Spaceflight on high gravity planet.

[jwl]

One quick thing I can think of is,

https://en.wikipedia.org/wiki/Project_O ... pulsion%29

https://www.ted.com/talks/george_dyson_ ... anguage=en

While some sort of chemical booster (And lots of it) might be needed to get the ship above the planets radiation belts, once at a good height the nuke pulse should keep lifting.

The shape would probably be a lot wider and flatter?

In theory it could work at least in a way that there is sufficient thrust and delta v available from nuclear fuel. Real dealbraker would be engineering and materials science. Very high liftoff thrust would mean nukes would have to detonate much closer to ship to provide more thrust than if taking off from Earth. So the ability of blast shield and shock absorbing system to take extra strain without becoming too heavy would be critical here.
There are people who think structural engineering even for Earth surface launched Orion craft would be extremely challenging, maybe beyond capabilities of existing materials. Real thing was only tested on small scale with chemical explosives so it is very difficult to say what kind of obstacles would be encountered if full scale surface launched ship was attempted to construct.

Here's a slightly wild idea then: ditch all of the computers and stuff in the payload that need shock-protecting, and just use a Project Orion-style device to launch a giant rock into orbit, high enough to not need station-keeping. Then send a probe up, with a lower delta-v, to do a flyby of this rock. As it flys by, it shoots harpoons into the rock, attached to a rope. This rope will be attached to a reel with a weak friction device on the probe that (relatively) slowly brings the probe up to the same speed as the rock.

When I say relatively, however, the forces are still going to be rather large to prevent the rope running out. According to my calculations, for a rope with negligible payload compare to the rope mass, it will need a specific strength at least equal to v^2/2. In this case that would be 600 kYuri. This is not possible with nylon rope, but Kevlar has a specific strength of 2500 kYuri, which is plenty. You'd still need a really long, thin rope to stop the harpoon being yanked out, but as far as I am aware you can make ropes longer and thinner pretty much indefinitely.

[Adam Reynolds]

I am pretty sure that in real life, pyramid-shaped rockets aren't structurally viable.

The math works out in theory for ideal structural bracing of nigh-unlimited strength, but that doesn't mean it'll hold together in flight under realistic conditions. There are contraptions you can make fly in Kerbal Space Program that would never in a thousand years get out of the troposphere without blowing apart in real life.

Most of them blow up in KSP too. It's just that reality doesn't have a reset button for when they do. I can't be the only one who has launched glorious deathtraps. For my first launch attempt I managed to launch my kerbonauts on a parabolic trajectory that led to to a fatal reentry rather than an orbit. It only got worse from there. Though Jeb or Val never stopped smiling until they died, pretty sure both of them are insane.

Val at least managed to get into orbit of Minmus with just her rocket pack after the lander crashed, so she is competent in addition to insane*. Recently my favorite bizarre game within the game is recreating The Martian in as many different environments as possible and coming up with clever ways to save theoretically doomed kerbonauts(or at least have other kerbonauts die trying). Ironically I haven't done anything on Duna. Current rescue rate is 6 for 10, probably not the best recruiting strategy. Especially since I lost an additional eight kerbonauts on attempted rescues, mostly as a result of bad launches with hastily constructed rockets in an attempt to reach kerbonauts before they ran out of air while in orbit. One case also killed the kerbonaut after the rescue vessel hit him and he had ran out of EVA propellant escaping his station when it began to deorbit.

* Kerbal YouTuber Scott Manley has a much more awesome version of this. He managed to get a kerbonaut in orbit of the Mun with only a rocket pack and damaged engine that is pointing upwards. I can't say I have replicated that feat.

[Sky Captain]

One quick thing I can think of is,

https://en.wikipedia.org/wiki/Project_O ... pulsion%29

https://www.ted.com/talks/george_dyson_ ... anguage=en

While some sort of chemical booster (And lots of it) might be needed to get the ship above the planets radiation belts, once at a good height the nuke pulse should keep lifting.

The shape would probably be a lot wider and flatter?

In theory it could work at least in a way that there is sufficient thrust and delta v available from nuclear fuel. Real dealbraker would be engineering and materials science. Very high liftoff thrust would mean nukes would have to detonate much closer to ship to provide more thrust than if taking off from Earth. So the ability of blast shield and shock absorbing system to take extra strain without becoming too heavy would be critical here.
There are people who think structural engineering even for Earth surface launched Orion craft would be extremely challenging, maybe beyond capabilities of existing materials. Real thing was only tested on small scale with chemical explosives so it is very difficult to say what kind of obstacles would be encountered if full scale surface launched ship was attempted to construct.

