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#26 2012-03-27 21:53:07

louis
Member
From: UK
Registered: 2008-03-24
Posts: 1,226

Re: Mars Semi-Direct with Falcon

RobS wrote:

Actually, Louis, I've been thinking about your question about small payloads, and maybe I have misunderstood you. What do you mean by "small"? And when do you favor small payloads?

For the first mission or two, I wouldn't favor dividing the mission into a bunch of small pieces, because the landing technology won't have been perfected yet and because you need to maximize your chance of success; otherwise, you could lose public opinion and the funding for future missions. You need to get the crew and the essentials of their mission to the surface in the fewest landings possible, so as to avoid the possible problem of losing essentials. Zubrin's Mars Direct does that pretty elegantly: three vehicles, two being identical Earth Return Vehicles to guarantee the crew can get home. If you lose one of the two ERVs, you still have the other. If you lose the hab, you lose the crew. If we can reduce that even further, to two ERVs (one with the arriving crew) maybe that's better. Or maybe not.

But if you plan to expand beyond arrival of 3 or 4 astronauts every 26 months (and leaving before the next crew arrives) then yes, cargo landers are essential. The first two or three manned vehicles won't be bringing a body imager and there's a good chance no one will get sick enough to need one, but eventually 10 tonnes of medical equipment, then 20, then 30 tonnes of medical equipment will be needed on Mars. Those don't need to come with a crew; better that they come slowly on a Hohmann trajectory. And if they are lost, they can be sent out again 26 months later.

The size of the cargo lander will have a lot to do with the size of the terrestrial boosters. The Falcon heavy, which can launch 53 tonnes to low Earth orbit, can land 11 tonnes on the Martian surface, according to Zubrin. That's possible if the 53 tonnes includes a properly sized LOX/liquid hydrogen TMI stage. Of the 11 tonnes, probably 1 tonne will have to be the fuel tanks for the landing fuel, a cargo platform, and landing legs. So a Falcon Heavy could land 10 tonnes of useful cargo on Mars. I could see Elon Musk adding TMI stages and landers to his rocket factory in southern California and mass producing them. If he can put 53 tonnes into low Earth orbit for $100 million, he can probably get 10 tonnes of medical equipment to Mars for $200 million, or $20,000 per kilogram (about the cost of the space shuttle to get cargo to the International Space Station!). Once that's done a dozen times, the technology will become more reliable and costs will go down further.

The next stage beyond that may be a reusable Mars shuttle. Cargo would be aerobraked into Martian orbit; the Falcon Heavy can put 14 tonnes into Martian orbit. I suspect a fairly small unmanned vehicle (total mass, 30 tonnes or so, fully fueled, if my fast back of the envelope calculation is right) would be able to take off from the Martian surface, go into orbit, rendezvous with the cargo pallet, and deorbit it. Such a vehicle could also launch Martian products into Martian orbit or boost them to trans-Earth injection (eventually colonies will have exports, after all; gold, rare metals like platinum, and heavy water are all possibilities).

In general terms I favour an Apollo style landing for the humans, but with pre-delivered supplies and habitat being available on the surface when they land (unlike Apollo). That then makes the task of getting them back safely a lot easier.

However, once we have a propellant manfuacturing capability on the Mars surface, then a Mars shuttle as you propose should be put in place.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#27 2012-03-27 22:30:10

louis
Member
From: UK
Registered: 2008-03-24
Posts: 1,226

Re: Mars Semi-Direct with Falcon

RobS wrote:

Interesting points, Louis. I view dust storms on Mars the way I view winter in Indiana: there are times you do agriculture and times you don't. Even in dust storm season, there are probably some crops you can grow. You just have to plan. Perhaps you supplement daylight artificially then. Yes, plastic enclosures won't be 100% transparent; in fact, they may be translucent. Translucent might actually be better because a point source produces shadows and a diffuse light source will hit all the leaves all the time. But the earth's atmosphere isn't transparent, either; it absorbs 10% or so of the usable daylight. I throw three sheets of translucent plastic over my goldfish pond in late October and remove it in late April (this year, mid March!) and there is always an algae bloom and vigorous growth and grass and weeds underneath when I remove it, because there's early warmth, even if there is a reduction in light.

Sadly, I think the evidence is that while the seasons are in some ways more predictable on Mars than on Earth, dust storms are not. Plus of course the growing seasons on Earth are not a brilliant match with those on Mars.

RobS wrote:

I also wonder whether, by the time we get to colonization, we won't have developed some genetically modified crops that are designed for Mars's lower light levels. Some plants deal with partial shade much better than others.

  Well I am sure there will be such developments, but we can grow the food and plants we want using artificial systems. We can grow dwarf wheat, salads, fruits, bamboo etc.

I would have thought there may also be problems in event of solar flare bursts, in terms of damage to plants where plants were not protected from the sun.

RobS wrote:

  Bricks: My problem wasn't making them, but laying them! It's labor intensive and we'll have a shortage of labor. Maybe robots can lay them, though. If it's too cold on Mars for concrete to set, it's also too cold for mortar to set. My guess is that construction will be carried out inside bubbles, so people can work in shirt sleeves and the4 temperature is comfortable for people and for terrestrial construction processes. The bubble might even be temporary if the resulting structures are air tight. I wrote a Mars novel once where a 40-meter "biome" bubble was placed on top of a prepared duricrete pad, building bubbles were inflated inside the "biome" bubble, buildings were then built inside their bubbles and siding was put up outside the building bubbles so that they just looked like buildings (even though they were airtight) and a steel frame was erected around the buildings and an agriculture terrace was completed above them. Thus each building had several meters of soil and water and vigorous agriculture above them to reduce cosmic rays and the courtyard between the two buildings was a pretty space with fruit trees, flowers, low vegetables, an eating area, and a basket ball court. All inside the "biome" bubble. Something like that might be possible eventually. It would involve importing plastic bubbles from Earth, at least at first, but construction conditions would be much easier.

