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Yet another Mars architecture. This time using equipment currently available. The problem with SpaceX is they want to send Starship on the first mission. That's one big rocket, requiring a hell of a lot of propellant to get to Mars. And a hell of a lot to get back. And issues landing on the surface, with unprepared ground. Etc, etc.
Simple solution: use Starship has a launch vehicle to deliver Mars Direct to LEO, then just MD. However, I want a bit more. Instead of return capsule being basically an Apollo capsule with 6 month zero-g return, I want something more substantial.
Parts: Mars Ascent Vehicle (MAV) instead of Earth Return Vehicle (ERV). The MAV designed to launch from Mars surface to Mars orbit, then act as the Trans-Earth Injection stage (TEI) to return to Earth. Using the MAV as the TEI stage allows ISPP for all return propellant. Since the MAV will only be occupied very briefly, one option is no life support, astronauts stay in spacesuits until they dock with the Interplanetary Transit Vehicle (ITV).
Habitat: basic tuna-can Mars Direct hab. 8.4 metre outside diameter, tiny cabins for crew, recycling life support for oxygen and water. Life support based on equipment demonstrated on the US side of ISS. However, the hab will have 1 deck. The lower deck will be rocket engines for landing on Mars, propellant tanks to feed landing rockets, RCS thrusters for transit from Earth to Mars, propellant tanks for RCS, solar panels, life support equipment, batteries (surface of Mars has night), airlock, stairway to upper deck, and storage chamber for a Mars rover. The storage chamber will be the size of a single-car garage, with a garage door that folds down to form a ramp. (To drive the vehicle out.) Also in the storage chamber will be surface science instruments, an inflatable greenhouse, soil trays and gardening equipment for the greenhouse. The inflatable greenhouse will be PCTFE film, with hold-down straps that tie to tent pegs. A separate pressure door from the landing at the base of the stairs to a polymer film tunnel to the greenhouse, with deployable staircase stored in the "garage" during transit. Once on Mars, everything in the "garage" will be deployed, never to come in again. This allows the "garage" to be used as a workshop, and a portion of it used for EVA prep once on Mars.
Once deployed, the greenhouse will be the width of a double-car garage, and twice as long. So 4 times the floor area of the "garage" on the lower deck of the hab.
Interplanetary Transit Vehicle (ITV). This is a name from the NASA Design Reference Mission aka Mars Semi-Direct. But it will work differently. The ITV will be sent with astronauts for out-bound transit. The stack will use rotation for artificial gravity during transit, using the spent upper stage as a counter-weight. Upon approach to Mars the cable will be cut, releasing the spent stage to fly off into space. The hab-ITV stack will de-spin, and aerocapture into Mars orbit. ITV will use a fabric heat shield made of Nextel-440, an artificial synthetic ceramic fibre that NASA has already identified as appropriate for a heat shield. The hab will use a carbon fibre fabric heat shield. NASA has been working on the carbon fibre heat shield since the 1980s, and this was included in the original Mars Direct: Adaptable Deployable Entry Placement Technology (ADEPT). The ITV itself will be one deck, designed for artificial gravity, and smaller than the hab. I'm thinking 6.6 metre outside diameter, the diameter the 3rd stage of Saturn V, and Skylab less it's pop-out micrometeorite shield. ITV would have recycling life support for return to Earth.
One advantage to this is the hab has food for transit to Mars and surface stay on Mars, while the ITV has food for transit back to Earth. In case of free return, astronauts will have access to all this food. They will also have access to ITV life support in case something goes wrong with the hab. And for out-bound transit, both the upper deck of the hab plus the ITV provides more living space.
Upon return to Earth, the MAV rendezvous with the ITV, and pushes it into a trans-Earth trajectory. Once in transit to Earth, the MAV is treated as a spent stage, used as counterweight for rotation. Again, connected via cable. Upon approach to Earth, the cable holding the MAV will be cut, allowing the MAV to fly off into space. The ITV will de-spin, prepare for aerocapture into Earth orbit. The ITV will use it's reusable fabric heat shield for aerocapture into Earth orbit. Then rendezvous with a space station (ISS), where it will dock and wait for the next mission to Mars. The ITV will be multi-mission.
As a safety feature, the MAV will have a Dragon capsule attached. Astronauts will load Mars samples into Dragon, and get into Dragon before aerocapture. If aerocapture into Earth orbit fails, then they will return via Dragon. Once docked to ISS, still use Dragon to return to Earth.
Launches:
Starship: MAV directly to Mars. With ISPP equipment.
Starship: hab to ISS, with landing propellant loaded, and TMI stage also loaded
Starship: ITV to ISS
Falcon 9: Dragon to ISS with crew
Second and subsequent missions will not have to lift the ITV, because it will be waiting at ISS.
