# 1-month Free Shipping... To Mars

Amazon has extended to Mars, and their Prime customers there need, if not 1-day shipping, at least 1-month shipping.

They have created a shipping mechanism involving some method, that allows them to ship items to Mars in 1 month. This method is fairly resource-intensive, but Amazon researchers have determined it as efficient as possible.

What is this method, how much does it cost to use, and what materials would be valuable enough on a Martian colony that it would be worth that cost?

• Obviously food is valuable on a Martian colony, but food also weighs a lot
• This Martian colony is similar to a real-life medieval colony; hopes to be self-sufficient, but it's not quite yet. It has access to basic food production, but it is not yet enough to have anything more then the bare minimum nutrition
• Please consider acceleration and deceleration of the material
• It's not necessary, but I would like the solution to involve a railgun, becuase they are cool. EDIT: After quite a few answers, I don't think this possible. No need to include this.
• Is having an Amazon Distribution Center on Mars an acceptable solution? Jan 4 at 19:06
• You don't use this method for things that are valuable, you use it for things that are urgent. With proper planning, you just need to send a resupply ship every month, and the colony will have a regular supply of goods - after the first trip, one ship arrives roughly every month, no matter how long the trip takes. Food is a very predictable resource need and would be a poor choice for rush shipping except in emergencies, since you never need it unexpectedly. Valuable but non-urgent goods still get shipped, but not in such a costly manner. Jan 4 at 19:17
• "Consider acceleration and deceleration of the material" ... "involving a railgun". Hmmm. Jan 4 at 19:54
• @ChrisH I guess that's what I consider "self-sufficient", though I guess you could make two definitions - one where they are self-sufficient in the sense of being able to produce all of their own goods, the other being that they are economically independent and have at least an economic balance of trade.
– J...
Jan 5 at 22:01
• I hope you mean "similar to a real-life medieval colony" only in the self-sufficiency aspect, and not that they gallop on horses, have knights and swords and armour, castles, serfs, and all the package... :-P Jan 6 at 13:20

The maximum distance between Earth and Mars is ~401.3 million kilometres. Leaving aside the pesky star in the middle for now, to cover this in 30 of your Earth days is going to take a fearsome rocket.

You'll be needing a continuous thrust rocket, where the engine has a steady acceleration up to the half-way point of the journey, at which point the rocket flips over and then does a stead deceleration burn to the destination. The brachistochrone equation can tell us what sort of oomph you need: given a distance $$d$$ of 401.3 million km and a time $$t$$ of 30 days, you end up with an acceleration $$a = \frac{4d}{t^2}$$ of about 0.24m/s2. That's not obviously a whole lot, but it adds up over 15 days of boosting to get you a peak speed over 300km/s which is pretty formidable.

With a required delta-V of ~620km/s, you're going to need a potent rocket engine, or a rather silly amount of fuel. Lets say we have a generous mass ratio $$R$$ of 10... that is to say, the loaded spacecraft masses 10 times as much fully fuelled as it does when its tanks are dry (or alternatively, the fuel masses 9 times more than the empty ship). You can use the specific impulse formula to work out that you need a rocket with a specific impulse of 27426 seconds, or an exhaust velocity of 268km/s. This is at the very top end of what a VASIMR might produce.

Lets say your spacecraft weighs about a 200 tonnes with full cargo but no fuel. That gives it a "launch" mass of 2000 tonnes. I put "launch" in quotes because I'll handwave this as leaving from high Earth orbit. To reach the required acceleration, you need an initial rocket thrust of nearly half a meganewton. With the required exhaust velocity, that means a rocket power of about 64 gigawatts. Clearly, no VASMIR is going to manage that, as it would require a giant nuclear reactor to operate. Clearly, you need a nuclear drive. I can't find any fission designs that are this efficient and powerful, so you'll be wanting fusion.

The ever useful Project Rho suggests two research papers on fusion driven spacecraft designs... this makes the designs plausible, if not yet actually possible.

