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SpaceX launches starship Mega-Rocket and catches its booster in midair on first try.
(www.smithsonianmag.com)
this post was submitted on 15 Oct 2024
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Um, no?
The rocket has been to orbit twice now, they've already demonstrated that. They're working on the bonus mission, landing everything and perfecting the hardware to the point where it doesn't need major refurbishment between flights.
As far as I understood it, SpaceX uses the word "orbit" liberally. If it reaches the hight where an orbit would be possible, that's "being in orbit" for them. In an actual orbit, the rocket would not fall back down again in an hour or so without active breaking. If my understanding is incorrect, I'm happy to be corrected. And even of that was achieved soon, it's still all without demonstrating that the starship could actually carry a load and return it safely. Not even an inexpensive dummy load. All SpaceX is showing in their live feeds are empty cargo holds that fill up with hot gases and fumes during reentry.
They've already demonstrated they can get it in orbit. The fact that they've not done it for this mission was intentional, not a limitation. They wanted the ship back, they didn't want it sitting around in orbit doing nothing being in the way. They don't actually have a mission for it yet, its mission is to prove that it works, so if they put it in orbit then what?
The whole point is that once it's in orbit it has virtually no fuel on board, because that's how they get around the rocket equation, they do fuel transfer on orbit. So in the testing scenario they would have a vehicle with virtually no maneuvering capabilities parked in a stable orbit more or less forever. Eventually its orbit would decay and it would uncontrollably into the Earth, which I think we can all agree is a bad thing.
No, that's not really right at all. With this last flight they brought the starship above 200km (100km is generally considered the point at which you're in space), so they definitely went much higher than they needed. In low earth orbit, the velocity needed to hold that orbit is about 28000 KM/H, they kept their velocity below 27000 KM/H for safety/responsibility reasons. That way, if something failed and they couldn't relight their engines, it would naturally come down anyway in a predictable manner. The closer you get to actual orbital speeds, the less predictable the re-entry and impact location will be, so 27000 KM/H is really as high as you want to go if you want to ensure predictable re-entry. It looks like they maxed out at 26750 kmh.
Also, after they reached 95% of orbital speeds, we know they still had lots of fuel in the tank because it had enough to slow down and land exactly where they wanted it to. And then... it still had enough to explode in a huge fireball, so clearly the rocket could have gone further. Or to look at it differently, all the propellant mass that got used up in that huge explosion at the end, that could have been payload mass. So clearly it has the capacity to put up a payload as well. I think the reason they haven't yet is that mastering the reusability aspects are just a higher priority than the payload bays, I think we all trust they can design a payload bay when it comes time for that.
In that case I stand corrected on the whole orbit bit. Thanks for taking the time.
Well I love talking about space, thanks for reading all that ;-)
So what you're saying is that SpaceX deliberatly doesn't let Starship orbit, to keep reentry predictable. Which is what [email protected] said; they don't actually orbit.
Also note that 100km is the minimum height to be "in space", not the minimum height for achieving orbit.
Finally, I disagree with the note that having "enough fuel" to reach orbit means they have demonstrated such capability; I believe they easily could achieve this, but they haven't actually demonstrated it yet.
That doesn't really mean anything. You could achieve an orbit at a lower altitude if you wanted to, it would decay faster, but you could do it. The 100km karman line is an arbitrary thing, there is no solid line where on one side you can orbit and on the other side you can't.
Well this seems like a bad semantic argument to me. I guess the question is, what does it mean to you to "demonstrate capability". Like, for you, what would be the difference between demonstrating a capability to do something and actually doing that thing? How would those two things look different? Or in this specific case, how could they have demonstrated that capability without putting their rocket into a stable orbit (because it would be negligent to do that with this prototype rocket)?
Given what they have done, is there any reason to doubt they could have gone a little bit further? And conversely, was there a good reason to stop where they were, or do you think they would have gone further if they could have?
I agree; the comment I was replying to seemed to imply that there was a minimum height requirement, or height by itself equaled orbit. But that's just my interpretation of it.
Maybe it is, but personally I prefer to see the result 100% finished. I am very impressed by the booster catch, and the non-stop camera feed on Starship was awesome, but I would like to see a full mission before saying that they reached orbit. And to me, demonstrating capability usually means doing it.
Lictblitz is saying they aren't capable of orbit. Which is very different from simply choosing not to.
No, I said they hadn't demonstrated it. But 95% is close enough, I stand corrected.
You're not really wrong, but I think you are missing a few things. If you can get your rocket on a ballistic trajectory with a height above the Kármán line (~100km), then going into LEO from there is just a matter of having enough fuel. Nobody doubts that Starship could carry enough fuel to do that.
They haven't bothered doing that in testing yet, because they wouldn't learn anything. Knowing how the heat shield survives reentry is far more important. The upper stage still hasn't been able to come down in a safe, controlled manner yet. Test 4 managed to splash down, but the heat shield took a lot more damage than anybody is comfortable with (if you watch the videos of it, you'll see why it was amazing it survived at all). This one was Test 5, and while the heat shield survived better, the upper stage blew up when it hit the water.
I thought it blew up because after tipping over the tanks ruptured - a normal result of a rocket tip-over. Am I mistaken?
It shouldn't rupture a tank just because of a splashdown, no. Even if they're able to chopstick catch the upper stage, or land it like Falcon 9's boosters, a splashdown may be needed in emergencies.