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Elon Musk's Amazing Grasshopper
Apr. 24th, 2013 10:13 pmVia ![[livejournal.com profile]](https://www.dreamwidth.org/img/external/lj-userinfo.gif)
daveon, a video of the latest test flight of SpaceX's 'Grasshopper' - a test vehicle for landing and reusing the first stage of the Falcon 9 rocket used to launch the Dragon resupply capsule to the Space Station.
Leaving aside the slightly cheesy choice of music, I'm very impressed by this. What SpaceX are trying to do is really hard. If you think about it, what you have is a a very large metal tank - a railway carriage would fit comfortably inside - that is mostly empty, and a rocket engine at the bottom. Not only are you trying to balance something tall and thin on a single engine's thrust, but the entire setup will be very sensitive to side winds. You now want to have this take off, climb, hover, and then descend again to land vertically.
Those of you who were watching space developments in the early to mid-90s may recall DC-X, a technology demonstrator for a vertical takeoff and landing rocket. Grasshopper is trying to replicate what DC-X did, but with a much larger vehicle that is likely to pose much greater control challenges.
So why is SpaceX trying to do this? DC-X was meant to be the first step towards a true single-stage-to-orbit (SSTO) launch vehicle, that would be completely reusable by virtue of not having to dump stages on the way up. But space launchers have stages for a good reason: it is very difficult to cram enough fuel to get to orbit into a structure light enough that a rocket can attain enough speed to get there. That's why rockets throw away parts of their structure on the way up. SSTO proved to be a dead end as it just didn't seem that anyone could realistically build a vehicle light enough to reach orbit, let alone carrying any payload. (DC-X showed that the takeoff and landing would work, but was very limited in performance, and I recall a rather acid comment that it was not so much SSTO as single-stage-to-six-thousand-feet.)
SpaceX isn't expecting to get all the way to orbit with a single stage. Instead, it wants to recover the first stage of Falcon 9 for reuse. The way it hopes to do this is to use some of the excess performance of the rocket to allow there to be some spare propellant left over at the end of the first stage burn. You might not think that would do a lot of good, seeing as how a few hundred tons of LOX and kerosene are needed to get the rocket to that point. But all that fuel went into accelerating the mass of the upper stage and payload. The separated first stage is mostly empty fuel tank, and it turns out that not much residual fuel is required to cancel out the speed it's gained and even send it back towards the launch site. Then, the last remaining fuel will in theory allow it to touch down back where it started, and it's that part of the process that Grasshopper is meant to test out.
On another note, I wonder what SpaceX used to film the flight? I can't believe a helicopter with crew would have been allowed anywhere near; perhaps one of those little remote-control helicopter cameras that seem to be all the rage for news-gathering?
daveon, a video of the latest test flight of SpaceX's 'Grasshopper' - a test vehicle for landing and reusing the first stage of the Falcon 9 rocket used to launch the Dragon resupply capsule to the Space Station.Leaving aside the slightly cheesy choice of music, I'm very impressed by this. What SpaceX are trying to do is really hard. If you think about it, what you have is a a very large metal tank - a railway carriage would fit comfortably inside - that is mostly empty, and a rocket engine at the bottom. Not only are you trying to balance something tall and thin on a single engine's thrust, but the entire setup will be very sensitive to side winds. You now want to have this take off, climb, hover, and then descend again to land vertically.
Those of you who were watching space developments in the early to mid-90s may recall DC-X, a technology demonstrator for a vertical takeoff and landing rocket. Grasshopper is trying to replicate what DC-X did, but with a much larger vehicle that is likely to pose much greater control challenges.
So why is SpaceX trying to do this? DC-X was meant to be the first step towards a true single-stage-to-orbit (SSTO) launch vehicle, that would be completely reusable by virtue of not having to dump stages on the way up. But space launchers have stages for a good reason: it is very difficult to cram enough fuel to get to orbit into a structure light enough that a rocket can attain enough speed to get there. That's why rockets throw away parts of their structure on the way up. SSTO proved to be a dead end as it just didn't seem that anyone could realistically build a vehicle light enough to reach orbit, let alone carrying any payload. (DC-X showed that the takeoff and landing would work, but was very limited in performance, and I recall a rather acid comment that it was not so much SSTO as single-stage-to-six-thousand-feet.)
SpaceX isn't expecting to get all the way to orbit with a single stage. Instead, it wants to recover the first stage of Falcon 9 for reuse. The way it hopes to do this is to use some of the excess performance of the rocket to allow there to be some spare propellant left over at the end of the first stage burn. You might not think that would do a lot of good, seeing as how a few hundred tons of LOX and kerosene are needed to get the rocket to that point. But all that fuel went into accelerating the mass of the upper stage and payload. The separated first stage is mostly empty fuel tank, and it turns out that not much residual fuel is required to cancel out the speed it's gained and even send it back towards the launch site. Then, the last remaining fuel will in theory allow it to touch down back where it started, and it's that part of the process that Grasshopper is meant to test out.
On another note, I wonder what SpaceX used to film the flight? I can't believe a helicopter with crew would have been allowed anywhere near; perhaps one of those little remote-control helicopter cameras that seem to be all the rage for news-gathering?
