Author Topic: Are Theodolites still used today?  (Read 4732 times)

Offline Bruhn

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Are Theodolites still used today?
« on: 07/17/2006 08:23 pm »
I know how Saturn V measured the alignment of the inertial navigation unit prior to launch.  It used a theodolite to aim a beam of light to prisms located on the intertial platform and the IU needed an opening for the light beam.

My question is; how do LVs align their INUs today.  Particularly EELVs.  Are we still using theodolites today or is their a new technology.  GPS perhaps?  If theodolites are still used for EELVs, does KSC (or whoever) measure the angles between the INU and a geodetic witness plate every time, or was it just done several times at the beginning of the program and stored in a database.

A non-Nav guy looking to upgrade his general knowledge.

Offline Jim

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Re: Are Theodolites still used today?
« Reply #1 on: 07/17/2006 08:30 pm »
Delta still does.  KSC doesn't support the EELV's

Offline Bruhn

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Re: Are Theodolites still used today?
« Reply #2 on: 07/17/2006 08:48 pm »
Quote
Jim - 17/7/2006  3:17 PM

Delta still does.  KSC doesn't support the EELV's

Delta IV or II or both?  Do you know if they take their measurement as part of the final moments of the launch countdown or days/hours before?  It seems like measurements would be hard to make if the upper stage is deflecting or swaying in the breeze.

Offline Jim

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Re: Are Theodolites still used today?
« Reply #3 on: 07/18/2006 12:41 am »
Both.  They use the same avionics suite.  Day of launch, during power up of the RIFCA

Offline guidanceisgo

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RE: Are Theodolites still used today?
« Reply #4 on: 07/18/2006 04:13 am »
I am surprised that Delta II or IV would not gyrocompass to align.  The nav unit senses earth rate and determines the heading after usually a period of ~ 4 minutes.  After that , the units can usually be sent into nav mode at any time.  Theodolite alignment, (although classic navigation) is really time intensive and isn't any fun in bad weather.  Anybody have any insight into why they still use the old poroprism and theodolite.

Offline Bruhn

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RE: Are Theodolites still used today?
« Reply #5 on: 07/18/2006 04:59 pm »
Like I said, I'm not a Nav-guy so I'm speaking way out of my experience box.  But I believe most IMUs are commanded to gyrocompass align themselves to East, North, and Up [ENU].  This is used to derive the vehicle body orientation relative to ENU.  But to get the body to geodetic orientation, you must measure the angles between the IMU and a geodetic witness plate at the pad.  My question was if theodolites are still used to do this or if a new technology was developed.  Sounds like theodolites are still used if Delta performs this measurement each time.

Anybody know how Shuttle does this?  Is there a window for the beam to pass through?

Offline Jim

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Re: Are Theodolites still used today?
« Reply #6 on: 07/18/2006 05:19 pm »
I know there it a point in the countdown to align the shuttle's IMU.  But there isn't a window except for the star trackers

Offline guidanceisgo

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RE: Are Theodolites still used today?
« Reply #7 on: 07/18/2006 08:01 pm »
Small launch vehicles went away from using the theodolite alignment when the gyrocompass technology became pretty common in IMU's.

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