NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: It's Moon-landing Monday
From: Brad Morris
Date: 2009 Jul 24, 11:59 -0400
From: Brad Morris
Date: 2009 Jul 24, 11:59 -0400
I suspect that method would work, albeit a bit clumsy. There will be a nasty transformation for the vector described by the telescope to the direction vector. This will be nasty simply because the window probably won't be orthogonal AND the craft will probably be tumbling in all three angular directions of roll, pitch and yaw simultaneously. That would be the job of a computer program and not hand driven reductions (Space Bygrave anyone?). And since it would be computer driven, there would be a corresponding hard mount location for the telescope, certainly not the ubiquitous duct tape! -----Original Message----- From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of frankreed@HistoricalAtlas.com Sent: Friday, July 24, 2009 2:22 AM To: NavList@fer3.com Subject: [NavList 9206] Re: It's Moon-landing Monday Brad you wrote: "That would be an interesting exercise. The sextant must therefore be aligned to the thrust axis of the vehicle. In other words, holding your sextant in your hand and pointing it out the window (with the previously agreed exercise on distance, RA and declination of the center of your vehicle) does not really tell you how your vehicle is pointed! Assuming that the roll of the vehicle doesn't matter, then the vehicular pitch and yaw will not be known UNLESS the sextant is referenced to the vehicle. I am not sure how we do that with our high end marine sextant!" How about this: take the telescope off the sextant and tape it to a window (with duct tape, always assumed to be available) so that the end of the telescope is flush against the glass. Now put the spacecraft in a slow roll about the axis of thrust for the main engine. We can assume that this can be done. Now you fire up your star chart software on your laptop and plot the stars that you see while you look through the telescope during one roll. Those stars will lie along a circle (probably not a great circle) on the celestial sphere, and the center of that circle is the direction in which you're oriented. When you fire your rocket, you will need to maintain that orientation, so you have to fire the thrusters occasionally while you look through the telescope maintaining whatever stars you see centered in the field of view. On the Apollo missions, there was a sextant built into the spacecraft but it was rarely used as a sextant is intended to be used --to measure angles between objects. Instead it was used to get spacecraft orientation (since it was built in, it was aligned to the spacecraft axes in a known way), and it was used as a telescope to observe the lunar surface. -FER "Confidentiality and Privilege Notice The information transmitted by this electronic mail (and any attachments) is being sent by or on behalf of Tactronics; it is intended for the exclusive use of the addressee named above and may constitute information that is privileged or confidential or otherwise legally exempt from disclosure. If you are not the addressee or an employee or agent responsible for delivering this message to same, you are not authorized to retain, read, copy or disseminate this electronic mail (or any attachments) or any part thereof. If you have received this electronic mail (and any attachments) in error, please call us immediately and send written confirmation that same has been deleted from your system. Thank you." --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---