Discussion in 'science, nature and environment' started by rover07, Mar 10, 2013.
Space X's Grasshopper reusable rocket gets its 3rd test flight.
is Jonny Cash strapped to the rocket?
Very similar to the delta clipper.
The aim is to have a reusable rocket, that the extra fuel would be more than covered for by the cost of not having to build a new rocket every time. Potentially game changing approach.
3x larger than the DC-X though.
Also, they're going to try "landing" the 1st stage of regular Falcon flights at sea from now on, as practice. The rocket will fall into the sea and sink, but hopefully it will have come to a controlled halt first. That should be fun to watch!
The next flight should be using the Falcon 9 v1.1, using the Merlin 1D engines which deliver more thrust. So they are going to use that as a test bed for some of the return to ground functionality. There is also a new version of grasshopper that they hope to launch to 300k ft (about 50 miles).
New footage of the grasshopper's latest hop. This time to 250m, and filmed from a remote controlled hexacopter. Watch it lean into the wind! They're landing with the thrust:weight ratio greater than 1 now, which takes precision timing. Seriously impressive. I can't wait to see one of these things come hurtling out of the sky after liftoff and come to a dead stop.
When you say "landing with the thrust:weight ratio greater than 1", I assume this is happens when the fuel is almost exhausted so simulating a likely landing scenario?
That's right. The "easy" way to land a VTVL rocket is to approach zero altitude asymptotically. You slow down gradually until you're "hovering" at zero altitude, with thrust exactly matching the mass of the vehicle. Then you turn the engine off and fall the last few centimeters onto your landing legs.
This requires deep throttling of the engine, as the mass of an empty rocket stage tiny compared to a full one. Throttling an engine tends to decrease its efficiency - you get less thrust per kg of fuel burned.
A more fuel efficient trajectory is to use the engine at full power, which slows you down much more quickly. The trick is to time it just right so that altitude and velocity reach zero at exactly the same time. If you keep the engine on like this, the falling rocket will slow, stop on the floor, then rise again. So you turn the engine off at the bottom of the curve.
Of course what you don't want to happen is start slowing down too late.
Or too soon.
Because you don't want to hit the ground, or waste fuel oscillating up and down.
In fact, someone over on this thread has done the calcs and found the most fuel efficient landing trajectory for a Falcon 9.1 first stage. It requires hurtling directly towards the landing pad at terminal velocity (150m/s, or 335mph), waiting until the altitude is 110m, 0.7 seconds before impact, before igniting two of the 9 engines at full throttle, which decelerates the vehicle at 10Gs and stops it just in time. Takes just 750kg of fuel . A wee bit risky, mind.
The real thing will bleed off some speed with a burn whilst on a falling trajectory that impacts the ocean. Only when the engine is confirmed to be running ok will it steer the trajectory onto land, after which the landing procedure will look a lot like the 2nd half of the video we just saw.
this may be a stupid question but how do they steer it/ keep it on course?
The main engine can be pointed left-right/up-down by a few degrees, which imparts a bit of sideways thrust. If you imagine balancing a broomstick on the palm of your hand, this is the side-to-side motion you need to do to keep it upright. In addition, the grasshopper has cold gas thrusters (which literally puff little bursts of compressed air) to control roll, along the long axis.
ah I did not spot those side cold gas thrusters that makes sense now. thank you
Very impressive new video. This has been done by smaller rockets, but nothing this big has shown such precision in moving sideways in flight.
It should be noted that the whole thing was done in a 20 knot crosswind, too. That's windy enough for the space shuttle to have cancelled a landing and stayed in orbit.
That would be fucking amazing to watch
You'll get the chance to see it on the next Falcon 9 launch. They'll be testing the return and landing procedure, except they'll be aiming for the ocean, not the land.
The actual return-to-pad trajectory will not be far off tbf. The rocket will come screaming in at terminal velocity on course to impact in the ocean near the pad, or into a specailly constructed "crash pit". Then it will turn the engine on and slow down rapidly (thrust:weight ratio of over 3), making a sideways move just like the one in the video in order to hit the pad instead.
Also, expect to see much higher hops, including engine shutdown, coast, relight flights using Grasshopper 2 at the Spaceport America site in New Mexico. 300,000ft maximum altitude.
It's not that hard
?? ...the McDonnell delta clipper rocket was doing all this and a hell of a lot more ,almost two decades ago ....?
Yes, but it was 1/3rd the size and designed specifically for that sort of manoeuvre. I read a lovely metaphor on the NSF forum:
Its not a toy though , and they have had two decades in which to scale it up
No doubt. If it hadn't been for X-33 eating all of NASA's SSTO R&D money, it could have gone somewhere.
But a VTOL SSTO is damned hard anyway. Your mass fraction is going to be terrible, if not zero, unless you use exotic engine technology like aerospike or mixed mode (air-breathing rocket).
I like the approach that SpaceX is taking - make the first stage reusable and you've already saved yourself the majority of the cost of the rocket. It's 90% of the engines and 75% of the tanking. It's much much easier than recovering the whole vehicle, and lets you test technologies while flying commercial missions. Win-win, IMO.
Helps when it doesn't crash and burn up...
DC-X didn't really crash, it just fell over. The project was being run into the ground anyway.
Besides, test vehicles are kind of *supposed* to crash. That way you find out what they can't do.
Yeah, I did have to change the post from explode to burn up too...
First launch of the new Falcon 9, today at 5pm.
I will be amazed if they manage to bring the 1st stage down in a controlled manner. It will look incredible if they do
Yep looking forward to seeing this! I hope they show it live!
How long after launch do you think it will be? I imagine it will come straight down after separation, 10 mins maybe?
It's a beautiful morning in California!
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