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I don't see how it can work without ISRU.  Zero LH2 boiloff in space is much easier than it is on the surface of Mars (which would probably require so much power for ascent performance hydrogen tanks that you might as well use ISRU anyway.)  Consider an easily achievable 450sec no ISRU oxyhydrogen system with a equally easily acheivable 92% ISRU oxymethane system with an Isp of 350sec.  Assuming you land a 60 tonne booster in each case and need to execute a 5000m/s ascent to an ERV in an elliptical orbit (why elliptical?  Zero boiloff is easier to achieve in an elliptical orbit and saves the ERV's propellant supply either from use for lowering the orbit, or from boiling off due to aerobraking heat.)

With the oxyhydrogen no ISRU zero-boiloff version, you reach orbit with a mass no higher than 19.33 tonnes (this includes the stage and payload for a single stage ascent; it is theoretically impossible to get more payload than this with staging.)

With the oxymethane 92% system, there needs to be an assumption about how much seed material (typically liquid hydrogen) you will have on board.  Let us assume that it is 20 tonnes, leaving 20 tonnes of booster (not much more than the 19.33 maximum above) and 20 tonnes of ISRU plant.  These numbers are quite reasonable.  The 92% ISRU leads to a mass multiplier of 12.5, so your 20 tonnes of seed hydrogen will be a part of 250 tonnes of complete oxymethane propellants.  With the given Isp, 250 tonnes of propellant can lift off with a mass of 326 tonnes, leaving 76 tonnes to share between the 20 tonne empty booster and its payload.  This translates into a 56 tonne payload, not including the stage structure!!

The directly comparable numbers are 19.33 tonnes orbital mass for the non-ISRU booster vs. 76.06 tonnes for an ISRU booster that is pretty conservative.  That's 56.72 tonnes more you can come home with (barring the inevitable complications from the ERV, which would probably bring that number down to around 40 tonnes.)

I would guess that ISRU will be far easier (cheaper) to design, build, test and qualify for flight than the 60 tonne lander!!  (ACMD (another thread) uses a 6 tonne lander for this reason.)

"60 tonne lander" means a lander designed to land a useful payload of 60 tonnes, same with "6 tonne lander"; the complete lander at entry is expected to amass about twice as much.

Thanks for volunteering!

For cIclops:

Aerospace proposals (in response to RFPs for example) for this scale of mission are usually measured in thousands of pages, so what's here is pretty summary in comparison.  The other thing is, because ACMD is so new, there really isn't much to point to for comparison, the usual method of summarizing something this complex.  I'll give it a shot anyway:

You break the mission down into smaller chunks at the bottlenecks of launch and entry to avoid the huge expenses of developing large mission scale items at these transitions.  This hasn't been done before (the second generation avoided transitions on Mars by not being about the surface exploration of Mars...the latest example of such a mission is Aldrin's proposal to go to Phobos first, IMHO a dumb idea because it is harder to support the mission there.  The second generation pushes the whole mission in large elements through these transitions, the famous example being Mars Direct with its BZ-Ares booster and big folding heatshield landers.)

Actually, it isn't, because you're in a free molecular environment, which means a shockwave doesn't form, which means that the molecules aren't bumping into each other, which means there is no sound, which means there is no sound barrier...the lack of existence of a barrier makes it difficult to break.  I learned this by ramming the door to my brother's house...which he flung open, leaving me to trip over the weather stripping at high speed (not a true story      )

Folks,

I'm Terry Wilson, founder of After Columbia Project, and this is my first major post in about four years (so long I had some trouble getting my account to work) if not my first major post ever.

I used to believe in the Space Shuttle, then that changed.  I used to believe in Mars Direct, then that changed.  I used to believe in some of my own ideas, then found out I really didn't have a clue.  I recently picked up a book entitled I Am Right, You Are Wrong, from this to the New Renaissance[i] by Edward de Bono, a general reading book about perceptual thinking.  Perceptual thinking is the core of creativity and "lateral thinking", a term coined by the same author in the 1960s which has come into general use.  This book allows me to explain what's going on inside my head, that is, changes in perception and intellectual humility (the skill required to easily change perspective.)  Just tossing that out, because in print, I tend to sound arrogant when I don't intend to be.  I'm also tossing it out because After Columbia Mars Direction (ACMD) does not resemble [i]anything previously proposed to fly humans to Mars...well, I could be wrong there.  There was a thread somewhere called "Mars 9 tonnes at a time" or something like that.
Humans to Mars: the First Generation.  Wernher von Braun, Mars opposition class, long trip, short stay, local orbit rendezvous, etc..  Probably better known today as "Battlestar Galactica".  (With all due respect to that work of fiction.  This term was coined by Robert Zubrin in his book, The Case For Mars)

