Venus Express Options

[tedstryk]

If all goes well, Venus Express will be a major topic for discussion in this forum a year from now. Does anyone know how good the surface coverage will be from VIRTIS and VMC? My understanding is that VIRTIS will obtain low resolution multispectral maps, and that VMC will, in addition to cloud monitoring, have one channel that can see the surface, but I don't know at what resolution or at what quality. It will be nice to have some non-radar images of Venus' surface besides the Venera snapshots and the shadowy images from Earth and Galileo's NIMS.

Ted

[brellis]

hi cndwrld

thanks for providing a window into the dataflow workings

"There was some discussion about getting data down from spacecraft, and frustration with the amount of time it takes. I think I finally figured out how to post images, so I'll put up a couple examples from VEX to show how this stuff gets downloaded.

When we do our planning, our ESA proprietary simulation tool will create a prediction of how much data the instruments accumulate each orbit, as well as how much we are able to downlink during each comm pass with the Cebreros Station in Spain."

Is the storage capacity on V.E. heavily-burdened?

As to transmission back to earth, I wonder if there could be a software on the spacecraft similar to the program that updates a web page, looking for numbers that change. For example, once a normal temperature range in a given area over a given time period has been established, the craft prioritizes data that appears outside the norm for sending back to earth.

Similarly, I've wondered how "smart" the Mars orbiters can get as they "pushbroom" their way around the planet. Perhaps they can automatically notice small changes like new gullies.

[cndwrld]

>>Is the storage capacity on V.E. heavily-burdened?
Well, yes and no. The instruments (particularly the imaging spectrometer VIRTIS and the VMC camera) could take much more data than they do. We are usually limited by our data rate, and our ground contact periods, not the SSMM volume.

>>I wonder if there could be a software on the spacecraft similar to the program that updates a web page, looking for numbers that change.

I'd see two problems with this. First, it only would work with housekeeping telemetry, not with science data. And the housekeeping is much less in volume than the science data. We dump a fixed 216 Mbits per orbit for housekeeping data; we dump about 4200 Mbits per orbit of science data. It might be a useful idea in some circumstances, though. Say, on spacecraft on long duration missions in cruise phase, where all you have housekeeping telemetry and no science, or commercial spacecraft.

Two, you'd only get data when it changed. But in that case, if you are looking at telemetry to find a problem, you would have to trust the numbers you don't have. You'd have to believe that if no data came down, that everything was working and the number you got last week is still the number you have now. I would have real trouble doing that. In my experience, data that doesn't exist has an unknown value, and the item generating the data doesn't work unless it proves it works by putting out data. Things 'fail silent' all the time.
Again, though, in certain circumstances, it might be useful.

[dvandorn]

>>Is the storage capacity on V.E. heavily-burdened?
Well, yes and no. The instruments (particularly the imaging spectrometer VIRTIS and the VMC camera) could take much more data than they do. We are usually limited by our data rate, and our ground contact periods, not the SSMM volume.

So, here's a question -- is the download rate limited more by intrinsic limits on data transfer rates (i.e., the spacecraft's transmitter power and the size of its dish), or by the relatively short periods of time you have the Cerberus facility available to receive downlink? (I know you have some attitude issues which result from VEX being designed to orbit Mars and not Venus, but I'm looking for average data transfer rates, here, not those that are constrained by other parameters.)

What I'm getting at, here, is whether or not a vastly expanded Deep Space Network would aid appreciably in getting more data off of the vehicle, thereby letting you take as much data as the instruments can actually collect.

I hate to see a valuable resource being under-utilized because of bottlenecks in our ability to get data back from it. And I'm wondering if it just isn't time for an expanded DSN to be started. If it could be funded by an international consortium that gets its seed money from something other than charging rapacious hourly rates, that would be even better... but I keep hearing more and more issues with the ability to get data back from our spacecraft that are out there exploring the unknown, and it just seems bass-ackwards to spend billions of dollars on a well-designed probe and then hamstring its science return because we have an antiquated DSN that can't keep up with demand and yet still charges thousands of dollars (or Euros, or what-have-you) an hour for the privilege of using it.

Maybe we ought to have everyone convert their unused Dish Network dishes into a vast distributed amateur Deep Space Network and offer its services to all comers, first-come-first-serve...?

-the other Doug