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So, SpaceX has finally landed their booster back to the land. BlueOrigin has achieved the same thing in a recent past, but I have read so many people commenting and criticizing the comparison of BlueOrigin and SpaceX landings.

In fact, Jeff Bezos has just published the following tweet,

Congrats @SpaceX on landing Falcon's suborbital booster stage. Welcome to the club!

but people are commenting on his tweet that your landing was nothing as compared to SpaceX's landing and it was easier.

Can someone please explain the difference between the two landings in layman's term ?

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    $\begingroup$ I am awaiting the day when Musk gets to tweet "Congrats Blue Origin on flying a revenue-positive mission. Welcome to the club!" $\endgroup$ – Russell Borogove Jan 4 '16 at 16:21
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enter image description here


You see that tiny thing on the far left?

That's the Falcon 1. It's a comparable size to Blue Origin's New Shepard spacecraft and SpaceX's Grasshopper (which accomplished a similar feat 6 times, around 3 years ago, but didn't *technically* enter space).


You see those 3 in the middle?

That's what SpaceX landed today. Grasshopper / Blue Origin were comparatively short, slow, experimental proof-of-concept flights. The Falcon 9 launch was a fully-fledged orbital rocket, delivering a real payload on an actual mission, operating at a level of difficulty an order of magnitude greater than the previous achievements of either company.


That's the difference. *Technically*, both landings count as "Launched a rocket into space and successfully re-landed".

But the first two were, essentially, "Fly straight up and come straight back down at sub-orbital speeds". Basically a scaled-up water-rocket. Specifically, New Shepard accelerates straight up to 40km, at 100,000 pounds of thrust, then coasts to 100.5km and comes straight down again.

The Falcon 9 has to handle 1.5 million pounds of thrust, reaches a maximum altitude of 300 km, takes a payload into space, at the time of detachment is travelling mostly horizontal to the earth's surface, at twice the velocity (and 10x the mass so 40x the kinetic energy), and has to then turn around!, re-enter the atmosphere, and land back at the launch site.

In terms of the difficulty involved and the commensurate level of achievement, today's landing is in a whole different league to anything that's come before.


In really simplified terms:

Grasshopper / New Shepard were "throwing a tennis ball high in the air and catching it".

Falcon 9 was "Shoot a cannonball at supersonic speed, sideways, with topspin, so that it curves through the air, bounces off that building over in the distance, comes back at you at 3x the speed and still lands exactly where you threw it from."


Addendum:

It should also be noted that New Shepard is small/nimble enough that it can throttle down its engine and hover above a landing site, allowing for a controlled landing and/or aborting a landing attempt and re-trying if it's not right. It can control its' descent velocity at will, coming down slowly and gently to the point where you could almost do it by hand-held remote.

Because the falcon 9 needs much larger engines (because it's far heavier at launch), and has lost almost all its' fuel mass by this point, it cannot hover. This means it has to land by a method called a suicide burn.

A suicide burn means that it fires its' engines at a very precise altitude, such that it decelerates and slows to a stop at the exact point where it touches down on the landing pad.

If the burn starts a tenth of a second too late, the rocket will hit the launch pad at several hundred m/s and explode. A tenth of a second too early, and it will level out a few hundred meters above the launch pad, run out of fuel and fall out of the sky.

It is easily an order of magnitude harder to do, and you don't get any re-takes.


In short, though still a historic achievement in its' own right, landing New Shepard is nothing compared to landing Falcon 9.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – called2voyage Dec 22 '15 at 14:49
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    $\begingroup$ This is a nice answer. But you don't really compare the two on merit. For example; turning around in orbit is a pretty easy task (attitude thrusters) yet this reads as if that's the biggest challenge that Falcon 9 overcomes. $\endgroup$ – ThePlanMan Dec 25 '15 at 10:56
  • $\begingroup$ @ThePlanMan Well do you have an objective score to rate how difficult various rocket landings are? All there really is to say is that landing any rocket is hard, but everything about Falcon 9's was an order of magnitude bigger/heavier/faster/more complicated etc. $\endgroup$ – Kaz Dec 25 '15 at 11:53
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    $\begingroup$ I'm just saying that biger/faster/heavier doesn't mean more complicated. Opening a 500 ml bottle of coke is not harder than a 2 liter bottle. $\endgroup$ – ThePlanMan Dec 25 '15 at 15:38
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    $\begingroup$ I do think this is a really good answer; I just thought that I should note that size doesn't always equal complexity. $\endgroup$ – ThePlanMan Dec 25 '15 at 15:56
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Here is an image of the two trajectories. (From Reddit)

