SpaceX Grasshopper Flies High • Hacker News Board

Re: SpaceX Grasshopper Flies High

#61

Post by chromaton » Tue, Apr 23, 2013, 2:23 PM UTC

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 focuses specifically on commercial companies trying to innovate in space travel: Armadillo, SpaceX, Bigelow, etc.

http://www.newspacewatch.com/

Re: SpaceX Grasshopper Flies High

#62

Post by InclinedPlane » Tue, Apr 23, 2013, 2:25 PM UTC

stuff4ben wrote: post #37

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 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.

Re: SpaceX Grasshopper Flies High

#63

Post by InclinedPlane » Tue, Apr 23, 2013, 2:30 PM UTC

TeMPOraL wrote: post #52

EthanHeilman wrote: post #42

Earlier quoted context omitted.

You can't direct where the rocket ends up, highly likely that the rocket will get damaged or much less likely that the rocket will damage something else (This is why NASA dumps it's rockets over the ocean). Then you have find a way to get the rocket home, which involves time and money. Why not just burn fuel (rocket fuel is only a few times more expensive that burning water) and bring the rocket home? If you need mor…

> 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, comparatively (this is a false savings, due to increased operational complexity, but it's still very tempting), so even if a significant amount of money could be saved per SRB through reuse it wouldn't have affected the cost a launch much.

Re: SpaceX Grasshopper Flies High

#64

Post by simonh » Tue, Apr 23, 2013, 2:31 PM UTC

deletes wrote: post #38

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.

Parachute and/or airbags are not necessarily lighter than fuel on a rocket as big as falcon. Parachutes don't scale linearly with the weight of the cargo. Plus they introduce an additional complexity and a point of failure.

On large heavy objects they also impose significant stress on it's structure.

Re: SpaceX Grasshopper Flies High

#65

Post by stigi » Tue, Apr 23, 2013, 2:39 PM UTC

"Unfortunately, this video is not available in Germany because it may contain music for which GEMA has not granted the respective music rights."

Here's a short link to bypass: http://www.ssyoutube.com/watch?v=sWFFiubtC3c

Re: SpaceX Grasshopper Flies High

#66

Post by lutze » Tue, Apr 23, 2013, 2:42 PM UTC

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.

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.

Re: SpaceX Grasshopper Flies High

#67

Post by nkoren » Tue, Apr 23, 2013, 2:47 PM UTC

chromaton wrote: post #61

luke_s wrote: post #9

Earlier quoted context omitted.

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 focuses specifically on commercial companies trying to innovate in space travel: Armadillo, SpaceX, Bigelow, etc. http://www.newspacewatch.com/

I second that recommendation. This is the successor to a site called "Hobbyspace" which was the best clearinghouse for all commercial space news since the mid-1990s. Although it was just a hobbyist's website, I have reason to believe that its comprehensive reporting and very clear-headed analysis actually bears some of the credit for catalysing the entire Newspace movement (eg., Elon Musk was a following and commenting there since before he founded SpaceX...).

Re: SpaceX Grasshopper Flies High

#68

Post by rplnt » Tue, Apr 23, 2013, 2:47 PM UTC

derekp7 wrote: post #54

rplnt wrote: post #12

Earlier quoted context omitted.

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.

Are you referring to that neat trick they pulled a half dozen times, where they landed a rocket on its tail in an airless environment with 1/6 gravity? That was still pretty impressive on a bunch of other levels.

No, I'm referring to on-earth tests, such as this http://www.youtube.com/watch?v=wv9n9Casp1o However I can't find the exact one I had in mind, or perhaps I was off with the date.

Re: SpaceX Grasshopper Flies High

#69

Post by nkoren » Tue, Apr 23, 2013, 2:50 PM UTC

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.

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).

Re: SpaceX Grasshopper Flies High

#70

Post by smackfu » Tue, Apr 23, 2013, 2:52 PM UTC

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.

Yeah, I was going to mention the DC-X. The video you link below shows what is probably a future grasshopper test, where they take the vehicle off of vertical to show it can really reorient itself.