Both these designs have much lower mass ratios than your ship needs, but they should give you a starting point. Critically, both ships have a fairly similar layout, showing quite how much space needs to be given over to heat sinks for your monstrously powerful nuclear engine:

Your delivery ship will have much more fuel, and a substantially larger engine because the Hope and the Discovery II are plausible ships with sensible milligee accelerations, and your nuclear monstrosity needs 10 to 15 times what they have.

Note that if you relaxed your shipping requirements slightly to be "30 days at closest point" (which gives you far fewer launch windows) you can use either of those ship designs as is for your needs. Only for the "30 days regardless" requirement do you need crazy rockets that carry ten times the fuel and have ten times the acceleration.

For the shortest possible trip, your rocket could make it in a little over 11 days with a mass ratio of more like 2.33, meaning it could carry several times as much cargo.

how much does it cost to use

Well, the trite answer is "as little as is required".

You do need to be able to put a few hundred tonnes of cargo into space cheaply (or manufacture everything you need out there) and you also need to be able to produce several hundred tonnes of refined nuclear fuel (requiring deuterium separation, tritium generation, lithium separation, etc) and get that up to the relevant orbit, too. You need to be able to do the same job at the Mars end of the journey, or your delta-V budget quadruples. One assumes that if you can't refine fuel in Mars orbit, you send it there via slow, infrequent but vastly cheaper and simpler Hohmann transfer.

The ship will need work after every flight. There will be micrometeor damage, radiation damage to the drive nozzle, neutron-activated drive components to replace and decontaminate, whatever else.

Clearly you are talking about a society which can do this, because flying to Mars in a month, on demand, regardless of its current orbital location with respect to Earth is a very technologically challenging, as I hope I've made clear.

what materials would be valuabe [sic] enough on a martian colony that it would be worth that cost?

Any piece of critical equipment in an emergency. Nuclear reactor parts, medical equipment, etc. Most likely it will be people that are the critical resource, and more importantly they're also the thing that suffers the most in long duration spaceflight.

A sensible colony would have backups of all the critical things, and replacement stocks would be kept topped up via slow but cheap(er) freight.

Please consider acceleration and decelleration [sic] of the material

A quarter of a tenth of a gravity. Don't you worry. Your ornate glasswear will be just fine.

Of course, landing stuff on the surface of Mars might be a bit more, uh, sporty. But clearly you can land people on there, so as long as whatever you're sending is no more squishy and fragile than J. Random Meatbag, it'll be fine.

It's not nessecary, but I would like the solution to involve a railgun, b/c they are cool.

With a max velocity at flipover of more than 300km/s, I simply don't know how you'd make a railgun that could throw a projectile fast enough to be of any use at all. Sorry about that. Some fusion reactor designs use railguns to throw plasmoids, but that's an internal detail of the reactor and not the sort of cool that you can really look at or interact with externally.

• Thank you for the excellent answer! I'm going to wait a bit, but if no better answers come in soon, I'm accepting this. Jan 4 at 22:48
• I'm going to accept this answer, but let it be knwon that if I could accept more than one, Nosajimiki's and Beyond Disbelief's would have my vote. Jan 5 at 20:35
• @Firedestroyer you can still upvote other answers after accepting one Jan 5 at 23:55
• @JoshPart All those answers I've already upvoted — I make a habit out of upvoting the answers that I like, before accepting them. Jan 6 at 12:00

Amazon is an interesting reference point to use. The thing about Amazon is their supply chain network is HEAVILY supported by data analytics and prediction algorithms.

I am confident in saying that so long it is not a one-of-a-kind product, by the time we colonize Mars, Amazon can easily promise same day "shipping" regardless of how long it takes to transport to Mars; Amazon would have the data to anticipate each item's day to day demand forecasting months in advance and plan their shipping schedule to fill them as needed. The Earth-made product is likely shipped to the Martian warehouse long before the cusotmer ordered it, and dispatched when they click "Checkout."

But wait! What about new releases? Amazon Prime has an entire legion of product/partnership managers - no, not managers for the product you're purchasing, but specific aspects of the "Amazon Prime" program. (I personally met one of Amazon Prime's product managers, her job is strictly in ensuring shipping times.) With Amazon's purchasing/negotiation power, they are likely coordinating with all significant businesses with their new product releases and have that headstart in shipping direct from manufacturers, so even an Earth-made product is released tomorrow, you bet Amazon can make sure Martians will get it on the same day for any company that's in the habit of synchronized worldwide release dates.

