Getting 2 km/s out of such low-impulse engines requires a propellant mass fraction of 57%, which means an empty Dragon V2 (with a dry mass of 4.2 tonnes) would need at least 5.6 tonnes of propellant in order to get off the surface of the moon, 370% of its current fuel capacity.
Consider the following:Elon Musk proposes the following to Hillary or Donald (I don't want to touch which one in this forum):* Boots on the moon with NASA badges on the shoulders and no Russian vehicles or speakers during the 2020 re-election campaign, for $5 billion. This is way cheaper than even a small military foray.* Major, sustained distraction from foreign policy nightmares by a team that has demonstrated ongoing ability to capture and keep the American public's attention.* Executed by a NewSpace company (free enterprise and all that).* Clears away all the old government SLS crap, appears decisive, and yet provides plenty of jobs in CA, TX, and FL. Also can be seen to validate the Commercial Crew initiative if under a Democratic administration.* Will be visibly different than Apollo: * high-def landing and relaunch video via preplaced unmanned lander * landing video of and from the lunar crasher stage. People love watching stuff go boom. * Lots of downlink bandwidth via three lunar orbiting relays * GoPros on practically everything, dedicated production staff similar to an NFL game, lots of earnest engineers explaining how it works (SpaceX has to get better at this). * bigger and better looking hardware that looks like an Apple product * more people on the surface at one time. Three will do. * obviously practice with the hardware for Mars landing, so there is a future. This means inflating stuff and driving around.
Quote from: IainMcClatchie on 03/22/2016 11:58 pmConsider the following:Elon Musk proposes the following to Hillary or Donald (I don't want to touch which one in this forum):* Boots on the moon with NASA badges on the shoulders and no Russian vehicles or speakers during the 2020 re-election campaign, for $5 billion. This is way cheaper than even a small military foray.* Major, sustained distraction from foreign policy nightmares by a team that has demonstrated ongoing ability to capture and keep the American public's attention.* Executed by a NewSpace company (free enterprise and all that).* Clears away all the old government SLS crap, appears decisive, and yet provides plenty of jobs in CA, TX, and FL. Also can be seen to validate the Commercial Crew initiative if under a Democratic administration.* Will be visibly different than Apollo: * high-def landing and relaunch video via preplaced unmanned lander * landing video of and from the lunar crasher stage. People love watching stuff go boom. * Lots of downlink bandwidth via three lunar orbiting relays * GoPros on practically everything, dedicated production staff similar to an NFL game, lots of earnest engineers explaining how it works (SpaceX has to get better at this). * bigger and better looking hardware that looks like an Apple product * more people on the surface at one time. Three will do. * obviously practice with the hardware for Mars landing, so there is a future. This means inflating stuff and driving around.Nice ideas, but lets see if whomever the POTUS is and congress can agree on anything at all first.I'm hopeful the next POTUS dumps the flat and lame asteroide mission thing and aims straight to the moon. Orion, SLS, commercial capabilities. But again they branches of government need to work at a primitive level first.
2. ISS to EML-1; crasher-stage direct ascent. Single Falcon 9 launch takes crew and Dragon V2 to ISS; docks. Falcon Heavy lifts Lunar Dragon to the ISS; crew and consumables transfer; Falcon Heavy transfers to EML-1 and then burns crasher-stage to drop a Lunar Dragon with additional fuel on the lunar surface. Lunar Dragon makes ascent and transfer to ISS and crew returns to earth via docked Dragon V2.
Quote from: sevenperforce on 03/21/2016 07:35 pm2. ISS to EML-1; crasher-stage direct ascent. Single Falcon 9 launch takes crew and Dragon V2 to ISS; docks. Falcon Heavy lifts Lunar Dragon to the ISS; crew and consumables transfer; Falcon Heavy transfers to EML-1 and then burns crasher-stage to drop a Lunar Dragon with additional fuel on the lunar surface. Lunar Dragon makes ascent and transfer to ISS and crew returns to earth via docked Dragon V2.This mission profile looks like a winner to me for the manned part of the mission. Here's why:1. Cheapest combination of launch vehicles: Falcon 9R and Falcon Heavy Expendable2. Unused seats on Commercial Crew spacecraft (possible subsidizing)3. Possible replacement of crasher stage and refueling of lunar dragon for future missions. ISS robotic arms courtd also prove useful in this operation. (possibly moving to Falcon Heavy reusable)4. Various present and future docking options: ISS, spacecraft to spacecraft, Bigelow5. Other options for earth to LEO crew delivery that can be substituted for both the spacecraft and launch vehicle.
