What is the best design for trans-atmospheric cargo ship?

Question

Backdrop

This is set in a world after an empire-state that controlled the entire solar system fell. They have incredibly efficient catalyzed direct fusion drives, which powers the heavy mining and shipping industry across the entire solar system, sending cargo in and out of the outer solar system and between the planets.

But there needs to be a solution to ferry light cargo and people on and off-world. These would mostly consist of light, extremely refined goods that cannot be made elsewhere, such as microprocessors, cryogenically-packed fruit and vegetables, and other goods only unique to earth.

The vast majority of freight stays orbital, or dropped down the gravity well on single-use, dirt-cheap reentry capsules.

Categories

There are two broad categories we can split designs into.

Space-Plane (launches sideways)

A VTOL space-plane is a fantastic all-purpose craft, easily combining the functions of a helicopter, a plane, and a spacecraft. Any explorer or scout ship will probably have it as a shuttle. In this setting, it has modified turbojet engines on pivoting nacelles, scramjets along the lats, and two catalyzed fusion engines on the back.

If you need fuel, you can skim off a gas giant. If you need a floating base of operations for a ground exploration, like on the side of a rough mountain, or a slow areal scan, then it can also do it. If you need to transfer cargo from one ship to another without docking, it can also do that.

It's a jack of all trades, but a master of none. Its key advantage here is that it can hover over or land basically anywhere with enough space, regardless of terrain and with little regard for weather, or landing infrastructure.

Basic Rocket (launches straight up)

The other category is firmly in the same group as the Starship, built by SpaceX, except that it's a fusion-powered SSTO Starship. But still a Starship.

It's a rocket that launches straight up, either air braking like the starship, or landing propulsively, like the falcon 9 and heavy boosters. It would also be reusable and if you had the technology to, and the delta V budget, be made as an SSTO rocket, making reuse even simpler.

Unfortunately, this kind of ship can only ferry cargo up and down, and would require highly specialized infrastructure for engine plume management system, keeping the energy away from the craft itself, so it isn't damaged by its fusion drive.

The Question

What is the best design for a ship that does one thing, and only one thing: Get cargo from the surface into orbit, then bring cargo back, and repeat? Industrial fright transport.

1. A heavier and bigger delta-wing space-plane.

2. Something like a heavy skiff and a landing bay, something like the Starship's chopstick arms, to have room for the deluge/engine plume management system. In the expanse, one of the concept arts shows a heavy shuttle profile, slightly smaller than the Roci.

3. A shuttle variant, which takes a leaf out of the ISV Venture Star's book, and a little like the lander from Destiny. It's a ship that is a compressive-tension truss, with its own (beefy) landing legs on the bottom. Above the folded legs are the stacks of cargo containers, covered with reflective material. Above it is the fusion reactor torus, and above it is the rigging, hinges and hydraulic shocks for an X shape of engine nacelles, angled away from the body. As aerodynamics becomes an issue, a shield/cone would sit above the engine pods, which doubles as the fuel and reaction mass tanks.

Such a design negates the issues that a traditional rocket has, as its engines are far enough away from the ground for reflected energy not to damage the landing gear. (See the image link for visuals.)

4. Or maybe something totally different.

That's my question. If you need to move industrial amounts of cargo on and off the surface, how?

Side-note

Sorry about asking the previous question, as clearly I didn't word it correctly, and didn't get the answer I needed, this should rectify it.

Answer 1

"Or maybe something totally different"

Bulk shipping operations doesn't want high performance spacecraft, they want infrastructure.

Operating fleets of contained nuclear explosions (e.g. a fusion reactor) safely is expensive, as o.m pointed out with the Kzinti Lesson, not to mention the capital expenditure involved in each spacecraft. Meanwhile, in today's world, maritime shipping vessels use the absolute cheapest and dirtiest bunker fuel to minimize operational expenditure, and air couriers buy secondhand passenger planes to save on capital expenditure. And of course, proper road and rail infrastructure is critical to overland shipping and economic development.