• This. In fact, many don't realise that this is actually how Amazon works. By pre-stocking inventory locally at each city, it is possible to deliver quickly within a day or two items giving them a complete advantage over traditional shipping companies. We use this method, and we have to send lots of stock to multiple city locations worldwide long Before they sell (even if there is relatively low demand), so Amazon can fulfil their delivery promise.
– flox
Jan 5 at 6:07
• I think the population on mars might be too small to apply any kind of machine learning forecasting. Jan 5 at 7:32
• @Vincent While that might be a fair point, given those parameters aren't defined by the OP and since Amazon is a private business, not USPS, I think its safe to assume by the time Amazon steps in the Martian colony is in fact of sufficient size. I personally live in a town of 60k pop and I regularly get my shipments under 24 hours despite selecting 5-9 days shipping option.
– user93359
Jan 5 at 7:36
• This is mostly viable other than the inevitable fact that Mars will be a year or two behind cutting edge tech devices and there isn't really a way around that. Retailers aren't going to hold back a flagship model they need revenue on for their next R&D for two years just so that Mars can get it at the same time, especially if the colony is small. Jan 5 at 16:24
• @BeyondDisbelief I'm not referring to supply impacts, but rather, a manufacturer sitting on their next big product for however long it takes to get them to Mars before having a release date. It could work in some circumstances I guess. It depends on what the product cycle from "done" to "available" looks like. Jan 5 at 18:35

Amazon solution to this apparently impossible problem is to put in orbit around Mars a 3D printing factory, which produces anything available on their catalogue and then send it on the planet. Then they send from Earth regular resupplies for the raw materials, which arrive roughly once a month.

• What do you think would be a more reasonable time for shipping? Jan 4 at 19:24
• @Firedestroyer You can get a decent 9-month delivery opportunity once every 26 months, for not too far a future technology, when the planets align such that you can travel along an elliptic orbit that meets both of the planets' at a tangent. Anywhere outside the window and the costs ... skyrocket. I'm not sorry. And of course, hardware failure or arrival means the cargo ends up in, to put it mildly, general heliocentric orbit. Jan 4 at 19:43
• @Firedestroyer the only other way to achieve 1 month delivery without using L.Dutch's method is to have a large fleet of ships, each carrying the entire content of the Amazon catalog on board. Due to their odd orbit between the earth and Mars, one could pass by would be 1 month, then they just drop the selected item from orbit as it passes by. This may be an answer, but its kind of stupid and I like L.Dutch's answer Jan 4 at 20:10
• At 9282km/s over 2592000 seconds (30 days) you'd cover about 24 billion kilometres. We want to go to Mars, not head for the Oort cloud! Jan 4 at 20:56
• What's the advantage of having the factory in orbit? Wouldn't it be far easier to just build such a factory (or ideally many factories) on the surface? Regular shipments of raw materials from Earth would still be needed, they'd just have to land them near enough to the factories to be retrieved and shipped the rest of the way on land. Jan 5 at 15:57

# Buzz Aldrin to the rescue

Mr. Aldrin is best known for his landing on the Moon in the Apollo 11 mission. Another contribution he made to humanity was the discovery of cyclers for the Moon and Mars.

A cycler is a trajectory that encounters two or more bodies regularly. Once the orbit is established, no propulsion is required to shuttle between the two, although some minor corrections may be necessary due to small perturbations in the orbit.

Aldrin discovered the first Mars cycler in 1985. Afterwards more cyclers were discovered, all listed in the link above.

The point is that, as other answers have already explained, Amazon would have goods going to Mars on a regular basis - think of a fleet of spaceships doubling as warehouses in solar orbit. This would all be controlled by algorithms and logistics etc. With cycler trajectories, you signal the next oncoming spaceship to prepare the packages to be sent to Mars. Upon closest approach, the warehouse sends a fleet of lander drones to delivery centers on Mars which will handle the last leg of the process. The warehouses are then restocked upon closest approach to Earth.

