To the Drawing Board

Even before the 2017 IAC presentation, the need for a mostly-cargo version of MCT/BFR was clear.  At the very least, the first few ships might as well be designed to carry a couple dozen people and a lot of cargo.  They will probably spend their whole lives in that capacity.

We've established our mission, but it bears repeating:  before large groups of people can go to Mars, there needs to be someplace to receive them.  Musk's 2016 presentation illustrates that pretty well--the hatches open, the colonists look out on Mars vistas--but those vistas are barren.  I couldn't help but think, "I hope they remembered to build a base before they sent 100 people."  My guess is that the ship will actually position its hatch so the passengers look out on a natural vista, mostly because early the early outpost won't have much capability to make things pretty.  Think Antarctic base and lose some of the dreamy vision.  So, let's assume the camera pans around to reveal the outpost we're going to design here.

To keep it simple, even assuming a colonist doesn't mass more than 100 kilograms, they're still going to need a lot more than 1.4 tons of support equipment each if they're going to set up shop on Mars.  Shotwell also confirmed this thought in 2014, without elaborating.  The Mayflower's 102 passengers brought only 180 tons of provisions, but they didn't need to worry about air.

What will be needed?  Let's start a list:

--Equipment to make oxygen

--Equipment to scrub carbon dioxide

--A pressurized habitat

--Equipment to recycle water

--Equipment to obtain water (for crops and human consumption, and for making fuel)

--To become self-sufficient, enough pressurized volume to grow crops.  It takes about an acre to feed a person on Earth.  Martian soil is closer to the Sahara Desert than a Nebraska cornfield, but the colonists will have 100% control over their crops--water supply, fertilization, bacteria, etc.  Well, they'll have that control once the water, fertilizer, bacteria, etc. are available, anyway.

--Until we're self-sufficient, lots of food.  Assuming supply ships every two years, an initial thought is there should always be enough food to handle the loss of the supply ships for an entire cycle.  (I assume you saw "The Martian.")

--A place to take shelter from solar radiation storms.  That poses some interesting problems for those crops.

--Equipment to produce electricity.

--Equipment to repair everything from shelters to spacesuits to rovers.  The colonists will need an awesome set of tools.  (Bonus points if you get the reference.)  Initially, this will require lots of spare parts; eventually, we'll want equipment to make the simpler parts.  3D printing and 3D metal printing leap to mind; both require feedstock.

--Spacesuits.

--Rovers.

--Cranes mounted on rovers to move the big stuff.

--We'll also need a propellant plant, so cargo ships can make the return trip to Earth, critical for them to bring more supplies.

That's a lot of cargo.  Let's talk about that last one first.

Ultimately, this whole process doesn't work if the ships can't get back to Earth.  So, one of the early things we need is in-situ-resource utilization (ISRU) to make propellant (oxygen and methane, both of which will need to be cooled to liquid form).  Just considering safety, this probably has to be the first thing we need. 

It's hard to imagine a manned mission to Mars that doesn't have the ability to get back if something goes wrong.  SpaceX has based its architecture on orbital refueling, reusability, and ISRU propellant manufacturing on Mars.  So, the big question to be asked is whether a crewed vehicle could really go to Mars before its return propellant supply is available.  In the 2017 IAC presentation, Musk says "yes."  To be blunt, I'm not yet convinced.  This is key, because the answer will drive our early architecture more than any other.  And this isn't only a SpaceX decision.  If the US government thinks SpaceX is going to create a serious long term problem (read:  a bunch of dead astronauts/colonists), they'll simply deny the launch license.  But regardless, even if the ship goes to Mars without return propellant being available, making it available will be a top priority.

Ultimately, we (or SpaceX) may decide we want option "A," but realize that for a variety of reasons, we must settle for option "B."  In the planning business, those are alternative courses of action (COAs).  We need to identify which COAs are acceptable from a safety standpoint and feasible from a technical standpoint. 

