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Orion SM RCS thruster placement
by
Jim
on 12 Oct, 2018 15:44
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Have fun comparing Apollo to Orion
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#1
by
HarryM
on 12 Oct, 2018 18:08
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Not very elegant...
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#2
by
Eric Hedman
on 12 Oct, 2018 18:34
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I liked the Apollo thruster layout better. It was clean and simple. I am assuming that the Orion layout was different due to the adapter ring between the capsule and service module. You can't have a thruster plume impinge on the ring. I would also assume that they did some research on the most efficient and effective placement of the thrusters given the geometry and center of gravity they had to work with and the most likely maneuvers required. If it works, fine. There is nothing really to complain about if they do the job.
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#3
by
freda
on 12 Oct, 2018 18:46
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I certainly am no expert, and this is way outside my field, but I guess for Orion+SM translation, the desire is to thrust through the center of mass (to prevent rotation)? For rotation (yaw, pitch, roll) the desire is to evenly distribute the rotating thrust around the same center of mass (to prevent translation)?
So the diagonal pointing thrusters would complicate the math, and would seem to require multiple thrusters to fire in varying amounts in order to rotate.
The Apollo SM thrusters seemed more 90-degree-ish, and easier for my poor old mind to grasp.
All interesting.
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#4
by
Lars-J
on 12 Oct, 2018 19:17
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I'm guessing the overly (seemingly) bizarre layout (and number) of RCS thrusters on Orion is due to redundancy - extreme redundancy. There seems to be backups (and double backups) for most of them.
Another reason is probably not wanting to impinge on the solar panels too much. Are they still movable in the latest design? If so that imposes yet another set of limitations.
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#5
by
Jim
on 12 Oct, 2018 19:17
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I liked the Apollo thruster layout better. It was clean and simple. I am assuming that the Orion layout was different due to the adapter ring between the capsule and service module. You can't have a thruster plume impinge on the ring. I would also assume that they did some research on the most efficient and effective placement of the thrusters given the geometry and center of gravity they had to work with and the most likely maneuvers required. If it works, fine. There is nothing really to complain about if they do the job.
I knew that was coming. Even without the ring, one of the faults of Apollo, it blasted docked vehicles. Also, it wasn't very robust when it came to failures.
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#6
by
Jim
on 12 Oct, 2018 19:19
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Should have a contest. People submit which thrusters will fire for X, Y & Z translations and P, Y & R rotations.
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#7
by
brickmack
on 12 Oct, 2018 19:54
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On the impingement issue, the paper/presentation Plume Impingement Analysis for the European Service Module Propulsion System has a bit of information. That was one of the issues (along with general reliability) that lead to moving to a 24 RCS engine layout instead of the initial 16 engine concept, the new layout has less impingement on the solar arrays
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#8
by
hektor
on 13 Oct, 2018 17:23
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Would be another interesting exercise to compare with the ATV layout since the Prime is the same.
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#9
by
woods170
on 13 Oct, 2018 21:00
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Not very elegant...
Nor was the RCS layout of the original LockMart 606/607 service module design. The RCS quads were located so close to the CMA that there was very significant plume impingement on the CMA.
It is not supposed to be elegant.
It is however intented to be functional.
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#10
by
woods170
on 15 Oct, 2018 06:46
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Should have a contest. People submit which thrusters will fire for X, Y & Z translations and P, Y & R rotations.
Throwing in a schematic of the ESM RCS thrusters to aid in Jim's challenge. The image is a dead give-away for the P(itch), Y(aw) and R(oll) rotations.
The thrusters needed for translations along the X, Y & Z axis can be easily deduced from the image as well as long as people remember that:
- Roll is around the X-axis
- Pitch is around the Y-axis
- Yaw is around the Z-axis.
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#11
by
Jim
on 15 Oct, 2018 14:22
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Not very elegant...
Very elegant. It is has multiple operating modes.
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#12
by
HarryM
on 15 Oct, 2018 15:45
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#13
by
Jim
on 15 Oct, 2018 17:44
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Throwing in a schematic of the ESM RCS thrusters to aid in Jim's challenge. The image is a dead give-away for the P(itch), Y(aw) and R(oll) rotations.
The thrusters needed for translations along the X, Y & Z axis can be easily deduced from the image as well as long as people remember that:
- Roll is around the X-axis
- Pitch is around the Y-axis
- Yaw is around the Z-axis.
The trick is doing couples with thrusters and not just rotation that also induces a translation.
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#14
by
Jimmy_C
on 15 Oct, 2018 22:51
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Should have a contest. People submit which thrusters will fire for X, Y & Z translations and P, Y & R rotations.
Throwing in a schematic of the ESM RCS thrusters to aid in Jim's challenge. The image is a dead give-away for the P(itch), Y(aw) and R(oll) rotations.
The thrusters needed for translations along the X, Y & Z axis can be easily deduced from the image as well as long as people remember that:
- Roll is around the X-axis
- Pitch is around the Y-axis
- Yaw is around the Z-axis.
Orion SM Pitch/Yaw thrusters are farther from the center of mass (eyeballing it), giving them more torque than on the Apollo SM. Furthermore, the thrustors fire perpendicular to the direction of translation when used in that mode, which presumably impacts whatever it is docked to much less. Finally, the roll thrustors can be used for x/y translation while the pitch/yaw thrusters can simultaneously compensate for any rotation created by the changing center of mass. It doesn't seem that Apollo SM RCS thrusters can easily perform that function.
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#15
by
woods170
on 16 Oct, 2018 07:12
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Throwing in a schematic of the ESM RCS thrusters to aid in Jim's challenge. The image is a dead give-away for the P(itch), Y(aw) and R(oll) rotations.
The thrusters needed for translations along the X, Y & Z axis can be easily deduced from the image as well as long as people remember that:
- Roll is around the X-axis
- Pitch is around the Y-axis
- Yaw is around the Z-axis.
The trick is doing couples with thrusters and not just rotation that also induces a translation.
Good addition Jim. Although obvious to a good number of people here.
The nice thing about this RCS setup is that none of the RCS thrusters is parallel to any of the X, Y and Z axis and thus always act along (at least) two of the three axis. Which in turn allows for a high degree of combined rotations/translations with minimal use of propellant.
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#16
by
hektor
on 16 Oct, 2018 11:32
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#17
by
woods170
on 16 Oct, 2018 12:58
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