We could get fancy and lift the hab with ITV for the first mission, and TMI stage on a separate launch. Second and subsequent missions would lift hab with TMI stage in one Starship launch.
If ISS is de-orbited by the time of the Mars mission, will there be a commercial space station where we can stage Mars missions?
Life support equipment was built by Hamilton Sundstrand. I would like to test it further on ISS before a Mars mission, but the idea is to use exactly the same equipment. Because it's proven in space. One test is to operate ISS with crew for the full duration of a Mars mission without any resupply from Earth.
I would prefer a robotic sample return mission to Mars to demonstrate ISPP before the first crew mission. Again, prove equipment. This would have to be designated a technology demonstrator to ensure nobody tries to remove ISPP this time.
For Mars Direct, the TMI stage was going to use a J-2 engine. In 1989/'90 that would have been J-2S, the updated version developed in 1979. In the early 2000s, J-2X was developed. However, manufacturing equipment for J-2X was sold off in September 2022, effectively cancelling this engine. An alternative is a pair of BE-3U engines, each with roughly half the thrust of J-2X, but also using liquid hydrogen/LOX. Manufactured by Blue Origin, used for the upper stage of New Glenn.
The MAV will require a liquid methane/LOX engine that can be throttled. Used for Mars ascent, and TEI.
Advantages over Mars Direct: food and life support for return are included in out-bound transit, so safer for free return. Additional risk: requires both a surface rendezvous and orbital rendezvous. However, orbital rendezvous has been done so many times for ISS that I do not consider that a risk. That is now a mature technology.
Also note: ballistic coefficient is an issue for larger entry vehicles. Surface area of heat shield increases as the square of diameter, but mass increases as a cube of diameter. So there's the problem that slowing sufficiently to deploy a parachute would descend too far into the atmosphere. Solution is something from Mars Direct: ADEPT. The carbon fibre fabric heat shield that opens like an umbrella. It increases surface area so the surface-to-mass ratio is the same as Curiosity rover or Perseverance rover. Parachutes will have to be larger, proportional to mass. But this is the same landing method. Instead of "sky crane" landing, the hab will land with built-in rocket engines like the Apollo LM. But instead of just one engine, it will have several smaller ones. The sky crane used several smaller ones. Viking landed with built-in rocket engines, and also used several smaller ones.
This would have to be a NASA mission instead of a purely commercial mission if we want to use a nuclear reactor for the MAV to produce return propellant. Access to nuclear technology is highly regulated. I would suggest using the SAFE-400 reactor. Mars Direct used the SP-100 reactor, because it was under development at that time. Mars Direct was first presented to NASA in June 1990, development of SP-100 was complete in 1992. SAFE-400 was developed by exactly the same team of engineers, produces exactly the same amount of electricity, but lower launch mass, and completed in 2007. So just use the new one.
Another option: instead of a robotic truck to carry the reactor to a crater away from the MAV, just attach the same wheels, drive motors, and navigation system as Curiosity rover, but attached directly to the reactor. This makes the reactor self-driving, and reduces launch mass, but means there's no robotic truck.
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Hmm. Starship fairing diameter is 9 metre, outside diameter. But inside is 8.00 metre. That means the hab must be reduced to 8.0 metre to fit. Starship specs say it could lift "up to" 150 metric tonnes to LEO, but that's 185km altitude. ISS orbits at 400km ±10km. What is Starship lift capacity to ISS? Would the TMI stage have to be launched separately? Again, this is assuming all Starship launches are fully reusable.
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Let's see. Shuttle could lift 28.8 tonnes to LEO or 16 tonnes to ISS. So can Starship lift 150/28.8*16= 83.3 t to ISS? Rendezvous and docking by onboard RCS thrusters on the hab. Dock at APAS or berth at CBM?
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Note one of the basic principles: Don't land your return vehicle on the planet!!! NASA tried to design Apollo to land the CSM on the surface of the Moon. That's why the main engine for the Service Module was so big. Problem was the stack was so heavy, even a Saturn V couldn't launch it. They tried splitting it into several stages, but that only works so far. They tried to design an even larger launch vehicle, and came up with a few proposals. While they were kicking around the idea of an even more giant rocket, one engineer from one American supplier recommended a "mother ship" left in lunar orbit, and a "Lunar Excursion Module" (LEM). The Command Module that North American was already developing was kept, and they shrunk the multi-stage landing and launch stack into the Service Module. The name for LEM was shortened to "Lunar Module" (LM) but still pronounced LEM.
My architecture leaves the return vehicle in Mars orbit, including the return capsule. So this is applying Apollo principles to Mars Direct.
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