We need to identify the COAs available and carefully examine each in turn.  But, we should also establish some design parameters that will probably hold true across all COAs.  That will let us focus the analysis on the important differences.  (This is also a basic planning premise.)

First, it looks very much like there will effectively be four types of ship, not just three.  Tanker, cargo, and manned versions were identified in Musk's presentation, but the manned versions will likely be "mostly cargo" in the first edition.  These will probably have been the developmental ships anyway, so presumably, only enough life support was installed for proving system reliability.  (Those lunar orbital trips.)  Assuming a crew size of 12 on each of 2 ships, we specify life support on each for 24--enought to sustain the entire crew of both ships.  The exact number entirely arbitrary, but this makes the math simpler, matches Musk's comments, and is high enough that a variety of equipment can be tested out.  We call these "mostly cargo" ships to distinguish them from later "mostly passenger" ships expected later.  These are different than the unmanned tankers or unmanned cargo ships. 

Let's give the various "ships" different class names, for convenience.  Calling everything "BFR" is going to get confusing, so let's just borrow from earlier terms.  To identify the unmanned cargo version, let's call it the Mars Freighter (MFR).  That acronym might also have an amusing alternate meaning.  The original mostly-passenger version was the Mars Colonial Transport, MCT.  So, let's make the new manned-but-mostly-cargo versions the Mars Colonial Cargo Ship, MCCS.  (Better options welcomed.)

Round numbers, the "mostly cargo" option gives us somewhere around 150 tons to Mars.  It appears the primary difference between freighter and crewed ships is what's carried in the "passenger" area.  For freighters, that will include lower density stuff.  It's clear that if we have access to a big ship, the first few need to be freighters.  (Musk and Shotwell agree.)  That will affect the overall program cost, since they will never generate revenue from passengers, but if we assume the first couple of ships were developmental, then they simply become the cost of doing business.  For most new airliners, the first few are never intended for commercial delivery.  They prove out the design and are then parked, put in a museum, or spend their careers in specialty service for the manufacturer.

Let's also establish that even for crewed ships, we're willing to accept a slower trip for more cargo, as long as we're only taking a couple dozen people.  If the ship is going unmanned, it should take the lowest energy trajectory available, to maximize cargo.

The "people-versus-cargo" question is largely one of volume, not mass.  Realistically, freighter and the mostly-cargo MCCS versions of the ship will carry more cargo than the later MCT simply because we'll accept a longer travel time, but we'll also be able to utilize the pressurized volume of the personnel section.  That's good, because it means the design changes required are minimal to accommodate high-volume cargo.  If you've ever seen a cargo version of an airliner, you get the idea.  Take out the seats, roll in the cargo. (If you haven't seen one I must recommend an airshow.  Or Bing.  Try "747 freighter.")

The second design parameter is safety margin.  Standard parameters for human-rated systems specify a 2.0 safety factor.  There's no compelling reason to go below this, and plenty of reasons to go above it, where practical.  This is incredibly dangerous stuff.  Our architecture needs to ensure that problems don't become tragedies, and tragedies don't become catastrophes.  No one in Europe knew or cared that half the Mayflower's passengers and crew died the first winter.  That won't be the case here.  However, this constraint will mostly drive the order of systems, equipment, and people arriving.  We can get the safety factor through redundancy and spare capacity versus over-engineering.

Okay, that should get us started.  Let's sketch out some COAs.

A a reference point from the 2016 IAC, the first thing to note about Mars Colonial Transport/Interplanetary Transport System (MCT/ITS) is that it's intended to carry 100 people to Mars, plus "luggage," everything a colonist can take in his or her mass allotment.  