Infrastructure-based space launch would consolidate high-tech, high energy technologies into a single hub, rather than spread out across the transport fleet. This would massively decrease shipping costs into space by simplifying operations of the actual spacecraft itself and take advantage of operational economies of scale within the launch center.

Types of Launch Infrastructure

Beam-Thermal Rockets

Instead of being powered by an internal fusion reactor, beam-thermal spacecraft would have their energy sourced externally, by wireless power transmission such as microwaves or lasers.

Skyhooks

Skyhooks are long cables in orbit, rotating opposite to the direction of orbital motion, such that the ends are nearly stationary relative to the planetary surface when they are at the point closest to each other. This allows for small suborbital craft to dock with the skyhook tip and be carried into orbit.

Here is a Kurzgesagt video on the subject https://www.youtube.com/watch?v=dqwpQarrDwk

Electromagnetic Launch

A massive coilgun accelerating payloads to orbital velocities at close to 1 G over 1000s of kilometers of land, typically exiting at the peak of a mountain range.

Loftstrom Loops

A Loftstrom Loop is a rapidly moving looped belt being held up by its own momentum, supporting a massive bridge holding up an electromagnetic launch system above the atmosphere.

Orbital Rings

An Orbital Ring is created by extending a Loftstrom Loop to circle around the planet's circumference, rather than looping at two points on the surface.

Space Elevators

The classic Space Elevator, a cable capable of withstanding enormous tension (and not being cut) is tensioned between the planet and a counterweight (say, an asteroid). However, because the cable "orbits" the planet at the speed of planetary rotation, the elevator would have to dock at a geostationary orbit.

If a moon is tidally locked to its planet (e.g. Earth-Moon), a space elevator could be built out from the Moon its Lagrange Points, which also are locked in a similar manner.

And if two bodies are tidally locked to each other (Pluto, Charon), an elevator could perhaps be built between the two.

Answer 2

With sufficiently efficient drives, think of the landscape.

Launching a chemical-propellant into Earth orbit is so difficult that torching the launch pad is among the least of your concerns. Just think of the stages that get dropped along the way ...

With a hyper-efficient drive, you can afford to worry about the blast effect, and you also need to worry about it more. Larry Niven called this the Kzinti lesson -- "a reaction drive's efficiency as a weapon is in direct proportion to its efficiency as a drive." So instead of doing VTOL, and toasting the tarmac, do HOTOL and toast the air behind the spaceplane.

You could of course have both, with different roles and drawbacks, if your style includes technobabble.

"What was that?" The detective stared at the wrecked hangar.
"That is what happens when a spaceplane uses the engines in an enclosed space and not on the runway. The backblast got them, too. No survivors."

---

"600 meters."
"Stand by to expand the drive focus and increase flow on my mark."
"500 meters. ... 400 meter, sir, should we-"
"Mark." At the touch of the switch, the magnetic nozzle reconfigured and the stream of reaction mass became a torrent. Even so, the deceleration was reduced to 2 G. The cargo lander settled in a cloud of dust.

---

"Have you ever been down in a lander? A bit more, hmm, energetic than a passenger spaceplane."
"Not since I was in the Marines."

Answer 3

Unfortunately, this kind of ship can only do one thing, and that is launch things into orbit and bring them back.

Well... Hold up there Hoss.

See, when we look at real-world applications, especially in Heavy mining and Industry - we find a plethora of Vehicles that specialize in doing one thing and doing it excellently.

For a planetary scale shipping endeavor - the cost of building a number of highly specialized vehicles for ferrying cargo from the Ports/Terminus on the ground into a stable Orbit, where they can be loaded into interstellar vehicles is minimal compared to the revenue generated by such a large-scale application.

I would imagine that with the exception of certain specific cargos, the preferred method would involve the futuristic equivalent of a Shipping Container - e.g. a standardized unit for moving - so I'd expect to see Space Vehicles built around this.

