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Space

The Grasshopper Can Fly Sideways 127

Posted by timothy
from the that's-how-they-sneak-up-on-you dept.
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."
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The Grasshopper Can Fly Sideways

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  • by OzPeter (195038) on Thursday August 15, 2013 @08:11AM (#44572427)

    I almost called dupe from SpaceX Grasshopper Launch Filmed From Drone Helicopter [slashdot.org] but this is new stuff.

    • by BitZtream (692029)

      Its not actually new either. Grasshopper is hardly the first craft, space craft or otherwise to move horizontally when it was vertically oriented. Its not even really impressive that they got it to work on the grasshopper. NASA sent a rover to mars and did it right on the first (and only) try, or you could look at the apollo program moon landers.

      Big deal, SpaceX found out they could mod an ardupilot fairly easy to make their rockets navigate horizontally. When guys playing with toys (I'm one of those ty

      • by amicusNYCL (1538833) on Thursday August 15, 2013 @12:07PM (#44574545)

        The way I see it, it's not so much that they can launch a vehicle vertically and then move it horizontally. The impressive part is that they do it with an actual rocket that is 106 feet tall, and that they have launched it 7 times with 0 failures. And this is all in prelude to their 9-engine 160-foot tall rocket that they will test at altitudes of up to 300,000 feet. When you have that working in your backyard, you let us know and we'll be happy to pat you on the back. Or, if you're as competent at designing rocket control systems as you seem to think, go ahead and work for them. I'm sure Elon Musk pays his people well.

        • I'm sure Elon Musk pays his people well.

          Actually I hear he notoriously doesn't pay or treat his people well. But if you want to be at the cutting edge and "change the world" you put up with it.

      • by mbkennel (97636)
        "When guys playing with toys (I'm one of those types of guys ;) can do it, your big billion dollar space ship doing it is hardly impressive."

        Yes it is.

        The ratio of control forces to mass is much smaller on a big rocket, and the ratio of money lost per bug is much much higher. And they got it to go sideways and back the same amount and hit a calibrated target.

        I can set up a web server by installing 5 standard linux packages. Does this meant that Google's search infrastructure is no big deal?

        Scale-up, comm
      • by c++0xFF (1758032)

        What makes this different is the 10 story rocket. The LEM was 18 ft tall. The Sky Crane was probably about the same, if not smaller. The scale here makes your "toys" kinda pathetic ... it's clearly not the same by any means.

        This is just a baby step to doing the whole thing from orbit, starting from hypersonic velocities (although I think a heat shield and parachutes do a significant amount of work before the rockets kick in).

        This project is ramping up to be something really impressive.

        • by Teancum (67324)

          I think this is especially important to note. A friggin 10 story tall structure with sloshing liquids and a very high center of gravity was able to land after moving about a half mile away from its starting point laterally and landed back on nearly the very same spot where it started. This is basically the 1st stage of a future Falcon 9 rocket which is being tested right now.

          The only comparable rocket that did something similar was an Atlas 1 rocket which "launched" by going up a half inch then came back

          • by Meski (774546)

            I think this is especially important to note. A friggin 10 story tall structure with sloshing liquids and a very high center of gravity was able to land after moving about a half mile away from its starting point laterally and landed back on nearly the very same spot where it started. This is basically the 1st stage of a future Falcon 9 rocket which is being tested right now.

            The only comparable rocket that did something similar was an Atlas 1 rocket which "launched" by going up a half inch then came back down.... with everybody on the launch pad and mission control scrambling like there was no tomorrow and literally praying to God that it wouldn't fall over. More than a few other rockets in similar situations did fall over and blow up (like the N1 rocket in the old USSR that became one of the top largest man-made explosions in human history).

            My gosh, what does it take to impress some of these idiots posting on Slashdot today?

            Praying that Atlas didn't shrug, as it were.

    • The impressive part is that they do it with an actual rocket that is 106 feet tall, and that they have launched it 7 times with 0 failures.

      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

  • by Anonymous Coward on Thursday August 15, 2013 @08:18AM (#44572445)

    "The shuttle went up that way but had to land like a plane, and anything else was considered impossible or impractical."

    XKCD just covered this! [xkcd.com] Good timing for the question.

    TL;DR: Heat shields aren't going away because they are efficient.

