Planetary landers

[Ultonius]

I would imagine that landers intended to engage atmospheric fighters would use missiles as their main armament, to keep the fighters at a distance, so that their superior manoeuvrability would be less useful. They could also have turreted weapons for point defence, as WW2-era bombers had.

A nuclear-powered lander might be able to use a planet's atmosphere as reaction mass, heating it and then expelling it to provide thrust. This could augment onboard reaction mass supplies when taking off, and perhaps replace them entirely when landing. GURPS calls this kind of engine a fission or fusion air ram.

[chornedsnorkack]

In Moon is a Harsh Mistress, the rebellion of Moon started with no space arms or armies, but some civil space infrastructure. Remember - you can have practical space travel but no specialized space arms, you cannot have interplanetary wars without also having civil tools practical for some purpose. Anyway, Moon had no arms or armies beyond what they could improvise/repurpose - Earth had arms and armies, but these were designed for Earth wars, not a space war.

When Earth soldiers were sent to Moon by a civil transport ship, they were promptly picked up by locals. All their reflexes were useless and misleading in 0,16 g.

That is an issue with planetary landers, too. After days and months of adapting to 0 g over the travel through space, the landers have to adapt to 1 g again. Their reflexes, their circulatory system and muscles take days and weeks to return to original performance. The local adversaries are adapted already.

Regarding the payload necessary for creating and sustaining settlements:
Mayflower II is 236 t displacement; the original carried 102 Pilgrims and a crew of about 50; they took over 2 months outbound (departing Plymouth 6th of September, 1620, arriving at Provincetown Harbout 11th of November) and the ship could be and was returned by the surviving crew of about 25 in 1 month (departing Plymouth 5th of April 1621, arriving 6th of May, 1621).
That displacement included the empty weight of ship, provisions of food and the payload. So how much was the load? Air and propulsion were available on sea; not sure if all fresh water was carried or some could be collected from rain on sea.

Bounty was 215 t, and sailed with 44 crew and 2 passengers. At the end, it could be and was sailed to Pitcairn by 9 whites, at least 10 passengers of Tahitian women and 6 Tahitian men - not sure if the Tahitian men were crew or passengers.

So much about creating a successful settlements with a single shipload. Both Mayflower and Bounty knew breathable air was available, and they were also right in hoping their cultivated plants could be grown at destination.

Now, as for sustaining settlements...

Portuguese India armadas were 806 ships total in 115 years from 1497 to 1612. So an average of 7 ships per year. The average weight of the ship was 400 tons. Smaller ships could be used - Vasco da Gama´s Sao Gabriel was 178 t, and his other ships were smaller - and Portuguese experimented with bigger ships but found them impractical. They settled for 400 t average.

The average crew was quoted as 127 men, plus any passengers and soldiers carried.

The trip from Lisbon to Goa was 5...7 months. So, the lifeline of East Indian empire that swept the Arab fleets out of Indian Ocean was something like 2800 tons per year minus the empty weight minus the provisions for months.

On the other side of Earth, Pacific could be crossed by small ships - Urdaneta had a ship of some 300 t - but the Spaniards found big ships more practical than Portuguese. They settled for an average Manila galleon of 1500...2000 t - and 2 ships sailing per year. Westbound route was 4...5 months, and eastbound was 6...8 months with usually no port stops. So the Philippines lifeline was 3000...4000 tons per year, again minus ship empty weight and provisions.

Note that the transoceanic sailing ships could not be beached, unlike Viking or Polynesian small ships. They needed to carry boats to deliver people or supplies to land.

[lPeregrine]

Regarding the payload necessary for creating and sustaining settlements:

You keep posting numbers but you don't seem to have any idea WHY the numbers matter. A 17th-century sailing ship hauling settlers to a place with plenty of food/water/raw materials/etc only needs to carry supplies for the trip and some manufactured goods but has a huge crew eating up space. A ship colonizing a new planet has to haul a lot more stuff (unless this is really soft scifi where every planet has edible food and clean water available) but can be completely automated with a token "crew" to keep an eye on the computers.

And that's on top of the obvious differences between sailing across the ocean and space travel followed by landing on a planet with the ability to take off again. If you try to include any realism at all in your technology you're going to quickly discover that your starship design is dictated by fuel needs and you have a tiny box of cargo and crew attached to a giant fuel tank.

[PeZook]

What? The LEM ascent engine was completely separate from the descent engine, with dedicated fuel tankage not connected to the lower stage. Completely running out of descent fuel would simply have forced an abort (immediate state separation and ignition of the ascent engine).

At the altitude they were at, an abort would've likely meant death anyways ; Once the DPS fuel ran out, the LM would've crashed into the Moon before stage separation could be completed and the APS fired up.

Nobody knows for sure, of course, but that's still enough for periodic nightmares. Whether or not Buzz motherfucking Aldrin gets any, I have no idea

Remember that the defenders on any inhabitable planet have a shield against kinetic missiles. Atmosphere.

Look at Chelyabinsk. 300 kiloton explosion - and Chelyabinsk, in Urals, is one of the prime targets for an attack, being a centre of Sovier/Russian military industry.

This is why you take a tiny bit of time to enclose your rocks with an aeroshell, or use actual re-entry vehicles and/or nuclear weapons instead. At our current technology levels, it would take us AT LEAST a decade to create weapons capable of reliably attacking ships in high orbit ; So an invader could easily dump pre-made kinetics at industrial centers, and then follow up with locally acquired resources.

