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One thing that just about all interstellar civilizations need if they want to be anything more than long-distance friends is a way to get from their starships down to the surface of planets and back up again. In other words, they need some flavor of shuttlecraft that can survive re-entry into a planetary atmosphere and then reach orbit again without the need for extensive ground support, as they may have to land on Earth today and Mars in a few days.

This craft must be able to:

  • Re-enter and land on the surface of rocky, not-too-hot planets (Earth works, Mars works, Venus or Mercury can be excluded though. Bonus points if you can get onto larger versions of Earth or Mars.)
  • Take back off again without the need for dedicated launch support facilities (a clearing, road, or ordinary runway should suffice -- can't have a strongback/TEU or ground refurb facility in this application)
  • Reach orbit without shedding large parts (leaving trash in other people's planetary space is rude, don't you think?)
  • Maneuver on-orbit in an agile fashion (i.e. not limited to preset orbital parameters or automatic guidance)
  • Operate without replenishment of consumables or refurbishment of the craft for 1 Earth week, minimum, including fuel/oxidizer/reaction mass and life-support consumables
  • Provide for an operating crew as well as roughly a dozen passengers and their supplies or two tons of cargo, at a minimum (more is better)

The builders have:

  • Ample supplies of materials that can withstand re-entry temperatures on Earthlike planets multiple times without refurbishment (or the worst case target planet if other than Earthlike)
  • The ability to develop engines capable of equal or greater specific impulse and delta-V to the state of the art in current rocketry (nuclear-thermal and fusion-thermal are both explicitly on the table, but if they can do better, they will)
  • A knowledge of structures, aerodynamics, and chemistry at least equal to ours, but still bounded by physical limits
  • The ability to use the main engines to generate ample electric power (not hard)

The builders are also land-dwellers with the ability to dexterously manipulate fine controls and are on a human-scale (provided the life-support is compatible, a human could ride in, or even be trained to operate, this craft).

What design of craft would pop out of this?

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  • $\begingroup$ Is antimatter-powered propulsion allowed? $\endgroup$ – Jarred Allen Mar 8 '17 at 4:58
  • $\begingroup$ @JarredAllen -- if you can think of a way to get it and all the shielding it'd need into a compact enough package, go for it! $\endgroup$ – Shalvenay Mar 8 '17 at 5:00
  • $\begingroup$ how big is the main ship ? $\endgroup$ – MolbOrg Mar 8 '17 at 9:19
  • $\begingroup$ @MolbOrg -- much larger than the shuttlecraft (presumably large enough to be awkward to deorbit and reorbit) $\endgroup$ – Shalvenay Mar 8 '17 at 12:35
  • $\begingroup$ Ok, I'll ask differently, it is more then let's say than 4 billion metric tons or is it bigger smaller than 2km diameter? Basically I'm asking is it big enough to be able to deploy orbital ring or space elevator. it is about billion metric tons or about 1km diameter it is big enough(depending on what type of engines they use) to have ring or space elevator as deploy-able payload. $\endgroup$ – MolbOrg Mar 8 '17 at 14:16
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What is wrong with using a smaller version of whatever allows the main ship to maneuver? It likely has a propulsion system that allows it to roam around a solar system easily. It should be able to land and lift a vehicle.

If for some reason that sub-light drive cannot be used to land on a planet, try keeping a hot pile of some fissionable. Pour water on it and throw the steam out the thrusters. The steam would not be radioactive unless your system was very poorly designed.

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I'll address the propulsion in general terms.

Your requirement specifies high thrust. It also implies high specific impulse.(must be capable of SSTO, must presumably be able to do more things too than just barely make orbit) These factors together mean you need high power.

Chemical energy is too feeble, and since the craft needs to operate independently, beamed power is off the table. You're left with nuclear - fission, fusion or even antimatter. Now, there are concerns other than your ability to generate the required power and couple it to the ship without vaporizing it - past a certain point, your lander will be about as friendly to the region it lands on as a nuclear strike. I'm assuming your civilization is able to produce pretty much any sort of engine we've conceived of, but even then they need to make a compromise between performance and power just so they can land somewhere without utterly destroying the surroundings.

In particular I would suggest a nuclear lightbulb. It's an advanced type of nuclear thermal rocket that's relatively "friendly" in that it doesn't contaminate the atmosphere with radiation and its wattage is modest enough that it won't turn everything into a glowing crater. Depending on just how optimistic you want to be about its thrust and isp, it should still be very capable of SSTO with propellant to spare. It may be designed to 'shift gears' such that it has a high thrust mode for landing and ascent and a low thrust, high efficiency mode for in space use. The craft will still be quite a dangerous thing - it doesn't leak radioactive material, but you don't want to be anywhere near it on the ground. Don't land right next to people people or they will be convulsing in radiation poisoning in short order. You'll need careful procedures for shutdown and getting on and off the ship, but these are solvable problems.

