Reaching orbit with Air-raft
 

Various canon Traveller sources state that Air-rafts can reach orbit and in my Traveller campaign precisely that situation arose during my weekend session with my kids. I assume here that the ship we want to match orbit with is in Low Earth Orbit (LEO). The problem is much simpler if the ship is hovering on its contragrav above the planet but that is not what the canon sources say; 'orbit' does not mean outside the atmosphere, it means outside the atmosphere with enough speed for centripetal forces to match gravity.

Has anyone playing a fairly realistic Traveller ran into this problem and how did you solve it (ruling out air-raft to orbit is one solution)?

If you dig into the problem there are lots of complications that crop up:

Problems with the vehicle:
An open topped vehicle is hardly built for vacuum as this costs a lot extra, so I guess the instrumentation, upholstery etc will break in vacuum. Another problem is that an air-raft produces something like 0.1 G thrust for propulsion which mean (ballpark calculations here) that to reach say 5 km/s orbital velocity they must accelerate for over an hour (ca 5000 seconds).

Problems with the calculations:
To match the orbit of a ship the air-raft driver must eyeball the ship and vector (yes, LEO ships can be seen at dusk or dawn by the human eye) and then match that orbit by hand with the air-raft over a more than an hour long acceleration phase. The air-raft will have no instrumentation for orbit matching and the like, just an accelerometer based (Traveller vehicles does not rely on the crude GPS system we use) absolute positional instrument that also indicate height as well as speed gauges. Calculating the orbital mechanics and driving the air-raft to comply is in my opinion a really hard problem for a spaceship pilot and impossible for mere grav-jockeys.
If you think orbit matching is a piece of cake try it yourself with the free PC space simulator Orbiter.

IMTU: My TL progression differs from canon and GURPS Traveller and this causes even more problems:
(I don't add gravtech until TL 10, so I can have cultures with jumpdrives without grav and floorfield, 'Hard-SF with jump' if you will)
Jumpdrives TL 9
Floaters TL 10
Floorfield TL 11
Gravthrust TL 12
Floater gravbelts TL 13
Reactionless drives TL 13
Gravbelts TL 14
Tractor beams TL 15
Presser beams TL 16
Rattlers (high freq tractor weapons) TL 17

Floaters are grav 'thrusters' that can only negate gravity, they can never create upwards or lateral thrust, just negate the downward pull of gravity. Floaters and gravthrust have 'thrust' proportional to local gravity so a 1G (Thrust = mass) floater will negate gravity on all planets, regardless of gravitation (simplifies designing gravvehícles and 'explains' why gravthrust is useless for interplanetary travel). Floaters come at TL 10, are much cheaper and require much less power per 'thrust' than regular gravthrust. Regular gravthrusters produce floating at the cost of x1/10 thrust (a 1G gravthrust would use 0.1 G for floating and 0.9 G for propulsion for example).
My air-rafts are so cheap they use floaters powered by a fuelcell for lift and turbojet for thrust (both the fuelcell and turbojet are hydrogen powered and need an atmosphere with oxygen to work).

So IMTU the air-rafts cannot reach orbit at all, they cannot even operate in anything near vacuum, fitted with compressors they can work in Very thin atmospheres, but that's it.

Re: Reaching orbit with Air-raft
 

Don't forget that many of the worlds that Travellers visit are effectively or actually in vacuum. I don't think this is an issue for Imperial (i.e., non-local) gear.

The original sources said that reaching orbit in an air/raft takes one hour per thousand miles of planetary diameter, so this is optimistic if anything.

Why not? It's not that difficult, and virtually a necessity to use the air/raft around small worlds.

I sincerely doubt that anyone except a sport enthusiast or show-off ever eyeballs an orbit or tries to calculate an intercept by hand. How hard would it be to contact the ship and have its computer calculate an intercept course, and then feed you regular updates using its collision-avoidance sensors? Or call space traffic control and ask for the orbital elements of the ship, so you can run it through your hand computer's intercept application?