Hell, since we're unable to do anything about it, they might leisurely spend time mining the outer system for raw materials to convert into millions of penetrator munitions and then only send them forth to Earth once they're done.

Now, you could drop rocks at even smaller speed - and hope they do not explode harmlessly high in atmosphere. But then, for one, they will be even less powerful. Yes, they´d create small craters, and kill people nearby. And some blast effect. But the thing is, your rock is still going to be tumbling randomly for the 100+ km path through atmosphere... your crater is going to be quite some distance from its intended target.

Or...you can aim to hit an ocean and cause some apocalyptic tsunamis to wipe out most of the human population. No tumbling problems there!

[Sea Skimmer]

This is why you take a tiny bit of time to enclose your rocks with an aeroshell, or use actual re-entry vehicles and/or nuclear weapons instead. At our current technology levels, it would take us AT LEAST a decade to create weapons capable of reliably attacking ships in high orbit ; So an invader could easily dump pre-made kinetics at industrial centers, and then follow up with locally acquired resources.

Not entirely defenseless, US Ground Based Interceptors could hit targets in very high orbits if we wanted with software mods, assuming the batteries on the kill vehicle will last long enough. It'd be limited since under thirty are deployed, but the burnout velocity on the things is enough to get tens of thousands of miles up, and by some unconfirmed accounts actually breach escape velocity by a wide margin, though this would mean no KV fuel left for a terminal attack. With rather more modification, Russian R-36M ICBMs should be more then able to lob a nuclear warhead onto the moon if we wanted, the smaller US Titan II ICBM was capable of this with a several megaton warhead. Indeed a number of smaller ICBMs should also be well capable of high orbit attacks, you'd just have to mod the guidance system some and use only a time fuse on the reentry vehicle, then fire a barrage. It isn't for nothing that more then one ICBM became a space booster. Depending on some details that are entirely classified, it may be possible to just point the existing weapons into space and let fly without any modifications at all. If this would be lethal or not depends on how much radiation shielding the alien spacecraft has as I'd expect to miss by dozens of miles with no terminal guidance. So no I don't think a decade is needed if the survival of the earth is on the line. But it does depend on how many aliens, how well armed they are with defensive weapons, and how you define reliable. Three hundred ICBMs to kill one spacecraft might be needed or some such.

[PeZook]

Huh...didn't know that! Thanks

Of course, you'd imagine intercepting such missiles should be pretty easy for people sitting out there in high orbit, since they'd take a while to reach their targets and would be nice and easy to track.

EDIT: Oh one more thing, how reliable would just firing all our weapons up into space be? Could we repeat it regularly? I mean, if it's just a one-time "give them all you got" attempt, all the attackers have to do is leisurely move away and then strike all the launch sites.

[Sea Skimmer]

Collectively the world is building maybe fifty or sixty ICBM class weapons a year, and about 75-80 space boosters a large fraction of which could be adapted to carry at least a several hundred kiloton nuclear warheads to a high orbit. So no, you aren't going to get several hundred missile barrages often year, nor in the case of space boosters could we fire them all in one go from lack of launch pads, but some production capability exists.

On the other hand if the space aliens are limited to really hard technology, they might be vulnerable to a single nuclear warhead even at a range of hundreds of miles, particularly if they are orbiting inside the van allen belts. That would make the defensive situation considerable more difficult for them.

Depending on the size of alien rocks, we might have some ability to destroy break them up and reduce damage with ABM systems, but only on a very limited regional basis.

[someone_else]

If you have a mothership in orbit, it can lend a hand with a Lazor or microwave beam to power up your crappy lander. You will likely want a decent weapon-grade Lazor for other stuff anyway, they are useful tools for various kinds of peaceful endeavours like examining asteroids from afar, doubling as LADAR and long-range directional comms.

If you are so strapped for cash/mass you can use biggish inflatable lenses. As long as you want to land on planets close enough to their sun to be somewhat Earthlike, that works fine as well. For airless shitty rocks chemical rockets are perfectly fine. (and you don't want to touch gas giants anyway)

Land close-ish to a body of water/ice and you ISRU and are ready to get up again.
Has the added benefit of not allowing the pesky rock-throwing motherfuckers living on that shithole to get on your shiny high tech mothership, because the lander does not move unless someone on the mothership powers the beams. And the beam can cook off light armor and people pretty well (as it is supposed to hit the lander to heat up its propellant for the whole voyage), so they had better remain in their caves.

Also since we are in a hardish setting, benign kinetics (not "soft" but very very small kamikaze drones with some maneuver ability, that smash on a pusher plate or a magnetic nozzle with a gas jet for them to "smash" onto and turn into plasma that is then harnessed by the mag nozzle) can be used to boost a depressingly anemic non-orbit-but-still-space-capable lander (a sub-orbital craft, like SpaceShipOne) in both descent and ascent, just send them in the opposite orbit to decelerate and in a way that they smack on your backside when you are in the ascending part of the sub-orbital parabolic trajectory. A pain in the ass to time right, but again much less prone to lander-jacking by unwanted parties.