 

If every brick laid saves say $10,000 in habitat haulage costs, it might be labour intensive but it has its own internal logic - especially if it means you can import say iron ore mining equipment which then gives you a basis for creating your industrial infrastructure.  However, this is a matter of judgement.  Labour time is certainly  a matter of real importance.

The biome bubble sounds good! Another idea I would like to see explored is to find a narrow gorge on Mars and cover that with a gas-sealed glass/plastic roof and then pressurise the enclosed space. Some artifical lighting could be used internally as well.

RobS wrote:

Lots of small payloads: I'd avoid that when starting the effort to explore Mars, if possible. Later, demand for cargo (imports and exports) will be so high the Martian colonists will be using reusable shuttles.

I agree that reusable shuttles should be introduced as soon as possible. However, small robot landers are, I believe, a quick and efficient way of delivering the "starter supplies" to Mars, not least because you can operate to lower safety standards if you separate cargo from crew.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#28 2012-03-28 01:54:43

RobS
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From: South Bend, IN
Registered: 2002-01-16
Posts: 1,448
Website

Re: Mars Semi-Direct with Falcon

I've done some further fiddling with the Falconet design and have made it slightly bigger, which makes it more useful for going to the moons. I've also figured that it would be a useful vehicle to refuel on the moons once a fuel making plant can be sited there. Phobos is better in terms of delta-v; a 6-tonne vehicle leaving Phobos with 56 metric tonnes of LOX/methane reaches low Mars orbit with 48 mt of propellant left, which is enough to push two 14-tonne cargo pallets to a trans-Earth injection and return the Falconet back to Phobos for refueling. The Falcon Heavy turns out to be a pretty useful size rocket for Mars, I think.

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#29 2012-03-28 02:03:47

RobS
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From: South Bend, IN
Registered: 2002-01-16
Posts: 1,448
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Re: Mars Semi-Direct with Falcon

Regarding a small lander for people, you may be right; that may be better. I don't think we know, yet. The danger is that a mistake will be made and the people will come down hundreds of kilometers from their supplies. Since they'll have a small lander, that's a recipe for almost certain death.

As for dust storms, they are pretty predictable; the really big ones come at perihelion and hit the southern hemisphere the worst. Smaller regional storms are reasonably short. But we have these meteorological phenomena on Earth, too. The Great Lakes in the US and the East Coast can get in cloudy patterns where the sun isn't visible at all for several weeks, except for a few minutes or an hour. Very depressing. Have they every published an insolation record for Spirit and Opportunity's landing sites? That would resolve the matter. I have seen data about the Viking landing sites, but that was a long time ago.

I have written a few Mars novels and so far I have always used 2 or 3 small landers in the 12-tonne cargo class to bring non-essential (though useful!) supplies. Anything that goes with the crew goes on a 6-month trajectory, which requires more propellant than a Hohmann trajectory. So essentials go with the people. Everything else takes the slow boat.

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#30 2012-03-28 03:42:21

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 6,307

Re: Mars Semi-Direct with Falcon

http://www.spacex.com/falcon_heavy.php

VEHICLE INCLINATION ORBIT PAYLOAD TO LEO
Falcon Heavy 28.5 degrees 200 km 53,000 kg

FALCON HEAVY
Mass to LEO (200 km, 28.5 deg): 53,000 kg (117,000 lb)
Overall Length: 69.2 m (227 ft) 
Width (body): 3.6 m (12 ft) x 11.6 m (38 ft)
Width (fairing): 5.2 m (17 ft)
Mass on liftoff: 1,400,000 kg (3,100,000 lb)
Thrust on liftoff: 17 MN (3,800,000 lbf)

The page for the dragon lists the carrying capability but not the units as a payload mass total for the heavy...

The Saturn V centuar stage was General Characteristics
Height 17.8 m (58.4 ft)
Diameter 6.6 m (21.7 ft)
Mass 119,900 kg (253,000 lb)

So twice the payload of a heavy...and next for just a repeat of a moon landing and return would be comparible to a

Apollo 15
Spacecraft name CSM: Endeavour
LM: Falcon
Command Module CM-112
mass 12,831 pounds (5,820 kg)
Service Module SM-112
mass 54,063 pounds (24,523 kg)
Lunar Module LM-10
mass 36,700 pounds (16,600 kg)

grand total 46,943 kg making another unit for an orbital assembly of the past....

Since these pieces must be broken down to allow for the connection from one to the next then there will be another increase in each sections mass and while they may not push it to beyond one more that will make it a 4 unit heavy for a lunar mission.

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#31 2012-03-28 12:27:37

louis
Member
From: UK
Registered: 2008-03-24
Posts: 1,226

Re: Mars Semi-Direct with Falcon

SpaceNut wrote:

Since these pieces must be broken down to allow for the connection from one to the next then there will be another increase in each sections mass and while they may not push it to beyond one more that will make it a 4 unit heavy for a lunar mission.


Interesting comparison, but of course  Space X mission would be far, far cheaper despite that, given the reduction in launch costs and the fact that the knowledge base from which you start is already great.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#32 2012-03-28 12:39:06

louis
Member
From: UK
Registered: 2008-03-24
Posts: 1,226

Re: Mars Semi-Direct with Falcon

RobS wrote:

Regarding a small lander for people, you may be right; that may be better. I don't think we know, yet. The danger is that a mistake will be made and the people will come down hundreds of kilometers from their supplies. Since they'll have a small lander, that's a recipe for almost certain death.

