[Sis-csi] Limit of Cislunar domain
Krupiarz, Christopher
Christopher.Krupiarz at jhuapl.edu
Mon Oct 10 12:54:01 EDT 2005
I'd suggest we keep it in. One possible source for justification is the
discussion in this document (search for SEL2):
http://planetary.org/aimformars/study-report.pdf
While it appears some of this report has been overcome by events, it may
be enough justification for at least keeping the option open.
Chris
-----Original Message-----
From: sis-csi-bounces at mailman.ccsds.org
[mailto:sis-csi-bounces at mailman.ccsds.org] On Behalf Of Kearney, Mike
Sent: Monday, October 10, 2005 12:13 PM
To: Jason A. Soloff; sis-csi at mailman.ccsds.org
Subject: RE: [Sis-csi] Limit of Cislunar domain
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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