To save on weight, a detour to the moon is the best route to Mars | Hacker News Reader

To save on weight, a detour to the moon is the best route to Mars

news.mit.edu

123 pointsjimsojim58 comments

  “This is completely against the established common wisdom
  of how to go to Mars, which is a straight shot to Mars,
  carry everything with you,” de Weck says. “The idea of
  taking a detour into the lunar system … it’s very
  unintuitive."

and later...

  “Assuming you can extract these resources, what do you
  do with it? Almost nobody has looked at that question.”

Give me a break. People discuss this sort of approach all the time. They don't necessarily publish their conclusions, though.

This topic was very much discussed on campus during my grad school days (10 years ago now). I'm quite sure that Dr. Gary Flandro discussed it with many people at great length. But then, that's one thing he's always done -- figure out how to get to new and exciting places in the solar system. He was very much in favor of using the Moon as a base for expansion into the rest of the solar system for exactly this reason. Once you set up a beach-head there with facilities for extracting materials and manufacturing goods, it's much easier to launch onward into the rest of the solar system. This, I recall, was a major theme of the Quick-Goethert lecture that Dr. Flandro gave in 2005. It was a great pleasure to attend that lecture.

So yes, just from that one example, I'll grant you that people discuss this sort of approach all the time. Dr. Flandro certainly wasn't the first, even then.

Yep. Even President Bush's 2004 NASA proposal included a return to the moon ("as early as 2015") and permanent moon base, specifically to "take advantage of lunar resources" and serve "as an eventual springboard to Mars". See:

http://www.nbcnews.com/id/3950099/ns/technology_and_science-...

They do sometimes; a lunar resources conference, in the aftermath of Apollo missions, had discussions regarding use of Moon regolith for things like refueling.

Yeah, there's loads of great analysis of lunar resource use from that era, and propellant for use beyond the Moon is a major motivation for the current interest in lunar polar volatiles. For them to act like the notion that lunar resources could be valuable for trips elsewhere is a major revelation is ridiculous.

A Lunar base & ISRU effort was not just a theory that existed, but the predominant conventional wisdom in NASA's planning, ten years ago.

And it was a bit silly even before they did the typical NASA thing of underfunding and cancelling essential bits in the bureaucratic infighting. ISRU on Luna is likely to be an effort with comparable scale to a Mars mission, with questionable amounts of translatable techniques. Most anything we can do on Luna other than ISRU, we could do in LEO. Luna is seen as a sort of cheaper prize than Mars by Lunar proponents who don't advocate 'stepping stones', but the cost of operating on Luna via Constellations is higher than the NASA HSF budget today, and would likely prevent serious attempts at Mars planning in the same way the ISS/Shuttle is doing today.

We still use chemical propulsion almost everywhere from cars to rocket engines, a breakthrough in propulsion systems will not only make solar system exploration feasible but will be greatly beneficial to our society by reducing pollution and costs.

We need the next steam engine for a new industrial revolution, space exploration and our society depends on it.

I think that all space resources should be channeled into this, our current approach to solar system exploration is the same as trying to explore the world by foot, expensive an inefficient and no matter how big our ambitions are we don't have the technology to accomplish them.

Exactly! Nuclear thermal rockets/fission-fragment rockets are the way to go, but you can't launch them directly from Earth because of the nuclear fallout.

Well, you can't use them for launch. And there's lots of other options for in-space propulsion.

The specific impulse is "only" double that of chemical ones, and there's potentially a large dry mass penalty.

You mean the specific impulse for nuclear thermal rockets, as far as I know the fission fragment rockets have ISPs in the 10^5 range.

You can already produce fuel on Mars itself using the Sabatier Reaction with technology available today, you have to bring along a little hydrogen but that's not too big of a deal.

Refueling on the moon requires an (almost pointless) web of infrastructure that balloons the cost of a mission, and more importantly, increases the time to carry out the mission.

Each US administration has a habit of cancelling the more ambitious NASA/JPL projects of the previous one, so if we really want to go to mars, it has to be a mission doable in as short a time span as possible, such as proposed by Zubrin's Mars Direct plan.

