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Ron Devu

Communications Glitch?

Question

     I have a relay sat around Duna that is behaving oddly. It shows a 69% signal to Kerbin and it shows green lines down to the surface where I have several landed craft. When I shift focus to anything on the surface, the craft show no connection and cannot transmit data home. Other relays around the Mun and Minmus seems to be functioning normally. I'm guessing my Duna relay, which has a pair of HG-55 dishes, has some kind of hidden power requirement or something. The power source on the relay is a pair of the smallest solar panels. The battery on the OKTO is full and enabled, but only holds 10 charge units. My Kerbin station is fully upgraded.

 

 It's been 2 days now and I haven't cracked this nut. Any suggestions?

Oh wait maybe the HG-55 isn't a relay. I better check that.Doh.

Gah! I just checked and found that even though it looks like a dish, the HG-55 blurb does not mention any relay capabilities. Well I hope this has some entertainment value for you all!

Edited by Ron Devu

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Correct. It's not a relay antenna. Only the ones that start RA-XX are relays, plus the HG-5.

 

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Well, you did figure out the problem on your own! So I think there is still hope for you. ;)

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5 hours ago, Ron Devu said:

And then a century later NASA put a rover or two on Mars using a sky crane that had the same configuration.... rockets on top, all the weight at the bottom Does this mean NASA is immune to pendulum fallacy?

It's not a fallacy when it's an actual pendulum.  The reason that the pendulum fallacy is a fallacy is because it involves the idea that a rocket essentially dangles from its tip because of gravity.  Aside from having no answer for what to do once it reaches free space where gravity is effectively nil and the concept of dangling needs to be redefined, there is the problem that a rocket is a rigid body, but a pendulum is not.  In order to work, a pendulum must hang freely from a fulcrum and be subject to forces external to itself--specifically, forces that are transmitted through the fulcrum one way or the other.  Normally, that's gravity on the pendulum and a normal force transmitting through the fulcrum, which is to say that the fulcrum holds the pendulum up against the pull of gravity with an equal-and-opposite force.  While it is true that a rocket is subject to gravity, it's also true that both the gravity and its own force of thrust work through the rocket's centre of mass (meaning that they work on the rocket in its entirety), and that it dangles from nothing.  In like fashion, a fulcrum under thrust or acceleration of some kind can be the fulcrum for a pendulum provided that the force on the fulcrum is transmitted through it to the pendulum.  A force that operates equally on both won't work, which is why a pendulum-driven clock won't work in free fall--the force is not being transmitted through one to the other but instead acts on both fulcrum and pendulum directly.  The technical term is restoring force and it refers to the tendency of a pendulum to hang along the gravitational pull so as to minimise its potential energy--i.e., the swinging action restores it to vertical.  A hanging object that generates its own force is no longer a pendulum, because the direction of the force changes orientation as the object does; it's no longer restorative.

A sky crane, on the other hand, is an actual pendulum because the rover hangs by a flexible cable and the force behind the hanging is gravity or an acceleration generated somewhere not on the payload, but still transmitted to the payload through the cable.  It's either from the rockets on the sky crane (which would be a pseudo-gravitational acceleration that impels the payload to hang) or it would be gravity itself if the crane is landing the payload on the surface of some other body and there is a hovering element involved in the landing.

On the gripping hand, a pendulum-like rocket would work just fine if the payload hung from the force generator by a flexible attachment and the force generator kept its orientation in despite of any motion of the payload.  That's the operating theory behind Medusa rockets (they're like Orion, but with the nuclear bombs going off in a sort of shroud in front of the rocket), or, for that matter, parachutes.

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4 hours ago, Ron Devu said:

A bar of steel suspended by a bearing in the upper end will oscillate just like a cable pendulum [snip]

But the rigid part of the pendulum--the steel bar--is still free to rotate about the fulcrum on the bearing.  That rotational degree of freedom is the necessary part.  My apologies if that was unclear; I cited flexible cables specifically because that's what real sky cranes use.

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You know Bewing, sometimes I think this game only exists to convince me I don't belong in the gene pool.

 

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15 hours ago, Ron Devu said:

You know Bewing, sometimes I think this game only exists to convince me I don't belong in the gene pool.

Goddard himself built the first liquid-fuelled rocket with the engine on top and the tanks on the bottom.  When it comes to making mistakes with rockets, you're in good company.

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9 hours ago, Zhetaan said:

Goddard himself built the first liquid-fuelled rocket with the engine on top and the tanks on the bottom.  When it comes to making mistakes with rockets, you're in good company.

And then a century later NASA put a rover or two on Mars using a sky crane that had the same configuration.... rockets on top, all the weight at the bottom Does this mean NASA is immune to pendulum fallacy?

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11 hours ago, Zhetaan said:

It's not a fallacy when it's an actual pendulum. ... (snip)

Really nicely argued, but there is problem with this approach. A pendulum can be a rigid object. A bar of steel suspended by a bearing in the upper end will oscillate just like a cable pendulum I like the centre-of-mass argument though. If the engine thrust is acting through the centre of mass, it will impart no rotation nor will it apply any restorative forces, so the rocket is indeed free to rotate around the centre of mass, and will if some force, say aerodynamic drag, is applied.

Thanks for the reply, it did a lot to clarify my thinking..This approach also makes gravity turns easier to understand.

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