What would it take to do "Mars Direct," let alone MCT?

[RonM]

Here is an interesting project from the University of Hawaii. They just recently completed a study where six participants stayed eight months in a dome structure to simulate a habitat on Mars.

http://hi-seas.org/?p=1278

Of course, the dome has wasted volume and is much larger than what we have been discussing for MCT, but it will be interesting to see how the crew held up psychologically.

They had 384 m³ or 64 m³ per person in the dome. If we take account the useable floor space, including the extra workshop, and factor in say a 2.2 m ceiling, then that works out to be about 320 m³. That's about 53 m³ per person.

While this experiment is for testing Mars habitat size, it still can be used to look at MCT requirements. Microgravity allows for more efficient use of volume. In this case, the loft with the relatively large bedrooms would not be needed. Individual space can be very small, like the sleeping quarters on ISS. Subtracting out the loft volume gets us down to 39 m³ per person.

That is still luxurious compared to what we have been discussing, but it will be a good reality check when the research papers are published. If the crew had no issue with their confined space, that would be a good sign.

In comparison, the MDRS Mars Hab in Utah setup by the Mars Society is about 220 m³ or 36 m³ per person (calculated with my 2.2 m ceiling assumption). The sleeping quarters in the Mars Hab are very small and seem to be a reasonable personal volume.

http://mdrs.marssociety.org/home/mars-hab-layout

One issue in using these examples is that the crew can suit up in "space suits" and take a walk outside.

[Robotbeat]

Of course, transit time is just ~3 months, not 8, so that's a big difference right there. Additionally, they likely did not sleep in shifts like you would on MCT colonization runs.

[RonM]

Of course, transit time is just ~3 months, not 8, so that's a big difference right there. Additionally, they likely did not sleep in shifts like you would on MCT colonization runs.

Good points.

I believe that gets us back in the Apollo (~5 m³) and Shuttle (~10 m³) range. Early explorers or colonists would have to have "the right stuff" and Apollo class accommodations would be sufficient. As full colonization ramps up, Shuttle class accommodations might be necessary for a wider range of colonists.

[Oli]

One hardship I see on an old slave transport is being stuck in the same place, next to the same people, all day every day for the duration of the voyage. Having some private personal space and common areas you can move about would make the voyage much more livable.

On average 15% of the slaves died at sea.

[philw1776]

I actually have trouble seeing it as that small (500m^3). If the rocket core is 10m, then the MCT will probably be 10-15m.

10m = 5m radius. 3.14 * 5m^2 = 78.5 m^2. So even if it's only 10m diameter, the habitable part would only be (500/78.5) = ~6.37 m tall.

That seems odd to me.

I think the SUV thing likely refers to individual cabin volume (excluding communal spaces) not total habitable volume divided by number of passengers.

I see the berthing/room & bathroom quarters for 50 people being inside a 2m tall, 15m diameter hull. That's 350m^3.
13 truncated pie slice rooms of 4 bunks each 2 bunks to a side.  OLED outer wall for scenery.  Inner corridor at 5m radius with center for bath/showers.
Add a 2nd tuna can 2m high module on top that's open for socializing, etc. Command & control.
The mass for this 2 floor tuna can living quarter structure should be not more than a couple 10s of mT.
Add another dorm can for 50 more passengers.

[guckyfan]

On average 15% of the slaves died at sea.

They were not healthy to begin with. Plus terrible hygiene and food. Hot and sticky under deck. Conditions to Mars will be very different. 8 m³ per person under microgravity will be quite acceptable.

[Impaler]

Of course, transit time is just ~3 months, not 8, so that's a big difference right there. Additionally, they likely did not sleep in shifts like you would on MCT colonization runs.

Do you have any idea of the DeltaV that would take?  Are you assuming some kind of VASIMR + Fusion power?

I'm increasingly convinced that they are going to need a BA2100 as the transit habitat for the 100 passenger target.  The BFR would easily be able to launch this and it would provide 21 m^3 per person, after subtracting equipment and stores you would then be looking at ~10 m^3 habitable volume per person which should be adequate.

500 m^3 is a reasonable cargo-hold but their would be no integral habitat as many have speculated, it makes much mores sense to load a large module into the cargo-hold which can be removed and left on the Mars surface to minimize the return mass.  This also has the advantage of eliminating separate crew and cargo variants.

