[Ships] Atmospheric Speeds?

[rust]

The 104 is hardly a brick, and one of my faves too -despite it having complicated my fathers job immensely (EOD/crash recovery)

I truly hated that aircraft. Germany bought 916 Starfighters, and 292 of
them crashed, killing 116 pilots. I had the questionable pleasure to serve
as a medic with an air force unit which used the Starfighter, and I really
got sick of attending funerals of crashed pilots.

 

[Ishmael]

Erich Hartmann argued against the Luftwaffe getting f104's.
If anyone knew about fighters, it was him!

 

[captainjack23]

The 104 is hardly a brick, and one of my faves too -despite it having complicated my fathers job immensely (EOD/crash recovery)

I truly hated that aircraft. Germany bought 916 Starfighters, and 292 of
them crashed, killing 116 pilots. I had the questionable pleasure to serve
as a medic with an air force unit which used the Starfighter, and I really
got sick of attending funerals of crashed pilots.

Interesting, and quite sobering. My dad cleaned up after american 104 crashes in Germany and over here. He doesn't have much nice to say except that, like some of the coolest fastest cars, it was really easy to get dead in. And the B-58; and the B-70 was a disaster from the git go. All high transonic operation airplanes, with mach 2+ operating speed.

All of which illustrate the problems of flying real fast in an atmosphere, even with designed aircraft, and highly trained crews. Small malfunctions or errors magnify wildly and quickly... and control is hard to regain when, at Mach 2 you can go from 30000 feet to 0 in 45 seconds.

 

[rust]

All of which illustrate the problems of flying real fast in an atmosphere, even with designed aircraft, and highly trained crews. Small malfunctions or errors magnify wildly and quickly... and control is hard to regain when, at Mach 2 you can go from 30000 feet to 0 in 45 seconds.

I think in the absence of gravitics a vehicle designed for flying very fast
in an atmosphere should have at least two engines, enough control sur-
faces to make it react well to the controls, and preferably good sensors
and a reliable flight computer that warns the pilot of dangerous situations.

 

[BP]

If a ship has fuel scoops then it must be capable of dealing with extreme pressures and heat - to say nothing of 'flying' thru hurricane force winds in a gas giants atmo.

Well, besides pressure and heat - there's also the little problem of colliding with local fauna (like birds).

But again, ships have to deal with debris and micro-meteorites all the time.


Of course, ignoring the technical limit - civilized worlds will have legal limits (for noise, pressure and thermal damage, navigational concerns, etc.) that will probably be far below the practical limits on the spaceship.

 

[captainjack23]

If a ship has fuel scoops then it must be capable of dealing with extreme pressures and heat - to say nothing of 'flying' thru hurricane force winds in a gas giants atmo.

Well, besides pressure and heat - there's also the little problem of colliding with local fauna (like birds).

But again, ships have to deal with debris and micro-meteorites all the time.


Of course, ignoring the technical limit - civilized worlds will have legal limits (for noise, pressure and thermal damage, navigational concerns, etc.) that will probably be far below the practical limits on the spaceship.

Actually, from what I've read here and on other trav sites, scooping isn't done at very high pressures at all; the friction is an issue though, as you point out.

Still, the issue is going to relate to mostly to reaction time or level of automation possible-the SR-71 has (as far as I know) a pretty good safety record -its profile is to fly very high and very fast -with minimum manuevering. Both altitude and steady courses are likely to ameliorate the reaction time issue of high mach speeds -which kills in combat aircraft which often have to fly much lower and jink around lots.

I suspect that scooping is a straightforward enough process that it is likely highly automated once begun, and can take full advantage of constant course and altitude. Much as with the shuttle, which is doing a very fast inbound flight, and it is entirely automated at that point -that deals with the reaction time issue , and assuming ground control has cleared the flight area, allows a predictable constant course.

Collisions are another matter at high speed -as illustrated by the shuttle at liftoff, unfortunately. Question for those who may know : has the inbound shuttle ever hit a bird ? Those do take out jets occasionally -but usually due to flameout or cockpit hits.

 

[EDG]

I suspect that scooping is a straightforward enough process that it is likely highly automated once begun, and can take full advantage of constant course and altitude. Much as with the shuttle, which is doing a very fast inbound flight, and it is entirely automated at that point -that deals with the reaction time issue , and assuming ground control has cleared the flight area, allows a predictable constant course.

