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SpaceX Grasshopper Flies High

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Re: SpaceX Grasshopper Flies High

#121

Post by bfe »

InclinedPlane wrote: post #63
TeMPOraL wrote: post #52

Earlier quoted context omitted.

> highly likely that the rocket will get damaged And because you don't know whether it is damaged or not (sometimes the damage may not be obvious), it's likely that the rocket will have to get a long post-flight inspection to check if it is suitable for another flight. It's something you can almost completely avoid if you land the rocket gently. I read somewhere, that the costs of recovering SRBs of Space Shuttle fro…

The SRB thing isn't true. The costs ended up being pretty much the same for new vs. refurbed. The thing is, with solid boosters the "rocket engine" tends to just be giant aluminum cylinders, almost all the complexity of the job is in casting the fuel and putting the segments together, which is completely orthogonal to the reusability aspects. Also, part of the allure of SRBs is that they are cheap to manufacture, com…

The SRBs don't just impose higher operational complexity, but also far higher acoustic load that requires much higher structural strength and therefore weight on everything else.

Re: SpaceX Grasshopper Flies High

#122

Post by jlgreco »

InclinedPlane wrote: post #62
stuff4ben wrote: post #37

Earlier quoted context omitted.

I thought the same thing. One of the Youtube commentswas pretty insightful in that it mentioned that when you do a parachute landing into the ocean, it's landing in salt water. Therefore the craft has to be taken apart inspected, cleaned, and put back together. So I'm assuming they've done the cost benefits and figured it's cheaper this way. I wonder if a combination parachute/thruster landing would be more feasible…

Perhaps on Mars, unlikely on Earth. With our dense atmosphere a vehicle like a mostly empty Falcon 9 first stage is going to have a fairly low terminal velocity, in the low hundreds of km/s range. Slowing down from that speed to a controlled hover/landing is pretty easy. The cost/benefit on Mars might be different though, since the atmosphere is thinner.

> in the low hundreds of km/s range

I think you might mean m/s? low hundreds of km/s is very supersonic. ;)

Re: SpaceX Grasshopper Flies High

#123

Post by Laremere »

jordan0day wrote: post #75
deepblueocean wrote: post #25

Earlier quoted context omitted.

I find this confusing. It's awesome, that's for sure. But it seems like lifting all the fuel needed to do a soft landing is inherently a tradeoff for less payload capacity. What is the benefit, then? Is it just so much cheaper to be able to re-use the first two stages?

I imagine there's a lot less fuel required to land than is required to take off. That is, on launch, the rocket is probably (eventually) reaching speeds of several thousand miles per hour. Upon landing, the atmosphere does most of the slowing-down for you, so you only need enough fuel to reduce the speed from terminal velocity (not sure what this would be for a rocket, probably several hundred miles an hour, at least…

Two other points to consider:

Atmosphere is slowing you down as you go up as well, so lift off requires fighting that as well. Therefore the energy you've expended is not entirely stored in potential energy. (Fun fact: If it weren't for the atmosphere, rockets would actually take off almost horizontally. They go up at first to get out of the thickest air before going sideways.)

The craft is much lighter, because it no longer has the payload, and also has used almost all of its fuel.

Re: SpaceX Grasshopper Flies High

#124

Post by jlgreco »

_mulder_ wrote: post #109

So what's the big water tower for in the background?

Probably water. ;)

Maybe for fire-fighting? Seems a little close for that though, if something went wrong it could be in the middle of it. I can't think of anything else though.

Edit: Maybe it feeds some sort of un-manned fire suppression system? That would be pretty smart.

Re: SpaceX Grasshopper Flies High

#125

Post by nanofortnight »

nawitus wrote: post #108
lutze wrote: post #94

Earlier quoted context omitted.

Right, excellent. Except the first stage doesn't run out of propellant does it, because it has to LAND again. Hence my puzzlement. I know why multi-stage rockets are used... I'm asking why this rocket needs them, since they solve a problem it doesn't have by design.

Are you saying it should be single-stage-to-orbit? That's currently technologically nearly impossible, even if the rocket doesn't need to land back to Earth.

Not as technologically impossible as you might think: http://www.reactionengines.co.uk/space_skylon.html

Re: SpaceX Grasshopper Flies High

#126

Post by jlgreco »

jessriedel wrote: post #116
lutze wrote: post #94

Earlier quoted context omitted.

Right, excellent. Except the first stage doesn't run out of propellant does it, because it has to LAND again. Hence my puzzlement. I know why multi-stage rockets are used... I'm asking why this rocket needs them, since they solve a problem it doesn't have by design.

Rockets don't have stages because they run out of propellant, they have stages so that you don't spend 99% percent of your fuel pushing engines and tanks into orbit which you don't need once you get there.

> "they have stages so that you don't spend 99% percent of your fuel pushing engines and tanks into orbit"

In fact you can kinda make a rocket that can reach orbit that doesn't have "stages" but rather jettisons engines themselves. Early Atlas rockets did this: they had one set of fuel tanks but two engines. About two minutes into the flight they would jettison one of the engines.

Re: SpaceX Grasshopper Flies High

#127

Post by InclinedPlane »

bfe wrote: post #121
InclinedPlane wrote: post #63

Earlier quoted context omitted.

The SRB thing isn't true. The costs ended up being pretty much the same for new vs. refurbed. The thing is, with solid boosters the "rocket engine" tends to just be giant aluminum cylinders, almost all the complexity of the job is in casting the fuel and putting the segments together, which is completely orthogonal to the reusability aspects. Also, part of the allure of SRBs is that they are cheap to manufacture, com…

The SRBs don't just impose higher operational complexity, but also far higher acoustic load that requires much higher structural strength and therefore weight on everything else.

They also complicate the range safety situation and make on-pad aborts after they've been lit impossible. Once they've been lit you're going wherever they're going, whether you like it or not.

Re: SpaceX Grasshopper Flies High

#128

Post by slackpad »

droz wrote: post #78

Anyone have experience working at, or with, SpaceX that can shed some light on what it's like to work there?

I've been on the Flight Software team at SpaceX for a little over three years. It feels a lot like a startup. The team is still relatively small and people are pretty passionate about what they are working on. The project variety is wide as well. Personally, I've gotten to work on low-level drivers and OS stuff, application code that runs on the vehicles and ground systems, Dragon's fault-tolerant platform, internal web-based tools, and operations in Mission Control during the Dragon missions. Can't really give details about any of this stuff but I do love working here.

There was an AMA with several of the software teams a little while back:

http://www.reddit.com/r/IAmA/comments/1853ap/we_are_spacex_s...

There are several openings right now for software engineers, including people with web experience (people usually don't think we're looking for those skills):

https://jobs.github.com/positions/bd54ba2a-a930-11e2-9c0e-5c...

Re: SpaceX Grasshopper Flies High

#129

Post by [deleted] »

jessriedel wrote: post #21

For those of you who haven't seen it, here is SpaceX's fantastic animation of their ultimate goal for Falcon 9 (complete with soundtrack by Muse): http://www.youtube.com/watch?v=sWFFiubtC3c This will give you an idea of how grasshopper fits into the full flight plan.

[deleted]
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