Deap Space Navigation

(Henry Spencer) wrote:

In article ,
Derek Lyons wrote:
The dominant method is radio tracking... These measurements
are combined using a sophisticated estimating process...
Some other techniques sometimes get added...

Damm - it's amazing how close that description is to the methods we
used to track targets using sonar. (Though our targets were usually
assumed to be non-cooperative.)

Somewhat the same problem, of course, apart from whether the target is
trying to help.

Somewhat the same - even without target cooperation, NASA can either
look up, or knows many of the terms we have to derive or constrain.

There may well have been some cross-fertilization on methods -- probably
mostly from NASA to the USN, given the security issues for information
traveling the other way.

I suspect it went the other way, as only certain parts (mostly
regarding specific equipment performance and specific tactics) is
actually classified.

NASA threw money at these issues in the early 60s, around the time when
the USN was starting large-scale deployment of gear intended to counter
Soviet nuclear subs, including the beginnings of sophisticated sonar, so
the time scale was about right.

The basic equations we use date back to WWII and beyond - we can just
fill them in with more accurate data and solve them faster. The first
time I saw a WWII era TDC, I could operate it immediately - having
been trained on it's 60's era equivalent. (And the last of that
system didn't leave the fleet until the late 1990's.)

D.
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Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

(Henry Spencer) wrote:

Would it help to put some sort of navigation beacon on the surface of
the target planet/moon? Something that the approaching probe could
use for it's own orbital insertion maneuvers?

In the long run, such things could help, at least for busy destinations,
but you need to invest substantial resources to build a GPS equivalent at,
say, Mars.

Do you really need a GPS analog? It seems a couple of beacons that
could act as a pseudo-Transit would be Really Handy - and much cheaper
and easier than a GPS type system.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

Somewhat the same - even without target cooperation, NASA can either
look up, or knows many of the terms we have to derive or constrain.

I don't believe that's true, at least to a large degree. Note that Henry,
in his original reply, said that the solution also involves "measuring" the
masses and orbits of the planetary objects involved. Remember G is only known
quite inaccurately (10^-5 or so, IIRC), GM for many bodies is known more
accurately (in large part due to such navigational exercises), and there are
some high-order effects that are difficult to characterize analytically. It
will be an "interesting" exercise to navigate Dawn, in particular.

Jan

"Derek" == Derek Lyons writes:

Derek John Stoffel wrote:
This was a great help, but now that we have more and more deep space
probes, and with the DSN network starting to get overloaded, how would
you make it easier to send probes so that they can do more of their
own navigation work?

Would it help to put some sort of navigation beacon on the surface of
the target planet/moon? Something that the approaching probe could
use for it's own orbital insertion maneuvers?

Derek I think the easiest solution would be to upgrade the DSN (I.E. add
Derek more antennas and site). It's _much_ easier to repair/replace/upgrade
Derek the hardware than beacons located in space.

Certainly, that would be a better solution, but that's a seperate pile
of money generally. While a new beacon could just be an add-on to an
existing orbiter or other mars bound vehicle.

Now I agree that DSN should be upgraded, but how? Are lasers
effective over interplanetary distances yet? Or something in the IR
range would be better? I dunno...

John

John Stoffel wrote:

"Derek" == Derek Lyons writes:

John Stoffel wrote:
This was a great help, but now that we have more and more deep space
probes, and with the DSN network starting to get overloaded, how would
you make it easier to send probes so that they can do more of their
own navigation work?

Would it help to put some sort of navigation beacon on the surface of
the target planet/moon? Something that the approaching probe could
use for it's own orbital insertion maneuvers?

I think the easiest solution would be to upgrade the DSN (I.E. add
more antennas and site). It's _much_ easier to repair/replace/upgrade
the hardware than beacons located in space.

Certainly, that would be a better solution, but that's a seperate pile
of money generally. While a new beacon could just be an add-on to an
existing orbiter or other mars bound vehicle.

Well, it's just more than simply adding it on. You have to have
weight available, and volume, and power - as well as taking any
thermal implications into account, as well as the effect of the beacon
on other systems and instruments. It's not really straightforwards.

There also a matter of scope - a beacon on a Mars orbiter or lander
only helps Mars bound craft. DSN upgrades help all spacecraft and can
also be used for radio astronomy.

Now I agree that DSN should be upgraded, but how? Are lasers
effective over interplanetary distances yet? Or something in the IR
range would be better? I dunno...

Niether. Upgrading the DSN is a matter of adding dishes and a general
overhaul and upgrade of the infrastructure, not changing technologies.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

"John Stoffel" wrote in message
...
"Derek" == Derek Lyons writes:

Derek John Stoffel wrote:
snip

Certainly, that would be a better solution, but that's a seperate pile
of money generally. While a new beacon could just be an add-on to an
existing orbiter or other mars bound vehicle.