Here's a slightly wild idea then: ditch all of the computers and stuff in the payload that need shock-protecting, and just use a Project Orion-style device to launch a giant rock into orbit, high enough to not need station-keeping. Then send a probe up, with a lower delta-v, to do a flyby of this rock. As it flys by, it shoots harpoons into the rock, attached to a rope. This rope will be attached to a reel with a weak friction device on the probe that (relatively) slowly brings the probe up to the same speed as the rock.

When I say relatively, however, the forces are still going to be rather large to prevent the rope running out. According to my calculations, for a rope with negligible payload compare to the rope mass, it will need a specific strength at least equal to v^2/2. In this case that would be 600 kYuri. This is not possible with nylon rope, but Kevlar has a specific strength of 2500 kYuri, which is plenty. You'd still need a really long, thin rope to stop the harpoon being yanked out, but as far as I am aware you can make ropes longer and thinner pretty much indefinitely.

That is something vaguely along the lines of Skyhook concept. Launching counterweight with atomic blast - not sure how it could work. You still need rockets to circularize orbit. Something launched from such atomic canon on the surface would either fall back or fly away if above escape velocity. If it is possible to make rockets and guidance system that can survive insane launch acceleration then it may work at least in theory.

Most of them blow up in KSP too. It's just that reality doesn't have a reset button for when they do. I can't be the only one who has launched glorious deathtraps. For my first launch attempt I managed to launch my kerbonauts on a parabolic trajectory that led to to a fatal reentry rather than an orbit. It only got worse from there. Though Jeb or Val never stopped smiling until they died, pretty sure both of them are insane.

I managed to make most of realism mods and prodedural parts work on my KSP install, also by messing with config values increased Kerbin size to 20 000 km diameter, changed gravity to about twice stronger. I tried Saturn V with 5 ton payload. Obviously not enough thrust to lift off. With about half of first stage fuel gone liftoff happened however after staging second stage lacked thrust to accelerate and fell back to ground. With suitable boosters I could make first stage lift off with full fuel load however second stage still too weak.
Tomorrow I will try to make custom rocket for this task. By eyeballing it I suspect all chemical approach is possible, It just will take rocket with liftoff mass somewhere in 3000 - 4000 ton range to launch 4 ton crew pod.

[jwl]

In theory it could work at least in a way that there is sufficient thrust and delta v available from nuclear fuel. Real dealbraker would be engineering and materials science. Very high liftoff thrust would mean nukes would have to detonate much closer to ship to provide more thrust than if taking off from Earth. So the ability of blast shield and shock absorbing system to take extra strain without becoming too heavy would be critical here.
There are people who think structural engineering even for Earth surface launched Orion craft would be extremely challenging, maybe beyond capabilities of existing materials. Real thing was only tested on small scale with chemical explosives so it is very difficult to say what kind of obstacles would be encountered if full scale surface launched ship was attempted to construct.

Here's a slightly wild idea then: ditch all of the computers and stuff in the payload that need shock-protecting, and just use a Project Orion-style device to launch a giant rock into orbit, high enough to not need station-keeping. Then send a probe up, with a lower delta-v, to do a flyby of this rock. As it flys by, it shoots harpoons into the rock, attached to a rope. This rope will be attached to a reel with a weak friction device on the probe that (relatively) slowly brings the probe up to the same speed as the rock.

When I say relatively, however, the forces are still going to be rather large to prevent the rope running out. According to my calculations, for a rope with negligible payload compare to the rope mass, it will need a specific strength at least equal to v^2/2. In this case that would be 600 kYuri. This is not possible with nylon rope, but Kevlar has a specific strength of 2500 kYuri, which is plenty. You'd still need a really long, thin rope to stop the harpoon being yanked out, but as far as I am aware you can make ropes longer and thinner pretty much indefinitely.

That is something vaguely along the lines of Skyhook concept. Launching counterweight with atomic blast - not sure how it could work. You still need rockets to circularize orbit. Something launched from such atomic canon on the surface would either fall back or fly away if above escape velocity. If it is possible to make rockets and guidance system that can survive insane launch acceleration then it may work at least in theory.

If it went up vertically, yeah. Wouldn't you be able to get it into an elliptical orbitbby launching it at an angle?

[Sky Captain]

If it went up vertically, yeah. Wouldn't you be able to get it into an elliptical orbitbby launching it at an angle?

No, you would need to do circularization burn after cannon launch otherwise periapsis of your orbit will be below ground level.

