SpaceX’s 10-Story Re-useable Grasshopper Rocket Takes a Bigger Hop

by Nancy Atkinson on November 4, 2012

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SpaceX is developing the “Grasshopper” reusable vertical takeoff, vertical landing rocket. Back in September, the 32-meter- (106-ft-) tall Grasshopper made a tiny hop – barely lifting off the pad just to test-fire its engines. But now the Grasshopper has made a second, bigger hop. Over the weekend, Elon Musk quietly tweeted a link to a video, saying, “First flight of 10 story tall Grasshopper rocket using closed loop thrust vector & throttle control.” Update: SpaceX later confirmed that the Grasshopper rose “17.7 feet (5.4 meters), hovered, and touched back down safely on the pad at SpaceX’s rocket development facility in McGregor, Texas.”

SpaceX hasn’t talked much about this rocket, but reportedly the goal with Grasshopper is to eventually create a reusable first stage for its Falcon 9 rocket, which would be able to land safely instead of falling back into the ocean and not being usable again.

Artist’s rendering of SpaceX Falcon 9 rocket landing itself. Credit: SpaceX

Here’s some info about the Grasshopper from a draft environmental impact assessment put out by the FAA in 2011:

The Grasshopper RLV consists of a Falcon 9 Stage 1 tank, a Merlin-1D engine, four steel landing legs, and a steel support structure. Carbon overwrapped pressure vessels (COPVs), which are filled with either nitrogen or helium, are attached to the support structure. The Merlin-1D engine has a maximum thrust of 122,000 pounds. The overall height of the Grasshopper RLV is 106 feet, and the tank height is 85 feet.

The propellants used in the Grasshopper RLV include a highly refined kerosene fuel, called RP-1, and liquid oxygen (LOX) as the oxidizer.

The reports goes on to say that the Grasshopper test program is to have three phases of test launches, at SpaceX’s facility in McGregor, Texas. Phases 1 and 2 would consist of very low test fires with the rocket rising to not more than 73 meters (240 feet) during Phase 1 and 204 meters (670 feet), which is below controlled-airspace. Both Phase 1 and 2 flights would last up to 45 seconds.

Phase 3 tests have the goal of increasingly higher altitudes with higher ascent speeds and descent speeds. The altitude test sequence likely would be 366 meters (1,200 feet); 762 meters (2,500 feet); 1,524 meters (5,000 feet); 2,286 meters (7,500 feet); and 3,505 meters (11,500) feet. The maximum test duration would be approximately 160 seconds. If all goes well, the Grasshopper would land back on the launch pad.

Here’s Grasshopper’s first little test hop in September, which SpaceX said went 2 meters (6 feet):

Look for more details on this exciting reusable rocket as SpaceX continues its tests of the Grasshopper.

Sources: Twitter, Parabolic Arc

About 

Nancy Atkinson is Universe Today's Senior Editor. She also is the host of the NASA Lunar Science Institute podcast and works with Astronomy Cast. Nancy is also a NASA/JPL Solar System Ambassador.

justatinker November 5, 2012 at 1:39 AM

Folks:

Very promising hop! I wonder what “closed loop thrust vector & throttle control” is?

tinker

Robert Gishubl November 5, 2012 at 1:50 AM

A small but important step forward in reducing cost and improving reliability by making re-usable space access. Well done!

Don Denesiuk November 5, 2012 at 2:00 AM

Closed loop means there is a sensor, in this case the inertial guidance system, that can determine the position and attitude of the vehicle and provide corrections to the engines to allow for outside perturbations like wind and correct the thrust vector to keep the vehicle on the desired course or position if hovering. One more small step, as they say, but the goal is to decrease the cost of getting to orbit by a few orders of magnitude. Sheer genius at work. By sacrificing some final payload weight to allow for the fuel and mechanisms (legs) to land the goal could well be achieved. Many more small steps to come, but once the lessons are learned the techniques could be applied to all the vehicles in Spacex’s line from the Dragon capsule to the Falcon Heavy.

balbaro51 November 5, 2012 at 4:50 AM

To be honest , IMHO this is still far from being a usable project.
Launch of a payload , reentry, descend and landing.
Thats what the intention is if i understood correctly.

Erwin Sevens November 5, 2012 at 5:27 AM
krenshala November 5, 2012 at 5:52 AM

Well, you do have to start low when doing this, or gets even more expensive than it already is. :)

This makes me wonder what progress Armadillo has made since February.

Valcan321 November 5, 2012 at 11:39 PM

Um no. Blue origin is a sub orbital hopper musk is looking to make SpaceX already active fully capably launch systems reuseable.

