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In Germany, there is a very well known sci-fi novel series in which some of the spaceships are spheres with a toroidal bulge around the equator in which the (downward pointing) engines are situated.

Assuming the spacecraft are used for flights inside the solar system including starting and landing on Earth and other planets and moons of the solar system (where this is reasonably possible), would such a spherical form with an equatorial ring of propulsion engines be a viable alternative to the needle-like rockets of today (in reality, not in science-fiction)?

At least it should be much easier to land such a spacecraft. Also, the payload space could be designed more generously. Of course, the more energy can be provided from the power source of the propulsion engine, the easier it should possibly be to change to a spherical form with higher air resistance than the current needle like forms. So another question is: Can a chemical energy powered spacecraft be built (and used, of course) in spherical form and if not would fission power suffice, or if not, then fusion energy power?

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  • $\begingroup$ Related: space.stackexchange.com/q/13495/8693 $\endgroup$ – Hohmannfan Apr 10 '16 at 20:41
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    $\begingroup$ Basic issue: What's the ISp of these engines? If it's something approaching $c \over {g_0}$ with >1 TWR, then you need not worry; climb to orbital altitude vertically, at a reasonable (even subsonic) speed, then begin the orbital dance from near standstill. If it's something comparable to our current achievements - maybe a couple thousands seconds - the losses due to nonoptimal ascent trajectory are unacceptable. $\endgroup$ – SF. Apr 25 '16 at 4:13
  • $\begingroup$ Also related: space.stackexchange.com/questions/10332/… $\endgroup$ – Digital Trauma Jun 7 '17 at 22:51
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The shapes of rockets today are based on the fact that fuel mass (and fuel volume) dominate any current launch vehicle. Inefficiencies in reaching orbit mean non-linear losses in payload. An extra 0.1% drag could require burning 5% more fuel to compensate.

Long, thin rockets are much more efficient in the atmosphere, both from direct drag losses as well as weight penalties on a sufficiently strong structure. As long as we have to start on the surface of the earth with fuel mass limited machines, almost any other shape seems useless. Once you're out of the atmosphere though, you can choose shapes based on other constraints.

Fission and fusion power have the theoretical potential to be more efficient than today's chemical rockets. But that doesn't necessarily mean they would be suitable for a launch vehicle. Almost any work on these fuels today is for power generation, not for thrust. In a spacecraft, this gives you the means to drive efficient but low-thrust engines for a long period of time out of the atmosphere. But it doesn't give a way to more easily reach orbit.

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  • $\begingroup$ True but not entirely. It depends on use case. As a first stage, for example, it could work assuming the first stage was reusable. The size, at that point, starts to matter less, as does the fuel load, except as it relates to the rocket equation. The biggest problem is aero. otherwise, such a first stage could eliminate gimbals and fins etc, and rely entirely on differential thrust for vectoring, since there is no preferred direction. $\endgroup$ – T. B. Jan 30 '18 at 23:05
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Spherical chemical-energy powered spacecraft can be built. I know this because they have been (at least roughly spherical). To wit, the Soyuz orbital module (seen here at the Energia Museum).

enter image description here

and Vostok enter image description here

As far as spherical boosters, none have been built to my knowledge. The drag penalty would be prohibitive. However, there was a serious proposal by Chrysler in the Space Shuttle Phase A design studies to build a squatty booster that approaches the spherical as closely as anything I know of.

enter image description here

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  • $\begingroup$ You are right about the spherical form of the Sojus, but it would not qualify as a spaceship or spacecraft in the sense of my question, as it could not start on its own but needed a classical rocket. Perhaps I was not fully clear about this in my question, but what I meant is a spherical replacement for a rocket like the SpaceX rocket which lands in total after flight, can be refueled and started again. $\endgroup$ – Jürgen Böhm Apr 10 '16 at 20:51
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    $\begingroup$ Ah, to those of us in the business, a "spacecraft" is different from a "booster". Sounds like you are asking about a booster. $\endgroup$ – Organic Marble Apr 10 '16 at 21:04
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    $\begingroup$ @OrganicMarble Actually, it sounds more like he's talking about a single stage craft. $\endgroup$ – called2voyage Jul 11 '16 at 18:09
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With respect to an equatorial ring of propulsion engines, realistic spacecraft cannot afford redundant mass.

Every extra gram of engine mass means many more grams of propellant must be carried due to the tyranny of the rocket equation. Since NASA does not have access to Arkonide Impuls engines, NASA spacecraft have one engine, or one engine cluster aimed in a single direction.

The spacecraft uses its reaction control system to change its orientation and thus the direction its engine is pointed at rather than the STARDUST class solution of having multiple engines pointed in all directions.

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With current technology, spherical spacecraft are non-practical for two reasons:

  1. Heat dissipation. A true (in your sense) spacecraft, AKA a Dropship would have to dssipate loads of heat into space in order not to fry its crew. This requires huge radiators, so the form would more look like a shuttlecock.
  2. Radiation exposure. If you put your power source in the middle of your space craft, you expose all parts of it equally to the deadly radiation. Since you need a form of nuclear propulsion for any reasonably advanced spacecraft design that renders a spherical craft impractical. The reactor needs to be as far as possible from the crew and shielded by as much mass as possible.