Blue New Sheppard vs Falcon 9

Here is a nice infographic explaining the differences between the two.

enter image description here

Kudos for both images above to Jon Ross of ZLSA Design.

And here is another fun size comparison (source unknown):

enter image description here

This video especially where I cued that link, should also show an aspect of the discussion.

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  • $\begingroup$ Looks at bottom of infographic - is there a rocket Top Trumps pack? $\endgroup$ – Baldrickk May 18 '17 at 13:20
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Blue Origin's flight was straight-up, straight-down, with a fairly small rocket that can't carry much useful payload. It's a great demonstration of technology, but it's only practical for space tourism.

Today's Falcon flight was a paid orbital payload mission. In order to get the payload to orbit, the first stage has to not only bring the second stage to high altitude, but start it going horizontally at fairly high speed; for the return-to-launch-site landing, it then has to cancel all that speed and make its way back, and all this with a much bigger rocket.

SpaceX did low altitude VTVL flights starting as far back as 2012; they could have matched what Blue Origin did within the last year or so if that had been the goal, but their preferred strategy is to take their big technological steps as part of paid payload missions.

None of this is intended to belittle Blue Origin's accomplishment. The two companies just have different goals, and very different ways of approaching them.

(Also, 1982 called to tell Blue Origin and SpaceX they both need to quit fronting.)

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  • $\begingroup$ Does anyone know what maximum velocity was achieved by the F9 first stage prior to separation from the rest of the stack and how that compares with the New Sheppard case? My understanding is that the latter is much closer to the F9 first stage return case than it is to the grasshopper trials (in velocity and altitude terms). I thought the grasshopper trials were to less than a thousand meters. $\endgroup$ – Puffin Dec 22 '15 at 13:43
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    $\begingroup$ @Puffin I read somewhere Max. Velocities: Mach 3.5 for new shepard, Mach 5.5-7.5 for Falcon 9 stage 1 $\endgroup$ – Kaz Dec 22 '15 at 18:27
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Blue Origins

  • Flew to just over 100 km (100.5), just enough to say it went to space.
  • Landed at the same site, presumably went straight up and down.
  • Carried a suborbital payload.
  • Announced only after the fact.

SpaceX

  • Separation from 1st stage at 79.3 km, 5929 km/hr (From webcast video)
  • At that point, the upward speed was about (86.6-75.3)/7 or 1.6 km/ second, as measured from the video. That being very rough, but still under the speed (5800 km/hr), indicates to me that likely most of the speed was in the upward direction, but there was a cross range speed of non-negligible difference.
  • Landing occurred at 9:42. Using Earth's surface gravity, and assuming no acceleration (Both bad assumptions), that means the booster likely topped 400 km, much higher than Blue Origins test.
  • SpaceX broadcast it to the world live
  • The Falcon 9 is much taller than Blue Origins.
  • SpaceX was performing a commercial mission while this was happening.

enter image description here

Bottom line, Blue Origin was a technology demonstration mission, which while quite cool, and worthy of some attention, SpaceX's is a more difficult, more useful demonstration of the technology. Both companies deserve merits for accomplishing this difficult task!

