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Meet the Auora, a new advanced space craft that was made in secret development 2 months ago. Now, Andrew the Astronaut Industries is happy to present it download link: https://kerbalx.com/Andrew_the_Astronaut/Auora -Andrew the Astronaut industries PR team manager

Hello, I've been thinking a bit on what I think could be a good mission that can be carried out with mostly existing or near-future equipment. While I think it's at least the basis for a solid mission, I'm short on some details, including some of the necessary physics. Overall mission description: study the effect of simulated low gravity (between microgravity and full Earth gravity) on astronauts and potential Moon/Mars equipment using a rotating pair of spacecraft attached by tethers. This, I suspect, will be a much lower-mass option than a true centrifuge module. Custom equipment necessary: counterweight module, habitat and service module, tethers. Near-future equipment requested: Commercial crew delivery program spacecraft (CST-100 Starliner, Crew Dragon). Backup in Soyuz. Possibly near-future heavy launch vehicles. Orbit: LEO? Must be at sufficient altitude that, if the tether gets cut at the unluckiest possible moment, habitat section perigee is still in LEO. Launches Necessary: Launch 1: Tether counterweight. Can optionally be replaced by a copy of the other sections, at obvious increase in cost. Launch 2: Habitat/Service Module. Will rendezvous and latch to tether counterweight. Rotation will not be initiated at this point. Will have 3-4 docking ports in addition to the counterweight latch. Launch 3: Cargo spacecraft: Cygnus, Dragon, Dream Chaser. Will dock to habitat, containing consumables, scientific equipment, and miscellaneous supplies. Launch 4: Crewed spacecraft: CST-100 Starliner, Crew Dragon, Soyuz. Contents: biological payload astronauts to conduct the mission. Will dock to the habitat. Launch On Demand: Rescue spacecraft, probably the same as the crewed spacecraft. Hopefully unnecessary. Upon docking to the assembly, the crew will first verify functionality of the habitat, then verify good docking and contents of the cargo spacecraft. If necessary, supplies can be transferred by EVA. Once the habitat-cargo-crew assembly is verified, the counterweight and habitat will tether to each other. My guess is the physical tethers would be on the counterweight module (which is otherwise dead mass). An EVA will be conducted to verify tether attachment, with any malfunctioning tethers either replaced or fixed by the astronaut(s) on EVA. Only once all this is verified will the counterweight and habitat separate to mission distance and begin rotation. Crew will likely be in the crew vehicle and in flight suits for an abundance of caution. Propellant for the separation and rotation can be carried on the counterweight, which again will mostly just be dead mass. Next: Science! Upon exhaustion of the crew transfer vehicle's endurance or the cargo vessel's supplies, rotation will be stopped, tethers withdrawn, and crew will return to Earth. Re-use of the mission would probably require another cargo spacecraft, another crewed spacecraft, and another LOD rescue spacecraft prepared. In event of habitat depressurization or other failure, crew will evacuate to the spacecraft and return to Earth. In event that cargo vehicle failure is only detected at mission start, either crew can return to Earth, or a readied cargo spacecraft can be sent. In event that the crew transfer vehicle fails, that's what the Launch On Demand spacecraft is for. In event of unplanned tether separation, crew is to very quickly return to the spacecraft and return to Earth. Simulated gravity will probably be pegged at lunar gravity (0.17G) initially, though the station should be designed for up to 0.5G (in excess of 0.38G Mars gravity), and down to... 0.05G? Maybe? If we use a 200 meter tether, and I didn't mess up the math, that would mean a range of linear velocities from 7 m/sec to 22.15 m/sec, with rotation rates of 4 degrees/second to 12.7 degrees/second. Assuming our tether is made out of Kevlar, each side of the tether is 50000 kg (probably an overestimate), the tethers have 4x the necessary tensile strength, and I still didn't screw up the math, we would need about 160 kg worth of tether material, with a total cross-sectional area of 5.4 cm2. If the rotation rate is too fast, tether mass goes up linearly with tether length, while rotation rate to maintain simulated gravity goes up proportional to the (-1/2) power. Launch vehicles: Counterweight and Habitat: ???. The mass and volume of these, I am really uncertain on, other than a suspicion they would require a heavy lift vehicle: Falcon Heavy, Delta IV Heavy, New Glenn, Proton, or Ariane 5. The counterweight's volume is small (mostly ballast), so it should fit in the existing Falcon 9/Heavy fairing, although a custom payload fairing adapter may be required. The habitat and service is likely to be larger in volume, particularly if a rigid habitat is chosen; I find it unlikely this would fly on the volume-limited Falcon 9/Heavy. Cargo spacecraft: I'm going to mix it up and suggest Cygnus launch on F9 and Dragon on Antares. I'm sure Orbital ATK and SpaceX would be very happy with this arrangement. Crewed spacecraft: Pairs exist for all of these. Atlas V 552 for CST-100 Starliner, Falcon 9 for Crew Dragon, Soyuz for Soyuz. One other element that I've kept in mind: the current commercial crew transport services are designed for the ISS, but the ISS is an aging station, and I have no confidence whatsoever that it will be promptly replaced, leaving us with crewed spacecraft and nowhere to send them. This would be a mission utilizing mostly either existing hardware or near-future hardware to fill in a gap in knowledge that cannot be practically addressed aboard the current ISS. EDIT: Naturally, I only think of a significant problem after I post: I'm not sure modern docking ports are designed to survive 0.05g accelerations, nevermind 0.5g! Crew and cargo spacecraft may have to dock at the center of the tether at a special non-rotating attachment point, and that ruins the nice contingency plan of "if the hab fails, just board the spacecraft!".