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Ira
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Re: SpaceX Grasshopper Sets Record new [Re: keithccr]
      #5821433 - 04/25/13 08:03 AM

It's more than just that. The whole scene looks uber real, too real to be real. Also the angle it was shot at adds to the sense of "animation". It was partially shot from above. How'd they do that?

/Ira


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Centaur
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Reged: 07/12/04

Loc: Chicago
Re: SpaceX Grasshopper Sets Record new [Re: Ira]
      #5821662 - 04/25/13 09:50 AM

Quote:

It's more than just that. The whole scene looks uber real, too real to be real. Also the angle it was shot at adds to the sense of "animation". It was partially shot from above. How'd they do that?





The camera was on a hexacopter, which is a tiny remote controlled helicopter: http://hexacopters.com


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deSitter
Still in Old School


Reged: 12/09/04

Re: SpaceX Grasshopper Sets Record new [Re: Centaur]
      #5821775 - 04/25/13 10:51 AM

The shadow lines of the rocket and the water tower should, and do, intersect on the horizon. That's near certain proof that this is real. It's just good video

I still do not understand what good will come of such a vehicle.

-drl


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Centaur
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Re: SpaceX Grasshopper Sets Record new [Re: deSitter]
      #5821887 - 04/25/13 11:50 AM

Quote:


I still do not understand what good will come of such a vehicle.





Did you read what I wrote in my third post in this thread?


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llanitedave
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Re: SpaceX Grasshopper Sets Record new [Re: Centaur]
      #5822411 - 04/25/13 03:17 PM

Quote:

Quote:


I still do not understand what good will come of such a vehicle.





Did you read what I wrote in my third post in this thread?




It's a pretty simple concept. As Musk said, "You don't throw away a brand new 747 after every flight."


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Ira
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Re: SpaceX Grasshopper Sets Record new [Re: llanitedave]
      #5823043 - 04/25/13 08:40 PM

I think Danny doesn't believe we're going anywhere soon.

/Ira


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seryddwr
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Reged: 02/19/10

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Re: SpaceX Grasshopper Sets Record new [Re: llanitedave]
      #5823439 - 04/26/13 12:25 AM

Quote:

Quote:

Quote:


I still do not understand what good will come of such a vehicle.





Did you read what I wrote in my third post in this thread?




It's a pretty simple concept. As Musk said, "You don't throw away a brand new 747 after every flight."



Wait... You mean I've been doing it wrong all this time?! I'd better cancel my next 20 orders with Boeing.


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David Knisely
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Re: SpaceX Grasshopper Sets Record new [Re: deSitter]
      #5823512 - 04/26/13 02:09 AM

deSitter posted:

Quote:

I still do not understand what good will come of such a vehicle.




Uh, like maybe figuring out how to re-use a costly booster by seeing if you can fly it back to the launch site? What is so hard to understand about that?

"The 60's weren't good to you, were they?" (Sarge from the movie CARS)


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Shadowalker
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Re: SpaceX Grasshopper Sets Record new [Re: David Knisely]
      #5823584 - 04/26/13 04:36 AM

The obvious disadvantage is that having the booster land under its own power requires propellant that won't be available to lift the payload. However, there is usually extra margin for most payloads. Also, the returning booster hasn't all the mass of the upper stage and payload and the spent propellant to lift. I haven't run any numbers, but I'd make a SWAG that returning to launch site or other recovery area would need about 15 to 20% of the propellant.

A tradeoff. Sacrifice some payload mass to recover a 150 million dollar booster? Worth it, I'd say.


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Centaur
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Re: SpaceX Grasshopper Sets Record new [Re: Shadowalker]
      #5824021 - 04/26/13 10:29 AM

Quote:

The obvious disadvantage is that having the booster land under its own power requires propellant that won't be available to lift the payload. However, there is usually extra margin for most payloads. Also, the returning booster hasn't all the mass of the upper stage and payload and the spent propellant to lift. I haven't run any numbers, but I'd make a SWAG that returning to launch site or other recovery area would need about 15 to 20% of the propellant.

A tradeoff. Sacrifice some payload mass to recover a 150 million dollar booster? Worth it, I'd say.




Of course gravity and not thrusting does the lowering, while atmospheric friction slows a falling object to its terminal velocity. For a person that is about 120 mph, and I imagine less for a nearly empty rocket. So the braking thruster only needs to become activated near the end of the descent.


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Jarad
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Reged: 04/28/03

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Re: SpaceX Grasshopper Sets Record new [Re: Centaur]
      #5824053 - 04/26/13 10:37 AM

From the video, I suspect it will need to be thrusting continuously to maintain attitude control. I think if it cut thrust completely and fell at terminal velocity it would probably start tumbling, then resuming controlled thrust would be difficult.

Maybe in combination with some drag chutes or something...

