Launch to Geostationary Transfer Orbit, circularize using on-board propellant. This is the standard model for how satellites are deployed into space. It is a mature process which has served us well for decades. However, when planning an exploration architecture, it has always been treated as irrelevant.

Here is a list of some current (and one near future) launch vehicles, their listed throw mass to GTO and the calculated mass that can be placed into the first Earth-Moon Lagrange point using a 312 second specific impulse storable propellant thruster (GTO to EML1 delta-v is 1.27 km/s).

Launch vehicle | Mass to GTO | Mass to EML1 |
---|---|---|

Falcon 9 | 4680 kg | 3090 kg |

H-IIB 304 | 8000 kg | 5282 kg |

Long March 3B/E | 5500 kg | 3632 kg |

Proton | 6360 kg | 4199 kg |

Atlas V 551 | 8700 kg | 5745 kg |

Ariane 5ECA | 10050 kg | 6636 kg |

Delta IV-H | 12980 kg | 8571 kg |

Falcon Heavy | 19000 kg | 12546 kg |

What should be obvious is that there is quite a healthy international stable of launch vehicle providers, and they're all geared up for sending payloads to GTO. What is perhaps not obvious is that by going from GTO to EML1 I am seriously cheating myself. I don't mind because throwing to a lunar transfer orbit is something all of these vehicles can also do and, in all cases, the subsequent transfer to EML1 will be less than a transfer from GTO. As such, we can accept the numbers above as accurate, even if they are overly conservative.

So what does this mean? Suppose we want to land a payload on the surface of the Moon. One option is to simply pick the biggest one of these rockets and fly it directly to lunar orbit and start our descent. The total delta-v for such a mission is likely to be about 3.2 km/s, which means we can land a maximum of 6676 kg.

Suppose, instead, we fly to EML1 and pick up fuel. The table above indicates we can put a maximum of 12546 kg to EML1, and the delta-v from EML1 to the lunar surface is 2.52 km/s, so we need 16043 kg of fuel to make the trip. Because we're using storable propellants, this can be delivered over a long time using whichever provider offers the best price, or over a short time by engaging as many providers as become available.

Although this is just a rough analysis, it shows that we can land twice as big payloads by building up EML1 with propellant, without the need for any new launch vehicles, new technologies or even new ways of doing business, and we could start doing it right now.