As for dropping rocks, unless we are speaking of Space Hitlers genociding Planetside Jews (and suddenly getting steamrolled by the rest of the galaxy), it makes a ton more sense to take a half-decent solar furnace (a it's just a few km2 of tinfoil actually) melt the damn rocks and with the metal you fashion something resembling telephone poles, slap some passable guidance pack on that and drop it from orbit. (from a disposable unmanned vehicle in case the ground forces can shoot down stuff in orbit) something like this

These rods should hit with ICBM levels of accuracy (kinda, at least in theory). It's hard to target asteroids at nations or even continents as they usually rotate and during reentry they can do all kind of shit veering off-course. And none gives a shit about a crater in the middle of a desert (or about a few meters high tsunami). I assume you are there to conquer something.

So an invader could easily dump pre-made kinetics at industrial centers, and then follow up with locally acquired resources.

I tend to disagree. Kinetics on military and defense stations. Then you land and capture industry and infrastructure. Genocide of the current population and "replacement" with your own colonists is optional.

The point is that the only really interesting resource a planet has, any planet has, is the infrastructure someone built on it.
Raw resources can be easily extracted from icy moons/planetoids with shitty gravity or asteroids. Both litter the universe, undefended, and in freefall conditions.

Also, if the planet in question is big, populous and and industrialized (not a single-city shithole) you don't want the invasion to last enough for the industrial power of the planet to kick in and actually matter in the fight, you either blitzkrieg or stay pacifist. Otherwise you have a helluva time managing your interstellar supply lines.

That is an issue with planetary landers, too. After days and months of adapting to 0 g over the travel through space, the landers have to adapt to 1 g again. Their reflexes, their circulatory system and muscles take days and weeks to return to original performance. The local adversaries are adapted already.

Psst: use spinning poles or have the whole craft spin like a bola (with engine in the middle or on the side).

I am personally very partial to robots. A soldier does not need to be particularly smart, and robots can compensate that with lightning reflexes, multi-spectrum or even see-through-walls vision and shot-pinpointing sound sensors.

But anyway, unless you are attacking seriously undermanned outposts or your engine technology is very far in the future, your main issue is that you are pretty much always massively outnumbered.

So your "infantry" is more like WWII paratroopers. Has to be used to do critical surgical strikes, not charge enemy infantry ala Star Wars's beige battle droids from the Phantom Menace.

Mayflower II is 236 t displacement;

I'd like to let you know that this kind of vessel was pushed by the wind, that does not exist in space.
Again, modern naval craft models aren't applicable in space, as again propellers are useless in space. They rely on pushing against water to work, in space liquid water does not exist.

Before calculating crew requirements and other ancillary stuff, I suggest to read a bit about the kind of engines that work in space, and the general mechanics of space travel. I suggest to look at a site called Atomic Rockets.

As a general rule of thumb, you are riding a small star, your vehicle is 70 to 90% fuel by mass and usually more by bulk if you use hydrogen, and your course-changing ability is more akin to a train's than to a seagoing or flying vehicle.

[chornedsnorkack]

Or...you can aim to hit an ocean and cause some apocalyptic tsunamis to wipe out most of the human population. No tumbling problems there!

Oh, there are. Aiming to hit an ocean assures that the explosions are harmless unless a rare ship winds up at exactly the wrong place.

Hitting the waters of a port might do something. At Halifax explosion, the tsunami did contribute some damage - but the direct air blast seems to have done more. And that was a few kiloton explosion.

Regarding the crew requirements: freight planes manage with 2 pilots - on missions under 8 hours. So a sufficiently automated ship that does not depend on muscle power to handle sails or shovel coal might do with a crew of 6...10 standing watches. Actually, some sailing ships can make do with skeleton crew of under 10, too. Bounty sailed to Pitcairn with 9 trained white sailors.

But note that the simplest 21st century big ships, namely supertankers, need 20+ crew. And when the shipping firms try to cut crew costs to get it down to 20, they find that the ships become unsafe. Crews are too fatigued and incompentent for all their various functions.

For a spaceship, look at Pearl of the Night:

Every lift-off and landing was a violation of the laws of physics. And not only physics.

The rest mass is specified as 28 000 tons.

[someone_else]

Oh, there are. Aiming to hit an ocean assures that the explosions are harmless unless a rare ship winds up at exactly the wrong place.

A well-placed asteroid (slow enough to not disintegrate at atmospheric contact and dense/compact enough to not disintegrate on the way down) hits with tens of times more BOOM than a nuke.
This site does have an asteroid impact calculator somewhere, try to play with it a bit.
Also this is a good read.

At Halifax explosion, the tsunami did contribute some damage

Halifax is a fart even compared to a nuke from 50 years ago. Hiroshima in WWII was kit by a nuke with a yeald of 15 Kt, that means the boom is theoretically close to the boom made by 16 thousand tonnes of TNT.
Now we have nukes that are 300 Kt, and back in the day they built and tested 1 Mt military nukes and experimental bombs up to 50 Mt.
As I said, asteroids can do much better with less cost. (but crappy accuracy)

Regarding the crew requirements: freight planes manage with 2 pilots

Yeah, and spacecraft can do perfectly fine without any crew even today. The last mars probe was big and heavy as a car and it was dropped on mars by a fucking rocket-powered skycrane with no real human input (due to communication lag). As long as you don't need anything fancy like that, just an interplanetary voyage, even 20-30 year old technology is enough for a fully automated spacecraft.
It is simple newtonian mechanics in a vacuum, no wind/currents/bullcrap.

