Technical Liftoff Question

[estar]

Does that take into account lift from wings or lifting body hull shape?

No, however if you have lift and in a suitable atmosphere then the ascent profile becomes easier. You will need a runway and of course wheels to take advantage of it. The main effect that with a lifting surface you can lift off with more weight.

For the descent profile you still need to slow down below the velocity that will cause re-entry heating. But once in the lower atmosphere you can fly down to the runway.

But with grav control and reaction-less maneuver drives there is little need for lifting surfaces for normal commercial operations if your thrust to weight ratio is greater than 1.

Now if your thrust to weight ratio isn't greater than one then having a lifting surface on a planet with a suitable atmosphere can get you into space. However your ship will need also to withstand atmospheric heating for both ascent and descent.

The problem that you will have to overcome is the fact that the dynamic pressure caused by moving through lower atmosphere will impose a maximum speed on your craft beyond which either you go out of control or just burn up. However without a thrust to weight ratio greater than one there is a limit to how high you can go as the atmosphere becomes to thin to sustain life.

But it possible to go up to your flight ceiling where the air is thinner accelerate to the fastest possible speed at that altitude and then fly a ascent profile that allows the craft to keep accelerating faster and eventually overcome the loss of lift by achieving a sub orbital ballistic arc into space and then time your thrust around apogee to establish an orbit.

I will add while you could do the math for this you don't gain anything for gaming purposes. All that matters that a referee understand why it works.

For example we could calculate the speed of water flowing a river if we know the type of river bed, the slope and other factors. But all really need for a RPG is to know if the water flow is a raging rapid, swift, or placid. The same for orbital manuevuers.

Also remember that I use weight deliberately. Mass is independent of gravity however for ascent weight is what important. It why that the Ascent Engine of the Lunar Module could achieve Lunar Orbit with a single stage. Because of the Moon's 1/6 gravity. But on Earth it would have been impossible to do that.

To summarize to ascend with a craft with lifting surface you

1) Take off from a runway.
2) Climb to maximum operating altitude
3) Accelerate to maximum speed
4) Ascend into a sub-orbital trajectory with the apogee in space.
5) Coast until before apogee time your thrust so that when you are past apogee you attain orbit.

The reason you are not doing a gravity turn is because you need to gain as much vertical velocity to get your apogee high enough into space so you have enough time to do a orbital insertion thrust. This is not very efficient however with a reactionless thrust you have unlimited delta-vee so you afford to fly like this.

Plus anybody can practice flying using Orbiter or the Kerbal Space Program. You will need to make a mod to simulate reactionless thrusters but that can be done in both with editing text files. To simulate this all you need to give the engines an extremely high specific impulse value. Kerbal has atmospheric heating so that the program to use if you want to play around with avoiding burning up. Orbiter simulates the aerodynamics of re-entry but it require creating a C++ add-on to get a craft to calculate and respond to the heating.

 

[estar]

I thought of something else last night.

Sticking just with Classic Traveller we know that we have reactionless-thrusters, and that we have grav plates that create artificial gravity. That grav-plates are not broken out as a separate item in the LBB or High Guard.

What to prevent a referee from saying that all starship hull have external grav plates as well internal plate. That the external plates don't provide thrust but negate the local grav field. This way it doesn't matter what your thrust to weight ratio is you will be able to lift off from any planet or moon.

Think about it we have a 1-G Grav field internally throughout the ship regardless of the external gravity.

However this has one major change that not reflect in the ship combat rules of the LBB. That is the effect of planetary gravity on the ship. If this is how starship works then the ship will be able "turn on" or "turn off" the effect of the gravity field. An option not present in the LBB.

 

[kilemall]

I thought of something else last night.

Sticking just with Classic Traveller we know that we have reactionless-thrusters, and that we have grav plates that create artificial gravity. That grav-plates are not broken out as a separate item in the LBB or High Guard.

What to prevent a referee from saying that all starship hull have external grav plates as well internal plate. That the external plates don't provide thrust but negate the local grav field. This way it doesn't matter what your thrust to weight ratio is you will be able to lift off from any planet or moon.

