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NameUnavail t1_j5ktpvf wrote

There's three major advantages to having the engines in the back:

  1. The Engine truss provides a convenient structural carrying element for stacking stages, since the engines need to a structural truss to attach too anyway.

  2. Because acceleration from the engine causes the fuel to pool at the rear end of the tank, the fuel outlet has to be there. Engines in the back means both less head required for the turbopumps, since they are aided by the acceleration of the vehicle, rather than having to suck fuel against it. For the same reasom they'd also be much less prone to fuel cavitation. And lastly the engines being close to the fuel outlet obviously means significantly shorter feed lines.

  3. Not blasting hot exhaust gases past/against your big tank of explosive fuels.

All 3 points are most crucial for chemical high thrust engines. For things like ion drives they are less relevant.

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[deleted] OP t1_j5kuju0 wrote

[deleted]

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The_Godless_Author t1_j5kv02f wrote

Yea, a trailing design would necessitate that the engines be slightly angled away so the payload wouldn’t be in the firing line, but I’ve heard arguments that it would be easier to make due to being tensile rather than rigid in nature and so having better resistance to g force. I’ve also heard the argument that you could just extend the tether to save mass on shielding by just increasing the distance between the modules and the engines

Also, wouldn’t the effectiveness of a solar sail decrease as you get further away from a star?

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space-ModTeam t1_j5kx787 wrote

Hello u/The_Godless_Author, your submission "Spacecraft design" has been removed from r/space because:

  • Such questions should be asked in the "All space questions" thread stickied at the top of the sub.

Please read the rules in the sidebar and check r/space for duplicate submissions before posting. If you have any questions about this removal please message the r/space moderators. Thank you.

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Usernamenotta t1_j5kx9pe wrote

You do not want thrusters at the front because you might have something similar to the Coanda effect, where the flow of gasses will tend to stick to the surface of the material due to superficial tension. This means the surface of the ship is going to be constantly battered.

If you wanted, I guess you could go for a 'Hammerhead' design, where the thrusters are at the front, but placed at a certain distance from the fuselage. This however increases the construction costs and the overall mass of the craft.

Such designs do however present the advantage of having the motor force at the front, which creates a bit more stability. But the much larger cross-section and mass might offset this advantage

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