[Simon_Jester]

To translate "periapsis of your orbit will be below ground level" into plain English, you can interpret that as "somewhat less than one full orbit from now, your satellite will slam into the ground like a meteor."

[Eternal_Freedom]

A thought has occurred to me. Presumably on this high-gravity world missiles will be less effective, so (for the sake of argument) a real-world ICBM might only count as medium-range, and so on.

Would this also apply to things like air to air missiles, or artillery rounds, or ordinary bullets? What effect would that have on warfare?

[LaCroix]

To translate "periapsis of your orbit will be below ground level" into plain English, you can interpret that as "somewhat less than one full orbit from now, your satellite will slam into the ground like a meteor."

[Simon_Jester]

A thought has occurred to me. Presumably on this high-gravity world missiles will be less effective, so (for the sake of argument) a real-world ICBM might only count as medium-range, and so on.

Would this also apply to things like air to air missiles, or artillery rounds, or ordinary bullets? What effect would that have on warfare?

The effective range of all purely ballistic weapons (including arrows, javelins, sling bullets, and thrown rocks) would be decreased by roughly a factor of two. All objects thrown into the air would coast to a stop in terms of up-down motion in about half of the time, and take only half as much time to fall back to the ground.

On the other hand, this means air resistance would be doing less to slow down projectiles, so the projectiles won't be less dangerous at a given range- they just physically won't travel as far. If anything they may be going slightly faster, because in the up-down direction their terminal velocity is higher.

Weapons that rely on falling from a great height (i.e. armor-piercing bombs) would be actively more effective, all else being equal- the more gravity, the better, for something like a WWII-era Tallboy bomb.

It would also be necessary to angle weapons upward far more than is normal in real life to hit a target at the same range, so aiming indirect fire accurately is even more important than in real life.

...

In ancient times, the (likely) greater strength of beings adapted to high gravity might offset the range disadvantage; stronger people can draw heavier bows that launch arrows more forcefully, and so on. However, in the gunpowder era this goes away, because the only way to get higher velocity from a bullet is to carry a bigger gun- and the strength that adapts you to high gravity won't mean you can carry a bigger gun than an ordinary person in ordinary gravity could. This tends to reduce the relative advantage of gunpowder weapons over muscle-powered projectile weapons a bit, although not as much as you might think, since the real limit on the effective range of such weapons prior to about 1870 was aiming, not projectile drop.

Missiles as such are actually an interesting case. Ballistic missiles obviously suffer from range reductions. But many air-to-air and cruise missiles aren't ballistic weapons. Either they use a long-lived engine like a jet or ramjet for propulsion, or they fire an engine like a solid fuel rocket and then glide to the target on pop-out wings. Either way, as long as the pop-out wings or whatever are suitably reinforced, the missile may well be able to glide or cruise about as far as it could in real life.

...

The main effect I see of shorter range is on 19th and 20th century warfare, in the age dominated by purely ballistic artillery weapons that were long enough range to hit targets over the horizon.

On land, shorter artillery range means that drastically fewer guns can be fired at a given target on land, and that the guns are more vulnerable to an enemy counterattack that breaks the lines.

At sea, shorter artillery range means ships have to get closer to one another to actually hurt each other. This has several effects. For one, it makes torpedoes more dangerous (since they have unchanged range, while naval guns are now shorter-ranged). For another, it means that relative to the (mostly) unchanged speed of the ships, gun ranges are shorter, and avoiding engagement becomes easier. Although ship design is also effected, as it takes more buoyancy to support a given weight of ship. This makes it difficult to equip ships with heavy armor plating or large weapons.

In the air, AA guns become drastically less effective- their effective ceiling is cut in half, so most guns won't even be able to physically reach altitudes above about 6000 meters, and will be very ineffective at those altitudes. Compensating for this is that the air may be less dense at higher altitude, which brings the planes back down toward the ceiling of the AA weapons.

However, AA guns also have reduced slant range and are harder to aim accurately, so that the bubble protected by AA gunfire is greatly reduced. This issue is less significant once surface to air missiles are developed, as it is still possible to design a long range SAM with pretty good effect.

[Eternal_Freedom]

If ship design has to change to have more buoyancy for a given weight, would the same not apply to torpedoes as well? Making them carry less fuel or a smaller warhead for instance?

[Jub]

If ship design has to change to have more buoyancy for a given weight, would the same not apply to torpedoes as well? Making them carry less fuel or a smaller warhead for instance?

