So what type of shapes could a top mount reusable vehicle look like with a large payload bay?
A lot like the Liberty crew vehicle, except with a sealed bay rather than a vacuum-exposed cargo rack. It probably would have had propulsive landing too.
I imagine it could have looked like a lot of things. It really –could- have looked like the Shuttle, with probably some cosmetic differences around the aft to it would correctly with the interstage from the S-II stage. Maybe more circular instead of more squarish like Shuttle and Buran.
Personally, as I have discussed previously in this thread, I would prefer a large reusable capsule rather than a winged orbiter. Basically, a Command module around the size of the Shuttle cabin, something along the lines of Big Gemini. So a large crew cabin for fairly long durations in LEO, with all the same facilities as the Shuttle, an airlock, a robotic arm, and even perhaps a small unpressurized cargo bay (for storing things like an MMU or some equipment to be used during EVA’s that you’d want to bring back down with you.). The capsule could have a pusher LAS system and land propulsively like Dragonrider, with parachute backup for ocean abort. It would really be a command module and service module all in one.
Behind it would be an expendable cargo carrier, similar to Direct’s SSPDM. The Big Capsule CSM would perform RCS and act as a tug, perhaps with some help from aft RCS thrusters on the SSPDM. Not sure if you’d need aft RCS thrusters or not to wrangle the SSPDM and cargo around. Be good to keep as much of that as possible on the CSM for reuse, and make the SSPDM as much just a simple static carrier frame as possible.
If not landing propulsively, it could land with a soft wing and skids like Gemini was intended to. The whole capsule would be fully reusable, with a metallic TPS or PICA heat shield. As the heat shield would be so large like on a winged space plane, the heavier metallic could be an option. Could even do tiles similar to Shuttle, as they’d be covered until reentry so no risk of damage during launch or in orbit.
You could also do something similar to that, with a small lifting body instead of the large capsule, but would function the same. Or perhaps even a very large lifting body. The Soviets seemed to think that was the way to go in that Astronautix article on Buran, and they thought the mass penalties for wings were too great:
“As far as the manned orbital vehicle itself, three different primary configurations were studied extensively, as well as a range of more radical proposals. The obvious choice was a straight aerodynamic copy of the US shuttle. The shuttle's form had been selected by NASA and the US Air Force only after painstaking iterative analysis of over 64 alternate configurations from 1968 to 1972. It would obviously benefit the Soviet engineers to take advantage of this tremendous amount of work.
However the NPO Energia specialists who had developed the Soyuz capsule disapproved of the winged US shuttle design. They knew from the extensive aerodynamic studies undertaken to develop Soyuz that there were large weight penalties and thermal control problems in any winged design. Their studies indicated that a lifting body shape capable of high angles of bank at hypersonic speed could nearly match winged designs in cross range. Therefore their preferred 1974 design was an unwinged spacecraft, consisting of a crew cabin in the forward conical section, a cylindrical payload section, and a final cylindrical section with the engines for maneuvering in orbit. This unwinged MTKVA would glide to the landing zone at low subsonic speed. The final landing maneuver would use parachutes for initial braking, followed by a soft vertical landing on skid gear using retrorockets. After a great deal of detailed analysis the definitive MTKVA design proposed in May 1976 had a refined aerodynamic shape with a rounded triangular cross section. The 200 metric ton vehicle had over twice the shuttle's mass and nearly three times the shuttle's payload.
The third configuration was a smaller spaceplane launched by a Proton-class booster. OKB MiG had been developing the Spiral lifting body spaceplane since 1965, but the project was underfunded and years behind schedule. Spiral was an ambitious concept that was to be launched by a hypersonic air breathing first stage. But the spaceplane itself had been refined in form as a result of years of analysis, wind tunnel, and sub-orbital sub-scale model tests. Chelomei's OKB, whose Raketoplan spaceplane had been cancelled in 1965 in preference to Spiral, also had a contender, the LKS. Evidently owing nothing to earlier Raketoplan designs, this used a shuttle-type wing on a smaller 20 metric ton spacecraft.”
But it sounds like the main reason they went with a copy of the Shuttle, was to maximize all of the research we’d already done, rather than have to do the research themselves.
“The specification of the TTZ set forth payload requirements a bit greater than those set for the US shuttle. It required that the OK orbiter be accomplish the following:
• Denial of the use of space for military purposes by the enemy
• Research into questions of interest to the military, science, and the national economy
• Applied military research and experiments using large space complexes
• Delivery to orbit and return to earth of spacecraft, cosmonauts, and supplies
• Delivery of 30 metric ton payload to a 200 km, 50.7 degree inclination orbit, followed by seven days of orbital operations and return of 20 metric tons of payload to earth.
• Exploit the technology developed for the American space shuttle in order to enhance Soviet space technology capability
The MTKVA and Vulkan were used as a starting point, but modified to meet this requirement. Study of the competing designs indicated that despite the evident advantages of the MTKVA approach, there were serious technical and operational problems with that design. There was considerable technical risk in realizing the vertical landing itself - and considerable operational risk in completing the fast and complex series of operations necessary to achieve the landing. There were also problems in ground handling - how to move the vehicle after it had landed, especially if this occurred outside of the normal landing zone. The final analysis of the problems indicated that the rational solution was an orbiter of the aircraft type. There was severe criticism of the decision to copy the space shuttle configuration. But earlier studies had considered numerous types of aircraft layouts, vertical takeoff designs, and ground- and sea- launched variants. The NPO Energia engineers could not find any configuration that was objectively better. This only validated the tremendous amount of work done in the US in refining the design. There was no point in picking a different inferior solution just because it was original.
Therefore a straight aerodynamic copy of the US space shuttle, was selected as the orbiter configuration on 11 June 1976.”
So, I’m not sure. Perhaps for a vehicle of it’s size and required payload capacity, something like the Shuttle and Buran was the logical choice. I think the side mount config on the booster was also copied, but obviously they thought putting it on top of the booster would be better. And I agree with that. I believe the reason for Shuttle side mount was because they wanted the hydrolox engines on the shuttle so they could be reused, so you can’t put it on top and do that obviously. Since the Soviets weren’t trying to reuse the hydrolox engines, there really wasn’t much reason Buran had to be on the side. Unless the horizontal transportation of the stack to the pad played some role in that. But Since our Shuttle would be stacked and transported vertically as Satrun V was, that wouldn’t have been an issue for us.
I wonder how much the cost of five new J2S engines per flight to be expended on the S-II vs. the per flight costs of manufacture and refurbishment of the SSME’s would come out? But I feel pretty sure cost wise, reusing the SSME’s would be on par or more expensive than mass produced J2S’s, that would have been rolling off the production line at a rate of 15 to 40 of them per year (3-6 launches per year was typical rate for STS, with up to 8 launches per year at times, so 40 J2S engines those years). We might have seen some Merlin 1 like economics of scale start to manifest after a few years of that rate. Plus it would have invited streamlining and automation in production for more savings as time went on. As I understand, the SSME was labor intensive because of their low production rate, and there was never any incentive to streamline and automate their production because of that low rate. Too hard to recoup the investment. But at up to 40 engines being produced a year? Certainly there would have been.