With the shortest Aldrin cycler, each warehouse would have a 146 days transfer between Earth and Mars. That means a minimum of five mega orbital warehouses could allow for a delivery time within one month of ordering. A fleet with dozens of orbital warehouses in the least would allow for better service level given backups, redundancies and the ability to possibly cycle stuff between warehouses.

• Looks like the minimum fleet size in this solution is 26~ the whole cycle takes 2.135 years(16 months of that beyond mars orbit) to return to earth. Interesting that Mars next delivery from earth is only 5~ months out though. Jan 6 at 20:46

Starfish Prime almost got it. He's got usable numbers for the course but he made the mistake of thinking rocket.

The answer here is clear--laser-pumped lightsail. (Although something outside the visual spectrum might work better.) You don't haul along the big powerplant, you have one at Earth and one at Mars. Big sail, small package, boost away from Earth, then Mars takes over and slows it back down.

Energy-wise you'll do better the harder you can push without melting things, a higher acceleration allows you to get there with less velocity and total energy use is effectively linear with velocity and at the .001c of turnover little is being lost to Mr. Doppler.

• I thought light-sails required absolutely massive sails for even a marginally heavier object? Jan 5 at 15:31
• @Firedestroyer Note: Laser-pumped. You can put as much energy on a bit of the sail as it can take without being damaged. The sail will be very large but that's not a problem. Jan 5 at 16:11
• @Firedestroyer Lightsails can be powered by laser beams/phased arrays rather than just sunlight. Related: en.wikipedia.org/wiki/Breakthrough_Starshot
– user93359
Jan 6 at 21:19
• @BeyondDisbelief And note that they're after a 100,000 m/s^2 boost phase. A terajoule delivered to an area a few meters across. While you're not going to be able to pull that with anything attached to the sail it means the sail itself can take that kind of energy--thus what I'm proposing is well within what we can envision. Jan 7 at 1:42

The time to get to get to Mars varies depending on transfer window - at your best closest approach, you have travel times of less than six months. Getting people there with nuclear engines is considered fast at a couple of months. Getting cargo there in such a short time simply is not necessary, nor really in the cards.

As I said, you have to target the right transfer window, a window that opens up approximately every two years. Because of this restriction, much cargo that would be used by humans on Mars would be sent in advance of humans being there, and redundant cargo would be sent. In the long term, humans on Mars would want to strive for being completely self sufficient, not needing to import anything from Earth.

I think for the purposes of your scenario, the best you could do is have a some kind of mass driver on the Moon. You'd have to dig into the numbers on this though, as I again, don't think that it would be nearly as fast as you desire, and could only arrive in the transfer window.

If you are flexible on increasing the time, but just want a regular delivery service to your people on Mars, the most realistic method besides a mass driver on the Moon would probably a Mars cycler. This would be (in the long term) a nuclear powered craft that is going back and forth between Mars and Earth, never stopping. I imagine this in the future being one of the most high volume ways to transport people and cargo to and from the red planet.

So I regret to inform you that unless you are willing to have very handwavy tech, this just isn't happening in its current form. It takes even light a full twenty minutes at some times to get between Earth and Mars.

All this being said, I think the most unrealistic part of this scenario is Jeff Bezos getting any sort of presence on Mars, when his twenty year old aerospace company Blue Origin has yet to send anything to orbit.