Does anyone writing these papers have any appreciation for the difficulties of producing liquid H2 appropriate for use in manned rockets? This is some seriously tricky stuff. Turning water into liquid H2 is one thing, making it out of dirty moon-frost is another. A little impurity here and there and your rocket engine becomes a bomb.

Detander - a gas liquifier - can be pretty small and lightweight even for a big flow. Industrial hydrogen liquifiers are built routinely since 1950s if not earlier.

If you're trying to liquify hydrogen, you'll find out that most - almost all - impurities in the gas become liquid or solid before hydrogen becomes liquid. That's a good way to clean hydrogen, so you won't have an odd mixture as the result.

Deleted comment

From the article:

> To see whether fuel resources and infrastructure in space would benefit manned missions to Mars, Ishimatsu developed a network flow model to explore various routes to Mars — ranging from a direct carry-along flight to a series of refueling pit stops along the way. The objective of the model was to minimize the mass that would be launched from Earth, even when including the mass of a fuel-producing plant, and spares that would need to be pre-deployed.

Asteroids are even better for resource utilization.

They might be far away in space but a lot closer by delta vee, and they can be reached, mined and escaped with low maximum thrust, meaning very efficient propulsion methods can be used.

This discussion just goes around in the same stupid circles for decades. We know so many better ways of doing things, but they can not be done for political / PR reasons.

If you have one hour if front of you, I highly recommend this documentary: https://www.youtube.com/watch?v=tcTZvNLL0-w

In it they explain how it would be feasible to be on Mars in ten years with current technology and not so much additional fundings.

I've done that in KSP, seems to be working.

KSP is an incredible intuition pump for stuff related to spaceflight. Highly recommended!

Do it in RSS, or even 64k. Stock KSP is a tiny tiny place.

Doesn't that just increase the gain of doing the refueling?

Seeing as the title could be a bit misleading, I'm glad the article clarifies:

>Ishimatsu says the research demonstrates the importance of establishing a resource-producing infrastructure in space. He emphasizes that such infrastructure may not be necessary for a first trip to Mars. But a resource network in space would enable humans to make the journey repeatedly in a sustainable way.

In other words if we want to get to Mars ASAP, setting up lunar mining and refueling infrastructure probably isn't the fastest way to go about that, even if it is more mass efficient.

I am curious as to why we just don't set that up on Mars to begin with. Set up a manufacturing infrastructure and an agricultural base.

Because everything you take to mars costs ~68% more fuel to get off of earth. Getting off of Earth is much harder than getting off of the moon, which has ~86% less gravity.

If you only take enough fuel to get to the moon, then you can load up there and enjoy a significantly easier time to get up to speed on the way to Mars.

I didn't see how much of a percentage difference it is in total fuel though, in the article. I'm expecting it is pretty close or they would have cited it instead of the Earth liftoff reduction.

Oh it is more than 68%. That 68% gets you a flyby of Mars, landing is another issue.

There are limits to what heatshields and parachutes can do in a thin atmosphere. If you wanted to accurately land something truly heavy you will have to bring fuel for the descent stage. Even just achieving a stable orbit would probably mean doubling that 68%.

Well another consideration is the additional time added to the Mars trip. Right now, going directly from Earth, around Earth a bunch of times, then straight to Mars will be 6-9 months one way, which I believe the opportunity to come back would be ~2 years after arriving (I may be wrong here). So, assuming we are doing a round trip and not one way, it's already a 3 year trip ish? Either way, I see building a launching space station orbiting earth as the best way. Use smaller rockets like the falcon 9, get a bunch of fuel into orbit, build the ship from many parts and trips, then launch from Earths orbit. Make the built ship reusable for many Mars trips. Like in the Martian...

A fuel station in LEO may be convenient, but it will still be much cheaper to ship fuel from the Moon than from the surface, Δv-wise. Per a handy Δv map[0], it's about 2.5km/s (if you aerobrake) vs. almost 10km/s to lift fuel from Earth.

[0] - http://i.imgur.com/SqdzxzF.png

Aerobrake a couple tons of liquid H2 and O2 in earth's atmosphere? Assuming it doesn't all boil off, it would certainly make for some nice fireworks.