The thing with scooping is that (unlike say, a ramjet) the gas is being sucked into a storage bay on the ship, not being immediately heated and used in the engine. I wonder how big a difference that makes - you basically need to decelerate the gas from having a high velocity relative to the ship to having zero velocity relative to the ship in a very short time and without increasing the temperature significantly enough to melt stuff - I imagine that's a bit problematic.

Either that, or it's done when the ship is just hovering there and it opens up big suction pumps to pull in the gas...

Collisions are another matter at high speed -as illustrated by the shuttle at liftoff, unfortunately. Question for those who may know : has the inbound shuttle ever hit a bird ? Those do take out jets occasionally -but usually due to flameout or cockpit hits.

Don't think one has ever hit a bird in flight, but it did hit one on takeoff at least once:

http://www.nasa.gov/mission_pages/shuttle/behindscenes/avian_radar.html

One presumes the bird landed up being roasted to a crisp in the engine blast...

 

[GypsyComet]

Either that, or it's done when the ship is just hovering there and it opens up big suction pumps to pull in the gas...

Depending on how you define the lift-and-drive available to a starship, this option may not be available to 1G and 2G ships. For low thrust designs, scooping may have to be a fancy form of aerobraking.

DGP assumed that scooping took place a bit deeper, as they wrote up one gas giant that was post off-limits for refueling due to floating indigenous life. DGP also allowed 400% overclocking of the MDrive for brief periods, so dawdling in the deeps of a gas giant might actually be feasible...

 

[BP]

Actually, from what I've read here and on other trav sites, scooping isn't done at very high pressures at all; the friction is an issue though, as you point out.

Sorry my Traveller ignorance must be showing - thanks for the correction!

(To me 'Fuel skimming' brings the mental picture of a ship ploughing through water or liquid hydrogen, not just sitting and sucking - quite dramatic that way - especially while fleeing! And quite silly, of course. If the hydrogen is liquid from a GG then the gravity probably would be too great for escape not to mention the effect on the structure of the ship. And hitting liquid at speed is like slamming into concrete - its incompressible.)

 

[EDG]

If the hydrogen is liquid from a GG then the gravity probably would be too great for escape not to mention the effect on the structure of the ship. And hitting liquid at speed is like slamming into concrete - its incompressible.)

If the hydrogen is in liquid form in a GG and a ship's trying to skim it, gravity is the least of its problems! Hydrogen would only become liquid in a GG at high pressures and temperatures - ships would be crushed long before they got to that depth.

 

[BP]

If the hydrogen is liquid from a GG then the gravity probably would be too great for escape not to mention the effect on the structure of the ship. And hitting liquid at speed is like slamming into concrete - its incompressible.)

If the hydrogen is in liquid form in a GG and a ship's trying to skim it, gravity is the least of its problems! Hydrogen would only become liquid in a GG at high pressures and temperatures - ships would be crushed long before they got to that depth.

Touche - hence my quip about 'the structure of the ship'

Though, on futher reflection - U.S. Navy deployed submersible which could withstand 1000 atmospheres (triste?) and I think liquid molecular hydrogen could exist around that. And the temp would not be greater than re-entry temp that ships would have to survive (shuttle does around 3,000F)... I'll have to look these things up...

I think the Galileo probe made it over half the way to Jupiter's 'ocean' (granted not a linear problem)

Anyway, 'skimming' liquid H2 is still silly. And Traveller ships may be able to escape a GG gravity well - but even armored might not take 1000 atmos of pressure (and I was referring to Water being incompressible - not sure about liquid H2)

 

[EDG]

Galileo got nowhere near it - the gaseous hydrogen gradually becomes liquid hydrogen around 1000 km below the cloudtops. The atmosphere probe got to about 150 km before it was crushed (at 22 atm pressure, and a temperature of 153°C).
(see http://en.wikipedia.org/wiki/Exploration_of_Jupiter )

 

[BP]

Galileo got nowhere near it - the gaseous hydrogen gradually becomes liquid hydrogen around 1000 km below the cloudtops. The atmosphere probe got to about 150 km before it was crushed (at 22 atm pressure, and a temperature of 153°C).
(see http://en.wikipedia.org/wiki/Exploration_of_Jupiter )

That's right - I was thinking it made it to 600km - I looked up NASA Media Kit - it made it to 200km before heat caused transmission failure. Of course it also used atmo to brake - and that was hot!

