Comments on: Random Thoughts: Tuggery and RCS http://selenianboondocks.com/2009/07/random-thoughts-tuggery-and-rcs/ Random Musings from the Warped Minds of Jonathan Goff, Ken Murphy, John Hare, and Kirk Sorensen Fri, 12 Mar 2010 16:37:49 -0800 http://wordpress.org/?v=2.8.4 hourly 1 By: Paul Breed http://selenianboondocks.com/2009/07/random-thoughts-tuggery-and-rcs/comment-page-1/#comment-5164 Paul Breed Tue, 14 Jul 2009 21:18:42 +0000 http://selenianboondocks.com/?p=1085#comment-5164 Can't you do full 6dof with 12 thrusters? Assume a sphere radius 1 with the center a 0,0,0 Draw traditional x,y,z axis through the sphere. Place thrusters in pairs where the axis pierce the sphere. Assume x,y,z At 1,0,0 thrusters point toward y+ and y- At -1,0,0 thrusters point toward y+ and y- This gives rotation around Z and translation in y At 0,1,0 thrustors point toward +/- z At 0,-1,0 thrusters point toward +/-z This gives rotation around X and translation in Z At 0,0,1 thrusters point toward +/-x At 0,0,-1 thrusters point toward +/-x This gives rotation around y and translation in x 6DOF with 12, 16 not required. Finding the proper locations for the 12 on something airplane shaped is "harder" Can’t you do full 6dof with 12 thrusters?

Assume a sphere radius 1 with the center a 0,0,0
Draw traditional x,y,z axis through the sphere.
Place thrusters in pairs where the axis pierce the sphere.
Assume x,y,z

At 1,0,0 thrusters point toward y+ and y-
At -1,0,0 thrusters point toward y+ and y-
This gives rotation around Z and translation in y

At 0,1,0 thrustors point toward +/- z
At 0,-1,0 thrusters point toward +/-z
This gives rotation around X and translation in Z

At 0,0,1 thrusters point toward +/-x
At 0,0,-1 thrusters point toward +/-x
This gives rotation around y and translation in x

6DOF with 12, 16 not required.

Finding the proper locations for the 12 on something airplane shaped is “harder”

]]> By: Dart http://selenianboondocks.com/2009/07/random-thoughts-tuggery-and-rcs/comment-page-1/#comment-5096 Dart Thu, 09 Jul 2009 12:47:19 +0000 http://selenianboondocks.com/?p=1085#comment-5096 This subject, like all really engineering ones, needs system level requirements to be answered correctly. By that I am certainly not criticizing your exploration of the subject but suggesting you develop a map of system functions and implications to be considered beyond simple redundancy. That, together with the great energy management requirements, are why rockets are so challenging. So consider: Do you have complete, redundant, control of the separation conditions or could you have rates induced when you are released? In addition to control redundancy, do you want any capability to maneuver for ascent underspeeds, collision avoidance, other cases? Do you care about cross-coupling with your control scheme? Do you have sufficient freedom in your configuration to assure the CG is convenient for the functioning of the thrusters? What kind of manifolding are you planning to manage leaks, thruster failed on, and other system level faults? Lots to think about..... This subject, like all really engineering ones, needs system level requirements to be answered correctly. By that I am certainly not criticizing your exploration of the subject but suggesting you develop a map of system functions and implications to be considered beyond simple redundancy. That, together with the great energy management requirements, are why rockets are so challenging.

So consider: Do you have complete, redundant, control of the separation conditions or could you have rates induced when you are released? In addition to control redundancy, do you want any capability to maneuver for ascent underspeeds, collision avoidance, other cases? Do you care about cross-coupling with your control scheme? Do you have sufficient freedom in your configuration to assure the CG is convenient for the functioning of the thrusters? What kind of manifolding are you planning to manage leaks, thruster failed on, and other system level faults?

Lots to think about…..

]]> By: MG http://selenianboondocks.com/2009/07/random-thoughts-tuggery-and-rcs/comment-page-1/#comment-5076 MG Wed, 08 Jul 2009 06:49:19 +0000 http://selenianboondocks.com/?p=1085#comment-5076 Ugh. At first glance, the title read "Thuggery and RCS". My reaction: What has Jon gotten himself into THIS time? Ugh. At first glance, the title read “Thuggery and RCS”. My reaction: What has Jon gotten himself into THIS time?

]]> By: Jonathan Goff http://selenianboondocks.com/2009/07/random-thoughts-tuggery-and-rcs/comment-page-1/#comment-5074 Jonathan Goff Wed, 08 Jul 2009 04:31:12 +0000 http://selenianboondocks.com/?p=1085#comment-5074 Aaron, NASA did some work with Camfield-joint thrusters that had a full hemispherical aiming capability. The problem is that I don't know how you would package those on an RLV or an upper stage. Maybe on a lander or a service module or something, but it would be tricky. ~Jon Aaron,
NASA did some work with Camfield-joint thrusters that had a full hemispherical aiming capability. The problem is that I don’t know how you would package those on an RLV or an upper stage. Maybe on a lander or a service module or something, but it would be tricky.

