SpaceX's Grasshopper RLV

[Dragon029]

Watch the video - it\'s a pretty amazing plan for real life.

SpaceX is seeking permits to fly it\'s \'grasshopper\' reusable rocket system - if they fly it and it\'s successful, I\'m going to be quite impressed.

[Guest GroundHOG-2010]

I am going to be more than impressed. I will want to work for them!!!

[thorfinn]

Why no drogue parachutes? I suppose they made their calculations, but they would make a powered landing much less time critical.

Maybe they\'re thinking about winds. But couldn\'t you just land on the salt lakes at Edwards AFB?

Powered landing for the CAPSULE also seems too much of a gamble to me. It\'s just too easy to kill everybody with even a minor malfunction.

Also, to land the first stage at Kennedy you would have to launch over the United States, and that would put a lot of undue pressure on the range safety officer IF they ever even allowed it. AND who knows if you could retain engine-out capability without losing the stage or failing the mission.

It\'s a nice plan anyway, and I think that somebody WILL get there, but just strapping legs to a Falcon 9 seems a bit of an oversimplification to me

[Tiberion]

Well don\'t take the video too literally, its a really simple representation of their idea of controlled re-entry.

They can still have the parachutes as backups (the capsule certainly will!) but if they can do a powered landing, why not?

I think its okay to progress past 'throw things up there, and hope they drop where we want'

[Howson]

The landing pad is conveniently built right next to the Ocean, so I guess if it doesn\'t work they will just parachute into the ocean

[Guest GroundHOG-2010]

The idea for the powered decent of the capsule insteed of a parachute is this, once your on the ground you don\'t have to pack it, test it and repack it. All you basicly need to do is refuel it (and that is alot cheaper ).

[thorfinn]

The idea for the powered decent of the capsule insteed of a parachute is this, once your on the ground you don\'t have to pack it, test it and repack it. All you basicly need to do is refuel it (and that is alot cheaper ).

And to stay inside the fuel constraints, which will be without a doubt strict, you have to fly a difficult maneuver in an extremely short time and have no engines quitting at the wrong moment, or you are done for. And no backup parachute will save you if they die at 30 meters from the surface: not enough time to deploy.

Seems to me just a little less brilliant than strapping a vehicle with a heat shield made of extremely fragile silica tiles to a towering, shaky, icy tank dropping frozen chunks into the supersonic wind.

[Guest GroundHOG-2010]

Its a great idea, but for manned missions I think they will use parachutes, for saftey

[Tiberion]

They\'ll always have parachutes for backup.. and I think its a pretty small window where a parachute wouldn\'t open fully and at least enable a hard-but-alive landing, and being low enough where an engine fails low enough that they just made a hard landing sans-chute.

Or they could go with a giant airbag like the mars rover

[Iskierka]

There are such a thing as zero-zero chutes. Which is to say, ones which will deploy near-fully at surface level and no velocity; such are used in ejector seats, since if an ejector is used, something has gone seriously wrong, and you can\'t make assumptions about what. I believe the mechanism for the insta-deploy is similar to airbags; ie. small explosives.

And fuel constraints don\'t necessarily have to be tight. Fuel is extremely cheap, the bigger concern would be designing in the capacity for it, and that\'s less of a concern on a reusable vehicle. Since, after all, you don\'t have to build the entire thing again, with all the extra tankage.

All that said, various details of the whole idea (and SpaceX\'s gradually declining record*) make me doubt this will fly.

* details such as the declining number of promised flights being brought through, and manned missions being pushed back. There\'s usually good reasons for these happening.

[Howson]

I think we need to wait until the grasshopper is actually flying before we go making assumptions. After all, they ARE rocket scientists

[feanor]

I think we need to wait until the grasshopper is actually flying before we go making assumptions. After all, they ARE rocket scientists

Some people commenting here could be rocket scientists aswell

Anyway, don\'t confuse Grasshopper with their nice shiny video; thats a whole other thing.

Grasshopper will be awesome, but it isn\'t anything particulary new; it\'s just a bigger version of Armadillo / blue origin. Blue origin was already going supersonic with their projects.

For the nice shiny video- remember, that is 10+ years away, or might not happen at all. spaceX have said they are working on a methane upper stage, so that is likely the 2nd stage- not developed yet. Reentry methods for 1st stage - using picaX on the fron of the stage while all the weight is on the back? issues need to be overcome.

And then there is the payload fraction in all of this, which will get smaller and smaller. If it works, awesome. But I doubt it\'ll look much like this.

Still, even if they just manage to get the 1st stage back, that\'d be huge. I hope the best!

About the chutes for reentry, of the dragon specifically; They\'ll test fire thrusters at a height that\'s still safe for parachute deploy. if they don\'t work, they\'ll go to backup chutes.

Thrusters are possibly even safer then chutes; you can test them often, and you can build in redundancy easily. The big advantage ( and likely reason why they chose this ) of thrusters vs parachutes is control. You can land pin-point on a pad. Imagine the stages coming down on a tree on parachutes- bye bye fuel tanks, some stick in your engine?

Or a sidewalk? if you are landing on parachutes, you need a vast flat area cleared of people. Possibly even waterproof the stages- and still have a shock absorber ( some sort of legs / airbad ) implemented. With good thrusters you just need a pad somewhat closely to the ocean. Trajectory will be that if the thrusters / landing engines don\'t fire, it\'ll overshoot the pad and land in the ocean.