• Blue Origin's mission statement is very different from SpaceX, though. Asteroid mining has much more economic benefits for Earth whereas SpaceX is more of a pipe dream. Musk can't even think of anything to incentivize people with other than a $400k one-way ticket for "tourism". – user93359 Jan 4 at 21:11 • @BeyondDisbelief I think this is getting a bit subjective... being critical of SpaceX's future goals is certainly warranted, but you seem to deny that they've had any impact on the space industry. Calling SpaceX a pipe dream in general is grossly inaccurate. I am hopeful of Blue Origin's future plans with Orbital Reef, but I think they are a great deal behind anything SpaceX will accomplish. Jan 5 at 0:15 • I'm speaking on the context of Mars. SpaceX has made nice strides in making launches cheaper, making sub-orbital flights a closer reality, but that is not Mars. Many critical questions about the touted Mars colonization objective were not answered, and I was not at all impressed by his SpaceX presentation. If you say Blue Origin wont get any sort of presence on Mars, there's no existing contendors that has made meaningful Martian progress. Also, Blue Origin != Amazon. Tesla != SpaceX. These are separate entities, and the accomplishments (or lack of) cannot be solely attributed to its leader. – user93359 Jan 5 at 0:27 • @BeyondDisbelief I will concede to your last point, connecting the companies together does not equal the same result. Amazon has shown with things such as Kuiper that they are willing to use other launch providers than Blue Origin. I'm not sure what you mean talking about SpaceX making suborbital flights a closer reality - SpaceX is the dominant US player in orbit, unless you mean suborbital Starship, which I do consider to be a concept they just kind of came up with to appease investors. In my eyes, even if Starship completely failed, SpaceX would get to Mars anyway with existing rockets. Jan 5 at 6:01 Given that the distance from Earth to Mars can be as little as about 40 million miles (64+ million kilometers), or as much as approximately 225 million miles (roundly 360+ million kilometers, with the Sun in between; minimum pass length during opposition would be above 400 million kilometers), this is a pretty tall order. For a railgun to supply a velocity high enough to reach oppositional Mars in under 30 days, it would need to be either extremely long, or use a very high acceleration (or both) -- and then you have to slow down the package at the Mars end, ideally without vaporizing it in an aerobrake maneuver. I don't think a railgun is going to do the job. What they need is a constant boost drive. That also avoids the problem of having to "shoot" too close to the Sun and risk heat damage during the day or so of closest approach; the delivery drone can vector its thrust to steer wide with little additional acceleration required. For the shortest distance, at 1G, the trip takes about a week; at the longer range, allowing for that all-important "don't melt the package", you'd need a bit more than 1G to finish the trip (including turn around and deceleration) in a month; without doing the math, I'd guess around 3-4 G will do the job. The good news is, anything you'd now trust to UPS or FedEx will survive the G load. The bad news is, the energy cost of this kind of drive would beggar whoever had to pay for the shipping. Four weeks of constant 4 G acceleration is on the ragged edge of what a projected Orion drive can manage (and I doubt either you or I want Bezos's spiritual descendants to have access to nukes, never mind thousands of them). ## Fusion Powered Engines The maximum distance between Earth and Mars is about 400,000,000km To get there in 30 days using constant thrust (to minimize G forces and maximize fuel economy), you must accelerate at ~0.23815m/s^2. This gives you a peek velocity of 308,642 m/s by the time you are half way there, you then turn around and slowly decelerate for the rest of the trip. This whole trip would require a total of 4.8e4MJ of thrust per kg of cargo. An ideal fusion generator is pretty much the most cost efficient system you can theoretically make using Newtonian Physics. If you could perfectly convert hydrogen into helium as a power source and perfectly turn that power into thrust you get about 3.4e8MJ of thrust per kg of fuel; so, it would only take about 1 gram of hydrogen fuel per kilogram of cargo to make the trip. Since hydrogen costs about \$1.80/kg in today's market, this would make the fuel cost for shipping less than a penny per kilogram of cargo. So, while such a ship may not be cheap to build, the overhead could be extraordinarily low making free shipping very affordable.