I really don't think that's a risk. They would know before they left if the supplies were in place (through radio signals, satellite observation and so on). Moreover, if you had a mini rover to inspect the supplies, you could establish they had not been damaged on landing.

RobS wrote:

As for dust storms, they are pretty predictable; the really big ones come at perihelion and hit the southern hemisphere the worst. Smaller regional storms are reasonably short. But we have these meteorological phenomena on Earth, too. The Great Lakes in the US and the East Coast can get in cloudy patterns where the sun isn't visible at all for several weeks, except for a few minutes or an hour. Very depressing. Have they every published an insolation record for Spirit and Opportunity's landing sites? That would resolve the matter. I have seen data about the Viking landing sites, but that was a long time ago.

I think you're right in general terms but there have I think been 9 month global dust storms before now. I do recall checking on the insolation issue (in relation to PV generation) and if I recall correctly they have never gone below 20% of peak insolation. They've certainly kept functioning all that time and PV power is all they have.

RobS wrote:

I have written a few Mars novels and so far I have always used 2 or 3 small landers in the 12-tonne cargo class to bring non-essential (though useful!) supplies. Anything that goes with the crew goes on a 6-month trajectory, which requires more propellant than a Hohmann trajectory. So essentials go with the people. Everything else takes the slow boat.

Yes, there's nothing wrong with the slow boats if you plan in advance (although I suppose solar flares may be an issue with some supplies).  The really encouraging thing I think is that Musk is talking in terms of getting the cost down to about $1000 per kg or less (for LEO).  Using my completely unscientific multiplier of x4 for supplies to Mars surface, we have a figure of $4000 per kg whereas even five years ago people were still quoting figures like $40,000 per kg. This is a really big change. Even if Musk is being a little optimistic, we can certainly think in terms of getting more tonnage to the surface if we wish to, which could greatly speed up colonisation.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#33 2012-04-06 22:53:11

RobS
Member
From: South Bend, IN
Registered: 2002-01-16
Posts: 1,448
Website

Re: Mars Semi-Direct with Falcon

Here's a new vehicle, the "Griffin." The "Dragon" is named for an imaginary animal and is designed for the Falcon 9; this successor is named for an imaginary bird and is designed for the large 5.2 meter payload shroud of the Falcon Heavy. It has at least three uses that I have identified:

Interplanetary cruise, with an inflatable hab: This would be the vehicle I'd use in my Falcon Semi-Direct system to transport 6 crew to Mars orbit. The three levels of the vehicle are used for the bulk of the daily work between planets--science, cooking, washing clothes, exercise--would contain the life support equipment and store the consumables, while the inflatable would only have the lower-mass tasks such as the living and sleeping quarters.

Descent to surface and ascent to Mars orbit: This is the basis of the MDAV I proposed for the Falcon Semi-Direct system. Here, the three levels of the vehicle would be used as follows: the lower level would be replaced by propellant tanks for descent and ascent fuel; the middeck would mostly be for cargo storage but would also have the egress area; the upper level would accommodate 3 (it's the size of a Dragon capsule).

Lunar transport: The upper level would accommodate 2 flight crew, life support, and galley; the middeck and lower deck would accommodate up to 10 passengers (this could be a tourist flight to the moon or crew rotation for a larger lunar facility). Another version of lunar transport would be more like the MDAV configuration, with a lower level replaced by descent/ascent propellant, the middle level to accommodate cargo and egress, and the upper level to hold crew. Note that if the crew were "mixed" (male and female) the two levels provide some separation and privacy as well.

-------------------

Griffin Interorbital Vehicle: 5.2 m base diameter, 9.7 meters high, pressurized volume is 62 cubic meters (Space Shuttle has 66, Dragon has 10, Apollo 6). It has the following components, top to bottom:

Docking Tunnel: 1.7 meters diameter, 1.2 meters high, volume 1.3 cubic meters. Can serve as storage for inflatable cabin during interplanetary cruises.

Upper deck “the nose”: 3.2 meters floor diameter, 8 square meters floor area, 2.2 meters ceiling diameter, 2.0 meters ceiling height; volume, 11.5 cubic meters. Interplanetary configuration: has space suit storage and serves as an airlock. Accommodates 1 when inflatable is unavailable. Mars Descent and Ascent configuration: Accommodates 3 crew for several days. Lunar transport configuration: serves as crew cabin (for 2 crew), flight deck, galley.

Middeck: 4.2 meters floor diameter, 14 square meters floor area, 3.2 meters ceiling diameter, 2 meters ceiling height; volume 21.5 cubic meters. Has a docking port for pressurized transfer and 4 portholes. Interplanetary configuration: serves as science control area, life support control, bridge. Accommodates 3 when inflatable is unavailable. Mars Descent and Ascent configuration: accommodates up to 10 tonnes cargo, serves as surface egress area. If fuel is available, can accommodate 3 extra crew in emergency. Lunar transport configuration: accommodates 4 passengers.

Utility deck “the tub”: 5.1 meter floor diameter (20 m2) but enclosed by ring of 0.6 meters of storage cabinets for consumables and equipment; usable floor 3.9 meters diameter, 12 square meters, ceiling height 2.5 meters; volume, 30 cubic meters. The lower level remains pressured at all times. No portholes. Interplanetary cruise configuration: Because it has liquid methane and liquid oxygen tanks under the floor and 0.5 meters of extra ceiling space for storage, it serves as the storm shelter. It has the galley, zero-gee hygiene area, clothing and dish washing units, animal and plant storage area, exercise area. Accommodates 6 in hammocks (gee) or vertical sleeping bags (zero-gee) in an emergency or 2 when inflatable is unavailable. Lunar transport configuration with 20 m2 floor: accommodates 6 passengers plus 2m2 waste management area; or accommodates cargo. The extra 0.5 meter of ceiling height allows 0.5 m of storage space overhead to accommodate pressure suits and luggage.