Humans on any modern spacecraft are there only to take decisions. You rarely have enough payload to make sense to have spare parts and do any real maintenance. Redundant systems/components is usually the only way.

For a spaceship, look at Pearl of the Night: The rest mass is specified as 28 000 tons.

If it is from Heinlein it's a torchship, a specific kind of fictional spacecraft with a magical engine that violates the most fundamental physics principles. Its specs are fictional too, so meaningless.

You should look at stuff proposed by NASA. Still a lot of wishful thinking involved, but at least they don't run on magic.

[Simon_Jester]

Actually, at least for the time being, yes, rocks are, and even if they weren't, I seriously doubt the people about to drop them onto your planet are in a mood to discuss the legalities.

You didn't get the reference.

Short form: someone raised the "just drop rocks" argument in the context of Warhammer 40k, as an alternative to all the bizarre WMD and energy bombardments the Imperium uses to kill worlds. The reply was a mock-bureaucratic post detailing the logistics problems associated with "just drop rocks."

http://wh40k.lexicanum.com/wiki/Rocks_Are_Not_Free!

More generally- moving a massive object onto an orbit that will cause it to strike a desired point on the planet soon requires a very serious expense of rocket fuel, if we don't have outright magic engines. It is not a foregone conclusion that one nuclear bomb costs more than one rock with equivalent yield. And since "put a nuclear bomb in a reentry-hardened casing and land it to a precision of a few hundred meters" is already a solved technological problem for ICBMs, there are strong arguments for sticking to that.

Remember that the defenders on any inhabitable planet have a shield against kinetic missiles. Atmosphere.

Look at Chelyabinsk. 300 kiloton explosion - and Chelyabinsk, in Urals, is one of the prime targets for an attack, being a centre of Sovier/Russian military industry.

The trick is to use manufactured projectiles. A random hunk of asteroid rock isn't going to withstand reentry very well unless it is of truly ridiculous size. And in being destroyed by reentry it may do no harm (but compare Chelyabinsk to the much larger Tunguska blast).

A tungsten telephone pole with a precision-shaped nosecone, on the other hand... wham. As with nuclear reentry vehicles, it is a solved problem to get hundred-ton objects through the atmosphere without burning up on reentry.

I would imagine that landers intended to engage atmospheric fighters would use missiles as their main armament, to keep the fighters at a distance, so that their superior manoeuvrability would be less useful. They could also have turreted weapons for point defence, as WW2-era bombers had.

With modern technology, any kind of projectile-firing gun is less than effective on an aircraft. Absolutely useless on an orbital fighter-bomber that's never meant to slow down below Mach 5 or whatever- what's the point of firing a gun whose bullets travel slower than you do? How would you even aim competently?

Lasers might be of some use, although the environment of reentry heat and hypersonic flight is a bit... unfavorable for accurate, effective laser fire.

The orbital fighter's main advantage would be its almost unlimited speed and altitude. It's very challenging for an air defense network to engage targets which travel scores of miles a minute and fly above the ceiling of conventional air-breathing fighters... and an orbital fighter would be well advised to do both.

Look at how much trouble the Russians had shooting down SR-71s (hint: they never managed it), and imagine what you'd have to do to stop an aircraft that travels faster and higher... and can shoot back.

That is an issue with planetary landers, too. After days and months of adapting to 0 g over the travel through space, the landers have to adapt to 1 g again. Their reflexes, their circulatory system and muscles take days and weeks to return to original performance. The local adversaries are adapted already.

Chorned, the thing that concerns me is that you keep switching around your assumption set, and changing the definition of what a planetary lander is for. Assuming that space travellers have to coast in free fall for weeks or months between trips, yes, they're not going to be staging any invasions. On the other hand there are no shortage of ideas for ways to keep people's strength up, and to allow artificial gravity, and in many SF settings the engines can keep up continuous acceleration that does a perfectly acceptable job of providing 'gravity' to passengers.

Also, there are many uses for craft that land on planets besides "invasion force."

Regarding the payload necessary for creating and sustaining settlements:

How about instead of using analogies from hundreds of years ago in different environments, you look at the fifty-plus years of active work people have put into designing sustainable lunar colonies? Not that Wikipedia is an authority by itself, but:

http://en.wikipedia.org/wiki/Colonization_of_the_Moon

That's at least a starting point.

People have thought this through. Using badly-informed historical analogies makes it harder to think clearly about the problem, as was shown when you decided to use WWII conventional bombing as your mental model of how orbital bombardment would work, and forgot about the existence of the atomic bomb.

So go looking for real studies on this problem, to at least get a sense of scale and what is and is not necessary.

This is why you take a tiny bit of time to enclose your rocks with an aeroshell, or use actual re-entry vehicles and/or nuclear weapons instead. At our current technology levels, it would take us AT LEAST a decade to create weapons capable of reliably attacking ships in high orbit ; So an invader could easily dump pre-made kinetics at industrial centers, and then follow up with locally acquired resources.

Not entirely defenseless, US Ground Based Interceptors could hit targets in very high orbits if we wanted with software mods, assuming the batteries on the kill vehicle will last long enough. It'd be limited since under thirty are deployed, but the burnout velocity on the things is enough to get tens of thousands of miles up, and by some unconfirmed accounts actually breach escape velocity by a wide margin, though this would mean no KV fuel left for a terminal attack.