Think about it we have a 1-G Grav field internally throughout the ship regardless of the external gravity.

However this has one major change that not reflect in the ship combat rules of the LBB. That is the effect of planetary gravity on the ship. If this is how starship works then the ship will be able "turn on" or "turn off" the effect of the gravity field. An option not present in the LBB.

The grav neutralization option was discussed extensively above under the buoyancy exchange, suggest you reread.

I would gather many have signed onto the grav drive model of the maneuver drive, which would provide both neutralization and thrust. I am going for a mixed model to highlight the difference between high end whisperliners and grungy industrial thruster ships, and giving the reaction ships a way out with profligate fuel use afterburners.

As for burning up, higher tech ships get deflectors which are both mini-repulsors and charged field to minimize the direct heat with conformal lift surfaces at higher TLs, and cryogenic hydrogen coolant release along the bottom of the hull like the National Aerospace plane was intended to have. The effect would be a bright burning trail in the sky for every 'hard' landing ship.

https://en.wikipedia.org/wiki/Rockwell_X-30

 

[estar]

The grav neutralization option was discussed extensively above under the buoyancy exchange, suggest you reread.

OK I missed it thanks for pointing it out.

I would gather many have signed onto the grav drive model of the maneuver drive, which would provide both neutralization and thrust. I am going for a mixed model to highlight the difference between high end whisperliners and grungy industrial thruster ships, and giving the reaction ships a way out with profligate fuel use afterburners.

If I read the details in #7 right about deflectors providing lift. Along with your OP then I would say the physics involved would be as I described for spaceplanes. You climb to up to where the atmosphere is thin but there still enough to get full lift out of your spacecraft. Accelerate to maximum dynamic pressure, then starting your final climb so that you angle into a sub orbital ballistic arc. Then near apogee start thrusting to establish your orbit.

For the 1-G ships reaction boosters should enough to get them into the sub-orbital arc from there the 1-G drives will be enough to attain orbit.

As for burning up, higher tech ships get deflectors which are both mini-repulsors and charged field to minimize the direct heat with conformal lift surfaces at higher TLs, and cryogenic hydrogen coolant release along the bottom of the hull like the National Aerospace plane was intended to have. The effect would be a bright burning trail in the sky for every 'hard' landing ship.

https://en.wikipedia.org/wiki/Rockwell_X-30

Except why bother you have effectively unlimited delta-vee. If your going grunge, the rust buckets and cheap-ass spacecraft will thrust retrograde keeping their vertical velocity low until their total velocity drops below the point that causes re-entry heating. Especially with the tail sitter designs you have they just would descend slowly down to a landing.

 

[aramis]

No, however if you have lift and in a suitable atmosphere then the ascent profile becomes easier. You will need a runway and of course wheels to take advantage of it. The main effect that with a lifting surface you can lift off with more weight.

You only need a runway if (1) you don't have standard Traveller maneuver drives (eg, TNE), (2) you don't have at least 1 G_local main drive† or (3) you're way overloaded*.

*TNE and T4 specify 10 Tonnes per Displacement ton as the default value; if you exceed that, you have to recalculate.

† MT:SSOM allows short pushes to 400% rated for up to 5 minutes, and 140% for up to "days", and 90° off axis is 25%, forward is 100%
TNE, on the other hand, has a system which makes your weight 2% of local weight (and remember, acceleration is a function of thrust and mass, but gravity is a function of weight, and you subtract out the gravity leg from the thrust leg)

A true runway is only needed if G_local > 0.35 * Mn...
and even then, it may not be truly needed, provided G_local ≤ 4 * Mn...

If 0.35 * Mn < G_local < 4 * Mn, you flare above the field and VTOL into place. (Which means, pretty much, all airframe commercial craft on almost all shirtsleeve worlds Siz <A, as local G will be in the range of 0.25 to 1.5.)

If G_local <0.35 Mn, you can hover in like an air/raft.