Wikipedia mentions Cassini and New Horizons - my father fab-ed equipment for both these missions. Jeeze - I missed New Horizon's Saturn flyby last year - time flys. And it won't reach Pluto till after my dad has retired. (And Dr. Alan Stern left SwRI in 2005? - nice guy - he was the director of my dad's boss - guess I need to checkout wikipedia more often)...

Anyway, back to Topic - a Traveller ship should be buildable to survive 1000+ atmo - I was recently designing a ship that would also be submersible in shallow waters - so related to this topic - now I wonder what pressures various hull armor might allow...

 

[rust]

Anyway, back to Topic - a Traveller ship should be buildable to survive 1000+ atmo - I was recently designing a ship that would also be submersible in shallow waters - so related to this topic - now I wonder what pressures various hull armor might allow...

You would have to turn the design process around and design a space-
going submarine, because otherwise your ship would most probably on-
ly float, not dive, because its flotation rating would be higher than its
weight.
It is also a difference between a hull that is designed to handle a pressu-
re of 1 atmosphere "outwards" and one designed to handle a pressure
of 1,000 atmospheres "inwards".
This is also something to remember if someone tries to use an airlock,
as a normal airlock system will hardly be able to handle water, especi-
ally under such pressure.
And you should remember to install a sonar sensor system, because elec-
tromagnetic sensor systems are not much use under water.

Apart from this and some other minor points it should not be a problem,
the construction materials would doubtless be up to the task.

 

[GJD]

Actually, skimming hydrogen wouldn't require excessive tempreatures or pressures. The critical point for hydrogen is about 30 or 40K if memory serves, and the accepted base of the troposphere for Jupiter, where the atmosphere blends into the fluid interior, is at the accepted level of 10 atmospheres (10 bar).

Of course, you have to get through the thermosphere first, which is hot hot hot at about 1000K, and there are the continent sized superstorms, terawatt lightning storms, intense magnetic flux, lethal radiation and supersonic wind shear.

G.

 

[BP]

Actually, skimming hydrogen wouldn't require excessive tempreatures or pressures. The critical point for hydrogen is about 30 or 40K if memory serves, and the accepted base of the troposphere for Jupiter, where the atmosphere blends into the fluid interior, is at the accepted level of 10 atmospheres (10 bar).

Of course, you have to get through the thermosphere first, which is hot hot hot at about 1000K, and there are the continent sized superstorms, terawatt lightning storms, intense magnetic flux, lethal radiation and supersonic wind shear.

GJD, I thinks that is the bottom of the cloud base, not the fog/transition to ‘liquid hydrogen’ – Galilleo probe was at 23 atm pressure when it stopped transmitting and wasn’t near the ‘ocean’ (tried a quick google, but didn’t get anything more useful – everything is about liquid metal hydrogen) – from memory (probably wrong) I think liquid molecular hydrogen starts at 1 kilobar and temp is 1000~4000K where the transition starts (and its more of a fog to liquid thing with no real border). The temp shouldn’t be a problem for the hull since it is around likely reentry temps – though re-entry is quick and going into a Jovian atmo not so much (without generating even greater heat) and there would be no place to bleed the heat (store it in the jump capacitors ha ha) if the hull isn’t an awesome insulator (reasonable to assume in Far Future – heck, check out the ‘starlite’ compound)

.. You would have to turn the design process around and design a space-going submarine, because otherwise your ship would most probably only float, not dive, because its flotation rating would be higher than its weight.

Got that covered – the hold would be flooded – but I like your start as a submarine approach – and I forgot about Trim tanks..

.. It is also a difference between a hull that is designed to handle a pressure of 1 atmosphere "outwards" and one designed to handle a pressure
of 1,000 atmospheres "inwards".

The question is what is the normal atmo pressure Traveller ships are designed for (dense atmospheres and this topic) and how much hull armor affects… 1000 atmo is way deep (unless we’re aiming for the Jovian surface), but enough for shallow depths would be cool

..This is also something to remember if someone tries to use an airlock, as a normal airlock system will hardly be able to handle water, especially under such pressure.
And you should remember to install a sonar sensor system, because electromagnetic sensor systems are not much use under water.

Excellent points – didn’t think about sonar (airlocks yes).

 

[GJD]

Actually, skimming hydrogen wouldn't require excessive tempreatures or pressures. The critical point for hydrogen is about 30 or 40K if memory serves, and the accepted base of the troposphere for Jupiter, where the atmosphere blends into the fluid interior, is at the accepted level of 10 atmospheres (10 bar).