The Second Generation: Robert Zubrin (and companies), Mars Direct.  Most of us know the basics by heart: launch your return booster empty to Mars, gas 'er up while she's there, then launch yourself to an established base with a fully fueled return booster waiting for you.  The biggest point made was make your own propellants on Mars using the martian atmosphere, a tactic known as ISRU.  The second biggest point was, if you're going to go to Mars, at least take a look around.  The first generation missions stayed at Mars 90 days tops (most prominent ones only 30 days in the vicinity of Mars, with only 7 days on the surface.)  Mars Direct and friends stay about 450 days, using convenient low energy transfers instead of a Venus fryby (sic) and the resulting enormous propulsion and consumables requirements.

It has problems:
- How are you going to land a 40 tonne payload on Mars?  ACMD has a couple of ideas, but they are expensive and solve entry problems, leaving you at a few thousand meters MOLA (standing for Mars Orbiter Laser Altimeter, the instrument on Observer and Global Surveyor that this average altitude is named after), a couple times the speed of sound with no parachute, no rockets, and no way to get out of your heatshield.  These ideas need some work, duh.
- No abort for the launch of the crew.  This was a minor oversight, but makes for a good introduction to...
- Needs a huge booster: The BZ Ares (BZ stands for Baker/Zubrin, to distinguish it from other projects that use the Ares name) is a big, rather fantastical booster with quite a few detail problems.  It is also a Shuttle Derived Vehicle, making it rather hard and very expensive for anyone other than NASA to acquire.

Most of the refinement has taken the Mars Direct plan (and minor variations of it) and attacked these problems with technological solutions.  ACMD seeks to eliminate them by using a different approach.  Actually, it uses several new approaches to sending humans to Mars, but they can be seen as a single approach because the different techniques enable each other.  ACMD started as Mars For Way Less in April 2007, and transitioned to becoming the MarsDrive Mission the following month.  In August, ex-Marshall Spaceflight Center engineer Ron Cordes took over the design team and immediately scrapped the MarsDrive Mission.  After Columbia Project then took it as its own and renamed it the After Columbia Mars Direction.

The main bottleneck to landing humans on Mars is the simple act of landing on Mars.  Getting from the bottom of an interplanetary trajectory to a safe landing on the surface of Mars is an enormous problem.  I believe that you can make the problem smaller by making the payloads smaller.  ACMD uses the approach of breaking down the overall mission into a number of individual landed payloads, and then assembling them on the surface.  It follows the pattern of military paradrop operations, especially the remarkable story of Flashline, the Mars Society research station on Devon Island (that story is in Mars On Earth, Robert Zubrin's 2003 book.)  I assumed a 48000kg payload and broke it down into eight 6000kg payloads as follows:

2 - crew landers and rovers.  The crew of six is landed three at a time in their large pressurized rovers directly onto their wheels like Science Laboratory using a standard hover crane landing system called the Stampede Lander.  They will be equipped with at least 30 days of consumables to allow surface rendezvous.
2 - Mars ascent boosters.  The booster has been named Destiny Booster and is designed to transport three crew members and a generous sample/hardware load to Mars orbit during a normal mission, or all six crew members without any additional payload during emergencies.  It probably will not use the same touchdown system as the other landers.  It is intended to be stationary on the surface of Mars.
3 - supply trailers.  Adequate supplies to complete the mission are provided in two supply trailers, leaving the third as a backup/redundant unit.  The crew rovers rendezvous with the supply trailers, which have independent mobility and keep alive power.  It is an open decision as to whether or not to put independent mobility power on them, which would allow the crew to teleoperate the rovers before rendezvous.  It may even be necessary for safety reasons if a crew rover is unable to move because of damage sustained during landing, or landing in impassible terrain.  Currently, it is assumed that the crew rover comes up to the supply trailer and hooks up a hitch and cable.  All wheels have motors, but only the crew rover has enough power to run them.
1 - inflatable habitat.  The inflatable habitat forms the base of operations and science laboratory for the crew.  It is landed unmanned and deployed once on the surface.

This arrangement is designed so that all remaining crew will survive if any one landing fails.  Assuming a pessimistic reliability estimate of 90% for each landing:

- ACMD has a 19.00% chance of losing three crew members during EDL
- ACMD has a 56.95% chance of losing one lander
- ACMD has a 43.05% chance of having all eight landers survive EDL
- ACMD has a 53.14% chance of losing one lander other than a crew lander
- ACMD has a 5.381% chance of losing two or more landers, and therefore the entire crew and mission (there are some small deductions, like say losing one supply trailer and one booster may be survivable, but they have not been analyzed.  This includes the 1% chance of losing both crew landers.)
- ACMD has a 94.62% chance of having a fully successful or mostly successful mission (not taking into account risk factors other than EDL.)