With rather more modification, Russian R-36M ICBMs should be more then able to lob a nuclear warhead onto the moon if we wanted, the smaller US Titan II ICBM was capable of this with a several megaton warhead. Indeed a number of smaller ICBMs should also be well capable of high orbit attacks, you'd just have to mod the guidance system some and use only a time fuse on the reentry vehicle, then fire a barrage. It isn't for nothing that more then one ICBM became a space booster. Depending on some details that are entirely classified, it may be possible to just point the existing weapons into space and let fly without any modifications at all. If this would be lethal or not depends on how much radiation shielding the alien spacecraft has as I'd expect to miss by dozens of miles with no terminal guidance.

The miss distance could be even worse if my enemy sees my missiles coming and decides to leisurely sidle out of the way during the many, many minutes it'll take my warheads to reach them. ICBMs can't duck, nor can metropolitan areas.

Although from your descriptions and what I know, GBI missiles might be able to handle that- with the kill vehicle holding its delta-v for when you approach the target.

If that won't work, then just developing the system will take a lot of time, unless your enemy is rather incompetent and totally unprepared to be shot back at.

Or...you can aim to hit an ocean and cause some apocalyptic tsunamis to wipe out most of the human population. No tumbling problems there!

Oh, there are. Aiming to hit an ocean assures that the explosions are harmless unless a rare ship winds up at exactly the wrong place.

Hitting the waters of a port might do something. At Halifax explosion, the tsunami did contribute some damage - but the direct air blast seems to have done more. And that was a few kiloton explosion.

You are underestimating the size of the relevant rock. He's talking "apocalyptic," and that means he's thinking of rocks that weigh many millions of tons. Moving them is hard work, but if you do it, it is sure to penetrate the atmosphere (unlike Tunguska) and sure to do damage (like Tunguska, but unlike Chelyabinsk, and much much bigger than both).

At that point the resulting tsunami becomes a very serious problem, because the energy release is comparable to that of a huge earthquake- which is what creates REAL damaging tsunamis in real life. And missing the target by many miles won't matter, as long as you hit the correct ocean.

Regarding the crew requirements: freight planes manage with 2 pilots - on missions under 8 hours. So a sufficiently automated ship that does not depend on muscle power to handle sails or shovel coal might do with a crew of 6...10 standing watches. Actually, some sailing ships can make do with skeleton crew of under 10, too. Bounty sailed to Pitcairn with 9 trained white sailors.

A sufficiently automated ship in modern times could make do with no crew. You need larger crews for ocean-going ships not because 20 is a magic number, but because there are a large number of jobs required to run the ship which may or may not be needed on a spacecraft.

Did the Apollo astronauts fail and die because they didn't have a crew of 10?

[someone_else]

The miss distance could be even worse if my enemy sees my missiles coming and decides to leisurely sidle out of the way during the many, many minutes it'll take my warheads to reach them. ICBMs can't duck, nor can metropolitan areas.

Interplanetary spacecraft engines don't lend well to sudden multi-gee burns, so yeah, serious spacecraft can't duck a lot either.

You can have additional rocket engines and use them to "duck" enough to get away from radiation radius, but it's far more effective to invest the same mass-budget in half-decent point defence systems of some kind.
Or never get so close in the first place. If you stay in high orbits, even the crappy interplanetary engines are enough to duck by the time the warhead reaches you, but if it has some kind of delta-v to correct the course then it's again a technology race.

[Me2005]

The miss distance could be even worse if my enemy sees my missiles coming and decides to leisurely sidle out of the way during the many, many minutes it'll take my warheads to reach them. ICBMs can't duck, nor can metropolitan areas.

Interplanetary spacecraft engines don't lend well to sudden multi-gee burns, so yeah, serious spacecraft can't duck a lot either.

Weren't the Chinese testing purpose-built anti-satellite missiles?

Something else that occurred to me - if your invading aliens insist on being in some kind of Earth-orbit, we can fire missiles that get close enough to force them to maneuver. Then it becomes a war of attrition - do we run out of missiles first, or do they run out of propellant? It'd probably be better (for the aliens) to park in an orbit where they can be out of range of our missiles (even if it's after they learn we have them). Alternatively, they could just build a base on the moon and basically attack us with impunity from there.

As for rock-dropping, you don't always need to move the rock very far - there have been near-misses, nudging one of those so it's a direct hit instead of a near miss wouldn't take much if it was done far enough out. Of course, then you've got to be able to find those rocks too, which is its own problem.

[chornedsnorkack]

As mentioned - rocks are not free. If you expect a rock to get through atmosphere at 15 km/s, then its explosive power it just 25 times its mass - whereas the Hiroshima bomb had 3000 times its mass. So, a rock which is small enough to be accelerated and maneuvered as a payload of your ship is small enough that it will NOT qualify as "asteroid".

To handle any bigger rocks, you need to happen to have your ship equipped and preadapted to tow an external load - worse, an external load NOT designed and built to be towed. Which also means you will need to have a large payload of specialized tools just lying aboard - and a large crew and a lot of time to improvise and figure out how to apply these tools to the task at hand.

