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I am curious whether a 30 cubic meter solar balloon made of black nylon and filled with ambient air would be detectable by the primary radar used by ATC in Continental Europe. Due to its size and light weight, a balloon of this kind is not required to carry a transponder to fly in European airspace. I wonder, given contemporary target-detection filters in primary radar relative to background 'clutter' or noise, whether an aerostat of this kind would be detectable. Thank in advance, Sasha

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  • $\begingroup$ If it's filled with ambient air, how's it going to get off the ground? $\endgroup$ – Harper - Reinstate Monica Oct 21 '19 at 15:22
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    $\begingroup$ @Harper: Black plastic absorbs sunlight, heats up, heats up the air inside, air expands, density becomes lighter than surrounding air, ascends. $\endgroup$ – Nyos Oct 22 '19 at 0:41
  • $\begingroup$ #learnsomethingneweveryday @Nyos $\endgroup$ – Harper - Reinstate Monica Oct 22 '19 at 2:58
  • $\begingroup$ This is not the same question as the lawn chair balloon question. First, the lawn chair has a non-zero and significant RCS. Second, the man seated in the lawn chair has an even more significant RCS, and is detectable frequently by primary radar. Third, a simple black plastic balloon has a very very small RCS, and would not be detected by primary radars. So to answer the OP question, the key lies in the material used in the solar balloon. It is likely that there will be a sputtered metalic coating, but if not the balloon in this question would have a slim chance of being detected. $\endgroup$ – mongo Oct 25 '19 at 0:28
  • $\begingroup$ @mongo, but the answer there is applicable also here (and what you say makes even more applicable). That makes it a duplicate $\endgroup$ – Federico Oct 28 '19 at 6:57

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