This would leave it perhaps 300 m^3 inside after accounting for the spacing with the cargo hold walls making it about the volume of the Mars desert research station mentioned earlier http://mdrs.marssociety.org/home/mars-hab-layout which would perhaps accommodate 6-7 Astronauts permanently.  Later flights the module would basically be airplane fuselage like at 3 m^3 per person and people disembark into a waiting base/city.

[guckyfan]

500 m^3 is a reasonable cargo-hold but their would be no integral habitat as many have speculated, it makes much mores sense to load a large module into the cargo-hold which can be removed and left on the Mars surface to minimize the return mass.  This also has the advantage of eliminating separate crew and cargo variants.

It is also extremely inefficient in structural mass. MCT is all about efficiency in structural mass.

[Robotbeat]

Impaler: yes, I've calculated the required delta-v. You don't need fusion, just leave fueled up from EML1/2 or similar energy orbit. And if we did want better performance (to save on numbers of launches), haul propellant to EML1/2 with cheap Hall thrusters (not super expensive VASIMR) powered by beamed energy from the giant fusion orb in the sky. Bringing only your power converter with you and not having to haul around the fusion reactor saves a huge amount of mass. I don't understand this obsession with hauling around your reactor with you if you're in the inner solar system.

And yes, SEP has been mentioned by SpaceX for possible use with MCT.

[RonM]

Impaler: yes, I've calculated the required delta-v. You don't need fusion, just leave fueled up from EML1/2 or similar energy orbit. And if we did want better performance (to save on numbers of launches), haul propellant to EML1/2 with cheap Hall thrusters (not super expensive VASIMR) powered by beamed energy from the giant fusion orb in the sky. Bringing only your power converter with you and not having to haul around the fusion reactor saves a huge amount of mass. I don't understand this obsession with hauling around your reactor with you if you're in the inner solar system.

And yes, SEP has been mentioned by SpaceX for possible use with MCT.

Sounds good to me.

Would MCT launch from Earth and head straight to EML1/2 or would it need to be refueled in LEO first?

[Robotbeat]

Impaler: yes, I've calculated the required delta-v. You don't need fusion, just leave fueled up from EML1/2 or similar energy orbit. And if we did want better performance (to save on numbers of launches), haul propellant to EML1/2 with cheap Hall thrusters (not super expensive VASIMR) powered by beamed energy from the giant fusion orb in the sky. Bringing only your power converter with you and not having to haul around the fusion reactor saves a huge amount of mass. I don't understand this obsession with hauling around your reactor with you if you're in the inner solar system.

And yes, SEP has been mentioned by SpaceX for possible use with MCT.

Sounds good to me.

Would MCT launch from Earth and head straight to EML1/2 or would it need to be refueled in LEO first?

Depends on how many stages BFR has. If MCT is acting as the upper stage for BFR (the simplest and safest and cheapest initial cost option), then it probably would refuel in LEO first.

[Robotbeat]

Some people wanted to know the source of the 5m^3 figure for per-steerage-passenger accomodations in 1908 steamships (including public rooms, lavatories, etc) it's here:
http://goo.gl/M27iha

In fact, the British figure is just 3m^3, but I used the American figure for the lowest deck, as MCT is American . Supposedly the British vessels were still better than the German ones as far as steerage accomodations. And in either case, it was difficult to get access to the open deck for steerage passengers.

It's going to be tough to get to Mars on an inexpensive ticket, but it ought not be made impossible. The entertainment and air quality can both be made much better than they were for 1908 steerage class passengers, and 7m^3 of space per passenger would be downright spacious compared to the conditions our great-great-grandparents had to endure in order to travel the seas on a working man's wage.

[Impaler]

500 m^3 is a reasonable cargo-hold but their would be no integral habitat as many have speculated, it makes much mores sense to load a large module into the cargo-hold which can be removed and left on the Mars surface to minimize the return mass.  This also has the advantage of eliminating separate crew and cargo variants.

It is also extremely inefficient in structural mass. MCT is all about efficiency in structural mass.

The most mass efficient thing is to NOT make it integral to the MCT.  The time when structural mass efficiently maters most is take off, and if we indent to me offloading people and not taking them back to Earth then all that habitat mass would be pure dead-weight on take off.

