Thrust-assisted fast orbit

[Brassbud]

Are there any add-on craft or modified autopilot abilities that allow for this?

Specifically, I want to obtain a circular LEO with a velocity higher than the Earth's gravity alone will allow by using thrust towards the Earth's center to assist in the acceleration required.

More specifically, I would like the additional acceleration provided by the thrust to equal 9.81 m/s or thereabouts for the purpose of simulating the gravity on Earth's surface.

Most simply I guess this could be accomplished by doing an upside-down H-level in a ship with powerful hover thrusters, but I would also like to see it done with the mains on a ship built like a skyscraper.

The default autopilot is probably not accurate enough to maintain such an orbit for very long, so are there any ships/space stations/autopilot mods out there made for this specific purpose? Thanks for any help.


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Also, I realize a thrust-assisted slow orbit would work fine for large bodies such as Jupiter where the acceleration from gravity would be greater than 9.81 m/s at a low altitude, but who wants to orbit Jupiter anyways, and going fast is cooler than going slow.

 

[Quick_Nick]

I don't quite understand. Out of what I did understand, are you planning on using gravity and thrust for getting TO orbit, or are you suggesting using gravity and thrust while on orbit? Your orbit can't remain the same if you thrust. Please expalain a little more.

 

[Andy44]

He wants to race around the Earth at LEO altitude at greater-than-LEO velocity. In order to keep his vertical velocity from going positive he needs a way to thrust in the nadir direction (downward) or else his speed will fling him out of orbit into deep space.

Currently I know of no autopilot or addon that will do this for you. You should be able to do this by hand, with some difficulty. But with most vessels you will run out of fuel pretty quickly, I would think.

 

[EliNaut]

Well, you could always set unlimited fuel on, just for testing of course.

 

[Quick_Nick]

He wants to race around the Earth at LEO altitude at greater-than-LEO velocity. In order to keep his vertical velocity from going positive he needs a way to thrust in the nadir direction (downward) or else his speed will fling him out of orbit into deep space.

Currently I know of no autopilot or addon that will do this for you. You should be able to do this by hand, with some difficulty. But with most vessels you will run out of fuel pretty quickly, I would think.

For any orbit there is only one possible velocity at a specific part of the orbit. There is no direction you can thrust that would give you an extra-fast LEO. Thrusting down will increase the altitude of your orbit on the opposite side and lower your altitude at your current position. The energy has to go somewhere. I don't believe it is possible to do what he wants... but, maybe. (it MIGHT be possible to find a way to thrust and cancel it out as you go)

 

[Andy44]

For any orbit there is only one possible velocity at a specific part of the orbit. There is no direction you can thrust that would give you an extra-fast LEO. Thrusting down will increase the altitude of your orbit on the opposite side and lower your altitude at your current position. The energy has to go somewhere. I don't believe it is possible to do what he wants... but, maybe. (it MIGHT be possible to find a way to thrust and cancel it out as you go)

Incorrect. If from a circular orbit you increase your forward velocity, which the OP wants to do, your vertical velocity will go positive. The only way to counter this is to thrust downward, in effect continuously turning your velocity vector downward in order to stay at the same altitude. The faster you want to fly forward, the more thrust you need to apply downward to keep from climbing in altitude, and, of course, the quicker you will run out of fuel.

This can be done with hoverjets if flown upside down, or you can use your main thruster by thrusting forward and pitching down in a coordinated maneuver. Either way is difficult to do manually, but it's possible.

 

[Kaito]

Tho I know very little about Orbital Mechanics, maybe this would work...
Thrust Prograde to obtain your desired speed, but also use the hover thrusters pointed AWAY from the earth (your ship would be upside-down) to keep your altitude in check?

 

[Andy44]

Tho I know very little about Orbital Mechanics, maybe this would work...
Thrust Prograde to obtain your desired speed, but also use the hover thrusters pointed AWAY from the earth (your ship would be upside-down) to keep your altitude in check?

Yes, that's what I was saying. It's still not very easy because you need to get the hover thrust just right to null out vertical speed, and even if you get it just right, you have to keep readjusting as your fuel mass burns off.

 

[Quick_Nick]

Incorrect. If from a circular orbit you increase your forward velocity, which the OP wants to do, your vertical velocity will go positive. The only way to counter this is to thrust downward, in effect continuously turning your velocity vector downward in order to stay at the same altitude. The faster you want to fly forward, the more thrust you need to apply downward to keep from climbing in altitude, and, of course, the quicker you will run out of fuel.

This can be done with hoverjets if flown upside down, or you can use your main thruster by thrusting forward and pitching down in a coordinated maneuver. Either way is difficult to do manually, but it's possible.

How about an example? I'm really skeptical right now.

Yes, that's what I was saying. It's still not very easy because you need to get the hover thrust just right to null out vertical speed, and even if you get it just right, you have to keep readjusting as your fuel mass burns off.

Or, as I think you may have suggested earlier, just use one set of engines (main) and angle the burn.
But still, I'm not sure that this will produce the desired effect. Or at least, it will be insanely fuel ineffecient for the thrust that will be required to cancel out the earlier parts of the maneuver.
Maybe in my mind I don't doubt its possibility, but its practicallity, and thus can't agree with the idea.

 

[TSPenguin]

I am confident this would work.
Basicaly you would always stay at periapsis and the apoapsis would alwas be half an orbit away. Assuming this is done on sub ejection speeds.
It seems to me, that this would be not so hard to calculate, but then again I can't do it.
I wonder how much faster your orbit would be. It could make people really sick looking up through the window and see the earth not moving above them, but spinning kinda quick.

