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#4220297 - 01/22/16 05:53 PM SpaceX Propulsive Landing Test  
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"In the vast library of socialist books, there’s not a single volume on how to create wealth, only how to take and “redistribute” it.” - David Horowitz
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#4220302 - 01/22/16 06:00 PM Re: SpaceX Propulsive Landing Test [Re: F4UDash4]  
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And for those that missed this from last year, an abort test:



"In the vast library of socialist books, there’s not a single volume on how to create wealth, only how to take and “redistribute” it.” - David Horowitz
#4220308 - 01/22/16 06:04 PM Re: SpaceX Propulsive Landing Test [Re: F4UDash4]  
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I take it that's the crew capsule? I'm familiar with the capsule ejection on the Saturn rockets but what's the purpose of hover flight? It makes sense from a learning opportunity perspective but parachutes seem to work pretty well for recovery.


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#4220316 - 01/22/16 06:16 PM Re: SpaceX Propulsive Landing Test [Re: F4UDash4]  
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That is the landing system, so that they don't have to splash down and be recovered from the ocean. In theory, it makes turn-around faster and cheaper.


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#4220318 - 01/22/16 06:19 PM Re: SpaceX Propulsive Landing Test [Re: Peally]  
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Originally Posted By: Peally
I take it that's the crew capsule? I'm familiar with the capsule ejection on the Saturn rockets but what's the purpose of hover flight? It makes sense from a learning opportunity perspective but parachutes seem to work pretty well for recovery.



The hover is to test controllability of the engines thrust which will be important later in landing the spacecraft with those engines, without using the parachute.


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#4220331 - 01/22/16 06:53 PM Re: SpaceX Propulsive Landing Test [Re: F4UDash4]  
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If it's a "Propulsive Landing test" shouldn't there be a landing? That was a "slowly stretch out the rope on which you're suspended" test. The thing drifted as it was coming down and that makes for a less than wonderful landing, as anyone who flies drones will tell you. If the upper portion of an object is still being acted on by the wind while its bottom is in contact with the ground, as is the case when an object is transitioning from hovering to landed, it can topple very easily. and the taller and more slender the object the easier it is.

Once again, this looks more like false propaganda: "Look what we can do...(under strictly controlled, not real world situations)." And it's something that's been done before. I believe the vast majority (if not all) of the Soviet Union's spacecraft landed on the ground using a combination of parachutes and timed retro-rockets. Color me unimpressed.


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#4220334 - 01/22/16 06:56 PM Re: SpaceX Propulsive Landing Test [Re: vonBaur]  
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Originally Posted By: vonBaur
If it's a "Propulsive Landing test" shouldn't there be a landing? That was a "slowly stretch out the rope on which you're suspended" test. The thing drifted as it was coming down and that makes for a less than wonderful landing, as anyone who flies drones will tell you. If the upper portion of an object is still being acted on by the wind while its bottom is in contact with the ground, as is the case when an object is transitioning from hovering to landed, it can topple very easily. and the taller and more slender the object the easier it is.

Once again, this looks more like false propaganda: "Look what we can do...(under strictly controlled, not real world situations)." And it's something that's been done before. I believe the vast majority (if not all) of the Soviet Union's spacecraft landed on the ground using a combination of parachutes and timed retro-rockets. Color me unimpressed.

Wow, tough crowd smile

The difference between this and what the Russians do is that the Russians use parachutes and then fire retro rockets at the very end to soften the impact. This is designed to actually lower the craft in a controlled fashion, all the way to the ground, so whereas the Russian rockets just fire downward, these provide steering and control.

As far as the test goes, it wasn't much, but you have to walk before you can run.


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#4220335 - 01/22/16 06:58 PM Re: SpaceX Propulsive Landing Test [Re: vonBaur]  
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Originally Posted By: vonBaur
If it's a "Propulsive Landing test" shouldn't there be a landing?



At some point there will be. This was, as I stated above, a test of controlability of the engines thrust, a necessary step before you go dropping the craft from 25,000 feet to see if it works.


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#4220337 - 01/22/16 07:00 PM Re: SpaceX Propulsive Landing Test [Re: F4UDash4]  
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And what the Russians do with Soyuz is NOTHING like this. The Russians simply set off some solid rocket motors about s econd before touchdown. The Dragon will land on rocket power alone.




"In the vast library of socialist books, there’s not a single volume on how to create wealth, only how to take and “redistribute” it.” - David Horowitz
#4220345 - 01/22/16 07:14 PM Re: SpaceX Propulsive Landing Test [Re: F4UDash4]  
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So you use nearly...maybe more, I don't know the exact physics but it has to be a lot...as much fuel to bring it all the way down like that as you do to lift off. All that fuel has to be carried with you on blastoff and that decreases the potential payload weight. Now think of the weight savings of a few High-performance parachutes to slow descent passively to a specific rate at a specific altitude, steering all the while, and then fire the rockets for the last hundred or so feet (just tossing out an altitude...make it 3,000 if you want, my point is the same).

Don't get me wrong, it looks cool and I'd love to watch one live. And reusing as much as you can is obviously a much better idea than building/buying a new one every time . I'm just not convinced this is the way to go.