Now I can not emphasize enough how idealized these values are. Various estimates for a near future fusion reactor are somewhere between 50-95% efficient, and they will use fuels that are much more expensive than common hydrogen. Deuterium gas (a more likely candidate for affordable fusion) costs about \$1000/kg. You also have to consider you are transporting the mass of the ship itself. So we can probably assume you are really transporting about 2kg of mass for every 1kg of goods when you compare it to other methods of shipping like semi-trucks, trains, and break bulk freighters. You also have to consider the power efficiency of converting the energy in your fusion reactor into thrust. Ion engines are currently the most efficient form of propulsion we have at about 90% power to thrust ratio... but they are not very strong using today's technology. If strong ion engines can not be developed, you could get a lot more thrust over time venting the fusion reactor directly into space, but you'd probably get something closer to the 35% efficiency we see out of chemical rockets. So, a more realistic (though still pretty idealized) guess is that a fusion powered rocket would more likely cost somewhere in the range of \$0.33-1.60 per kg of fuel. The freight trucks that Amazon uses today have an average efficiency of about 180mpg/ton. So, to ship 1kg 1000 miles by truck has a diesel fuel cost of only about \\$0.02/kg. So, between the longer operational time, and higher cost of fuel, it would probably still cost Amazon about 30-100 times as much to send a package to Mars as ground shipping does here on Earth. Ultimately, Amazon Prime would probably not be able to cover the cost of shipping on all goods sent between Earth and Mars unless they could develop a viable fusion engine that works off of normal hydrogen. But even a deuterium powered fusion engine could make shipping affordable enough that many consumer goods like electronics, medicines, clothing, and even food could be more cost efficient to manufacture on Earth and send to Mars than to try to make on Mars itself, and the Rare-Earth elements that you may be able to mine from Mars (or at least near by asteroids) generally go for enough here on Earth to make the cost of shipping those back this way worth while.

SIDE NOTE: This answer excludes the cost of actually getting goods in and out of our planet's gravity well... for this you need an initial acceleration of well above 0.23815m/s^2, but you would only need to reach 11,200m/s leaving Earth or 5,300m/s leaving Mars at this higher acceleration before you can drop down to your lower acceleration. Assuming you are using the reactor venting method of propulsion here to achieve chemical rocket like accelerations, this should not significantly change your cost.

• "To get there in 30 days using constant thrust (to minimize G forces), you must accelerate at ~155m/s^2" - please double check you math. Jan 4 at 22:32
• @Alexander Wow, I don't know what I did there, but yes I was off by a few orders of magnitude there. Instead here is the answer I was originally thinking about before I got that insanely high energy cost. Jan 5 at 16:20

# Nuclear powered railgun ship.

Amazon has mastered railguns and nuclear fusion, and has a space ship that does both.

By firing massive railguns behind them with their enormous electricity from fusion they can accelerate at 0.05 G, and reach Mars in 26 days even at the greatest distance.

The cost of nuclear fusion engines and futuristic railguns is unknown, but probably high.

# The main value probably wouldn't be from mars colonists, so you could transport them whatever, but from hauling parts for asteroid mining.

Mars has a deep gravity well. It's hard to get anything useful from them. The asteroids are more useful. It wouldn't be too expensive to strap a small fusion engine to an asteroid, move it to mars, wait till earth is close, move it to earth orbit, and mine it. Mars is a great waypoint for such missions, and the colony is probably there to make mining more efficient. No need to go on an expensive trip home if your family is on mars!

Any space mission is gonna be incredibly expensive, but not getting valuable ores and metals and rare earth stuff from asteroids is more expensive. Any components needed for mining will as such be shipped very quickly to Mars, to ensure that they stay functional. Computers, drill bits, scanning tech, spaceship parts, all the advanced materials that are hard to make.

There would likely be a fixed amount of cargo for mining, a fixed amount of key colony goods to maintain the colony and a certain amount of extra space for whatever else people wanted to order. You'd bid for parts by weight, so people would probably mostly order expensive computer parts that were weight efficient, hard drives of valuable info, mementos from home, small animals, and manufacturing equipment to make stuff locally.

If you are min-maxing for high production value and low mass, pharmaceuticals and semiconductors are at the top of the list. Even if the Mars colony has readily available 3d printers and machine shops, bootstrapping yourself up to a tech-base that can produce nanometer-scale integrated circuits takes a long time and an enormous amount of effort. Similarly, vaccines and other drugs, besides having astoundingly expensive R&D costs, are also extremely difficult to produce--we only can afford them because they're mass produced.

Fortunately, neither computer chips nor pills are particularly vulnerable to high accelerations, so an orbital railgun that fires small reentry-capsules loaded with processors and ibuprofen in the general direction of Mars could probably turn a profit. Even if 99% of the chips miss Mars or burn up on reentry and are destroyed, they cost basically nothing here on Earth to produce.