    • by Anonymous Coward on Thursday August 15, 2013 @08:35AM (#44572523)

      TL;DR: Heat shields aren't going away because they are efficient.

      And the rocket equation is not. People need to be aware what they are looking at in these videos. This is not a spacecraft coming back to the Earth to land after it did some awesome mission. It is a depleted lower stage of a rocket, where the upper stage(s) has separated and continued on. Now the light lower stage has just enough fuel to fly home (because it is so light after burning up most of its fuel). It is a really, really clever idea for reusable lower stages. But it does not allow rockets to reenter the Earth's atmosphere at orbital velocities, slow down, and land. A phrase scientists and engineers use when they talk about the rocket equation is tyranny [nasa.gov]. Tyranny is right. It took a rocket the size of a skyscraper and weighing as much as a diesel submarine to go to the Moon and back. Without the heat shield, the rocket would have to be the size of an aircraft carrier.

      • by Tx (96709)

        +1 Informative, but boy, would I have liked to see a rocket the size of an aircraft carrier!

        • Here ya' go... [wikipedia.org]

          • by kermidge (2221646)

            Thank you for that. Although I'd heard of Bob Truax somewhat, from the JATO pack and from his work on Thor and Polaris, I'd no idea of the SeaBee and SeaHorse projects, nor the full design of the Sea Dragon - only bits and pieces that showed up in popular venues.

            Sea Horse looks freaking amazing; it's way too bad it and the NASA Future Studies group got shut down. The results from the two proof-of-concept projects seems encouraging to me, and I have to wonder why no one has given serious thought to re-visi

        • by Anonymous Coward

          Let's do a rough estimate. You would need to lift a return rocket roughly the size of a Saturn IB into orbit (which has a mass of 590 tonnes) plus your mission mass of 50 tonnes or so. There is one rocket [wikipedia.org] that might be able to do it, with a little upgrading: the Sea Dragon. In the early 1960s NASA wanted to figure out how to go to Mars. Someone did the math and learned that heavy lifting capability was the key factor and designed a rocket for it that would be built in a shipyard, towed out to sea, ballasted

        • To heck with that. I would have liked to see Project Orion [wikipedia.org]. That is, from a distance :-)
      • by Holi (250190)

        No it took a rocket the size of a skyscraper and weighing as much as a diesel submarine to get a tiny capsule to the moon. The rocket itself was destroyed in the process.

      • by AJWM (19027)

        The Saturn V had a payload to Earth orbit of 260,000 lb, which happens to be the weight of a fully-fueled Atlas missile. So in theory the Saturn V could orbit a vehicle which could use rocket braking to de-orbit and land without a heat shield.

        Impractical as hell, of course.

        Heck, even in my fictional future T-space stories, where we have warp, fusion, but no anti-gravity*, ships tend to use aerobraking. (Given the ridiculously high power and Isp of their thrusters, they could do a retrofire to landing, but

        • by Xaedalus (1192463)
          Ya know, if you ever felt like writing some humor, you could come up with a couple of scenarios on anti-grav testing. I think you could probably come up with some hilarious yet believable testing scenarios that don't involve messy death.
      • But it does not allow rockets to reenter the Earth's atmosphere at orbital velocities, slow down, and land.

        How about the Moon and Mars? It seems to me that the fuel capacity of Dragon isn't enough to do both lunar descent and ascent just on the Super Draco thrusters and the trunk's fuel capacity.

    • by ClayJar (126217) on Thursday August 15, 2013 @08:40AM (#44572559) Homepage

      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.)

      • Even if they never succeed at recovering the second stage, just reusing the first stage could cut the cost per flight in half, if not more. But they seem to be making pretty good progress thus far, and Musk has said he hopes to attempt a 1st-stage recovery as early as next spring. So I wouldn't be surprised to see them succeed with the 2nd stage too.

        Here's a video of the shceme. [youtube.com]

        • Pretty good progress thus far? I'm inclined to add a few 4 letter expletives in amongst those words, that video left me staring in awe. : ) A few days back we had a video about an autonomous quadcopter thing that spent the better part of 10 minutes randomly turning in circles as it wandered through a building mock-up. This thing jumps up a few hundred feet vertically and horizontally away from the pad and then drops back down like a boss, utter perfection from my armchair.

