Question: Ships leaving atmosphere

[GamerDude]

So a streamlined lifting body (real world definition) is not streamlined (MgT definition) because the real world does not have magic drives and fusion power to allow it to fly like an airplane?

Actually, going to http://www.dictionary.com I got:

http://dictionary.reference.com/browse/streamlined
stream·lined
   /ˈstrimˌlaɪnd/ Show Spelled[streem-lahynd] Show IPA
–adjective
1. having a contour designed to offer the least possible resistance to a current of air, water, etc.; optimally shaped for motion or conductivity.

http://dictionary.reference.com/browse/lifting+body
lifting body 
–noun Aeronautics .
an aircraft or spacecraft configuration in which there are no wings, and lift is obtained by aerodynamic forces on its body.

While I wouldn't say this are totally exclusionary of each other you can't say one is the other.

... and the 'typo' about standard hulls (MgT definition) being able to land to engage in wilderness refueling from the ocean, but being unable to lift-off from that ocean is correct.

MGT Core Rulebook, pg 106

Streamlining a ship increases the cost of the hull by 10%. This streamlining includes fuel scoops which allow the skimming of unrefined fuel from gas giants or the gathering of water from open lakes or oceans. Streamlining may not be retrofitted; it must be included at the time of construction.

A standard-hull ship may still enter atmosphere but is very ungainly and ponderous, capable only of making a controlled glide to the surface. Getting it back into space requires an elaborate launch setup and considerable expense. A standard-hull ship may have scoops for gathering fuel from a gas giant but the process will be much more difficult and less efficient. Larger ships of this type will often carry a specialized sub-craft (such as a modular cutter, see page 135) to perform the actual atmospheric skimming. See Atmospheric Operations on page 137.

I can't see what typo you mean. I copied those straight out of my PDF copy, checked them with my dead-tree copy (second printing, nicer graphics) and they are what I've posted here.

I don't know how you came to the understanding it was regular hulls that could scoop from oceans and such, I mean I can't find this 'typo' in any book (I might have missed one)

Time to agree to disagree.

I would accept that IF others were ensuring what they were referencing/quoting was done fully, completely, and accurately. And (for me) it's not about me being 'right' but about not accepting bad info, misinformation, and misrepresentation. I've already agreed about the description of the various hull types were a bit nuts... they are.

And a more personal note, I have recollection of reading how ships like the Far Trader etc had 'contra-grav' but I can't find it. I know it is NOT in MGT (which is what we are discussing) so it doesn't apply here but it makes sense to me to have it. You still need streamlining because if you don't reduce the friction to air flow over the hull you are going to spend a whole lot more power and fuel to get where you are going. Even then, the ship wouldn't just point its nose at the sky and 'whoosh' is up in orbit. Having to 'fly' up, matching how an air raft does it, to me makes the most sense.

But that's just me, able to seperate other versions (and my personal tastes) from what I'm reading in the books.

 

[rust]

I can't see what typo you mean.

Well, I brought it up and joked about it, so I will explain it - again. :wink:

MGT core rules, starship operations chapter:

BOARDING, DOCKING AND LANDING
Landing: Any ship with a standard or streamlined hull may land on
the surface. Unstreamlined ships suffer a –2 DM to any Pilot checks
made in atmosphere while a ship with a Distributed hull suffers a
–4 DM to any Pilot checks, and is likely to take severe structural
damage if it lands. Landing at a starport is a Routine (+2) task for
most ships taking 10–60 seconds (so most pilots will take extra
time and get a +1 or +2 DM on top of this – see page 50).
Most ships have landing gear, allowing them to touch down ‘in
the wild’, which requires an Average (+0), Diffi cult (–2) or even
Very Diffi cult (–4) check, depending on local conditions. Nondistributed
ships can also land on bodies of water without sinking.
Failing a landing roll means that the ship has landed improperly
or even crashed.

- Any ship, standard or streamlined, can land.
- Most ships have landing gear.
- Standard hulls have a -2 for landings in the wild.
- A standard hull is a nondistributed ship.
- Nondistributed ships can land on bodies of water.