Depending on your desire to invent Tech - my thoughts would be something like an Aircraft carrier catapult, possibly a Mass Driver type system. This would accelerate the launch vehicle on the ground with enough speed/energy to get into the thinner atmosphere where Rocket engines can work more efficiently.

This is to reduce the Fuel/Energy needed in that initial phase from being carried on the vehicle - Every kilo that isn't cargo that you need to shift into orbit is a Kilo that isn't profitable - and that initial phase is where you have the most atmospheric Drag - so offloading some of that requirement to an external device would be good.

Answer 4

a ship that does one thing, and only one thing: Get cargo from the surface into orbit, then bring cargo back, and repeat?

Cargo ship with rockets.

You made it easier for me because you called it in the OP.

Unfortunately, this kind of ship can only do one thing, and that is launch things into orbit and bring them back.

Thats what it does. No fru-fru. Other ships take care of all that. This is a heavy lift up, then fall back down and brake before break. Rinse. Repeat.

Answer 5

The answer is very obviously a spaceplane.

And not like the stuff you describe in your first paragraph. There will NOT be VTOL capabilities on the commercial ones. That's just unnecessarily added weight and complexity.

Air-breathing engines with bypass-thrust are simply magnitudes more efficient than any rocket-like contraption you could build, as long as there is air to breathe and move.

The wings also mean that you don't have to actively burn against gravity while accelerating for orbit (remember: Orbit isn't that far up, it's mainly going sideways fast).

We might see foldeable wings because on the way down you need much more rigid but smaller ones than going up, but there will be wings.

SpaceX doesn't need them because they just land empty rockets with pretty much zero weight. They're recovering their plane, 0 cargo. And having to carry up fuel just to slow down on the way back is an absolutely unnecessary cost factor.

Edit-Addition: Alternatively a two stage Virgin-Galactic kind of system could be in use. A Rocket consisting of mostly payload would be carried as high as possible and then launched the rest of the way into orbit. This would still mean that the expensive bit of rocketry (all the time spent at or near ground level and the forces necessary to escape from there) can be negated by proven-efficient plane technology. Even more stages including RAM- and SCRAMjets could also be thinkeable for increased efficiency.

Generally this system would not only be cheaper, but also have a higher cadence per infrastructure than a classical spaceport

Answer 6

Bulk Freighters will be Ovoid shaped.

When it comes to optimizing structural integrity with air resistance, the best shape is an ovoid (egg shaped). The forces involved in atmospheric acceleration and re-entry are significant, and the larger and heavier you get, the more integrity becomes the biggest issue you face. Making a long skinny rocket shaped ship will suffer more crush force over its smaller cross section as you get too big, a perfect sphere would have too much drag, and anything with sharp corners like a cube is less structurally sound under the heat and stress. Wings are especially fragile as you scale up in size and speed; so, while space planes are great for smaller loads (100 tons or so), they would be terrible for larger ships.

Container Ships

In real life, goods are typically transported either via bulk carrier for transporting massive volumes of unpackaged products or container ships for when you have lots of smaller parcels to deliver and distribute like consumer goods. Ovoids will of course be perfect for bulk carriers since things like grain, water, ore, fuel, etc. don't really care what shape they are in, but container ships will require a bit of extra engineering.

Shipping containers are cuboid for many reasons. They are ideal for putting smaller boxes into, they make good use of the space, and they are able to be directly loaded onto trucks for transporting the maximum amount of goods for distribution. So it is best not to mess with the cuboid shape of a shipping container, but it does lead to concerns about how tightly you can pack your cargo in a spheroid. For it's length, width, and height a spheroid has ~47.6% less internal volume than a cuboid. So, while cubes can't survive high delta-Vs or air breaking nearly as well as a sphere can, they may still be the ideal solution.

