# Have guidelines for red & green navigation light placement on spacecraft been established?

update: Cropped screen capture from SpaceX Demo-1 Crew Dragon Docking to ISS - Part 2 after about 00:25:00 in the video:

I am curious if guidelines for the placement of red/green navigation lights on spacecraft been established. In maritime and most aviation situations, right/left have meaning because up/down does.

A highly related question would be:

Does this mean that the grapple fixture on Dragon is on the "bottom"? Is this the negative Z direction of this spacecraft's coordinate system?

above: From Spaceflight Now's SpaceX supply ship completes journey to space station (cropped). Caption: The Dragon spacecraft’s navigation lights illuminate the cargo ship during a nighttime orbital pass. Credit: Thomas Pesquet/ESA/NASA

## For background on the use of red/green navigation lights in other craft:

above: from this answer to the Quora question Why is the right navigation light of an aircraft green and the left one red? There are multiple answers shown there.

• Sadly, the ISS coordinate systems documents on the internet have all the visiting vehicles except the Dragon in them :( – Organic Marble Feb 24 '17 at 2:33
• @OrganicMarble I've just edited a bit. After reading your comment I realized I've asked two questions in one. Now the Dragon coordinate question is secondary, and "Have guidelines been established..." is now primary. – uhoh Feb 24 '17 at 2:39
• What if the space ship is rotating slowly around its axis? 4 or more navigation lights around the ship and the leftmost red light and the rightmost green light are switched on? – Uwe Nov 7 '18 at 19:54
• @Uwe that is an excellent question! Ask it as a new question please! ;-) – uhoh Nov 8 '18 at 1:46

Two lights isn't enough to determine orientation of a spacecraft, but I'd put the grapple fixture on the top, on the basis that navigation lights are supposed to point forward, making the pointy end the back. That fits with the orientation for reentry, though the navigation lights appear to be on the trunk rather than the capsule itself.

I wouldn't expect to see any navigation light standards for purely orbital spacecraft - ship/aircraft navigation lights are important for collision avoidance because they show direction of movement, not just orientation. That doesn't work so well when the other vessel is routinely upside down and/or backwards.

Cygnus does have navigation lights with the addition of white and yellow for up and down, but that's in the context of docking, where orientation matters and any configuration can be agreed with the single spacecraft you are trying to dock with.

Where standardized navigation lights would make sense is after reentry - certainly the space shuttle could reasonably be covered by existing civil aviation rules - but all examples to date have been government/military systems and not required to have lights at all.

• Interesting answer! You've pointed out some good things to thing about, like what if anything could "direction of motion" mean in an orbital context. If a spacecraft had the same plane, period, and argument of apses as the ISS, but a different eccentricity, it might loop around and around the ISS, and if it always pointed "orbit-forward" rather than pitch at the same rate, it would have to swap the color of the lights every 46 minutes. – uhoh Feb 24 '17 at 3:30
• I've added an image from the first Dragon-2 docking and the red and green lights are prominently visible in the video. Does the orientation still match what you describe? – uhoh Mar 4 '19 at 4:56

Tangential to the question the poster child for space planes did not actually have navigation lights so does not set a useful precedent. Have not yet found anything useful for Buran or X-37 though would be guessing that the weight penalty of a compliant navigation lighting setup would be hard to justify given the typical descent profile.

• The fairly recent development of efficient, bright, light weight, and reliable LED lighting probably also makes these lights a lot easier to justify now than it would have then. – uhoh Nov 7 '18 at 10:16
• @ uhoh: LEDs are very temperature sensitive - suspect it is still possible to mount one into a wingtip that does re-entry but the engineering to block and move heat would be non trivial. In classic bulbs the critical part is white hot in operation anyway so you would just be hardening the rest of the bulb/housing. – GremlinWranger Nov 7 '18 at 12:04
• Yes I see what you mean, LED's may not like atmospheric reentry. – uhoh Nov 7 '18 at 12:13
• Follow up to my own comment after some more searching- seems shuttle wing interior temp was around 100C, below the maximum for LEDs of 130 so not as impossible as I thought. Still needs the weight and engineering to get the light through the heat shield in some way. – GremlinWranger Nov 7 '18 at 12:20