You could just make torpedoes bigger, expanding the casing of something like a mk. 48 heavy torpedo from 21 to 23 inches gives an extra 63,000 cubic inches of volume to use for buoyancy, adding an extra 22 inches of length to keep things proportional gives an extra 99,000 cubic inches. Given that the skin of the torpedo is going to mass much less than the fuel and warhead, it shouldn't take that much extra size to get the required extra buoyancy. Even if you need to straight up double the volume that only means a 21" by 228" torpedo becomes a 26.5" by 287.25" torpedo, it's bigger, but not bigger enough to be unusable.

[SpottedKitty]

To translate "periapsis of your orbit will be below ground level" into plain English, you can interpret that as "somewhat less than one full orbit from now, your satellite will slam into the ground like a meteor."

I think the technical term is "lithobraking".

[Simon_Jester]

Ayup; I'm one of the term's proponents.

First saw it from Eleventh Century Remnant here, and I don't know where he got it from (or for that matter, if; it's the sort of thing he'd think of).

If ship design has to change to have more buoyancy for a given weight, would the same not apply to torpedoes as well? Making them carry less fuel or a smaller warhead for instance?

You know, this may be a false alarm.

Basically, the upward force due to buoyancy is equal to the difference between the weight of the water displaced by the hull, and the weight of the part of the hull below the waterline. So ideally you want, say, a 7000-ton hull that pushes aside 10000 tons of water, at which point you can pile up 3000 tons of stuff on top of the waterline.

Double the gravity, and you double the weight of the hull, including the weight of the part above the waterline. But you also double the weight of the displaced water, which should cancel out the effect now that I think about it.

I somehow got the idea that you'd need the ship to displace extra water to compensate for the increased weight of the stuff above the waterline (in other words, the upper stuff now weighs 6000 tons, so your hull has to be twice as big to support it). But now that I've had a nap, I'm pretty sure that's not true.

Either way, this has no effect on torpedoes, which are entirely submerged and (ideally) pretty close to neutrally buoyant. All that matters is that they have just about exactly the same density as the water they move through.

[Eternal_Freedom]

Hmm. I had a suspicion that some military-related things would essentially cancel out (like lower ceilings for AA guns and possibly lower ceilings for planes). Good to know my gut was right on at least something.

I'm willing to bet that aircraft carriers would not be as feasible in this world. Presumably aircraft would need more power/more speed/longer takeoff distance to get airborne? More than a ship-mounted catapult can provide I suspect.

[Jub]

Hmm. I had a suspicion that some military-related things would essentially cancel out (like lower ceilings for AA guns and possibly lower ceilings for planes). Good to know my gut was right on at least something.

I'm willing to bet that aircraft carriers would not be as feasible in this world. Presumably aircraft would need more power/more speed/longer takeoff distance to get airborne? More than a ship-mounted catapult can provide I suspect.

The atmosphere at sea level should be denser, so that might allow you to get airborne without as much of a struggle as one might think. Worst case you can always design carrier planes around the use of JATOs.

[Eternal_Freedom]

JATOs? That's a new one to me. I hadn't considered air density to be honest.

This is a fascinating thought experiment.

[Jub]

JATOs? That's a new one to me. I hadn't considered air density to be honest.

This is a fascinating thought experiment.

Jet Assisted Take Off, basically strapping rockets to your planes to give them more go juice. They've been used to get big heavy things airborne with less runway, and to make smaller interceptors reach altitude in a hurry.

[Eternal_Freedom]

Ah. I remember watching some crash test footage of a Hercules trying the rocket-assisted takeoff and landing. Takeoff went fine, but on landing the rockets ripped the wings off. Made quite a mess.

[Jub]

Yeah, they didn't tend to work as well unless the aircraft was designed with them in mind. They worked fine on the F-84, F-100, F-104 among others.

See also zero-length launch.

[SpottedKitty]

Ah. I remember watching some crash test footage of a Hercules trying the rocket-assisted takeoff and landing. Takeoff went fine, but on landing the rockets ripped the wings off. Made quite a mess.

Not sure how common it is, but some JATO designs drop the rockets after the plane's high enough they're unlikely to bounce back up and rip the wings off, etc. All that's left bolted to the airframe is a mounting bracket.

[jwl]

If it went up vertically, yeah. Wouldn't you be able to get it into an elliptical orbitbby launching it at an angle?

No, you would need to do circularization burn after cannon launch otherwise periapsis of your orbit will be below ground level.

I see, I can visualise it now. So they would need some Orion-type equipment to survive up to above the atmosphere. It still would be easier than protecting a full scientific payload though, I would imagine.

