General Objects at rest wrt each other

[SpaceBadger]

What would y'all say is the correct term (both full and shorthand, if different) for an object being at zero relative velocity with respect to some other object. A spaceship meeting up to another ship, or to a station, for example. Obviously they're both moving with respect to the system primary star, with respect to various planets and other objects, not to mention pretty much everything outside this individual star system. But they're at rest relative to each other. Is there a shorter word for that?

I've been reading some books in which the author consistently refers to this "at rest" condition as being at "zero delta-v" relative to another object, and it makes me want to pull my hair out, delta-v being change in velocity, not relative velocity!

 

[Dragoner]

Coelliptic orbit or rendezvous.

"Coelliptic orbit: A relative reference for two spacecraft—or more generally, satellites—in orbit in the same plane. "Coelliptic orbits can be defined as two orbits that are coplanar and confocal. A property of coelliptic orbits is that the difference in magnitude between aligned radius vectors is nearly the same, regardless of where within the orbits they are positioned. For this and other reasons, coelliptic orbits are useful in [spacecraft] rendezvous"."

List of orbits - Wikipedia

en.wikipedia.org

 

[SpaceBadger]

Thank you, Dragoner. Despite my continuing interest in the subject, all orbital mechanics beyond basic 1st year physics just seem to elude me. I need to find something like "Orbits for Dummies" if such exists. I'm probably hindered by 1) not having used (and therefor forgotten) my highschool calculus at all in the past 42 years, and 2) brain injury 8 years ago that makes "complex" thinking and attempts at learning extremely physically painful. But I will soldier on and try to make my understanding of this subject as complete as possible.

 

[Dragoner]

Thank you, Dragoner. Despite my continuing interest in the subject, all orbital mechanics beyond basic 1st year physics just seem to elude me. I need to find something like "Orbits for Dummies" if such exists. I'm probably hindered by 1) not having used (and therefor forgotten) my highschool calculus at all in the past 42 years, and 2) brain injury 8 years ago that makes "complex" thinking and attempts at learning extremely physically painful. But I will soldier on and try to make my understanding of this subject as complete as possible.

You are welcome, I am sorry to hear of your injury and am glad to help. I am a big space fan and follow a lot of the NASA and other space groups. There is also orbital station-keeping:

"In astrodynamics, orbital station-keeping is keeping a spacecraft at a fixed distance from another spacecraft or celestial body. It requires a series of orbital maneuvers made with thruster burns to keep the active craft in the same orbit as its target. For many low Earth orbit satellites, the effects of non-Keplerian forces, i.e. the deviations of the gravitational force of the Earth from that of a homogeneous sphere, gravitational forces from Sun/Moon, solar radiation pressure and air drag, must be counteracted."

Orbital station-keeping - Wikipedia

en.wikipedia.org

 

[mike wightman]

They are both in the same reference frame.

 

[Spinward Flow]

What would y'all say is the correct term (both full and shorthand, if different) for an object being at zero relative velocity with respect to some other object.

Zero relative velocity can shorthand to ZRV, as well as spelled out as zero relative velocity quite nicely. It's convenient because it's a reasonably accurate description that can be used in a point of view sense. That way, you can set the frame of reference as being "your craft" and then describe the movement of another object or craft relative to the movement/velocity frame of your own craft.

Thus, ZRV can become an acronym shorthand for orbital station keeping (as referenced by @Dragoner above), but orbital station keeping is a more specific descriptor of a condition. Orbital station keeping is a specific frame of reference (orbital motion) around a a gravity well of some kind, where the gravity well source is used as the frame of reference, rather than using one of the two (or more) craft in orbit as the frame of reference ... a subtle but important distinction between choices in frames of reference.

Kind of like the difference between:
1+2=3
x+y=z

You can use x+y=z to replicate 1+2=3 if you set the variables correctly, but x+y=z yields more answers than just that single one (for example).



Of course, for those of us "crusty old farts in a bathrobe" who remember original Star Trek ... we're familiar with Kirk telling Sulu to assume a "standard orbit" when arriving at a new planet (of the week).

 

[coliver988]

well there are standard orbits according to the Star Trek tech manual (sorry for the bad scan - don't want to bend my 40+ year old book to much!)

 

[Kakistocrat]

Zero relative velocity can shorthand to ZRV, as well as spelled out as zero relative velocity quite nicely.

The acronym “ZRV” could be the etymological source of a new noun, “zerve” (zero relative velocity, to rhyme with “serve”), in case there is no existing short verb for the concept. “Let the delegation know that we’re currently in zerve with the Xyzzy.”

 

[Spinward Flow]

The acronym “ZRV” could be the etymological source of a new noun, “zerve” (zero relative velocity, to rhyme with “serve”)

Frustrated Pilot: "These guys have got a lot of nerve zerve!"

 

[coliver988]

Frustrated Pilot: "These guys have got a lot of nerve zerve!"

a lot of zero relative velocity? an infinite amount of zero is still zero. I can see the opposite if they are moving away fast: "These guys have NO zerve!"

 

[whulorigan]

So to reiterate and quote everybody above, I think any of the following might work as general spacer terminology or spacer slang:

• "@ Station" --OR-- "Bearing XXX/YYY, Range DDD @ Station"
• "@ Zero-Relative" --OR-- "Bearing XXX/YYY, Range DDD @ Zero-Relative" --OR-- "Bearing XXX/YYY, Range DDD, Zero-Relative"
• "@ ZRV" --OR-- "Bearing XXX/YYY, Range DDD, ZRV"

The "/" can be your Star Trek "Mark" if you like . . .

 

[whartung]

well there are standard orbits according to the Star Trek tech manual

I wonder how they came up with .174 and .376.

 

[Dragoner]

NASA Thesaurus:

rendezvous
DEF The event of two or more objects meet-
ing with zero relative velocity at a preconceived
time and place. The point in space at which such
an event takes place, or is to take place.

https://sti.nasa.gov/nasa-thesaurus/

 

[aramis]

Zero relative vector is the term I'd use in game. Or "Vee-Ar-Zero" (V_R=0)

 

[Commander Truestar]

Well, since the OP didn't refer to objects in orbit, I saw the question as 2+ objects "anywhere", which could be a dead space smuggler meet up.

So, I simply say the objects have matched vector.
This applies if you are playing carousel around a giant rock or if there's no giant object in the neighborhood

 

[Kakistocrat]

I wonder how they came up with .174 and .376.

I don’t have that book, but 0.376 of Earth’s equatorial radius is 1110 km, so my guess is that R″ represents an altitude in a planet’s exosphere that’s above that planet’s thermopause. (That altitude could of course vary from one planet’s atmosphere to another, so perhaps its general application is for planets with atmospheres that support typical sophont life.)

Looking at the diagram, my thought was that 0.174 of Earth’s equatorial radius was chosen for R′ to make a half-hexagon that seems to be used to determine points B and C (the endpoints of the communications “blind zone” for point A), but a more precise half-hexagon would have used 0.1547 rather than 0.174. Mathematically, 0.174 is right around 12.5% greater than 0.1547, so perhaps there’s some “slop” factored in for R′.

 

[Jame]

And if you have ZRV, you get to watch your solar system move away at a light second per hour!