3 ms·

Crazy. Just put 10 complete systems in some radiation shielding.

iancmceachern 6y ago
Too heavy
myrandomcomment 6y ago
Which is more weight. The single highest factor in all space design is cost per kg lifted. The only thing that is more costly - lifting it successfully and then having it break.
- wlesieutre 6y ago
  For a rover it's not just lifting it, you have to put it back down once it gets to Mars. That's a 3-stage process with the aeroshell, parachute, and powered descent. Heavier rover? You'll need more fuel for the skycrane's engines. And that fuel adds weight, so don't forget that you'll need more fuel to lift the extra fuel. Now your rover and skycrane are bigger and heavier. Do you need a bigger parachute? Does everything still fit in the aeroshell? Is the fuel capacity for orienting and stabilizing the aeroshell still sufficient with the increased mass?
- plutonorm 6y ago
  The board in my phone is less than 100g. That's 1kg for ten of them.
  - colejohnson66 6y ago
    You’re assuming these computers are the size of a mobile phone
scottLobster 6y ago
We're talking launching stuff into space, every kg of extra weight is critical, particularly for scientific missions that are trying to do as much as possible. Also no amount of radiation shielding is going to make you perfectly shielded from cosmic rays. It's actually a chronic problem with Voyagers 1/2. The teams that maintain them regularly experience weird, unplanned behavior because a cosmic ray bit-flipped some register or other, and then they have to manually figure out what erroneous command got executed and how to recover from it, and those are extremely simple systems compared to what's running on Perseverance. So yeah, you need radiation hardened parts in space or you're just begging for a dead probe.
- pklausler 6y ago
  There are three computer systems on each Voyager. They are dedicated to specific tasks (Flight Control System, Attitude and Articulation Control System, and Computer Command Subsystem), each with two instances for redundancy.
  - scottLobster 6y ago
    Right, but that redundancy to my understanding is in case of component/system failure. It's a backup, not a judge-actor or error-correcting architecture. Case in point: https://www.jpl.nasa.gov/news/engineers-diagnosing-voyager-2-data-system-update https://www.jpl.nasa.gov/news/engineers-diagnosing-voyager-2... "Engineers successfully reset a computer onboard Voyager 2 that caused an unexpected data pattern shift, and the spacecraft resumed sending properly formatted science data back to Earth on Sunday, May 23. Mission managers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., had been operating the spacecraft in engineering mode since May 6. They took this action as they traced the source of the pattern shift to the flip of a single bit in the flight data system computer that packages data to transmit back to Earth. In the next week, engineers will be checking the science data with Voyager team scientists to make sure instruments onboard the spacecraft are processing data correctly. "
retSava 6y ago
It's not just the weight, there's also the complexity of handling 10 (or whatever) systems. It's not always easy to know when a system fails. How can you be sure that the output is invalid? Detecting complete blackouts is fairly easy, after a while when a watchdog tickle is absent for too long, but bad output due to flipped memory? Consensus-style systems can be used, but they are also a complexity in itself, and the point here was to replace a hardened single point of failure with redundancy.
moftz 6y ago
There is also a time-domain problem with regards to total integrated dose. All the parts will degrade over time. Radiation hardened parts can have lives of 15 years or more in a GEO environment. A commercial part might be lucky to make it 1 year. Radiation shielding is not as easy as you may think. Heavy ions in space can pass through anything and will impart a charge in whatever they hit as well as creating secondary sources of radiation. Neutrons are not as common in space but can be found near reactors, they are also very penetrating.
Rebelgecko 6y ago
Not all radiation problems can be solved by rebooting/voting/watchdogging. Over time the hardware itself will die.

Too heavy

Which is more weight. The single highest factor in all space design is cost per kg lifted. The only thing that is more costly - lifting it successfully and then having it break.

wlesieutre 6y ago
For a rover it's not just lifting it, you have to put it back down once it gets to Mars. That's a 3-stage process with the aeroshell, parachute, and powered descent. Heavier rover? You'll need more fuel for the skycrane's engines. And that fuel adds weight, so don't forget that you'll need more fuel to lift the extra fuel. Now your rover and skycrane are bigger and heavier. Do you need a bigger parachute? Does everything still fit in the aeroshell? Is the fuel capacity for orienting and stabilizing the aeroshell still sufficient with the increased mass?
plutonorm 6y ago
The board in my phone is less than 100g. That's 1kg for ten of them.
- colejohnson66 6y ago
  You’re assuming these computers are the size of a mobile phone

scottLobster 6y ago

We're talking launching stuff into space, every kg of extra weight is critical, particularly for scientific missions that are trying to do as much as possible. Also no amount of radiation shielding is going to make you perfectly shielded from cosmic rays. It's actually a chronic problem with Voyagers 1/2. The teams that maintain them regularly experience weird, unplanned behavior because a cosmic ray bit-flipped some register or other, and then they have to manually figure out what erroneous command got executed and how to recover from it, and those are extremely simple systems compared to what's running on Perseverance. So yeah, you need radiation hardened parts in space or you're just begging for a dead probe.

pklausler 6y ago
There are three computer systems on each Voyager. They are dedicated to specific tasks (Flight Control System, Attitude and Articulation Control System, and Computer Command Subsystem), each with two instances for redundancy.
- scottLobster 6y ago
  Right, but that redundancy to my understanding is in case of component/system failure. It's a backup, not a judge-actor or error-correcting architecture. Case in point: https://www.jpl.nasa.gov/news/engineers-diagnosing-voyager-2-data-system-update https://www.jpl.nasa.gov/news/engineers-diagnosing-voyager-2... "Engineers successfully reset a computer onboard Voyager 2 that caused an unexpected data pattern shift, and the spacecraft resumed sending properly formatted science data back to Earth on Sunday, May 23. Mission managers at NASA's Jet Propulsion Laboratory in Pasadena, Calif., had been operating the spacecraft in engineering mode since May 6. They took this action as they traced the source of the pattern shift to the flip of a single bit in the flight data system computer that packages data to transmit back to Earth. In the next week, engineers will be checking the science data with Voyager team scientists to make sure instruments onboard the spacecraft are processing data correctly. "

retSava 6y ago

It's not just the weight, there's also the complexity of handling 10 (or whatever) systems. It's not always easy to know when a system fails. How can you be sure that the output is invalid? Detecting complete blackouts is fairly easy, after a while when a watchdog tickle is absent for too long, but bad output due to flipped memory? Consensus-style systems can be used, but they are also a complexity in itself, and the point here was to replace a hardened single point of failure with redundancy.

moftz 6y ago

There is also a time-domain problem with regards to total integrated dose. All the parts will degrade over time. Radiation hardened parts can have lives of 15 years or more in a GEO environment. A commercial part might be lucky to make it 1 year. Radiation shielding is not as easy as you may think. Heavy ions in space can pass through anything and will impart a charge in whatever they hit as well as creating secondary sources of radiation. Neutrons are not as common in space but can be found near reactors, they are also very penetrating.

Rebelgecko 6y ago

Not all radiation problems can be solved by rebooting/voting/watchdogging. Over time the hardware itself will die.