Mars and Luna are not mutually exclusive goals
In early 1999, a new popular theme arose among Mars pundits claiming that it's easier to get to Mars than to Luna because we need less fuel to get there. Unfortunately, there's nothing easy about getting to Mars.
Don't get us wrong -- we agree that developing human settlements on Mars will be a fantastic human adventure, and we enthusiastically support the technical work of the Mars Society. We have been working on ways for the lunar community to support missions to other planets since the start of the Artemis Project. You will find some of this work in section 2.5 of the Artemis Data Book.
We don't see Luna and Mars as mutually exclusive goals, but some people fear that lunar development will somehow distract resources that could otherwise be focused on exploring Mars.
The bad news is that there's lots more to it than fuel. The worse news is that even the fuel argument turns out to be untrue.
How much fuel we need depends on what we assume
If we assume that our crewmembers ...
Tragically, each of these assumptions -- except maybe the aerobraking maneuver -- is just plain silly. If we sent a human being to Mars with this scenario, the most we could hope for is to deliver a human weight of dessicated, radioactive sausage to the surface.
The Lunar Transfer Vehicle could fly to Mars, sort of
This tragic scenario begs the question: What sort of Mars mission could we mount using a vehicle similar to the moon mission?
Moon ships could, indeed, be used for a Mars mission, at least to Mars orbit, with just a bit of modification. Consider the case of the Artemis Project's Lunar Transfer Vehicle.
To get from Low Earth Orbit to Mars, counting both ends of a minimum-energy Hohmann transfer trajectory, we need a total delta-V of 18,372 ft/sec; or 36,744 for the round trip from Earth to Mars and back to Earth orbit. So let's see what this baby can do.
We designed our Lunar Transfer Vehicle to fly from Earth orbit to lunar orbit and back again. So at the moment the LTV is ready to depart from Earth orbit, it has enough fuel aboard to all these maneuvers:
|Translunar injection||10,045 ft/sec|
|Lunar Orbit Insertion||2,807 ft/sec|
|Lunar Orbit Circularization||100 ft/sec|
|Transearth injection||3,212 ft/sec|
|Earth orbit insertion||10,572 ft/sec|
|See the Reference Mission Timeline for details.|
That's a total of 26,636 ft/sec of delta-V for the complete trip from Earth orbit to lunar orbit, and return. When the LTV first makes its burn out of low Earth orbit, it has to have enough fuel on board for all those maneuvers.
That's not quite enough for the round trip, but we can still take the Lunar Transfer Vehicle on a nifty mission. Let's make some broad assumptions:
We can't assume aerobraking to the surface of Mars unless we increase the structural weight of the Lunar Transfer Vehicle by an order of magnitude. This vehicle is designed for spaceborne operations, not atomospheric entry maneuvers.
Well, that gets us there. Our crew will arrive in Mars orbit a little threadbare and in pretty bad shape from 9 months in zero g, but at least they will be alive long enough to see the red planet close up with their own eyes.
Whether we ever see them again depends on how much infrastructure we send ahead; but perhaps that would be cheating. If we assume an elaborate infrastrucure for this Mars venture, we'd have to compare the mission to the same effort applied to lunar infrastructure. With a travel time of 3 days each way, compared to 9 months, and with lower delta-V requirements, we would have vastly more infrastructure developed on the moon for the same amount of effort.
Admittedly, a one-way suicide mission to Mars orbit doesn't hold a lot of appeal to most folks; but this exercise demonstrates what they're really saying when they tell you it's easier to get to Mars than to get to the moon.