High Efficiency Fusion engines are crazy cheap to operate compared to traditional rockets, and are basically immune to the tyranny of rockets problem. Assuming Perfect Efficiency, each ton of cargo fired at traditional Delta-V only requires about 2 grams of hydrogen fuel. Let's say we consider "High Efficiency" to mean some fraction of perfect. Now we need to make up some exact number for what "High Efficiency" means... but I think most people will interpret this to mean some tangibly large fraction of the total energy. Conventional Rockets are about 70% efficient; so, let's go with that and say you need about 3g of fuel per ton. This means that the fuel cost per ton of launch weight is about /$0.003/ton if you are using hydrogen fuel. While some of you might be thinking that fusion will require much more expensive deuterium, tritium, or He3, current research into fusion technology predicts that heavy versions of hydrogen can be created as part of the nuclear process before we reach economic viability, much less high efficiency. So, plain old hydrogen is the most likely fuel source at this tech level.

The reason this is all so important is that it means you don't need over 4G of acceleration to get to space on a budget. A cuboid container ship will need to burn a lot more fuel and move a lot more slowly than an aerodynamic round ship, of similar mass, but the cost of getting to space will still be super cheap. Even if you burn 10x as much fuel going up at a modest 0.5G all the way. That still places your at only 3 cents per ton in fuel costs... now the extra weir and tear on your thrusters will likely be a lot more expensive than that, but the extra efficiency of stackable containers should still out weigh this fact.

For structural reasons, you will still want your ship to have a rounded bottom (plus you want them to be able to use the same ports as bulk carriers); so, the whole bottom will be the same as the other ships, but the top section can just be shipping containers bolter together in a more or less cylindrical pattern.

More cubic shaped designs will be oncourse be viable for smaller container ships.

Space Port Design

Space port design will work more or less like a normal modern rocket pad. But because you have "incredibly efficient catalyzed direct fusion drives", you can handle WAY bigger payloads using the same space port technology. The largest rockets used today weigh about 4000 tons with a 150 ton lift capacity, but with direct fusion drives your fuel efficiency is about 500,000 times better than Rocket fuel; so, a 4000 ton ship needs only needs about 11.4 to 100ish kg of fuel to reach orbit depending on if you are trying to maximize your delta-V or just make it as smooth of a ride as possible.

Furthermore, traditional rockets have a much smaller base section than these ships meaning that issues like distance to landing struts, sonic and thermal kick-back etc will be more spread out and less of a problem. In fact, height, and not total size is a much better gauge of how hard it is to make an appropriate launch platform; so, using the squattier designs like the ones shown above could easily be 10x the mass of a Saturn V Rocket, and not require any additional technology to make an appropriate launch-pad for. You just need to make it wider.

Furthermore you can overcome many of the things that make normal VLS rockets difficult. In a normal space rocket, your goal is to accelerate as fast as possible with as little complexity as possible because the more time you spend getting off the ground, the more total Gravity you have to overcome. This is especially complicated at take-off because that means your first stage rocket gets a lot of kickback both in terms of heat and sonic reflection. We currently solve for this by shooting up jets of water at the thruster as it takes off which absorbs the heat, boils, and then the bubbles absorb the sonic feedback. The other thing we do is limit initial takeoff accelerations to about 5m/s^2 (which is much lower acceleration than once it gets away from the pad). However, in a ship where fuel is less of an issue, you could limit takeoff acceleration to much slower (1m/s^2) reducing actual downward thrust and kickback at launch and landing time at the cost of using a bit more fuel. This means that you could go an additional 50% bigger (in all directions) and modern space pad technology would still get the job done.

This places the maximum mass of a heavy freighter somewhere in the 135,000 ton category when fully loaded... though I suspect something in the 40,000 ton weight class may be more common since throughout most of civilization, the majority of cargo ships seem to be about 1/3rd the mass of "top-end" ships because it makes building to tolerances much easier. Given this size, economy of scale, and figures taken from various sources, I'd estimate this as being 15-30% ship/fuel, and the remainder of the mass as cargo.

