Reloading a returned MCT with cargo is an issue. If modular, cargo could be transferred by BFR and a tug.Landing on Earth is not required for maintenance.The MCTs could be staged somewhere in cis-lunar space instead of LEO to reduce outgoing and return delta V requirements. Makes it more difficult to stage, but could be worth the effort.
Quote from: RonM on 10/09/2015 02:40 pmReloading a returned MCT with cargo is an issue. If modular, cargo could be transferred by BFR and a tug.Landing on Earth is not required for maintenance.The MCTs could be staged somewhere in cis-lunar space instead of LEO to reduce outgoing and return delta V requirements. Makes it more difficult to stage, but could be worth the effort.Why bring back the MCT to cis-lunar space or LEO if you do not land on Earth? Just keep it at Mars. Use it to shuttle cargo/personnel from Mars orbit to the surface.
Why doesn't SpaceX just build the MCT with a metholox plug nozzle engine and strap 8 Falcon 9's around it to launch it off earth? They already have the Falcon 9's.
But the point being, to say the the pieces being joined where they can separate in an emergency is "hideously complex" may be a tad over stated. ;-)
Quote from: Lobo on 10/09/2015 12:30 amBut the point being, to say the the pieces being joined where they can separate in an emergency is "hideously complex" may be a tad over stated. ;-)
I think that's a good point about the difference between NASA Mars and SpaceX Mars. NASA Mars is very much focused on rotation. SpaceX Mars is to create a colony. I doubt they would be short of customers who would be willing to spend some cash (probably affordable to a lot of people via selling their home) and up sticks and become a resident of Mars.....and not return (the element of increasing the population, as opposed to several years stays and coming back).
By the time people have payed off their home or have enough equity in their home to pay for the couple to move to Mars they would have already raised their kids. Not good to start a colony with people who have already raised their kids. More likely the first colonist will be sent there by sponsors.
I think the Separate Bi-conic is attractive in this regard because rocket stages are cheaper to develop per unit of dry weight then manned capsules which are very nearly the most expensive things in aerospace development,
I estimate a bi-conic would have a mass of around 75 mT, and the 2nd stage would be 72 mT. I expect the Integrated version would have a mass greater then 75 but probably less the the raw additive 150 of the two separate vehicles due to some savings on redundancies, but it will probably have a development cost that is per pound equal to the smaller bi-conic I'm looking at. This will wipe out the advantage of not developing a 2nd stage and makes the total cost greater unless the integrated vehicle has an exceedingly low mass or the cost ratio between stages/capsules is extremely low perhaps due to the difficulty of 2nd stage reuse engineering.I would really like to hear some exact mass number from Lobo about the whole vehicle stack, dry masses for the first stage, the integrated bi-conic dry mass (without abort systems if that's your preference) and propellant loads in each so I can plug them into the launch vehicle performance calculator I've been using http://www.silverbirdastronautics.com/LVperform.html and do an apples to apples comparison to see how gross take off weight differs.
Quote from: TomH on 10/09/2015 04:40 pmQuote from: Lobo on 10/09/2015 12:30 amBut the point being, to say the the pieces being joined where they can separate in an emergency is "hideously complex" may be a tad over stated. ;-)And your point with this image is...?
And its not just a lifeboat. That would be one thing. In the system Lobo proposes, the "lifeboat" is a major section of the re-entry system for the MCT and the primary propulsion for landing.
A short return trip adds few extra requirements onto the MCT as there already are requirements for a short trip to Mars. However a long return trip which goes into the orbit of Venus adds requirements that are not needed on other phases of the mission. For cargo it adds a few extra requirements, but for crew it adds far more, especially as the MCT will be limited to 25% payload on the return trip.....I think Elon will be satisfied if the 90% cargo missions can be reflown in 1 synod while the 10% crew missions are reflown in 2 synods. Crew MCT probably need far more refurbishment than cargo MCT so it would be a push to get them reflown the next synod anyway.
Quote from: MikeAtkinson on 10/09/2015 01:18 pmA short return trip adds few extra requirements onto the MCT as there already are requirements for a short trip to Mars. However a long return trip which goes into the orbit of Venus adds requirements that are not needed on other phases of the mission. For cargo it adds a few extra requirements, but for crew it adds far more, especially as the MCT will be limited to 25% payload on the return trip.....I think Elon will be satisfied if the 90% cargo missions can be reflown in 1 synod while the 10% crew missions are reflown in 2 synods. Crew MCT probably need far more refurbishment than cargo MCT so it would be a push to get them reflown the next synod anyway.If you can do a short trip to Mars with a longer return trip, to fit into 1 synod, I would assume you could do a long trip to Mars with a short return trip.From an Earth perspective a human-return MCT would return from Mars just a few months after the main fleet leaves for Mars. The people would offload, and it would be refurbed and leave with cargo only (having missed the short trip window) for a 1 year trip to Mars. From the Martian perspective you'd have that cargo MCT arriving a year after the passenger MCTs (which have been sent back with cargo on a slow return already). Offload the cargo, load with passengers, and launch back on a quick trajectory again.It allows each MCT to be used once per synod - but I apologise in advance that I don't have a good enough grasp of the orbital mechanics involved. Is there any reason we hear more about a short trip to Mars, 1 month stay, with long return - and not the opposite long trip to Mars, 1 month stay, with short return?