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  • $\begingroup$ New Shepard was also capable of hovering (it appeared to come to a vertical stop so many meters above the pad), while the Falcon 9 can't, even at ~8% (70% x 1/9) of full thrust (though it weighs about 6% of what it does at launch when the tanks are empty). $\endgroup$ – Nick T Dec 22 '15 at 17:50
  • $\begingroup$ @NickT - the Grasshopper and F9Dev both hovered quite a bit, and also steered themselves sideways before landing again. Here is a video of the F9R doing that - youtube.com/watch?v=ZwwS4YOTbbw $\endgroup$ – kim holder Dec 22 '15 at 18:27
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    $\begingroup$ @kimholder true, but the orbital booster version can't throttle down that much. From what I can find, the Merlin 1D can only throttle from 70% to 100% (of 73 tons-force), and the dry mass of the first stage is about (iffy figures) 30 tons, leaving a TWR around 1.6: significantly above 1 = cannot hover. $\endgroup$ – Nick T Dec 22 '15 at 18:36
  • $\begingroup$ Spaceflight 101 has the dry mass of the Falcon first stage as 22 or 23 tons -- remarkably, unofficial numbers for New Shepard have its booster dry mass at around 15-20 tons, despite its much more compact configuration. Grain of salt? $\endgroup$ – Russell Borogove Dec 22 '15 at 18:53
  • $\begingroup$ Hmmm, I doubt the tonnage, and will remove them. $\endgroup$ – PearsonArtPhoto Dec 22 '15 at 18:55
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Several of the answer have stressed the difference in size of the vehicles, and that the trajectories are very different. While those are all good points, I think the fundamental thing which makes SpaceX's feat a good deal more impressive though is that it was done with a lower stage which was being used as part of a regular mission, and not by a vehicle specifically designed for suborbital VTOL-flights. That makes a world of difference.

On a launcher, roughly every 10kg of extra weight in the lower stage (landing gear, propellant, grid fins, everything) make 1kg less payload to orbit. It would be very easy to end up with a system which is so heavy that you can't carry your satellites to orbit anymore. A rocket designed specifically for suborbital VTOL hops faces similar control issues, and must for instance also have engines capable of deep throttling (not easy). It can afford to invest far more weight into those systems however, for all the required gear and the propellant needed to get it back to the ground safely, than a launcher can. It also doesn't have to supply all that extra delta-V for the horizontal velocity. On a launcher, weight is everything, up to their first actual attempt to land on the barge, many space experts would have said that what SpaceX was trying to do was close to impossible.

VTOL under rocket power with a specifically designed vehicle on the other hand, had been done a couple of times before. Examples include the low-gravity Apollo lunar landings, but also vehicles on earth such as the Grumman Lunar Lander XChallenge landers (though the distances and velocities here are much smaller), and perhaps most prominently the DC-X prototype in the 90s. There's a great video of the DC-X online:

What SpaceX did with the 1st stage of their launcher is so difficult from a technical standpoint that it will probably be a long time, perhaps a decade or more, until anyone else manages to pull that off.

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  • $\begingroup$ Hi Manik, welcome to Space Exploration. SpaceX hasn't registered patents for much of its technology. Elon Musk once said since many of their main competitors are governments, patents wouldn't help. Doesn't that make it easier for others to duplicate their achievement? $\endgroup$ – kim holder Jan 4 '16 at 15:27
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    $\begingroup$ Not really. if you file a patent you make the knowledge of how to do something publicly available, if you don't, everyone has to figure it out for themselves, and the devil is in the details. You can't buy an F9 and take it apart, so reverse-engineering it is difficult. The vehicle has to be designed with VTOL in mind and you need certain key technologies like multi-start capability & deep-throttling engines, which few groups have. SpaceX went down that particular road from the start, but the development cycle for a new launcher is generally a decade or more (Ariane V was 12 years). $\endgroup$ – Manik Jan 4 '16 at 16:24
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    $\begingroup$ Where the deep-throttling engines are concerned for instance, it's not that SpaceX is the only people who have them: many others (companies and space agencies alike) have designed and built engines capable of one or another those things, but you need a whole combination of technologies. They have to be in that size, with that thrust, multi-start-capable, flight-proven, and so on, and getting all that experience and know-how takes a lot of time. $\endgroup$ – Manik Jan 4 '16 at 16:33

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