[A_M_Swallow]

500 m^3 is a reasonable cargo-hold but their would be no integral habitat as many have speculated, it makes much mores sense to load a large module into the cargo-hold which can be removed and left on the Mars surface to minimize the return mass.  This also has the advantage of eliminating separate crew and cargo variants.

It is also extremely inefficient in structural mass. MCT is all about efficiency in structural mass.

The most mass efficient thing is to NOT make it integral to the MCT.  The time when structural mass efficiently maters most is take off, and if we indent to me offloading people and not taking them back to Earth then all that habitat mass would be pure dead-weight on take off.

So follow the "2001 A Space Odyssey" patten. Change spacecraft at a spacestation in LEO.

[Russel]

I would suggest that there are some very important differences between a sailing boat and a space ship.

Alcohol might be useful on a sailing ship. And if someone gets drunk you can just lock them up. May not work that well on a space ship. If someone gets violent he can be subdued and locked up. And there was always the ever present threat of escalation of violence (lash, pistol etc). That aint gonna work too well on a space ship.

Plus a sailing ship could get away with a low average space per person because there was enough room overall for certain spaces dedicated to certain purposes. And there was still room (in most cases) to be able to stretch your legs and stare out to sea. Not so on a space ship.

Might I suggest that yes, you can take a small group of well disciplined and trained people and put them in a relatively small space and they generally won't stab each other, that its still a good idea if you want people to function efficiently, remain sane, not be homicidal and mostly importantly not arrive on Mars in a depressed state, to give them some creature comforts and a little bit of room to be alone.

I think also when it comes down to small groups, like 4 crew, you might find that the necessary volume of food and water (including water for radiation protection reasons) might be larger than you think. And that the structural mass of the volume you need to enclose isn't as important as the mass of all the hyper-reliable, redundant life support systems you need to take.

[KelvinZero]

padded cells in space would be pretty easy and actually sort of fun.

[Russel]

Maybe you just need four buttons and some wires to keep them amused...

[Pipcard]

Here is the ERV diagram from Zubrin's presentation. Let us focus on the volume and not the mass of the crew cabin which is most likely underestimated (we can also say that this mission doesn't need a direct launch injection to Mars - refueling in Earth orbit is acceptable). Let us also assume that the habitable volume of the ERV is in the 5.6-m-tall truncated cone section.

Based on some pixel measuring, the top diameter is 4.95 m (2.475 m radius) and the bottom is 6.5 m (3.25 m radius).

The formula for the volume of a truncated cone is 1/3 * π * h(R₁² + R₁R₂ + R₂²). Plugging the numbers in results in a volume of about 145 m³ or 36 m³ per person for the six-month trip (this is, of course, not counting any equipment, so the actual volume would be lower than that).

[Pipcard]

Why was the Semi-Direct plan created in response to Mars Direct? Why do I keep trying to compare Mars Direct with MCT?

In 1991, Dr. Robert Zubrin came up with an interesting and ambitious proposal he called “Mars Direct”. Like the Case for Mars mission studies, Zubrin proposed sending an ISRU unit ahead of the crews to generate consumables and fuel needed for their forthcoming surface stay. Also, quite ambitiously, he proposed that this ISRU capability could be utilized to not only provide consumables and fuel for the crews surface activities, but also to generate all of the propulsive fuel necessary to send the crews not only through the ascent to Mars’ orbit, but also to escape velocity and onto the trans-Earth trajectory. This feat would have been accomplished via a single ERV sent to the surface ahead of the crews. A small nuclear reactor onboard it would provide the power necessary to generate the large quantity of fuel required to send the crew and their return habitat through ascent and departure from Mars. The crew of four would be sent to Mars within their surface habitat using a conjunction-class trajectory, with enough supplies onboard to last 550 days on the surface, before using their rovers to perform a surface-rendezvous with the awaiting ERV. Both the Hab and ERV would be launched into a direct trans-Mars trajectory using a single Saturn V class HLV each. Thus IMLEO requirements are kept low, and the need for orbital assembly is eliminated. The long surface stay allowed more science to be conducted for each mission. However, many viewed such a mission plan as too technologically ambitious to be credible – citing a myriad of issues, such as hopelessly optimistic technology assumptions, and lack of adequate mass margin.