As for how expensive these space ports are... they are not really more expensive than a normal airport. Yes you need a large exclusion zone because of the power of the thrusters being so loud and hot, but because it is a VTOL design, you don't need long paved runways; so, a fairly small total facility in the middle of the desert or a small rocky peninsula would suffice.

That said, smaller versions of this design would not need specialized launch pads at all. 50 ton ICMBs can be launched directly from the back of a truck in the middle of a normal road; so, smaller ships with this wider profile (500 tons, maybe even bigger) could still be launched and landed safely from open fields or simple paved surfaces just like these 50 ton missiles. In all reality, your fusion engines should mostly make space planes obsolete since anything too big to VTOL will also be too big for wings. The biggest application I see for space planes will be where sustained in-atmosphere maneuverability and speed will be important or if fusions reactors simply need to be to big to work with smaller ships, and you need good old fashion chemical propulsion for smaller crafts... so, you'd probably still see them used for military purposes where you need aircraft that can perform both air and space missions and/or for non-bulk purposes.

Do you really need ships that can carry 100,000 tons?

... the transported cargo (up to space) would mostly be small, extremely refined goods like microprocessors, cryogenically-packed fruit and vegetables, and other goods only unique to earth. The vast majority of freight stays orbital, or dropped down the gravity well on single-use, dirt-cheap reentry capsules.

Because you have such cheap fuel, it is actually better to not do this. Fusion engines and reactors are very expensive and hard to make... but a few kg of hydrogen is very cheap. In fact the total fuel cost of launching 100,000 tons of cargo into space would be between about /$400-4000 in today's economy. In terms of shipping, that is dirt cheap. You could potentially run hundreds of missions with a reusable heavy freighter for less cost than it would take to build 1 single use rig.

This means that you want to have a 2-way freighter designed to go both ways and be reused over and over again. This is very different then modern rockets where the fuel is really expensive and the rocket is by comparison cheap. Even if your return trip back to space is only carrying a few tons of processed good, for every 100,000 tons you are bringing down here, it's still worth it. Being able to send your fusion engine assembly back up into orbit is already a necessary cost, so might as well use the ships you've already got... not to mention, manufacturing and refining on Earth will be much cheaper; so, most if not all ships, ship parts, and fuel production will need to be done planet side anyway.

Answer 7

Use both for different applications

what you are describing is a type of spacecraft I'd like to call a shuttle, an SSTO spacecraft designed to move cargo and people in and out of a gravity well.

I'd use a VTOL spaceplane design for an atmospheric passenger shuttle, as aircraft tend to not apply a lot of G-force on passengers that may not be used to high G's. these would probably require specialized landing pads and an atmosphere to function.

Rocket SSTO shuttles could be used for ferrying large amounts of cargo and on bodies with no atmosphere (such as Earth's moon). these just shoot the cargo containers (or people) out into orbit for a swift 15-minute accent, but at the cost of extremely high g's, so only ai pilots or human pilots that have trained their bodies to survive the accent. they may also be able to land on most solid surfaces and be over all less complex than VTOL Space planes, so they would be a good choice for early colonization of planets.

VTOL Spaceplanes and SSTO Rockets aren't the only methods to shuttle things on and off worlds, a disposable space crane could be a cheap alternative to these systems, at the price of reusability and carrying capacity. Probably only good for getting cargo to the surface of a body.

Other uses for these craft types besides surface-to-orbit transfer:

• A space plane could dive into an atmosphere, travel along a straight line, scout out the planet, do some quick atmospheric science and ascend up out of the atmosphere
• short-range orbit-to-orbit transit in a rocket SSTO (I.E from Earth to luna or between the moons of a gas giant)
• any shuttlecraft type could be used as a lifeboat in case of emergency, so long as you can stuff it full of crew (see s1 ep 1&2 of the Expanse)
• as a bomb/missile (see s4, ep 10 of the Expanse)

Answer 8

Assuming no crazy sci-fi tech, like space elevator, I feel that Starship-like reusable rockets would be best. With fusion that you have mentioned, it would reduce risk of dealing with tons of fuel and oxidizer. And would allow for faster turnover. But it would be only for one-way trips from ground to orbit.