There are certainly situations where this is an intractable problem (uncooperative ship above an uninhabited world), but in most cases the orbital mechanics are the least of your problems. Do your gravitics allow floaters to reach orbit at all? If so, does anyone want to spend multiple hours in a vacc suit to get there?

Re: Reaching orbit with Air-raft
 

Essentially nothing built in the Imperium will have a problem with this. If you are building for export you *don't* get to assume anything about the atmosphere your product will be operating in. If something other than a standard atmosphere would be a problem for it (and really vacuum is not that hard on most equipment, there are lots worse environments) it will be sealed.

So? Reaching orbit isn't the same thing as matching a specific orbit. On the other hand I'm not sure why you assume an air raft has no orbit matching instrumentation - it's not really a tremendously hard calculation, well within the capability of an autopilot, assuming you don' simply hand the problem off the local traffic control system. If you are planning on using your air raft as an interface vehicle, buy one with decent electronics.

Do not attempt to stress this if your players are technically oriented types. It's inviting things like we'll use it to float relative to the gravity of the sun (or the galaxy) rather than the planet and.... Straight reactionless thrust with "contragravity" being a popular misnomer actually suffers from a lot fewer problems.

Then problem solved. If you've redefined the air raft so it's very different from canon, why is it even an issue that it has different capabilities from canon?

Re: Reaching orbit with Air-raft
 

/facepalms

Re: Reaching orbit with Air-raft
 

Canon already has a tech level with JDrives but without gravitics. The GT mangling of Tech Levels to fit GURPS rendered missing.

In actual GDW Traveller, not GT nor MgT, TL 9 has no artificial Grav nor gravitic thrust, but has Jump 1; gravitics come in at TL 10.

This not appearing to exist in GT is simply an artifact of GT's tech level compression past TL 8.

Re: Reaching orbit with Air-raft
 

Air/rafts are TL8 (Book 3, pp. 15 and 23), as are GCarriers and Speeders (Book 3, p. 23).

Re: Reaching orbit with Air-raft
 

Well, I wanted a TL with the so called contragrav things GURPS Spaceships use as well as TNE in that you get lift but not thrust, to allow flaoting grav thingys with jetegnines and the like.

MA Lloyd: My floaters merely negate any and all gravity from all directions so none of the problems you depict occur. 'Floaters' break the law of momentum conservation as does reactionless thrusters, you cannot really say that one is worse than the other.

When air-rafts where built using Megatraveller design system or Fire Fusion and Steel they didn't put radars etc needed for matching a ship in orbit. I am pretty sure that the air-raft in GURPS Traveller (built using GURPS Vehicles?) didn't have the needed instrumentation and sensor either.

I'm sorry if I offended anybody by pointing out some, in my opinion, unrealistic stuff from old canon. I am actually a bit surprised at the strong reaction, especially from mr Lloyd - is this the same Lloyd who wrote the awesome additions to Vehicles with audio signatures and realistic falloff for communicators and sensors, way back?

Re: Reaching orbit with Air-raft
 

Thank's! The old LBB Traveller universe was kind of boring in that sense as the TL progression was kind of like this:

Various historical inventions appear all the way up to TL 7. After that they invent fusion, grav etc at TL 8, jump at TL 9 and from then on only small increment in capabilities occur.

Re: Reaching orbit with Air-raft
 

At least GDW was relatively consistent about it: per capita GNP doubled between TL5 and TL6, TL6 and TL8, and TL8 and TL12, and arguably wouldn't have doubled again until TL20 (Striker, Book 2, p. 38, under "Integration with Traveller"). This implies that the differences between TLs become finer the higher one goes on the scale.

Re: Reaching orbit with Air-raft
 

True. GURPS way of making each TL a separate culture works better but then maybe the different Traveller societys (Imperium, Zhodani, K'Kree etc) should have a TL rating and the planets should instead have a more fine grained production rating than the standard sequence: Low pop -> Non Industrial -> Regular -> Industrial.