Above: Zubrin's minimalist Hab and ERV landers, shown in close proximity on the surface of Mars. An example of the "vertically-split" surface-rendezvous mission profile. Note the very small presurized rover that is squeezed in with the Hab lander. Later NASA DRMs delivered a much larger rover alongside the smaller MAV lander.   

The Mars Semi-Direct architecture proposal that followed (also 1991) might be interpreted as a partial rebuttal to some of these concerns. Instead of specifying such a wildly ambitious “do it all” ERV vehicle, the function of ferrying the crew from Mars surface back to Earth was split up into two parts, to be performed by two separate vehicles: A Mars ascent vehicle (MAV), which needed only to generate enough fuel for the crew to ascend to Mars’ orbit, and the Earth return vehicle (ERV) which was pre-placed in Mars’ orbit – and which would perform the propulsive maneuver needed to send the crew back to Earth. This was exactly the Mars orbital rendezvous (MOR) mode of operation that earlier mission plans had specified. Combined with the other elements of the Mars Direct architecture (pre-sending unmanned assets, maximal utilization of ISRU, no orbital assembly) the result was the more robust “Mars Semi-Direct” plan – perhaps a natural culmination of the “vertically-split” approach.

For the next two decades the core of the Mars Semi-Direct philosophy appears to have gone un-trumped. Theoretical work appears to be focused on providing definition of more realistic mass and technology requirements, rather than on exploring wildly different mission options. NASA’s own DRM series of architectural studies is perhaps one example of this. Other variants of the Semi-Direct approach have also been explored – such as Wilson & Clarke’s MarsOz (which attempted to better define EDL requirements as well as explore photovoltaics as a potential replacement for surface nuclear power), and Bonin’s Mars for Less (which brought the idea of orbital assembly back in to allow use of EELVs rather than HLVs).

Required surface payloads, however, remain high for all of the mission concepts explored above – 25 to 60 tonnes – two orders of magnitude above what has been able to be accomplished by robotic craft to date. Furthermore, the payload mass fractions specified (often 60% or higher) would seem hopelessly optimistic in comparison to the payload mass fractions of the robotic landers (closer to 30%). In 2006, Grant Bonin, the lead designer of the Mars for Less mission concept, acknowledged this discrepancy, stating that both Mars for Less and Mars Direct were unrealistically optimistic in their EDL assumptions. Even NASAs own DRMs may not be immune, with recent EDL studies indicating that their assumed EDL methods are not viable in their current form, and will have to be revised. So while there have been many purported “showstoppers” in the quest for Humans to Mars, the task of getting massive payloads through the bottleneck of EDL is perhaps still the most relevant – and, arguably, still remains unresolved. In short, the pieces are still too big.

Now of course, Mars Direct has most likely underestimated the mass requirements, but if there were concerns about a "'do it all' ERV vehicle" and 30-tonne surface payloads being too "ambitious," then MCT is even worse! 100 tonnes to surface, an all-in-one reusable Mars Transfer Vehicle/Surface Habitat/ISRU Plant/one-stage Mars Ascent & Earth Return Vehicle...

I see Zubrin get dismissed as a crank sometimes, but aside from the optimistic mass budget and direct-to-Mars launch profile, Mars Direct is nothing compared to the MCT. That doesn't mean that I am not eager to see the actual plan once its revealed, though. It just means that it can finally be scrutinized instead of speculated upon. The main thing is that I just don't get why Zubrin's plan isn't taken as seriously on this forum as MCT is.

At least he's not talking about landing 30 tons on the surface with a heat shield this time.

[guckyfan]

I see Zubrin get dismissed as a crank sometimes, but aside from the optimistic mass budget and direct-to-Mars launch profile, Mars Direct is nothing compared to the MCT. That doesn't mean that I am not eager to see the actual plan once its revealed, though. It just means that it can finally be scrutinized instead of speculated upon. I just don't get why Zubrin isn't taken seriously on this forum while MCT is.

The difference is that MCT assumes a separate already installed ISRU capability. You cannot land MCT just anywhere, you need that infrastructure in place. Which in all likelihood means you have to send one or two disposable MCT first which may or likely may not fly back to earth many years later. A MCT mission can by definition not be a one off unless you are willing to splash out for all that infrastructure for every landing location. Which may still be cheaper than other architectures due to cheap reusable launch capability on earth.