back to article Elon Musk's SpaceX to build 'Grasshopper' hover-rocket

SpaceX, the upstart start-up rocket company founded by famous techwealth kingpin Elon Musk, is to build and test-fly a "Grasshopper" hover rocket based on the massive first-stage fuel tank of the company's Falcon 9 vehicle, capable of carrying ten tonnes of cargo or seven people into orbit. As yet SpaceX is not discussing the …

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Anonymous Coward

"capable of carrying ten tonnes of cargo or seven people into orbit."

Now, c'mon, I know Americans are supposed to be fat...

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It's not the weight.

It's the luggage. We need an entire SUV to carry our kit for a weekend trip to the beach, nevermind into space.

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Coat

Ok, I understand.

One question: What are you planning to do with an SUV in space?

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Human spaceflight hardware

Life support, food, water, seats, spacesuits, cargo for the mission, survival equipment, toilet facilities.

Soon all adds up you know.

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Look for a limey bastard to drop it on?

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How soon we forget...

"the first stage must fall to Earth and be destroyed"?

Shuttle's SRBs were re-used, after falling into the ocean.

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Definition of reused

Afaik the shuttle boosters were closer to Recycling than reuse.

Presumably anything actually landing would need far less servicing.

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SRBs

Come with almost no moving parts, very little complex plumbing. It was relatively easy to refurbish them rather than a liquid-fuelled stage. I think the Shuttle is the only liquid fuelled rocket which has been reused and the engines there didn't have the indignity of ending up in the North Atlantic.

The Soviets were going to reuse the four strap-on liquid-fuelled boosters for the Energia rocket; AFAIK it was not done for either the Polyus or Buran launches and the boosters would eventually be redesigned into the disposable Zenit launcher.

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Anonymous Coward

In reality the SRB needed so much work done that it cost more to re-use them than sell them as scrap and build new ones.

Stripping them down, cleaning out the salt/sea water, testing every part for cracks, reassembling with new O-rings (the bit that caused one disaster) and re-fueling with solid propellent was a massive cost.

The estimates were that putting a shuttle up cost between five and ten times the cost of each Apollo launch.

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Unhappy

Denied!

When I first read the headline, I had visions of Gerry Anderson's UFO moon hoppers. I'm so disappointed.

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scrap.

I was expecting it to be the Vulture from Salvage 1

(although possibly not made out of scrap metal!)

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i thought i was the only one to remember this movie!

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Almost nobody seems to remember it.

I used to watch the TV series as a kid in about 1979/80. No so long ago, I couldn't remember what it was called, and whenever I described it to people, nobody seemed to have heard of it - I even started to think that maybe it was some part of my childhood that I'd just imagined!

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Actually it was a TV series. I loved it as a kid. Remember one episode where they used Salvage 1 to propel an ice berg.

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Happy

Pack a parachute anyway...

...cuz rockets do fail...

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Devil

Parachutes were successfully tested

Parachutes were successfully tested either on a Proton or Soyuz-Fregat. I cannot remember off the top of my head which one it was around 10 years ago. The analysis of the first stage returned to earth this way however showed that there is little benefit in reusing it.

You have to design something to be reused which in turn puts extra weight and extra cost on the first stage. So it is not just fuel which is the problem here. Overall, at the current level of technology we are still most likely in the "diminishing returns" part of the curve in any such design.

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Why not parachutes?

I still don't get this. Parachutes are in daily use by armies for delivering troops and vehicles, and by skydivers all over the place, with a failure rate as close to zero as makes no difference. Parachute design is massively mature. When it comes to space, again parachutes are the tool of choice for dropping payloads onto planets with atmosphere, and they've generally worked pretty well, given that this kit has been completely out of contact with Earth and working on its own, and these atmospheres have been either corrosive (Venus) or unhelpfully thin (Mars).

So what's the technical problem with putting a parachute on a lower-stage booster rocket which is <1s comms from anywhere on Earth so any problems can easily be overridden remotely, the atmosphere is nice and dense so there's something to push against, and it doesn't actually have to get all the way out of the gravity well so extra weight isn't quite so much of an issue? It's a complete "does not compute" for me.

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Stop

First stages burn out above the lower atmosphere - almost in a vacuum (very close). they also tend to burn out at extreme speeds (Mach 6 or higher). any parachute deployed at those speeds will just burn up in seconds as soon as the atmosphere is 'hit' on descent.

the parachutes you're talking about on planetary landers were specially designed for Mach 2-3 (at huge expense for 70s Mars landers), and are only deployed after the lander has aerobraked using a large, heavy, heatshield. SpaceX seems to be planning to relight one of the engines to substantially slow the stage before it hits the atmosphere, deploy parachutes, then possibly relight the engine again just before touchdown to reduce landing damage in the ocean, or even do a powered landing on eg a large ship.

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DC-X

I wish someone would dust off the first rocket to take off and land vertically - the McDonnell Douglas / NASA DC-X. The DC-X first took off (checks Wikipedia) - OH MY GOD - 20 years ago:

http://en.wikipedia.org/wiki/McDonnell_Douglas_DC-X

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DC-X redux

@Mike -- Somebody did; Jeff Bezos at Blue Origin:

http://blue-www.s3.amazonaws.com/img/vid7.jpg

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Alien

@ Graham RE "Parachutes"

Probably because the stage separation would occur far down range, over an ocean, from where the launch site was.

If they wanted quick/easy turn around it is likely that the designers plan to have the first stage return to home site to save transport costs.

Of course, given a Florida Launch, you could have it fly a path similar to the Shuttles Trans-Atlantic Abort (TAL) and land the first stage at a prepared site in Africa or Spain then return home by ship.

Hmmmm...

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Why not just contract Armadillo Aerospace? They been doing VTVL for years with huge success for very little cash.

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Robert -- @Probably because that haven't gotten very far height-wise for their size (cash or otherwise).

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*intriguing* combination

Musk has said the stage has a mass fraction of 30:1. This, given the Isp of the Merlin 1d is (in principle) *more* than enough to do an expendable SSTO.

The interesting question would be does the fact you have fewer large cheap bits (the tanks mostly, although there's still that 2nd stage engine) increase the *relative* costs of the expensive bit (flight computer, IMU etc) that you'd take a serious hit in your profit margin to launch not much of a payload?

OTOH if the use *most* of the F9 stage 1 design you should inherit it's successful launch record, while keeping the production line working which *together* might justify this as an option

1 Stage design -> 3 options (SSTO, F9, FH)

It looks like some kind of test vehicle, but for what?

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Vision

Dolts... Not earth SSTO. Replace with same thrust LH2 or methane engine. 60 ton thrust engine lunar lander fueled with lunar LOX. Ferry stage from LEO to Lunar orbit fuel depot. Fully robotic. For the payload of the Falcon XX in LEO? Ferry a thousand tons a year to the moon? THINK BIG! Bet he is.

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Also...

something that a lot of people seem to haver forgotten is that SpaceX have been discussing landing their Dragon capsules in this way too. Any development will provide data for designing this capactity into the Dragon so this maybe a testbed for this technology.

Do like Redrum's lunar shuttle idea though. 8-)

Andrew

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Boffin

Merlin engines

The currently flying version of the Merlin engine is the 1C, while this glasshopper variant is the 1D. Th e1D has a throttle capability (1C does not), and the 1D is heading for use on the Falcon Heavy.

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1d will be used on the entire line - F9, FH, and also F1e (if they decide to go ahead with it.. looks unlikely).

there were enough 1c's made for six F9 launches (two launched so far), after that it will be 1d all the way (they're cheaper, easier to build, and far more powerful).

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