The Astronomy Thread

wormie · Apr 15, 2015

Malakriss_sl said:
But what if he's wrong and it's really positive numbers that don't exist?

I believe you misunderstand the Furry's Theorem of Trailer-Parkidness. It states that since negative numbers cannot be observed in nature, they do not exist. This being physics, the "proof" is by observation.

Cad · Apr 15, 2015

Having the rocket just land is pretty sweet too because then it can literally be refueled and re-launched. After X number of launches it needs to be refitted/cleaned/whatever. The rocket itself is more complex but if it can be used 10 times, it can be 3 times the cost and still be 3 times cheaper.

khalid · Apr 15, 2015

Abefroman_sl said:
The rocket chose to crash.

Nice

wormie · Apr 15, 2015

That rocket has to suffer a fair bit of damage upon re-entry. I wonder what the life of that thing is projected to be.

Tuco · Apr 15, 2015

I don't understand the feasability of it either. It seems like the additional weight from re-entry rockets necessary to control the landing is so much more limiting than wings, parachutes etc.

I finally watched Interstellar last night. The

only thing I really had problems with was the time dilation on the water planet. 1 hour = 7years just seems so extreme. It turns out that in order to experience that level of dilation, Gargantua needs a mass of 100 million suns and needs to spin at just barely under the speed of light. And then the planet needs to orbit at 55% the speed of light.

My questions about it:
1. I don't really understand how it'd be possible to even land on a planet that's moving that fast unless its relative speed decreases as you enter the gravity well near it?

2. I also don't understand how everything near it, including the water world, isn't just torn asunder from the massive forces. You get some queer tidal wave, and then generally calm 2 foot water. It doesn't make sense to me.

3. It seems like there's this binary switch of time dilation where the mother ship did not experience it, but the crew did. That just seems a little unnecessary. It seems like they could've had a time dilation scale that increased the closer they got to the planet, but still getting dilated outside of it. And since it could take two years (for example) to move from the wormhole to the planet, all that time dilation they'd be constantly experiencing would've caused 27 years to age on earth just the same.

4. It made zero sense to me for them to even consider going to a planet near a black hole. From the story it makes sense because it only works if Mcconaughey flies into the black hole, but I feel like we were missing a scene with Matt Damon and Michael Caine saying, "Fuck the planets near the black hole" and later being forced to change their minds.

Cad · Apr 15, 2015

Tuco_sl said:
I don't understand the feasability of it either. It seems like the additional weight from re-entry rockets necessary to control the landing is so much more limiting than wings, parachutes etc.

I finally watched Interstellar last night. The

only thing I really had problems with was the time dilation on the water planet. 1 hour = 7years just seems so extreme. It turns out that in order to experience that level of dilation, Gargantua needs a mass of 100 million suns and needs to spin at just barely under the speed of light. And then the planet needs to orbit at 55% the speed of light.

My questions about it:
1. I don't really understand how it'd be possible to even land on a planet that's moving that fast unless its relative speed decreases as you enter the gravity well near it?

2. I also don't understand how everything near it, including the water world, isn't just torn asunder from the massive forces. You get some queer tidal wave, and then generally calm 2 foot water. It doesn't make sense to me.

3. It seems like there's this binary switch of time dilation where the mother ship did not experience it, but the crew did. That just seems a little unnecessary. It seems like they could've had a time dilation scale that increased the closer they got to the planet, but still getting dilated outside of it. And since it could take two years (for example) to move from the wormhole to the planet, all that time dilation they'd be constantly experiencing would've caused 27 years to age on earth just the same.

4. It made zero sense to me for them to even consider going to a planet near a black hole. From the story it makes sense because it only works if Mcconaughey flies into the black hole, but I feel like we were missing a scene with Matt Damon and Michael Caine saying, "Fuck the planets near the black hole" and later being forced to change their minds.

My limited understanding of time dilation is that it come about two ways: one would be either being deep in a gravity well (close to the black hole) or going really fast. Maybe those two things are the same in this case because to orbit that deep in a gravity well, you'd have to be moving a significant fraction of the speed of light (as you pointed out). My issue is for the ship to not be in that gravity well or going that fast, it'd either have to accelerate to a significant fraction of the speed of light in order to land on the planet (impossible) or it'd have to be going the same speed as the planet to conduct a landing, in which case the time dilation would be the same on the ship. For the time dilation on the mother ship and the lander to be that different, the speed differential would have to be remarkable, and it just wasn't. Now I'm an armchair physicist so I am sure I'm missing something but that just seemed completely wrong.

Lithose · Apr 15, 2015

Tuco_sl said:
I don't understand the feasability of it either. It seems like the additional weight from re-entry rockets necessary to control the landing is so much more limiting than wings, parachutes etc.

That's the thing, though. They don't need extra rockets--their primary rockets have design features which let them operate with only an extra set of fins, and the landing legs. Again, this is what I've read--they've made several advances in the rocket design. Like being able to reignite the main engines. The main loss in payload comes from having to keep extra fuel to work the engines. The payload loss per flight is about 25-30% but the trade off is they get to refurbish and the 54 million dollar rocket and use it again.

iannis · Apr 15, 2015

Yeah, sure, I'm mostly being a jackass. I have to imagine they prototyped just about everything they could think of during planning phases.

It just really DOES seem like you could use some sort of shell on the thing to prevent water damage and it would be easier than what they're trying to do. But what they're doing is still impressive, and even if it winds up never quite working reliably enough in real world situations, like the Osprey(?), they still will have advanced the physical science/engineering/toolkit of it by leaps.

And what the fuck do I know about it anyway. I'm no rocket surgeon.