If you want the performance to just sort of effortlessly lift off from Earth, take a joyride to Mars, perhaps land there and just sort of cruise around all over the place without a refuel, the energy your craft must put out will start looking like a minor nuclear exchange. In principle, there is no reason something like Project Orion couldn't be used for this. Perhaps your civilization wouldn't use something as crude as nuclear bombs, but some sort of nuclear pulse drive, perhaps ignited with magnetic fields or antimatter, seems likely. Any way you slice it, you need similarly huge amounts of energy anyway, so if you land on a road there won't be a road anymore afterwards. You'll have to be careful not to fry half the satellites on Earth orbit and to take care where you land, because you'll kill anything nearby and the engine's shine will burn everyone's retinas from tens of kilometers out. You'll contaminate the atmosphere enough that people might be irate. Not likely enough to actually kill or injure anyone though, as long as they're nowhere near when you come in.

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  • $\begingroup$ You might want to consider two or more different engines: one for operation inside the atmosphere (i would suggest jets or even turboprops, combined with good old wings to create lift from motion), and a second one when massive power is required. (e.g. get out of the gravity well, using maybe your nuclear rocket, but start it only after reaching a "safe" altitude above your friend's driveway) $\endgroup$ – Burki Mar 8 '17 at 11:53
  • $\begingroup$ @Burki -- what stops you from having a nuclear turbine engine? (AIUI, it'd simply require replacing the combustor stage with a heat exchanger...) $\endgroup$ – Shalvenay Mar 8 '17 at 12:37
  • $\begingroup$ In principle you might be able to use the nuclear rocket in jet mode: Instead of internal propellant, have air intakes and run atmospheric air around the reactor. How the plumbing would work out is anyone's guess. This would let you cruise around the atmosphere as much as you like, but it wouldn't solve the radiation issue. I think if you wanted a separate landing engine basic chemical rockets would work better than jets since they're much lighter. $\endgroup$ – Elukka Mar 8 '17 at 12:38
  • $\begingroup$ Yeah, the radiation problem would probably be a real nuisance from a mass penalty perspective, but it's probably not unsolvable either -- the USAF has flown a reactor on an airplane before, and although the mass penalties aren't nearly an issue on/in water as they are in the air, the USN has this nuclear-powered ship thing pretty well down pat $\endgroup$ – Shalvenay Mar 8 '17 at 12:40
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    $\begingroup$ @Elukka afaik jets win the comparison when you take the weight and storage of the fuel into account: a rocket carries its own oxygen, a jet takes it from the atmosphere, which also means the storage does not have to withstand large pressures. $\endgroup$ – Burki Mar 8 '17 at 12:41
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Material shuttlecraft have repeatedly proven to be problematic{1}, so moving, projected force fields are now more typical for ground-to-orbit trips.

After repeated close calls with transporter beams, most advanced galactic races now use force-field bubbles, powered and controlled from orbiting ships. Although the energy cost is enormous, it is short-lived, and eliminating the shuttlecraft, bay, hatches and maintenance gear leaves more in-hull space for replacement DiLithium crystals.


{1} Federation and even Klingon case studies (at least those declassified to date) and historical analysis show a shockingly high rate of (matter-based) shuttle-craft accidents and total losses -- almost as if they were written as plot devices in cheesy SF series....

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    $\begingroup$ This looks really short. Could you elaborate your idea in greater detail? Otherwise such a short answer might get deleted, as it might be better off as a comment. $\endgroup$ – Secespitus Mar 8 '17 at 12:38
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Rocket propulsion, even funky beamed-cored antimatter engines, are so last ice-age. They all use an insane power source, dangerous and unstable, to push a small mass really really fast and let conservation of momentum take care of the rest.

Instead, all the cool species have switched to using force-fields. The early models were simple electromagnetic devices that pushed against a planetary magnetic field, but that doesn't work on places like Mars. The new models are still electromagnetic in nature, but take advantage of quantum shenanigans to create a field which pushes against every atom of the planet. Instead of a small mass being pushed really hard, it is a large mass which is being pushed very gently. The result is the shuttle craft only needs to supply its own final kinetic energy, not lift its own reaction mass as a conventional rocket must, and even then it only needs energy as fast as it rises through the gravity well: with this drive, you could take off with only the solar panels covering the hull, provided you didn't mind it taking a week to reach orbit (something a conventional rocket could never do because of gravity losses). Neither do you need to worry about re-entry, because the drive can easily work in reverse and slow you down before the shuttle's hull touches the thicker layers of atmosphere at the high speed that causes all the problems.

But what if you want to do take-off and landing in a hurry, instead of a week? Perhaps a storm is coming your way? That's alright, just as electric cars use regenerative braking to recharge their batteries while slowing down, so to does your shuttle. The energy levels are far too large for a conventional battery, so instead the shuttle pumps the excess energy into a tiny lump — 47g per tonne of shuttle mass — of 178m2Hf: a relatively safe half-way-house between a nuclear laser and a nuclear battery. (Safe enough to keep around, so why not use it as a nuclear rocket? Because when it discharges it only emits gamma radiation, and while you can shield against that without difficulty, gamma radiation is the worst exhaust to use for a rocket if you care about saving energy).