The reusable MCT is capable of putting 300 tons in LEO.  Since it's refueled in orbit, this means the plan is also for it to put around 300 tons on Mars.  The exact mass depends on the launch opportunity, and ranges from 200 to 450 tons, depending on the delta-V required (200 tons with a 6 km/s delta-V, 450 tons when 4 km/s works--which can be a favorable planetary alignment, or when a slower trajectory is acceptable).  There is also mention that in "expendable" mode, it can put 550 tons in LEO.  Presumably, that equates to putting up a large space station module or something else that doesn't need to land, ever.  (An Aldrin cycler comes to mind, but that's a topic for another day.)  An expendable version would probably just use the second stage engines and tanks, with all the personnel and cargo space replaced by the payload.  (We see the same thing with Falcon 9--the payload can be a reusable Dragon, or it can be satellites.  The cargo a Dragon delivers is much less than the size of a satellite a Falcon 9 can put up.) 

In his IAC presentation, Musk says his goal is to put one million people on Mars within about one hundred years.  Throughout the presentation, the discussion mostly revolves around putting large groups of people on Mars at every launch opportunity--at least the 100 passengers on one MCT, but preferably several MCT's leaving together.  So, that also makes clear he's talking about how large numbers of people go once there's an infrastructure in place to receive them.  In the press Q&A afterwards, and other venues, he's mentioned the initial base ("Mars Base Alpha") might start with around 12 people.  (The Q&A was edited out of the available online presentation, presumably because the questions were absolutely horrible.  Sorry if one of those questioners is reading this now.  The transcript is available at http://toaster.cc/2016/10/04/IAC_Press-Conf-Transcript/.) 

Our focus here is on that much earlier stage, which Musk also clarifies is not completely designed.  To make our design goal clear and keep it laser-focused, we spell it out in the site's tag line.  I'm a fan of mission statements, so:

Mission:  To establish a permanent, self-sustaining colony of 100 people on Mars, with the capability for further expansion.

The number is entirely arbitrary, of course, but there's something deep in the human psyche about round numbers, particularly when they jump to a new level.  A question to ponder:  would you rather be the 100^th person on Mars, or the 99^th?

To set the stage, it's worth spending a couple paragraphs establishing some reasonable assumptions about what SpaceX had planned for early MCT development and testing.  That will hopefully avoid cul-de-sacs later.  The presentation showed several years of testing, so we have a fair amount of latitude in deciding what technologies we can safely assume have been proven reliable.

Before the first MCT heads to Mars with any kind of load, several precursor steps will have naturally occurred.  1) Unmanned launch to orbit, followed by recovery on Earth.  2) Unmanned launch of MCT and tanker to orbit, with on-orbit refueling.  That raises the question, "What to do with all that fuel?" which is a problem no spacecraft since Apollo 9 has had to face.  3) To use up that fuel, how about a trip around the Moon, followed by an accelerated return to Earth, with reentry at Mars-return speeds.  Wait...there's a plan for that.

Musk hints that there may be some "local" opportunities with MCT; he mentions rapid intercontinental flight specifically.  (Essentially, the spaceship alone becomes a realized version of the X-30 National Aerospace Plane, or Orient Express.)  But, there's another economic opportunity that we'll need to exercise anyway to prove out the life support:  multi-week trips for small groups of people.  Sorry, Jeff Bezos.  You want $250,000 for a 20 minute suborbital flight?  For the same price, how about a 2-week trip orbiting the Moon?

Long before 100 people ride on a ship, we'll want to take 10 or 20 up to ensure everything works as expected.  (For consistency, let's use Musk's suggestion of 12 people initially, and make it 12 to 24 during development and near-Earth test.)  To be blunt, the only way to be sure your zero-gee toilet works right is to put it in a zero-gee environment and use it for a while.  Lunar orbital trips are one possibility; as we extend the test missions, with a large amount of fuel available, missions to a near-Earth asteroid would be worth examining.

Both of these mission concepts were put to the SpaceX CEO, Gwynne Shotwell, in 2014 on the Space Show (http://thespaceshow.com).  At that time, she indicated SpaceX had little interest in lunar opportunities, and was unfamiliar with NASA's plans for visiting near-Earth asteroids.  (In fairness, NASA's plans aren't exactly crystal clear.)  However, I submit these aren't distractions; they're an opportunity to prove out technology, make a little money on the side, and generate tremendous buzz.

