SpaceX's Grasshopper Rocket Flies Higher Than Ever in Recent Demo
March 11, 2013 2:20 PM
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The Grasshopper lifted to 24 stories (262.8 feet) off the ground
SpaceX took its reusable
for another hop last week at the South by Southwest festival in Texas.
SpaceX CEO Elon Musk was there to demonstrate the Grasshopper's fourth test flight, which was twice as high as the reusable rocket has ever gone in previous demonstrations.
"Grasshopper touched down with its most accurate thus far on the centermost part of the launch pad," said SpaceX. "At touchdown, the thrust-to-weight ratio of the vehicle was greater than one, proving a key landing algorithm for Falcon 9."
The Grasshopper lifted to 24 stories (262.8 feet) off the ground, hovered for about 34 seconds and then landed safely back on the ground.
The Grasshopper is a Falcon first stage with a landing gear that's capable of taking off and landing vertically. It does this by shooting into orbit, turning around, restarting the engine, heading back to the launch site, changing its direction and deploying the landing gear. The end result is a vertical landing.
The reusable rocket was tested in September, November, December and last week Thursday.
Check out this video of Thursday's demonstration:
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3/12/2013 1:18:48 PM
It's not a new concept or particularly amazing. The Douglas DC-X program started more than 20 years with a successful first flight a few years later. The last flight of the DC-XA achieved an altitude of 3,140 meters with a flight duration of 142 seconds. It only makes sense if operating on a planet or other celestial body with little or no atmosphere. Taking off from the surface of Earth, why carry oxidizer for the first stage when the atmosphere is ~21% oxygen? Why carry propellants for a descent when wings will work far more efficiently? The best means of achieving orbit from the surface of Earth for a small to intermediate payload mass such as astronauts with some equipment and supplies is probably a two-stage to orbit vehicle using a fly-back first stage booster and a winged orbiter. Unfortunately, U.S. military and space agencies have been gun shy about that approach since the tragic loss of a Lockheed M-21 in 1966. They would have to deal with the technical difficulties of separating two hypersonic vehicles at relatively low altitude (125,000-130,000 ft. ASL). Guessing that current computational fluid dynamics modeling techniques would render that problem somewhat less than intractable.
3/12/2013 4:37:29 PM
wings add ~ 10% weight to a launch vehicle
a h2/02 rocket with a specific impulse of ~450 secs gives you a mass fraction of ~93% for an ssto.
thus for an ssto 93% of the weight of the fully fueled rocket must be propellant. the 7% includes , fuel tanks, engines, (wings!), re-entry system and oh the payload.
you dont need much propellant to land. even the space shuttle only gave the appearance of flying - it essentially had the aerodynamic properties of a brick and only really used the wings to generate lift and control its direction of flight in the last few minutes of sub sonic flight. the re-entry was a 95% ballistic.
thats a hell of a lot of weight to carry for very little in the way of payoff (other than the fact that it looks like an aeroplane and fools politicians into thinking that it will be cheap, safe and reliable).
the fuel to land a rocket that has slowed down to terminal velocity through atmospheric frcition takes up ~ 10% of the weight of the EMPTY rocket - a lot lot less than the weight of wings.
a winged rocket only really makes sense if they are used to generate lift during ascent.
gravity being what it is and the fixed specific impulse of chemical propellants mean that a conventional chemical rocket engine won't cut it.
thus to make a winged ssto work we need new technology - the skylon program will work - this uses atmospheric o2 during ascent to essentially give an advantageous specific impulse. this program looks very promising - however at the moment nobody seems to want to pay for its development.
another technology would be a nuclear thermal rocket. weight and greenpeace/ecomentalist issues make this difficult.
thus a winged ssto is going to need
1: some uber engineering to make a really light, really strong winged fuselage
2: some uber engineering to make novel propulsion systems
3: a bucket load of cash
the space x way has its issues, but there is little risk in terms of technology development and it is relatively cheap to develop (given that the falcon 9 production line is already up and running and paying for itself).
3/13/2013 9:23:53 AM
Your mass fraction may work in theory, but in application it just ain't there. Lockheed Martin tried to go there with Venture Star, but as they got deeper into its design, the payload capability was -5000 pounds. And yes, that IS a minus sign in front.
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