Leaving Orbit (A contradiction of canon rules)

[Judas Iscariot]

Something that I wanted to point out, that is in direct dontradiction with canon rules is the rule from the LBBs that a starship cannot leave a world unless it has an M-Drive rated greater than the g rating of the world (a product of its size in CT)...

This is actually wrong. A spaceship may launch from a planet and leave orbit with just a fraction of a G in thrust.

It will take it a long while to get airborn, and then a long while to get up enough velocity to exit the atmosphere, and then more time accellerating to leave orbit...

But it can be done... Ion drives of today are a good example and the ESA ion drive craft SMART-1 left earth orbit and travelled to the moon on just a fraction of a G in thrust.

Deep Space-1, the NASA Ion drive craft, has demonstrated greater performance than its ESA counterpart, but it used an APU to get out of earth orbit.

Still.. It is proof of fact that you do not need to have a drive rating greater than the G rating of a planet to get off of it and into deep space... Just a lot more fuel and time accellerating.

 

[Judas Iscariot]

Something that I wanted to point out, that is in direct dontradiction with canon rules is the rule from the LBBs that a starship cannot leave a world unless it has an M-Drive rated greater than the g rating of the world (a product of its size in CT)...

This is actually wrong. A spaceship may launch from a planet and leave orbit with just a fraction of a G in thrust.

It will take it a long while to get airborn, and then a long while to get up enough velocity to exit the atmosphere, and then more time accellerating to leave orbit...

But it can be done... Ion drives of today are a good example and the ESA ion drive craft SMART-1 left earth orbit and travelled to the moon on just a fraction of a G in thrust.

Deep Space-1, the NASA Ion drive craft, has demonstrated greater performance than its ESA counterpart, but it used an APU to get out of earth orbit.

Still.. It is proof of fact that you do not need to have a drive rating greater than the G rating of a planet to get off of it and into deep space... Just a lot more fuel and time accellerating.

 

[BillDowns]

Dude, SMART-1 was lofted into orbit by Ariance Flight 162 and Deep Space 1 by Delta 7326-9.5 Med-Lite.

Big difference between surface and orbit.

 

[BillDowns]

Dude, SMART-1 was lofted into orbit by Ariance Flight 162 and Deep Space 1 by Delta 7326-9.5 Med-Lite.

Big difference between surface and orbit.

 

[Commander Drax]

I think it's got more to do with the fact that a 1G rated drive won't be able to escape from a 1G rated field (at least straight up) as 1G would only negate gravitational attraction. Hence the 2G rating of most scout ships. Obviously these can be allievated by aspects of design such as an airframe hullform generating aerodynamic lift (in real life) although a strong boost to orbit will still be needed such as a fast burning rocket engine.

Later editions of Traveller such as MT postulated that 1G rated drives could be safely overdriven for short periods (4 or 5 mins for 400-500% increase, or several days at 40% increase) thus your 1G rated ship could safely pull 1.4G when leaving the planets surface and make it into orbit in a timely fashion. TNE decided that Contragrav lifters negated gravitational attraction allowing even moderate thrust (plasma drives, rockets etc) could push a craft skyward and make orbit as effectively they would be travelling in Zero-G as long as the contragrav lifters functioned.

In short many different technologies exist in the Traveller universe so just come up with an explanation that satisfies yourself and enjoy.
I like the TNE explanation as it is most true to the original edition of high guard in which it was stated that a M-drive behaved like a 'plasma gun'

 

[Commander Drax]

I think it's got more to do with the fact that a 1G rated drive won't be able to escape from a 1G rated field (at least straight up) as 1G would only negate gravitational attraction. Hence the 2G rating of most scout ships. Obviously these can be allievated by aspects of design such as an airframe hullform generating aerodynamic lift (in real life) although a strong boost to orbit will still be needed such as a fast burning rocket engine.

Later editions of Traveller such as MT postulated that 1G rated drives could be safely overdriven for short periods (4 or 5 mins for 400-500% increase, or several days at 40% increase) thus your 1G rated ship could safely pull 1.4G when leaving the planets surface and make it into orbit in a timely fashion. TNE decided that Contragrav lifters negated gravitational attraction allowing even moderate thrust (plasma drives, rockets etc) could push a craft skyward and make orbit as effectively they would be travelling in Zero-G as long as the contragrav lifters functioned.

In short many different technologies exist in the Traveller universe so just come up with an explanation that satisfies yourself and enjoy.
I like the TNE explanation as it is most true to the original edition of high guard in which it was stated that a M-drive behaved like a 'plasma gun'

 

[aramis]

It is theoretically possible to accelerate to a low orbit with shy of local Surface G, if you have a lifting body, and can handle the drag. You do need enough thrust to develop aerodynamic lift... someone did the math years ago, and showed an expectation of about .7G local should be sufficient in standard atmospheres, if fuel is no limit

Once one is in orbit, breaking requires only minimal thrust. All you need is t be accelerating faster than your impacts cost you.

Spaceship One uses Aerodynamic lift for much of its rise to space; it was suborbital. the next gen is likely to be able to make it higher, due to scale efficiencies in drag. It's touchy, though, and it's also got more than 1G.

