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GAO: The DSN is actually falling apart
Guest_BruceMoomaw_*
post May 24 2006, 11:55 PM
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http://www.gao.gov/docsearch/abstract.php?rptno=GAO-06-445
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Guest_Analyst_*
post May 26 2006, 09:14 AM
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No Reply yet, although without the DSN no planetary exploration (unmanned or manned) can happen. The DSN is part of the invisible infrastructure we simply need before we start thinking about actual missions (like (E)ELVs, launch sites etc). It's very sad this essential networt is not in an optimal shape. A lot of missions with high data rates will stress the DSN and there is still only talk (and no money) about arraying a lot of small antennas (9m to 12m each) or optical communication. The DSN is the bottleneck. Part of the problem is no single mission pays for it, it's fixed costs nobody wants to pay but everybody uses the services. The situation also reminds me of the Apollo age infrastructure at KSC (VAB, pads etc.): 40 years and still useable, but how long?

Analyst
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Guest_Richard Trigaux_*
post May 26 2006, 10:44 AM
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Things will not spontaneously become better.

DSN is based on a set of large antenna all around the world, so that a given source (for instance the MERs on Mars) can be received 24/24 hours.

In more of the quoted problem, a critical failure can occur, like the loss of one of the antenna (crashing down, like it aleady happened to a large dish, or a political setback in a country). I am afraid that for some timezones there is no redundancy, and the loss of only one antenna would create a blind zone, unability to receive certain sources at certain hours.

Anyway the only way to increase both safety and capacity of such a network is to increase the number of antennas all around the world. (whatever it is with few large antennas or many small ones)


With my opinion, such a unvaluable resource should become international and be managed by the UN. But the US government is known not to agree with such options, see with the ICANN. So international funding should come into the network, into the form of new antennas in new places, the whole thing managed like an economical association, and technically by a centralized unifom authority.
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Jim from NSF.com
post May 26 2006, 11:44 AM
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QUOTE (Richard Trigaux @ May 26 2006, 06:44 AM) *
Things will not spontaneously become better.

DSN is based on a set of large antenna all around the world, so that a given source (for instance the MERs on Mars) can be received 24/24 hours.

In more of the quoted problem, a critical failure can occur, like the loss of one of the antenna (crashing down, like it aleady happened to a large dish, or a political setback in a country). I am afraid that for some timezones there is no redundancy, and the loss of only one antenna would create a blind zone, unability to receive certain sources at certain hours.

Anyway the only way to increase both safety and capacity of such a network is to increase the number of antennas all around the world. (whatever it is with few large antennas or many small ones)
With my opinion, such a unvaluable resource should become international and be managed by the UN. But the US government is known not to agree with such options, see with the ICANN. So international funding should come into the network, into the form of new antennas in new places, the whole thing managed like an economical association, and technically by a centralized unifom authority.




Why does it have to be a terrestrial system, an orbital system could work without the international implications.
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Guest_Analyst_*
post May 26 2006, 12:21 PM
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(Upfront and/or operating) costs? Size (70m) and pointing problems? As for international problems: Australia and Spain are quite stable, aren't they?

Analyst
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Guest_Richard Trigaux_*
post May 26 2006, 02:28 PM
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QUOTE (Jim from NSF.com @ May 26 2006, 11:44 AM) *
Why does it have to be a terrestrial system, an orbital system could work without the international implications.


Untill now, any spaceship ot satellite belongs to a country (except a bit for the ISS). So the legal problems are still the same, unless the things belong to a really international institution, like the UN.


Antennas in space have multiple advantages, they cannot be closed by a political setback, they can be pointed to a given source more time a day, etc. But make a 70m antenna in space is not among what is immediatelly feasible. And to maintain them seriously would require a space shuttle.
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Guest_Richard Trigaux_*
post May 26 2006, 02:45 PM
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QUOTE (Analyst @ May 26 2006, 12:21 PM) *
As for international problems: Australia and Spain are quite stable, aren't they?