RobWest November 5, 2012 at 8:51 AM

This has been done several times over by others… why waste the fuel? Put wings on the parts you want back and glide it in… geez!

TerryG November 5, 2012 at 9:28 AM

The weight of the wings and matching thermal protection system, flight controls, landing gear and associated hydraulics, power source etc. is more than that of the Grasshopper’s landing legs and fuel reserve.

Torbjörn Larsson November 5, 2012 at 10:03 AM

This has been tried several times over by others… no success so far, regardless of configuration.

Torbjörn Larsson November 5, 2012 at 9:42 AM

That seems to be a well rounded test program for the following months. We will have to be patient with the young Grasshopper then.

To expand on “closed loop thrust vector & throttle control”, the latter would be some means to adjust the engine power.

The most popular control method is if you can simply pulse an activator by Pulse Code Modulation, between limits and simplest on-off. On-off wouldn’t work, because you have to use pyrotechnics to restart the exhaust flame. Pulsing would likely not work, because you would induce pulsations through an easily resonating pipe structure (the tank).

Perhaps it is enough to throttle the turbo pump speed that feeds the Merlin engine with fuel & oxidant. The trick then is to keep the exhaust jet controlled as it will collapse from the outlet walls due to atmosphere pressure. It looks that way from the video, a narrower jet can at times be seen.

The throttle control will work as the accelerator on a car. Unfortunately there will be no brake. Gravity will help like an incline for a car, but the control problem is inherently worser than in Musk’s Tesla.

JohnSankey November 5, 2012 at 12:34 PM

It’s interesting that the control complexity, fuel & landing gear save weight compared to the parachute that the shuttle used. Wouldn’t have thought so.

Richard_Kirk November 5, 2012 at 1:38 PM

It seems logical to me. You have a big tube that goes up in the air full of fuel, and then comes down again almost empty. As it descends, the tube will be slowed down by the thickening atmosphere. It probably would not take a lot of extra fuel to slow the craft down so it lands gently. You can probably work out a rough figure for the extra mass fraction from the ratio of the descent velocity to the velocity of the mass leaving the rocket jets. This is a slight underestimate, but it should be roughly right provided the thing does not hover unnecessarily. The only extra weight for this system apart from the extra fuel is the legs.

There is another good option: it is unmanned so you do not have to land it safely. If something goes wrong and you cannot get to the intended trajectory, you can use the extra fuel in other ways, such as bringing down the payload over water.

phamnuwen November 5, 2012 at 7:52 PM

Other than the extra fuel and legs, you probably need to beef up the structure in general in order to make it stand multiple launches. So you’ll lose some payload there as well.

Richard_Kirk November 5, 2012 at 9:05 PM

Maybe, maybe not. If you are going to have a one-off rocket, you might make the tube of something cheap, as it would only be used once. It might be a bit heavier but you would put in a bit more fuel, and the total cost might be lower. However, If you knew you were going to get several flights out of it, you might spend a bit more money and make it out of something thinner and stronger. I don’t think you need to beef up the structure much for the landing, as it will be almost empty when it is decelerating to land. Interesting to see how this one pans out.

justatinker November 5, 2012 at 9:26 PM

Richard:

Composites come to mind. Maybe like the carbon/aluminum composites SpaceX uses for it’s Falcon inter-stage and Dragon trunk. Fabrication costs can even be a lot more expensive if the fuselage of the stage is rated for hundreds of flights. The stage really only has to survive two return events; entry interface with the atmosphere and landing in one piece. Having the Falcon 9 v1.1 first stage separate earlier in flight will help reduce the load on the stage during entry, Grasshopper will prove the landing technology. SpaceX may even test the fly-back capabilities of the first stage in upcoming flights before the system is integrated. Second stage recovery can also be tested at an independent rate. When it all works, then SpaceX can work on putting it all together.

tinker

Torbjörn Larsson November 5, 2012 at 6:55 PM

If you mean recovery of the STS boosters, this is the approach SpaceX tried first. But the core stages of the current Falcon goes further up and comes down pretty much trashed.

phamnuwen November 5, 2012 at 7:49 PM

Chances are it doesn’t. The point of the retro rocket landing is that you don’t need to go fishing in the ocean for the stages with all the costs and problems (like salt water corrosion) associated with that.

spell7 November 6, 2012 at 9:01 PM

I hope this proves successful. I am skeptical due to the compounding effect of re-allocating fuel from increasing vehicle velocity to landing. Need to run some calculations to see how large the reserve fraction will need to be for landing.

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