6 ms·

Does anyone know what type of data compression is being used to transmit these images? There's been huge progress since the last rover.

NL807 6y ago
I'm speculating here, but I think these images are transmitted in some kind of raw format, or close to it, making them more resilient to data corruption. Compressed images will incur greater data loss when compressed, compared to raw images where you might lose a few image blocks at a time.
- Robotbeat 6y ago
  They compress them but transmit with forward error correction. They do have the ability to retransmit if the images are too damaged. Totally uncompressed images are not a very efficient way to transmit images if you want to ensure they're scientifically accurate.
- kadoban 6y ago
  Naively, I'd doubt that. There are all kinds of error correcting codes to deal with that and you'd end up with a substantial increase in effective bandwidth (with the compression). There may be error correction built in to the protocol itself already.
- sandworm101 6y ago
  Compression can also include backup/padding/parity data to correct for errors and transmission losses.
Robotbeat 6y ago
They use the same kind of compression as the last mission. JP2, I believe. https://en.wikipedia.org/wiki/JPEG_2000 https://en.wikipedia.org/wiki/JPEG_2000 I'm not sure that data compression has progressed that much since Curiosity in 2012 or Insight in 2018. There have been some formats that have improved compression at the expense of large amounts of memory or processing power, but neither of those are abundant on a rad-hardened processor. Neither is electricity. Neither are the toolchains to process such images very widespread or as well understood.
- hanniabu 6y ago
  Any idea how much storage it has? I would think it'd have to be TBs to store all these images, logs, and other data for years while making sure they have enough memory so that they're not limited and if the rover stays there for longer than intended.
  - Hnrobert42 6y ago
    Why would it need to continue to store things after successful receipt on Earth?
    - leephillips 6y ago
      Very off-site backup.
  - azernik 6y ago
    Once it's been sent to Earth, they drop it. Curiosity's main computer had a flash drive of 2GB, and each of the big cameras had an 8GB flash drive on board. I doubt Perseverance is much changed from that; the main computer is IIRC a spare part from the Curiosity production. Rad-hardened computer hardware is expensive and bulky. You don't add storage or processing power that you don't absolutely need. See https://www.ontrack.com/en-us/blog/how-to-store-data-on-mars https://www.ontrack.com/en-us/blog/how-to-store-data-on-mars and https://mars.nasa.gov/mars2020/spacecraft/rover/brains/ https://mars.nasa.gov/mars2020/spacecraft/rover/brains/
- walrus01 6y ago
  One of the obvious constraints is that for science reasons they transmit each image in a lossless format, so we're up against the limits of what a lossless image compressor can do. If there were a future mission's requirement to send back lossy images first, and CPU power was significant, something like AVIF or JPEG-XL would likely be a candidate. https://netflixtechblog.com/avif-for-next-generation-image-coding-b1d75675fe4?gi=87b2c9da8c1c https://netflixtechblog.com/avif-for-next-generation-image-c... ICER appears to be what they're using now for lossless: https://en.wikipedia.org/wiki/ICER https://en.wikipedia.org/wiki/ICER
Denvercoder9 6y ago
> There's been huge progress since the last rover. One thing that changed in the last 8 years is that there are now two new orbiters around Mars (MAVEN and ExoMars TGO), which can retrieve data from the rovers faster, cache it and send it to Earth faster.

NL807 6y ago

I'm speculating here, but I think these images are transmitted in some kind of raw format, or close to it, making them more resilient to data corruption. Compressed images will incur greater data loss when compressed, compared to raw images where you might lose a few image blocks at a time.

Robotbeat 6y ago
They compress them but transmit with forward error correction. They do have the ability to retransmit if the images are too damaged. Totally uncompressed images are not a very efficient way to transmit images if you want to ensure they're scientifically accurate.
kadoban 6y ago
Naively, I'd doubt that. There are all kinds of error correcting codes to deal with that and you'd end up with a substantial increase in effective bandwidth (with the compression). There may be error correction built in to the protocol itself already.
sandworm101 6y ago
Compression can also include backup/padding/parity data to correct for errors and transmission losses.

Robotbeat 6y ago

They use the same kind of compression as the last mission. JP2, I believe. https://en.wikipedia.org/wiki/JPEG_2000 https://en.wikipedia.org/wiki/JPEG_2000 I'm not sure that data compression has progressed that much since Curiosity in 2012 or Insight in 2018. There have been some formats that have improved compression at the expense of large amounts of memory or processing power, but neither of those are abundant on a rad-hardened processor. Neither is electricity. Neither are the toolchains to process such images very widespread or as well understood.

hanniabu 6y ago
Any idea how much storage it has? I would think it'd have to be TBs to store all these images, logs, and other data for years while making sure they have enough memory so that they're not limited and if the rover stays there for longer than intended.
- Hnrobert42 6y ago
  Why would it need to continue to store things after successful receipt on Earth?
  - leephillips 6y ago
    Very off-site backup.
- azernik 6y ago
  Once it's been sent to Earth, they drop it. Curiosity's main computer had a flash drive of 2GB, and each of the big cameras had an 8GB flash drive on board. I doubt Perseverance is much changed from that; the main computer is IIRC a spare part from the Curiosity production. Rad-hardened computer hardware is expensive and bulky. You don't add storage or processing power that you don't absolutely need. See https://www.ontrack.com/en-us/blog/how-to-store-data-on-mars https://www.ontrack.com/en-us/blog/how-to-store-data-on-mars and https://mars.nasa.gov/mars2020/spacecraft/rover/brains/ https://mars.nasa.gov/mars2020/spacecraft/rover/brains/
walrus01 6y ago
One of the obvious constraints is that for science reasons they transmit each image in a lossless format, so we're up against the limits of what a lossless image compressor can do. If there were a future mission's requirement to send back lossy images first, and CPU power was significant, something like AVIF or JPEG-XL would likely be a candidate. https://netflixtechblog.com/avif-for-next-generation-image-coding-b1d75675fe4?gi=87b2c9da8c1c https://netflixtechblog.com/avif-for-next-generation-image-c... ICER appears to be what they're using now for lossless: https://en.wikipedia.org/wiki/ICER https://en.wikipedia.org/wiki/ICER

Denvercoder9 6y ago

> There's been huge progress since the last rover. One thing that changed in the last 8 years is that there are now two new orbiters around Mars (MAVEN and ExoMars TGO), which can retrieve data from the rovers faster, cache it and send it to Earth faster.