SpaceX Tuesday...
Discussion
hidetheelephants said:
craig_m67 said:
The thin stuff (brake line) looks like a fire suppression system?
Could be sensor lines.Caruso said:
I was just looking up why rockets throttle down at Max Q and the answers didn't satisfy.
Now matter how fast you're accelerating, Max Q remains the same i.e. the maximum aerodynamic pressure which is related to your speed not acceleration.
But I suppose the acceleration is pushing up from the bottom at the same time that Max Q is pushing down from the top, so reducing thrust does reduce the overall compressive stress on the rocket body. Or have I missed something?
Always assumed that was it. Plus maybe a little vibration reduction. Now matter how fast you're accelerating, Max Q remains the same i.e. the maximum aerodynamic pressure which is related to your speed not acceleration.
But I suppose the acceleration is pushing up from the bottom at the same time that Max Q is pushing down from the top, so reducing thrust does reduce the overall compressive stress on the rocket body. Or have I missed something?
Caruso said:
I was just looking up why rockets throttle down at Max Q and the answers didn't satisfy.
Now matter how fast you're accelerating, Max Q remains the same i.e. the maximum aerodynamic pressure which is related to your speed not acceleration.
But I suppose the acceleration is pushing up from the bottom at the same time that Max Q is pushing down from the top, so reducing thrust does reduce the overall compressive stress on the rocket body. Or have I missed something?
Throttle down to reduce acceleration and subsequent velocity in the thicker part of the atmosphere, reducing the peak pressure on the rocket body.Now matter how fast you're accelerating, Max Q remains the same i.e. the maximum aerodynamic pressure which is related to your speed not acceleration.
But I suppose the acceleration is pushing up from the bottom at the same time that Max Q is pushing down from the top, so reducing thrust does reduce the overall compressive stress on the rocket body. Or have I missed something?
It's the velocity rather than the acceleration.
annodomini2 said:
Throttle down to reduce acceleration and subsequent velocity in the thicker part of the atmosphere, reducing the peak pressure on the rocket body.
It's the velocity rather than the acceleration.
I think it is both. You want a rocket with good acceleration, but the drag on the ship increases the faster you go (at a given altitude). As you climb, drag reduces because there is less air to shove out of the way.It's the velocity rather than the acceleration.
Drag increases with speed, and decreases with air density. You’re opposing drag with the engines, as well as accelerating the rocket. The rocket has to withstand the shove (down) from the top and the shove (up) from the bottom. If you exceed the design capability, the bit in the middle crumples.
The drag equation maximises at a certain speed and air density. You want to go through that maximum with less acceleration happening, and then throttle up again afterwards. Basically you want a rocket that can get to max Q quickly, coast through it, and then put the hammer down again.
rxe said:
Basically you want a rocket that can get to max Q quickly, coast through it, and then put the hammer down again.
If you accelerate too quickly you get more drag losses though, and you're carrying a heavier engine than you need to in order to accelerate that quickly. But if you accelerate to slowly you get more gravity loses as you're burning upwards for longer. RizzoTheRat said:
If you accelerate too quickly you get more drag losses though, and you're carrying a heavier engine than you need to in order to accelerate that quickly. But if you accelerate to slowly you get more gravity loses as you're burning upwards for longer.
Well yes, but then you have to factor in the fact that the weight of the ship is decreasing rapidly. By the time you get to MaxQ, you've burnt nearly half your fuel. So, the engines that managed to drag you off the ground are more than capable of breaking your rocket with acceleration if you are careless. Rocket science is hard! 
RizzoTheRat said:
rxe said:
Rocket science is hard!
Definitely. I find the speed SpaceX have progressed to be astounding. Meanwhile Blue Origin are still only about half way to orbit. 
Einion Yrth said:
Since orbit is about speed rather than height, new Shepard at around 1km/s is about an eighth of the way to orbit.
You got me wondering there, as once out of atmosphere and burning horizontally you haven't got the losses you incur on the way up. This article reckons it's got about 3300m/s dV, so around a third of what it would need for orbit
jonny142 said:
Having stacked the 7th bit of the launch tower, busy day in Starbase TX.Einion Yrth said:
jonny142 said:
Having stacked the 7th bit of the launch tower, busy day in Starbase TX.Gassing Station | Science! | Top of Page | What's New | My Stuff