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The Grasshopper Can Fly Sideways
Phoghat writes "I'm of a 'certain age' and as a child grew up watching shows like "Rocky Jones, Space Ranger and others popular at the dawn of the space age. They always showed rocket ships sitting on their tails and blasting off, and landing, straight up. The shuttle went up that way but had to land like a plane, and anything else was considered impossible or impractical. Now, the Space X's rocket Grasshopper can not only do that, but has demonstrated sideways flight also."
I almost called dupe from SpaceX Grasshopper Launch Filmed From Drone Helicopter but this is new stuff.
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XKCD just covered this! Good timing for the question.
TL;DR: Heat shields aren't going away because they are efficient.
When I see vertical-takeoff-vertical-landing my first thought is Armadillo Aerospace and their years of work on those rockets. Now that Armadillo is largely mothballed, have some of their guys turned up at SpaceX?
Never approach a vast undertaking with a half-vast plan.
The Space shuttle can fly in over a thousand different directions -at the same time- if its heat shield is damaged.
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Actually, pretty quickly after takeoff, a rocket's inclination is changed to 25ish degrees. If you just go straight up, you're just going to fall back to earth and never achieve orbit.
Diverts like this are an important part of the trajectory in order to land the rocket precisely back at the launch site after re-entering from space at hypersonic velocity."
While watching the video, I just imagined the "gas" gauge needle sinking fast to 'E'.
Having to carry all the extra fuel to land like that is going to drastically reduce the payload.
That's why space missions usually land some other way - parachute, blow up balls, crash land, etc ... more room for equipment.
Heat shields are the efficient way to slow from orbital speeds for reentry (e.g. the Shuttle), but conveniently for recovery the first stage isn't orbital. Grasshopper is basically a modified Falcon 9 first stage, and the goal of the testing is recovery of the first stage of Falcon 9-R, which is much easier than reentry from orbit..
We're not talking single stage to orbit here, and recovery of the second stage would certainly involve a heat shield. The first stage is a different animal. SpaceX seems to be intending to use a boost-back trajectory concept. I look forward to seeing how that works. (The controlled water "landing" attempt will be something to see, too, of course.)
Are we talking 25 degrees off an axis perpendicular to the ground or parallel to the ground? Because the former is still close enough to the perpendicular to be considered pointing "mostly down" rather than "mostly sideways" or, if NASA copies my Kerbal designs, "mostly up, no over, no down, no up again".
bad comparison. the LM actually operated in reverse. it landed at a site, then took off. that is very different from taking off and then landing back at that exact same site. furthermore, the part that took off was a totally seperate piece with its own rocket engine, so technically it was two craft (or two stages) performing two seperate operations, not one craft performing both. the grasshopper is also far far larger than the LM, and exercising greater degree of control and precision in a heaver gravity and different atmosphere.
and while you alude to the crew capsules landing without fuel, the current crop of LAUNCHERS in use, are disposable single use entities, which means you apparently missed the entire point of this experimental rocket is to validate the concept of a reusable launcher, which would dramatically reduce costs.
short version: shutup
The guy who said the election was rigged won the presidency with the second-most votes.
Trouble is, the DCX never made it to orbit (not even close) whereas the Falcon 9 has.
This is a modification to the existing F9 platform. IIRC, they expect it to reduce the payload capacity by about 25~30%. And yes, they intend to salvage the upper stage too. If they can do that, they'll reduce costs to a few million$ per launch. (About $250k in fuel; skirt/solar module for the Dragon; launchpad services, etc..)
They generally launch from Cape Canaveral, though they are trying to get the legislature to approve a launch site in Texas too.
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Am i the only one who wondered when parent poster was going to get to something relevant to walking trees? I was really baffled. I didn't know what Ents had to do with bugs.
Am i the only one who wondered when the quoted text was going to get to something relevant to recursion? I was really baffled. I didn't know walking a tree had nothing to do with bugs.
Am i the only one who wondered why the quotes were forming some strange iterative behavior? I was really baffled. I didn't know why the stack trace was missing several parent posters; Probably -O dead code elimination, self referential side effect, or a GOTO bug.
I post therefore I was.
Note that in real life you do the gravity roll much earlier than you do in KSP --- this is to get the vehicle clear of the launchpad so that if you're not going to space today, the debris doesn't land on your technicians.
In KSP you leave the gravity roll quite late so that you waste as little fuel as possible pushing through the dense part of the atmosphere (I usually do it at 15km).
We used to call it "thrust vector control". I worked in the Morton-Thiokol TVC lab for a while. The video shows a really excellent example of the technique, which is not new or controversial.
You can do TVC with hydraulics (heavy, but parts are easy to source and last longer) but you'll get better impulse numbers for the vehicle as a whole if you can divert some proportion of the pressure from the combustion chamber into mechanical actuators that change the direction the nozzles are physically pointing. With multi-nozzled rocket motors (regardless of whether they have multiple combustion chambers or not) you can point some thrust down and some to the side (which appears to be happening in the video) and get this kind of behavior.
Similar things can be done with moving vanes in the exhaust plume, but those will erode even faster than the mechanism described above, and will be far slower to change the thrust vector. Erosion of parts that have high pressure hot gasses flowing through them is a huge issue in rocketry, although fairly well understood at this point. External aerodynamic vanes like the space shuttle's wings will obviously work too, and won't erode much (during liftoff) but they are also slow and clumsy.
When I say the technique's not new, I do not mean to denigrate the achievement. I can confidently state that it's really, really hard to do it as well as is being shown in this video. I would love to be able to work with these guys, because they are clearly just full of the right stuff.
Another alternative system to TVC is separately fueled ACMs - Attitude Control Motors - such as vernier thrusters or the solid fuel ACMs on hypersonic crusie missiles. When you use gimballed nozzles to achieve TVC, though, you can potentially have the entire force of the main thrusters available for attitude control, and the fuel delivery system can be much more concentrated and simple.
Graphical overview of the common methods of TVC here
Using the same engine, rather than treating the engine as a disposable object that only performs one burn in its lifetime. Most rocket engines can't be throttled, can't be shut down and then restarted in flight or otherwise.
The tricky part is going to be for any stage to have enough delta-V to return to the pad after lifting a payload to orbit. Also, as far as I can tell, this takes a drag chute for lower stages, and a re-entry shield for upper ones.
Bruce
Bruce Perens.