Service Module: 5.2 meters diameter, 2 meters high, consisting of 1 meter of heat shield, engines, and pumps, and 1 meter of propellant tanks (volume, 20 m3).

The top two can be depressurized separately. The lower deck always remains pressurized.

Masses:
Structure: 1 tonne per level, roughly
Propulsion module: 1 tonne (3 tonnes if it includes the lower deck)
Power: 0.5 tonne
Reaction control: 0.5 tonne
Heat shield: 2.0 tonnes
Life support: variable (0.25 mt, MDAV; 2.0 mt, interplanetary; 0.5-1.0 mt, lunar)
Personnel mass: 0.1 mt each (including luggage)
Max. mass: about 15 tonnes (based on 2 tonne heart shield)
Space suits: 0.1 mt per crew
Propellant: variable
Consumables: variable

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#34 2012-04-11 19:01:18

RGClark
Member
From: Philadelphia, PA
Registered: 2006-07-05
Posts: 294
Website

Re: Mars Semi-Direct with Falcon

It may be possible to do the manned mission with a single Falcon Heavy based on fully using aerocapture and fully using in situ production of the return propellant.
Recall the calculations that fully used aerocapture to eliminate propellant burns at Mars and at Earth:

Index » Human missions » Developing the cis-Lunar economy and infrastructure
http://www.newmars.com/forums/viewtopic … 11#p111711

It was only 10.2 km/s total delta-V, 3.8 km/s for the outbound trip from LEO to Mars, and 6.4 km/s for the return trip from Mars to LEO. Let's suppose we need 20 mT payload. I'm considering something like the Bigelow Sundancer as the hab module. This was to have a pressurized volume of 180 m^3 and mass of 8,618.4 kg for a crew of 3. The original NASA Transhab might also work. It was to have a pressurized volume of 339.8 cubic meters at a mass of 13.2 mT. The Bigelow 330 derived from Transhab would probably be too heavy since even though the internal volume was the same, the mass was up to 20 mT.
For the outbound trip we would need a Centaur style upper stage with a 465.5s Isp at 30 mT propellant load and 3 mT dry mass: then we would get a 3.8 km/s delta-V: 465.5*9.81ln(1 + 30/(3 +20)) = 3,812 m/s.
I'm assuming all the consumables, aerobrake, thermal protection, power systems, would be contained within the left-over mass allowance from 20 mT once you subtract off the mass of the hab.
But the problem is how do you get the 6.4 km/s delta-V for the return trip? The only thing I could think was to carry some empty drop tanks along from Earth. Then on Mars fill up these tanks as well. Remember the entire propellant load for the return trip is taken at Mars. I calculated you would need to take on an additional 50 mT of propellant in these drop tanks. But then you also have to figure in the mass of the empty tanks and subtract this off from the payload allowance. Probably with lightweight composites you can get the mass of these under 1 mT, even considering that hydrolox tanks are comparatively heavy.


   Bob Clark


Single-stage-to-orbit was already shown possible 50 years ago with the Titan II first stage.
Contrary to popular belief, SSTO's in fact are actually easy. Just use the most efficient engines and stages at the same time, and the result will automatically be SSTO.
Blog: exoscientist.blogspot.com

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#35 2012-04-12 01:41:34

RobS
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From: South Bend, IN
Registered: 2002-01-16
Posts: 1,448
Website

Re: Mars Semi-Direct with Falcon

3.8 km/sec and 6.4 km/sec are the numbers for Hohmann (minimum energy) transfers, which take 8-9 months each way and are not free return trajectories. If you go a bit faster (4.3 km/sec outbound and about 7 km/sec inbound) you make the trip in 6 months instead and you put yourself into a 24-month solar orbit, so if you miss Mars on the way out (say, because of damage to the craft) you come back to Earth anyway. You also cut down on consumables.

Zubrin calculates that a Falcon Heavy putting 53 metric tonnes in LEO, including a hydrogen-oxygen stage, can push 17 tonnes to trans-Mars injection, put 14 metric tonnes into orbit, and 11 metric tonnes on the surface. I suppose those numbers represent 3 metric tonnes of heat shield and retrorocket fuel and 3 tonnes of TMI staging. If you can protect the stage with your heat shield, you can probably land it on Mars as well, but that probably means a bigger heat shield and more landing fuel, so your 11 tonnes of cargo diminishes to maybe 10 or 9. As we have noted elsewhere, the "Red Falcon" project manages to put even less on the surface, probably because they are using bigger margins and RP1/LOX propellant all the way.

Nine or 10 tonnes may be enough for a 1-way trip for 1 or 2 people, but it'd be hard to include enough other stuff to make it a round trip. If you already have solar panels and a robotically drilled water well, it might be barely enough, but I doubt it. You'd do better by launching two Falcon Heavies, one with a dedicated LH2/LOX stage to which the earlier launch would dock. Both Falcon launches would need to include propulsion stages, but the one with the cargo would have a much smaller stage and your payload mass doubles; a bit more than doubles, probably. If you can land 22 or even 24 tonnes on the surface, you're getting close to the Mars Direct ERV (28.6 tonnes).

