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SpaceX: “Close, but no cigar. This time”

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Re: SpaceX: “Close, but no cigar. This time”

#271

Post by lsaferite »

Crito wrote: post #131
lsaferite wrote: post #40

Earlier quoted context omitted.

Oh the confusion. Perhaps 'Nikola Tesla' would have been better.

More business sense than Tesla. Less in the way of personal technical/scientific achievements. He's not very popular on the internet for a variety of reasons, but I think that Edison is a better comparison. Not the first person I'd compare him to, but I'd sooner compare him to Edison than Tesla.

My point was using 'Tesla' in the same sentence as Elon Musk is ambiguous and mildly confusing in this case. I was saying the poster should have used Tesla's first name as well to remove confusion.

Re: SpaceX: “Close, but no cigar. This time”

#272

Post by [deleted] »

elif wrote: post #262
sillysaurus3 wrote: post #223

Earlier quoted context omitted.

Whoops, I see. Sorry for the confusion! That's an interesting idea, but are you sure that thermal expansion imparts enough force against 175 miles of steel in order to push it all the way to the station? 175 miles of steel would be incredibly heavy. It seems like the heating/cooling might even cause the steel to weaken enough such that, rather than rolling the tube towards the station, it would start to scrunch like…

forgive my amateur and completely unscientific postulation here, but is it possible that this conversation is moot seeing as normal train tracks do not have to extend at normal train stations, despite the rails being steel and continuous?

[deleted]

Re: SpaceX: “Close, but no cigar. This time”

#273

Post by schiffern »

elif wrote: post #262
sillysaurus3 wrote: post #223

Earlier quoted context omitted.

Whoops, I see. Sorry for the confusion! That's an interesting idea, but are you sure that thermal expansion imparts enough force against 175 miles of steel in order to push it all the way to the station? 175 miles of steel would be incredibly heavy. It seems like the heating/cooling might even cause the steel to weaken enough such that, rather than rolling the tube towards the station, it would start to scrunch like…

forgive my amateur and completely unscientific postulation here, but is it possible that this conversation is moot seeing as normal train tracks do not have to extend at normal train stations, despite the rails being steel and continuous?

Continuous steel rails do have problems with large temperature swings. See the link I posted about "sun kinks." They cause about 50 derailments per year. http://www.climatecentral.org/news/climate-change-warp-railr...

Rail lines have more curves which can take up that slack, and the positional tolerances are much more forgiving. Because of its high speed operation the hyperloop is both incredibly straight and incredibly sensitive to kinking.

Re: SpaceX: “Close, but no cigar. This time”

#274

Post by schiffern »

avmich wrote: post #164
SEJeff wrote: post #140

Earlier quoted context omitted.

Not sure what you're saying reflects reality. When Orbital Science's rocket recently exploded, Elon's words were nothing but polite: https://twitter.com/elonmusk/status/527247155954610176 And his comment on their rocket being the butt of a joke, using engines literally made in the 1960s and stored in Siberia were true. It is upsetting, but still not as surprising that they suffered catastrophic failure having such an…

> And his comment on their rocket being the butt of a joke, using engines literally made in the 1960s and stored in Siberia were true. That was quite misleading on Elon's side. Engines were manufactured in 1970's (I believe in 1973-1974) after quite an extensive RND program - actualy, remake of similar engines, NK-15, which weren't nearly as good. NK-33 engines were tested as perhaps no others of theirs caliber - wit…

>with tests like throwing metal chips (nuts?) into pumps

SpaceX did this test with the Merlin engines too. http://www.airspacemag.com/space/is-spacex-changing-the-rock...

The chamber pressure (and therefore Isp) are both dialed back for the sake of reusability. They're stated multiple times that they're not running those engines anywhere near their physical limits.

Re: SpaceX: “Close, but no cigar. This time”

#275

Post by 32faction »

shasheene wrote: post #258
32faction wrote: post #141

I feel if the 1st stage booster had an attitude control system toward the top like the BRAHMOS missile [1], the lean could've been corrected to at least have the rocket be upright when it impacted the platform. Although the choice to add an attitude control system would probably take up more space and add mass which is critical for a stage rocket. [1] http://i.imgur.com/5RWkvem.gif

The Falcon 9 does have attitude control system towards the top: the nitrogen cold gas thrusters in the Reaction Control System is located in the interstage portion of the vehicle - right at the top of the first stage The gimballing engines give attitude control at the bottom, as far as I understand

Nitrogen cold gas thrusters don't give enough "oomph". Maybe if the rocket was inclined at angles xBut I'm sure with the hydraulic fluid corrections a stronger control system won't be needed to fix large angles of attack but it would be nice to have as an emergency system.

