41–50 of 53 posts
Durr. Was this even necessary to say? It's like reading the little disclaimer on a crash test dummy commercial. "Do not try this at home." To say that this video was 'sped up' is basically telling your readers you think they're handicapped.
We detached this subthread from https://news.ycombinator.com/item?id=11791424 and marked it off-topic.
Earlier quoted context omitted.
I saw the video some hours ago and I have been wondering since: how did the camera survive the re-entry? And how did the lens stay so clean?
With regards to re-entry: the rocket was going much slower than orbital velocity, and the re-entry was therefore much more moderate. Some ballpark math: The 1st stage was travelling at 8,300 kph at MECO, and almost of that velocity would have been horizontal. There was no boost-back burn, so it would have kept that velocity until re-entry. Furthermore, it would be re-entering with some vertical velocity. They mention…
No, the drag force grows with the square of velocity. https://en.wikipedia.org/wiki/Drag_(physics)#Drag_at_high_ve...
Force * distance / time = power, so the heating will scale with the velocity cubed. Therefore at 1/2 the speed, it would experience 1/8 the heating.
Earlier quoted context omitted.
I saw the video some hours ago and I have been wondering since: how did the camera survive the re-entry? And how did the lens stay so clean?
With regards to re-entry: the rocket was going much slower than orbital velocity, and the re-entry was therefore much more moderate. Some ballpark math: The 1st stage was travelling at 8,300 kph at MECO, and almost of that velocity would have been horizontal. There was no boost-back burn, so it would have kept that velocity until re-entry. Furthermore, it would be re-entering with some vertical velocity. They mention…
and thats not including the fact that someone else pointed out that it would go with velocity cubed.
Please somebody justify SpaceX because "Science!" isnt cutting it for me anymore.
Glibness aside, it's a private enterprise and is profitable, so even without mentioning Musk's ultimate goal of colonizing Mars, its existence needs no further justification. It makes money and its shareholders are happy.
And before someone jumps in with the "SpaceX-is-propped-up-by-the-government" canard, the U.S. government also saves money when it launches military satellites with SpaceX. According to [1] (among many other sources), SpaceX quotes around $60m, compared to the United Launch Alliance price of about $125m (or even, depending on how you count, $200m).
[1] http://arstechnica.com/science/2016/03/ula-executive-admits-...
Earlier quoted context omitted.
Think about the bare minimum it would take a software developer not to get fired. It's actually quite low. Now realize how many people do the bare minimum at their job. Including politicians (bare minimum == get elected).
What would you call a politician's maximum job performance?
Earlier quoted context omitted.
I saw the video some hours ago and I have been wondering since: how did the camera survive the re-entry? And how did the lens stay so clean?
With regards to re-entry: the rocket was going much slower than orbital velocity, and the re-entry was therefore much more moderate. Some ballpark math: The 1st stage was travelling at 8,300 kph at MECO, and almost of that velocity would have been horizontal. There was no boost-back burn, so it would have kept that velocity until re-entry. Furthermore, it would be re-entering with some vertical velocity. They mention…
Also your calculation is not correct: You add another vertical 4,200 kph of free fall starting from apogee, but didn't factor in that of course the vehicle also slows down as much in the 2 minutes before reaching apogee. Since MECO is at about 65 km height at 8,300 kph, it will also have 8,300 kph at 65 km height when falling down again (minus a little atmospheric drag).
You also can't just add 8,300 kph horizontal (and it's not actually all horizontal, look how quickly the altitude is rising around MECO) and 4,200 kph vertical speed. Those are not scalar values but vectors, so you need to apply pythagoras for vector addition. 8,3 km/s horizontal plus 4,2 km/s vertical speed is just 9,3 km/s total speed.
Earlier quoted context omitted.
With regards to re-entry: the rocket was going much slower than orbital velocity, and the re-entry was therefore much more moderate. Some ballpark math: The 1st stage was travelling at 8,300 kph at MECO, and almost of that velocity would have been horizontal. There was no boost-back burn, so it would have kept that velocity until re-entry. Furthermore, it would be re-entering with some vertical velocity. They mention…
It's actually doing an entry burn to slow down before hitting the atmosphere, you can see it starting here: https://youtu.be/zBYC4f79iXc?t=27m34s Also your calculation is not correct: You add another vertical 4,200 kph of free fall starting from apogee, but didn't factor in that of course the vehicle also slows down as much in the 2 minutes before reaching apogee. Since MECO is at about 65 km height at 8,300 kph, it…
Earlier quoted context omitted.
With regards to re-entry: the rocket was going much slower than orbital velocity, and the re-entry was therefore much more moderate. Some ballpark math: The 1st stage was travelling at 8,300 kph at MECO, and almost of that velocity would have been horizontal. There was no boost-back burn, so it would have kept that velocity until re-entry. Furthermore, it would be re-entering with some vertical velocity. They mention…
Because the energy grows with the velocity squared, it's more like a quarter of the heat of a typical orbital re-entry. No, the drag force grows with the square of velocity. https://en.wikipedia.org/wiki/Drag_(physics)#Drag_at_high_ve... Force * distance / time = power, so the heating will scale with the velocity cubed. Therefore at 1/2 the speed, it would experience 1/8 the heating.
Please somebody justify SpaceX because "Science!" isnt cutting it for me anymore.
How about "Money!". Glibness aside, it's a private enterprise and is profitable, so even without mentioning Musk's ultimate goal of colonizing Mars, its existence needs no further justification. It makes money and its shareholders are happy. And before someone jumps in with the "SpaceX-is-propped-up-by-the-government" canard, the U.S. government also saves money when it launches military satellites with SpaceX. Accor…
Well, actually, any flight to the ISS is a total waste of money as virtually no science is done there. It's just a bunch of people trying to stay alive in a bacteria-ridden tin can.
Durr. Was this even necessary to say? It's like reading the little disclaimer on a crash test dummy commercial. "Do not try this at home." To say that this video was 'sped up' is basically telling your readers you think they're handicapped.
Please don't post uncivil comments here. We detached this subthread from https://news.ycombinator.com/item?id=11791424 and marked it off-topic.