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Artemis II safely splashes down

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Re: Artemis II safely splashes down

#241

Post by gcanyon »

seizethecheese wrote: post #187
roughly wrote: post #163

Earlier quoted context omitted.

Astronauts are, as a group, extremely risk loving. Every single person who signs up to go into space knows what they’re signing up for - they’ve spent their entire life working for the opportunity to be put in a tin can and shot into orbit atop a million pounds of explosives. There’s a very valid critique that NASA has become far too risk averse - we owe it to the astronauts to give them the best possible chance to c…

Highly recommend The Right Stuff by Tom Wolfe about the Gemini astronauts. They mostly were test pilots prior.

The movie was good too. I haven't seen it in years, but from memory:

Gordo! Who's the best pilot you ever saw? -- You're lookin' at him!

Loan me a stick of Beemans.

Light this candle!

It just blew!

No bucks, no Buck Rogers.

Re: Artemis II safely splashes down

#242

Post by shash »

stetrain wrote: post #159
irjustin wrote: post #51

Earlier quoted context omitted.

> Artemis acceptable crew mortality rate is 1 in 30. This seems insane to me. That X decades later we accept, with all our advancements in tech, a weaker system than ever before. That if we send 30 people we _accept_ that one is possible to die. That's the starting point? That's what we document as acceptable?

1 out of the 12 crewed Apollo missions resulted in the death of the crew, so a 1 in 12 effective mortality rate. Apollo 13 was a very close call. If that had ended in failure the mortality rate would have been 1 in 6. So 1 in 30 would be a pretty clear improvement from Apollo, and we are a lot better and more thorough at modeling those risks and testing systems than we were during the Apollo program.

Is 12 enough of a sample size to make a statistical judgement? What if there were 20 more which didn’t have a loss of life? Is it then 1/30? What if there were 20 more?

The risk factor is calculated _per mission_ from what I understand. You can have three accidents in a row and nothing for decades but the risk itself can still be 1 in 30.

Re: Artemis II safely splashes down

#243

Post by segmondy »

irjustin wrote: post #51
areoform wrote: post #11

Glad that they're safe and sound. It's worth pointing out that this is the first extremely public, widely acknowledged high risk mission NASA has done in over 50 years. The Shuttle was risky, but it wasn't thought of or acknowledged by NASA as being risky until very late in its lifecycle. According to NASA's OIG, Artemis acceptable crew mortality rate is 1 in 30. Roughly 3x riskier than the shuttle. There genuinely i…

> Artemis acceptable crew mortality rate is 1 in 30. This seems insane to me. That X decades later we accept, with all our advancements in tech, a weaker system than ever before. That if we send 30 people we _accept_ that one is possible to die. That's the starting point? That's what we document as acceptable?

Insane to you? why don't you tell us what you have contributed to the world to improve this outcome even if by .01%

Re: Artemis II safely splashes down

#245

Post by pdonis »

SV_BubbleTime wrote: post #197
pdonis wrote: post #175

Earlier quoted context omitted.

> The pull of the moon had very little effect. No, it had a very significant effect: it's what made possible the free return trajectory while observing the far side of the moon.

Ok, but no not really. This is incorrect, the “free return” would have happened if they launched entirely in the wrong direction. Like I said, the gif you saw makes it look that way. Here is a link that explains it very well. https://youtu.be/MF8IbYbVIA0?t=269 I’ll agree, it seems crazy that it left earth, made it to the moon, and never really left earth orbit at all. That the furthest we’ve been away is still destin…

> the gif you saw makes it look that way.

Makes it look what way?

Watch the NASA video carefully. It's clear that, even before the "loop" begins, Artemis is slowed down and is soon going to reverse direction relative to Earth. Which of course it would anyway, as you say--because, as the video you linked to points out, it doesn't have Earth escape velocity. The TLI burn gave it just enough velocity to reach the Moon's orbit with a little extra speed left over to get it about 4000 miles further.

But what would not happen without the Moon there is the "backwards" part of the loop--the part that took Artemis around the far side of the Moon. The Moon's gravity is what did that. In the Moon-centered frame in the video, yes, it looks like just a slight deflection--because that frame is moving with the Moon, whereas Artemis was moving backwards--in the opposite direction from the Moon in the Earth-centered frame.

Without the Moon there, Artemis would never have moved backwards, relative to the Moon's orbit, at all. Its trajectory in the Earth centered frame would have been a simple ellipse, with a maximum altitude from Earth a little higher than what it actually achieved (since the Moon's gravity did pull it back a little bit).