Takeoffs are trickier...
As long as G_local < 1.4 * Mn:
You don't need a runway to take off - you can lift and rotate to vertical and not need the airframe to work.
If G_local < 0.35, you can lift on sustainable overthrust and helicopter or air/raft type flight mode.
If 1.4 * Mn ≤ G_local < 4 * Mn:
you can lift, and go forward - the takeoff roll is actually likely to be on gravitics


So, pretty much 90% of worlds, the airframe isn't needed for landing nor takeoff.

 

[atpollard]

So, pretty much 90% of worlds, the airframe isn't needed for landing nor takeoff.

Official and bogus ... "the airframe isn't needed because my 1G ship is really 1.5 to 4 G for takeoff" is an unsatisfying solution.

[Just like TL8 air rafts make all other modes of access to space superfluous.]
[da rulez sukz ]
YMMV

(and Aramis, that wasn't personal at you ... I just needed to :rant: )

 

[warwizard]

https://en.wikipedia.org/wiki/Density_of_air

The density of air, ρ (Greek: rho) (air density), is the mass per unit volume of Earth's atmosphere. Air density, like air pressure, decreases with increasing altitude. It also changes with variation in temperature or humidity. At sea level and at 15 °C air has a density of approximately 1.225 kg/m3

So if you pump all the air overboard prior to lifting you could gain some 2 1/2 metric tons of buoyancy in a standard atmosphere. (figuring some 70% of your volume is occupied by air .7 *2800*1.225= 2400 Kg)
I know it's not much but if the engineer is trying everything to get off the ground that's one of the things to do. (Note: pumping it into tanks gains nothing, the mass is still there)

Large disposable hydrogen lifting envelope... to get you to high altitude before you start your burn.

I too am developing a hard SCI fi dawn of Terra campaign without any gravetics for the Terrans initially, (until they see examples of the imperials using it at Bernard's star and get their hands on some "samples") and then will go through experimental and early stages before reaching the TL 9 stage, treating the Terran Gravetics technology like it is TL 7 at the start of the campaign.

at TL 9 (using T4 FF&S here) Fusion power plants are enormous and use deuterium not hydrogen, so the smaller ships will still have fission power plants and rely on strap on boosters for initial orbit, so vertical launch is the rule, however deck plans are designed for minimal acceleration using advanced ion drives and fusion rockets and the habitat sections use spun sections for environmental gravity. As everybody is strapped into acceleration couches for launch there is no need for tail sitter type deck plans yet.

Only the exploration ships and colony ships will have wilderness refueling and or landing capabilities, and the colony ships once down are down for good or until the colony can build boosters that is.
In this IMTU setting the shuttles handle the interface from surface to orbit and the starships are space only.

 

[Patron Zero]

Mind no aerospace engineer here, far from it as my experiences in model rocketry so exhibited but do understand a few things.

Any object, streamlined or not, moving with sufficient velocity through a thick atmosphere is going to acquire heat and resistance doing such.

Given the transfer of enough kinetic energy, a brick could achieve hyper-sonic speeds, just not likely to be the same object once so accelerated.

 

[aramis]

Official and bogus ... "the airframe isn't needed because my 1G ship is really 1.5 to 4 G for takeoff" is an unsatisfying solution.

[Just like TL8 air rafts make all other modes of access to space superfluous.]
[da rulez sukz ]
YMMV

(and Aramis, that wasn't personal at you ... I just needed to :rant: )

I much prefer it, for its space opera feel, to the TNE/T4 CG Lifters 98% off weight rule... which makes VASIMIR a capable launch mode.

Think Star Trek, and pushing.

Or WWII...
Or certain military aircraft (WWII era, mostly), where you can, literally, "Push her past the wire". (The safe operation limit was set on such aircraft with a wire between two adjustable slides, and blocked pushing the throttle past. It was pretty light, and in a pinch, you could push her past redline, but it would break the wire to tell the mechanic to do a deep maintenance on the engine.) Full Military Throttle was at the wire; War Emergency Power was past the wire. (I've about 6 hours sticktime on a C-119 under instruction. It had just such a setting. The mechanic replaced the wire with one from his loaf of bread...)

