Submitted by marketrent t3_yfa5pz in space
alle0441 t1_iu2pje5 wrote
Reply to comment by djdsf in NASA spacecraft records epic ‘marsquakes’ as it prepares to die by marketrent
It's more just that the probe isn't designed to last a long time. Original designed lifespan was 2 years and it's coming up on 4. Sure they could do things to extend the life, but that would be spending extra time, money, added weight, complexity when the requirements don't ask for it.
moeriscus t1_iu2qrbm wrote
Fair point, but I think it's obvious that NASA lowballs the expected lifespans in order to avoid overpromising/underdelivering to the public and to budgetary committees
Lasombria t1_iu2xp16 wrote
My father worked for JPL for 40+ years, and no, they really don't. What they do is make the projected lifespan as guaranteed as possible. A happy side effect of that is these great extended-mission lifespan, but the goal is hitting the primary lifespan securely.
Dsiee t1_iu3txgw wrote
No, it is an artificat of designing for a high sucess probability. For a simple example, let's say you want a robot for a 1 year mission with 90% probability of it lasting two years. You design the robot so that it has a failure rate of 5% per year. As a result it is highly likely (~80%) that it will last four years or twice the required mission length.
Obviously this is a very simplified example, but hopefully it illustrates the point that you cannot easily determine the exactly lifespan of a piece of equipment.
djdsf t1_iu2q0ea wrote
While that's true, wouldn't the argument that keeping something alive for longer is also cheaper than building a whole new one and sending it to space again?
I'm understand new tech as well, but come on, there has to be a world somewhere where keeping this thing alive for an extra year for maybe $3M more is cheaper than sending another one that will run 3 years for $70M right?
Count_JohnnyJ t1_iu2qzi0 wrote
"Cheaper" doesn't matter when you have X budget, and if you don't spend it, you'll have a smaller budget the next year because you obviously didn't need that much.
Ex_Machina77 t1_iu3txs8 wrote
That only applies to rolling budgets like the US Army utilizes. But essentially that's a myth propagated by terrible supply personnel, who failed to do their jobs properly.
CartmansEvilTwin t1_iu39520 wrote
That's not really how this works.
These things have a specified lifetime of e.g. 2 years. That means, each component is built and designed to last 2 years with a probability of 99,9%. That in turn means, that there's a high likelihood for the device to survive much longer then two years. Adding additional safety margins for a designed lifetime of 4 years will make the whole thing much more expensive and maybe even less capable, simply because it's going to be heavier.
And additionally, NASA engineers often enough hack devices to work much longer. The Kepler telescope for example had one too many reaction wheels fail and was thought to be dead, but some clever engineer find a way to use the remaining ones to still do some science.
Viewing a single comment thread. View all comments