[Ultonius]

With modern technology, any kind of projectile-firing gun is less than effective on an aircraft. Absolutely useless on an orbital fighter-bomber that's never meant to slow down below Mach 5 or whatever- what's the point of firing a gun whose bullets travel slower than you do? How would you even aim competently?

Lasers might be of some use, although the environment of reentry heat and hypersonic flight is a bit... unfavorable for accurate, effective laser fire.

The orbital fighter's main advantage would be its almost unlimited speed and altitude. It's very challenging for an air defense network to engage targets which travel scores of miles a minute and fly above the ceiling of conventional air-breathing fighters... and an orbital fighter would be well advised to do both.

Look at how much trouble the Russians had shooting down SR-71s (hint: they never managed it), and imagine what you'd have to do to stop an aircraft that travels faster and higher... and can shoot back.

I was mainly thinking of lasers as the point-defence weapons. I was also thinking in terms of a troop lander, as the OP seemed to be, rather than a fighter-bomber, which wouldn't necessarily have to be a lander at all. A troop lander would, by necessity, have to slow to speeds comparable to a conventional aircraft and drop below their flight ceiling in order to land, and would be vulnerable at such speeds and altitudes.

Did the Apollo astronauts fail and die because they didn't have a crew of 10?

The Apollo astronauts had three or four shifts of more than ten flight controllers monitoring every system aboard their spacecraft 24/7. On a long-range military mission, the people performing those functions would probably have to be aboard the spacecraft.

[lPeregrine]

The Apollo astronauts had three or four shifts of more than ten flight controllers monitoring every system aboard their spacecraft 24/7. On a long-range military mission, the people performing those functions would probably have to be aboard the spacecraft.

They also did it with 1960s technology. By the time you're building interstellar spacecraft it's pretty much guaranteed that you have better computer systems and can have computers doing all of the monitoring (and wake up the sleeping token crew member if necessary). Then you only need a token crew to handle important decisions.

Just consider the similar situation in airline travel: you used to have five or so crew members, including a dedicated engineer and navigator. Over the past 50 years we've seen a steady reduction in crew until you could theoretically have the plane fly itself with a single pilot doing nothing more than watching to make sure the autopilot doesn't do anything stupid and dealing with any potential emergency. The biggest limit there isn't technological, it's that the customers won't like it.

[someone_else]

The Apollo astronauts had three or four shifts of more than ten flight controllers monitoring every system aboard their spacecraft 24/7. On a long-range military mission, the people performing those functions would probably have to be aboard the spacecraft.

The last mars probe was dropped by a fully-autonomous rocket skycrane that deployed after a bit of conventional reentry with heatshields. Yes, there was a ground control, but they were working on 20 to 30 minutes old information due to light lag, so the craft had to do all the voyage maneuvers and descent on its own. And operating a skycrane is NOT easy, even on Mars where gravity is less.
Yeah, automation can certainly replace the crew of a spacecraft even with modern technology.

[PeZook]

Problem is, for an interstellar ship that has no FTL, the ship must be able to handle a worst-case scenario all by itself, and the probability of a fault or error ocurring at some time during the voyage is vastly higher. If your automation tech does not allow you to use robots for such emergency repairs, you will still need a sizeable crew of specialists capable of fixing all the critical systems by themselves, so the point about taking aboard the support crew that normally stays groundside is pretty sound.

For inter-system missions, yeah, any civilization capable of interstellar travel should be prefectly fine using fully automated spacecraft - I mean, at worst its engines crap out and you recover it at a further point in its orbit, or it crashes, no biggie.

[someone_else]

That's what redundancy is for. It is usually less mass-intensive than adding a big enough support module for the human techs plus spare parts and telepresence crap to allow the humans to get close to massively radioactive parts of the craft like say the engine or the reactor.

And in most cases, you don't really know than something is not working as it should until it's too late OR you would need a shipyard to do that anyway (oh, the engine does not work, let's make a new one from spare parts!). Redundancy saves you in those situations, a bunch of techs onboard cannot.

This is the aircraft way to do things, btw.

[PeZook]

That's what redundancy is for. It is usually less mass-intensive than adding a big enough support module for the human techs plus spare parts and telepresence crap to allow the humans to get close to massively radioactive parts of the craft like say the engine or the reactor.

I suppose a lot depends on the actual tech in question. Redundancy will quickly become pointless if the trip will take long enough and each of the redundant systems will be faulty enough that the probability of failure over say fifteen decades remains high anyways.

And in most cases, you don't really know than something is not working as it should until it's too late OR you would need a shipyard to do that anyway (oh, the engine does not work, let's make a new one from spare parts!). Redundancy saves you in those situations, a bunch of techs onboard cannot.

This is the aircraft way to do things, btw.

Yeah, but aircraft, or even our current manned spacecraft, are never lightyears away from help. When the worst-case (recoverable) scenario occurs on an aircraft (loss of all engines) you do your best to put it down and as long as people walk away from it, it's fine. With an interstellar ship this is just not an option.

But, well, I suppose it's all in the details and we obviously have no idea how a future STL ship will look like when it comes to those

[someone_else]

I suppose a lot depends on the actual tech in question. Redundancy will quickly become pointless if the trip will take long enough and each of the redundant systems will be faulty enough that the probability of failure over say fifteen decades remains high anyways.