"Have it and not need it/Need it don't Have it" really doesn't work with rockets because of the mass requirements

Re: SpaceX: “Close, but no cigar. This time”

#276

Post by avmich »

schiffern wrote: post #274
avmich wrote: post #164

Earlier quoted context omitted.

> And his comment on their rocket being the butt of a joke, using engines literally made in the 1960s and stored in Siberia were true. That was quite misleading on Elon's side. Engines were manufactured in 1970's (I believe in 1973-1974) after quite an extensive RND program - actualy, remake of similar engines, NK-15, which weren't nearly as good. NK-33 engines were tested as perhaps no others of theirs caliber - wit…

> with tests like throwing metal chips (nuts?) into pumps SpaceX did this test with the Merlin engines too. http://www.airspacemag.com/space/is-spacex-changing-the-rock... The chamber pressure (and therefore Isp) are both dialed back for the sake of reusability. They're stated multiple times that they're not running those engines anywhere near their physical limits.

It's certainly good that SpaceX uses many ways to test hardware, including those approaches successfully used before. During development of F-1 some interesting debugging techniques were invented, some could be well applied in SpaceX.

Gas generator cycle in general doesn't allow reaching effective Isp as high as closed loop cycle. On the other hand, smaller pressure reduces stress and generally considered safer. NK-15 were single use engines, but NK-33 and most other modern engines are all reusable.

Re: SpaceX: “Close, but no cigar. This time”

#277

Post by dlwj »

Someone1234 wrote: post #63
sixQuarks wrote: post #23

Sorry for sounding like such a fanboy, but during my 40 years on this earth, I have never been more impressed with a human being. The guy is pushing the envelope on perhaps the most difficult engineering/technological endeavor ever attempted by a private company - and he's making it look cool and futuristic. As if that wasn't enough, he's doing this in two different industries simultaneously. I'm not saying he can do…

> I'm not saying he can do no wrong, but I'm just flabbergasted that there are still so many armchair critics and naysayers when it comes to Elon Musk. That's why you're a fanboy. Nobody is perfect, and Elon Musk likes to make fun of the competition quite publicly when they have an issue, while ignoring his project's own failures. It is hard to even discuss the man on HN as anything that could even be taken as critic…

Imagine you need to cross a tightrope to do something amazing and everyone is afraid of heights.

Some forms of criticism are useful but yelling out "Hey, it's 2300 meters to the bottom, be careful!" is not very useful.

People often know the negatives, it's just easier to do the task when you don't look down. Often this requires self delusion. Otherwise "Don't look down, or think of white polar bears" would work for everyone.

Re: SpaceX: “Close, but no cigar. This time”

#278

Post by pbnjay »

32faction wrote: post #168
pbnjay wrote: post #147

Earlier quoted context omitted.

It does ( https://www.youtube.com/watch?v=DgLBIdVg3EM ), it just ran out of hydraulic fluid in this case.

Those are just grid fins which are used more for steering than attitude control. If I kick the rocket over those fins won't do any thing because they can't correct the force I applied to kick the rocket over. An active thruster (an attitude control system) can recorrect the force of my kick and reorient the rocket vertically.

How are you going to kick a rocket falling from outer space? You don't need active thrusters (and all the extra weight that comes with it) when gravity and wind will do the job for you just as well.

Re: SpaceX: “Close, but no cigar. This time”

#279

Post by 32faction »

pbnjay wrote: post #278
32faction wrote: post #168

Earlier quoted context omitted.

Those are just grid fins which are used more for steering than attitude control. If I kick the rocket over those fins won't do any thing because they can't correct the force I applied to kick the rocket over. An active thruster (an attitude control system) can recorrect the force of my kick and reorient the rocket vertically.

How are you going to kick a rocket falling from outer space? You don't need active thrusters (and all the extra weight that comes with it) when gravity and wind will do the job for you just as well.

> How are you going to kick a rocket falling from outer space?

I meant if there was some external force like a wind shear or grid fin/hydraulic line failure that pushes the rocket hard enough on descent to alter it's vertical orientation, those grid fins won't really do much to correct that force.

> Gravity and wind will do the job for you

You cannot control gravity or wind. You just have systems that manipulate those forces. Grid fins are a passive system in that they manipulate the fluid the rocket is in to steer it on course but not to correct drastic attitude alterations.

But again, if the updates to the hydraulic lines work out, then they won't need the active thruster system. Adding an active thruster system is just engineering for worst case scenarios.

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