Analyst


Yes they are, but if an international problem occurs, as far as we know it will be unpredictable, unforeseen. So, when thinking of redundancy and reliability, we cannot say a priori that some countries are stable and others not. It is only a matter of probability. There is little political interest to duplicate an antenna in Spain, but anyway if the network is saturated, this antenna will have to be duplicated and it will be safer to do this in another country.

Think that Europe is in the process of duplicating the GPS system (with Galileo) at high cost, for the only reason that it is controlled by the USA, however a long friend, ally and helper country. This is not a criticism of the USA, but a wise caution.
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djellison
post May 26 2006, 03:28 PM
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QUOTE (Jim from NSF.com @ May 26 2006, 12:44 PM) *
an orbital system could work without the international implications.


Would cost an extraordinary ammount of money, would still require a groundstation, and would be impossible to improve over time.

Doug
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RNeuhaus
post May 26 2006, 04:03 PM
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What would be the solution? More 70 meters antennas or the same ones but bigger antennas, 140 meters? or employing a new antenna technology (no circular pads but somewhat a grid of lines). I am taking without thinking the money restrictions but only the next most recommeded antenna type for the new coming explorations which means more traffics, more wide-band requirements.

Rodolfo
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Guest_Richard Trigaux_*
post May 26 2006, 05:46 PM
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A suggest RNeuhaus, there exist new antenna technologies which could do the same job than a large dish at a lesser cost. But it is physically impossible to reduce the size of the antennas, as this size is necessary to:
-gather signal power
-obtain a directionnal effect. (Both characteristics go together).


-dipole arrays. As indicated, they are simple receivers (dipoles or other microwave devices) mounted in an array. Each dipole has a phase shifter commanded by a computer in such a way that when we combine all their outputs, we receive the signal from only a specified direction. Such arrays are used for military radars in aircraft noses, saving the wheight of the orientation mechanism. At a pinch, the dipoles can be set on a non-planar surface, provided that the computer knows their position. The cost of such an antenna will rise as the square of their diametre, as each dipole has its own electronics. I don't know if they are cheaper than conventionnal dishes, probably not as there are no attemps to build any. Anyway it is simple to built phase shifters for a fraction of the wavelength, but a large dish would require electronic phase shifters for many times the wavelength, so I don't know if this is possible.


Flat striplines antennas use printed-circuits to build dipoles (or slots) and achieve their coupling. They still need to be oriented and rigidified like a dish, so like this we don't gain much. But, combined with the previous technology, we could use only one phase shifter per rank of dipoles. Such phase shifters, much less numerous, could be mechanical, and thus cheaper and with as much shift as desired. Such an antenna could simply lie flat on the ground (or better on water), needing only to be oriented into azimuth, the phase shifters doing the job of tuning the site. This is, as far as I know, the only way to save the building of a large mechanical structure, which makes all the cost of a large dish.



New materials with designed electromagnetic properties. This is very new in antenna technologies: materials which are regular arrays of filled conductors and gaps. Their geometries can be designed for, as an example, set a given propagation speed th electromagnetic waves travelling into them. So we could design lenses made of such materials. For a space application, the lens could be made of wires, rolled into a deflated baloon. Once into space, the baloon is inflated, putting all the wires in place. Then all the thing is rigidified, for instance with some polymer which hardens with UV. The ballon soon loses its gas, but no matter. The receiver is a but further, at the focal point of the lens. The advantage of this is that it don't require a large sized construction into space, a thing we don't know to do.