Of course. But in a situation like this adding the techs and their support equipment to the equation does not make the overall plan sound much better. Imho it adds more issues than solves.
Now you have to bring with you a full recycling system able to break down damaged stuff and recycle its components and enough equipment to make almost anything from scratch.

Plus a way to make sure the bunch of techs supposed to run this zoo don't suddenly all vote republican and let the whole thing go to hell in the name of some vague belief and pork-barreling.

Although what matters for failures to happen is the time as experienced from the ship's frame of reference, so a relativistic craft could manage to pull this off as the "onboard" time is much slower and you should be able to run around the galaxy in... 100 "onboard" years maybe? Don't remeber . If someone manages to find a way to make it relativistic in the first place, anyway.

When the worst-case (recoverable) scenario occurs on an aircraft (loss of all engines) you do your best to put it down and as long as people walk away from it, it's fine. With an interstellar ship this is just not an option.

Again, in these worst possible cases having a bunch of technicians is useless as you would need a shipyard and/or a very specialized factory to do serious repairs.

Above I was not saying that redundancy saves your ass 100% of the times, just that having tech support staff and spare parts is worse, both mass-wise and cost-wise, and adds a lot of potential points of failure that before didn't exist. So on average is a bad idea.

Hell, it's relativistic interplanetary voyage, not a walk in the park. Man up and take some risks!

[Sea Skimmer]

Of course. But in a situation like this adding the techs and their support equipment to the equation does not make the overall plan sound much better. Imho it adds more issues than solves.
Now you have to bring with you a full recycling system able to break down damaged stuff and recycle its components and enough equipment to make almost anything from scratch.

Who says you have to recycle anything? You need to be prepared for large numbers of failures, most of which will never happen. Above a certain point it will be lighter and more compact to bring along raw materials and machinery to make parts on demand then a vast oversupply of spare parts. That's just a physical reality unless you can predict all failures. In both cases the situation will be helped considerably by designing the ship to be repaired with as much standardization as possible and plenty of maintenance access. Modern spacecraft of course are designed completely opposite to this philosophy. Where the turning point between spare parts vs on board manufacturing, and standardization vs optimization for lower mass/volume lie depend on details we don't have.

[Simon_Jester]

The miss distance could be even worse if my enemy sees my missiles coming and decides to leisurely sidle out of the way during the many, many minutes it'll take my warheads to reach them. ICBMs can't duck, nor can metropolitan areas.

Interplanetary spacecraft engines don't lend well to sudden multi-gee burns, so yeah, serious spacecraft can't duck a lot either.

Weren't the Chinese testing purpose-built anti-satellite missiles?

Something else that occurred to me - if your invading aliens insist on being in some kind of Earth-orbit, we can fire missiles that get close enough to force them to maneuver. Then it becomes a war of attrition - do we run out of missiles first, or do they run out of propellant? It'd probably be better (for the aliens) to park in an orbit where they can be out of range of our missiles (even if it's after they learn we have them). Alternatively, they could just build a base on the moon and basically attack us with impunity from there.

Building a permanent base on the moon would probably be worse than being 'parked' in geosynchronous orbit. If we want to hit a target on the moon we can; hundred-kiloton nuclear bombs don't weigh any more than the probes we routinely send there on medium to heavy-lift rockets. A moon base can't dodge; it can shoot back, but it's ten times farther away from the highly visible boost phase of a missile, far enough away to make targeting them before they burn out very difficult.

Other people here are probably right about the merits of large spacecraft dodging versus shooting down missiles, given near-future technology. If we rule out the "torchship" concept, dodging isn't so rewarding, I'm not going to dispute that.

As for rock-dropping, you don't always need to move the rock very far - there have been near-misses, nudging one of those so it's a direct hit instead of a near miss wouldn't take much if it was done far enough out. Of course, then you've got to be able to find those rocks too, which is its own problem.

Yes, and you've got to be willing to wait years for your weapon to hit the target, and you've got to assume the enemy can't launch a deflection mission. Not very helpful in a tactical environment where you need bombardment now, or for that matter as preplanned support for an operation a month from now. Most effective as a very indiscriminate strategic weapon, if you happen to dislike the whole planet you're targeting.

As mentioned - rocks are not free. If you expect a rock to get through atmosphere at 15 km/s, then its explosive power it just 25 times its mass - whereas the Hiroshima bomb had 3000 times its mass. So, a rock which is small enough to be accelerated and maneuvered as a payload of your ship is small enough that it will NOT qualify as "asteroid".

To handle any bigger rocks, you need to happen to have your ship equipped and preadapted to tow an external load - worse, an external load NOT designed and built to be towed. Which also means you will need to have a large payload of specialized tools just lying aboard - and a large crew and a lot of time to improvise and figure out how to apply these tools to the task at hand.

On the large scale, anyone prepared for interplanetary war will probably have solved the problem of redirecting asteroids and be prepared to do that too. One of the first things a sane person would do in the colonization of space is think "how could I prevent a large asteroid from striking my own planet?" One of the next things is "how can I control the course of asteroids so that I can use them for materials and habitat space?"

If you assume an interplanetary conflict, on a large enough scale that people are actually thinking in terms of being able to fight meaningfully other than "drop 1000 nukes, war over..." then yes, redirecting asteroids becomes a credible strategic weapon. It's not cheap, but neither is nuclear carpet-bombing.