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#36 2012-04-12 06:01:56

RGClark
Member
From: Philadelphia, PA
Registered: 2006-07-05
Posts: 294
Website

Re: Mars Semi-Direct with Falcon

RobS wrote:

3.8 km/sec and 6.4 km/sec are the numbers for Hohmann (minimum energy) transfers, which take 8-9 months each way and are not free return trajectories. If you go a bit faster (4.3 km/sec outbound and about 7 km/sec inbound) you make the trip in 6 months instead and you put yourself into a 24-month solar orbit, so if you miss Mars on the way out (say, because of damage to the craft) you come back to Earth anyway. You also cut down on consumables.
Zubrin calculates that a Falcon Heavy putting 53 metric tonnes in LEO, including a hydrogen-oxygen stage, can push 17 tonnes to trans-Mars injection, put 14 metric tonnes into orbit, and 11 metric tonnes on the surface. I suppose those numbers represent 3 metric tonnes of heat shield and retrorocket fuel and 3 tonnes of TMI staging. If you can protect the stage with your heat shield, you can probably land it on Mars as well, but that probably means a bigger heat shield and more landing fuel, so your 11 tonnes of cargo diminishes to maybe 10 or 9. As we have noted elsewhere, the "Red Falcon" project manages to put even less on the surface, probably because they are using bigger margins and RP1/LOX propellant all the way.
Nine or 10 tonnes may be enough for a 1-way trip for 1 or 2 people, but it'd be hard to include enough other stuff to make it a round trip. If you already have solar panels and a robotically drilled water well, it might be barely enough, but I doubt it. You'd do better by launching two Falcon Heavies, one with a dedicated LH2/LOX stage to which the earlier launch would dock. Both Falcon launches would need to include propulsion stages, but the one with the cargo would have a much smaller stage and your payload mass doubles; a bit more than doubles, probably. If you can land 22 or even 24 tonnes on the surface, you're getting close to the Mars Direct ERV (28.6 tonnes).

Thanks for the info. My plan certainly has slim margins.
My numbers for landing on Mars are actually similar to Zubrin's if you use the larger numbers, for instance 4.3 km/s for outbound, for the delta-V for the shorter transit times. You would also get about 17 mT, instead of 20, for the TMI mass for my architecture using the larger delta-V requirement. Now consider that I am fully using aerobraking for landing on the surface so no or minimal propellant is used for landing after arrival at Mars.

I also believe that production of hydrolox propellant on Mars will be easier than expected due to nearly pure water ice close to the surface on Mars. Separating hydrogen and oxygen by electrolysis is a simple process. It even appears in children's science toys.
Some exciting recent discoveries show that water ice is close to the surface even in the mid-latitudes on Mars:

Water Ice Exposed in Mars Craters.
by Andrea Thompson
Date: 24 September 2009 Time: 02:18 PM ET

Byrne told SPACE.com that it was surprising to the team to find the bluish ice, though "in retrospect maybe it shouldn't have been." Scientists knew of the existence of underground ice and had been monitoring craters as they formed, but "I guess we didn't put the two together," he said.
Several of the craters were also near the landing site of the Viking Lander 2. Viking also looked for water ice on Mars, but was only able to dig down about 6 inches (15 cm) below the surface ? about 4 inches (10 cm) shy of where Byrne and his colleagues think the ice table sits.
"It's a shame that didn't happen," Byrne said. "You might have been having this conversation 30 years ago."

http://www.space.com/7333-water-ice-exp … aters.html

Water ice seen in fresh craters on Mars.
DR EMILY BALDWIN & KEITH COOPER
ASTRONOMY NOW
Posted: September 24, 2009

“The scientifically heartbreaking aspect of this work is that these craters are located very close [350 miles] to the Viking 2 lander site, which landed on Mars in 1976, and dug a trench about 4-6 inches deep,” says Cull. “What this new study is telling us is that if Viking 2 had been able to dig down a few more inches, it would have hit ice. That would have been a major discovery for our understanding of Mars, and it was literally inches away from our robotic fingertips.”

http://www.astronomynow.com/news/n0909/24mars/

What I would like though is a method where you could just dig down the required shallow depth and remain stationary there to process the water ice there rather than have a rover constantly digging up fresh ice. Still thinking about that one.

My architecture has the advantage of simplicity in only requiring a single stage for the space trip. It's in fact SSTO at least from the Mars surface.

   Bob Clark


Single-stage-to-orbit was already shown possible 50 years ago with the Titan II first stage.
Contrary to popular belief, SSTO's in fact are actually easy. Just use the most efficient engines and stages at the same time, and the result will automatically be SSTO.
Blog: exoscientist.blogspot.com

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#37 2012-04-12 12:08:53

louis
Member
From: UK
Registered: 2008-03-24
Posts: 1,226

Re: Mars Semi-Direct with Falcon

RobS wrote:

3.8 km/sec and 6.4 km/sec are the numbers for Hohmann (minimum energy) transfers, which take 8-9 months each way and are not free return trajectories. If you go a bit faster (4.3 km/sec outbound and about 7 km/sec inbound) you make the trip in 6 months instead and you put yourself into a 24-month solar orbit, so if you miss Mars on the way out (say, because of damage to the craft) you come back to Earth anyway. You also cut down on consumables.

Zubrin calculates that a Falcon Heavy putting 53 metric tonnes in LEO, including a hydrogen-oxygen stage, can push 17 tonnes to trans-Mars injection, put 14 metric tonnes into orbit, and 11 metric tonnes on the surface. I suppose those numbers represent 3 metric tonnes of heat shield and retrorocket fuel and 3 tonnes of TMI staging. If you can protect the stage with your heat shield, you can probably land it on Mars as well, but that probably means a bigger heat shield and more landing fuel, so your 11 tonnes of cargo diminishes to maybe 10 or 9. As we have noted elsewhere, the "Red Falcon" project manages to put even less on the surface, probably because they are using bigger margins and RP1/LOX propellant all the way.

Nine or 10 tonnes may be enough for a 1-way trip for 1 or 2 people, but it'd be hard to include enough other stuff to make it a round trip. If you already have solar panels and a robotically drilled water well, it might be barely enough, but I doubt it. You'd do better by launching two Falcon Heavies, one with a dedicated LH2/LOX stage to which the earlier launch would dock. Both Falcon launches would need to include propulsion stages, but the one with the cargo would have a much smaller stage and your payload mass doubles; a bit more than doubles, probably. If you can land 22 or even 24 tonnes on the surface, you're getting close to the Mars Direct ERV (28.6 tonnes).

