It's easier to get to Mars.

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 ...

• don't eat,
• don't drink water,
• can wait six to nine months to go to the bathroom
• can stand direct, unattenuated cosmic radiation for up to two years, and
• don't mind being cooped up in a vehicle suited for a three-day trip to the moon,

• we using aerobraking in the upper atmosphere to slow down below Mars orbital velocity, and
• rely on nothing but parachutes to get all the way to the Martian surface, and
• use landing bags to absorb the impact,

• our aerobrake and parachutes and landing bags have zero mass, and
• the additional structure required to absorb the stresses from high accelerations in all these maneuvers has zero mass,
• our crewmembers can stand a 50-g impact on landing,

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:

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:

1. We're not landing; this mission is just to get a close-up look at the red planet with real human eyeballs. Or maybe somebody sent the landing craft ahead; but see the note below about comparing infrastructure on Mars to the same effort applied to developing the infrastructure for lunar industries.

   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.

2. When we get to Mars, a nice, friendly robot from Ahrzee Advance Robotic Fuel Systems is going to meet us in Mars orbit and provide the return fuel for the trip. Either we again make leap of faith about infrastructure on Mars, or it's a one-way trip. Of course, if there's no lander, a one-way trip would be a suicide mission; but what the heck.

3. We trade off the weight of the entire landing stack for radiation sheilding and supplies. We really need that radiation shielding. Without it, our crew will soak up about 4 Sieverts of radiation during the trip (or more, if the sun is in a really bad mood). That's 16 times the career effective dose for female astronauts recommended by the National Council on Radiation Protection and Measurements. Without radiation shielding, our crew will be several times dead by the time they get to Mars.

4. Since we're only going one way, we don't need all that fuel. We only need 18,372 ft/sec of the available 26,636 ft/sec of delta-V to get into Mars orbit. So let's broadly assume that the reduction in fuel load will pay us back for the provisions our crew will need to remain alive. (Maybe someone will work out this mission plan in detail. Assume we're recycling the water. There's not going to be enough room in the LTV for much more in the way of a bioregenerative life support system.)

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.