3 ms·

"doubled" the lower bound on what was surely an extremely conservative estimate meant to avoid a perception of failure if things didn't go perfectly. The Opport

"doubled" the lower bound on what was surely an extremely conservative estimate meant to avoid a perception of failure if things didn't go perfectly. The Opportunity rover had a "90-day" expected lifetime and lived until 15 years old. It's great that Ariane performed superbly but this "doubling" calculation is pretty silly.

mrtksn 5y ago
> The Opportunity rover had a "90-day" expected lifetime and lived until 15 years old. It's great that Ariane performed superbly but this "doubling" calculation is pretty silly. Yeah, no. JWST has a limited lifetime because of the finite fuel, that's completely different from building a machine for a purpose and the machine not falling apart at the end of the initial mission. When people say Ariane doubled the lifetime of JWST, they mean Ariane performed much better than the allowed margins, thus pushing the fuel efficiency to its limits. Think this, a Toyota has a lifetime of 100K miles but many get 200K out of it. That's completely different from achieving 80mpg on a car rated 40mpg. When someone tells you that they are driving so precisely that they are getting twice the milage, is it appropriate to say "So what, my car was supposed to last 100K miles but lasted 200K"? I think, no.
- 1125spacex 5y ago
  There's really no telling how good Ariane was here though, without a lot more information. Maybe if it was perfect it could have "tripled" the lifetime. Using your driving analogy, this is like you getting 80mpg on a car that needs to hit 40mpg or heads will roll. Maybe everyone driving it would get 80mpg. Maybe someone driving extremely precisely would get 120mpg. There's not enough information here to say how well Ariane did other than public comments from the engineers which were vague but positive.

3 ms·

"doubled" the lower bound on what was surely an extremely conservative estimate meant to avoid a perception of failure if things didn't go perfectly. The Opport

by arcticfox 5y ago

mrtksn 5y ago
> The Opportunity rover had a "90-day" expected lifetime and lived until 15 years old. It's great that Ariane performed superbly but this "doubling" calculation is pretty silly. Yeah, no. JWST has a limited lifetime because of the finite fuel, that's completely different from building a machine for a purpose and the machine not falling apart at the end of the initial mission. When people say Ariane doubled the lifetime of JWST, they mean Ariane performed much better than the allowed margins, thus pushing the fuel efficiency to its limits. Think this, a Toyota has a lifetime of 100K miles but many get 200K out of it. That's completely different from achieving 80mpg on a car rated 40mpg. When someone tells you that they are driving so precisely that they are getting twice the milage, is it appropriate to say "So what, my car was supposed to last 100K miles but lasted 200K"? I think, no.
- 1125spacex 5y ago
  There's really no telling how good Ariane was here though, without a lot more information. Maybe if it was perfect it could have "tripled" the lifetime. Using your driving analogy, this is like you getting 80mpg on a car that needs to hit 40mpg or heads will roll. Maybe everyone driving it would get 80mpg. Maybe someone driving extremely precisely would get 120mpg. There's not enough information here to say how well Ariane did other than public comments from the engineers which were vague but positive.