I have been toying with the idea to have the population limiting what one can produce: 1 million inhabitants and they can produce items that cost 1 MCr in local currency, everything more expensive has to be imported or 'hand built' ie much more expensive. The population limit would not apply to Industrial planets, they are the heavy lifters of industrial production in Traveller.

Re: Reaching orbit with Air-raft
 

TTB, p87: air rafts are TL8. Grav Vehicles (big line) TL10. Identical to Bk3 p15.

All it proves is that TL8 air rafts are possible, not that they are gravitic at that TL. (Tho', digging through striker errata says yes, TL8 gravitic lift.) They might be fusion powered vectored thrust. Along with G-Carriers. (Much like what we see in Blade Runner or Albedo.) It's sloppy.

MT is explicit, however, No Artificial gravity until TL10. TNE as well, plus no compensation til TL10.

Re: Reaching orbit with Air-raft
 

Blade runner Spinners are definately not vectored thrust for lift, they seem to use it for acceleration only which very much fit my Floater vehicles; some tech thing that negates all gravity but you still need expell gas or whatever to go somewhere. Kind of like the Watto character in the latest (bad) Star Wars movies. He has wings for sure but only a retard would think they generate his lift, he probably has some Floater gravbelt hidden away on his person and uses the wings to move about.

Re: Reaching orbit with Air-raft
 

If you'll examine the chart carefully, you'll see that Air/Rafts are located under the "Transportation -- Air" column. The big line at TL10 indicates that Grav Vehicles become standard for water and land transportation as well. This parallels the text on p. 22: "Beyond tech level 10, other vehicle types are rarely seen except in a few specialized situations."

The text on pp. 22-23 lists all three vehicles and the Grav Belt under "Grav Vehicles."

So CT is not "actual GDW Traveller"?

Hmmm.

Re: Reaching orbit with Air-raft
 

Now, now, Chris. Wil is merely selecting the official source of information that makes the most sense to him. ;-)


Hans

Re: Reaching orbit with Air-raft
 

Then they don't float. From the perspective of the planet you are on they accelerate, possibly rather violently, along some vector combination of outsystem, rimward and away from Andromedia.

Re: Reaching orbit with Air-raft
 

The earth pulls us towards its center at 1G, the moon and the sun pulls with some really puny acceleration, the rest is so insanely weak it doesn't matter at all. Sure, a floater unattended longe enough would float away from the earth from centrifugal force of the earth's rotation around it's axis. Much longer term it would start moving away from the sun as it would continue along a tangent while earth would still circle around the sun, etc etc.

Do the math Sir!

Re: Reaching orbit with Air-raft
 

I would assume that air/rafts are typically enclosed, simply vs. weather. Much like modern cars out here in the real world.

Re: Reaching orbit with Air-raft
 

Air-rafts according to canon text and illustrations are all open topped vehicles. You'll need a vacc suit to do the orbit thing.

Re: Reaching orbit with Air-raft
 

Actually, you can't tell that, because for the larger structures, like say our supercluster, you have nothing fixed to measure against. Everything we see could be gravitationally accelerating at a billion gravities in some direction and we couldn't tell, and in any case have to account for the as yet not well defined repulsive effect at very large scales, which may or may not be be altered by contragravity.

For the Sol system the effects we can account for are fairly low (the centripetal force of the rotation of the Earth is about 0.03 m/s^2, for the orbit about the sun 6x10^-3 m/s^2, for the galaxy about 2x10^-10 m/s^2; and 3x10^-5 m/s^2 for the moon) but of course that doesn't have to be the case in other star system - many worlds in Traveller have shorter days or are a lot closer to their primaries. And isn't really negligible here on Earth either, leave your contragravity on an hour and 0.03 m/s^2 has given you a 250 mile per hour velocity in some direction you didn't intend to go. This isn't terrible for a vehicle, though you have to have an engine you can run constantly and which can thrust in all directions, on a continuously changing basis to compensate for it, but it isn't negligible. And it does pretty well simplify the reach orbit with the air-raft problem. Turn off the compensating thruster and in a couple hundred hours you'll have reached a point your inherent velocity puts you in some sort of orbit, then you turn off the contragravity. Admittedly it'll probably be a pretty elliptical orbit.

