Re entry in a grav vehicle

[Infojunky]

Y'all I was thinking about this very topic this evening while I was out doing errands, and the chunk of the question I keep hitting on is "How High is Orbit?" once we have that the rest just kinda falls out of the math.

 

[simonh]

Y'all I was thinking about this very topic this evening while I was out doing errands, and the chunk of the question I keep hitting on is "How High is Orbit?" once we have that the rest just kinda falls out of the math.

That will depend on the size of the planet (or moon, etc) and how dense it's atmosphere is, and thus how high the atmosphere extends. I'm more familiar with the orbital characteristics of Kerbin myself, but for earth, space is considered to start at 100 km up, but practically speaking any orbit below about 160 km isn't going to be stable for long as it will decay due to atmospheric drag. The ISS orbits at just above 400km altitude, but even it is experiencing enough atmospheric drag that it's orbit decays over a period of decades.

Simon Hibbs

 

[Reynard]

The Low Earth Orbit for Earth is 100-1200 miles while the Medium Earth Orbit (Geosynchronous) is 1200-22000 miles. Beyond that is Geostationary. This will vary with other world based on gravity and atmosphere. Atmospheric density affects drag which causes orbital decay while gravity forces objects to need higher and faster orbits to maintain orbit. Some references place grav vehicle limits to LEO and MEO while a maneuver drive is needed to boost to Geostationary. LEO and MEO is the common orbit for starships, spacecraft and space stations.

Rather than trying to create tables for every world size and atmosphere combinations assume the conditions of a particular world have an ideal that traffic orbits are placed. Higher gravity worlds and denser atmospheres will place LEO and MEO orbits farther out. For a weird, extreme case a ship or station on a vacuum world with low gravity can have a slow orbit only miles above the surface.

 

[Anonymous]

Lots of talk about orbit which is all good but if you're using your grav drive to maintain altitude above the surface you aren't technically orbiting (OK, I know that's semantics... :wink and I'd say that most craft would be set up to be immune to atmospheric effects - drag isn't really coming into this as there is little to no velocity relative to the planet.

I guess that the star port traffic control would organise layers for craft wishing to use anti gravity to maintain altitude and those wishing to actually orbit. Again, more thinking out aloud while visualising but how would you organise the space above a planet?

 

[dragoner]

Y'all I was thinking about this very topic this evening while I was out doing errands, and the chunk of the question I keep hitting on is "How High is Orbit?" once we have that the rest just kinda falls out of the math.

From here: http://earthobservatory.nasa.gov/Features/OrbitsCatalog/

 

[sideranautae]

I would imagine most orbital starports would be in geostationary or a geosynchronous orbits. That would leave any position in a lower altitude than station but, over that same part of the planet requiring "grav hovering" to maintain relative position.

 

[Anonymous]

I know there's little (no?) mention of them in the Third Imperium but do any of you have beanstalks (from 2300) in YTU?

 

[sideranautae]

I know there's little (no?) mention of them in the Third Imperium but do any of you have beanstalks (from 2300) in YTU?

I've read about those in a post here a while ago. With grav tech appearing at TL 8 (same as beanstalks) cost wise, grav wins hands down, many times over. That's why no mention of them in 3I.

 

[dragoner]

I know there's little (no?) mention of them in the Third Imperium but do any of you have beanstalks (from 2300) in YTU?

IIRC, Trojan Reach has a world write up with one. I'll use them because they are able to be an automated cargo/people conveyance, and not needing the personnel and other infrastructural requirements that ubiquitous grav vehicles require.

 

[Reynard]

LEO orbits are mostly for satellites, proves and vehicles conducting surveys and such. The MEO or geosynchronous orbit has vehicles and stations moving faster than relative rotation in order to counteract gravity. Both orbits are normally within an atmosphere enough to be affected by drag the lower you go. The lower limit of LEO is defined by the point drag affects an object enough to make energy needed to maintain orbit very difficult or impossible.

Geostationary is the point where an orbit's centripetal force balances against gravity and hold the object at a single point relative to planet rotation. The atmosphere is very thin and no significant drag. The limit is also considered above underpowered vehicle grav plates.

 

[sideranautae]

Both orbits are normally within an atmosphere enough to be affected by drag the lower you go..

MEO's 2,000+ KM altitude aren't really effected by atmospheric drag. LEO's can be.