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#4220347 - 01/22/16 07:19 PM Re: SpaceX Propulsive Landing Test [Re: F4UDash4]  
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Let's talk about why this is important - commercial viability.

If we're going to put Joe Public in space he's not going to want to be brought down to earth under a chute into the ocean or a chute and then a big BANG at the end with a "little bump."

If part of a mission including being full on tased for two minutes, astronauts would describe it as "little jolt of electricity."

Joe Public (okay, Joe Millionaire) wants to be brought back to Earth gently in a predictable spot (within 100 yards of the announced location) and on time. Showing up back home with a fanfare of rocket fire and roar is a plus, naturally.

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#4220353 - 01/22/16 07:38 PM Re: SpaceX Propulsive Landing Test [Re: vonBaur]  
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Originally Posted By: vonBaur
So you use nearly...maybe more, I don't know the exact physics but it has to be a lot...as much fuel to bring it all the way down like that as you do to lift off.


No, not at all. Two reasons:

1- the mass coming down is a tiny fraction of that lifting off and therefore requires much less energy to slow from 17500 mph than to get the much larger mass up to 17500 mph

2 - the vast majority of the slowing down from 17500 mph to 0 is done by the friction of the atmosphere on the spacecraft during re-entry. If no propulsive or parachute braking were done at all the space craft would impact at earth at only a few hundred mph, the parachutes / engines only have to counter THAT residual velocity

Of course there is a small amount of thrust needed to slow the spacecraft from orbital velocity just enough to begin re-entry but that is marginal



"In the vast library of socialist books, there’s not a single volume on how to create wealth, only how to take and “redistribute” it.” - David Horowitz
#4220361 - 01/22/16 07:55 PM Re: SpaceX Propulsive Landing Test [Re: vonBaur]  
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Originally Posted By: vonBaur
So you use nearly...maybe more, I don't know the exact physics but it has to be a lot...as much fuel to bring it all the way down like that as you do to lift off. All that fuel has to be carried with you on blastoff and that decreases the potential payload weight. Now think of the weight savings of a few High-performance parachutes to slow descent passively to a specific rate at a specific altitude, steering all the while, and then fire the rockets for the last hundred or so feet (just tossing out an altitude...make it 3,000 if you want, my point is the same).

Don't get me wrong, it looks cool and I'd love to watch one live. And reusing as much as you can is obviously a much better idea than building/buying a new one every time . I'm just not convinced this is the way to go.


You forget that those very same rockets are also used for the launch escape system, so they would have to be carried anyway. Also, it's pretty impressive that they can be throttled from 100% all the way down to 20% thrust, and restarted multiple times.
They also need a way to land heavy objects on Mars, which is their longterm goal, where parachutes aren't all that effective due to the thin atmosphere.


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#4220381 - 01/22/16 08:58 PM Re: SpaceX Propulsive Landing Test [Re: F4UDash4]  
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I didn't say I wasn't impressed. Ok, I did, but that wasn't about the power and precision, but rather about the usefulness of the exercise. We've (humans, not me and you in particular) managed to hit a moving target that's however far away Pluto is within probably meters of deadon. And how far away and how big was that asteroid? That's more impressive than this, from an engineering/technical aspect, IMO (see Annoying Words and Phrases thread).

Ummm, what exactly is your frame of reference for an estimated "few hundred mph"? Gravitational acceleration is a constant, terminal velocity is not. A few years ago a guy jumped from a helium balloon at only 128,000 feet...the edge of space...and went supersonic within a minute. And that was from a stationary platform. This thing will already be going at orbital speeds when it starts its descent and it's much more streamlined than a human being in a stable freefall position. How do you figure its terminal velocity will be only a few hundred mph? And the amount of energy needed to slow something that massive from that speed is going to be significant. And that energy requires fuel that has to be lifted off, thus impacting the potential payload weight.

Which brings me to Dachs. Please reread what I posted and you quoted. I didn't say anything about the rockets, only the fuel.

You want a gentle, precise landing in a reusable package? Two words...Space Shuttle.


*edit*
Let me clarify.
Manned...shuttle or shuttle-like.
Unmanned...how about parachutes and bubble-wrap, like they've been doing for years with the Mars rovers?

Last edited by vonBaur; 01/22/16 09:03 PM.

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#4220397 - 01/22/16 09:38 PM Re: SpaceX Propulsive Landing Test [Re: F4UDash4]  
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Well, a launch escape system needs fuel too, likely not as much though of course..
I'm pretty sure this is aimed at manned spaceflight, and at putting humans on Mars in particular. I don't think shuttle type vehicles would work on Mars?

This is really just the first part of that development, so instead of spending a lot of resources building and inventing stuff that only works here on earth, they're going for something usable for soft landings on Mars from the start.
At least that is my understanding of the longterm plans of SpaceX..
Anyway, no matter what, all this competition and new stuff happening in the space business is damn cool to be a witness to!


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#4220398 - 01/22/16 09:42 PM Re: SpaceX Propulsive Landing Test [Re: F4UDash4]  
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And it's redundancy. The same rockets used for launch abort safety are are capable of softening touchdown during a Soyuz style parachute landing. And as demonstrated with this test, capable of providing a direct-to-pad powered landing.