Add moar heatshields, eh? ;).

Also, I was thinking more about dipping in the atmo a little, doing the kind of aerobraking the ISS has to fight all the time. You don't have to make the entire insertion in one orbit.

A slow series of aerobrakes would run up against the time factor. Today's H2 storage boils off about 1% per day. So if you spend a few weeks slowing things down gradually you quickly defeat the advantage as much of your fuel has escaped.

Didn't consider that. Thanks!

EDIT: Maybe there are some improvements for storage available that don't make sense on Earth given H₂ prices? A magnetic containment field, perhaps? Or whatever chemistry shenanigans are used for hydrogen fuel cells? You would be trading the time factor for mass and volume (the latter doesn't matter that much in space, and could even help with aeroinsertion), but it may still add up moneywise.

You have to at least aerobrake enough on the first pass to get into some orbit, and it's preferable if the orbital period isn't a few months before you get the second pass.

If you are returning from the moon, capture isn't the issue. You are already captured because the moon is captured. You are in a highly elliptical orbit around earth. So aerobraking is still an option, as opposed to the more violent aerocapture maneuver where it all has to happen in the first pass.

Ah sorry I didn't pay enough attention :-( I thought we were talking about returning from Mars, not insertion into Earth orbit from the Moon.

Because setting up infrastructure on Mars could already benefit from having fuel plant on the Moon.

The Moon is a pretty interesting place. It's just three days out, which makes it orders of magnitude easier to set up and support (and evacuate in case of an accident), and a fuel plant there could help reduce cost of all interplanetary missions.

Interesting. This was the claim of the Bush administration, that the moon was the route to Mars, but that program was cancelled after being ridiculed.

This point is key:

"assuming the availability of resources and fuel-generating infrastructure on the moon"

Sure, if the moon is a gas station, then stopping there to fuel up on the way to mars makes sense. But it's making a big leap of faith that refueling infrastructure and raw materials can be reasonably built on the moon.

ESA seems to be interested in pushing that angle. The recent announcement was very refreshing to hear[0].

I like to imagine it's Musk radiating enthusiasm for rubbing progress into our faces, but whatever it is, something seem to have caused a renewed interest in manned space projects. Maybe it's just ESA and NASA stepping up their PR game. But whatever it is, I'm thankful and have high hopes!

[0] - http://www.space.com/29285-moon-base-european-space-agency.h...

Low-Earth Orbit -> Low Lunar Orbit: 1.31km/s

Low Lunar Orbit -> Lunar surface: 2.74km/s

Lunar surface -> Low Lunar Orbit: 2.74km/s

Total: 6.8km/s

That's more delta-V than a straight flight to Mars, which is between 4 and 5km/s, depending on trajectory.

If the Moon were made of fuel, it would still not make sense to land there and take off again.

This scenario describes setting up a Moon base and then shoot fuel into LEO (either directly, or with an electromagnetic catapult). From LEO, the fuel is indeed useful, but the industrial infrastructure may be excessive unless you're talking... low-hundreds of launches?

The moon is rich in He3 - both mining He3 and creating a rocket fuelled by it are in the realm of theory, but it may be possible.

That was my first thought. How do you get all the infrastructure to the moon, and probably regular personnel. For the first few trips this should not be the smart way.

if you remove mass from the moon for fuel, does that not effect the orbit of the moon, and with that the tides?

If you start spinning counterclockwise, you're robbing Earth of angular momentum and shortening the day. Source: https://xkcd.com/162/.

The point is, Moon is big. It will be long, long time before we could do anything there that could make a measurable difference in Moon's orbital parameters or tidal forces it generates.

A single asteroid hitting the moon is more than we could possibly mine.

Actually simply the mass from solar wind hitting the moon is probably more than we could mine.

(And to whoever downvoted him, this is not reddit, save the downvotes for off topic messages.)

Another issue with this would be that a Mars vehicle would probably be big, and to a large extent designed to never land on anything. Getting it down to the Moon safely and back out again would be very complicated. The solution is to do a fuel run with a smaller craft that can disengage from the main craft several times, but then you're doing several landings and takeoffs and that's going to shoot the risk WAY up.

