[Sis-csi] Limit of Cislunar domain
Kearney, Mike
Mike.Kearney at nasa.gov
Mon Oct 10 12:12:46 EDT 2005
Aha! That makes sense. So earth-moon L2 is clearly part of lunar
mission infrastructure.
I'm a little concerned that if we include sun-earth L2, it begs the
question about why we're doing that for cislunar missions (or maybe it
is better to say for lunar programs). Unless there is some indicator
that there is some use for lunar missions with relays out that far. But
it's hard to see why sun-earth L-points would be part of a lunar
infrastructure.
We can always say, as Keith said, that "10 seconds is a nice boundary".
Lunar infrastructure that we know about is at ~3.5 seconds, so for
"margin" for unanticipated elements, we picked the next round number up,
namely 10 sec. I favor that, because if we list the sun-earth L2 points
as a consideration for cislunar, someone will challenge us to say what
lunar mission stuff is out there. Or maybe not. Actually, it's
probably not a big deal either way.
Keith (Scott), I think you need to decide first, whether we use the
table (per my input in Sec 2), and second, if we do, whether we mention
sun-earth L2 as justification for the 10-second round-up.
-=- Mike
Mike Kearney
NASA MSFC EO-01
256-544-2029
________________________________
From: Jason A. Soloff [mailto:jason.a.soloff at nasa.gov]
Sent: Sunday, October 09, 2005 10:57 PM
To: Kearney, Mike; sis-csi at mailman.ccsds.org
Subject: RE: [Sis-csi] Limit of Cislunar domain
Mike -
The thinking at Earth-Moon L2 is to use a halo orbit that keeps Earth in
view at the same time it provides coverage to the lunar far-side. There
are a number of these orbits studied within Exploration as well as in
the SCAWG. No decision has been made whether or not to use the L2 halo
orbit, but its a nice option to have in your pocket...
- Jason
____________________________________________
"It's kind of fun to do the impossible." - Walt Disney
Jason A. Soloff
Chief Engineer
Exploration Communication & Navigation Systems
Constellation Systems
NASA / Goddard Space Flight Center
Code 567 / B19 / S046
Greenbelt, MD 20771
Phone: (301)286-1368
Blackberry: (301)356-3708
Fax: (301)286-1750
E-Mail: Jason.A.Soloff at nasa.gov
________________________________
From: Keith Hogie [mailto:Keith.Hogie at gsfc.nasa.gov]
Sent: Sunday, October 09, 2005 7:35 PM
To: Krupiarz, Christopher
Cc: Kearney, Mike; sis-csi at mailman.ccsds.org
Subject: Re: [Sis-csi] Limit of Cislunar domain
I used the Sun/Earth L1/L2 values to give a worst case
boundary based on propagation delay. Technically they are beyond the
Moon's orbit but they are locations that are already being used (e.g.
SOHO, WMAP). I included them because their delay is not real bad and
you could probably still hold a voice converstation, run TCP, or do
something interactive over that sort of link. Once you get beyond them,
the next stop is pretty much Mars and those delays put you in a whole
different category. 10 seconds seemed to be a nice boundary that also
fit with locations being used.
I didn't worry about the Lunar Lagrange points since they are
not that far from the Moon. It looks like they are 61,500 Km away from
the Moon. I was listing delays from an Earth centric view which
probably fits with Cislunar. I guess the question is whether we want to
stick to purely Cislunar at 2.5 seconds or if we want to stretch to
Sun/Earth L1/L2 which would cover anything out to 10 seconds.
Keith Hogie
________________________________
From: sis-csi-bounces at mailman.ccsds.org
[mailto:sis-csi-bounces at mailman.ccsds.org] On Behalf Of Kearney, Mike
Sent: Sunday, October 09, 2005 9:18 AM
To: sis-csi at mailman.ccsds.org
Subject: RE: [Sis-csi] Limit of Cislunar domain
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.
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.
But another source says that L2 is 92,000 Km past the moon.
http://www.projectpluto.com/interest.htm
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.
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?
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.
-=- Mike
Mike Kearney
NASA MSFC EO-01
256-544-2029
________________________________
From: Krupiarz, Christopher
[mailto:Christopher.Krupiarz at jhuapl.edu]
Sent: Saturday, October 08, 2005 10:15 PM
To: Kearney, Mike; sis-csi at mailman.ccsds.org
Subject: RE: [Sis-csi] Limit of Cislunar domain
Mike,
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.
Chris
-----Original Message-----
From: sis-csi-bounces at mailman.ccsds.org on behalf of Kearney,
Mike
Sent: Sat 10/8/2005 10:10 PM
To: sis-csi at mailman.ccsds.org
Subject: RE: [Sis-csi] Limit of Cislunar domain
Keith (Hogie): I was plugging your table below into section
2...
0000.1 sec - Interaction between rovers, landers, (e.g. local
environment)
0000.1 sec - Low-Earth orbit ( a few hundred kilometers
one-way)
0000.1 sec - Low-Lunar orbit ( a few hundred kilometers one-way)
0000.1 sec - Low-Mars orbit ( a few hundred kilometers
one-way)
0000.5 sec - Earth geosync orbit (36,000 kilometers one-way)
0002.5 sec - Earth-to-Moon (384,000 kilometers one-way)
0010.0 sec - Earth to L1 or L2 (1,500,000 kilometers one-way)
------------------Limit of Cislunar domain
0366.0 sec - Earth to Mars (closest = 55.000.000 kilometers
one-way, 6
minute, RTT)
2673.0 sec - Earth to Mars (farthest = 401,000,000 kilometers
one-way,
45 minute RTT)
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?
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.
Anyone have any insight into that?
I ask the question, because a better description of what might
be done
at the Lagrangian points would help the "mission
characteristics"
section.
-=- Mike
Mike Kearney
NASA MSFC EO-01
256-544-2029
________________________________
From: sis-csi-bounces at mailman.ccsds.org
[mailto:sis-csi-bounces at mailman.ccsds.org] On Behalf Of Keith
Hogie
Sent: Thursday, September 08, 2005 12:55 AM
Cc: sis-csi at mailman.ccsds.org
Subject: Re: [Sis-csi] IP Header Compression
Adrian J. Hooke wrote:
At 01:40 PM 9/6/2005, Keith Hogie wrote:
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.
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?
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?
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.
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):
0000.1 sec - Interaction between rovers, landers, (e.g. local
environment)
0000.1 sec - Low-Earth orbit ( a few hundred kilometers
one-way)
0000.1 sec - Low-Lunar orbit ( a few hundred kilometers one-way)
0000.1 sec - Low-Mars orbit ( a few hundred kilometers
one-way)
0000.5 sec - Earth geosync orbit (36,000 kilometers one-way)
0002.5 sec - Earth-to-Moon (384,000 kilometers one-way)
0010.0 sec - Earth to L1 or L2 (1,500,000 kilometers one-way)
------------------Limit of Cislunar domain
0366.0 sec - Earth to Mars (closest = 55.000.000 kilometers
one-way, 6
minute, RTT)
2673.0 sec - Earth to Mars (farthest = 401,000,000 kilometers
one-way,
45 minute RTT)
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.
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.
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.
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.
----------------------------------------------------------------------
Keith Hogie e-mail:
Keith.Hogie at gsfc.nasa.gov
Computer Sciences Corp. office: 301-794-2999 fax:
301-794-9480
7700 Hubble Dr.
Lanham-Seabrook, MD 20706 USA 301-286-3203 @
NASA/Goddard
----------------------------------------------------------------------
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