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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'>Keith (Hogie): I was plugging your table
below into section 2…</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=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'>0000.1 sec - Interaction between rovers, landers,
(e.g. local 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 minute,
RTT)<br>
2673.0 sec - Earth to Mars (farthest = 401,000,000 kilometers one-way, 45
minute RTT)</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 I started wondering about the usage of
L1 and L2. L1 is closer to earth than the moon, so it would really not be
a factor in establishing the boundary of cislunar missions in terms of time
delay. L2 is on the far side of the moon and wouldn’t have much
value for comm relays. Did you have some other mission in mind? </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 terms of comm relays, I was wondering
if L4 or L5 (preceding or following the moon in earth orbit) have more value as
comm relays. And I started wondering if anyone what Exploration was
considering as possible uses for those Lagrangian points. I’m not
confident in my understanding, and I just want whatever text that goes into the
Cislunar GB to be credible. </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'>Anyone have any insight into that? </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 ask the question, because a better
description of what might be done at the Lagrangian points would help the “mission
characteristics” section. </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>
<div>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial'> -=- Mike</span></font></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial'> </span></font></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial'>Mike Kearney</span></font></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial'>NASA MSFC EO-01</span></font></p>
<p class=MsoNormal><font size=2 color=black face=Arial><span style='font-size:
10.0pt;font-family:Arial'>256-544-2029</span></font></p>
</div>
<div>
<div class=MsoNormal align=center style='text-align:center'><font size=3
color=black face="Times New Roman"><span style='font-size:12.0pt;color:windowtext'>
<hr size=2 width="100%" align=center tabindex=-1>
</span></font></div>
<p class=MsoNormal><b><font size=2 color=black face=Tahoma><span
style='font-size:10.0pt;font-family:Tahoma;color:windowtext;font-weight:bold'>From:</span></font></b><font
size=2 color=black face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma;
color:windowtext'> sis-csi-bounces@mailman.ccsds.org
[mailto:sis-csi-bounces@mailman.ccsds.org] <b><span style='font-weight:bold'>On
Behalf Of </span></b>Keith Hogie<br>
<b><span style='font-weight:bold'>Sent:</span></b> Thursday, September 08, 2005
12:55 AM<br>
<b><span style='font-weight:bold'>Cc:</span></b> sis-csi@mailman.ccsds.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [Sis-csi] IP Header
Compression</span></font></p>
</div>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'> </span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'>Adrian J. Hooke wrote: </span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Times New Roman"><span
style='font-size:12.0pt;color:blue'>At 01:40 PM 9/6/2005, Keith Hogie wrote:<br>
<br>
</span></font></p>
<p class=MsoNormal><font size=3 color=blue face="Times New Roman"><span
style='font-size:12.0pt;color:blue'> I agree we need to consider issues
with small packets and low rates, but how low do we need to go. In all of
the missions I have seen (non deep space), the lowest data rates are 125
bps. This is over an order of magnitude difference from your 10 bps.
<br>
<br>
For the Cislunar environment, we need to figure out what some of our
limits are. Do we really want to burden the Cislunar design with issues
that only relate to Deep Space?</span></font></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3 color=black
face="Times New Roman"><span style='font-size:12.0pt'><br>
Aren't the Lunar missions supposed to be "training" for going to
Mars? For critical emergency commanding operations, shouldn't we be developing
a robust, unified, reliable, tested system that works wherever you go?</span></font></p>
<p class=MsoNormal><font size=3 color=black face="Times New Roman"><span
style='font-size:12.0pt'> <br>
For emergency commanding I don't see any difference between Cislunar or
Deep Space. In both cases the solution is to send a string of bits that
gets decoded by hardware and do not need any protocol. The critical
hardware commands are their own frame sync, authentication, and command all
packed into a highly unique string of bits. Most hardware decoders pick
off the bits they are looking at directly from the receiver and don't involve
any flight software. This means that there is no complex packet
processing and the hardware is just looking for particular sequence of
bits. The length of this sequence is not a function of any CCSDS or IP
headers. Getting the command to the spacecraft just requires radiating
the proper string of bits. The length of the hardware command is just a
function of how many bits you think you need to make sure your command doesn't
occur in normal data transfers. <br>
<br>
My main concern is for all the other operational modes there is a very
large disconnect between things that will work in a Cislunar environment and a
long haul link to Mars. If you consider the following round trip times
(RTT):<br>
<br>
0000.1 sec - Interaction between rovers, landers, (e.g. local 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 minute,
RTT)<br>
2673.0 sec - Earth to Mars (farthest = 401,000,000 kilometers one-way, 45
minute RTT)<br>
<br>
When you look at distances like these there is a huge break between
Cislunar ones and Mars. In the Cislunar area it is actually
possible to do interactive things like interactive audio, video, and data
access. You can consider security protocols that negotiate security
details. At L1 and L2 things get a bit uncomfortable at 10 seconds RTT but
that is still manageable. At Lunar distances you can do most anything you
do on Earth. A 2.5 second delay is a bit long for some interactive
operations but it is not really any longer than what happens when you surf the
open Internet and hit a bit of congestion. The main point is that out to
L1 and L2 you can actually do interactive operations This also applies to
systems on Mars and orbiting around Mars. <br>
<br>
However, when you move to the long haul link between Earth and Mars, the
RTT jumps up to over 100 or 1,000 times that of the Earth and Moon. With
a 6 to 45 minute RTT, you can't carry on an interactive voice or video
conversation and lots of interactive data access just doesn't work. On a
Earth-to-Mars link you are forced to shift to an operations concept of two
one-way links. Operations must shift into email-like 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
commanding solution in Cislunar or Earth-to-Mars scenarios. Some file
store-and-forward and one-way streaming operations will also work for both
environments. Of course any acknowledgments on the file-store-and forward
will take lots longer. <br>
<br>
My concern is that other there are lots of protocols and applications
that will work fine in an interactive Cislunar environment but just don't work
for Earth-to-Mars. We don't want to limit our Cislunar solutions to only
those that will also work for Earth-to-Mars. I think we need to develop
our Cislunar solutions and then see if any of them will also work in a
Earth-to-Mars scenario. <br>
<br>
</span></font></p>
<pre><font size=2 color=black face="Courier New"><span style='font-size:10.0pt'>----------------------------------------------------------------------</span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'> Keith Hogie e-mail: <a
href="mailto:Keith.Hogie@gsfc.nasa.gov">Keith.Hogie@gsfc.nasa.gov</a></span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'> Computer Sciences Corp. office: 301-794-2999 fax: 301-794-9480</span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'> 7700 Hubble Dr.</span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'> Lanham-Seabrook, MD 20706 USA 301-286-3203 @ NASA/Goddard</span></font></pre><pre><font
size=2 color=black face="Courier New"><span style='font-size:10.0pt'>---------------------------------------------------------------------- </span></font></pre></div>
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