Has Buzz Aldrin’s Line-of-Sight rendezvous method ever been used?

Buzz Aldrin’s 1963 doctoral thesis describes a line-of-sight (LOS) rendezvous technique which is independent of computer and radar ranging input. Basically, it uses a sight reticule, eyeball and slide rule. The reticule is calibrated for a specific circularized “waiting orbit” below the target’s orbit and the intercept trajectory evolves over a 90° orbital phase angle. It uses slightly more propellant than an idealized rendezvous trajectory. The LOS technique was developed for the planned Gemini program.

LOS was proposed as a back-up rendezvous method. The first orbital rendezvous, Gemini 6, was initiated under computer control . The rendezvous commenced from a lower orbit (as per the LOS technique) so Aldrin's LOS technique could have potentially been used as a back-up. From https://ntrs.nasa.gov/api/citations/20110023479/downloads/20110023479.pdf :

A terminal phase initiated from a coelliptic orbit was selected that allowed … the use of manual backup guidance techniques in the event of system failures. The crew flew an inertial final approach by controlling closing rate and the rotation rate of the inertial line-of-sight to the target.

Was Gemini 6 equipped with a reticule to perform an Aldrin LOS rendezvous as a back-up to the computer?

Has the Aldrin LOS technique ever been used?

  • 3
    $\begingroup$ Gemini spacecraft were equipped with a Crew Optical Alignment Sight (COAS) but I am not sure if the purpose of it was "to perform a LOS" rndz. You might be interested to read "A History of Space Shuttle Rndz" which despite the name covers Gemin rndz in some detail. ntrs.nasa.gov/api/citations/20110023479/downloads/… $\endgroup$ Nov 15, 2021 at 20:39
  • 2
    $\begingroup$ Thanks. Great resource. The LOS reticule measured angles between fixed stars and the target. The source mentions using a sextant on Gemini IV to (unsuccessfully) take elevations above the earth horizon. The COAS was used for "closing operations" (within 150 ft). I don't think it was suitable for rendezvous, which require measuring approach angles at 100+ miles. $\endgroup$
    – Woody
    Nov 15, 2021 at 22:10
  • $\begingroup$ Makes sense, the COAS was a prox ops "sensor" on shuttle IIRC. $\endgroup$ Nov 16, 2021 at 0:14
  • 1
    $\begingroup$ The COAS is a non-magnifying reticule sight, very much like a “heads up” rifle scope. In future spacecraft, I think NASA plans to replace them with commercially available rifle scopes using a holographic reticule. ui.adsabs.harvard.edu/abs/2011SPIE.8044E..0RM/abstract . Rambo meets Buck Rogers. $\endgroup$
    – Woody
    Nov 16, 2021 at 1:22
  • $\begingroup$ I took a picture of the shuttle COAS - as you say, it's just a tube that projects a reticule onto an angled piece of glass that the crewperson looks through. i.imgur.com/oftXoCs.png $\endgroup$ Nov 16, 2021 at 21:18

1 Answer 1


Is this the same as the trigger angle targeting used in the terminal rdvs for Apollo 11?

I blogged a bit on this in https://nbodyphysics.com/blog/2020/02/24/trigger-angle-rendezvous/.

There is paper from 2007 that describes this in some detail: https://www.researchgate.net/publication/257284923_Trigger_Angle_Targeting_for_Orbital_Rendezvous


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.