Re: Reaching orbit with Air-raft
 

Standard Grav thrust is available at TL9 in MT. RM p65 and p66.

It's only artificial grav plating that is limited from TL10 up RM p81. Anti grav thrust is good from TL9, (or TL8 via government resurach and development).

Regards,

Ewan

Re: Reaching orbit with Air-raft
 

Eh no, gravity is caused by masses attracting each other and no cosmological theories posit such insane masses as to generate the huge accelerations you pluck from thin air (huge solid sheets of black holes or what?). The 'as yet not well defined repulsive effect' is just cosmologists attempts to save their theories from the WMAP data. I refuse to take the current state of cosmology into account when rationalising my Traveller handwavium.

Well thanks for doing the calculations but there are some overlooked points here: A balloon is subject to the exact same centripetal forces but we do not see them zoom off at 250 mp/h after an hour in the air, right? Air drag against such a minute force would act exactly the same on our Floater and a balloon. Or, let us say that our air-raft is using a reactionless engine (that mr Lloyd propsed would give much less scientific problems) that produces a thrust that completely opposes the pull of gravity, very much like a hovering helicopter, balloon or zeppelin, wouldn't they experience exactly the same cetripetal force. What is it with my floaters that all of a sudden turn these minute forces into something to bother with?

Reaching orbit from centripetal forces alone won't work either. The air-raft would have the same rotational speed as it had on the ground so it would be in orbit in the same sense as you and I are in orbit ie not at all. The air-raft would simply fall back onto the planet when turning off the Floater. Circular orbit means the kinetic energy is equal to the potential energy and this tell us that the higher up you are the MORE velocity is needed to stay in orbit.

If my take on Floaters are bothersome (negating gravity completely), just posit them as gravthrusters that can only thrust along the gravity gradient vector. That way they'd behave like my Floaters yet be immune to the insane million gravity homogenous fields posited by mr Lloyd. They would still behave the same visavi centripetal forces of course. So, at TL 10 we can make gravthrusters that thrust along the gravity gradient only, at TL 11 we can have gravthrusters that can thrust in any direction as long as there is a gravity gradient and at TL 13 we get the reactionless thrusters that can thrust without relation to gravity (the relativistic rock generators, if you will).

The lesson here: A drive that magically nullifies gravity in all directions through electric power breaks no more laws of physics than a drive that magically creates thrust from electricity alone; conservation of momentum and conservation of energy are broken in both cases. Breaking the two most fundamental laws of nature means that we know for certain there will be problems as there always is when one adds this amount of handwavium but I think I have shown that we are equally frakked with the gravthrusters. We also learn that the small forces values of centripetal acceleration are present on all bodies; ballooons, helicopters, floaters and gravvehicles alike and as we don't bother with them for the real owrld versions we don't have to bother with the fictious ones.

Re: Reaching orbit with Air-raft
 

Yes. So? So is a rock sitting on the ground. But both of those are also subject to gravity. Balloons don't float because they are not affected by gravity, but because air is heavier. The force of gravity on anything is greater than the centripetal force of the Earth's rotation by exactly the same ratio - both are linear in the mass of the object. Contragravity changes that. In effect it's equivalent to lowering the mass of the Earth while keeping everything else constant. And if you do lower the mass of the planet, then yes, eventually stuff is thrown off centrifugally. Small enough objects spinning fast enough *do* rip themselves apart, though it's not a familiar sight, since engineers try to keep that from happening.