The bottomline is: You might end up with a spherical head section (living quarters, command and control etc.) but the whole spacecraft will look quite different from your typical STARDUST class ship.

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Sphere

Needs to figure out, what spherical shape good for.
Atmosphere landing - not so good, but less surface to cool, bigger volume for coolant, less material(mass) of craft, ability to rotate surface for even heat distribution, there is something to think about.
One of good things is: Maximum volume with minimum surface(and mass as result).

First of all, you have to need that volume, for some reason.
Less surface, means less mass of construction, which is always good for spaceship, if it uses reactive propulsion. And this is pretty universal reason to have spherical form, but how much it affects on decision of choose spherical form, depends on: our goals, needs, which possibility's we have to implement our wishes, etc.

So talking about form, prior to define all of that, is bad idea.

Spherical form is good for space and space ship, not so good for landing on Earth or planets with atmosphere.
Let assume we have plenty activities to do in space.

Good

  1. Less surface
    • less craft mass
    • less surface repairs
    • less material for radiation protection.
  2. Spherical form
    • there no defined axis of symmetry (indefinite numbers of them). It means no preferred direction for micrometeorites to hit from, all directions kinda equal, in therms of impact results. That good in case if there no preferred direction for them to come from, if they intended to destroy ship. Projection is same from different angles.
    • less inertia momentum, good for maneuvers
  3. Volume
    • recreation
    • industry
    • ship repair capability (may place all needed equipment, just in case, and use if needed)
    • volume to place reactors or energy sources, shields if needed.
    • food production
    • waste utilization
    • size of crew personal volume
    • artificial gravity (cylinder is better though, less tech needed)
    • more equipment for mission, which may be used at arrival.
  4. Propulsion system + Spherical form + maneuvering
    Main propulsion system may be attached on surface of that sphere and may be movable. It means that we don't need to have extra engines to maneuver and no need to spend much energy or reactive mass to fight inertia momentum of the main part of the ship. Which may be big, huge, in case if it transports much hydrogen, for mars terraforming(as example)

Construction
You may or may not to be able build ship in space.
If not, if you can't, there is not much to choose. Almost everything depends on your capabilities to carry payload to orbit. You fit that construction to satisfy payload requirements. Is that BEAM or anything else.

If you can build construction in space, there is not much difference between cube, sphere, cylinder. In therms of building, at least.

Heat dissipation One thing people constantly mention, and usually they mention it as stop factor, without defining some circumstances, which are important in that topic.
$$ \frac{Radiative Power}{Surface Area}=j=\sigma T^{4} $$ $$ \sigma=\frac{2\pi^5 k^4}{15c^2h^3}= 5.670373 \times 10^{-8}\, \mathrm{W\, m^{-2}K^{-4}} $$ $T=100K, j \approx 5.7W/m^2$
$T=200K, j \approx 91W/m^2$ ISS uses NH3, near freezing for it, with normal pressure
$T=240K, j \approx 188W/m^2$ ISS NH3 boiling point, with normal pressure
$T=300K, j \approx 460W/m^2$ Kinda room temperature
$T=336K, j \approx 726W/m^2$ Temperature of thin sheet heated by Sun on earth orbit $T=400K, j \approx 1452W/m^2$ Something thick with low heat conductivity, surface temperature
$T=823K, j \approx 26014W/m^2$ 550 Celsius, Steam in steam turbines $T=1273K, j \approx 149kW/m^2$ 1000 Celsius
$T=1773K, j \approx 560kW/m^2$ 1500 Celsius, Some cobalt based cutting tools work even that hot

It is Very important to understand what $T^4$ means, to have grasp how fast it grows, it makes big difference in efficiency.

It is also important, how energy is generated. Because of $T^4$ it is even more important then heat dissipation in space.
As example if solar will work, when all it part are at temperature 400K (is doable) then using that energy, you pretty easy may have $823K, 26014W/m^2$ dissipation from surface of the ship.

Living volume as heat source
Let say there is 50kW heat sources per capita, volume 1000 $m^3$ per capita(food growing, living rooms, storages, service rooms etc), and heat dissipation $5kW/m^2$ (ca 270 Celsius ship surface temperature, not big problem, if there is energy), with 50% efficiency of cooling system - this ship may be 250 meters in diameter.
10 by 10 by 10 meters minus all service etc stuff - not to much room to live, not so pleasant.
Same as above and 10000 $m^3$ per capita - ship may be 2500 meters in diameter.
In such cases there will be equilibrium between Radiative heat dissipation and needs in that dissipation.(less diameter and it will loose heat faster then it is generated)

So ship may be pretty big.
If that ship have to transport some goods, resources etc - living volume would be fraction of it's volume, so even ISS approach may work well, just using surface of ship.

Engines as heat source
Depends on engines, on their efficiency. Current engines handle that issue, and no reasons to think oppositely. Current engines are pretty efficient. But that is not much connected with ship shape. Good thing there is no need to place there engines inside ship, with spherical ship it even better to be outside.

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protected by Community Jan 10 '18 at 15:39

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