Has Dr. Zubrin Addressed Mars Direct Objections? - A few questions?

Euler · 2004-12-10 02:00:12

If you disagree with Dr. Z (as he seems to be called), fine, if you can argue successfully why he's wrong. I haven't seen someone do that satisfactorially yet, but I suppose I could be proven wrong at any time.

Look at Zubrin's mass estimates for the ERV. Even if you assume his mass estimates for the launcher and the propellant production factory are accurate, that still leaves you with an ERV crew capsule that is lighter than Soyuz. And it is supposed to keep 4 astronauts alive for 6 months? It just won't work, and there is nothing that you can cut on the ERV to improve the situation.

Since the ERV makes its propellant on Mars it will be able to return substantial amounts of samples to Earth, this is still viable stuff.

No, you can't take much back to Earth. I don't think that the ERV would be able to get the astronauts back to Earth even if they did not take any samples with them.

SpaceNut · 2004-12-10 06:23:45

I guess I do not understand the ERV? It lands empty of crew, creates fuels from insitu material, crew boards with samples, launches to Mars orbit, and is the size of a soyuz.

Ok then what's in orbit to dock with if anything from the trip from Earth to the red planet?

Where's all the consumables for the return trip if there is nothing in orbit?

How will you get the needed fuel for the return to earth burn since it was all exhausted to get to mars orbit?

RobertDyck · 2004-12-10 08:15:43

Robert Zubrin's Mars Direct calls for the http://www.marssociety.org/images/direc … .gif]Earth Return Vehicle to launch from Mars surface directly to Earth. It has 2 stages and a capsule with unspecified internal size and layout, but must include life support for the 6-month trip back to Earth.

His plan has several bullet points to reduce mass:
• aerobraking, eliminate fuel to enter Mars orbit
• ISPP, bring only 1/18 of the fuel for return to Earth
• land all crew on Mars surface, no need for long-term radiation/micrometeor protection in Mars orbit
• conjuction class and express trajectory, only 6 month interplanetary trip
• launch vehicle is an enlarged version of an existing vehicle, and uses existing launch facilities

The express trajectory uses 10% more propellant than a Hohmann transfer orbit, but reducing trip time to 6 months instead of 8½ reduces food and life support consumables. An opposition class trajectory could use a Venus fly-by to reduce propellant, but it significantly increases trip time (food and life support) and exposes astronauts to radiation in Venus orbit.

Any successful Mars mission must include these bullet points. NASA's DRM uses ISPP for ascent to Mars orbit, but the ITV brings fuel for return to Earth all the way from Earth.

GCNRevenger keeps calling for a clean-sheet built-from-scratch heavy lift launch vehicle. That's expensive. Until we have a customer to use such a vehicle, other than a Mars mission, it'll never be built.

BWhite · 2004-12-10 08:33:33

Isn't any mass budget issue solved simply by using 2 launches to assemble a large ERV and two launches to assemble a larger Mars vessel? That is the entire Delta IV theory right, multiple launchs and "on orbit" assembly.

Launch the ERV and the crewed Mars vessel in one piece without the fuel needed for Mars and launch fuel tanks as cheaply as possible by purchasing the cheapest road to LEO.

Several "Thiokol SRB plus RL-10/RL-60 upper stage" could carry LOX & LH2 to LEO and mate with the ERV lifted by Ares (or maybe even shuttle C if the ERV were launched without fuel for going to Mars) and just re-use the same RL-10/RL-60 cluster than got you to LEO to push the ERV to Mars.

= = =

Summary for a new ERV architecture:

A much bigger ERV launched via shuttle B/C or Ares with NO engines or fuel for the Mars insertion burn.

Mate with "several" RL-10/RL-60s lifted by lone SRBs (need some clever dual fuel tank system)

Go to Mars.

= = =

PS - - if GCNRevenger is correct on these criticisms then he should also admit that the VSE is all hocus pocus if it intends to use EELV to do anything useful..

