Apollo was a large gamble anyway, that was always a few mm away from catastrophic failure during its flights.
This is a mith that I read several times; while it is true that the safety standards weren't those of today and the Apollo missions faced countless problems, "a few mm away from catastrophe" is a bit exaggerated statement regarding the Saturn V launches, IMHO.
That said... Soyuz has various staging events and still is the most reliable manned rocket in the world.
If Loru will chose to use real (existing) engines, realism will impose to chose a model that is actually air-startable or that can support this capability. Not trivial for an SSME-class engine.
Funnily, the J-2 engine failed only on the S-II stages and never on the S-IVB, I am not sure if this is really just luck or dark art.
If I recall correctly, the S-IVB engine on Apollo 6 performed poorly during the first burn and completely fails the in-orbit restart, forcing to use the Apollo SPS to raise the orbit.
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Is there any benefit to having the orbiter mounted low on the launch vehicle like STS? I know for STS it was logical because the main engines were in the orbiter and you didn't want them melting the ET, but for this vehicle (especially if you decide to implement a LES) wouldn't it be beneficial to have the orbiter placed higher up on the LV? Because then there's less chance of stuff falling onto it and damaging it.
The only thing I can think of is it would be a little harder to mount the orbiter, and the COG might be easier to work with if it's mounted lower, but then I don't know a whole lot about spaceplane operations, so.
With Eridanus we chose to place the orbiter higher for a series of safety and cosmetic reasons:
1) the crew compartment is above the tanks, not directly next to it (the nose cone of the rocket is basically empty space), that is safer in case of a major failure.
2) the LES has a wider free horizon in case of use.
3) the crew compartment isn't subject to the falling pieces of foam, eliminating the need of protecting it and thus requiring a somewhat smaller protection shield for the spaceplane during the launch.
4) the spaceplane is better placed during the final run, when the core stage is almost empty and the engines must gimbal even more to match the CoG that migrate laterally. Because our core stage is far smaller and lighter than Energia's one, placing the spaceplane in a Buran-like position would probably require a prohibitive gimbal for the rocket engines to match the CoG in the last seconds of thrust.
5) The stack looked different from STS and Energia-Buran.
Naturally that weird placement of Eridanus, in a real world would pose, I think, significant drawbacks as:
1) Far higher drag especially around the Max-Q
2) Problematic bending loads on the core stage, especially when the stack is on ramp awaiting tankage.