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Deep Space Hardware (MARS)

Posted by: rpspeck - Tue Mar 22, 2005 4:57 am
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Deep Space Hardware (MARS) 
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Post Comment = Response on 1 mW Signal Strength   Posted on: Fri Apr 24, 2009 9:51 pm
4/18/09 Comment

Interesting reading, as always. However, I'm wondering how you arrive at that 1 mW RF would be sufficient...

At 500 MHz and 100 km, the free space loss would be 126 dB so, since 1 mW is 0 dBm, your signal strength will be less than -126 dBm. The best sensitivity I've seen in professional communication receivers for VHF/UHF is around -130 dBm for very narrow bandwidth that might be too narrow for this use. Galactic noise and polarization losses (Faraday effect) will also have significant influence on VHF/UHF when you are so close to the limit.

RPS
I have personally observed 10 nanovolt 50 Ohm RF signals with a 0.5 dB noise figure preamp in "single sideband" CW mode (0.01 microvolt). This is not unreasonable with <1 nanovolt/sqrt(Hz) noise level for the front end (300K source temperature), but implies about 100 Hz bandwidth for my ear at the optimum tone frequency. The 50 Ohm 0.01 Microvolt RF would be -147 dBm.

Few people are talking about 100 Hz bandwidth, but I have achieved signaling with much lower bandwidth using synchronous detection - which is inherent in the phase locked modes. Data rates would be limited, but 100 Baud actually requires less bandwidth than this. SMAD (Wiley J. Larson) lists 300K, 100 baud, 0.01 uV RF with an OK (10^-3) Bit Error Rate, even without error correction.
(Eb/No = 6.8 dB)

I did not suggest that this would be accomplished with a dipole receiving antenna. I was just looking at a 14.4 dBd, 70 cm Ham antenna. Four of these would provide a very nice tracking array. Using dynamic mixing to combine these signals, a net gain of >20dBd would be available. If each was modified to Cross Element configuration, and the resulting 8 RF signals properly amplified and processed, dynamic mixing of the cross components would accommodate Faraday and mechanical rotation with little loss. These antennas might also approach 30K “Galactic Noiseâ€


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Post Control and Telemetry in a Phase Locked System (2)   Posted on: Fri Apr 24, 2009 9:56 pm
Many communications systems now use narrow band FM = Frequency Modulation to add information to an RF signal. (This is somewhat different from “widebandâ€


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Post Control and Telemetry in a Phase Locked System 3   Posted on: Mon Apr 27, 2009 7:32 pm
The best modulation method, for these systems, produces the greatest energy efficiency and maintains Phase Lock with a single “quirkâ€


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Post    Posted on: Mon Apr 27, 2009 10:26 pm
You should talk to my ECE professor, Bruce Land, who teaches the microcontrollers (and FPGA) design class here at Cornell. He's also the main AXP electronics prof here, and knows a lot about making really advanced electronics systems on the cheap. Seeing as your stuff is pretty cutting edge as far as that kind of stuff goes I'm sure you could find some interesting collaboration with some of his students in the future, good project suggestions are really valuable to a lot of people and the scope of these projects can be pretty broad. Mine didn't end up working out as well as I'd hoped but still managed to get a pretty decent telemetry system out of it.

PS will you be hiring next year?

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Post    Posted on: Wed Apr 29, 2009 6:04 pm
TerraMrs wrote:

PS will you be hiring next year?


God knows!

Results from my efforts to find support, or paying customers, has been pathetic!


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Post LEO to Lunar Transfer   Posted on: Wed Apr 29, 2009 6:06 pm
Before detailing how the Precision Doppler system described last week can be used to guide the critical Lunar Transfer operation, I want to discuss other systems enabled by the Phase Locked RF mode.

If the ground station, in the Phase Locked link, offsets its uplink, Reference signal by the same amount (but opposite direction) that the returned, Doppler shifted downlink signal is offset, then the spacecraft transmitter's frequency (halfway between the two signal frequencies seen at the ground station) can be precisely maintained. It can be as accurate as the ground station's best frequency reference. The low cost, low power and fraction of a gram transmitter in a small spacecraft can thus achieve “Part Per Billion (= ppb)â€


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Post Absolute Distance Recapture   Posted on: Fri May 01, 2009 4:17 pm
The integrated Doppler offset, in the phased locked link systems, is of course the number of RF cycles that can fit into the round trip time delay. The physical distance measurement is no more precise (as an absolute measurement) than the frequency control used to create the Radio Frequency. As noted earlier, with care, this can easily approach one part per million, and with a “GPS Disciplined, Ovenized crystal oscillatorâ€


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Post Some COTS D $$: New Human Spaceflight is looking up!   Posted on: Wed May 13, 2009 5:18 pm
So $80 Million (COTS D estimated new funding) buys < 1.6 seats with the current Russian "Opportunity Pricing" ($51M each) for the Soyuz.

Perhaps NASA will want to buy more than 2 seats, for flight to the ISS, in 5 ++++ years?

I hope this proves to resemble being “a little bit pregnantâ€


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Post CHANGES   Posted on: Wed May 20, 2009 9:17 pm
I have been forced to downsize facilities I had made available for “Deep Spaceâ€


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Post    Posted on: Sat May 23, 2009 6:06 pm
does anyone other than me read this thread?

i'm surprised you haven't found someone to buy your navigational cores (i presume you're patenting the novel techniques you're describing here), that seems really useful and highly un-obvious. space hardware or not pretty much everything you've been talking about sounds like pretty cutting edge rf technology and there's a big market for that. i wouldn't be surprised if there's something you've designed that would be useful on commercial comm sats if only by replacing more expensive components with simpler ones. i'll ask a couple veterans at loral when i get into work what they think...

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Post    Posted on: Sat May 23, 2009 6:09 pm
I do :)

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Post    Posted on: Mon May 25, 2009 12:10 am
Rob Goldsmith wrote:
I do :)


fair enough. i should have guessed.

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Post    Posted on: Mon May 25, 2009 8:26 am
There are always more people who read than reply, there's actually a large audience reading without having a forum user account.

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Post    Posted on: Sun Jun 14, 2009 5:36 am
I read this thread, with text books out and all.

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Post    Posted on: Mon Jun 15, 2009 4:29 pm
haha yeah i always want to cross-reference with wikipedia but generally assume that my initial guess is more or less correct, or it'd be over my head anyways. probably no longer safe to assume that but it takes too long to get through 1 post otherwise.

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