Author Topic: LIVE: Atlas V 501 - X-37B OTV-3 - Dec 11, 2012  (Read 125172 times)

Online Space Ghost 1962

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Re: LIVE: Atlas V 501 - X-37B OTV-3 - Dec 11, 2012
« Reply #360 on: 04/27/2015 08:14 PM »
Now that the official photos have been released, one of my own.

Why is the engine off centered? Is it the deployable solar panel?

The X-37 was changed several times during development. It was once to have 2 engines, but later one was deleted.

But dont you want the engine push to go through the center of the mass of the craft? How can they just get rid of one of the engines and be off centered and maintain thrust without pushing the craft to one side?
TVC.

Offline kevin-rf

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Re: LIVE: Atlas V 501 - X-37B OTV-3 - Dec 11, 2012
« Reply #361 on: 04/28/2015 01:33 AM »
Does that engine have TVC? The simplest solution is just cant it through the vehicle's (including the payload) center of mass.

Most LV solids do that.
« Last Edit: 04/28/2015 01:34 AM by kevin-rf »
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Offline happyflower

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Re: LIVE: Atlas V 501 - X-37B OTV-3 - Dec 11, 2012
« Reply #362 on: 04/28/2015 04:04 AM »
Does that engine have TVC? The simplest solution is just cant it through the vehicle's (including the payload) center of mass.

Most LV solids do that.

Since I dont know enough about it, i"ll just take space ghosts word for it.

Online Space Ghost 1962

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Re: LIVE: Atlas V 501 - X-37B OTV-3 - Dec 11, 2012
« Reply #363 on: 05/04/2015 06:43 PM »
Does that engine have TVC? The simplest solution is just cant it through the vehicle's (including the payload) center of mass.

Most LV solids do that.

Since I dont know enough about it, i"ll just take space ghosts word for it.

He's right that you don't need a controlled system to vector the thrust through the CM, just a fixed angle that intersects it. In any case where the thrust vector is offset from center,  cosine losses, RCS offset thrust, and GNC that can cope with thrust asymmetry are required.

The cost of using TVC is complexity/reliability, the benefit can be lower total prop usage (less RCS offset thrust, shorter maneuvers) due to its greater control authority. And there are things you can do with it you can't any other way.

Offline kevin-rf

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Re: LIVE: Atlas V 501 - X-37B OTV-3 - Dec 11, 2012
« Reply #364 on: 05/04/2015 06:53 PM »
Space Ghost, don't forget with no "air resistance" in space a single offset engine canted through the center of mass has no cosine losses.

You only have loses when you cant more than one engine or are trying to fly through atmosphere with canted engine(s).

Getting back to TVC, did the AJ-10 on the Shuttle use TVC, or rely on RCS for fine tuning?
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Online Space Ghost 1962

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Re: LIVE: Atlas V 501 - X-37B OTV-3 - Dec 11, 2012
« Reply #365 on: 05/04/2015 07:37 PM »
Space Ghost, don't forget with no "air resistance" in space a single offset engine canted through the center of mass has no cosine losses.

You only have loses when you cant more than one engine or are trying to fly through atmosphere with canted engine(s).
Sure where drag occurs. But if you have a fixed angle offset engine, attitude control before/through/after the burn is maintained by RCS (or CMG) solely. If the guidance for the burn is inexact, say to slight CM shift (prop/consumable depletion etc), then cosine terms come into play, as you "waste" part of RCS/engine burn cancelling the error. That was what I was referring to.

Quote
Getting back to TVC, did the AJ-10 on the Shuttle use TVC, or rely on RCS for fine tuning?

OMS engines are gimballed. FRCs/ARCs for adjusting vector so as not to exceed gimbal rate/limits.

I can go through the entire OMS thrusting maneuver control sequence (attitude hold, ...) and decisions. Variable forward/aft depletion on Shuttle RCS was a big deal, you could have surprises on mission/mission planning often as a result.

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« Last Edit: 05/04/2015 07:46 PM by Space Ghost 1962 »

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