I've alwayus reckoned on getting something like 200 tonnes to orbit, so 4 Falcon Heavies, so you get 44 tonnes to the surface.  There might be a requirement for smaller supply missions, landing robotic craft. So we might have more than four launchs. But 200 tonnes to LEO is "only" $1billion at $5000 per kg - and will likely be far less in 10 years' time. That's a very reasonable "platform" on which to build a mission costing somewhere between $10billion and $20 billion over ten years - max. $2 billion per annum.


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#38 2012-04-12 13:17:23

RobS
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From: South Bend, IN
Registered: 2002-01-16
Posts: 1,448
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Re: Mars Semi-Direct with Falcon

Bob Clark: I don't think you can do 100% aerobraking. That article for which I sent the link, about the difficulty of landing large cargos on Mars, said that a large human craft would need a parachute 100 meters across, and no one knows how to make something that big that's reliable. The problem isn't just that the atmosphere is thin, but that the zone where a chute will work isn't very tall, so the chute doesn't have enough time to work.

Zubrin assumes a landing delta-v of 700 meters per second (about 1,400 mph) and that may actually be too small.

But I agree 100% with you about water ice. The evidence of its abundance is widespread. I'd chose a landing site with known water ice near the surface in the northern hemisphere and as close to the equator as possible. That guarantees maximum sunlight for panels. As for recovering the water, you drill a shaft down into the ice at a diagonal angle and pump heated Martian air down a plastic tube in the middle of the shaft. The air flows back up along the outer walls of the shaft and picks up water vapor. The water-rich air is brought inside the ship and cooled with a heat exchanger, condensing the water. This will produce a cavity underground and eventually it will collapse, so that is a potential issue. The farther down you can drill, the better.

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#39 2012-04-12 21:54:02

louis
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From: UK
Registered: 2008-03-24
Posts: 1,226

Re: Mars Semi-Direct with Falcon

RobS wrote:

Bob Clark: I don't think you can do 100% aerobraking. That article for which I sent the link, about the difficulty of landing large cargos on Mars, said that a large human craft would need a parachute 100 meters across, and no one knows how to make something that big that's reliable. The problem isn't just that the atmosphere is thin, but that the zone where a chute will work isn't very tall, so the chute doesn't have enough time to work.

Zubrin assumes a landing delta-v of 700 meters per second (about 1,400 mph) and that may actually be too small.

But I agree 100% with you about water ice. The evidence of its abundance is widespread. I'd chose a landing site with known water ice near the surface in the northern hemisphere and as close to the equator as possible. That guarantees maximum sunlight for panels. As for recovering the water, you drill a shaft down into the ice at a diagonal angle and pump heated Martian air down a plastic tube in the middle of the shaft. The air flows back up along the outer walls of the shaft and picks up water vapor. The water-rich air is brought inside the ship and cooled with a heat exchanger, condensing the water. This will produce a cavity underground and eventually it will collapse, so that is a potential issue. The farther down you can drill, the better.

I agree Bob - northern  hemisphere close to the equator.

This suggests that there are huge masses of ice in the equatorial region.

http://www.newscientist.com/article/dn1 … uator.html

Best of all would be a glacier that could be accessed laterally by a robot digger or robot laser/microwave machine.

Last edited by louis (2012-04-13 00:35:45)


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#40 2012-04-12 23:47:28

RobS
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From: South Bend, IN
Registered: 2002-01-16
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Re: Mars Semi-Direct with Falcon

That article says mid latitudes (30-60 degrees) not the equator. But there must be ice near the equator somewhere, too. I said "as close to the equator as possible" for this reason.

Hellas would be interesting and low. The Chryse lowlands near the mouth of Kasei would be interesting, too, but Chryse doesn't seem to have a lot of subsurface ice. It's too bad.

P.S.: Somewhere, someone said the Dragon's heatshield seems to be only 8% the mass of the vehicle, rather than the normal 16%. What's the evidence of that? I'd like to see that info.

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#41 2012-04-13 00:36:16

louis
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From: UK
Registered: 2008-03-24
Posts: 1,226

Re: Mars Semi-Direct with Falcon

RobS wrote:

That article says mid latitudes (30-60 degrees) not the equator. But there must be ice near the equator somewhere, too. I said "as close to the equator as possible" for this reason.

Hellas would be interesting and low. The Chryse lowlands near the mouth of Kasei would be interesting, too, but Chryse doesn't seem to have a lot of subsurface ice. It's too bad.

P.S.: Somewhere, someone said the Dragon's heatshield seems to be only 8% the mass of the vehicle, rather than the normal 16%. What's the evidence of that? I'd like to see that info.

You're quite right - the title was rather misleading.


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#42 2012-04-13 04:45:54

Josh Cryer
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Registered: 2001-09-29
Posts: 3,827

Re: Mars Semi-Direct with Falcon


Some useful links while MER are active. Offical site NASA TV JPL MER2004 Text feed
--------
The amount of solar radiation reaching the surface of the earth totals some 3.9 million exajoules a year.

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#43 2012-04-13 12:35:20

RGClark
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From: Philadelphia, PA
Registered: 2006-07-05
Posts: 294
Website

Re: Mars Semi-Direct with Falcon

RobS wrote:

Bob Clark: I don't think you can do 100% aerobraking. That article for which I sent the link, about the difficulty of landing large cargos on Mars, said that a large human craft would need a parachute 100 meters across, and no one knows how to make something that big that's reliable. The problem isn't just that the atmosphere is thin, but that the zone where a chute will work isn't very tall, so the chute doesn't have enough time to work.

