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Watching the video of the first Blue Origin New Shepard vehicle launch, it takes off from ground level, and does not seem to have an exhaust trench:

Most launchers of reasonable size have a trench, so that the exhaust has somewhere to go, other than impinging back on the vehicle. On top of that, they often have a Niagara water system, where huge amounts of water are dumped on the pad, to vaporize (absorb heat energy) and absorb sound energy to protect the launch vehicle.

Why does the Blue Origin vehicle not need such systems?

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  • $\begingroup$ Looking at the video, it appears that there are deflectors under the vehicle which redirect exhaust out to the sides. While not a trench, it would seem to satisfy the purpose - give the exhaust somewhere to go other than back up toward the vehicle. $\endgroup$ – Anthony X May 3 '15 at 5:13
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I may have my own answer.

It looks like this test vehicle uses a single BE-3 engine, which only has about 110,000 lbs of thrust.

We have seen the SpaceX Grasshopper and F9R Dev1 vehicles take off from flat surfaces on a single engine as well, and the Merlin 1D engine produces 145,000 lbs of thrust (in 85% performance mode that apparently it has been running in for the first 15 or so F9 launches. SpaceX reports it plans to run it at 100% for GEO launches to provide margin from returning the first stage).

So we have seen that 145,000 lbs of thrust does not require an exhaust trench, nor a Niagara water system. Thus a 110,000 lb thrust launcher is probably fine.

On the other hand, we have seen the Saturn V (7.5 million lbs of thrust), the Space Shuttle (7 million lbs of thrust), and Falcon 9 (1.3 million lbs of thrust) do require both a trench and a Niagara system.

Would be interesting to find how high you can go without those systems before issues arise.

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They are planning to take off and land vertically, so the vehicle has to be designed to tolerate engines firing close to the ground without a trench anyway.

The amount of thrust that an engine provides doesn't determine the need for a trench by itself. You could, for example, raise the entire vehicle or provide protection on the engine itself instead of having a trench. These tend to be less desirable approaches though -- especially for lower thrust engines.

This video shows some more details on the space below the engine on launch and landing:

Blue Origin concept video

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  • $\begingroup$ If you look at Soyuz, they build the launch table into the side of a hill, so that it is all empty space below it. Is that a trench? Well technically yes and no. If you raise it high enough, so there is sufficient empty space that is closely indistinguishable from a flame trench. If you look at Sea Launch, they leave the deck open for exhaust to hit the ocean down below. Is that a trench? Sort of? $\endgroup$ – geoffc Apr 30 '15 at 18:13
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    $\begingroup$ Landing is almost always at a much throttled down value as compared to launch. Almost by definition. You launch fully fueled, and land mostly empty. SpaceX has the issue that the Merlin 1D has too much thrust even at 70% throttle to allow an empty first stage to hover. And they needed 9 engines to get off the ground. That is at least a factor of ten difference in launch/land thrust or more. $\endgroup$ – geoffc Apr 30 '15 at 18:14
  • $\begingroup$ Isn't NS designed to launch from its landing gear? $\endgroup$ – Erik Apr 30 '15 at 18:18
  • $\begingroup$ Maybe it is? And maybe the answer is similar to mine with a twist. As a suborbital test vehicle, with only one BE-3 it is fine. The orbital vehicle may differ? $\endgroup$ – geoffc Apr 30 '15 at 18:25
  • $\begingroup$ I'm thinking the gear are large enough to void the trench requirement $\endgroup$ – Erik Apr 30 '15 at 18:26

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