Docking with such a station would also be really interesting!

 

[Andy44]

Well, docking would be out of the question, since you'd be under constant propulsive acceleration. The only application for something like this would be racing around the world, or perhaps some sort of military maneuver. In both races and military operations, fuel is wasted like it's going out of style.

As for just using the main thruster, you would not really spend much time angling the burn; once you reach the desired forward speed your main engine should be thrusting you straight down vertically and have no horizontal component of thrust. What you're doing in essence is trying to add your engine acceleration to the acceleration of the planet's gravity, thus forcing a faster orbit.

 

[tblaxland]

It seems to me, that this would be not so hard to calculate, but then again I can't do it.

OK:

Height of orbit = 300km
Radius of Earth = 6371km
Radius of orbit = 6671km

Radial acceleration due to gravity = mu/r^2 = 8.96m/s/s or 8.96e-3km/s/s
Radial acceleration due to thrust = 9.81m/s/s
Total radial acceleration = 18.77e-3km/s/s

Horizontal velocity = sqrt(acceleration * radius) = 11.19km/s
Vertical velocity = 0

 

[TSPenguin]

Docking would be essential.
Assuming a big station with a giant array of ion drives, you'd have to constantly deliver fuel.
And just give it time, someone will come up with good fake reason to have such a thing

 

[Andy44]

Well, the station would have to be under the same acceleration as the specaecraft, so it would be burning its own fuel, so why have a spacecraft?

 

[MajorTom]

OK:

Height of orbit = 300km
Radius of Earth = 6371km
Radius of orbit = 6671km

Radial acceleration due to gravity = mu/r^2 = 8.96m/s/s or 8.96e-3km/s/s
Radial acceleration due to thrust = 9.81m/s/s
Total radial acceleration = 18.77e-3km/s/s

Horizontal velocity = sqrt(acceleration * radius) = 11.19km/s
Vertical velocity = 0

Fantastic. (Although it might pay to include the vertical (or radial) accel. term again at the end, to emphasize what's keeping you in this orbit.)

I like to visualize this odd orbit as one being under the influence of an extra-strong force of gravity, like orbiting a neutron star.

Or being tied to the point at the center of the earth with a super-strong string, that would force you to go in a circle around the earth no matter how fast you go.

But what kind of vessel would have the fuel to be constantly accelerating in this fashion? How about the USS Enterprise? :rofl:

 

[tblaxland]

I like to visualize this odd orbit as one being under the influence of an extra-strong force of gravity, like orbiting a neutron star.

In Orbit MFD it would look like a hyperbolic orbit with an eccentricity of about 1.1. The line of the apsides would be rotating so that your vessel was always at periapsis.

I agree that it is a very impractical orbit, but it is not the job of the mathematician to question whether or not his calculations are of practical value

 

[Brassbud]

Remember guys that I don't want to do this for the purpose of going faster (although that's a nice plus), but rather to maintain an Earth-like environment on a spaceship/station.

With a few small changes to the orbiter autopilot, this would be possible. First, the "horizon level" feature would have to be inverted. Second, the "hold altitude" feature would have to be inverted so that gaining altitude triggered thrust, not losing it.

Lastly, the autopilot would probably lag behind in H-level at fast angular velocities, so there would be a small component of thrust forward which you would have to null out with retro-boosters.

I'm not just doing this for ****s and giggles though. I think it is quite likely space travel will go this direction once engine technology allows for it in the distant future(think fusion and beyond). It allows for what average humans would need for extended space travel without requiring some magical gravity-generator, and does so by providing the benefits of an Earth-sized rotating space station without needing an Earth-sized rotating space station.

 

[TSPenguin]

I'm not just doing this for ****s and giggles though. I think it is quite likely space travel will go this direction once engine technology allows for it in the distant future(think fusion and beyond). It allows for what average humans would need for extended space travel without requiring some magical gravity-generator, and does so by providing the benefits of an Earth-sized rotating space station without needing an Earth-sized rotating space station.

I doubt that it will go this way as you require constantly fuel. Not to speak of the extra fuel you need just to get there.
You are right that this would be equal to a rotating station the size of earth, but I think it is not far fetched that it would be more economical to use that fuel to build a giant space station, or two that are tethered. At some point you won't notice the difference and that point is far before an earth sized station.
Keep in mind that no matter how good you are at producing energy, you still need reaction mass to produce thrust...

Happy Orbiting

 

[Brassbud]

Continuous thrust (albeit small thrust) vehicles are already being considered as a means to to reduce the time required for space travel (at a certain point time is more valuable than fuel). So imagine this orbit as just the way you park your spacecraft of the future.

As far we know you can theoretically get about 20 megatons of energy out of 1 kg of mass. Fusion being at best maybe one percent of this, its not unbelievable to think that someday this won't be that big of a deal.

 

[James.Denholm]

I remember reading "The Cassini Division" by Ken Macleod, what he predicted was a craft that was fuelled by ice (argh, I think it was some fusion thing...), which was capable of transferring from Earth to Jupiter in a matter of days. All it did was accelerate at a rate of 9.81 m/s for half the trip, spin around at the half-way point, and then de-accelerate at a rate of 9.81 m/s. Atmittedly, I remember thinking to myself: Whoa, the fuel compartments of that ship must be like the Tardis, but that's science fiction for you. Perhaps a real vessel would be able to do this by convering electrical energy, hence solar energy, into some sort of kinetic energy or something.