It only has an isp of about 312 s?
Put a 40kW electric tug on it (could be built using essentially a modified off-the-shelf commsat bus with a bigger or a couple extra solar arrays and some extra Xenon tanks... big commsats now do about 20kW), and you could put a Apollo-or-larger lander (up to maybe 20mT) in LLO with just an RS-68A Delta IV Heavy. A much bigger one if you used the cheaper Falcon Heavy. It'd take a few years to get all the way there (less if you used a Falcon Heavy and could tolerate a lower Isp, or if you could use a 100kW modified commsat or something it'd take proportionally less time), but so what? A lander in LLO with a single launch of an EELV Heavy. Or a really big lander in LLO with a Falcon Heavy. Have to use storable propellants with the lander, but that's not a huge deal.Might even be cheaper than developing a hypergolic Earth Departure Stage that is refuelable.Or heck, if you had a 18mT reusable single-stage hypergolic lander (probably needed to equal the performance of a 14mT two-stager), you launch a big tank of hypergolic propellant on a single Falcon Heavy along with a 100kW modified-commsat-tug, and you could refuel like 3 times per Falcon Heavy launch (alternately, between 6 and 9 refuelings per SLS launch, depending on which version of SLS... but you'd need a bigger tug or you'd need to launch multiple tankers per flight...).A yet more efficient architecture would use a hydrolox un-crasher stage and a near-zero-boiloff depot fed by fully reusable tugs and a future fully reusable launch vehicle like the envisioned F9R with reusable upper stage.
...Um, that sounds too complex.
Quote from: Robotbeat on 08/29/2013 04:28 am...Um, that sounds too complex. Exactly. Better is the enemy of good enough. The point is that trivial solutions like a storable propellant earth departure stage is cheaper than SLS.
From my calculations you will need 158 metric tons of storable propellant to make this work from LEO.
5 launches will cost *more* than an SLS launch for the same performance, costing you $540 million vs the SLS at ~$500 million, just for the launch vehicle.You are throwing money away with this route.
Quote from: Downix on 08/29/2013 05:30 amFrom my calculations you will need 158 metric tons of storable propellant to make this work from LEO.Please show your work.. I did.
Quote5 launches will cost *more* than an SLS launch for the same performance, costing you $540 million vs the SLS at ~$500 million, just for the launch vehicle.You are throwing money away with this route.Only in pixie land is that the cost of an SLS launch.
I checked yours. You neglected the weight of the lander itself.
Quote from: QuantumGOnly in pixie land is that the cost of an SLS launch.That's the cost on-record.
Only in pixie land is that the cost of an SLS launch.
Sorry to hurt your bash-SLS fest.
According to this article, which has it's own thread, NASA wants a 43 ton lunar lander.. for some reason.. and they say the only way to get a payload that big into lunar orbit is with the SLS.I don't get it. What's wrong with just using a storable propellant Earth departure stage? Let's be conservative and say it only has an isp of about 312s, and a propellant mass fraction of 90%, how big would it be?According to my math, please check me, I figure it would be about 10,458 kg dry and 104,579 kg when full. This would provide the 3107 m/s of delta-v to get through TLI, with the lunar insertion to be done by the lander (as in the NASA architecture).I know 105 tons sounds like a lot, but it's only two Falcon Heavy launches, and because we're using storable propellant there's no time pressure. If you really wanted to you could do it with Falcon 9 v1.1.
Quote from: QuantumG on 08/29/2013 01:49 amAccording to this article, which has it's own thread, NASA wants a 43 ton lunar lander.. for some reason.. and they say the only way to get a payload that big into lunar orbit is with the SLS.I don't get it. What's wrong with just using a storable propellant Earth departure stage? Let's be conservative and say it only has an isp of about 312s, and a propellant mass fraction of 90%, how big would it be?According to my math, please check me, I figure it would be about 10,458 kg dry and 104,579 kg when full. This would provide the 3107 m/s of delta-v to get through TLI, with the lunar insertion to be done by the lander (as in the NASA architecture).I know 105 tons sounds like a lot, but it's only two Falcon Heavy launches, and because we're using storable propellant there's no time pressure. If you really wanted to you could do it with Falcon 9 v1.1.A very good idea, kind of "cheap and dirty" lunar architecture. I see your point - Falcon Heavy is cheap, storable propellants are straightforward technology, they don't boiloff with time. I have no doubts this would work pretty well. So what's wrong, do you ask ? Simple...NASA obsession with LOX/LH2. Never, ever, would they consider something else for the TLI. That paradigm also apply to SSTO, btw. It is a little annoying, because issues with liquid hydrogen have long been obvious...
Exactly. Better is the enemy of good enough. The point is that trivial solutions like a storable propellant earth departure stage is cheaper than SLS.