I agree about days being too long... but the 140% capability over cruise is about the same relationship as Flank vs Cruise on a naval warship. And engineers can push past that by changing some parameters and exceeding the redlines. They usually get commendations for doing it in wartime... posthumous if it failed, valor if successful. They get punshed for doing it the rest of the time.

James D'Angina, Vought F4U Corsair, @google books

 

[BlackBat242]

I've only read through the last 3 pages of this thread (having given up after the first page back when the thread was started), so I don't know if this has been suggested.....


As far as I'm concerned, in order to land on any body that generates greater than .25G at the surface to be landed on and/or has an atmosphere of 4 or thicker, the ship needs to be at least semi-streamlined (as this produces a stronger hull that is stressed for landing & parking on bodies with significant gravity and/or a significant atmosphere), and to be less than 800dt (1,000dt for military vessels).

Non-streamlined ships and large ones cannot properly self-support their structure in a significant gravity field.

I also prefer to use a technology proposed by Murray Leinster in his sci-fi "Med Ship" series from 1959 to 1967 (all 8 of which are collected in the anthology Med Ship (Baen Books, August 2002) ISBN 0-7434-3555-9).
https://www.sfsite.com/~silverag/ml_series.html

There was a landing grid in the spaceport city on Maris III. From its control room instructions should be sent, indicating a position some five planetary diameters from the surface of that world.
.....
The giant landing grid should then reach out its specialized force field, lock onto the ship, and bring it gently but irresistibly to the ground.

The reverse process is used to launch ships from the landing field to "5 diameters" orbit.

The grid can also really abuse a small ship, as Med Service medic Calhoun was to discover shortly afterwards. Fortunately, the "50 ton" Med Service cutters have auxiliary landing rockets, which he uses to land elsewhere on the planet.

Here is a description of the landing grid:

The only exception to gracefulness {referring to the architecture of the city described in the preceding paragraph} was the massive landing grid, a mile and a half across, which was a lacework of monster steel girders with spider-thin wires of copper woven about them in the complex curves its operation required. Inside it, Calhoun could see the ship of the invaders. It had landed in the grid enclosure.

This is well within Traveller tech - as made clear by the presence of "repulsers" in CT book 5 (2nd edition), for bay mounts at TL10 and up. All this is is a scaling up of those items, using a ground-based power source and the large projecting grid.

I would put these landing grids as being in use from TL12 for ships below 500dtons, increasing by an order of magnitude per TL (5,000dtons @TL 13, etc). They would be present at class "A" downports on TL12+ worlds, class "A" and "B" downports on TL13+ worlds, and class "A", "B", and "C" downports on TL14+ worlds. They would never be present on class "D" or worse downports regardless of TL.

Of course, the landing field itself needs to be re-enforced enough to support the ship's "resting mass", and likely also uses support cradles (similar to the blocks in a drydock), which are adjusted to each specific ship to be supported.

 

[aramis]

BlackBat: Jeff Swycaffer used just such landing grids in his Exonidas Spaceport adventure (dragon issue 59 — March 1982, pages 34-48).

 

[BlackBat242]

I've read a couple of his Traveller-based novels, but not that adventure. Now I need to go do that.

Thanks.

 

[estar]

As far as I'm concerned, in order to land on any body that generates greater than .25G at the surface to be landed on and/or has an atmosphere of 4 or thicker, the ship needs to be at least semi-streamlined (as this produces a stronger hull that is stressed for landing & parking on bodies with significant gravity and/or a significant atmosphere), and to be less than 800dt (1,000dt for military vessels).

You don't with reactionless m-drives. As long as you can maintain a thrust to weight ration of greater than 1 (1G on Earth) You can descend as slow as you want.

Because of limited fuel real world spacecraft do a retrograde thrust so that the perigee (low point) of their orbit is well into the atmosphere. As they enter the atmosphere the air will compress and slow down the ship causing it to shed it velocity down to the terminal velocity of it's shape.