Actually, if you jump you are in an orbit, it happens to be a really eccentric elliptical one that intersects the surface of the Earth. If you turn off gravity then the rotational velocity of all the objects on the Earth throws them off tangentially. I suppose arguably this is not an orbit either, it's the maximally dengenerate case of a hyperbola with the center of the Earth at a focus, and never loops back on itself, but these kinds of things are often called "grazing orbits", and if you turn the gravity back on before the object gets too far out, you'll pull it into an elliptical path. And yes, it will be very elliptical. If the planet had a radius of zero, then you'd be right, you would fall straight back after launching this way.

If you lower the gravity of the Earth to that 0.03 m/s^2 (or equivalently had a "partial contragravity" device that reduced the effect of gravity by 99.7% so that weight was reduced to that) then objects at the Equator *would* be in a circular orbit - try it youself, figure the orbital velocity around something with the necessary mass to reduce gravitational acceleration to that and compare it to the speed of the rotation of the Earth. This pretty well ought to prove to you that you can reach an orbit with a contragravity device capable of 100% negation, if you pulsed it on and off on say a 99.7/0.3 millisecond duty cycle, it turns into approximately a 99.7% weight reduction and you are in a circular "orbit" right away.

No. Close, but it's potential energy relative to infinity, not the surface of the Earth. That is, it's zero at infinite distance, so the kinetic energy (and hence velocity) you need to stay in orbit infinitely far away is likewise zero, and the potential energy gets *more negative* as you drop toward the Earth, and your orbit speeds up. Another way of thinking about it is the circular orbit velocity is always square root (1/2) times the escape velocity (the one you need to reach infinity, and hence compensate for the potential energy you lost falling toward the planet from there). Yes, it's a weird convention from the standpoint of the way planetbound people think of potential energy.

Sure. But the practical consequences, in terms of how easy it is to understand the results, and how easy it is to set up an abusive exploit that will allow you to derive vast energies from nothing, are quite different.

Re: Reaching orbit with Air-raft
 

No, not at all. Being in 'orbit' is NOT the same as being in 'freefall', being in orbit is having such a velocity vector that you will be able to do at least one complete ORBIT around the object you are orbiting. Hitting the retros on the shuttle so its path will take it into the atmosphere is called 'de-orbit' for a reason.

Correct, my bad.
I hope you see for yourselves that you are a bit ridiculous when you have to write "orbit" with quotes as you very well know that this isn't really orbit in the same sense everybody else uses it. Stutter-orbit maybe :)
Also note that the gravthrust vehicle would be able to do EACTLY the same feat.

My problem basically was that using an air-raft to dock with an orbiting ship would be very hard to do in the reality of Traveller, something the short, canon, paragraph about air-rafts had led me and probably other referees to believe. I'm sure most other agree as the air-raft design for GURPS Traveller lack the neccessary instrumentation, I don't even thiink they have paid for vaccuum proofing the vehicle. I stand by my statement that Floaters and Gravthrusters have the same problems with reality.

When we disagree so much on even fundamental assumptions such as what 'orbit' really means, whether or not there are huge gravitic fields from cosmology pulling on us etc that there is very little knowledge we can gain from each other in this discussion - I think we can bury it by that. We are like fantasy roleplayers arguing what magic system is more realistic.

Re: Reaching orbit with Air-raft
 

Okay, just to chime in here...

GURPS Traveller, 2nd Ed. by Wiseman, pg 147 (ISBN 1-55634-408-2)

Air/Raft, Open Topped (TL12)

...This vehicle (and its close-topped cousin) is one of the most commonly produced TL12 vehicles within the Imperium, and innumerable variants are produced....

....Long-range radio comm; low-res imaging radar; PESA; terrain-following radar; small computer, complexity 6....

...Aerial top speed 160 mph, aAccel 2 mph/s...aDecel 20 mph/s...