Edited By BWhite on 1102689363

BWhite · 2004-12-10 08:47:56

LEO to the Moon and LEO to Mars both require fuel mass of 4x the net payload mass (very roughly calculated) correct? In other words, about 20% ( + / - ) of what reaches LEO can arrive at the Moon or Mars

Thus, it seems to me that the mission critical job is to get useable LOX / LH2 in LEO as cheaply as possible. If mutiple launches can do it cheaper than a single big rocket like Ares, well fine. If not, then go that way.

Its all bean counting, and political resolve to accomplish something.

Edited By BWhite on 1102690098

GCNRevenger · 2004-12-10 08:55:06

"Like you said earlier, any sort of humans-to-Mars program (perhaps barring battlestar galactica-type boondoggles) will have a much higher science return per dollar spent than robotic missions."

Which is entirely irrelivent. I am comparing human missions to human missions, not human to robot. The marginal bennefit of the larger crew is very much worthwhile and within fiscal reach... Now about MD some more:

Similar issues with the mass budget for the rovers, the reactors, the cramped HAB module, among other things... one floor of the already tiny HAB/ERV module is asking too much of the crew for that duration. I also belive that the radiation shielding on MarsDirect is a bigger question mark then Zubrin thinks.

As calculated by several board members, even using quite optimistic assumptions the big rover will likly not meet mass and performance targets safely, even some MarSoc branches don't think the target can be met.

The reactors, supposedly to be based on the thermoelectric NASA/USAF SP-100 reactor, would likly weigh in the region of 4-5MT perhaps six with extended radiators, not counting its mobile transporter... Thats about 1/5th of the whole vehicle mass. The only way to hit Zubrin's target would be to load less fuel, which would severely cut into operational life.

This kind of thing is not unique to any number of componets of the arcitecture, but are systemic... almost everything about the mission is to some degree forcast to weigh or perform less then it should. There isn't even enough mass for a good drilling rig to collect ground samples with.

I would like to reiterate that MarsDirect doesn't make an unlimited supply of fuel, the ISRU plant is limited by the amount of Hydrogen you can along, which in turn will increase ERV mass even more or severely limit the propellant you can make.

Advancing technology could improve the situation, like bulk amorphous metals or advanced composits, but none of these will make MarsDirect light enough to fly with a full crew safely and would drastically increase cost. Somthing would have to be cut that shouldn't.

Which leaves me with only a few possible conclusions...
1: Zubrin was never serious about his plan to start with and made the idea as a thought experiment only in actuality.
2: Zubrin knows it won't work, but is so attractive that if it were adopted, it would be un-cancelable.
3: Zubrin is foolish in his blind rush to Mars and has placed too much faith in ingenuity & clever tricks to overcome weight concerns.

And MY concern is that MarsDirect will become a "Martian Apollo," that because of its very low capacity and "just enough" philosophy, that the arcitecture has negligible future worth beyond exploration. If "the next big thing" is not spoken of in the same breath as the speech commemorating the last exploration mission, then we are better off not going until it can be.

In order to "grease the wheels" for a Mars presence beyond MarsDirect, vehicles with much greater capability are obviously needed... so why bother making one dinky arcitecture only to throw it away and make a bigger one later? Develop one arcitecture capable of both exploration and heavier transport instead of two.

BWhite · 2004-12-10 09:01:45

Okay, then double the mass of the ERV. Launch via shuttle B/C. No Ares development costs. If there is room for RL-60s and some fuel, well good.

Launch a standardized deep space chemical propulsion module. (Call it the DSCPM - a fancy acronym for a handful of RL-10s or RL-60s attached to tanks filled with LOX & LH2.)

Bolt as many DSCPMS to the ERV (or Mars crew habitat) as needed. Light some candles.

Fuel tankers are the real issue. Do we really want to be slogging fuel to LEO in a Rolls Royce RLV?