I think that we would be wise to invest in a space elevator on the Moon. We can't support one on Earth with currently understood technology, but the Moon is different and it could be done with modern materials. A plan of this sort would seriously reduce the cost of lunar development and increase the viability of the plan in the article.

From the 4th paragraph:

>They found the most mass-efficient path involves launching a crew from Earth with just enough fuel to get into orbit around the Earth. A fuel-producing plant on the surface of the moon would then launch tankers of fuel into space, where they would enter gravitational orbit. The tankers would eventually be picked up by the Mars-bound crew, which would then head to a nearby fueling station to gas up before ultimately heading to Mars.

TLDR, the main Mars vehicle wouldn't land on the moon.

The risk of multiple moon landings and takeoffs is really quite small as the moon has no atmosphere.

Perhaps not mission critical small, it might be in the range of 0.1-2% risk for each landing/takeoff cycle. So if you require 10 refuelling launches, your total risk is 1-20%.

Say you had a large moon lander, or multiple landers that make up a robotic fuel collection and refining system. Then you have a reusable lander-launcher that lands, collects the fuel and delivers whatever it doesn't use for takeoff/landing into a orbital fuel deport orbiting either the moon or earth. Actually might be best to have your deport orbiting the moon until it's full then send it on a slow, low-fuel, multi-month path back to earth orbit, perhaps you meet the Mars transfer vehicle there.

If at any point the fuel transfer lander-launcher fails, you can launch a new one from earth and push back your Mars mission. Perhaps you have multiple fuel transfer landers as a contingency, or to increase throughput (fuel in orbit isn't just useful for a single Mars mission)

Only once you have your fuel ready, do you launch your Mars crew.

You could do a similar setup at Mars to collect fuel for your trip and avoid having to drag that fuel from the moon. But a Mars fuel transfer lander-launch would be much more complex and risky, and it would be a lot harder to land the fuel collection/refining facility.

Don't forget to add the rendezvous risk. It would also be extremely difficult to try and send it to meet the vehicle during the Mars transfer - the launch window eventually closes, and even during the launch window the ideal trajectories are quite different.

Another way to "save on weight" is to use the lowest-cost launch from Earth, and rendezvous in orbit. We're going to know what the risk and cost of reusable Falcon 9 and Falcon Heavy is long before we'd start building this lunar base. A 75% reduction in SpaceX's already low launch rates would be a big savings.

We even have experience launching fuel to ISS on the Russian and European unmanned supply ships.

I bet the author just installed Kerbal Space Program...

Can't find paper but I wonder if he'd taken into account near future technologies, like orbital construction (look at the IIS, that was 'built' in orbit) and fully reusable rockets.

Anyway I do believe we need to establish a resource operation on moon just because debugging a resource operation on mars as our first space colony would be all too risky.

I first read about this idea in http://www.amazon.com/Orthogonal-Galaxy-Book-ebook/dp/B00QD3...

Obviously getting a chance to refuel en route is huge for saving dv - the rocket equation is a harsh mistress. Honestly, I'm a little surprised that it isn't more efficient to move the fuel for lunar orbit to LEO.

If you're flying prograde wrt. the Moon, you'll still be burning enough Δv to reach the Moon, so it may seem to be more efficient to just get yourself captured there, fuel up, and continue away.

I haven't had time to play KSP in half a year, so my intuition may be a little off.

On a similar note, I do think that best way to get a shot at better and more investments in space would be to build a hotel on the moon.

(Maybe I should submit my blogpost about that to a journal to get academic cred.)

Oh wat no slingshot?

Once you've refuelled on the Moon, you can do an Earth flyby (with a small burn) to reduce the delta-v required to escape the Earth-Moon system. This is what the Nozomi craft tried to do:

https://en.wikipedia.org/wiki/Nozomi_%28spacecraft%29

But what about the mass depletion to the moon! (https://en.wikipedia.org/wiki/The_Moon_Is_a_Harsh_Mistress)

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