BFS?
Quote from: Lars-J on 04/20/2016 06:34 amBFS?Big Freakin' Spaceship
It may not be part of the existing design plan, but why couldn't MCT have some temporarily expandable section, a la Bigelow, which could be temporarily expanded during transit to Mars in order to provide necessary interior space during the months-long journey, and which could then be un-expanded or jettisoned before Mars arrival?
Quote from: Lars-J on 04/20/2016 06:34 amBFS?MCT = BFR + BFS.People previously assumed just the Mars stage was the "MCT", but apparently Musk uses that name for the whole system. IMO, it's less confusing for everyone to adopt Musk's nomenclature, since he's not likely to adopt ours; unfortunately most posters persist in using "MCT" for just the BFS.
Quote from: Paul451 on 04/20/2016 06:42 pmQuote from: Lars-J on 04/20/2016 06:34 amBFS?MCT = BFR + BFS.People previously assumed just the Mars stage was the "MCT", but apparently Musk uses that name for the whole system. IMO, it's less confusing for everyone to adopt Musk's nomenclature, since he's not likely to adopt ours; unfortunately most posters persist in using "MCT" for just the BFS.I remember back a year or so ago when people argued that Elon's MCT nomenclature implied a single monolithic vehicle which was clearly absurd. Unfortunately most speculation today is hardly much improved with a compulsive desire to make simplistic and monstrously large 'direct' approaches.
Landing the same spacecraft on Mars that was launched from Earth and returning it to Earth or LEO would be "off the wall". Even with LEO refueling before Mars transit.I think there will be additional "enhancements" in the plan.Elon says 2025, but in Elon time that means mid 2030s, even his 2:1 schedule slip would be fantastic.
Quote from: Impaler on 04/21/2016 01:17 amQuote from: Paul451 on 04/20/2016 06:42 pmQuote from: Lars-J on 04/20/2016 06:34 amBFS?MCT = BFR + BFS.People previously assumed just the Mars stage was the "MCT", but apparently Musk uses that name for the whole system. IMO, it's less confusing for everyone to adopt Musk's nomenclature, since he's not likely to adopt ours; unfortunately most posters persist in using "MCT" for just the BFS.I remember back a year or so ago when people argued that Elon's MCT nomenclature implied a single monolithic vehicle which was clearly absurd. Unfortunately most speculation today is hardly much improved with a compulsive desire to make simplistic and monstrously large 'direct' approaches.They still do, you know? They think the development will cost less because it is only one vehicle design.
Another thing that virtually no one here talks about is MARS ORBITAL RENDEZVOUS.If the BFS can be refueled in LEO then it can likewise be refueled in LMO if propellant can be brought their.This would break the DeltaV budget for Earth return into two legs, assent to LMO and then TEI resulting in a vastly smaller vehicle AND a faster Earth return then would be possible with a single direct launch of even a huge vehicle.To make the vehicle capably of departing for Mars it must start at EML-1 fully fueled which again will allow for a faster transit then a large vehicle starting in LEO.To get the propellants to LMO and the vehicle to EML-1 you use the same solution a SEP tug, fist it moves the BFS to EML-1, picks up and drops off fuel between LEO and EML-1, then makes a fuel run all the way out to mars to rendezvous with the BFS a second time and finally returns to Earth to repeat the cycle.The BFS would only need around 4-5 km/s DeltaV capability in this scenario which makes it hugely smaller and simpler, to launch to LEO the BFR is a 2 stage rocket like F-9 but with reusable 2nd stage which can carry payloads other then the BFS on top.
Quote from: Impaler on 04/22/2016 04:22 amAnother thing that virtually no one here talks about is MARS ORBITAL RENDEZVOUS.If the BFS can be refueled in LEO then it can likewise be refueled in LMO if propellant can be brought their.This would break the DeltaV budget for Earth return into two legs, assent to LMO and then TEI resulting in a vastly smaller vehicle AND a faster Earth return then would be possible with a single direct launch of even a huge vehicle.To make the vehicle capably of departing for Mars it must start at EML-1 fully fueled which again will allow for a faster transit then a large vehicle starting in LEO.To get the propellants to LMO and the vehicle to EML-1 you use the same solution a SEP tug, fist it moves the BFS to EML-1, picks up and drops off fuel between LEO and EML-1, then makes a fuel run all the way out to mars to rendezvous with the BFS a second time and finally returns to Earth to repeat the cycle.The BFS would only need around 4-5 km/s DeltaV capability in this scenario which makes it hugely smaller and simpler, to launch to LEO the BFR is a 2 stage rocket like F-9 but with reusable 2nd stage which can carry payloads other then the BFS on top.Orbital rendezvous and refueling does make things more mass efficient, but I think ferrying fuel from earth may not be the right approach. Instead consider a tanker variant of the BFS which is sent to Mars and uses local ISRU to loft fuel to LMO for refueling the returning BFS.
The Battlestar Galactica thing made me think and put some numbers, just plug data in the rocket equation to see what happens. I'm assuming the 'land the whole thing' architecture because, in order to transport a lot of cargo and people to Mars, you need a big and heavy lander anyway, so it does make sense to use the same ship to make the interplanetary part as well. I'm also assuming a pure chemical rocket propulsion system, although G Shotwell mentioned other possibilities being studied.As a reference I used Saturn V (I'm taking Apollo XVII numbers), obviously the only comparable succesfull system so far, yes the Nova designs where more like it, but they remained paper rockets, no ppt in those happy days.Plugging the Saturn IC data in the rocket equation shows that deltaV was just over 3.3 Km/s, it also staged at a pretty low altitude (good for the RTLS thing). Let's assume that the MCT booster does likewise, that leaves about 7 Km/s deltaV to the second stage (aka BFS) which is ok if you plan to refuel and do a TMI burn. As per word of Musk, the ship will be capable of putting 100 t of useful mass on Mars, so let's make it another 100 t for structure (engines, TPS, legs, you name it). So that leaves a 200 t dry mass vehicle, capable of 7 km/s deltaV, with engines giving a Isp of 380 s you need a whopping 1150 t of propellant and a total BFS mass at lift off of about 1350 t. This also pushes the BFR mass to 3200 t, more than a Saturn V GLOW. Indeed, it's not a small ship, so the term Battlestar does apply here.
The other question is how they will want to size the Raptor. At the currently stated 2300kN a single Raptor would be rather underpowered for throwing 100t into LEO, although probably not worse than the Centaur US. A single 2300 kN engine would be ideal for TMI and Mars return though, and dragging extra engines to Mars and back isn't ideal.