SpaceX And/Or Rocketry In General

mikey
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RE: So yes, if your timing

Quote:


So yes, if your timing is good then much comes for free without extra effort.
:-)

Cheers, Mike.

Don't forget about all the 'stuff' orbiting around up there now too, they need to miss all of it on the way up and back too. I've always thought that would be a cool mission, go up grab stuff with an arm and redirect it into outer space, ie the Sun, or back to the Earth to burn up in re-entry. Clean up the junk and take out the trash so to speak.

Phil
Phil
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@Mike - Thanks for the

@Mike - Thanks for the detailed answer about the launch. You firmed up the garbled thoughts floating around in my brain housing group. I was on the right track, I just couldn't paint the picture.

@Mikey - I'm picturing a recycling truck with retros on the back end...maybe AnnieT can make us a picture when she gets back.

The fact that the rocket actually hit the target ship with a disabled guidance fin tells me SpaceX has a heck of a system on their hands. Like Mike posted earlier, I'm really starting to like this Elon guy. Anybody with that much money who cracks jokes after losing millions to a RUD is cool in my book. I can't wait to see what they do in the future.

Phil

tullio
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On Jan 29 they should launch

On Jan 29 they should launch the DSCOVR (GoreSAT) observatory towards a Lagrange point and then attempt the rocket landing.
Tullio

Mike Hewson
Mike Hewson
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What comes to my mind is the

What comes to my mind is the old English idiom about not being shy in expense when waterproofing boat hulls :

Quote:
Spoil the ship for a ha'pworth of tar


and John Glenn's absolute gem :

Quote:
I guess the question I'm asked the most often is: "When you were sitting in that capsule listening to the count-down, how did you feel?" Well, the answer to that one is easy. I felt exactly how you would feel if you were getting ready to launch and knew you were sitting on top of two million parts -- all built by the lowest bidder on a government contract.


I don't think for a moment that Elon and SpaceX have that approach to safety, but it's a reminder about that mythical 20c part that fails, for want of a nail a shoe was lost etc.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

mikey
mikey
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RE: What comes to my mind

Quote:
What comes to my mind is the old English idiom about not being shy in expense when waterproofing boat hulls :
Quote:
Spoil the ship for a ha'pworth of tar

and John Glenn's absolute gem :

Quote:
I guess the question I'm asked the most often is: "When you were sitting in that capsule listening to the count-down, how did you feel?" Well, the answer to that one is easy. I felt exactly how you would feel if you were getting ready to launch and knew you were sitting on top of two million parts -- all built by the lowest bidder on a government contract.

I don't think for a moment that Elon and SpaceX have that approach to safety, but it's a reminder about that mythical 20c part that fails, for want of a nail a shoe was lost etc.

Cheers, Mike.

I would bet Elon Musk IS as concerned about cash flow as any other businessman, and watches every penny he spends just like the rest of us. Sure he has more pennies to spend, but spending 300 million dollars on a part he could get for 100 million dollars would not be his better choice. Meaning he is STILL doing it on the lowest bid basis! Now HOPEFULLY his 'minimum specs' are MUCH higher than Nasa, a government agency, had to deal with as it's HIS dollars being spent not everyone elses. HOPEFULLY when he identifies a problem he doesn't say' it's okay we will deal with it as it is' he instead says 'take the time to do it right', as that's what private money CAN do. And yes I'm sure he has financial backers, the key is how much say they have in the spending process, too much and we are back to the "for want of a nail a shoe was lost etc."

robl
robl
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RE: RE: What comes to my

Quote:
Quote:
What comes to my mind is the old English idiom about not being shy in expense when waterproofing boat hulls :
Quote:
Spoil the ship for a ha'pworth of tar

and John Glenn's absolute gem :

Quote:
I guess the question I'm asked the most often is: "When you were sitting in that capsule listening to the count-down, how did you feel?" Well, the answer to that one is easy. I felt exactly how you would feel if you were getting ready to launch and knew you were sitting on top of two million parts -- all built by the lowest bidder on a government contract.

I don't think for a moment that Elon and SpaceX have that approach to safety, but it's a reminder about that mythical 20c part that fails, for want of a nail a shoe was lost etc.

Cheers, Mike.

I would bet Elon Musk IS as concerned about cash flow as any other businessman, and watches every penny he spends just like the rest of us. Sure he has more pennies to spend, but spending 300 million dollars on a part he could get for 100 million dollars would not be his better choice. Meaning he is STILL doing it on the lowest bid basis! Now HOPEFULLY his 'minimum specs' are MUCH higher than Nasa, a government agency, had to deal with as it's HIS dollars being spent not everyone elses. HOPEFULLY when he identifies a problem he doesn't say' it's okay we will deal with it as it is' he instead says 'take the time to do it right', as that's what private money CAN do. And yes I'm sure he has financial backers, the key is how much say they have in the spending process, too much and we are back to the "for want of a nail a shoe was lost etc."

Elon Musk has already demonstrated his commitment to quality. While I am sure he like anyone else carefully monitors expenses he is not going to do so at the risk of reliability. He wants that contract. He wants a Mars mission. An example of cost cutting at the expense of reliability was the failed resupply launch off the Virginia coast. Musk laughed at his competitors decision to use Russian engines to save money. There is no savings in "unreliability" and the Russian engines were known to be less than sterling. This guy is a genius and it will show in his results.