          • I'm inclined to add a few 4 letter expletives in amongst those words

            You'll get no argument from me. Musk has had a hell of a run the last couple of years, and from my chair here it looks like he's just getting warmed up.

            And it's not just him... there's a ton of cool stuff in the pipeline over the next few years. There's half a dozen other players in the "NewSpace" market, such as Masten, Sierra Nevada, XCOR, MoonEx... And these will enable further ventures such as Planetary Resources and Deep Space Industries.

            And it's not just in space... We're going to have grid-level elec

            • by Teancum (67324)

              The sad thing is that John Carmack has all but shut down Armadillo Aerospace, primarily due to a lack of funds. They had several projects which seemed to be doing pretty well and might have even started to earn some money to sustain the company, but the current recession has pretty much dried up any funds they were going to get from the entrepreneurs involved. It was always a skeleton crew anyway, but there are some signs of collapse as well.

              On the other hand, if the American economy picks up again and re

          • To be fair - this is in some ways a much, much easier task than navigating through a building.
            The rocket does not have to navigate in a more advanced way that remembering one point, and doing a simple manouever.
            Sure - the propulsive hardware is about eleven million times harder - but the navigation aspects could be implemented on an arduino, without straining it.

          • by kermidge (2221646)

            Perhaps even more amazing is that the thing has to continuously compute mass, fuel (and its dwindling mass), height and rate of descent, and allow enough fuel and distance for the precisely increased thrust needed to bring it to a stop on the ground with zero speed. Wow, rocket science.

    • by nedlohs (1335013)

      You can use the atmosphere to slow down without having landing as a plane.

      See basically everything but the space shuttle that has gone into orbit and returned to earth.

      Doesn't mean you want to use a rocket rather than a wing or parachute of course, but doing so does not mean you don't use the amosphere to shed as much velocity as possible.

    • by Megane (129182)

      Note that Grasshopper does NOT have to return from orbital velocity. It has to fight whatever horizontal vector the first stage got from its primary job of launching the vehicle, but that's nowhere near orbital speed. So it doesn't have to worry about all the fun of orbital re-entry.

      Also, the main job of Grasshopper is to go down to a controlled landing. It doesn't need to be able to go full sideways like the DC-X did. It just tilts itself in the general direction of where it needs to go vertical.

  • And a rocket's motor is at the back. Of course it is going to point down to counteract. No matter which way you point the rocket, the motor must point mostly down.
    • by i kan reed (749298) on Thursday August 15, 2013 @08:33AM (#44572511) Homepage Journal

      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.

      • 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".

        • No, it's 25deg above the horizontal. The point is to increase your "sideways" velocity parallel to the earth's surface, which (in space) is what really determines the height of your orbit.

        • by david.given (6740)

          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).

          • by Rhacman (1528815)
            Ahh, see NOW you're talking my language! Come to think of it, most of the junk from my failed KSP launches has been raining down all over the Kerbal Space Center.
            • by david.given (6740)
              That's half the fun!
            • by lgw (121541)

              I should really make time to play with KSP. Can you put a RSD on those rockets? I mean I'm sure enough of them blow up on their own, but blowing them up on command seems fun as well. Why do I have this feeling my game will end when I get lynched by Kerbals?

        • by vux984 (928602)

          if NASA copies my Kerbal designs

          Aren't those the six words words you never say at NASA?

          http://xkcd.com/1244/ [xkcd.com]

      • by rossdee (243626)

        " If you just go straight up, you're just going to fall back to earth and never achieve orbit."

        If you have an efficient enough rocket (not chemically powered) you can achieve escape velocity by going straight up, then you will never fall down (to the earth) again.

        • by ibwolf (126465)

          If you just go straight up, you're just going to fall back to earth and never achieve orbit.

          If you have an efficient enough rocket (not chemically powered) you can achieve escape velocity by going straight up, then you will never fall down (to the earth) again.

          While true, you'll also never achieve orbit going straight up.

          • If you just go straight up, you're just going to fall back to earth and never achieve orbit.

            If you have an efficient enough rocket (not chemically powered) you can achieve escape velocity by going straight up, then you will never fall down (to the earth) again.

            While true, you'll also never achieve orbit going straight up.

            You may escape Earth's gravity that way, but you'll still be in a solar orbit... one that will likely intersect with a certain insignificant little blue green planet sooner or later.