 

[Infojunky]

Y'all I was thinking about this very topic this evening while I was out doing errands, and the chunk of the question I keep hitting on is "How High is Orbit?" once we have that the rest just kinda falls out of the math.

Ok, I probably didn't quite ask the right question, I did answer it through a little edition spelunking.

The question is How high is considered to be a "standard" orbit?

Then a quick perusal of CT's Book 3 gives me this in the description of a standard Air/Raft: An air/raft can reach orbit in several hours (number of hours equal to planetary size digit in the UPP); passengers must wear vacc suits.

With this I can surmise that a "Standard" orbit is considered to be 100 km times planetary size digit as the operational speed of said Air/Raft is 100 kph. (Note this is the book 3 Air/Raft, not Mgt's version).

 

[sideranautae]

Then a quick perusal of CT's Book 3 gives me this in the description of a standard Air/Raft: An air/raft can reach orbit in several hours (number of hours equal to planetary size digit in the UPP); passengers must wear vacc suits.

With this I can surmise that a "Standard" orbit is considered to be 100 km times planetary size digit as the operational speed of said Air/Raft is 100 kph. (Note this is the book 3 Air/Raft, not Mgt's version).

Sounds good. The only remaining question. Does that mean that the air/raft reaches orbit (with the velocity that implies)? Or, only reaches the altitude of an orbital path without actually being in orbit?

 

[Infojunky]

Then a quick perusal of CT's Book 3 gives me this in the description of a standard Air/Raft: An air/raft can reach orbit in several hours (number of hours equal to planetary size digit in the UPP); passengers must wear vacc suits.

With this I can surmise that a "Standard" orbit is considered to be 100 km times planetary size digit as the operational speed of said Air/Raft is 100 kph. (Note this is the book 3 Air/Raft, not Mgt's version).

Sounds good. The only remaining question. Does that mean that the air/raft reaches orbit (with the velocity that implies)? Or, only reaches the altitude of an orbital path without actually being in orbit?

In my game the answer would be Yes, you can safely rendezvous with the ship in a unpowered orbit. As the book say reach orbit I would loosely say yes, just for the ease of play.

 

[sideranautae]

Then a quick perusal of CT's Book 3 gives me this in the description of a standard Air/Raft: An air/raft can reach orbit in several hours (number of hours equal to planetary size digit in the UPP); passengers must wear vacc suits.

With this I can surmise that a "Standard" orbit is considered to be 100 km times planetary size digit as the operational speed of said Air/Raft is 100 kph. (Note this is the book 3 Air/Raft, not Mgt's version).

Sounds good. The only remaining question. Does that mean that the air/raft reaches orbit (with the velocity that implies)? Or, only reaches the altitude of an orbital path without actually being in orbit?

In my game the answer would be Yes, you can safely rendezvous with the ship in a unpowered orbit. As the book say reach orbit I would loosely say yes, just for the ease of play.

That would account for the time listed to reach orbit too.

 

[Anonymous]

Is there a listing for G values that vessels other than ships and small craft have? In order to calculate the time to reach orbital velocity... yeah, I know that's more detail than most want, just asking is all...

I seem to recall this is something FF&S had but I don't recall seeing it for other vehicles and certainly not MgT.

 

[sideranautae]

Is there a listing for G values that vessels other than ships and small craft have? In order to calculate the time to reach orbital velocity... yeah, I know that's more detail than most want, just asking is all...

I seem to recall this is something FF&S had but I don't recall seeing it for other vehicles and certainly not MgT.

I remember that from MT. I don't have latest MgT vehicles book so don't know.

 

[Infojunky]

Is there a listing for G values that vessels other than ships and small craft have? In order to calculate the time to reach orbital velocity... yeah, I know that's more detail than most want, just asking is all...

I seem to recall this is something FF&S had but I don't recall seeing it for other vehicles and certainly not MgT.

Technically No, but if you have Striker or Mt, you can use the Gs to Kph table backwards to give a rough performance in Gs. Or you can work the formula backwards from what is given in FF&S but that will an iterative process to find the best fit.

 

[sideranautae]

Technically No, but if you have Striker or Mt, you can use the Gs to Kph table backwards to give a rough performance in Gs.

I think I found it from MT:

 

[Reynard]

Do remember that table was given an errata. The title was changed to MAXIMUM ACCELERATION.