...sAccel 0.08 Gs. Most air/rafts can reach orbit (this one would require vacc suits be worn), but are rarely used for such.


I know, we aren't talking TL12, but here is a GURPS reference that may aid in the discussion. Looks like this text has enclosed versions with a decent computer and can reach orbit.

Guess it comes down to your hand-waving of the science.

Re: Reaching orbit with Air-raft
 

You need to be able to reach orbit with an open-topped air raft so that you can re-create Marc Miller's commute.

(And even though the link-dumping has died down a bit, I'll still add that the link is really to YouTube, the intro scene from Heavy Metal. Thus spoiling the joke, but rules is rules.)

Re: Reaching orbit with Air-raft
 

Actually closed and ragtop air/rafts have been around since MegaTraveller and TNE has the default as "ragtop" with a "hardtop availabel"

Re: Reaching orbit with Air-raft
 

In CT. GT has closed-topped variants (well, okay, it mentions them).

However, my first Traveller which was TNE, which had an illustrated closed-top one. (And I didn't actually read the entry, which states that the top isn't enclosed, until years later. So IMTU closed-top air/rafts are standard, just as closed-top cars are standard in the real world. The difference is that ground-cars would never need to be pressurized.)

Re: Reaching orbit with Air-raft
 

Air-rafts posed several headaches with real design systems. They were open-topped yet capable of reaching orbit. Unless one had a separate lift system with much less powerconsumption and cost than the one producing thrust, it was really hard to come up with an excuse for why they were so damned slow (110 km/h cruisng speed or something like that).
That was my real excuse for adding the 'gravity nullifier' / 'can only thrust along gravity gradient' lift system. Set the TL for air-rafts so low that one could only build Lift systems and needed to supply thrust by propellers, turbofans etc.
At higher TLs the grav vehicles would be much fatser and therefore also enclosed for the comfort of the occupants.

Re: Reaching orbit with Air-raft
 

I may adopt that if any of my players ask how it works. (Provided if I remember it.)

Re: Reaching orbit with Air-raft
 

Erm, I'm pretty sure that being in orbit (assuming you're not thrusting or rotating) IS effectively identical to being in freefall. That's why people in orbit (e.g. in the ISS) are in zero gravity when they're only about 100 km above the earth (where the gravitational field strength pulling you down is still pretty close to 9.8 m/s² because that's still very close to Earth)

see http://en.wikipedia.org/wiki/Weightl...n_a_spacecraft

Re: Reaching orbit with Air-raft
 

Yeah, but I'd sympathise if someone didn't what to say that anyone who jumps a ditch or falls out of a tree was "in orbit". So I would accept a definition of "orbit" that excluded free-fall trajectories which intersect the ground.

Furthermore, I recognise the term "powered orbit" for trajectories in which the object is not in free fall, but is accelerating continuously.

Re: Reaching orbit with Air-raft
 

But "freefall" has a specific meaning that applies here. It means "the motion of a body when gravity is the dominant force on it". When you're jumping in the air, you are in freefall for the time it takes for you to fall from the peak of your motion to the ground (or even from when you leave the ground, technically).

See e.g. http://en.wikipedia.org/wiki/Free_fall
"Orbit" has a specific meaning too, but you can get paths that intersect planets are still technically orbits. (See http://en.wikipedia.org/wiki/Orbit#Understanding_orbits )

An "orbit" that goes completely around an planet is essentially "a path that keeps missing the ground". It's not unlike when they say in the Hitchhikers books that "flying is throwing yourself at the ground and missing" ;).

I may sound like I'm being pedantic, but these things have specific meanings, and saying that they mean something else is only going to confuse people.

Re: Reaching orbit with Air-raft
 

Yes, and that is exactly why I say that a boy who falls out of a tree or who jumps across a ditch is in free fall.

That article classifies trajectories that intersect the ground or the atmosphere as sub-orbital trajectories, distinct from orbits.