So, nothing in the rules prohibits a standard hull ship with fuel scoops to
land on water for ocean refuelling. However, according to the starship
design chapter, a standard hull ship would need an expensive and ela-
borate launch facility to take off again. An expensive and elaborate fa-
cility is almost impossible to construct on an ocean in the wild.

So, a standard hull ship is allowed by the rules to land on an ocean in
the wild for ocean refuelling - but if this ocean is really in the wild, it
can never again take off from there.

 

[phavoc]

A number of posts have talked about reentry stresses and heat. Which make sense if you are de-orbiting like the space shuttle does.

But, when you have anti-gravity and essentially unlimited reaction mass, there's nothing to prevent you from gently entering the atmosphere (at say a few hundred KPH as opposed to thousands of KPH), and slowly dropping down to your landing zone. Which my admittedly low-level of aerospace design and physics knowledge tell me that there would not be any excessive heat generated, nor would you be placing a lot of stress on your hull.

Is this a correct assumption?

 

[rust]

Is this a correct assumption?

In theory, yes. But unfortunately the ship would have to get through the
jet streams of the upper atmosphere, which requires a certain structural
strength. It could still sink slowly like a balloon, but not entirely without
stress.

 

[phavoc]

Is this a correct assumption?

In theory, yes. But unfortunately the ship would have to get through the
jet streams of the upper atmosphere, which requires a certain structural
strength. It could still sink slowly like a balloon, but not entirely without
stress.

Oh, didn't think about jetstream. But, if a ship can withstand 1-6Gs of stress in space, surely it could take 100mph jetstream? If not, it should at least be able to avoid it.

 

[rust]

But, if a ship can withstand 1-6Gs of stress in space, surely it could take 100mph jetstream? If not, it should at least be able to avoid it.

I would think so, at least for the huge majority of all starships. Some dis-
tributed hulls could have serious problems and suffer damage or even
break apart because they would have a different kind of stress than un-
der acceleration or deceleration (shear effects and thelike), but in my
view these would be rare exceptions.

 

[BP]

This is the type of thing that benefits from being ambiguous in rule books - especially as the starting point depends on a handwave (gravitics).

Several technical points (fairly easily addressed in game using DMs fairly close to what is done in MgT):

First, keep in mind a planet's atmosphere moves with the planet... if it didn't, the wind speed of, say, Cape Canaveral, would get about a 1,500 km/h boost (one of the reasons to launch vehicles to the East near the equator) while polar regions are much slower.

Additionally, well above the Jet streams, the ionized gas 'wind' can exceed 600 kph - given the density, this is not as bad as say the jet streams rust mentioned with their shear stresses and the like - but it is bad news temperature and surface-wear wise (and something that affects R/W satellites).

More importantly, in the upper atmosphere, everything not meteorically plummeting or ballistically rising without grav tech is moving at or near orbital speeds of tens of thousands of km/h. Hitting even a small object can be bad news (not that the same doesn't hold true in space, but the odds are quite different near a planetary gravity well).

Starting at orbital speeds, one could descend at slow deceleration (being 'magically' grav powered an all) and take a buffeting at certain levels, but with drastically increased odds of getting hit by orbital speed objects, especially if one is making, say, a 5+ hour deceleration through the atmo (to reduce orbital speeds to surface speeds, while also counteracting gravity's pull).

 

[DFW]

More importantly, in the upper atmosphere, everything not meteorically plummeting or ballistically rising without grav tech is moving at or near orbital speeds of tens of thousands of km/h. Hitting even a small object can be bad news (not that the same doesn't hold true in space, but the odds are quite different near a planetary gravity well).

Starting at orbital speeds, one could descend at slow deceleration (being 'magically' grav powered an all) and take a buffeting at certain levels, but with drastically increased odds of getting hit by orbital speed objects, especially if one is making, say, a 5+ hour deceleration through the atmo (to reduce orbital speeds to surface speeds, while also counteracting gravity's pull).

