[Sis-csi] Limit of Cislunar domain
Keith Hogie
Keith.Hogie at gsfc.nasa.gov
Sun Oct 9 20:35:30 EDT 2005
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
Krupiarz, Christopher wrote:
> Mike,
>
> It's Keith's table. I agree, it's a nice table to have and would be
> great to include in the Green Book.
>
> I think you are right about the L1/L2 definitions. Those are
> Sun/Earth distances in the table.
>
> 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?
>
> Chris
>
>
> -----Original Message-----
> From: sis-csi-bounces at mailman.ccsds.org on behalf of Kearney, Mike
> Sent: Sun 10/9/2005 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
> <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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--
----------------------------------------------------------------------
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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