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Not to go all steampunk on you, but the best interface vehicle for visiting disparate worlds with variant weather and negligible ground support is...

a tethered bathysphere.

Have your ship enter a low geosynchronous orbit then detach the bell and lower it down to the surface. The electrical and life support needs of the crew can be piped down through tubes in the tether, with on-board reserves of both to handle short term disconnects. Descent and return ascent are handled by winches on the orbiting vessel, saving most of the bathysphere's excess carrying capacity for shielding.

The vehicle could also be equipped with orbit-capable rockets which in case of a tether disconnect can carry one end of a strong thin cable up to the orbiting vessel. That cable can then be used to drag a new tether down into the planet's gravity well and guide it to the otherwise stranded bathysphere.

It is a low tech solution to a deceptively difficult engineering challenge.

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    $\begingroup$ Low geosynchronous orbit? Ho ho! But is there such a thing? "It is a low tech solution to a deceptively difficult engineering challenge." Actually your 'tethered bathysphere' is a space elevator in a false bread & dark glasses. Not so low tech after all. But why a bathysphere? To avoid using a submarine, perhaps. Joking aside, lowering & retrieving astronauts via a cable is a nice concept. Practical I'm not so sure, but a nice concept nonetheless. $\endgroup$ – a4android Mar 8 '17 at 8:33
  • $\begingroup$ @a4android, How else do you prepare an airfoil based aircraft for the variety of air densities and wind conditions which may be encountered on other planets? At least I didn't suggest lowering a boarding ladder (a.k.a. a stairway to heaven)! $\endgroup$ – Henry Taylor Mar 8 '17 at 13:33
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Look at the good old ships exploring the ocean in the past centuries for a reference.

They used the mother ship to explore the seas surrounding a new found land, but to explore the land they used smaller boats.

Reasons:

  1. you don't risk your only ship by venturing in unexplored waters
  2. you are more agile if you need to escape sudden dangers
  3. you don't risk your entire crew on unexplored lands

If you put it into space, you also add the need for having to escape the gravity well with a flabbergasting huge and massive ship, which will cost a hell of fuel. Plus, designing your ship to withstand gravity will add additional weight to it, which is unwanted in space navigation.

Therefore they can use a reusable rocket (no nuclear engine, if you are concernced about leaving back a empty module I assume you don't want to leave back radioactive garbage, too) to land and take off from the planet, and the rocket thrust will put a limit on the maximum gravity they can afford to escape and the maximum load they can carry on returning exploration ("that cow is a nice souvenir, honey, but it weight more than the 50 kg allowance we have").

Once on the planet they can choose to use lightweight

  • wheeled rovers (for solid surfaces exploration)
  • jet propelled ships (for liquid surfaces exploration)
  • manned drones (for air exploration)
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  • $\begingroup$ The major problem with current reusable designs is that they require ground fueling and refurbishment support (something our civilization can't count on having) $\endgroup$ – Shalvenay Mar 8 '17 at 12:43
  • $\begingroup$ Can't they take the needed fuel with them upon landing? The LEM did. $\endgroup$ – L.Dutch Mar 8 '17 at 12:50
  • $\begingroup$ Taking fuel with is an option, but a limiting one... $\endgroup$ – Shalvenay Mar 8 '17 at 23:18
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I would suggest a hybrid antimatter driven system: The shuttlecraft takes a form of a simple, not too high tubular rocket with retractable landing legs. Depending on the atmospheric properties, it either lands with parachutes, or powers up it's engines before touchdown. It's liftoff engines are antimatter solid core units:

http://www.projectrho.com/public_html/rocket/enginelist.php#amsolid

These are lightweight, high-thrust engines, being simple and clean, and not putting out anything but hydrogen, and only a small amount of promt radiation. They require minuscule amounts of antimatter fuel. Their specific impulse is moderate, which means, that, in order to make LEO with a 10 ton spacecraft, they would need 15 tons of liquid hydrogen. But the shuttle only carries 6 ton propellant. This (4700 m/s of dV) is enough to secure powered touchdown, and shot the shuttlecraft again on a sub-orbital spacejump. After they are in space, they rechannel their antimatter into a small gas/plasma/beam core antimatter engine. (The exact solution depends on, how good they are with superconducting magnets and lightweight gamma shields. If not too good, they chose gas core, and carry more hydrogen, if very advanced, they invest into shield, and use a beam core with astronomical Isp. ) It's thrust is low, but they have time to make orbit and manouver to rendezvous.

Of course, generating and storing antimatter is a hard task, but since they have achieved manned interstellar spaceflight, they need to have at least fusion energy source, which means, that they are experts in magnetic containment, and have enormous energies at hand on the mothership. To survive interstellar trip, they would need lightweight radiation shields too, which are handy, if you are using AM rocket.

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