It's enough to make one wonder--on the day SpaceX starts really bending metal on the MCT or something similar, what happens to NASA's SLS?  Blue Origin's New Glenn is at least partly reusable, but SLS is expendable and costs $500 million per vehicle.

At the very least, perhaps SLS needs a LOX/methane upper stage, refillable in orbit?

A thought for another day.

 

At the 2016 International Astronautical Congress, Elon Musk made a presentation, "Making humanity a multiplanetary species (http://www.spacex.com/mars)."  In it, he outlined a wildly ambitious plan to put 1 million people on Mars within 100 years.

What made this presentation different from previous pronouncements by Presidents and advocates alike is that Musk isn't calling on someone else to do it.  He's planning to do it, and he has a plan to get the resources.  He's built a multibillion dollar enterprise with the express purpose of creating the necessary infrastructure.  And, as a privately-held company, SpaceX is able to do something no publicly-traded corporation can:  it can reinvest its profits wherever necessary, for as long as necessary.  It can make whatever technology bets it finds useful, and it need fear failure only to the extent that affects customer confidence.  If Musk succeeds, it won't be because he's the only one who can.  It will happen because he's one of the few who has both the desire and the resources.

Following the IAC presentation, Musk and SpaceX went largely silent on Mars plans.  There was a Reddit AMA, a National Geographic "Mars" mini-series, and a somewhat-mysterious pressure test of the carbon-fiber tank Musk revealed at the end of his IAC presentation.  But details on the the transport system, the Mars Colonial Transport for travel to Mars and back, weren't forthcoming.  The plan to send a Red Dragon to Mars in 2018 slipped to 2020, and now Red Dragon seems cancelled altogether, as its Dragon 2 predecessor undergoes changes in preparation for manned flight.

Musk himself has offered some tantalizing tweets, suggesting that the MCT/Interplanetary Transport System may have been a bigger bite than SpaceX could chew--certainly it faced a chicken-and-egg situation with regards to manned missions to Mars, to say nothing of the enormous development costs.  Next week promises some answers, as the 2017 IAC kicks off.

Regardless, it remains clear that SpaceX is continuing undeterred.  The first flight of Falcon Heavy is scheduled for later this year, a possible Apollo 8 reprise is in the cards, and with or without landing legs, Dragon 2 development continues.  Perhaps most importantly for his Mars ambitions, Musk has indicated he's "figured out how to pay for it."  Mostly likely, that means he's figured out how to make it pay, potentially opening up additional requirements for engineering solutions.

In addition to all the technical things we'll need for Mars, the people who go will need to figure out a lot of non-technical stuff, too.  What law will apply on Mars?  What social safety net will exist?  What limits will Earth impose on colonists?  What happens to a colonist if he or she commits a crime, becomes depressed and unable to work, or refuses to abide by some Earth-directed rule (say, planetary protection)?  All good questions, but not the focus here.

The focus here is on all the technical things that "those future people" will need to figure out.  Because, in one stroke, Musk made "those future people" into us.  We may not actually get there; the Mars Colonial Transport may never be built.  But we might; it might.  And if we do, that means that the engineers who will need to figure this out won't be born in a hundred years, or even fifty.  They're us.  And if we don't figure those things out, the Mars Colonial Transport won't have any place to go. 

So, let's assume MCT or something like it happens, even if it takes longer than SpaceX would like.  Then, bit by bit, I'd like to explore what needs to be built, what the mission design parameters might be, what order things need to happen, and so on.  Sure, others have worked on this--Zubrin and Aldrin come to mind; both have sketched out detailed architectures for getting to and exploring Mars.  But, they didn't have the MCT or its smaller sibling as a forcing function, and a company and a billionaire focused on making it happen now, not when a group of governments decides to.  That's new, and MCT makes every previous plan OBE. 

With a little luck, others will join the discussion and move it along more quickly.

Oh, one other note as we start--I don't know Elon Musk.  I can't bring myself to call him "Elon" when I've never met the man.  Maybe, if this takes off, some of the SpaceX engineers will join in, and recommend he drop by.