Since a lot more freight would have to be hauled to Mars than people. In space could be done by SEP tugs on a continuous bases. LEO to LMO via one or more SEP tugs. A specialty lander for use on Mars could indeed take freight from LMO to the surface. The lander could have ISRU equipment/solar panels to manufacture it's fuel from Martian atmosphere when not in use or there could be a separate fuel farm nearby. Once refueled, it could go pick up another load. Humans could travel at a much faster rate with the MCT. This plan would require the BFR.It would require a reusable second stage.It would require a fleet of large SEP tugs.A cargo carrier that can be transferred from the second stage to the SEP tug.A re-usable lander at Mars.A fuel farm at Mars or a lander large enough to have it's on ISRU equipment. An MCT that could be refueled in LEO and fly to Mars. It might not need to land on Mars, just transfer the human habitation module to the lander. MCT would fly back to earth. Lander would take people to Mars surface. The habitation module could be or would be about the same size as a cargo module. This plan might be cheaper to operate overall, but would require a lot of building and development of specialty components. It would also require a lot of in space dockings and transfers. However, these specialty components could be built by other companies or countries to have a stake in the colonialization process. On the other hand, if everything Musk wants to build is big, then It might be more simple to go directly from Earth to Mars will a couple of refueling stops for both humans and cargo an have contributors supply fuel or Martian surface cargo to have a stake in colonialization.
The lander could have ISRU equipment/solar panels to manufacture it's fuel from Martian atmosphere when not in use or there could be a separate fuel farm nearby. Once refueled, it could go pick up another load.
Cargo or freight on the other hand might travel a different way.
I'm one of those who in this thread adheres to Musk quotes like "land the whole thing" for the purpose of coherent speculation. However I'll bet that most here agree that SX's concepts for MCT have likely evolved considerably from the few sometimes off the cuff statements by Elon, many several years old. I'll state further that I believe it probable the MCT that actually flies will again have notable differences from the MCT concept that Musk reveals later this year, if he even meets that schedule.
Impaler, Lars-J, spacenut, etc.,I wonder if the following might be an 'evolutionary' path that SpaceX might pursue: Have an MCT that initially is used for all phases of the mission (launched to Earth orbit via BFR, is refueled there, launches to Mars, lands, drops off cargo and some/most crew, is refueled via ISRU, launches and does a direct return to Earth, lands on Earth). This MCT would not ever transport 100 passengers, much less 100 passengers plus their cargo. Instead it would be used for all expeditionary missions - those used to perform discovery (find easily accessible water sources), setup habitation and other infrastructure (IRSU, comms, modest chemical plants), prepare launch/landing sites, etc. This would proceed for several synods. Crew would be on the order of 5-15 people. Some staying, some rotating out.Meanwhile, the SEP interplanetary transporter is being assembled in LEO (or other staging area). When this is complete, and a sufficient number of expeditionary missions have transpired, the function of the MCT vehicles transforms: At Earth, they are used to shuttle colonists and their cargo from the surface to the SEP transporter. At Mars, they are used for the converse - they launch empty from the Mars surface, dock with the SEP transporter, offload passengers and cargo, and return to Mars surface. Each SEP transporter will in fact transport 100 (or more) passengers, plus their cargo.I think this minimizes the number of vehicles developed, stays consistent with SpaceX's reusability ethos, and is mostly consistent with all of the statements thus far ("land the whole thing", "100 passengers at a time", "we're looking at everything, including SEP", etc.)Impaler, I know you doubt the technical feasibility of an MCT craft that could do all of the phases listed in the first paragraph, but if it only has to accommodate a max crew of, say, 12, does that change the outlook?
Quote from: GORDAP on 11/06/2015 09:13 pmImpaler, Lars-J, spacenut, etc.,I wonder if the following might be an 'evolutionary' path that SpaceX might pursue: Have an MCT that initially is used for all phases of the mission (launched to Earth orbit via BFR, is refueled there, launches to Mars, lands, drops off cargo and some/most crew, is refueled via ISRU, launches and does a direct return to Earth, lands on Earth). This MCT would not ever transport 100 passengers, much less 100 passengers plus their cargo. Instead it would be used for all expeditionary missions - those used to perform discovery (find easily accessible water sources), setup habitation and other infrastructure (IRSU, comms, modest chemical plants), prepare launch/landing sites, etc. This would proceed for several synods. Crew would be on the order of 5-15 people. Some staying, some rotating out.Meanwhile, the SEP interplanetary transporter is being assembled in LEO (or other staging area). When this is complete, and a sufficient number of expeditionary missions have transpired, the function of the MCT vehicles transforms: At Earth, they are used to shuttle colonists and their cargo from the surface to the SEP transporter. At Mars, they are used for the converse - they launch empty from the Mars surface, dock with the SEP transporter, offload passengers and cargo, and return to Mars surface. Each SEP transporter will in fact transport 100 (or more) passengers, plus their cargo.I think this minimizes the number of vehicles developed, stays consistent with SpaceX's reusability ethos, and is mostly consistent with all of the statements thus far ("land the whole thing", "100 passengers at a time", "we're looking at everything, including SEP", etc.)Impaler, I know you doubt the technical feasibility of an MCT craft that could do all of the phases listed in the first paragraph, but if it only has to accommodate a max crew of, say, 12, does that change the outlook?That is very nearly exactly what I have been saying, only with the MCT being slightly less capable. I think the MCT will be dependent on SEP tug assistance to do initial crew missions at an acceptable speed (for crew health/GCR issues), but may