Similar system could be adopted for getting stuff from orbit to ground. A container would be attached to a "descend module". This would be a heat shield with a landing parachute or rockets. A booster would then be attached, which would deaccelerate the module, so it starts air-breaking. The booster would detach before that and boost back up into orbit to be reused.

The main issue with the above system is that it is not kind to the cargo. Both Gs and shaking puts limits on what kind of cargo and people can be carried. With fragile cargo, you risk breaking it. And most people would find it uncomfortable or even dangerous to travel like that.

If you want to be more kind to your cargo, you would definitely need a shuttle-like aircraft. It would be strongly aerodynamic and need two types of engines. One to get off the ground and into air and sufficient height. Then, it would use the fusion engines to slowly accelerate into orbit. It is the return trip that is the difficult part. The design would need to avoid air-braking to reduce stress on people and cargo. This would result in "weird" design where the engines would also face forward. This is to reduce the aerodynamic drag when going through upper atmosphere, while also being able to slow down slowly and gradually.

Answer 9

Use single use re-entry vehicles

This answer will probably not make you happy, but you may find solace in it being much more grounded in current tech.

As described by Tsiolkovsky rocket equation any rocket-like vehicle will be inherently limited in the amount of weight it can transport so it is best to avoid it entirely. Instead of lifting materials from planets, I suggest that most materials and products would be manufactured in spaces and dropped on planets with single use vehicles. If raw materials were shipped from orbit to ground, the eartbound vehicle could be extremely simple as a large chunk of homogeneous material is likely very resilient.

The empire state could conceivably use VTOLs for passengers, critical supplies, VIPs, secret documents and such, so there shouldn't be a lack of coolness. However with very large volume of product landing earthside with parachutes.

This answer does not take into consideration space elevators / coil guns of any sort.

Answer 10

I would like to suggest Skylon for transporting people and their hand luggage.

Most stuff you have taken into space is probably more valuable in space because you have put the effort into lifting it. If most of the weight is coming down some other way, then the transporter for the remainder will be very plane-like.

Answer 11

Spinlaunch plus skyhooks

Spinlauch is a great system if you don't have to take squishy humans along. It is made to move cargo. It works even better if it only has to reach lower orbits at an angle. Combine it with skyhooks and you can scalable fuel minimizing launch system. Fusion gets you energy not fuel, you still need to minimize fuel to keep your rocket equation economical.

Spinlaunch gets most of its impulse from a ground based powerplant, with only a small fuel component (even less if it only has to reach low orbit). It is a high G delivery system, horrible for living things, great for cargo. Essentially spin a counterbalanced system up to high speed in a low pressure environment then throw the rocket most of the way with only a small rocket component. You can see a great breakdown of how it works here.

skyhooks do one thing catch things in lower orbit and move them to higher orbit or vice versa for virtually no fuel. With high turnover cargo as long as you have roughly the same mass going down on average as going up, it works for practically free. Unlike space elevators you could build one today. Better yet it gets cheaper to run the more you use it since it gets its energy mostly from its cargo. for some great idea try the Kurzgesagt video on the subject to see just how far you can take tethers just using existing materials.

Combine both technology and you have a system that can move non-fragile cargo very cheaply. Nothing you describe is fragile to these kinds of G-forces.

Answer 12

There are plenty of excellent ideas for this that have already been said, but I have an idea of my own. A variable-wing spaceplane could fill this task nicely. It could take off with its wings folded (Since your universe powerful engines, this shouldn't cause a lift problem. Anything with a powerful enough engine can fly.) to reduce drag. It could then dock with an orbiting freight station, transfer its cargo, undock, and reenter the atmosphere. It would unfold its wings to slow itself down, and glide like the space shuttle for landing.