[Adam Reynolds]

Ah. I remember watching some crash test footage of a Hercules trying the rocket-assisted takeoff and landing. Takeoff went fine, but on landing the rockets ripped the wings off. Made quite a mess.

That wasn't just JATO, it was the one-off aircraft intended to rescue the American hostages from Iran. I don't believe it even used JATO, instead relying on a hodgepodge of borrowed rocket motors from things like ASROC. The failure was due to the fact that the rockets were fired early as a result of the fact that the pilots could not see anything and thus had no frame of reference.

As for carrier operations, they would likely require catapults from the first aircraft. Historically it was possible, though not generally worth the effort. Though most cruisers and battleships had catapult launched seaplanes for reconnaissance. As well as the wonderfully successful CAM program that turned merchant vessels into aircraft carriers. Which had the distinction of being the only fighter unit to have a negative kill ratio against converted airliners. Though they were still somewhat successful in their intended role of protecting convoys from air attack.

For modern aircraft, even if it led to full sized carriers operating smaller aircraft like the original Hornet, it would still be worth having. The Midway and Independence classes served through Desert Storm with nothing heavier than Hornets onboard. The limitation towards lighter aircraft would also bias ground based fighters as well. Fighter would almost certainly have lower thrust to weight ratios, but as this would affect both sides equally, it would change combat in interesting ways. In any case, a bigger limitation would be for things like transport aircraft or helicopters.

Though another deeper question is whether heavier than air flight would really be built given the diminishing returns for a heavier gravity environment. Surface travel might just stay dominant.

[Simon_Jester]

Air travel would still have major early advantages in niche applications. It's fast, drastically faster than anything else which can be built using 20th century technology. You wouldn't see so much proliferation of cargo aircraft and bulk passenger travel. But you'd still see plenty of use of airplanes to carry mail in the equivalent of the early 20th century (since nothing can compete with them for speed even if it IS hard to get them off the ground). Aerial reconnaissance would still be a thing, and eventually someone would start creating fighters to harass enemy scout aircraft and bombers to turn the mail planes and so on into weapons of war.

However, the overall development of the "air threat" might wind up being sort of... atrophied... until the rise of the guided missile era.

Hmm. I had a suspicion that some military-related things would essentially cancel out (like lower ceilings for AA guns and possibly lower ceilings for planes). Good to know my gut was right on at least something.

I wouldn't assume they truly cancel out. The effect of reduced gravity on AA guns is deterministic and simple- the result of solving an equation anyone who paid attention in first year algebra can master.

The effect of increased gravity on atmospheric pressure is more complicated and there are more variables in play.

I'm willing to bet that aircraft carriers would not be as feasible in this world. Presumably aircraft would need more power/more speed/longer takeoff distance to get airborne? More than a ship-mounted catapult can provide I suspect.

While it would probably be possible to get combat aircraft airborne from a big enough, properly equipped carrier, I suspect it would be considerably harder to make said aircraft competitive with land-based planes taking off from long airstrips.

[Sky Captain]

Tested some of my custom rocket designs and came up with something that worked fairly well. First stage with 10 Space shuttle main engines and 8 boosters powered by 1 RD 170 engine each. Second stage powered by 1 Space Shuttle main engine and third stage by one RL 10 engine. Total payload to low orbit around 8 tons if counting unused third stage fuel as payload too. Delta v spent to achieve orbit around 17 km/s Launch mass 3450 tons.

So chemical launch to low orbit from Super Earth type planet with 2 G surface gravity using existing chemical rocket technology is definitely possible although challenging and would be extremely expensive because many very expensive high performance engines are required even for small payloads. Using nuclear upper stages would improve payload, although costs would go up too. Anything beyond low orbit would require either solar electric or nuclear propulsion otherwise truly enormous rockets are needed. 10 000 ton rocket to send probe to other planet or communications satellite to geosynchronous orbit just don't look very cost effective.

[SpottedKitty]

I'm willing to bet that aircraft carriers would not be as feasible in this world. Presumably aircraft would need more power/more speed/longer takeoff distance to get airborne? More than a ship-mounted catapult can provide I suspect.

I'm envisioning that requiring something even bigger than a RL supercarrier or ultramegahyoooge container ship (both coming close to 1/4 mile long, I think) with a catapult — or some kind of power-assisted launcher, anyway — running most of the deck length. It might be easier, cheaper, and quicker to build a runway (within the limits of the geography) wherever you want to put one.

The feasibility of a monster like that is left as an exercise for the student.