If they can't operate on that scale, they will drop 1000 nukes and the war is over.

On the smaller scale, yes, kinetic bombardment weapons don't have as favorable a mass-to-yield ratio as nuclear weapons. They have some other advantages, though. One is that they can be made small, much smaller than any efficient nuclear weapon, for things like sinking an aircraft carrier at anchor without destroying the whole city it's docked at. De-orbiting a telephone pole on someone may be a practical response at times when de-orbiting a fission bomb is not.

Another is that for a civilization which already has large scale spacefaring infrastructure, preparing kinetic weapons for dropping may be more cost-effective than inventing a new class of nuclear weapons it doesn't already have. If you're already using a mass driver to fire hundred-ton projectiles to escape velocity from your world's surface, firing those projectiles at somebody isn't very much of a stretch.

I was mainly thinking of lasers as the point-defence weapons.

That works for a lander (see below), but not so well for hypersonic aircraft in atmosphere. Under those conditions you might be able to aim a laser, but the turbulence and superheated air right around the craft is a serious problem for the kind of precision you need for antimissile work. It's also hard to stick the laser on the hypersonic aircraft in a way that won't cause drag problems, but that's a probably-solvable problem.

I was also thinking in terms of a troop lander, as the OP seemed to be, rather than a fighter-bomber, which wouldn't necessarily have to be a lander at all. A troop lander would, by necessity, have to slow to speeds comparable to a conventional aircraft and drop below their flight ceiling in order to land, and would be vulnerable at such speeds and altitudes.

In that context your idea makes more sense. Good one.

Did the Apollo astronauts fail and die because they didn't have a crew of 10?

The Apollo astronauts had three or four shifts of more than ten flight controllers monitoring every system aboard their spacecraft 24/7. On a long-range military mission, the people performing those functions would probably have to be aboard the spacecraft.

On the other hand, better automation makes it likely that the number of people required could be reduced.

It's not that you're wrong, I don't disagree with you so much. The problem is that Chorned keeps making rather silly analogies between, say, interplanetary colonization and the Mayflower, or between the London Blitz of 1940 and orbital bombardment in 2140 or whatever. That's the context I originally said this in- one of Chorned's bad analogies.

[Me2005]

Building a permanent base on the moon would probably be worse than being 'parked' in geosynchronous orbit. If we want to hit a target on the moon we can; hundred-kiloton nuclear bombs don't weigh any more than the probes we routinely send there on medium to heavy-lift rockets. A moon base can't dodge; it can shoot back, but it's ten times farther away from the highly visible boost phase of a missile, far enough away to make targeting them before they burn out very difficult.

Maybe; while we have rockets that can send up probes, we don't have those rockets set up for firing nukes, and I'm dubious that just any ballistic missile could hit the moon. It'd take some time to set that up, and as long as the aliens didn't do anything obviously hostile we wouldn't just start shooting until the aliens were established. If the aliens built on the dark side and dug in effectively, I don't think there'd be anything we could do until after it'd be too late. There's also loads of free mass just lying around on the moon for use as armor or weaponry, and the lift-off requirements are nill. Failing that, it'd be easy to set up several launch sites habitats far enough apart that hitting everything becomes troublesome for us.

Yes, and you've got to be willing to wait years for your weapon to hit the target, and you've got to assume the enemy can't launch a deflection mission. Not very helpful in a tactical environment where you need bombardment now, or for that matter as preplanned support for an operation a month from now. Most effective as a very indiscriminate strategic weapon, if you happen to dislike the whole planet you're targeting.

I suppose this comes from my assumption that the reason we need a there-and-back lander is to conquer the planet and establish a base there. Hitting it with a rock redirected from the outer solar system should be easy for an interstellar traveler, and since they've been waiting at least decades as it is, a few more years waiting for it to hit won't matter much. I agree though, it would be best for softening entire planets before you show up.

[Simon_Jester]

Maybe; while we have rockets that can send up probes, we don't have those rockets set up for firing nukes, and I'm dubious that just any ballistic missile could hit the moon. It'd take some time to set that up, and as long as the aliens didn't do anything obviously hostile we wouldn't just start shooting until the aliens were established.

In the time it takes you to build a moon base, I strongly suspect that the Department of Defense could put a nuclear warhead on an Atlas-Centaur and prepare to boost it to the moon.

If the aliens built on the dark side and dug in effectively, I don't think there'd be anything we could do until after it'd be too late. There's also loads of free mass just lying around on the moon for use as armor or weaponry, and the lift-off requirements are nill. Failing that, it'd be easy to set up several launch sites habitats far enough apart that hitting everything becomes troublesome for us.

Agreed- all this is a very relevant concern.

I suppose this comes from my assumption that the reason we need a there-and-back lander is to conquer the planet and establish a base there. Hitting it with a rock redirected from the outer solar system should be easy for an interstellar traveler, and since they've been waiting at least decades as it is, a few more years waiting for it to hit won't matter much. I agree though, it would be best for softening entire planets before you show up.

Well, you also have to accept the risk that you'll accidentally ruin some of the best and most conquest-worthy things about the planet, such as ecosystems with interesting products, or industrial infrastructure that can be put to work. Plus, honestly, it doesn't make a lot of sense to talk about interstellar war unless you have interstellar travel of the "Warp factor five, Mr. Sulu" type.