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SpaceX Grasshopper Flies High

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Re: SpaceX Grasshopper Flies High

#101

Post by InclinedPlane »

luke_s wrote: post #9
InclinedPlane wrote: post #6

Earlier quoted context omitted.

The pace of progress seems to have been faster than even SpaceX anticipated. Within the next year we'll see very significant tests of core components of the system and flight profile (for the first stage at least). The very next Falcon 9 flight (out of Vandenberg) will use the performance overhead provided by the v1.1 upgrade to do a controlled reentry of the 1st stage and then after it has reached terminal velocity…

Thanks for the detailed rundown! If you don't mind me asking - where did you find all this out? I've been looking for a good source of SpaceX news. The official website/g+/facebook/etc just posts short updates whenever a mission occurs. I'm looking for news about what is on the horizon and more detailed analysis.

newspacewatch.com is probably the best overall resource. spaceflightnow.com is decent for news of what's happening right now in space. Otherwise there isn't any single source for everything. It helps to run to wikipedia for any new thing you read about and then spend time poking around any other websites you run across.

Re: SpaceX Grasshopper Flies High

#102

Post by lutze »

rst wrote: post #72
lutze wrote: post #66

Earlier quoted context omitted.

I don't understand the need for the intermediary stages, couldn't the main rocket just deliver the payload and then land? As it is in that video, it's having to carry engines and fuel for 3 separate stages, for no apparent reason.

The video actually shows two stages and the Dragon capsule, which is payload. As to the use of staging, there are several reasons: 1) During the late stages of the boost, the one second stage engine is pushing only its single engine, fuel and tankage. You're no longer dragging around the nine engines of the first stage and their tanks. That weight saving means you get a lot more delta-V for each unit of expended fuel…

Good answer, thanks.

I've been playing too much Kerbal Space Program, I assumed the first stage had already reached orbital velocity.

Re: SpaceX Grasshopper Flies High

#103

Post by ChuckMcM »

rplnt wrote: post #12
StylifyYourBlog wrote: post #2

Its likely that full-fledged Space Travel with reusable rockets will be possible in the coming years

I believe same thing was done by NASA in the 70s. So not really big step forward in this particular regard. edit: Can't find it at the moment. So far I've found http://en.wikipedia.org/wiki/McDonnell_Douglas_DC-X which did what grasshopper and more almost 20 years back. I still believe I've read something earlier though. Will edit when/if I find it.

Actually not true, but I suspect if you've been researching this you've discovered that. NASA has of course researched vertical landing techniques from the beginning, both with manned missions (Apollo) and robotic. However, it was "on the list" prior to the great de-funding and generally sat in the 'to be looked at' drawer from then on.

The DC-X program, and others like it were spawned by private industry who were betting on a huge 'single stage to orbit' (or SSTO) model for satellite launches that would be needed for the Reagan 'Star Wars' missile defense program. They died when Star Wars died and NASA briefly assumed control of DC-X when its private backers pulled out but was stretched too thin to give it any real push.

That said, Elon and others will tell you that the current crop of rockets would not be possible without the work that NASA did and has shared. SpaceX also has benefited from computer systems that are 10,000X more powerful than the ones that NASA had available for their use, and materials that are 1/3 to 1/2 the weight and yet stronger than their NASA counterparts. Sensors that are 100x more sensitive and 1/1000th the cost. A six degree of freedom inertial unit was $125,000 in 1970 and resolved differences of .1G. A 9 degree of freedom unit from Sparkfun Electronics [1] is now $125, and reliably resolves 1/4096'th of a G. So I don't doubt that the same engineers at NASA could build what SpaceX is building today, today, but I assure you they didn't have the tools to build it back in the 70's or even in the 90's.

[1] https://www.sparkfun.com/products/10736

Re: SpaceX Grasshopper Flies High

#104

Post by mikeash »

wiredfool wrote: post #98
mikeash wrote: post #84

Earlier quoted context omitted.

To put it in perspective, the fuel used to launch a Space Shuttle cost in the neighborhood of $1 million, while the cost of the entire launch was somewhere around $500 million to $1 billion.

Another perspective is that the Falcon9 carries about as much kerosene as a 747.

That's a good one, although a 747 gets its oxygen for free.

Re: SpaceX Grasshopper Flies High

#105

Post by InclinedPlane »

JshWright wrote: post #89
nkoren wrote: post #69

Earlier quoted context omitted.

Nope, aside from the Lunar Excursion Module and its simulators, NASA did nothing like this until the 1990s, with the Delta Clipper. And that wasn't really NASA - it was a BMDO project which later got taken over by NASA. (NASA then crashed the Delta Clipper on their first flight with it, and promptly went back to their preferred innovation strategy: very large contracts which result in absolutely nothing).

>very large contracts which result in absolutely nothing That's a moderately ironic statement, given the fact that SpaceX wouldn't be doing anything remotely close to what they're doing today without the very large contract they got from NASA.

Without NASA contracts (to be noted: fixed price contracts predicated on delivery of goods, for the most part) SpaceX would have much less cash on hand and their pace of R&D would be much slowed. But they would still exist and still be pushing the state of the art, just at a slightly slower pace. They have one of the most competitive orbital launchers on the market, they have a ton of commercial business already on the docket, and the next 3 SpaceX launches are, in fact, non-NASA commercial flights (a Canadian weather satellite, a commsat for servicing East Asia and Oceania, and several Orbcomm commsats).

Re: SpaceX Grasshopper Flies High

#106

Post by InclinedPlane »

JshWright wrote: post #82
jordan0day wrote: post #75

Earlier quoted context omitted.

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…

Not to mention that the giant flying fuel tank (er... 'rocket') is _substantially_ lighter now that you've burned most of the fuel off.

And separated from the 2nd stage and the payload, of course.

Re: SpaceX Grasshopper Flies High

#107

Post by anonymfus »

InclinedPlane wrote: post #60
petenixey wrote: post #35

Earlier quoted context omitted.

But why not just use a parachute and airbags? They're going to be a vast amount lighter than the fuel you'd need for a rocket landing.

Parachutes are a pain in the ass to replace. But more than that taking a dunk in the ocean isn't so good for rockets, and spending the better part of a day with a search and recovery team and all the relevant equipment necessary out looking for the rocket and hauling it back home isn't cheap, it also adds a lot of delay to the whole workflow. Compare that to a propulsive landing on the launch pad next to the assembly…

But why everybody compares landing solely on parachutes in ocean with landing solely on engines on land? For example, Soyuz use multiple parachutes for slowing down and engines for guiding and final soft landing on land.

Re: SpaceX Grasshopper Flies High

#108

Post by nawitus »

lutze wrote: post #94
gamegoblin wrote: post #74

Earlier quoted context omitted.

"A multistage (or multi-stage) rocket is a rocket that uses two or more stages, each of which contains its own engines and propellant. A tandem or serial stage is mounted on top of another stage; a parallel stage is attached alongside another stage. The result is effectively two or more rockets stacked on top of or attached next to each other. Taken together these are sometimes called a launch vehicle. Two stage rock…

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.

Re: SpaceX Grasshopper Flies High

#110

Post by rst »

JshWright wrote: post #23
savrajsingh wrote: post #20

Can someone share some details on how the rocket is stabilized? There are a few different ways to do it -- how does this one work?

I assume it's some sort of gimbal control/vectoring of the thrust (since I don't see any 'extra' exhaust further up the rocket)

It gimbals the engine for pitch and yaw, and uses cold-gas thrusters for roll (around the vertical axis).
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