Now I agree that DSN should be upgraded, but how? Are lasers
effective over interplanetary distances yet? Or something in the IR
range would be better? I dunno...


I think we just need MORE of the current RF technology DSN. Accurate range
and range rate info I think is good enough for navigation. Data flow is
also needed. I think all we need is to put up some more DSN antenaes.

Danny Dot
www.mobbinggonemad.org

John

In article ,
John Stoffel wrote:
Now I agree that DSN should be upgraded, but how? Are lasers
effective over interplanetary distances yet? Or something in the IR
range would be better? I dunno...

DSN has been thinking about optical communications (most likely in the
near IR rather than the visible) for a long time, and has done some
deep-space experiments (e.g., firing Messenger's lidar at Earth), but it
would be a big change.

The two really big snags are that the spacecraft transmitter would have to
be pointed very precisely indeed -- you pay a price for that much-narrower
beam! -- and you would need several more DSN sites because any single site
may be clouded over at a critical time.

The #1 way to upgrade DSN is just to build more antenna dishes to roughly
the existing designs. It's the *dishes*, not the radio frequencies, which
are being saturated with traffic.

It would also be very helpful to have a second southern-hemisphere DSN
site, perhaps in South America. Having only one can become a severe
bottleneck when busy parts of the solar system are in the southern sky.
--
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Henry Spencer wrote:


It would also be very helpful to have a second southern-hemisphere DSN
site, perhaps in South America. Having only one can become a severe
bottleneck when busy parts of the solar system are in the southern sky.



Due to the plane of the ecliptic, all the planets well stay at pretty
much the same inclination in the sky all of the time and be visible to
telemetry dishes in the northern hemisphere at least sometime each day
until you get into the Arctic Circle in winter.

Pat

"Henry" == Henry Spencer writes:

Henry In article ,
Henry John Stoffel wrote:
Now I agree that DSN should be upgraded, but how? Are lasers
effective over interplanetary distances yet? Or something in the IR
range would be better? I dunno...

Henry DSN has been thinking about optical communications (most likely
Henry in the near IR rather than the visible) for a long time, and
Henry has done some deep-space experiments (e.g., firing Messenger's
Henry lidar at Earth), but it would be a big change.

I can see it being a complete change in philosophy, but wouldn't the
bandwidth gains be worth it?

Henry The two really big snags are that the spacecraft transmitter
Henry would have to be pointed very precisely indeed -- you pay a
Henry price for that much-narrower beam! -- and you would need
Henry several more DSN sites because any single site may be clouded
Henry over at a critical time.

Hmm, how about using near UV instead of IR for the frequency? Would
that help since it could punch through cloud cover better? Or would
you want a microwave wavelength? I'm ignorant of the issues here in a
large part, but I can see how the details really count. Oh wait,
microwaves probably wouldn't be too good either in rainy weather. I
remember how the BBN high speed microwave links in Boston in the late
80s and early 90s would get trashed by rain, and killing bitnet and
early internet connectivity/performance.

So the real benefit of going with an IR comm link is not the frequency
change, but the narrowing of the beam so you nead less energy on the
Mars transmitter for a given data rate, but you now need to point
within a degree or two of your receiver? What kind of pointing
requirements do the radio transmitters have? 5-10 degrees?

And does the data rate go up when you can point more accurately?

Henry The #1 way to upgrade DSN is just to build more antenna dishes
Henry to roughly the existing designs. It's the *dishes*, not the
Henry radio frequencies, which are being saturated with traffic.

Hmm... can they do the same thing with the dishes as they do with
radar and make them electronically steered instead, so you don't have
to build the big huge 70m dishes for DSN work? Or is the real problem
the lack of transmitter power from the craft in mars and they need the
big dishes to amplify as much of the signal as possible for clean
communitcations?

Henry It would also be very helpful to have a second
Henry southern-hemisphere DSN site, perhaps in South America. Having
Henry only one can become a severe bottleneck when busy parts of the
Henry solar system are in the southern sky.

I would think that just having something on or near the equator would
be a good thing. How around working with ESA and putting in a large
set of dishes at the Arianespace launch complex? I can't imagine that
they don't have the land and the needs of their own to communicate
with spacecraft.

Thanks,
John

In article ,
Derek Lyons wrote:
...you need to invest substantial resources to build a GPS equivalent at,
say, Mars.

Do you really need a GPS analog? It seems a couple of beacons that
could act as a pseudo-Transit would be Really Handy - and much cheaper
and easier than a GPS type system.

I'm not sure how well that would work for certain important cases like
navigating incoming spacecraft; I'd have to think about it for a while.
The Transit scheme is at its best when the navsat is passing fairly near
the observer at fairly high relative velocity, e.g. a LEO pass over a
ground observer on Earth.

Might help enough to be worth doing even if it didn't provide a complete
navigation solution, mind you.
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