Small objects moving at those glacial speeds (orbital) wouldn't even be noticed by a space ship hull in Trav.

Also, you match ground speed before you enter atmosphere

 

[far-trader]

...Also, you match ground speed before you enter atmosphere

Riiight. So you enter atmo at something like 11,000kph for an Earth size world? Toasty

Or more, upwards of 28,000kph.

 

[atpollard]

Small objects moving at those glacial speeds (orbital) wouldn't even be noticed by a space ship hull in Trav.

Is it possibe that small Ultra High Velocity objects punch thru starships travelling to Jupiter with some frequency, only the tiny hole is little more than a petty maintenance problem. The odds of hitting someone are ... astronomical. :wink:

 

[simonh]

Starting at orbital speeds, one could descend at slow deceleration (being 'magically' grav powered an all) and take a buffeting at certain levels, but with drastically increased odds of getting hit by orbital speed objects, especially if one is making, say, a 5+ hour deceleration through the atmo (to reduce orbital speeds to surface speeds, while also counteracting gravity's pull).

Spaceships have to deal with micrometeorite damage all the time, so nothing special there.

If you are arriving at a planet via jump, why bother going into orbit at all? Plot a course tangential to the planet, in it's direction of rotation so that at the point you enetr the atmosphere yor relative ground speed is zero. Jet streams aren't 'that' much of a problem.

On a seperate issue, the problem of 1G thrust ships taking off from planets with higher than 1G surface gravities. This has been a concundrum for Traveller GMs since the very early days of Traveller. I remember discussing it with my brother soon after buying our first copy in the early 80's. If it comes up in game (most players rarely notice) I just say that for very brief periods you can overdrive the engine, but not for long enough to make a difference in space combat, and anyway afterwards you have to run the engine in a lower power mode for a while to de-stress, so over the timescales in space combat it averages out.

Simon Hibbs

 

[DFW]

Is it possibe that small Ultra High Velocity objects punch thru starships travelling to Jupiter with some frequency, only the tiny hole is little more than a petty maintenance problem. The odds of hitting someone are ... astronomical. :wink:

Umm, no. People don't live long after what just passed through the hull, passes through them. Fuel tanks may be self sealing, people aren't.

 

[DFW]

Riiight. So you enter atmo at something like 11,000kph for an Earth size world? Toasty

Or more, upwards of 28,000kph.

You think that the the Earth rotates at 28,000kph?

No, the atmosphere is going the same speed as the planets rotation is what I'm talking about. Earth (at equator) is going 1670 kph.

 

[atpollard]

Is it possibe that small Ultra High Velocity objects punch thru starships travelling to Jupiter with some frequency, only the tiny hole is little more than a petty maintenance problem. The odds of hitting someone are ... astronomical. :wink:

Umm, no. People don't live long after what just passed through the hull, passes through them. Fuel tanks may be self sealing, people aren't.

You misunderstand my statement, of course it will hurt (probably kill) anybody hit by hypervelocity sand.

However, 99.9% of the office space where I work is NOT a human being. A single random hypervelocity grain of sand passing through my office would have less than a 1 in 1000 chance of hitting me. If one random hypervelocity grain of sand struck the 20 person building where I work every year, then over a 10 year period the odds of ANYBODY being struck by it are still only 1 in 100 and the odds of it striking ME are 1 in 2000.

By volume people occupy less than 1/1000 the volume of a typical starship. A ‘reasonable’ hull will deflect or stop most small objects that it encounters. Those 6-G trips to gas giants are rare. Space is mostly empty, etc ...

... Would it really change the game so much if hulls were not made of impenetrable handwavium? The chance of a serious impact are small and the chance of a death from that impact are even smaller.

I can live with 1 in 1000 spacers die from hull penetrations during their career. It is better than the normal rate of cancer deaths on Earth (1 in 500).

The point is simply that the impenetrable hulls that people like to complain about while quoting energy in kilotons or megatons, don't actually NEED to be impenetrable. The event just needs to be uncommon enough to not be worth modeling in game terms.