Well, if you say that a little boy who falls out of a tree is in orbit until he hits the ground that is going to confuse people. But he is definitely in free fall, and therefore the two things cannot be the same.

Re: Reaching orbit with Air-raft
 

Actually, all orbits eventually either intersect the orbited body or result in tidal locking, given enough time. That said, an orbit that intersects the body orbited must take it around at least one full time around that body; if it's less than one full time around, it's suborbital.

Almost all satellites are in orbits which will decay and eventually intersect earth.

Re: Reaching orbit with Air-raft
 

That's incorrect.

An orbit will only decay if there is drag on it, or if other perturbations change it so that it intersects the planet - otherwise it'll be stable forever. Satellites in low orbits close to the atmosphere may decay as things like heating from solar flares can change the height of the atmosphere and cause unanticipated additional drag. Satellites orbits that are higher up, beyond the range of an extended atmosphere will not decay though.

Also, orbits do not necessarily end in collision or tidelocking - given enough time, the orbiting body may be forced outwards by tidal evolution so far that it orbits the sun instead of the planet. Even though the moon is tidelocked to face the Earth, orbital evolution is continuing to push its orbit outwards, and will continue to do so until either the earth's rotational period is equal to the moon's orbital period, or until the moon is lost into a solar orbit (whichever happens first. Either won't happen before the Sun expands into a red giant, which might render the whole thing moot if it engulfs the earth/moon system).

Re: Reaching orbit with Air-raft
 

There is no non-theoretical orbit without drag, Dr. Thomas, and you know that. That drag may be minimal, but it's present, since space is not true vacuum. (If it were, Traveller's low-relativistic velocities wouldn't be an issue...)

And until tidelock, the orbiting body and body orbited both produce drag on each other due to gravity effects. In the case of tiny satellites, negligible effect on the orbited, and much more profound on the satellite.

Re: Reaching orbit with Air-raft
 

Yeah, so there's one or two atoms in every cubic centimetre in space. But it would take a ridiculously long time for the orbit of anything bigger than a dustgrain to be affected by "drag" because of that (and if we're talking about dustgrains then you need to include things like the Yarkowsky Effect, which accounts for light pressure from photons).

For something orbiting a planet, it's simply not an issue. You may as well raise "all things will eventually decay into photons" as if it were a valid point.

It's actually because angular momentum is being transferred between the two bodies, and both objects are being heated up as energy is disspiated within them. And while your statement is otherwise correct, it's not really relevant to the point I was making.

Re: Reaching orbit with Air-raft
 

If you are in in (unpowered) orbit implies that you are in freefall, being in freefall does NOT imply that you are in orbit. If you jump off a trampoline you are in free fall but certainly not in orbit.

Re: Reaching orbit with Air-raft
 

Come to think of it, shouldn't that matter to the large satellites too? I know you can get measurable position changes from photon pressures on the trajectories of interplanetary probes over the course of just a few years, and there is a constant perturbative force away from the sun on the sattelites. I suppose the perturbation could average out to zero over the course of a year, but it seems unlikely it would unless the Earth's orbit were perfectly circular and satellite periods are exactly integer divisions of a sidereal year.

I'd think the tidal and magnetic drag would be pretty signficant on anything not in geosynchronous orbit too, and signficant lunar perturbations on anything not co-orbiting with the moon. Ancient artifacts that have been sitting in close stable orbits around planets for a few million years may well be science fantasy.

Re: Reaching orbit with Air-raft
 

Yes, and matters get worse around smaller objects such as the moon where high density points on the surface (from asteroid impacts) make the gravity field significantly differ from the point mass ideal required by mr Newton. Low orbits over the moon are more or less impossible to maintain over long periods, that's why we have no 'permanent' sattelites around it.

No, those Ancient things should be parked ON asteroids, moons etc to be credible - or better yest; inside complicated cave labyrinths guarded by monsters, just like magical items of D&D does.