
Three spacecraft heading to Mars this summer - Hooke
https://www.nytimes.com/interactive/2020/science/mars-perseverance-tianwen-hope.html
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choeger
I am wondering why NASA only sends one rover. Considering the investments into
development, planning, and control and the relatively low launch costs
nowadays, I would think it logical to send two or more probes to mitigate the
risk of catastrophic mistakes.

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WalterBright
Yes. Consider the Hubble space telescope. I would expect that building a pair
rather than one wouldn't cost that much more than one, especially if they were
built side by side.

This would likely have been far, far cheaper than the repair mission sent to
fix the sole Hubble.

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KineticLensman
> This would likely have been far, far cheaper than the repair mission sent to
> fix the sole Hubble

If two Hubbles had been built the same, both could have had the same
implementation error [0] that required the first repair flight.

[Edit] Although I guess the second one could have been fixed on the ground
based on experience from the first, assuming a non-simultaneous launch.

[0]
[https://en.wikipedia.org/wiki/Hubble_Space_Telescope#Flawed_...](https://en.wikipedia.org/wiki/Hubble_Space_Telescope#Flawed_mirror)

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WalterBright
That's right. It would make sense to space the launches out a bit to be able
to correct defects on the second.

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jcun4128
Curious if they have to register/coordinate their intended flight path/orbits
so they don't hit each other(probably very unlikely). Probably don't have
onboard radar or something like that?

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choeger
> probably very unlikely

Literally astronomically unlikely. If at all they might want to coordinate
radio emissions.

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onion2k
_“Scientists have calculated that the chances of something so patently absurd
actually existing are millions to one. But magicians have calculated that
million-to-one chances crop up nine times out of ten.”_

Terry Pratchett in Mort

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enkid
Sergeant Colon looked wretched. "Weeell, what if it's not a million-to-one
chance?" he said.

Nobby stared at him.

"What d'you mean?" he said.

"Well, all right, last desperate million-to-one chances always work, right, no
problem, but...well, it's pretty wossname, specific. I mean, isn't it?"

"You tell me," said Nobby.

"What if it's just a thousand-to-one chance?" said Colon agonizedly.

"What?"

"Anyone ever heard of a thousand-to-one shot coming up?"

Carrot looked up. "Don't be daft, Sergeant," he said. "No one ever saw a
thousand-to-one chance come up. The odds against it are—" his lips
moved—"millions to one."

"Yeah. Millions," agreed Nobby.

"So it'd only work if it's your actual million-to-one chance," said the
sergeant.

"I suppose that's right," said Nobby.

"So 999,943-to-one, for example—" Colon began.

Carrot shook his head. "Wouldn't have a hope. No one ever said, 'It's a
999,943-to-one chance but it just might work.'"

\- Guards! Guards!

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prando
I am curious to know this - how do various nations/ space programs ensure that
the objectives of their missions are significantly different that they don't
end up repeating the work/ results of other missions (from other nations)? Do
all space agencies work together to determine what the focus would be (I guess
not, but it'd be cool, if it were like that)!

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linuxftw
Digital camera technology is leaps and bounds beyond the last rovers we sent.
Hopefully we get top quality photos this time around.

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kevin_thibedeau
COTS sensors don't work well in a high radiation environment.

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merricksb
[https://archive.md/7Xxfn](https://archive.md/7Xxfn)

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sixothree
I know I'm a fuddy duddy, but I absolutely hate the naming scheme of our mars
rovers - Curiosity and Perseverance are things you feel not things you do. I
just hate it. Stop it NASA.

