Why would a remote sensing satellite use tape storage?

[mercanucaribe]

http://www.digitalglobe.com/about/quickbird.html

Does anyone have any idea why a satellite launched in 2001 would use tape instead of solid state? 128 gigabits at that, which is only 16 gigabytes. Landsat 7 was launched around the same time with 375 gigabits of solid state. It can't be cost, because it costs so much to launch a satellite anyway.

In any case, it's a nice satellite.. with the best commercially available resolution. 60 centimeter pixels.

 

[mercanucaribe]

Pics: http://www.satimagingcorp.com/gallery/quickbird-brussels-lg.html
http://www.satimagingcorp.com/gallery/quickbird-overview.html

http://www.satimagingcorp.com/gallery.html

 

[Armitage]

Where do you see tape on there? I just see 128gbit

 

[mercanucaribe]

Oops.. It was this site that said tape. http://www.eurimage.com/products/quickbird.html

 

[spidey07]

possibly because tape could be recovered via a crash and solid state could not?

 

[PottedMeat]

I would guess one of the contractors had one laying around, they knew how reliable it would be so maybe its cheaper to just cram that in than space qualifying/designing a new storage system.

The fat pipe from the satellite to ground would probably matter the most though, so i guess it just needs minimal storage for guidance/whatever.

'320 Mbps X-band' - that seems like alot

 

[mercanucaribe]

Originally posted by: PottedMeat
I would guess one of the contractors had one laying around, they knew how reliable it would be so maybe its cheaper to just cram that in than space qualifying/designing a new storage system.

The fat pipe from the satellite to ground would probably matter the most though, so i guess it just needs minimal storage for guidance/whatever.

'320 Mbps X-band' - that seems like alot

The storage is for when it's out of view of a base station. It's in constant use.

 

[Armitage]

Originally posted by: mercanucaribe
Oops.. It was this site that said tape. http://www.eurimage.com/products/quickbird.html

ic...
Not sure - I'm not into the satellite hardware area myself. Could be all kinds of considerations - weight, power, reliability, rad hardness, etc. It would seem that solid state should win on at least the first 3 of those at least, but I really don't know.

Regarding the storage size vs. LandSat - I'd guess that might be driven more by their ground infrastructure. If they can download regularly - ie. lots of groundsites, then they don't have to have as much onboard storage. Maybe LandSat doesn't have as large a ground infrastructure or the chosen orbit doesn't overfly them as often. Could be the instruments also.

 

[Armitage]

Originally posted by: spidey07
possibly because tape could be recovered via a crash and solid state could not?

You won't be recovering anything usable from this when it decays & burns up. This is to store the collected imagery when the satellite is out of view of a base station (ie. almost all of the time). Then when it overflies the base station it dumps it down.

 

[spidey07]

Armitage,

wouldn't they want some record of what failed and why? Kind of like how they use tape in the "black box" of airlines. Surely you could design something to withstand entry into the atmosphere.

then again, maybe you couldn't.

But I see the purpose in this storage.

 

[mercanucaribe]

Originally posted by: spidey07
Armitage,

wouldn't they want some record of what failed and why? Kind of like how they use tape in the "black box" of airlines. Surely you could design something to withstand entry into the atmosphere.

then again, maybe you couldn't.

But I see the purpose in this storage.

How is tape better able to handle a hypothetical crash than flash memory?


I found a cool site showing how they come up with the high res color images. http://www.geosage.com/highview/imagefusion.html

 

[spidey07]

I was just thinking if the ICs were cracked or damaged the data couldn't be recovered vs a physical magnetic medium that if ripped apart could probably be restored.


don't know. Never designed a satellite.

 

[Armitage]

Originally posted by: spidey07
Armitage,

wouldn't they want some record of what failed and why? Kind of like how they use tape in the "black box" of airlines. Surely you could design something to withstand entry into the atmosphere.

Satellite decay isn't an accident. You know when it's going to happen and nothing failed to make it happen. It's just the end of the mission lifetime - you've expended all of your fuel, and drag wins.

This storage is just to collect the imagery. Health and status information is typically stored and relayed via a different onboard system.

And yes, you can design something to withstand reentry - it's difficult, expensive and heavy. No particular need for it here.

then again, maybe you couldn't.

But I see the purpose in this storage.

 

[Armitage]

Originally posted by: spidey07
I was just thinking if the ICs were cracked or damaged the data couldn't be recovered vs a physical magnetic medium that if ripped apart could probably be restored.


don't know. Never designed a satellite.

Actually, after the Columbia accident, some data was recovered from solid state memory found in the debris. And I believe also from a tape reel. Go figure. But then, Columbia wasn't a typical reentry.

 

[mercanucaribe]

My friend says that tape is more reliable than solid state, especially with radiation.

 

[Injury]

Perhaps for archiving purposes.

 

[Savij]

IC's don't like radiation at all and need a bunch of shielding (weight). Maybe the tape system does not have that limitaion.