Mike Hewson
Mike Hewson
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As for : RE: (b) The

As for :

Quote:
(b) The Dragon's final approach to the ISS is from below in stages along 'r-bar' ie. the vector from the centre of the Earth to the ISS. To get the Dragon to go precisely along r-bar toward the station why is the thrust to achieve that not along the line of r-bar ?


There are a number of equivalent ways to explain this. I'll go classical and describe matters from the point of view of a distant observer. Alas many explanations freely mix reference frames, as they are known, without signalling the switches in such context.

While the craft are in free fall in a ( near ) vacuum, they are not in free space. There's this big planet next to them. A craft nearer to the Earth will have a ( slight but noticeable ) greater attraction to the planet, per unit of craft mass, than the further away one. This is due of course to the inverse ( square ) nature of gravity, as per Newton. If F = ma is solved for a craft then provided no-one is firing thrusters the inner craft will orbit quicker than the outer one. This gives the general rule that if you want to 'catch up' in orbit you go low, if you want to 'dawdle' you go high. For instance the ISS has an orbital period of ~ 90 minutes whereas the Moon has an orbital period of a Moonth ... :-)

[ A good 'magic' figure to remember is 7 km/sec - with respect to Earth's surface - that being the minimum speed to get into any orbit at all. This is regardless of the craft's mass. Even if you use the catapult effect from the Earth's surface - best at the equator evidently - you'll only get 0.5 km/sec at most for your trouble. Which is still worth seeking eg. the preference for equatorial launch sites, and initial easterly headings for that matter. It also explains why we all don't fly off the Earth's surface, unaided. Fortunately. Orbits around Earth have a lower limit on their radius ~ 6400 km, otherwise you hit the planet's surface !! This also suggests a hint on how to get back down ie. lose speed ... ]

Now when we have labels like 'low' and 'high' the implication is an energy one. Potential energy, or gravitational potential energy in this scenario. You know this in everyday life : if you jump off something you will speed up as you fall. We describe this by saying that you have 'stored up' potential energy when you climbed up ( the tree or whatever ) and got that back again later as kinetic energy on the way down. This is true for Dragon and ISS too. When the Dragon's thrusters are fired to go towards the ISS then not all of the energy thus expended ( strictly speaking it is the kinetic energy of the recoiling fuel that I refer to as being 'spent' here ) goes into Dragon's kinetic energy ie. speed. Some of it goes into 'climbing up'.

These considerations of orbital speed and potential energy are still very much in play, certainly are not trivial, over the distance of several hundred meters of separation. It is only when the objects are very close and/or are considered over short time periods that one can successfully approximate by pretending the Earth isn't there. But it is all a matter of degree.

Punchline : if the thrust was directed purely along a radial line then the Dragon would go higher but then lag the ISS ie. come in to the same orbital path as the ISS but behind wrt the direction of orbit. That's not what we want for hatches to align etc. So you have to spend a bit of thrust in the 'onwards' sense of the orbit in order to arrive at the ISS ie. same height above Earth with speed matching.

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

mikey
mikey
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RE: For instance the ISS

Quote:

For instance the ISS has an orbital period of ~ 90 minutes whereas the Moon has an orbital period of a Moonth ... :-)

Cheers, Mike.

COOL a new definition to use, a "Moonth" equals the time it takes the Moon to circle the Earth!

David S
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Mikey wrote:Don't forget

Mikey wrote:
Don't forget about all the 'stuff' orbiting around up there now too, they need to miss all of it on the way up and back too. I've always thought that would be a cool mission, go up grab stuff with an arm and redirect it into outer space, ie the Sun, or back to the Earth to burn up in re-entry. Clean up the junk and take out the trash so to speak.


Phil wrote:
@Mikey - I'm picturing a recycling truck with retros on the back end...maybe AnnieT can make us a picture when she gets back.


That gives me an idea for a terrorist plot, if not in real life then at least in a cheesey sci-fi movie.

Rogue nation/terrorist organization launches a rocket into the descent path from ISS, then announces that if the good guys (government of the US/UK/EU/ESA, etc.) don't pay a zillion dollars or release all the prisoners from Gitmo or whatever, it will disperse a miles-wide cloud of sharp metal shards that they can't fly through without catastrophic damage. To increase the sense of urgency, throw in a deadline (crew is running out of oxygen or something and only has a few days before they MUST return, or one of them has been injured somehow and needs to come down for surgery). I can see two possible endings: either the good guys create and deploy (on impossibly short notice) Phil's recycling truck (probably requiring the irreplaceable expertise of a couple of reluctant retired guys a la Space Cowboys), or they kill the bad guy a split second before he pushes the button that commands the rocket to blow (what James Bond would do).

[edit]
I just came across this article on the subject.

David

Miserable old git
Patiently waiting for the asteroid with my name on it.

robl
robl
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Musk just got a $Billion from

Musk just got a $Billion from Google and Fidelity.

He also announced a new project aimed at putting up to 4,000 satellites into low Earth orbit to provide low-cost Internet access.

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