Author Topic: Dragon v/s Orion  (Read 192307 times)

Offline Robotbeat

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Re: Dragon v/s Orion
« Reply #340 on: 09/04/2013 04:11 am »
Voyager, no momentum wheels
Spin stabilized, aren't they?

 - Ed Kyle
the Pioneers were, not the Voyagers.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline Comga

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Re: Dragon v/s Orion
« Reply #341 on: 09/04/2013 06:36 am »
Voyager, no momentum wheels
Spin stabilized, aren't they?

 - Ed Kyle
the Pioneers were, not the Voyagers.
The New Horizons probe to Pluto and the Kuiper belt also has no momentum wheels. It even does the maneuvers for the Ralph imager with TDI (Time Delay Integration) using its little monoprop thrusters.

I believe that the JPL just activated the backup attitude control system on Voyager 2 and turned off the primary attitude control system  after something over a third of a million impulses.  A lot of control can be had with a little bit of fuel.  Momentum wheels are not needed in many cases.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline IRobot

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Re: Dragon v/s Orion
« Reply #342 on: 09/04/2013 07:26 am »
To save space and fuel, could a mixed system of RCS + ion engines be used? RCS would do fast corrections while ion engines would do over the time attitude compensation, saving fuel.

Offline Jim

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Re: Dragon v/s Orion
« Reply #343 on: 09/04/2013 11:21 am »
To save space and fuel, could a mixed system of RCS + ion engines be used? RCS would do fast corrections while ion engines would do over the time attitude compensation, saving fuel.

That wouldn't save space

Offline IRobot

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Re: Dragon v/s Orion
« Reply #344 on: 09/04/2013 12:29 pm »
It saves space on hydrazine RCS tank size, if the mission is long enough.

Offline Jim

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Re: Dragon v/s Orion
« Reply #345 on: 09/04/2013 01:19 pm »
It saves space on hydrazine RCS tank size, if the mission is long enough.

Which would be taken up by the ion propellant and systems, for no net savings.  You asked a question and the answer is no.  Ion systems are used for velocity adjustments and not attitude control.
« Last Edit: 09/04/2013 01:20 pm by Jim »

Offline Robotbeat

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Re: Dragon v/s Orion
« Reply #346 on: 09/04/2013 03:10 pm »
It saves space on hydrazine RCS tank size, if the mission is long enough.

Which would be taken up by the ion propellant and systems, for no net savings.  You asked a question and the answer is no.  Ion systems are used for velocity adjustments and not attitude control.
Ion systems are used for both, though not in every case.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline mmeijeri

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Re: Dragon v/s Orion
« Reply #347 on: 09/04/2013 03:13 pm »
Ion or arcjet? Not that either could replace chemical RCS thrusters on Orion.
Pro-tip: you don't have to be a jerk if someone doesn't agree with your theories

Offline Robotbeat

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Re: Dragon v/s Orion
« Reply #348 on: 09/04/2013 04:15 pm »
Ion or arcjet? Not that either could replace chemical RCS thrusters on Orion.
Ion. Boeing's 702SP is all-electric (no chemical RCS) and I believe uses Boeing's XIPS thrusters, though I can't find technical details anywhere.

And this is off-topic....
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Online oldAtlas_Eguy

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Re: Dragon v/s Orion
« Reply #349 on: 09/04/2013 06:44 pm »
So basicly we have determined that manned Dragon would need an unknown additional amount of RCS prop for longer duration BEO like missions. BTW cargo Dragon with nothing moving inside would not need more RCS prop (or very small increase if any used during drift) which is why some sats get by without reaction wheels for long duration missions.

The amount of additional RCS prop may be within the current DragonRider's designed RCS prop margins once actual usage becomes known from several DragonRider flights.

Offline baldusi

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Re: Dragon v/s Orion
« Reply #350 on: 09/04/2013 07:03 pm »
Do we know about heat rejection? Power budget for the ECLSS? The improved ECLSS? A toilet system?

Offline Sohl

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Re: Dragon v/s Orion
« Reply #351 on: 09/04/2013 08:57 pm »
Quote
So basicly we have determined that manned Dragon would need an unknown additional amount of RCS prop for longer duration BEO like missions.

So, why not re-orient the crew's exercise bike/treadmill daily as needed to counter unwanted rotation?  ::)  Just joking!

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