Now if the craft had enough fuel then it could not only keep thrusting retrograde but "waste" thrust to minimize the vertical velocity component of it's path while reducing horizontal velocity.

In real life you will run out of fuel before this does any good for re-entry. But with a reactionless m-drive you have effectively unlimited fuel where you can take all the time in the world to fly a profile that doesn't involve re-entry heating.

Now if you need to ascend or descend in minimum time with a 1-G or 2-G drive well then you better have something to shield against re-entry heating.

You don't have to take my word for it. You can fly itself yourself using Orbiter Space Simulator or the Kerbal Space Program.

Non-streamlined ships and large ones cannot properly self-support their structure in a significant gravity field.

That doesn't really make sense. A 1,000 Traveller style ton cube is eminently self-supporting but not aerodynamic in any form. Nor it does it make sense in term of classic traveller where unstreamlined ships can land and lift off from vacuum worlds.

Now say if you made your ship something like a dispersed structure then yeah you have a point.

 

[estar]

Given the transfer of enough kinetic energy, a brick could achieve hyper-sonic speeds, just not likely to be the same object once so accelerated.

Actually no, at a high enough velocity the air will compress and the brick will shatter as if it ran into a solid object.

However understand the general concept to avoid this is easy to understand. As you move faster you angle higher so that while you are moving faster the atmosphere is thinning. Above 50 km you can start to go all out.

If your thrust to weight ratio is less than 1, you are more restricted in your profile due to the need to maintain lift so that you have a vertical velocity. Which is why you try for a profile that launches you into a sub-orbital ballistic arc.

 

[kilemall]

If I read the details in #7 right about deflectors providing lift. Along with your OP then I would say the physics involved would be as I described for spaceplanes. You climb to up to where the atmosphere is thin but there still enough to get full lift out of your spacecraft. Accelerate to maximum dynamic pressure, then starting your final climb so that you angle into a sub orbital ballistic arc. Then near apogee start thrusting to establish your orbit.

For the 1-G ships reaction boosters should enough to get them into the sub-orbital arc from there the 1-G drives will be enough to attain orbit.

Works for me as an alternative for expensive fuel burns. They'll be out of luck with too low a TL ship though.

Except why bother you have effectively unlimited delta-vee. If your going grunge, the rust buckets and cheap-ass spacecraft will thrust retrograde keeping their vertical velocity low until their total velocity drops below the point that causes re-entry heating. Especially with the tail sitter designs you have they just would descend slowly down to a landing.

Because sometimes the skies are too busy for optimal flight paths, and sometimes you just gotta leave Mos Eisley RIGHT NOW.

 

[kilemall]

Official and bogus ... "the airframe isn't needed because my 1G ship is really 1.5 to 4 G for takeoff" is an unsatisfying solution.

[Just like TL8 air rafts make all other modes of access to space superfluous.]
[da rulez sukz ]
YMMV

(and Aramis, that wasn't personal at you ... I just needed to :rant: )

Air/Raft shuttling is too damn slow, and most passengers are not keen on sitting in vacc suits for routine trips.

I can see quite a tourist trade in such trips for yokels though, and for D/E ports they probably are just about it for shuttle service.

 

[kilemall]

This is well within Traveller tech - as made clear by the presence of "repulsers" in CT book 5 (2nd edition), for bay mounts at TL10 and up. All this is is a scaling up of those items, using a ground-based power source and the large projecting grid.

I would put these landing grids as being in use from TL12 for ships below 500dtons, increasing by an order of magnitude per TL (5,000dtons @TL 13, etc). They would be present at class "A" downports on TL12+ worlds, class "A" and "B" downports on TL13+ worlds, and class "A", "B", and "C" downports on TL14+ worlds. They would never be present on class "D" or worse downports regardless of TL.

Of course, the landing field itself needs to be re-enforced enough to support the ship's "resting mass", and likely also uses support cradles (similar to the blocks in a drydock), which are adjusted to each specific ship to be supported.