 

[aramis]

It is theoretically possible to accelerate to a low orbit with shy of local Surface G, if you have a lifting body, and can handle the drag. You do need enough thrust to develop aerodynamic lift... someone did the math years ago, and showed an expectation of about .7G local should be sufficient in standard atmospheres, if fuel is no limit

Once one is in orbit, breaking requires only minimal thrust. All you need is t be accelerating faster than your impacts cost you.

Spaceship One uses Aerodynamic lift for much of its rise to space; it was suborbital. the next gen is likely to be able to make it higher, due to scale efficiencies in drag. It's touchy, though, and it's also got more than 1G.

 

[Anthony]

Originally posted by Aramis:
It is theoretically possible to accelerate to a low orbit with shy of local Surface G, if you have a lifting body, and can handle the drag. You do need enough thrust to develop aerodynamic lift... someone did the math years ago, and showed an expectation of about .7G local should be sufficient in standard atmospheres, if fuel is no limit

If fuel is no limit and you have a hull capable of withstanding re-entry level temperatures for extended periods, all you need is a Lift/Drag ratio exceeding (1/thrust). Doing it at 0.1G is perfectly possible.

 

[Anthony]

Originally posted by Aramis:
It is theoretically possible to accelerate to a low orbit with shy of local Surface G, if you have a lifting body, and can handle the drag. You do need enough thrust to develop aerodynamic lift... someone did the math years ago, and showed an expectation of about .7G local should be sufficient in standard atmospheres, if fuel is no limit

If fuel is no limit and you have a hull capable of withstanding re-entry level temperatures for extended periods, all you need is a Lift/Drag ratio exceeding (1/thrust). Doing it at 0.1G is perfectly possible.

 

[Supplement Four]

Originally posted by Commander Drax:
In short many different technologies exist in the Traveller universe so just come up with an explanation that satisfies yourself and enjoy.
I like the TNE explanation as it is most true to the original edition of high guard in which it was stated that a M-drive behaved like a 'plasma gun'

Is that first edition HG? I don't see it in second edtion HG.

 

[Supplement Four]

Originally posted by Commander Drax:
In short many different technologies exist in the Traveller universe so just come up with an explanation that satisfies yourself and enjoy.
I like the TNE explanation as it is most true to the original edition of high guard in which it was stated that a M-drive behaved like a 'plasma gun'

Is that first edition HG? I don't see it in second edtion HG.

 

[far-trader]

Yep, 1st ed HG had (iirc) the maneuver drive usable as a fusion gun (energy weapon) equal in USP to the number of Gs but only at close range and immediately putting you at long range. Something like that, I can look it up later to check.

EDIT: Actually there was no official rating of USP that I see now. Must have been a house rule making it USP = Gs.

 

[far-trader]

Yep, 1st ed HG had (iirc) the maneuver drive usable as a fusion gun (energy weapon) equal in USP to the number of Gs but only at close range and immediately putting you at long range. Something like that, I can look it up later to check.

EDIT: Actually there was no official rating of USP that I see now. Must have been a house rule making it USP = Gs.

 

[Plankowner]

Modern aircraft do not have anything close to a 1-G rating for their drive (the F-16 is a notable exception). Using wings etc, vehicles can lift off with considerable less than 1-G accelleration. Once speed is built up, and altitude is gained, a STREAMLINED vessel could reach orbit with less than 1-G accelleration all the way. Once in orbit, the vessel already has ALMOST enough velocity to escape the gravity of the planet, so only a little more is needed to fully escape the gravity well.

 

[Plankowner]

Modern aircraft do not have anything close to a 1-G rating for their drive (the F-16 is a notable exception). Using wings etc, vehicles can lift off with considerable less than 1-G accelleration. Once speed is built up, and altitude is gained, a STREAMLINED vessel could reach orbit with less than 1-G accelleration all the way. Once in orbit, the vessel already has ALMOST enough velocity to escape the gravity of the planet, so only a little more is needed to fully escape the gravity well.

 

[Ishmael]

for aero lifting, one thing that seems to be forgotten is that lift is proportional to air density, so worlds with thin atmospheres will give give ships that use aerolift fits.

 

[Ishmael]

for aero lifting, one thing that seems to be forgotten is that lift is proportional to air density, so worlds with thin atmospheres will give give ships that use aerolift fits.

 

[far-trader]

Originally posted by Ishmael James:
for aero lifting, one thing that seems to be forgotten is that lift is proportional to air density, so worlds with thin atmospheres will give give ships that use aerolift fits.

Not forgotten by this Traveller, but fortunately it's the small worlds with light gravity that will typically have thin atmo, and the big worlds with more gravity will have more atmo. I figure most of the time it will balance nicely enough that an airframe will work with the maneuver drive to about the same parameters regardless.

 

[far-trader]

Originally posted by Ishmael James:
for aero lifting, one thing that seems to be forgotten is that lift is proportional to air density, so worlds with thin atmospheres will give give ships that use aerolift fits.

Not forgotten by this Traveller, but fortunately it's the small worlds with light gravity that will typically have thin atmo, and the big worlds with more gravity will have more atmo. I figure most of the time it will balance nicely enough that an airframe will work with the maneuver drive to about the same parameters regardless.