As far as we know all MCT, both cargo and passenger, will go on trajectories that allow them to return after a short stay on Mars and return in the same synod. At least that is what Elon Musk has set as a goal for his transport system to reuse them every synod instead of every second synod.That means the return leg will be significantly longer than the leg earth-mars. You are introducing a new requirement for shorter return flights that would mean that manned MCT could not be reused every synod. That may or may not be the case. IMO it is just a reason to reduce the number of people who return to earth to a minimum, maybe have more water as shielding for at least a part of the crew space for the return leg. But that is problematic as the mass budget available for return is much smaller.
Quote from: Oli on 10/09/2015 03:20 pmQuote from: RonM on 10/09/2015 02:40 pmReloading a returned MCT with cargo is an issue. If modular, cargo could be transferred by BFR and a tug.Landing on Earth is not required for maintenance.The MCTs could be staged somewhere in cis-lunar space instead of LEO to reduce outgoing and return delta V requirements. Makes it more difficult to stage, but could be worth the effort.Why bring back the MCT to cis-lunar space or LEO if you do not land on Earth? Just keep it at Mars. Use it to shuttle cargo/personnel from Mars orbit to the surface.I'm assuming a reusable interplanetary vehicle would be useful. Also direct entry to Mars instead of going into Mars orbit. I believe that is what Elon has in mind. Of course, other options are possible.
I'm strongly in favor of SEP and see considerable use for it making VERY FAST transit possible.How is this possible? Wouldn't the system need to be huge and have magical power sources and such (insert anything Zubrin has ever said). NO, you can get a Fast transit on the order of 100 days to Mars with a slow, low power SEP system.The trick is you use your SEP to move your Mars bound vehicle with propellants up to high Earth orbit and then then drop by the Earth for a huge Oberth assisted burn. For 2 km/s you should leave Earth with huge escape velocity and reach mars in 100 days (average). Now the problem is capturing at mars, the answer is Magneto-Plasma Aerocapture, this lets us avoid expensive propulsive capture and is then followed by about a week of Plasma assisted aerobraking which lets the eventual EDL be from a gentle 4 km/s. So we get to have both fast transit and easy low speed EDL. The SEP system has not even left Earth yet in this scenario, so you can do either one of two things, bring it back down to LEO for refueling and do it again (basically making it a Cis-lunar tug), or send it to mars by the conventional slow method of spiraling out from the Earths SOI (the SEP is too delicate to take the high thrust of the Oberth maneuver). In the latter case your going to arrive much later then the manned capsule but if this is a conjunction mission the crew will be spending around 600 days on mars so their is plenty of time for the SEP to arrive before it is needed for departure which is what I favor.The MCT would only need to reach low Mars orbit and would then rendezvous with the SEP and head for Earth, this return transit is made reasonably short by the fact the MCT is a completely dry shell now of only 100 mT (75 vehicle mass + 25 return cargo) and the SEP is nearly dry too so power to weight ratios are increased, also were not aiming to match Earth's orbit and capture gently, were going to simply intersect it on an elliptical orbit around the sun, that cuts the DeltaV needed. At Earth we used the Magneto to capture again and bring both SEP and the MCT down to LEO (they probably need to separate to do this as the SEP is more delicate and would slow the process down for the MCT). The crew can be retrieved via a Dragon capsule now, and we need to send another tanker to LEO to put landing propellants into the MCT, if we use enough the MCT can do a lot of retro-propulsion on entry and bring it's entry speed down from the 7.7 km/s of orbit down to the range of 4 km/s which matches it's mars entry speed, so all the thermal protection systems can be designed for this low performance point.IMLEO is estimated at 570 mT of which 100 mT is the cargo load, 75 mT is the MCT dry mass, 200 mT is chemical propellant in the MCT (2 tanker loads of 100 mT each), 155 is SEP propellant, 15 mT is the SEP tank and 22 mT is the SEP hardware which has a power output of 4.5 MW which corresponds to an alpha value of 5 kg/kw.BTW Using a braking system like Magneto Plasma is the only way I can see an Integrated Bi-conic and direct Earth return being viable, without it the entry conditions are too extreme to meet the low dry mass fractions that it's advocates are proposing.
That sounds far too ambitious. First of all, why VERY FAST transit? What's the point? Not worth the effort IMO, not in any near future.
You probably want some chemical propulsion on your SEP stage, at least for the crew transfer, but not anything on the scale of MCT.
Magneto-Plasma Aerocapture? Are you sure that's not only for aerobraking? Either way, probably far from ready.
Why take the Lander back to LEO if you do not need it for aerocapturing? If they can't "refurbish" it on Mars at the beginning, you might as well expend it.
4.5MW is huge and 5kg/kw is far below the numbers I've seen.
The SEPs can cycle between LEO/HEO and HEO/Mars, that way they are back a lot faster and you need less power.
375t is a freaking huge payload for SEP. You can divide that into cargo/hab/lander and get 100t+ pieces. Again, less power.