Discussion SpaceX's Grasshopper RLV

[Hlynkacg]

Maybe that dead mass is worth it.

Also, I am not sure what amount of propellant would be required (my gut feeling is that it'd be a scary, penalty-inducing amount), but the whole fly-back-and-land-vertically thing might well be better than dumping your stages in the ocean from a reusability perspective.

I don't understand why everyone's so wrapped around the axle about fly back capability. I thought the whole point of launching from Texas was so that the first stage could be recovered at KSC (the second of course would do a once-around).


You don't need enough proppelant to fly back, only enough to make a soft landing, and maybe a plane-change.

 

[orb]

Spaceflight Now: SpaceX's reusable rocket testbed takes first hop

Aviation Week: First Hop For SpaceX Grasshopper

SPACE.com: Reusable 'Grasshopper' Rocket Concept Makes 1st Test Flight

 

[Thunder Chicken]

Just so I have the story straight - is the first stage essentially supposed to do a shuttle-like RTLS and land back at the launch site? That would remove constraints on launch inclination and weather (if weather is good for launch you are likely good for return).

Seems somewhat expensive, but then again the stage would be nearly empty - just needs to null velocity, get velocity pointing back to the pad, and then decelerate for touchdown. If it gives you the engines and perhaps the whole stage back then the fuel is peanuts.

 

[Hlynkacg]

Seems somewhat expensive, but then again the stage would be nearly empty - just needs to null velocity, get velocity pointing back to the pad, and then decelerate for touchdown. If it gives you the engines and perhaps the whole stage back then the fuel is peanuts.

Doesn't even need to do that if you recover it at a site down-range.

 

[Thunder Chicken]

Doesn't even need to do that if you recover it at a site down-range.

But that would restrict your orbit inclination. A return-to-launch-site first stage would let you recover from launches to any inclination.

To do a once-around, you would essentially have to add dV to the empty first stage to get it nearly to orbit, then negate all that dV to bring it back. Plus you would have a small plane change maneuver to accomplish. I haven't done the math, but just decelerating and returning a suborbital first stage doesn't sound nearly as bad energy-wise.

 

[MattBaker]

Found this video on Mr Musk's twitter:

http://twitter.yfrog.com/09qmmivexdorhtchxitvhjzsz

A small hop for SpaceX (but a big leap to cutting costs for spaceflight?)

 

[orb]

Parabolic Arc: SpaceX Granted Experimental Permit for Grasshopper Flights:

SpaceX has been granted an experimental permit for its Grasshopper test vehicle, which is designed to test reusable technologies for the Falcon 9 rocket.

Under the permit, SpaceX authorized to conduct:

1. An unlimited number of flights of the Grasshopper Reusable Launch Vehicle within the operating area identified by permit order A; and
   
   
2. Pre-flight and post-flight ground operations at McGregor Test Site associated with flight of the Grasshopper Reusable Launch Vehicle.

{...}

 

[orb]

Elon Musk via Twitter:

First flight of 10 story tall Grasshopper rocket using closed loop thrust vector & throttle control http://twitter.yfrog.com/f362mloybjbosdefkdeoytqsz

 

[orb]

Here's video from the message above, uploaded to YouTube:
[ame="http://www.youtube.com/watch?v=n-VjaBSSnqs"]Grasshopper Two-Story Hop 11/1/12 - YouTube[/ame]

 

[orb]

Elon Musk via Twitter:

View of Grasshopper test rocket from the water tower. Note SUV and person nearby for sense of size. pic.twitter.com/r9yuTRGL

 

[Thunder Chicken]

I have to say that I was skeptical of the grasshopper concept when I saw the first animation, but the fact that they are already playing with it on nearly full scale hardware causes me to respect the effort. I'm an engineer and I know that 2 story hop was a hard thing to pull off.

The thing might tip and blow up, or fail in some other spectacular fashion, but maybe it won't. Kudos to SpaceX for their go-big-or-go-home attitude. New things are being tried and tested - that is always a good thing.

 

[orb]

Parabolic Arc: A Closer Look at SpaceX’s Grasshopper


SPACE.com: Private Reusable Rocket Prototype Takes 2-Story Test Hop

RIA Novosti: Reusable Rocket Makes Highest Test ‘Hop’

 

[orb]

spacexchannel:

SpaceX's Grasshopper takes a 12-story leap towards full and rapid rocket reusability in a test flight conducted December 17, 2012 at SpaceX's rocket development facility in McGregor, Texas. Grasshopper, a vertical takeoff and landing vehicle (VTVL), rose 131 feet (40 meters), hovered and landed safely on the pad using closed loop thrust vector and throttle control. The total test duration was 29 seconds. Grasshopper stands 10 stories tall and consists of a Falcon 9 rocket first stage, Merlin 1D engine, four steel landing legs with hydraulic dampers, and a steel support structure.

 

[SiberianTiger]

Incredible sight!

 

[RGClark]

With reduced weight of the Merlin 1D while at increased efficiency, the Falcon 9 v1.1 first stage will have SSTO capability. Then ironically Elon is emulating the original purpose of the DC-X program in testing the Grasshopper VTVL stage without realizing it.

Bob Clark

 

[Hlynkacg]

The engine mass may be lighter but the all-up mass of the stage is heavier.

 

[SpaceNut]

Elon has gone over the math on this and works out to be more or less just barely feasible...

Typical payload to orbit is 2-3 percent of take off weight.

Added bits to make it reusable ~2 percent.

If the efficiency of payload to orbit can be extended to 4 percent (just 1 percent more), and you keep the added bits for reusability to 2 percent, then you can get 2 percent to orbit on a rocket that is both fully and rapidly reusable.

With the net cost of a falcon rocket about 54 million, imagine the cost reduction that could be achieved with an ultra conservative 10 launches per lifetime of each rocket. Your net cost per launch is a relatively tiny cost of $5.4 million per launch! Reusability changes the game, and yes, it's by no means easy, but it's pretty clear Elon Musk has shown multiple times that things previously thought impossible are not. Lately, it's not been a good bet to say SpaceX can't do what they're setting out to do, so my money's on SpaceX, if anyone, making this a reality.

 

[Mader Levap]

With the net cost of a falcon rocket about 54 million, imagine the cost reduction that could be achieved with an ultra conservative 10 launches per lifetime of each rocket. Your net cost per launch is a relatively tiny cost of $5.4 million per launch!

...plus cost of refurbishment (fuel, checks etc). It is never that simple. Anyway, not gonna happen any time soon.

Not that it is reason for other companies to sit and do nothing. I always find it funny that traditional areospace companies, so risk-averse, in this case do thing that is most risky - ignoring Musk.

Sure, he may fail, but you cannot afford to just assume that and do bussiness as usual.

 

[rct3master44]

I think that if the rocket would have full recovery then SpaceX would have to make the first and second stage larger to carry fuel for descent.

 

[Urwumpe]

I think that if the rocket would have full recovery then SpaceX would have to make the first and second stage larger to carry fuel for descent.

The grasshopper is already way larger than anything we had built before in terms of VTOVL vehicles. It is even bigger than the DC-X.

Also the problem is not carrying enough fuel for landing a nearly empty stage, you don't need more than a few seconds of thrust for that. If acceleration is no limitation, a dry first stage could come to a full stop in less than 5 seconds of full thrust. Even if you are trying to be gentle, you are not needing multiple tons of fuel for that for a rocket of that size.