~Jon

]]> By: Aaron Williams http://selenianboondocks.com/2009/07/random-thoughts-tuggery-and-rcs/comment-page-1/#comment-5073 Aaron Williams Wed, 08 Jul 2009 04:27:53 +0000 http://selenianboondocks.com/?p=1085#comment-5073 I assume you're talking fixed direction thrusters, is there something preventing thrust vectoring? If it was practical, it seems like 3 thrusters with a full hemisphere of motion would let you translate/rotate any way you want. I assume you’re talking fixed direction thrusters, is there something preventing thrust vectoring? If it was practical, it seems like 3 thrusters with a full hemisphere of motion would let you translate/rotate any way you want.

]]> By: Ian http://selenianboondocks.com/2009/07/random-thoughts-tuggery-and-rcs/comment-page-1/#comment-5072 Ian Wed, 08 Jul 2009 00:52:09 +0000 http://selenianboondocks.com/?p=1085#comment-5072 Jon, 3 thrusters is the bare bare minimum, if you don't mind unnecessary translations. 6 is the minimum that will let you rotate without translation. I haven't done the math but I'll believe Doug that 12 gives you redundancy. Besides, it's not also the # of thrusters, but also the fuel. A LOT less if you're only doing rotations, and you can use just momentum wheels, as it was mentioned before. Ian Jon,
3 thrusters is the bare bare minimum, if you don’t mind unnecessary translations. 6 is the minimum that will let you rotate without translation. I haven’t done the math but I’ll believe Doug that 12 gives you redundancy. Besides, it’s not also the # of thrusters, but also the fuel. A LOT less if you’re only doing rotations, and you can use just momentum wheels, as it was mentioned before.
Ian

]]> By: Jonathan Goff http://selenianboondocks.com/2009/07/random-thoughts-tuggery-and-rcs/comment-page-1/#comment-5066 Jonathan Goff Tue, 07 Jul 2009 19:31:25 +0000 http://selenianboondocks.com/?p=1085#comment-5066 Ok, so somewhere between 6-12 thrusters (with 12 being the paranoid but probably right number, and 6 being the bare minimum number)? Thanks Doug! So it's not a huge improvement, but it does make a difference. Ok, so somewhere between 6-12 thrusters (with 12 being the paranoid but probably right number, and 6 being the bare minimum number)? Thanks Doug!

So it’s not a huge improvement, but it does make a difference.

]]> By: Doug Jones http://selenianboondocks.com/2009/07/random-thoughts-tuggery-and-rcs/comment-page-1/#comment-5065 Doug Jones Tue, 07 Jul 2009 19:09:32 +0000 http://selenianboondocks.com/?p=1085#comment-5065 +/- pitch, yaw, roll requires 6 thrusters minimum, and 8 (properly arranged) can provide partial redundancy. For full safety (and because we're slightly paranoid) we plan to have two full sets of 6 in the A and B RCS for Lynx, a total of 12. A 16 thruster system can give six axis control and redundant 3-axis control, but if prox ops are _always_ handled by the tug, 12 should do just fine. +/- pitch, yaw, roll requires 6 thrusters minimum, and 8 (properly arranged) can provide partial redundancy. For full safety (and because we’re slightly paranoid) we plan to have two full sets of 6 in the A and B RCS for Lynx, a total of 12.

A 16 thruster system can give six axis control and redundant 3-axis control, but if prox ops are _always_ handled by the tug, 12 should do just fine.

]]> By: Randy Campbell http://selenianboondocks.com/2009/07/random-thoughts-tuggery-and-rcs/comment-page-1/#comment-5064 Randy Campbell Tue, 07 Jul 2009 19:07:19 +0000 http://selenianboondocks.com/?p=1085#comment-5064 Tet Ships: http://www.clowder.net/hop/tetships/tetships.html For the "heck" of it :) Randy Tet Ships:
http://www.clowder.net/hop/tetships/tetships.html

For the “heck” of it :)

Randy

]]> By: Jonathan Goff http://selenianboondocks.com/2009/07/random-thoughts-tuggery-and-rcs/comment-page-1/#comment-5060 Jonathan Goff Tue, 07 Jul 2009 14:58:39 +0000 http://selenianboondocks.com/?p=1085#comment-5060 HH, I'd still want at least attitude control--it's tons easier grappling something that is actively cooperating. Martijn, No, this is just more thinking along the same lines. For existing upper stages, it means they probably have all the control they need. For new upper stages or RLV upper stages it just means that they really have no reason to give them "the works" when it comes to RCS. ~Jon HH,
I’d still want at least attitude control–it’s tons easier grappling something that is actively cooperating.

Martijn,
No, this is just more thinking along the same lines. For existing upper stages, it means they probably have all the control they need. For new upper stages or RLV upper stages it just means that they really have no reason to give them “the works” when it comes to RCS.

~Jon

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