Which article is this? I've read some articles on solutions to this such as ballutes, retro-propulsion, etc.


  Bob Clark


Single-stage-to-orbit was already shown possible 50 years ago with the Titan II first stage.
Contrary to popular belief, SSTO's in fact are actually easy. Just use the most efficient engines and stages at the same time, and the result will automatically be SSTO.
Blog: exoscientist.blogspot.com

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#44 2012-04-13 18:28:24

louis
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From: UK
Registered: 2008-03-24
Posts: 1,226

Re: Mars Semi-Direct with Falcon

Sadly can't access that from the UK. Do you have any highlights to report?


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#45 2012-04-13 20:07:01

RobS
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From: South Bend, IN
Registered: 2002-01-16
Posts: 1,448
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Re: Mars Semi-Direct with Falcon

Here's an example of a reusable transportation system. I am calling it the Gryphon shuttle (Gryphon looks cooler than Griffin, but it's basically the same design I was using before, with some modifications):


Gryphon Shuttle:
Upper deck (11.5 m3)                1.0
Middeck (21.5 m3)                1.0
Lower deck (20 m3)                1.0
Propulsion stages                3.0
Crew of 5 plus suits and possessions        1.0
Life support                    3.0
Inflatable and furniture            1.5
Essential Cargo and margin            10.0 (consumables are about 4 mt)
Advanced Heat shield                1.5
TOTAL:                     23 mt
CH4/LOX propellant                55.0 mt (Ve = 3.65 km/sec, ΔV = 4.4 km/sec)


The three decks of the capsule-shaped vehicle together have a volume of 52 cubic meters; the Space Shuttle provided 68, if I recall, so it's similar in size to the shuttle. The mass includes 1.5 tonnes for an inflatable and furniture (Zubrin used 200 kg for a two-person inflatable). I am assuming a crew of up to 7. If the inflatable fails en route they'd have to retreat into the Gryphon and the space would be very tight, but presumably people would survive. The 10 metric tonnes of cargo would be the 4 metric tonnes of consumables needed on the trip out plus 6 metric tonnes of various things the crew of 6 needs on the surface (some essential equipment, some consumables). The rest of the consumables and equipment arrives by Hohmann trajectory 2 months after the crew arrives. Ideally, the hab can be retracted, deorbited to the Martian surface, and used there as well.

The delta-v of 4.4 km/sec is carefully chosen; that's what you need to go from low Earth orbit to Mars in 6 months (4.3 plus 0.1 for mid course corrections). You need 4.1 km/sec to go from the Martian surface to low Mars orbit; very similar. The idea is to refuel the vehicle in low Earth orbit, launch to Mars, aerobrake, refuel in low Mars orbit sufficiently to land, refuel on the surface, return to low Mars orbit, refuel there sufficient for TEI, and head for Earth. The fuel in Mars orbit could be made on Phobos, Deimos, or the Martian surface and delivered. A round trip would require 55 tonnes out, maybe 5-10 tonnes to land, 55 tonnes to return to Mars orbit, and about 15-20 tonnes for TEI.

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#46 2012-04-14 00:43:05

louis
Member
From: UK
Registered: 2008-03-24
Posts: 1,226

Re: Mars Semi-Direct with Falcon

RobS wrote:

Here's an example of a reusable transportation system. I am calling it the Gryphon shuttle (Gryphon looks cooler than Griffin, but it's basically the same design I was using before, with some modifications):


Gryphon Shuttle:
Upper deck (11.5 m3)                1.0
Middeck (21.5 m3)                1.0
Lower deck (20 m3)                1.0
Propulsion stages                3.0
Crew of 5 plus suits and possessions        1.0
Life support                    3.0
Inflatable and furniture            1.5
Essential Cargo and margin            10.0 (consumables are about 4 mt)
Advanced Heat shield                1.5
TOTAL:                     23 mt
CH4/LOX propellant                55.0 mt (Ve = 3.65 km/sec, ΔV = 4.4 km/sec)


The three decks of the capsule-shaped vehicle together have a volume of 52 cubic meters; the Space Shuttle provided 68, if I recall, so it's similar in size to the shuttle. The mass includes 1.5 tonnes for an inflatable and furniture (Zubrin used 200 kg for a two-person inflatable). I am assuming a crew of up to 7. If the inflatable fails en route they'd have to retreat into the Gryphon and the space would be very tight, but presumably people would survive. The 10 metric tonnes of cargo would be the 4 metric tonnes of consumables needed on the trip out plus 6 metric tonnes of various things the crew of 6 needs on the surface (some essential equipment, some consumables). The rest of the consumables and equipment arrives by Hohmann trajectory 2 months after the crew arrives. Ideally, the hab can be retracted, deorbited to the Martian surface, and used there as well.

The delta-v of 4.4 km/sec is carefully chosen; that's what you need to go from low Earth orbit to Mars in 6 months (4.3 plus 0.1 for mid course corrections). You need 4.1 km/sec to go from the Martian surface to low Mars orbit; very similar. The idea is to refuel the vehicle in low Earth orbit, launch to Mars, aerobrake, refuel in low Mars orbit sufficiently to land, refuel on the surface, return to low Mars orbit, refuel there sufficient for TEI, and head for Earth. The fuel in Mars orbit could be made on Phobos, Deimos, or the Martian surface and delivered. A round trip would require 55 tonnes out, maybe 5-10 tonnes to land, 55 tonnes to return to Mars orbit, and about 15-20 tonnes for TEI.

Sounds like you have some good ideas there. I certainly think a key design feature should be that the crew can abandon the inflatable hab at any point when that becomes necessary and still survive.

So you don't have a separate supply module?


