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In the spirit of Why does this rocket have a nose cone “cozy”? I'd like to ask why the SpaceX Hopper has a propellor on top, or at least something that looks reminiscent of Beany's propeller.

What is this thing; what's it for, what does it do, how's it used exactly, etc.?

enter image description here

context: Beany and Cecil

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    $\begingroup$ Look like a marine navigation radar but not understanding why it's there $\endgroup$ – GremlinWranger Jun 11 at 8:13
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    $\begingroup$ Presumably this is part of range safety, I have read (citation needed) that operations are held or aborted if there are any marine craft down-range. Edit : considering marine craft, down-range would be towards the water. No point looking landward. $\endgroup$ – Brian Drummond Jun 12 at 11:04
  • $\begingroup$ @BrianDrummond from this particular site, which direction is "down-range"? Don't they just hover and return to the ground? See the video in Why did Starhopper's exhaust plume become brighter just before landing? My guess is that the radar will be used to check for aircraft when they start going for higher hops. $\endgroup$ – uhoh Jun 12 at 11:07
  • $\begingroup$ (edit aborted by 5 min cutoff) : considering marine craft, down-range would be towards the water. No point looking landward. You probably want it to land on land, but during testing ya never know. $\endgroup$ – Brian Drummond Jun 12 at 11:10
  • $\begingroup$ What's the difference between a 'propeller' and a 'propellor'? A propeller is a device that supplies impetus to move an object. A propellor is a device that forces an object into motion, with severe penalties for non-compliance! ;-) $\endgroup$ – Tom Spilker Jun 12 at 23:45
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It's a radar intended to observe nearby boats.

Sources:

tweet by NASA Spaceflight Reporter Michael Baylor:

SpaceX has asked the FCC for permission to operate a Garmin radar on top of a water tower in Boca Chica.

The "water tower" looks familiar.

FCC filing: Space Exploration Technologies Corp. 0459-EX-CN-2020:

...d) List any natural formations of existing man-made structures (hills, trees, water tanks, towers, etc.) which, in the opinion of the applicant, would tend to shield the antenna from aircraft:

This radar will be attached to the top of a water tower and is masked between 164 to 290 degrees to avoid illuminating launch or test vehicles. Please note that a TFR will be in place when the radar is operating.

Details of the application include a frequency range of 9300 to 9500 MHz, consistent with Marine Radar in the X-band.

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    $\begingroup$ Thank you for your answer and Welcome to Space! Are you sure it will not also be used to look for nearby aircraft? It is a rocket after all ;-) $\endgroup$ – uhoh Jun 11 at 9:29
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    $\begingroup$ @OrganicMarble: What are you talking about? i.imgur.com/Hb3bDEA.png is clearly a water tower. $\endgroup$ – Christopher James Huff Jun 11 at 12:56
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    $\begingroup$ @ChristopherJamesHuff Notably the radar is absent from that photo... $\endgroup$ – Darrel Hoffman Jun 11 at 20:16
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    $\begingroup$ @uhoh I had guessed similarly (except the radar is something recently added, long after its flying days were over). In structure and hazards, it's essentially identical to a water tower. For the purposes of the application, it's entirely reasonable to treat it as one, rather than going into a lengthy and quite irrelevant description of its origin and nature as an experimental rocket vehicle and how it can be treated in every way as if it were a water tower. $\endgroup$ – Christopher James Huff Jun 12 at 1:38
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    $\begingroup$ @ChristopherJamesHuff ah, it's an ex-hopper now $\endgroup$ – uhoh Jun 12 at 2:52

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