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#4220404 - 01/22/16 09:59 PM Re: SpaceX Propulsive Landing Test [Re: F4UDash4]  
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Wow, Dachs, two liftoffs and two powered landings. This is going to take more and more fuel all the time. If I ever do hit the lottery I'm going to sink the money into a space refueling station. My income will be out-of-this-world, in more ways than one. wink

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Already done, except for actually testing an aborted liftoff.


I'm just saying that, while it's cool, I'm not sure they've taken any real first-steps, here.

Years ago, before it became known that Will Hayden was a child-molester, I used to watch "Sons of Guns". Watched it from the first, half-hour episodes through all the "drama" episodes. One time Will got hold of a Lewis machine gun (belt-fed, not drum-fed). He decided he was going to try to synchronize its firing to a simulated propeller, "to see if it could be done". Uh, Will...it was...a hundred years ago. This just strikes me the same way. Lots of publicity for being the...what, fourth or fifth or more...person to do this.


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#4220418 - 01/22/16 10:44 PM Re: SpaceX Propulsive Landing Test [Re: F4UDash4]  
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vonBaur, While this test didn't demonstrate anything new, I think the idea of landing a spacecraft on Earth without a parachute at all is new, so they are working on something that hasn't really been done before.

The Space Shuttle had its own issues, and was incredibly expensive, and while a smaller version could be (and is being) developed, it has its own issues (two were lost, and any winged vehicle has structural overhead that may add weight that doesn't contribute to payload hauling, similar to the fuel in this case).

Coming down with a parachute is fairly imprecise, and landing with wings requires a runway - thrusters can address both issues because the spacecraft won't drift in the wind and lands vertically. They get that flexibility and cost savings and convenience by carrying a little more fuel than is needed for just the emergency system.


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#4220438 - 01/22/16 11:57 PM Re: SpaceX Propulsive Landing Test [Re: vonBaur]  
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Originally Posted By: vonBaur
I didn't say I wasn't impressed. Ok, I did, but that wasn't about the power and precision, but rather about the usefulness of the exercise.



It is useful in that it brings spaceflight a step closer to "routine". How useful would airliners be if they could only land in an ocean or lake via parachute and the passengers had to be retrieved by naval task force ala the Apollo days?


Originally Posted By: vonBaur
Ummm, what exactly is your frame of reference for an estimated "few hundred mph"? Gravitational acceleration is a constant, terminal velocity is not. A few years ago a guy jumped from a helium balloon at only 128,000 feet...the edge of space...and went supersonic within a minute.


Yes, while he was still very high in very thin atmosphere. Had he continued his free fall he would have slowed down due to increased air resistance.

Keep in mind the Dragon spacecraft, like all capsule type manned spacecraft and unlike a head down streamlined skydiver trying to break a speed record, is designed to maximize drag on re-entry.


Originally Posted By: vonBaur
And the amount of energy needed to slow something that massive from that speed is going to be significant. And that energy requires fuel that has to be lifted off...



Again, no. The spacecraft deorbits by firing the retro rockets on the service module portion of the Dragon spacecraft, not the landing rockets demonstrated in the video. All that is required is a short burn that lowers the periapsis of the orbit such that it intersects Earths atmosphere, then the atmospheric drag does the rest down to terminal velocity which as I have already explained is very low for a high drag body like a blunt spacecraft.

So the retro firing slows the spacecraft by ~100mph, the landing rockets slow it from a terminal velocity of less than 500mph to zero. The remaining ~16900 mph (17500 orbital velocity minus 600) is taken care of by atmospheric drag.


Originally Posted By: vonBaur
... thus impacting the potential payload weight.


Wrong again because it is a NASA requirement that every manned spacecraft has to have a launch escape system, the Superdraco rockets on Dragon serve that purpose. In other words they have to have that weight anyway but on Dragon it serves two purposes rather than one.

Your argument is like saying it is better to belly land aircraft on snow or in water rather than have landing gear and all the associated hydraulics etc because those things cut into the payload the aircraft can carry.

Originally Posted By: vonBaur
You want a gentle, precise landing in a reusable package? Two words...Space Shuttle.



You don't want to carry fuel to land with because it cuts into payload but you want to carry two gigantic wings that weigh much more that that fuel (which also serves the launch abort function as already mentioned, which wings can't)?


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#4220441 - 01/23/16 12:10 AM Re: SpaceX Propulsive Landing Test [Re: Arthonon]  
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Originally Posted By: Arthonon
vonBaur, While this test didn't demonstrate anything new, I think the idea of landing a spacecraft on Earth without a parachute at all is new, so they are working on something that hasn't really been done before.


It isn't a new concept. Americans landed on the Moon six times with only rocket power in exactly the same manner (other than not having any atmosphere to aid in the deceleration process) over 40 years ago.

But it is new for SpaceX. If you intend to land a human carrying spacecraft back on earth using nothing but rocket power you need to test it. That's what this video is about. They can't say "Oh it's been done before I'm sure it will work". No one else is doing this, no one else has ever done this for returning to earth from space.


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