Actually, as I recall in the original novelization that's how the Millenium Falcon took off from Mos Eisley, with a planetery repulsor in place for supporting ships to and from, which didn't make sense to me as they could then cut the beam and the Falcon would never have gotten away.

Repulsors are used extensively in the SW universe-

http://starwars.wikia.com/wiki/Repulsorlift

 

[atpollard]

Air/Raft shuttling is too damn slow, and most passengers are not keen on sitting in vacc suits for routine trips.

I can see quite a tourist trade in such trips for yokels though, and for D/E ports they probably are just about it for shuttle service.

Just to clearly articulate my complaint: :rant:

TL 7 is roughly the 1970's ... when the game was written.
If you want to get from Earth to orbit using TL 7 technology, you build a giant Saturn V rocket ... or you build a giant fuel hog Space Shuttle.
But at TL 7, we have dreams of Scramjet SSTO reusable rocket planes, and Delta Clippers with linear Aerospike engines, and even Space Elevators or ground based lasers that ignite a solid fuel engine to provide lift. There are plans for fuel depots at LEO and space taxis to boost you from LEO to an L2 station for transfer to anywhere in the solar system. Book after book of wonderful ideas waiting to be explored ...

THEN COMES TRAVELLER TL 8:
With anti-gravity, infinite power fusion which find expression in the ubiquitous "Air Raft" (which comes in an enclosed and pressurized version as well). Nothing else can compete economically. All those wonderful future technologies get crumpled into a ball and tossed into the trash can. And magic flying boxes become the vanilla (one bland flavor fits all) solution for all space access from TL 8 to TL 17? ... teleportation replaces the air raft/modular cutter option somewhere around TL 17, doesn't it.

So my lament is for the future that never was because Grav and Fusion both happen right around the corner at TL 8 ... crushing all other possible futures for Millenia to come.

 

[kilemall]

Just to clearly articulate my complaint: :rant:

TL 7 is roughly the 1970's ... when the game was written.
If you want to get from Earth to orbit using TL 7 technology, you build a giant Saturn V rocket ... or you build a giant fuel hog Space Shuttle.
But at TL 7, we have dreams of Scramjet SSTO reusable rocket planes, and Delta Clippers with linear Aerospike engines, and even Space Elevators or ground based lasers that ignite a solid fuel engine to provide lift. There are plans for fuel depots at LEO and space taxis to boost you from LEO to an L2 station for transfer to anywhere in the solar system. Book after book of wonderful ideas waiting to be explored ...

THEN COMES TRAVELLER TL 8:
With anti-gravity, infinite power fusion which find expression in the ubiquitous "Air Raft" (which comes in an enclosed and pressurized version as well). Nothing else can compete economically. All those wonderful future technologies get crumpled into a ball and tossed into the trash can. And magic flying boxes become the vanilla (one bland flavor fits all) solution for all space access from TL 8 to TL 17? ... teleportation replaces the air raft/modular cutter option somewhere around TL 17, doesn't it.

So my lament is for the future that never was because Grav and Fusion both happen right around the corner at TL 8 ... crushing all other possible futures for Millenia to come.

Easy there, who says you get air rafts at TL 8.0? Maybe it's more a TL 8.8 thing and in the meantime there is a lot of spacework to be done?

One thing I have going on is TL8 fusion isn't L-Hyd fusion, it's He3 fusion, and redonkulously expensive fuel, so fission plants are all over the place TL8 and 9 until L-Hyd gets invented TL10.

Space elevators are still a win especially since you can power them with solar instead of burning fuel and probably come in far cheaper per invested 100,000 Cr for ton-lift, and a lot less manpower to boot (grav vehicles would be like trucks, elevators like trains).

Cheap portable fusion largely puts paid to laserbase propulsion, but probably heavily used for ore transport.

 

[aramis]

Air/Raft shuttling is too damn slow, and most passengers are not keen on sitting in vacc suits for routine trips.

I can see quite a tourist trade in such trips for yokels though, and for D/E ports they probably are just about it for shuttle service.

Most d/e ports lack the TL for local supply/repair of air/rafts....