          • The moon could be used to give you a horizontal push into orbit, also you start with the Earth's rotational velocity, so if you go high enough that will be enough to orbit.

          • by Trogre (513942)

            This is also true. However orbit isn't necessarily always the goal. A rocket destined for Mars, for example, has no need to be in an Earth orbit.

  • by szquirrel (140575) on Thursday August 15, 2013 @08:27AM (#44572477) Homepage

    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?

    • by samkass (174571)

      And are these the same guys who worked on DC-X and DC-Y [wikipedia.org] back in the day which also achieved Grasshopper's same milestones 20 years ago?

      • by dywolf (2673597)

        Nice, you can link to wikipedia.
        Now try reading it.

        the DCX and DCY were not reusable launchers/stages.
        they were intended as entirely reusable Single Stage to Orbit (SSTO) vehicles. By comparison grasshopper is testing many things, but the most important aspect is the concept of a reusable launcher seperate from the actual vehicle put into orbit.

        They also had a completely different designed flight profile and capabilities (never tested as the project never got that far). specifically, this:

        One desired safety requirement for any spacecraft is the ability to "abort once around", that is, to return for a landing after a single orbit. Since a typical low earth orbit takes about 90 to 120 minutes, the Earth will rotate to the east about 20 to 30 degrees in that time; or for a launch from the southern United States, about 1,500 miles (2,400 km). If the spacecraft is launched to the east this does not present a problem, but for the polar orbits required of military spacecraft, when the orbit is complete the spacecraft overflies a point far to the west of the launch site. In order to land back at the launch site, the craft needs to have considerable cross-range maneuverability, something that is difficult to arrange with a large smooth surface. The Delta Clipper design thus used a nose-first re-entry with flat sides on the fuselage and large control flaps to provide the needed cross range capability. Experiments with the control of such a re-entry profile had never been tried, and were a major focus of the project

        Your comparison i

      • by h4rr4r (612664)

        Those were single stage to orbit. That makes no sense.

        Grasshopper is about recovering the first stage. A way more sensible goal.

        • by Anonymous Coward

          The actual vehicles were tech demonstrators for their takeoff/maneuver/landing capability, and the exact demo they used was to lift off, move sideways, and land again. Seems relevant enough.

    • by Anonymous Coward

      Maybe they just took on someone who knows his differential equations? After all, VTOL is only 'rocket science' if you don't have any actually control engineers on the team ;-)

  • The Space shuttle can fly in over a thousand different directions -at the same time- if its heat shield is damaged.

    • by ibwolf (126465)

      I don't know which is worse, the joke itself or that someone actually thought it was funny.

      • by Extremus (1043274)

        First I found it funny. Then I felt guilty. Then I read your comment and found the joke funny once again. Sorry.

  • Watching the video (Score:2, Insightful)

    by Anonymous Coward

    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.

    • by dywolf (2673597) on Thursday August 15, 2013 @09:08AM (#44572739)

      Actually the article misses the point. This isnt the reentry vehicle. This is the launcher. The first stage of a multistage vehicle, and it never leaves hte atmosphere. The idea is to create completely reusable launchers and thus lower cost. Now the upper stages could also benefit from this series of experiements and developmental work; this craft is testing multiple things, and a reentry vehicle that simply lands vertically back home has a few advantages (no really big landing field at really high speed like the shuttle, no uncontrolled parachute descent like current capsules).

      But the main thrust (pun) of it is reusable launcher stages, with a side benefit of also being able to apply the tech to upper stages and the reentry vehicle as well. So its not a SSTO (single stage to orbit) vehicle like the old DC-X mcdonnel douglas was toying with.

    • The fuel isn't extra fuel. The fuel is buffer fuel, as in "We need x tons of fuel to boost the upper stage, so put x+y on board so we don't run out too soon". They're flying back on the y.
      • by BitZtream (692029)

        And then you have to add buffer fuel for the flight back because flying only part of the way back and landing on someones house because you ran out of gas is the exact reason the buffer fuel is there int he first place.

        1ST rule of rocket engineering: YOU NEVER FUCKING PLAN TO USE YOUR BUFFERS. YOU PLAN TO NEVER EVER EVER EVER USE YOUR BUFFERS, and then use them only when the alternative is death.

