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Artemis II safely splashes down

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Re: Artemis II safely splashes down

#231

Post by m4rtink »

api wrote: post #154
zhoujing204 wrote: post #79

Earlier quoted context omitted.

"As of 1 April 2026, there have been five incidents in which a spacecraft in flight suffered crew fatalities, killing a total of 15 astronauts and 4 cosmonauts.[2][how?] Of these, two had reached the internationally recognized edge of space (100 km or 62mi above sea level) when or before the incident occurred, one had reached the U.S. definition of space at 266,000 ft, and one was planned to do so. In each of these a…

2.4% is not bad given how new this still is and how extreme the speeds and energies are. Note that all the fatalities have been launch or landing related, not in space itself. Clawing out of this gravity well is tough. Make Earth a bit larger and you’d never get off it without something like NERVA or nuclear pulse Orion. I wonder sometimes if that’s another thing to toss in the Fermi paradox bucket. Many rocky planet…

NERVA as envisioned had terrible thrust to weight ratio, not really usable to launch from a Super Earth. Nuclear lightbulb, orion or heck NSWR would likely work though. And bonus points for not having to think about landing systems for the return trip. ;-)

Re: Artemis II safely splashes down

#232

Post by _moof »

TomatoCo wrote: post #70
devilbunny wrote: post #29

Earlier quoted context omitted.

Not just excess - excess and toxic. Hydrazine derivatives and nitrogen tetroxide, IIRC. They are hypergolic, too, so the easiest way to vent them is just to run the engines until empty. However, to prevent moving the craft too much, you do short bursts.

There should be an opposite thruster for each axis. I wonder if the short bursts were due to heating limits.

The short bursts are just the period of the control cycles. Control cycle starts, loop sees error, commands thrust; next control cycle starts, loop sees error is nulled (or in deadband), commands no thrust.

Re: Artemis II safely splashes down

#233

Post by dyauspitr »

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?

Eh yeah? This is frontier, pioneer stuff. We should have a greater appetite for risk as long as it’s completely transparent and the astronauts know what they’re getting into. Realistically though, there is essentially a rocket a day going up and they rarely fail anymore, so the true risk is probably much lower than 1 in 30.

Re: Artemis II safely splashes down

#234

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…

> This is incorrect

No, it's not. You aren't responding to what I actually said. See below.

> the “free return” would have happened if they launched entirely in the wrong direction.

But it would not have been a free return that let them see the far side of the moon, which is what I said. The Moon's gravity is what made that possible. And that was very significant.

Re: Artemis II safely splashes down

#235

Post by m4rtink »

bombcar wrote: post #121
atonse wrote: post #101

I had to explain to my wife and kids (not that I'm in this field, but I also have to remind myself) that we are able to pinpoint where the craft will land, when it will land down to the minute, because of ... just ... math. And we're able to get them there and back because of science. It all boils down to equations that describe the world accurately, and a way of experimentation, iteration, thinking that gets us all…

The analogies for these things like "hitting a golf ball into a hole in one 5,000 miles away" are always fun. I like starting from the fact that Ptolemy was able to get the accuracy of the "motions of the heavens" down so well that it took more than a thousand years to get observations that showed discrepancies. The math, it maths.

I always feel like these analogies don't really fit the real space flight as you quite often have a lot of time to correct the trajectory if you get it roughly right during launch and even that takes a couple minutes. You also have closed circuit guidance and external radar stations to verify the trajectory.

You really don't have anything like that when playing golf, so I don't thin it is a good analogy.

But for the old Sprint anti balistic missile - that was spot on. :D Hitting ICBM warheads kilometers abobe ground, second before detonation - yeah, that fits. It also dispelled the myth that you can't communicate to compact craft due to re-entry plasma. Of course you can, just use a 30 MW radar beam & it will get through just fine! Not to mention the Sprint missile was protected by an ablative heatshield and covered by plasma going up during launch. :D

Re: Artemis II safely splashes down

#236

Post by pibaker »

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?

It honestly says something about how absurdly risk averse our society has become that an 1/30 chance of death is considered too high for a literal moonshot. You can advertise a 1/3 rate of slowly choking in vacuum and I bet you will still get a five mile long queue of people signing up for the mission.

If you want a historical comparison, over 200 men left with Magellan on his voyage around the globe and only 40 returned.

Re: Artemis II safely splashes down

#237

Post by pwndByDeath »

tomhow wrote: post #186
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…

The guidelines ask us to avoid being curmudgeonly. I'm sure you didn't mean to come across that way, but could you try not to make Hacker News the kind of place that responds with “meh” to a successful space mission?

My pessimism comes from a hindsight that the Apollo missions, while amazing failed to create the future they promised. Looking at how the missions were designed, the political focus, the academic infighting of NASA scientists trying to keep niche research funded. I fail to see how this time, the same strategy will produce a different result.

I also don't expect benevolent billionaires to fill that either. I hope I would in their place, but I'll not likely get the chance.to find out.

To end on an optimistic note, tang and Velcro are pretty dope.

Re: Artemis II safely splashes down

#238

Post by dehrmann »

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?

We stopped going to the moon because it's a vanity project. It's expensive, risky, and there isn't much more science to do or that can't be done by robots.

Re: Artemis II safely splashes down

#240

Post by m4rtink »

numpad0 wrote: post #81
philistine wrote: post #18

Earlier quoted context omitted.

I’ll note, since it is supremely interesting to me, that Starship is able to communicate with the ground during its whole reentry due to its sheer size and ability to connect with Starlink satellites. I assumed loss of signal due to reentry was a given for any spaceship!

Shuttle in its last days had antennas that protruded outside the plasma just enough for telemetry. Apollo and Artemis reentry are also direct entry from Lunar-Earth transfer orbit using ablative heat shields, so the plasma would be hotter and thicker than suborbital Starship shots with Shuttle style ceramic tiles.

I'm pretty sure it did not stick anything through the plasma sheet- that is impossible. You would eithe melt the thing or just shift the plasma sheet a bit. It forms as air is compressed on contact, simple as that.

What IIRC was actually done was that some antennas were placed on the back of the shuttle & its size was big enough that the plasma bubble would not fully envelope it - it would be open up to space. And that antenna on the back would communicate with TDRS satellites through this gap, enabling contact through the whole re-entry.

Starship does basically the same, just with Starlink satellites instead of TDRS.

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