Tuco · Apr 15, 2015

Lithose_sl said:
That's the thing, though. They don't need extra rockets--their primary rockets have design features which let them operate with only an extra set of fins, and the landing legs. Again, this is what I've read--they've made several advances in the rocket design. Like being able to reignite the main engines. The main loss in payload comes from having to keep extra fuel to work the engines. The payload loss per flight is about 25-30% but the trade off is they get to refurbish and the 54 million dollar rocket and use it again.

Have they ever answered why they don't use a parachute and use their rockets for re-entry?

I flew a few hobbyists rockets as a kid and they had parachutes, so I'm an expert on the matter.

Abefroman · Apr 15, 2015

Tuco_sl said:
Have they ever answered why they don't use a parachute and use their rockets for re-entry?

I flew a few hobbyists rockets as a kid and they had parachutes, so I'm an expert on the matter.

Once you deploy parachutes you lose the precision needed to land on a platform in the water. You also wont be able to use the fins and rockets to adjust the trajectory.

Furry · Apr 15, 2015

I have no idea how this rocket works, but I do know that rockets that go to space and come back generally start a lot heavier than they end up. Drastically changing the center of mass does a lot of weird things aerodynamically, especially if your thrust is in a fixed location and you are relying on it for stability. Perhaps their chief rocket designer had an air force background.

Abefroman · Apr 15, 2015

Itzena_sl · Apr 15, 2015

Iannis_sl said:
Yeah, sure, I'm mostly being a jackass. I have to imagine they prototyped just about everything they could think of during planning phases.

It just really DOES seem like you could use some sort of shell on the thing to prevent water damage and it would be easier than what they're trying to do. But what they're doing is still impressive, and even if it winds up never quite working reliably enough in real world situations, like the Osprey(?), they still will have advanced the physical science/engineering/toolkit of it by leaps.

And what the fuck do I know about it anyway. I'm no rocket surgeon.

If it helps, landing on the barge-platform thing is an intermediate step. The final goal is to park it back on a landing pad, refuel it, strap a new upper stage on top, and send it back up again.

Denamian · Apr 15, 2015

It was always my understanding that landing on a barge was just a safety precaution and eventually this will be done on land.

Watching the video, I guess things didn't go quite as well as I had though, as the vine SpaceX had posted earlier cuts out before things go sideways.

Szlia · Apr 15, 2015

If they really want to have their rocket work that way, maybe they should have a landing pad that "catches" the rocket as it comes. No clue if the chassis of a rocket would allow that though.

Lithose · Apr 16, 2015

Tuco_sl said:
Have they ever answered why they don't use a parachute and use their rockets for re-entry?

I flew a few hobbyists rockets as a kid and they had parachutes, so I'm an expert on the matter.

Yes, they actually tried parachutes until 2011. As Abe said, in order for the chutes to work, they need a lot more stuff to stabilize them as they have to deployed a good way up in the air. Their deployment, would prevent their new computer controlled "hyper sonic" fins from being useful. The fins, on a fast moving drop? Can actually control the aircraft really well, but they need the speed to do it. If the chute is deployed at this speed, it just burns up.

So the best way to control and slow it was to not use chutes at all..and just let the finds control it on an extremely fast descent down--then have a burn slow it down, and guide it in. From the articles I read, this is all only possible thanks to all the new computer/drone systems on board, which allows very precise moment to moment measurements. It makes "needing to slow down" not as much of a requirement until the end. (I think this is all under the Grasshopper lander on the wiki page--they've made some fascinating advances in Rocketry. Space X is not fucking around.)

Khalan · Apr 16, 2015

Szlia_sl said:
If they really want to have their rocket work that way, maybe they should have a landing pad that "catches" the rocket as it comes. No clue if the chassis of a rocket would allow that though.

The whole point is to also prototype for a potential mars mission, where there would be nothing to catch it.

Tuco · Apr 16, 2015

Lithose_sl said:
Yes, they actually tried parachutes until 2011. As Abe said, in order for the chutes to work, they need a lot more stuff to stabilize them as they have to deployed a good way up in the air. Their deployment, would prevent their new computer controlled "hyper sonic" fins from being useful. The fins, on a fast moving drop? Can actually control the aircraft really well, but they need the speed to do it. If the chute is deployed at this speed, it just burns up.

So the best way to control and slow it was to not use chutes at all..and just let the finds control it on an extremely fast descent down--then have a burn slow it down, and guide it in. From the articles I read, this is all only possible thanks to all the new computer/drone systems on board, which allows very precise moment to moment measurements. It makes "needing to slow down" not as much of a requirement until the end. (I think this is all under the Grasshopper lander on the wiki page--they've made some fascinating advances in Rocketry. Space X is not fucking around.)

cool.

Brad2770 · Apr 17, 2015

JPL | News | Dawn Glimpses Ceres North Pole

Jysin · Apr 27, 2015

Incredibly cool photo, considering the skill / timing involved.

The featured image was taken ... with an exposure time of only 1/1000 of a second. In contrast, the duration of the transit of the ISS across the entire Moon was about half a second.

APOD: 2015 April 27 - Space Station over Lunar Terminator

The Astronomy Thread

Asshat wormie

2023 Asshat Award Winner

scientia potentia est

Unelected Mod

Asshat wormie

2023 Asshat Award Winner

I got Tuco'd!

scientia potentia est

Buzzfeed Editor

Musty Nester

I got Tuco'd!

Naxxramas 1.0 Raider

🌭🍔🇺🇦✌️SLAVA UKRAINI!✌️🇺🇦🍔🌭

Naxxramas 1.0 Raider

shitlord

Night Janitor

Member

Buzzfeed Editor

Trakanon Raider

I got Tuco'd!

Avatar of War Slayer

Ahn'Qiraj Raider