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#47 2012-04-14 11:53:25

RGClark
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From: Philadelphia, PA
Registered: 2006-07-05
Posts: 294
Website

Re: Mars Semi-Direct with Falcon

RobS wrote:

...
The three decks of the capsule-shaped vehicle together have a volume of 52 cubic meters; the Space Shuttle provided 68, if I recall, so it's similar in size to the shuttle. The mass includes 1.5 tonnes for an inflatable and furniture (Zubrin used 200 kg for a two-person inflatable). I am assuming a crew of up to 7. If the inflatable fails en route they'd have to retreat into the Gryphon and the space would be very tight, but presumably people would survive. The 10 metric tonnes of cargo would be the 4 metric tonnes of consumables needed on the trip out plus 6 metric tonnes of various things the crew of 6 needs on the surface (some essential equipment, some consumables). The rest of the consumables and equipment arrives by Hohmann trajectory 2 months after the crew arrives. Ideally, the hab can be retracted, deorbited to the Martian surface, and used there as well.
The delta-v of 4.4 km/sec is carefully chosen; that's what you need to go from low Earth orbit to Mars in 6 months (4.3 plus 0.1 for mid course corrections). You need 4.1 km/sec to go from the Martian surface to low Mars orbit; very similar. The idea is to refuel the vehicle in low Earth orbit, launch to Mars, aerobrake, refuel in low Mars orbit sufficiently to land, refuel on the surface, return to low Mars orbit, refuel there sufficient for TEI, and head for Earth. The fuel in Mars orbit could be made on Phobos, Deimos, or the Martian surface and delivered. A round trip would require 55 tonnes out, maybe 5-10 tonnes to land, 55 tonnes to return to Mars orbit, and about 15-20 tonnes for TEI.

I like the idea of having refueling stations in orbit at Earth and Mars, and the reusable shuttle between the two planets. These two concepts might indeed make possible Elon Musk's concept of a Mars ticket for a few hundred thousand dollars.


Bob Clark


Single-stage-to-orbit was already shown possible 50 years ago with the Titan II first stage.
Contrary to popular belief, SSTO's in fact are actually easy. Just use the most efficient engines and stages at the same time, and the result will automatically be SSTO.
Blog: exoscientist.blogspot.com

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#48 2012-04-15 15:24:58

louis
Member
From: UK
Registered: 2008-03-24
Posts: 1,226

Re: Mars Semi-Direct with Falcon

RGClark wrote:
RobS wrote:

...
The three decks of the capsule-shaped vehicle together have a volume of 52 cubic meters; the Space Shuttle provided 68, if I recall, so it's similar in size to the shuttle. The mass includes 1.5 tonnes for an inflatable and furniture (Zubrin used 200 kg for a two-person inflatable). I am assuming a crew of up to 7. If the inflatable fails en route they'd have to retreat into the Gryphon and the space would be very tight, but presumably people would survive. The 10 metric tonnes of cargo would be the 4 metric tonnes of consumables needed on the trip out plus 6 metric tonnes of various things the crew of 6 needs on the surface (some essential equipment, some consumables). The rest of the consumables and equipment arrives by Hohmann trajectory 2 months after the crew arrives. Ideally, the hab can be retracted, deorbited to the Martian surface, and used there as well.
The delta-v of 4.4 km/sec is carefully chosen; that's what you need to go from low Earth orbit to Mars in 6 months (4.3 plus 0.1 for mid course corrections). You need 4.1 km/sec to go from the Martian surface to low Mars orbit; very similar. The idea is to refuel the vehicle in low Earth orbit, launch to Mars, aerobrake, refuel in low Mars orbit sufficiently to land, refuel on the surface, return to low Mars orbit, refuel there sufficient for TEI, and head for Earth. The fuel in Mars orbit could be made on Phobos, Deimos, or the Martian surface and delivered. A round trip would require 55 tonnes out, maybe 5-10 tonnes to land, 55 tonnes to return to Mars orbit, and about 15-20 tonnes for TEI.

I like the idea of having refueling stations in orbit at Earth and Mars, and the reusable shuttle between the two planets. These two concepts might indeed make possible Elon Musk's concept of a Mars ticket for a few hundred thousand dollars.


Bob Clark


Yes, I have always felt that is the best way to conceptualise it, so that at either end you have smaller shuttle vehicles.


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#49 2012-05-31 14:22:39

RGClark
Member
From: Philadelphia, PA
Registered: 2006-07-05
Posts: 294
Website

Re: Mars Semi-Direct with Falcon

RobS wrote:

3.8 km/sec and 6.4 km/sec are the numbers for Hohmann (minimum energy) transfers, which take 8-9 months each way and are not free return trajectories. If you go a bit faster (4.3 km/sec outbound and about 7 km/sec inbound) you make the trip in 6 months instead and you put yourself into a 24-month solar orbit, so if you miss Mars on the way out (say, because of damage to the craft) you come back to Earth anyway. You also cut down on consumables.

How much delta-v would you need for the outbound trip if you don't use full aerobraking, as I was assuming, for the arrival at Mars, but instead reserved some amount of propellant for powered landing and/or capture?


  Bob Clark


Single-stage-to-orbit was already shown possible 50 years ago with the Titan II first stage.
Contrary to popular belief, SSTO's in fact are actually easy. Just use the most efficient engines and stages at the same time, and the result will automatically be SSTO.
Blog: exoscientist.blogspot.com

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#50 2012-05-31 17:38:26

RobS
Member
From: South Bend, IN
Registered: 2002-01-16
Posts: 1,448
Website

Re: Mars Semi-Direct with Falcon

From what I have seen, I think the atmosphere can slow you down to about 1.5 km/sec or even to 1 km/sec, something like that, so that's all the propulsive delta-v you'd need.

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