Likely bit rate from low Earth orbit

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View
This is necessarily akin to asking the length of a piece of string.

Still, anyone have a handle on the likely bit rates that are achieved  
when downloading data from low Earth orbit imaging satellites?

We know, or at least think we know, that the USA, and other countries,  
have spy satellites capable of significantly higher resolutions than  
those offered by commercial providers, but I wonder what scope they have  
to providing high resolution imagery over large areas (e.g. southern  
Indian ocean). I suspect that it is constrained by downlink bandwidth.

Sylvia.

Re: Likely bit rate from low Earth orbit
On Mon, 17 Mar 2014 15:20:46 +1100, Sylvia Else wrote:

Quoted text here. Click to load it

DSS TV has to offer some clue about what's feasible.  "Lots", I suspect.

--  
Tim Wescott
Control system and signal processing consulting
We've slightly trimmed the long signature. Click to see the full one.
Re: Likely bit rate from low Earth orbit
Quoted text here. Click to load it

With a 25m dish on the ground I'd not be surprised if they get comparable
bandwidth to communications satellites like the one sky uses.

But, to invoke another cliche, I suspect anyone that could tell you he  
real figure would subsequently have to kill you.

--  
Neither the pheasant plucker, nor the pheasant plucker's son.



Re: Likely bit rate from low Earth orbit
On a sunny day (Mon, 17 Mar 2014 15:20:46 +1100) it happened Sylvia Else

Quoted text here. Click to load it

Digital tv broadcasting, 12 transponders at 32 megabits / second each per sat,
of which there are hundreds geostationary working in the 10 GHz range

But recently things have gone optical, they use lasers from one sat to the other to ground.
Now we are talking terabits/second.

IIRC they are just trying it from a moon orbiting sat too.

Re: Likely bit rate from low Earth orbit
Quoted text here. Click to load it

<http://www.parabolicarc.com/2013/10/22/nasa-laser-system-sets-record-data-transmissions-moon/

622Mbps from Lunar orbit during tests.

--  
Bob Milutinovic
Cognicom


Re: Likely bit rate from low Earth orbit
On Mon, 17 Mar 2014 15:20:46 +1100, Sylvia Else

Quoted text here. Click to load it

Look at the specification for some of the recent TDRS satellite.
The TDRS satellites are geosynchronous and receive data from low orbit
satellites and sends the data back to fixed ground stations.


Re: Likely bit rate from low Earth orbit
On 17/03/2014 6:33 PM, snipped-for-privacy@downunder.com wrote:
Quoted text here. Click to load it

Not sure the geosynchronous satellites tell us that much.

The low Earth orbit satellites move across the sky (quite fast, indeed),  
so the higher the antenna gain (both on Earth and on the satellite), the  
more accurately it must be pointed at a moving target.

On the other hand, it's a lot closer, which helps with the signal strength.

Sylvia.

Re: Likely bit rate from low Earth orbit
On Mon, 17 Mar 2014 19:17:57 +1100, Sylvia Else

Quoted text here. Click to load it

At least the early TDRS satellites had multiple antennas and receivers
for a specific band. The individual antenna signals were then moved
with frequency translator to a big downlink.  

On the ground station, individual signals from the different antennas
were then extracted and frequency translated from the big downlink and
combined  with various delays to create an electrically steerable
antenna lobe. Such electronic beam forming does not have problems
tracking the LEO satellite, which is in the field of view for about 30
minutes.

Depending on the ground equipment capability, multiple satellites can
be simultaneously tracked, even if they fly in the opposite direction
i.e. N->S vs. S->N.


Re: Likely bit rate from low Earth orbit
On 17/03/2014 6:17 PM, Sylvia Else wrote:
Quoted text here. Click to load it

Once upon a time, NASA had tracking stations scattered around the world  
in the STADAN network tracking near earth satellites. In order to save  
money and give real time control of the birds, NASA launched the TDRSS  
network to relay the data direct to the US no matter where they are in  
orbit, and shut down the STADAN stations including Orroral Valley in the  
ACT.

http://en.wikipedia.org/wiki/Tracking_and_Data_Relay_Satellite_System

Re: Likely bit rate from low Earth orbit
On Mon, 17 Mar 2014 15:20:46 +1100, Sylvia Else wrote:

Quoted text here. Click to load it

Exactly, so coverage Vs detail is what you have to decide.


Re: Likely bit rate from low Earth orbit


Sylvia Else wrote:
Quoted text here. Click to load it

This post reminds me of a young Australian entrepreneur I heard about on ABC  
radio recently who is implementing a "flock of dove" satellites (not much  
bigger than bread box) to map a continuous up to date image of the entire  
earth.



The satellites were prototyped with off the shelf smart phones, but the  
production models are more sophisticated able to be repositioned in orbit.


http://gigaom.com/2014/01/09/planet-labs-mini-satellites-take-flight-toward-the-international-space-station/?

http://www.planet.com/




Re: Likely bit rate from low Earth orbit


Vote 99% Greens wrote:
Quoted text here. Click to load it

Satellites being released into orbit from International space station

https://twitter.com/dfjsteve/status/433402061963939840



Re: Likely bit rate from low Earth orbit
On 17/03/2014 3:20 PM, Sylvia Else wrote:
Quoted text here. Click to load it

I found the specs for Digital Globe's satellites.

http://www.digitalglobe.com/resources/satellite-information

Their two most recent satellites have 800 Megabits/second.

Sylvia.

Site Timeline