It was impressive how it maintained balance on top of just a single engine.

Jarad


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llanitedave
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Re: SpaceX Grasshopper Sets Record new [Re: Shadowalker]
      #5826244 - 04/27/13 12:42 PM

Quote:

The obvious disadvantage is that having the booster land under its own power requires propellant that won't be available to lift the payload. However, there is usually extra margin for most payloads. Also, the returning booster hasn't all the mass of the upper stage and payload and the spent propellant to lift. I haven't run any numbers, but I'd make a SWAG that returning to launch site or other recovery area would need about 15 to 20% of the propellant.

A tradeoff. Sacrifice some payload mass to recover a 150 million dollar booster? Worth it, I'd say.




I think what I'm reading is that they're looking at about a 40% performance hit for re-usability, but I think that includes the second stage as well. If each stage can be re-used 10 or more times with a minimum of refurbishment (gas and go, more like an airliner than the Space Shuttle), that will lead to a huge reduction in launch costs.

And if they have a customer that absolutely requires maximum payload capacity, then they can use an end-of-life stage for that particular launch and expend it. They can charge a premium for that flight while still undercutting the expendable-only competition.


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llanitedave
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Re: SpaceX Grasshopper Sets Record new [Re: Jarad]
      #5826248 - 04/27/13 12:44 PM

Quote:

From the video, I suspect it will need to be thrusting continuously to maintain attitude control. I think if it cut thrust completely and fell at terminal velocity it would probably start tumbling, then resuming controlled thrust would be difficult.

Maybe in combination with some drag chutes or something...

It was impressive how it maintained balance on top of just a single engine.

Jarad




I believe the re-usable booster will have cold gas thrusters at the top for stability control.


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GlennLeDrew
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Re: SpaceX Grasshopper Sets Record new [Re: llanitedave]
      #5837963 - 05/03/13 10:05 AM

Might not gyroscopes be installed in any recoverable stage so as to control, or facilitate control of attitude?

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llanitedave
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Reged: 09/26/05

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Re: SpaceX Grasshopper Sets Record new [Re: GlennLeDrew]
      #5838013 - 05/03/13 10:31 AM

Each stage would have to have its own avionics system.

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Jarad
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Reged: 04/28/03

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Re: SpaceX Grasshopper Sets Record new [Re: GlennLeDrew]
      #5838023 - 05/03/13 10:33 AM

I'm sure they have gyroscopes, but the gyro's usually just measure the attitude, you still need thrusters or something to control it.

I couldn't see any thrusters at the top in the video, but they could have been there and just not visible compared to the brightness of the main thruster. I just assumed that they were controlling it with fine adjustments to the main thruster, but I don't actually know that to be the case... Maybe one of the JPL guys knows?

Jarad


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llanitedave
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Re: SpaceX Grasshopper Sets Record new [Re: Jarad]
      #5838036 - 05/03/13 10:37 AM

From what I understand the current Grasshopper has no thrusters, its attitude control comes only from engine gimbaling. Grasshopper 2 will need them, because it will experiment with shutting off and relighting its engine during free fall.

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Ravenous
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Reged: 11/14/09

Loc: UK
Re: SpaceX Grasshopper Sets Record new [Re: llanitedave]
      #5838262 - 05/03/13 12:23 PM

Aerodynamic braking for a part-empty rocket stage with the engines shut down... that would be an interesting problem. There would probably be a quarter or so of the fuel sloshing around in the tanks, the off-centre weight would make attitude control tricky, unless they either use a big drogue chute or a "don't care" attitude.

Having said that perhaps the stage return and landing could be done with an extra, central, fuel & oxidiser tank. Extra complexity but would allow a separate pressurisation system as well as better control of balance.

Not saying aero braking is what they plan to use (because I don't know) but it's an interesting idea, and an interesting problem...


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Whichwayisnorth
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Loc: Southern California
Re: SpaceX Grasshopper Sets Record new [Re: Ravenous]
      #5843848 - 05/06/13 03:43 PM

You folks are acting like they don't already know what they are doing and how they are going to do it. This isn't just "hey wouldn't it be cool if" and "lets do some experiments to see if". This is "we are doing this so step aside".

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Jarad
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Re: SpaceX Grasshopper Sets Record new [Re: Whichwayisnorth]
      #5843908 - 05/06/13 04:19 PM

And this is us speculating about how they are planning to do it.

We don't expect them to listen to us or change what they are doing, but it's both fun for us to speculate about it, and occasionally some of the guys who are rocket scientists read this and enlighten us about what they are actually doing.

As for the "let's do some experiments to see if", the video in the OP was one of those experiments. The rest of the thread is us speculating about what's next in their plan, and how it would be used in a real launch.

As far as stepping aside, we're already standing on the side, we're just cheering them on.

Jarad


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