, I think it’s safe to
say that lunar missions could have some TBD elements at L2, hence extending our
definition of Cislunar to that point. </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>But another source says that L2 is 92,000
Km past the moon.</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><a
href="http://www.projectpluto.com/interest.htm">http://www.projectpluto.com/interest.htm</a></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>The earth-moon distance is 385,000 Km, and
the round trip time delay for earth-moon is 2.5 sec, I would think that the L2
round trip time would be only 3.5 sec or so. Not the 10 sec in your
table. </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>385+92= 477,000 Km for earth-moon L2, not
the 1,500,000 Km that you listed. I wonder if you got the distance for
earth-sun L2 instead of earth-moon L2? </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>I’m still confused about who wrote
this table up to begin with. Was it Chris or Keith (Hogie)? It’s
a great way to define the cislunar domain, IMHO, anyway. </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> -=- Mike</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Mike Kearney</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>NASA MSFC EO-01</span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>256-544-2029</span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> Krupiarz,
Christopher [mailto:Christopher.Krupiarz@jhuapl.edu] <br>
<b><span style='font-weight:bold'>Sent:</span></b> Saturday, October 08, 2005
10:15 PM<br>
<b><span style='font-weight:bold'>To:</span></b> Kearney, Mike;
sis-csi@mailman.ccsds.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> RE: [Sis-csi] Limit of
Cislunar domain</span></font></p>
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12.0pt'> </span></font></p>
<p style='margin-bottom:12.0pt'><font size=2 face="Times New Roman"><span
style='font-size:10.0pt'>Mike,<br>
<br>
L2 being on the far side of the Moon is what makes it nice as a comm relay for
assets that are also on the far side. I'm not sure about L4 and L5, but
I'm with you about not being confident in my knowledge of how these points
could be used. Off-hand if you're using relays to save power/mass on a
lander, it would seem using L4 & L5 wouldn't help much. 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>
----------------------------------------------------------------------</span></font></p>
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