Yeah, it's nice. The biggest drawback here is that it requires the largest dV for the lander. Getting from the lunar surface to LLO requires 1.9 km/s; getting from the lunar surface to Earth aerobraking trajectory requires 2.8 km/s; getting from the lunar surface to LEO requires a whopping 5.9 km/s. Direct ascent to Earth aerobraking is so much cheaper than direct ascent to LEO.
Quote from: sevenperforce on 03/23/2016 04:58 pmYeah, it's nice. The biggest drawback here is that it requires the largest dV for the lander. Getting from the lunar surface to LLO requires 1.9 km/s; getting from the lunar surface to Earth aerobraking trajectory requires 2.8 km/s; getting from the lunar surface to LEO requires a whopping 5.9 km/s. Direct ascent to Earth aerobraking is so much cheaper than direct ascent to LEO.Yes if your only talking about dV and not cost, but I'm assuming the profile you gave was still plausible for a useful manned mission. Was I incorrect in this assumption?
I think, though, that it makes more sense to wait a few years, let NASA set up an Orion-serviced way station in high lunar orbit, and use that for your reusable lander resupply shop. The delta-V requirements to get to the lunar surface from HLO and back are much lower than those quoted for LLO, aerocapture and LEO, right?
I like option 3 too of course, but I have to wonder how much work has to be done on that Dragon to make it dual purpose verses a Dragon derived lunar lander.
You need the trunk. Why don't you put the extra propellant there?
Quote from: stoker5432 on 03/23/2016 08:40 pmI like option 3 too of course, but I have to wonder how much work has to be done on that Dragon to make it dual purpose verses a Dragon derived lunar lander.It would take a lot of work, but not necessarily any more work than it would take to build a single-function Dragon-derived lunar lander. The major issue would be installing an auxiliary fuel tank inside the cabin without introducing significant risk. You end up with a significantly smaller payload, but the advantage of only needing a single vehicle for both the Moon and Earth cannot be overstated.
Getting from the lunar surface to LLO requires 1.9 km/s; getting from the lunar surface to Earth aerobraking trajectory requires 2.8 km/s; getting from the lunar surface to LEO requires a whopping 5.9 km/s. Direct ascent to Earth aerobraking is so much cheaper than direct ascent to LEO.
Regardless, SpaceX's major advantage disappears if you wait for a cislunar station. The Falcon family has very poor BLEO performance. The advantage exists if and only if SpaceX can boast lunar capability now, despite the low performance of their platforms.
Quote from: CuddlyRocket on 03/22/2016 08:50 pmI don't think SpaceX will be going to the Moon until after the BFR/MCT has been developed. A system capable of getting to Mars and back will in all likelihood be capable of going to the Moon and back (perhaps with some modifications). I expect SpaceX would be willing to utilise the system on lunar missions - they would be useful test flights - and especially if someone else is paying!I would imagine that if SpaceX can go to the moon now, with existing platforms, they would jump at the opportunity to test the tech and operations needed for Mars.
I don't think SpaceX will be going to the Moon until after the BFR/MCT has been developed. A system capable of getting to Mars and back will in all likelihood be capable of going to the Moon and back (perhaps with some modifications). I expect SpaceX would be willing to utilise the system on lunar missions - they would be useful test flights - and especially if someone else is paying!
The moon is a lot closer than Mars, and if they can use non-mission-critical legs of lunar missions to test technology like orbital propellant transfer, repeat rendezvous, uncrasher stages, hoverslam landings, and so forth, they can get to Mars that much earlier.
And as far as the bill is concerned...if SpaceX can offer a return to the moon 5-8 years earlier than the closest competitors, I am sure someone high-ranking at NASA would at least consider it.
Quote from: sevenperforce on 03/23/2016 08:53 pmQuote from: stoker5432 on 03/23/2016 08:40 pmI like option 3 too of course, but I have to wonder how much work has to be done on that Dragon to make it dual purpose verses a Dragon derived lunar lander.It would take a lot of work, but not necessarily any more work than it would take to build a single-function Dragon-derived lunar lander. The major issue would be installing an auxiliary fuel tank inside the cabin without introducing significant risk. You end up with a significantly smaller payload, but the advantage of only needing a single vehicle for both the Moon and Earth cannot be overstated.Won't work.The final mass of the Dragon 2 after ascent will be about 8 tonnes, needing about 10 tonnes of propellant. This extra propellant will take up essentially the whole of the cabin.This 8 tonnes includes the trunk as Dragon can only survive a short time without the power and cooling provided by the trunk. Also fuel margin and residuals, extra tank(s) and predestination system. Also crew, ECLSS supplies, etc.