For comparison, Mars Direct does about this well with a 90% reliable lander:
- Mars Direct and NASA's DRM have a 19.00% of losing one of their two mission critical surface elements
- Mars Direct and NASA's DRM have a 10.00% chance of losing the entire crew on landing.
- Mars Direct and NASA's DRM have an 81.00% chance of having a fully successful or mostly successful mission (not taking into account risk factors other than EDL.)

Stampede Lander is designed as a limit case for the Viking/Apollo heritage.  It enters the atmosphere at 12000kg and lands a useful payload of 6000kg.

Going downstream, to the return phase, ACMD requires an orbiting ERV.  The reason for this is because the Destiny Booster must be as small as possible to accomodate the limitations of the Stampede Lander that apply.  This is done by setting the easiest possible mission objectives, and an aggressive ISRU strategy.  Destiny becomes impossibly large if she has to carry the habitat for the return leg and all the consumables necessary for the crew to survive.  The success of the rendezvous can be taken for granted when other dangers are considered (the chance of success for the ascent, ISRU phase, the ERV's survival, the return ejection maneuver, etc..  The lack of any required orbital rendezvous in Mars Direct is one of its weaker arguments.)  The ERV is likely the heaviest element at departure from Earth.  After ascending from Mars, the ERV uses one or more oxymethane "departure stages" to leave Mars.  This departure stage is used for in-space propulsion throughout the ACMD architecture.  The ERV alone will require several: it needs to depart from Earth after being assembled on orbit, insert itself into Mars orbit (aerocapture has not been seriously considered, but is very unlikely to be of benefit.  I estimate that an aerocapture vehicle will be 30% aerocapture systems and 70% payload, whereas a rocket maneuver at a specific impulse of 3505m/s (357.3sec) typical of oxymethane would "break even" with this at a delta-v of 1250m/s, which is a bit more than the anticipated MOI delta-v of 1200m/s.  So masswise, aerocapture of the ERV is of little or no benefit, but it would save a whole whack o' cash to simply copy the departure propulsion system for this maneuver.)  The ERV's final major maneuver will be the return of the crew to Earth.  It is anticipated that there will be an aerobraking phase that will lower the ERV's orbit, not all the way to low energy orbit (LEO, a term I use for any body, i.e: Earth LEO, Mars LEO) but to one intermediate between the anticipated two day initial orbit and low energy orbit.

Going upstream, the ACMD depends heavily on the ideas of Grant Bonin, who has worked primarily on the "departure problem" (getting from the surface of the Earth to the beginning of the interplanetary trip to Mars.)  His 2006 plan was entitled Mars For Less and should be pretty famous around here.  If not, click on http://www.marsdrive.com/component/opti … ils/gid,2/ (note: at time of writing, this link is dead, but it might work again later.)  Since then, Grant discovered that placing a staging event in planetary missions at around an energy of C3=0 during departure can be of benefit, so he suggested a high energy staging orbit for ACMD (then MarsDrive Mission).  This was contary to the LEO assembly scheme of Mars For Less, so I respected him a lot for that suggestion.  I studied the possibility of using such a staging orbit by using Delta Glider IV in the Orbiter Simulator (respectively http://orbiter.dansteph.com/ and http://www.orbitersim.com).  For typical launch vehicles where two maneuvers are available for the upper stage (the first to complete ascent to LEO, and the second within two hours), the rendezvous target needed to be on an orbit where the launch vehicle's second maneuver resulted in a rendezvous insertion at the periapsis.  This meant that the orbit needed to have a period that was an exact multiple of or fraction of one to three siderial days to be of benefit, producing orbit periods like 48 hours, 36 hours, 24 hours, 18 hours, 16 hours, or 12 hours (launch opportunities from one site every 2, 3, 1, 3, or 2 days, once or twice per day for the 12 hour orbit, since the launch site may be able to use both crossing nodes.)  The orbital design process would be more complex than this, since it would need to take into account apsidal and nodal precession, and because of these complications, each such orbit would probably have only one departure opportunity.