        You utterly fail to understand sound engineering practices.

        • by Erich (151)
          Your "1ST rule of Rocket Engineering" can also be stated: You always develop sub-optimal rockets.

          Seems like a stupid rule to me.

          If an engine goes out, or there is some other problem, you need extra fuel to accomplish the mission (increased gravity drag). So you have some extra fuel and extra delta v, and that's a good thing.

          But if those events are rare -- and, eventually, they should be -- then you often have extra fuel. If you can use that fuel to return the craft intact to reuse and make more mone

        • And then you have to add buffer fuel for the flight back...

          Not if what is left over after the boost phase is finished is beyond ample for the task. In other words, Y>R+M, where R is what you need to return, and M is a safety margin.

          I disagree with never planning to use your buffers. You have a flight plan for nominal flight. You have a flight plan for engine out. You have a flight plan for two engines out, etc. You plan for every foreseeable contingency, and some of those flight plans will specify using the buffers. Now, for a nominal flight plan, yes,

        • by Teancum (67324)

          First of all, the booster stage is never going to have people on it when that "buffer fuel" is going to be used. If it needs to be used for safety purposes, the booster stage can be thrown away afterward just as it currently is being done right now for rockets like the Falcon 9 (where the 1st stage is being thrown away into the bottom of the Atlantic Ocean and soon to be Pacific Ocean). You plan on having that buffer for emergencies, but can you do something with it after that contingency is no longer nee

  • They always showed rocket ships sitting on their tails and blasting off, and landing, straight up[1]. The shuttle went up that way but had to land like a plane[2], and anything else[3] was considered impossible or impractical. Now, the Space X's rocket Grasshopper can not only do that

    Do what?

  • Am i the only one who wondered when the summary was going to get to something relevant to entomology? I was really baffled. I didn't know what rockets had to do with bugs :/
    • Am i the only one who wondered when the summary was going to get to something relevant to entomology? I was really baffled. I didn't know what rockets had to do with bugs :/

      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.

  • Tony Stark has been doing this for 50 years.
  • I always found this video [youtube.com]to be impressive. It's a little scary in a terminator sort of way too.
  • by Medievalist (16032) on Thursday August 15, 2013 @10:27AM (#44573391)

    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 [wikipedia.org] 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 [wikipedia.org] 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 [nasa.gov]

    • by adamgundy (836997)

      there is only a single nozzle on the grasshopper - one merlin 1D engine. the second, angled off to the side, jet of flame that you see is the low pressure exhaust from the gas generator on that engine, which has then ignited on contact with the oxygen in the air, since it runs fuel rich.

      it provides very little in the way of thrust, and is not controllable on the 1D. on the merlin 1C vacuum version, it was directed and used for roll control - it appears that the merlin 1D-VAC directs the turbopump exhaust in

      • Thanks! I find this stuff fascinating even though I haven't been in the rocket science biz for quite a while now. If I could get a good-paying job with a commercial spaceflight company without moving my family, I'd be all over it... but the last offer I got would have required I move to the Mojave desert. Not gonna happen.

  • Am I the only one who clicked through to this while scanning headlines, thinking it referred to living creatures?
  • The controlled burn decent shown in the video looks impressive but will always be impractical from a financial perspective.

    In fact, it is the most horrific way to land a rocket coming from space due to the amount of fuel that would need to be used to decelerate it. We use parachutes or wings to slow things down for landing in an atmospheric environment because it saves a lot of energy compared to doing a direct burn for deceleration.

    Essentially, you have to use at least as much fuel as you needed to get th

  • Is anybody else disappointed that TFA doesn't have slow-motion video of an actual grasshopper (the insect) flying sideways? That'd be pretty cool.

  • by Anonymous Coward

    This is a nice step in Musk's plans to make the 1st stage of Falcon 9 re-usable... but before people swoon over this apparent realization of SciFi fantasy and start talking of warp drives and teleporters, a few points are in order:

    1. This has been demonstrated before by several other teams (DC-X being most famous, and Amazon's Jeff Bezos, with his Blue Origin vehicle, being hardly noticed). The thing the grasshopper demonstrates is not that the general concept works, but rather that Musk's team has mastered

  • No wonder Kwai Chang Cane had a hard time catching one.

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