All those previous methods have the obvious drawback that they have a limited bandwidth. Only a true parabole could have a large bandwidth.

inflated parabolic dish . This idea is not new, and it is appealing: just with inflating a baloon in space makes a dish. But obstacles are many:
-inaccurate building
-the baloon soon loses its gas.
To overcome this I would suggest some use of electrostatic forces, repelling the two sides of the baloon, and keeping it "inflated" without gas. On the reflecting side, there would be many electrodes, each commanded independently, like into the adaptative optic mirrors. So they could maintain a correct shape, accurate enough, and focalise waves on the other side of the baloon where the receivers would stand. Into space this would work neatly.
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djellison
post May 26 2006, 06:22 PM
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Were there any problems w.r.t. politicis, one could simply use a large ex-oil-facility such as they use for Sea Launch - pointing might be a bit of a problem in heavy seas - but it would be a hell of a lot cheaper and easier than an orbital facility.

But of course we're missing the point. We don't need any of this and the huge budget it would require..what we need is a more moderate investment in the current DSN.


Doug
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elakdawalla
post May 26 2006, 06:46 PM
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There was a lengthy presentation by Bob Preston from the DSN at OPAG on what the DSN wants and needs to do to improve over the coming decades, and it basically involves replacing all the gigantic, one-of-a-kind antennas with arrays of 6-, 12-, or 18-meter dishes (they are still experimenting to figure out which one will be the optimal size). Unlike the big dishes, each of which needs its own operator, whole arrays can be operated by a single person; also they can plan to have some percentage of all the dishes down at any given time for routine maintenance. Also they can just devote as many dishes as they need to a single spacecraft, splitting the array to support several spacecraft at once or using the whole array for high bandwidth. They've got to be replaced because the big dishes cannot be upgraded to support Ka-band communications.

--Emily


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My blog - @elakdawalla on Twitter - Please support unmannedspaceflight.com by donating here.
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Jim from NSF.com
post May 26 2006, 07:01 PM
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QUOTE (djellison @ May 26 2006, 11:28 AM) *
Would cost an extraordinary ammount of money, would still require a groundstation, and would be impossible to improve over time.

Doug


It would be the same as the TDRSS, but with larger antennas and facing outward. Only one US ground station would be required (spacecraft can crosslink). No atmospheric distortion. maintenance is easy, back up satellites. Upgrades would be easier, would be done like the GOES program, cut in upgrades in each series. O&M costs (after the initial investment) are lower since there is less manpower involved.

Antennas could be larger than any ground based.

Initial costs would be large, but lower in the long run.
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Guest_Richard Trigaux_*
post May 26 2006, 07:12 PM
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QUOTE (elakdawalla @ May 26 2006, 06:46 PM) *
They've got to be replaced because the big dishes cannot be upgraded to support Ka-band communications.

--Emily


Yes if the price of a large dish is proportional to more than the square of the diametre, it is better to use a collection of smaller dishes, which cost is only proportional to the square of the (simulated) diametre.


Upgrading the larger dishes to higher frequencies would require to resurface them with a greater accuracy, a thing impossible as the dish somewhat flexes with its movement or with wind, it would need to be rigidified, that means completely rebuilt. So the price of a large dish sharply increases with frequency, while not with small dishes.

Maybe the solution would come from many small dishes spread by clusters or isolated all over the world, in more or less politically stable places, by any state which would want to contribute, or even by private owners. To cut the cost, we would use mass production for the dishes, and ship them by sea.
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RNeuhaus
post May 26 2006, 07:29 PM
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QUOTE (elakdawalla @ May 26 2006, 01:46 PM) *

Very informative is the Planetary Society's blog about DSN. This has satisfied me almost all my inquiries. smile.gif

Rodolfo


QUOTE (Richard Trigaux @ May 26 2006, 12:46 PM) *
A suggest RNeuhaus, there exist new antenna technologies which could do the same job than a large dish at a lesser cost. But it is physically impossible to reduce the size of the antennas, as this size is necessary to:
-gather signal power
-obtain a directionnal effect. (Both characteristics go together).
...

Thanks much for the detailed antenna technologies. I think that the array of antenna along with optical antennas are the best candidates to attend the future increased bandwidth and transmission traffic.

Rodolfo
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