China's Space Program News Thread


Richard Santos

Senior Member
Registered Member
Today marks the one year anniversary of the Tianwen Mars mission.

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Courious why the exhaust from the strap on booths are cants outwards. Are the nozzles on th strap on boosters gimble mounted?
 

j17wang

Junior Member
Registered Member
Looks like that HERD experiment with Europe has been confirmed:

Wow... $310m for an experiment!! If I am not mistaken, someone here mentioned the Tianhe core costed around that or slightly less. Now in this picture I've attached, HERD is attached to a new module. Perhaps that's also coming?
View attachment 75017

The real shocker in that picture is the China-Italy module. Is that real? It looks legit since the rest of the tiangong modules are represented accurately.
 

Richard Santos

Senior Member
Registered Member
Think of the exhaust as legs on a stool. By aiming them slightly outwards instead of directly down you increase the vehicle's stability.
I don’t believe that works from physics point of view. the plumes are not solid objects that can give static stability with a wider stance by allowing a larger tilt before center of gravity moves outside its footprint.

The effects of multiple canted or vertical plums are the same. Their individual thrust vectors combined to for just one single resultant vector that pass through the center of mass..

To offer stability, the individual plumes have to either gimble, or throttle, or both. This allows the resultant vector to be aimed on the fly instead of going through center of mass by default. Hence my question if those strap on boosters are gimbled?
 

Engineer

Major
Looks like that HERD experiment with Europe has been confirmed:

Wow... $310m for an experiment!! If I am not mistaken, someone here mentioned the Tianhe core costed around that or slightly less. Now in this picture I've attached, HERD is attached to a new module. Perhaps that's also coming?
View attachment 75017
Funny. I was looking at cosmic rays composition and energy distribution the other day, and this project came up in my search results. Ever since then, it seems to make an appearance everywhere.
 

taxiya

Brigadier
Registered Member
I don’t believe that works from physics point of view. the plumes are not solid objects that can give static stability with a wider stance by allowing a larger tilt before center of gravity moves outside its footprint.

The effects of multiple canted or vertical plums are the same. Their individual thrust vectors combined to for just one single resultant vector that pass through the center of mass..

To offer stability, the individual plumes have to either gimble, or throttle, or both. This allows the resultant vector to be aimed on the fly instead of going through center of mass by default. Hence my question if those strap on boosters are gimbled?
It doesn't matter if it is solid or plume. They provide the same thing to keep the body from falling to the side, the force. Canted force means a greater area below the center of gravity, therefor increased stability before TVC is required. A hovering rocket (0 vertical velocity) is no different from a stool on the ground except side way forces. A stool can counter that to a limited point due to friction force of the legs and ground. In rocket, TVC does that job. You can see that most small stools would employ canted legs for the same purpose.

Yes, LM-5's inner engines of the boosters are on gimbal mounts.
 
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Richard Santos

Senior Member
Registered Member
It doesn't matter if it is solid or plume. They provide the same thing to keep the body from falling to the side, the force. Canted force means a greater area below the center of gravity, therefor increased stability before TVC is required. A hovering rocket (0 vertical velocity) is no different from a stool on the ground except side way forces. A stool can counter that to a limited point due to friction force of the legs and ground. In rocket, TVC does that job. You can see that most small stools would employ canted legs for the same purpose.

Yes, LM-5's inner engines of the boosters are on gimbal mounts.


It is actually very different. Canted legs on a stool works because static forces on the legs change in response if the stool begins to tilt. This produces a torque to counter act the tilt. The angled plumes produce the same thrust regardless of whether the rocket is tilting or not. Angling the plume does nothing to improve stability. The plumes must be actively throttled or gimbled to vary the forces they transmit to the rocket to help the rocket stabilize.

You needn’t argue with me. My degrees are in engineering physics and astronautics.
 
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Arcgem

New Member
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The side boosters are angled/gimbaled so the plume axes intersect somewhere between the center of pressure and center of gravity of the rocket. This minimizes the net torque applied to the entire rocket by balancing atmospheric drag with the thrust.

Small thrust imbalances between boosters may push the rocket off a bit, but the direction the rocket points would remain largely the same, easing the active stabilization.
 

winword

Junior Member
Registered Member
It is actually very different. Canted legs on a stool works because static forces on the legs change in response if the stool begins to tilt. This produces a torque to counter act the tilt. The angled plumes produce the same thrust regardless of whether the rocket is tilting or not. Angling the plume does nothing to improve stability. The plumes must be actively throttled or gimbled to vary the forces they transmit to the rocket to help the rocket stabilize.

You needn’t argue with me. My degrees are in engineering physics and astronautics.
They work differently but that doesn't mean tilted boost doesn't make sense. A tilted booster has less torque as the force passes closer to center of mass.
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Imbalance of booster is less likely to cause tilting of the rocket/ easier to compensate.
This should be easy to understand for someone with a degree, you don't need to stress that.
 

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