Re: Artemis II safely splashes down

#246

Post by m4rtink »

albumen wrote: post #84
llbbdd wrote: post #52

Earlier quoted context omitted.

Would this capsule had been been able to communicate if it was integrated with starlink or is the size more important? I'd imagine if they could have achieved communication via Starlink they would have done it, but just curious.

No, the plasma forms a teardrop shape around small craft like Orion, completely cutting off radio comms. Larger craft like starship or the shuttle which have a roughly cylindrical shape (vs Orion’s circular cross section) aren’t fully enclosed by the plasma. The shuttle had a transmitter attached to its tail for later flights, which could send back telemetry during re-entry.

Well, provided you had a 30 MW microwave transmitter on board, you could punch through the plasma just fine, it has been done:

https://en.wikipedia.org/wiki/Sprint_(missile)

"Sprint accelerated at 100 g, reaching a speed of Mach 10 (12,000 km/h; 7,600 mph) in 5 seconds. Such a high velocity at relatively low altitudes created skin temperatures up to 6,200 °F (3,400 °C), requiring an ablative shield to dissipate the heat. The high temperature caused a plasma to form around the missile, requiring extremely powerful radio signals to reach it for guidance. The missile glowed bright white as it flew."

Re: Artemis II safely splashes down

#247

Post by ksymph »

ksymph wrote: post #229
WalterBright wrote: post #205

Earlier quoted context omitted.

> one more known source of risk to eliminate. How could they have eliminated that risk?

We can look at what NASA did after the Columbia disaster; namely, redesign the external tank, employ stricter quality control of the foam across the board, better monitoring of the heat shield integrity, and adding contingencies for being stuck in space with a damaged shuttle. - They replaced the specific foam insulation that struck Columbia with external heaters, and redesigned other areas where foam was necessary t…

Worth mentioning, this is all particularly fresh in my mind because of a recently released video by the excellent Classic Aerospace History channel on YT, "A Brief History of the Space Shuttle". It's two hours long and provides a reasonably detailed overview of the program, would recommend if you're into that sort of thing: https://www.youtube.com/watch?v=WtmOVxcga-Y

Re: Artemis II safely splashes down

#248

Post by stetrain »

shash wrote: post #242
stetrain wrote: post #159

Earlier quoted context omitted.

1 out of the 12 crewed Apollo missions resulted in the death of the crew, so a 1 in 12 effective mortality rate. Apollo 13 was a very close call. If that had ended in failure the mortality rate would have been 1 in 6. So 1 in 30 would be a pretty clear improvement from Apollo, and we are a lot better and more thorough at modeling those risks and testing systems than we were during the Apollo program.

Is 12 enough of a sample size to make a statistical judgement? What if there were 20 more which didn’t have a loss of life? Is it then 1/30? What if there were 20 more? The risk factor is calculated _per mission_ from what I understand. You can have three accidents in a row and nothing for decades but the risk itself can still be 1 in 30.

So the risk factor for Apollo could have actually been 1/1000 but they were just really unlucky?

Re: Artemis II safely splashes down

#249

Post by pwndByDeath »

icehawk wrote: post #164
pwndByDeath wrote: post #49

As a long time space nerd, I'm not sure what this accomplishes by repeating the previous stunts that failed to usher in the promised space frontier. Apollo was, IMO, not successful at changing the course of human history. A really cool footnote, sure, but everything else that was to follow, nope, just a bunch of neat, interesting but ultimately meh science missions. An exciting change would be more like Delta-V/Criti…

We can't build a TV from 50 years ago, much less a space rocket. Because we stopped, we get to do everything over again with hardware from this century.

My point is this path doesn't lead to the future, it leads to the sad state of space between Apollo and this Shark Jump.

The first Orion (nuclear pulse) has a much more interesting story and would have made us an interplanetary species before we had the iPhone. But it was killed by Kennedy, became space wasn't what he was worried about.... And maybe hundreds of nukes in space might make some countries edgy.

Re: Artemis II safely splashes down

#250

Post by accrual »

WalterBright wrote: post #214
dgfl wrote: post #193

Earlier quoted context omitted.

Yes, this is a fair point. I agree that orbital mechanics is trivially easy compared to everything else. The chances of a math mistake in particular are null, these trajectories have all been calculated years in advance.

The lumpiness of the moon's gravity is not well mapped out.

It is now better mapped after the GRAIL mission: https://en.wikipedia.org/wiki/Gravity_Recovery_and_Interior_...
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