 

[Rikki Tikki Traveller]

On a seperate issue, the problem of 1G thrust ships taking off from planets with higher than 1G surface gravities. This has been a concundrum for Traveller GMs since the very early days of Traveller. I remember discussing it with my brother soon after buying our first copy in the early 80's. If it comes up in game (most players rarely notice) I just say that for very brief periods you can overdrive the engine, but not for long enough to make a difference in space combat, and anyway afterwards you have to run the engine in a lower power mode for a while to de-stress, so over the timescales in space combat it averages out.

Simon Hibbs

Actually the answer exists in the real world right now. No commercial planes and very few military planes are capable of 1G of acceleration. That is why they have WINGS, even a shape with a small wing (or a Lifting Body shape) would be able to generate a few extra percent lift to allow a ship IN AN ATMOSPHERE to take off from a planet with a stronger gravity.

The design parameter used in the aerospace industry is called "Lift-to-Drag Ratio" or L/D. Most commercial planes generate an L/D of 10-20, with military planes a bit lower than that. By comparison, the Space Shuttle has an L/D of just over 1 (A flying brick), but that is because the wing shape doesn't generate much lift since it was designed for control and to survive the reentry speeds; more modern designs for space planes have a much better L/D.

If a ship had an L/D of 1.3 it could take off from a Size A world (assuming a standard density atmosphere).

In the Hull Shapes.. that is where Traveller breaks down on their descriptions. A Standard Hull shape apparently has an L/D of about 2 (enough to take off) but most of the ARTISTIC drawings of the small craft and shuttles do not adequately address SOME KIND of lifting surface or shape. The Scout/Courier is probably OK, but none of the rest of the designs really show enough lifting surface for a 1G ship to takeoff and land on Earth or a similar planet.

 

[DFW]

A Standard Hull shape apparently has an L/D of about 2 (enough to take off) but most of the ARTISTIC drawings of the small craft and shuttles do not adequately address SOME KIND of lifting surface or shape.

No only the streamlined hull is described as being a lifting body. Not the standard hull.

 

[far-trader]

Riiight. So you enter atmo at something like 11,000kph for an Earth size world? Toasty

Or more, upwards of 28,000kph.

You think that the the Earth rotates at 28,000kph?

No, but that's the rough speed of an object maintaining a ground stationary aspect at LEO. The slower 11,000kph is at higher geostationary orbit. You think you're going to just float down from orbit? I don't think it works that way even with antigrav/contragrav or whatever magic thrust agent you're using.

 

[far-trader]

...I can live with 1 in 1000 spacers die from hull penetrations during their career.

You're forgetting about how much of the "non-spacer" volume of a starship, equally vulnerable to the damage, which contains elements critical to keeping ALL the spacers inside the hull alive. Some elements of which will do much more direct and widespread damage to the said spacers if hit. So yes, you pretty much do need a nigh impenetrable hull or some effect to prevent that from happening.

 

[rust]

You think you're going to just float down from orbit? I don't think it works that way even with antigrav/contragrav or whatever magic thrust agent you're using.

Whether the speed has any meaning depends on your frame of reference.
For example, the geostationary satellites you mentioned remain stationary
over a certain region of the earth because their speed in relation to these
regions of the earth is not 11,000 km/h, but 0 km/h. So, as long as the
speed difference between the starship and the surrounding air is 0 km/h,
their speed in any other frame of reference is meaningless.

 

[DFW]

No, but that's the rough speed of an object maintaining a ground stationary aspect at LEO. You think you're going to just float down from orbit? I don't think it works that way even with antigrav/contragrav or whatever magic thrust agent you're using.

We aren't talking about orbital velocities. Also, That isn't the speed at that altitude to maintain a position over a fixed spot on Earth.

If you are geo stationary at 100 miles altitude, you ground speed is zero. The atmosphere is also not moving relative to you.

Also, if you have the available thrust in G's you can go up and down at any low speed you desire. If you have a rocket with enough fuel and G's of thrust, you could lift out at 50mph if you wanted to. Basic, undeniable, physics.