Of course, you have to get through the thermosphere first, which is hot hot hot at about 1000K, and there are the continent sized superstorms, terawatt lightning storms, intense magnetic flux, lethal radiation and supersonic wind shear.

GJD, I thinks that is the bottom of the cloud base, not the fog/transition to ‘liquid hydrogen’ – Galilleo probe was at 23 atm pressure when it stopped transmitting and wasn’t near the ‘ocean’ (tried a quick google, but didn’t get anything more useful – everything is about liquid metal hydrogen) – from memory (probably wrong) I think liquid molecular hydrogen starts at 1 kilobar and temp is 1000~4000K where the transition starts (and its more of a fog to liquid thing with no real border). The temp shouldn’t be a problem for the hull since it is around likely reentry temps – though re-entry is quick and going into a Jovian atmo not so much (without generating even greater heat) and there would be no place to bleed the heat (store it in the jump capacitors ha ha) if the hull isn’t an awesome insulator (reasonable to assume in Far Future – heck, check out the ‘starlite’ compound)

The troposphere is the lowest level of the gaseous atmosphere of a planet. The pressure in Jupiters atmosphere actually decreases prior to it reaching the fluid surface, so it's denser in the cloud layers above the troposphere. Because the tempratures and pressures hover around the critical point of hydrogen, there is no sharply defined cutoff point for the bottom of the atmosphere and the start of the fluid surface, rather a broad and changeable band of phase transiftions dependent upon temprature and local pressure, which varies with weather conditions.

What you will see is areas of low pressure and temprature will result in columns of fluid apperaing higher up in the troposhere, in the gaseous layer, possibly going as high as the exosphere before they begin to heat and pass the critical point. The gas will continue to rise until it is chilled again and will fall, untili it starts to condense and possibly precipitate out . Banks and fogs of lower phase state fluids will appear and dissapear depending on local conditions.

There is a nice article here: Look at the Orange clouds, Ma! that shows a handy-dandy graph of pressure and temprature. It's in milibars, so remember that 10^3 milibars is equal to 1 bar, or about 1 atmosphere (1013mbar = 1 atmosphere).

This all refers to standard, liquid hydrogen, helium, methane and so on, not the "sea" of metallic hydrogen below.

G.[/url]

 

[BP]

Since the lower boundary of the atmosphere is ill-defined, the pressure level of 10 bars, at an altitude of about 90 km below the 1 bar pressure level with a temperature of around 340 K, is commonly treated as the base of the troposphere

Thanks GJD, nice article - but the quote above refers to a 'designation' of the end of the troposphere and the source abstract is about the Galileo probe - so I think the pressure is too low at those temps to 'liquefy hydrogen'. Google-ing didn't turn up much for me, except (for Saturn)

Under the conditions found within the planet, hydrogen behaves as a liquid rather than a gas at pressures above about one kilobar, corresponding to a depth of 1,000 km (600 miles) below the clouds; there the temperature is roughly 1,000 K (1,340 °F, 730 °C).

Given the temps here the problem as I understand it (or don’t :? ) is that its not really 'liquid' so much as 'liquid-like' (supercritical liquid) - so no surface tension and its compressible like a gas, but otherwise acts like a solvent. My layman’s knowledge is useless here and the stuff I googled is confusing and contradictory.. (no nice equations/tables)

 

[Supergamera]

If you're looking at hot, 1 kbar conditions, wouldn't hydrogen embrittlement be a potential problem?

Also, H2 leaking through seals could be considered more dangerous than water leaks, so you may be looking at having positive pressure seals around any openings in the hull.

For game purposes, you might define pressure limits as a function of armor value and hull configuration.

 

[BP]

If you're looking at hot, 1 kbar conditions, wouldn't hydrogen embrittlement be a potential problem?

There would be a great many problems!
The real problem is this started when I stated my delusions about Fuel Skimming ... but on the plus side I think it highlights some possibilities (for success and failure - and inadvertantly contributed to one of my current projects)

For game purposes, you might define pressure limits as a function of armor value and hull configuration.

That's my thoughts - just have to balance it with the effects of armor value against weapons to come up with 'plausible' values.

Then this will help answer the original posted question - how fast can a ship go in atmo... (once one factors in atmo density, heat and altitude)