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First Public Shuttle Engine Test
Guppy06 writes: "NASA's John C. Stennis Space Center (Mississippi, near the gulf coast) will be opening its doors to the public for the first time this Saturday. As part of its celebrations of the 20th anniversary of the first space shuttle launch (as well as flight-certifying a Pratt & Whitney fuel turbo pump), there'll be a 520-second static test of an SSME around 2000 CDT. Translating that into English for the non space geeks, that means they'll be lighting up a space shuttle main engine (attatched to a large steel frame, grounded in a big chunk of concrete so it doesn't go anywhere) for about 9 minutes around 8:00. The press release is available here. Now if only they did stuff like this more often, there might be more interest in NASA ..."
I didn't want to write anything long because your posts will get archived while mine will disappear (unless you quote what I say). But given the effort that you put, I think that you deserve something in return.
You're not hopeless. You're quite knowledgeble, and you can undoubtedly solve many physics problems involving mass, momentum, and the like. But that's not enough. To be a Jedi, you need the feel conservation of energy and conservation of momentum as second nature. These are the two most important concepts in mechanics, and will save your butt countless times.
You mentioned 5 other things to take into account, and accurately said that it wasn't an exhaustive list, but sometimes there's a trick. If I ask you what is (exp(sin(Pi/9))+sqrt(17+log(23))) - (exp(sin(Pi/9))+sqrt(17+log(23))), you're still busy parsing the first few calculations while anyone with a global view will immediately say this is equal to zero, without even worrying whether I meant log base-10 or base-e.
Same here. In the rocket engine problem, you put a big box around the Earth such that the boundary of the box will be space. That's a closed system. The total momentum inside of that box doesn't change, as long as nothing gets out of the box (which is the case since I chose a large box, going halfway to the moon, say). Conservation of linear momentum says that the integral of density(x,y,z)*velocity(x,y,z) over that box remains a constant, unchanged by rocket engines, volcanos, or people jumping up and down.
Now you can say "ah ha but I don't count people or the air to be part of Earth". Fine, but you still have: integral of density(x,y,z)*velocity(x,y,z) over the Earth + integral of density(x,y,z)*velocity(x,y,z) over not-Earth = constant. In other words, the average velocity of the Earth times Earth's mass + the average velocity of the non-Earth times non-Earth is a constant. But these two average velocities are equals, else the Earth and people would be spreading apart and be completely separated given enough time. It really makes no difference if you don't count people and air, as long as people and air don't fly off the Earth.
The upshot: Earth's orbit won't change at all, and you don't need to worry about the deformation of the steel frame and concrete block or anything else to get that answer. That is why you should worship conservation of momentum as your new God.
This is it:
Who cares about the position of the Earth right after the push? The main thing happening is a change of velocity of v=a*520. The difference in position is then a function of time, roughly x(t) = v*t. (think t = days or weeks)
I didn't want to write anything long because your posts will get archived while mine will disappear (unless you quote what I say). But given the effort that you put, I think that you deserve something in return.
You're not hopeless. You're quite knowledgeble, and you can undoubtedly solve many physics problems involving mass, momentum, and the like. But that's not enough. To be a Jedi, you need the feel conservation of energy and conservation of momentum as second nature. These are the two most important concepts in mechanics, and will save your butt countless times.
You mentioned 5 other things to take into account, and accurately said that it wasn't an exhaustive list, but sometimes there's a trick. If I ask you what is (exp(sin(Pi/9))+sqrt(17+log(23))) - (exp(sin(Pi/9))+sqrt(17+log(23))), you're still busy parsing the first few calculations while anyone with a global view will immediately say this is equal to zero, without even worrying whether I meant log base-10 or base-e.
Same here. In the rocket engine problem, you put a big box around the Earth such that the boundary of the box will be space. That's a closed system. The total momentum inside of that box doesn't change, as long as nothing gets out of the box (which is the case since I chose a large box, going halfway to the moon, say). Conservation of linear momentum says that the integral of density(x,y,z)*velocity(x,y,z) over that box remains a constant, unchanged by rocket engines, volcanos, or people jumping up and down.
Now you can say "ah ha but I don't count people or the air to be part of Earth". Fine, but you still have: integral of density(x,y,z)*velocity(x,y,z) over the Earth + integral of density(x,y,z)*velocity(x,y,z) over not-Earth = constant. In other words, the average velocity of the Earth times Earth's mass + the average velocity of the non-Earth times non-Earth is a constant. But these two average velocities are equals, else the Earth and people would be spreading apart and be completely separated given enough time. It really makes no difference if you don't count people and air, as long as people and air don't fly off the Earth.
The upshot: Earth's orbit won't change at all, and you don't need to worry about the deformation of the steel frame and concrete block or anything else to get that answer.
That is why you should worship conservation of momentum as your new God.
"I will take the Ring," he said, "though I do not know the way."
This kind of even is good for future generations of engineers and scientists. Even if they don't decide they would like to work for NASA, this is the type of event that will ignite a desire to learn about science in children, and hopefully it will encourage parents to help their children learn.
Guppy06 - please spell check.
Keeping
Tour guide: On your left, we have the Research Building, the restrooms and the caffeteria. On your right...
FWOOSH!
Tour guide: Er... we have, or rather had, the souvenir stand. Thanks you all for coming and, uh, here's a free pin for y'all, and please let's keep this a secret betwen ourselves, OK?
Tongue-tied and twisted, just an earth-bound misfit, I
Tongue-tied and twisted, just an earth-bound misfit, I
Learning to fly, Pink Floyd.
Thanks, everyone. I appreciate the explainations in all their variety. It brings to mind something that my dad told me. He said "If you can't be smart, be funny." I've generally had to live by this advice, now more than ever in the face of such learned dissertations. I thought that I was just asking a humorous question, but apparently it more earth-moving than I realized.
- - - If the sun is a star, why can't I see it at night?
Will having all the people in India stamp their feet for those 9 minutes cancel the effect?
- - - If the sun is a star, why can't I see it at night?
I should have pointed out that the 5+ million Danes will only have to jump once. If you want a bunch of people jumping for the entire 520 seconds, you'll only need about 10,235 people, roughly the population of Satellite Beach, FL. (Thank you, Google)
The scheduled firing was scheduled for 8:00. I got to the gate around 7:00, and spent the next hour stuck in traffic along the five-mile stretch to the designated parking area. In that traffic jam, most of the lisence plates were from Mississippi and Louisiana. There were plenty from Alabama (70+ miles away), too many for them all to be military. There was even one from Ontario.
Upon reaching the parking area (where the people trying to organize parking ran out of designated space), I joined the crowd of 400-500 people waiting on about 4-5 busses (and I only saw one bus owned and operated by NASA). 8:00 came and went with no firing, and around 8:45 (still in line for a bus) somebody started moving through the crowd with a bullhorn saying something about "indefinately postponed" because of technical difficulties.
I can't really blame them for not expecting the turnout they got. I don't know how well the press release was covered in the Biloxi area, but I know that the bit barely got three paragraphs in some sidebar in New Orlean's Times-Picayune. I guess everybody wanted to get an up-close view of part of that thing that sets off everybody's car alarm whenever it comes in for a landing.
There's been no official word that I can see yet when they'll try again, and whether it will be public again or not.
All in all, anybody who think Americans don't care about their space program deserves to get smacked hard.