There are some disadvantages.  Because of the single opportunity aspect, you want to have your vehicle stacks ready early.  This means that the crew is going to be on board at least a week in advance, and will pass through the Van Allen belts several extra times as a result.  The biggest advantage of the high energy staging orbit is that the mission itself need only impart a small delta-v to get started on its way to Mars, and that the propulsion system enjoys many of the thermal benefits of high energy orbit, allowing a cryogenic stage to be more easily stored.  This cryogeic stage was an oxyhydrogen stage with the first version of ACMD in April, and also in Mars For Less.  Once the high energy orbit was adopted, use of the same stage as the ERV was now possible, so it became "The" departure stage, the only new in-space propulsion system required for the mission (not including any that might need to be developed for the boosters at both ends.)  The high energy assembly orbit is enabled by the small lander.  The smallest booster required by a mission landing 40 tonne payloads on Mars is about 80 tonnes LEO equivalent (assuming that 50% of the lander's mass is landed payload).  The 80 tonne heavy lifter lifts the lander on one booster, and the departure stage on the other.  With a 12 tonne lander and high energy orbit assembly, a 40 tonne class booster could be used.  This booster ( i.e.: Atlas VI HLV, currently referred to as "Phase 1 Evolution" in Atlas V documents from www.ulalaunch.com ) would launch the surface portion of the mission to three different high energy assembly orbits something like this:

Stack 1: Cargo landers
Launch A: Supply Trailer 1
Launch B: Supply Trailer 2
Launch C: Destiny Booster 1
Launch D: Departure Stage

Stack 2: Cargo landers
Launch A: Supply Trailer 3
Launch B: Inflatable Habitat
Launch C: Destiny Booster 2
Launch D: Departure Stage

Stack 3: Crew landers
Launch A: Cruise Stage (including outbound inflatable habitats for use during cruise)
Launch B: Crew Rover 1
Launch C: Crew Rover 2
Launch D: Departure Stage
Launch E: Crew Ferry (with the crew on board)

The ERV would probably require about eight launches, for a total of 20 launches (not including the crew's launch, which will require a smaller booster.)  The sheer number of launches per mission is usually seen as a turnoff, but it is actually an advantage.  Instead of having a big booster of Shuttle derived or all-new design, a commercially derived booster, or all-new booster intended primarily for commercial missions, can be mass produced.  The new heavy booster would not be able to find commercial customers until the exploration market led to a commercial market through space tourism or colonization (for historical examples, you can look at the colonization of the Americas, or better, the overland exploration of the Northwest and Canada and later colonization via fur trade routes and the famous "Oregon Trail", whose Conestoga covered wagon gave its name to more than one launch vehicle concept in today's age of space exploration.)  Because ACMD uses a smaller booster that can be used commercially, there will be more flight history to back up its reliability than merely those of ACMD (although probably not much with ACMD using 20 launches every 26 months) and the fact that this booster launched the first crew to Mars would be a big marketing bonus.  I'm pretty sure we could get one via an RFP process.

ACMD does have a number of open decisions:

- Exactly what sort of lander?  The current Stampede Lander is highly volume limited.  The mass category can be retained, but an inflatable aeroshell (such as Hypercone or ILC Dover's ideas) can allow more volume and in more convenient shapes.  Since these aeroshells eliminate the parachute, the uncertainty of stretching the Viking parachute to its theoretical limits is eliminated.
- Exactly what assembly orbit over Earth?  The higher the orbit is, the bigger the booster must be to launch the necessary payload, however the less work the departure stage must do, so those are made smaller and fewer.  Because the delta-v from LEO to the assembly orbit is likely being performed by a highly efficient oxyhydrogen stage without a need to last more than a few hours, it can provide this delta-v much more cheaply than the mission's departure stage.  Mathematical optimizations will probably produce an orbit that doesn't match one of the ones available for phasing, so the closest practical orbit would be chosen.
- Exactly what orbit for the ERV over Mars?  This is a more complex optimization, since the cryogenic propellants (which are cold obviously) must survive the aerobraking phase of the ERV (which generates heat.)  Also, every m/s aerobraked out must be provided by those propellants for the departure maneuver.  Finally, there is the ability of the Destiny Booster to ascend to the orbit to rendezvous with the ERV.  This is going to be a very complex trade study.
- Crew provisions during cruise...how much habitable volume?  how much artificial gravity?  how much wash water?  how much radiation protection?  how much communication power?  These are all hotly debated questions whose answers have a huge effect on the cruise element design.
- Surface element stuff: perhaps the habitat should be a tent trailer instead of a fixed structure.  Perhaps this can be done to all the supply trailers to form an initial mobile base.
- Crew Size?  6 is the current number, but it is not well anchored.  Also, ACMD can easily be adjusted to any multiple of three without major rework.  Finally, logistical matters leading to odd numbers like 5 or 7, where one of the two rovers lands with one more crew member, can't be ruled out either.

That's it for now.  My hope is that this post starts a lively discussion about new ways to get people to Mars.  People have mistaken it for a final design.  Please don't!!  It's just one idea among many (some of which are just as big a departure from Mars Direct thinking.)

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Thanks...its good to feel welcome...anyone here I know from Orbiter? ( http://orbit.m6.net/v2/boardtalk.asp )