be able to do cargo missions on it's own.We have argued a lot about achievable DeltaV values, let me lay down some numbers that express the DeltaV achieved from full propellant loads with different amounts of cargo, 100 mT (the outbound cargo goal), 25 mT (the return cargo goal which would be some kind of habitat), and 0 mT (presumably the return from a cargo mission).100 mT Cargo + 300 mT propellant + 75 mT dry mass -> 3.7 km/s25 mT Cargo + 300 mT propellant + 75 mT dry mass -> 5.1 km/s0 mT Cargo + 300 mT propellant + 75 mT dry mass -> 6 km/sThese numbers are a lot lower then other people want to see but I think they are realistic and if intelligently combined an evolving set of missions can be created that serve both cargo and passenger missions. The empty 6 km/s allows direct Earth return on a hohmann transfer of an empty cargo mission, if the 100 mT cargo is ISRU equipment which deploys to the surface, pumps propellants into the MCT and then remains behind on launch, then a propellant farm is built up without abandoning any vehicles and the return capability is well validated before humans are sent. The 4.9 km/s assent with 25 mT cargo is enough to reach mars orbit AND have enough propellant for another decent with FULL cargo (800 m/s propulsion), this allows the vehicle to be a reusable tanker to mars orbit depositing 25 mT per trip of any desired mass, and to act as a rapid reusable downward cargo hauler AT THE SAME TIME. Also it means that the MCT fully fueled in mars orbit can do rapid transit back to Earth (150 day) though this would require 12 tanker-up/cargo-down flights to get the necessary propellants in orbit (with the first flight staying in orbit to act as a depot), but this is consistent with the expected 10:1 crew/cargo ratio. The very first exploration missions wouldn't have so many MCT's or propellants available and will refuel via SEP tugs sent to mars with propellants. Only once a high rate of propellant production is in place could this many MCT's be refueled and relaunched.This will also allow the unloading of cargo from an in-space-only freight vessel while simultaneously refilling that vessel with propellant for Earth return. These large freight vehicles would be a later addition to the system and would greatly increase the cargo delivery rate and it's efficiency, but are not necessary for the initial deployment as cargo can be sent in the MCT directly all be it with poor amortization.The 3.7 km/s when fully loaded allows the vehicle to make a fast transit to mars (150 day) from a high orbit (EML1 followed by lunar and Earth slingshot burns) while retaining enough propellants to land at mars. It would be placed in high orbit and sent propellants by a SEP tug in the 1 MW power range, if we were sending cargo by slow hohmann transfer then only 1/6th of the full propellant load (~50 mT) is needed at EML1 which may be low enough to just have it carried in the MCT from LEO eliminating propellant transfer for such cargo missions.It also makes the fully loaded MCT ideal for making the fast (3-5 day) transfer from LEO to EML1 to quickly ferry passengers when the numbers are great enough to make use of Dragon or other small taxi craft inconvenient. Being such a short transit the accommodations can be far more cramped then would be possible for the full transit and I expect some from of transit-hab will be employed. The MCT in question will likely be docked to and towed by the transit vehicle which would transfer the necessary landing propellants and passengers back to the MCT which would land and disembark the passengers at mars using the same short term accommodations.It is all an extremely elegant arrangement, at each cargo loading point the vehicle has sufficient DeltaV for the critical mission legs it would actually face at that point while dove-tailing well with force-multiplier vehicles that would be added later like SEP tugs.
Burninate: Terminal velocity at Mars is much, much lower than 1.5km/s for any reasonable ballistic coefficient and for any of the low altitude landing sites that are likely to be used. For Dragon-like ballistic coefficient of 300kg/m^2, you have about 350m/s terminal velocity. And terminal velocity is proportional to the square root of ballistic coefficient, so even if you think I'm wrong about ballistic coefficient, it won't make much difference.
That is from high speed direct entry and low L:D ratio, I am proposing just the opposite.
100 mT Cargo + 300 mT propellant + 75 mT dry mass -> 3.7 km/s25 mT Cargo + 300 mT propellant + 75 mT dry mass -> 5.1 km/s0 mT Cargo + 300 mT propellant + 75 mT dry mass -> 6 km/s
SEP is not a difficult technology and I propose HALL thrusters which SpaceX is going to produce for it's own satellite swarm, the Solar panels are likewise a well established technology, the only challenge is scale
I estimated all tanks and propellant lines at 5% of the propellant mass for a total of 15 mT,
and 6 mT of engines.
their are lots of other parasitic masses involved in such a vehicle, it is not just a big rocket stage with single digit dry mass fraction.
I really can't see SEP being used. [....]- the LV is already supposed to be too big for existing infrastructure, so the marginal cost of making it even larger may be relatively small
Quote from: Vultur on 11/10/2015 10:47 pmI really can't see SEP being used. [....]- the LV is already supposed to be too big for existing infrastructure, so the marginal cost of making it even larger may be relatively small I'm not seeing your reasoning here. I would think that transferring much of the TMI and TEI requirements onto a separate SEP vehicle would allow the MCT (demoted to a lander) to be smaller, not larger. Ditto its Earth launcher.
MCT would be a heck of a lot better propellant taxi and tanker if it had good mass fraction.
My objection is in creating/development an extra vehicle not the base technology itself needing development.It's well withi [EDIT: well within their capabilities, certainly.]
That seems high. IIRC FH side booster is more like a mass ratio of 30 (at least that's what's been quoted on this forum) and that includes engines, etc.
Assuming a TWR of 100:1 or better that seems reasonable
Certainly. It needs a heat shield, it needs landing legs and a cargo container, it needs better communication than a rocket stage so it can talk to Earth from Mars. But I don't think those will force them to limit the delta-v drastically. They'll just end up with a huge vehicle.(Passenger version needs a lot more stuff but that will come out of the cargo-version max capacity...)