GCNRevenger · 2004-12-10 09:20:28

His plan has several bullet points to reduce mass:
Any successful Mars mission must include these bullet points. NASA's DRM uses ISPP for ascent to Mars orbit, but the ITV brings fuel for return to Earth all the way from Earth.
GCNRevenger keeps calling for a clean-sheet built-from-scratch heavy lift launch vehicle. That's expensive. Until we have a customer to use such a vehicle, other than a Mars mission, it'll never be built.

None of which is sufficent to make the vehicle light enough for a four-man crew.

NASA's DRM correctly recognized that it is a better idea to send TEI fuel from Earth to LMO with the ERV then it is to try and make enough on Mars for the burn AND to lift the ERV to LMO.

I think that the superheavy clean sheet is a superior solution because it reduces mission complexity and provides future growth options. Building Ares or any SDV will be expensive, given the modifications to the main tank and development of the engine pod and upper stage. I think that building a clean-sheet superheavy launch vehicle gives you better value then building Ares, and is not excessively expensive to develop given how long we will use it... If Ares is affordable, why not clean sheet?

If not, then I am not strongly opposed to a "SDV Gemini" two launch solution, where the payload and TMI stage are launched seperatly on Shuttle-C or Shuttle-Z style vehicles along the same strategy I advocate for EELV-VSE to the Moon.

The problem with this is, that the TMI stage must be launched within one month of departure, which will require the payload to sit on orbit for some time while the next TMI stage is readied, probobly with a crew CEV launch between each HLLV flight, which adds considerable complexity and will make delays fatal to the mission.

Edit: On-orbit assembly should be limited to only two flights Bill, because the Hydrogen fuel boils off too fast. The "SRB medium launcher" won't be much cheaper per-pound then HLLV anyway. The old NASA DRM V 1.0 calls for a 65MT ERV, not counting fuel.

SpaceNut · 2004-12-10 11:16:47

The occupied ERV lander seems to not have the down mass capability for the rover and consumables needed for the duration. What would the numbers be for a bare bones unmanned (ERV) lander that is derived from the manned version? In other wards less crew weight, oxygen system, heaters ext... Would this new vehicle be capable then?

RobertDyck · 2004-12-10 11:20:45

The reactors, supposedly to be based on the thermoelectric NASA/USAF SP-100 reactor, would likly weigh in the region of 4-5MT perhaps six with extended radiators, not counting its mobile transporter... Thats about 1/5th of the whole vehicle mass. The only way to hit Zubrin's target would be to load less fuel, which would severely cut into operational life.

You only need enough life for the mission. A multi-year nuclear reactor is unnecessary and only waists mass.

cramped HAB module... one floor of the already tiny HAB/ERV module is asking too much of the crew for that duration

Robert's original plan called for a http://www.marssociety.org/images/direc … gif]single floor for the outgoing mission, and storage in the lower floor for propellant tanks for landing, and storage for the rover, inflatable greenhouse, garage tent, and surface science instruments. It didn't specify what happened to that space after landing. Later designs called for using that space for laboratory and EVA prep after landing. Unfortunately the analog habitats at FMARS and MDRS fully utilize all this space so there's no place for storage. I think it is appropriate and clever to pack science instruments away and only get enough space to set-up the lab after removing surface equipment. However, you'll notice I suggested using an all-inflatable habitat with only a capsule during landing, but such inflatables are a recent development; MD was developed using then-available technology.

One feature of launch vehicles is that assembly in Earth oribit requires fuel for orbital circularization; that isn't needed for direct launch. Orbital assembly also requires some sort of rendezvous and docking mechanism, and increased structural strength at the coupler. All that adds weight, so there is a price for orbital assembly. Robert tried to avoid that by sending both parts directly to Mars. The cost for his strategy is the long-range rover.

The advantage of Ares over a clean-sheet design is use of existing VAB, launch pad, Mobile Launcher and crawler, SSME and SRB, and the external tank only changes to a cylinder instead of tear-drop shape. The shape change accomodates an upper stage, but it can still be built at Michoud. No new factory, no new launch facilities. The down-side of Ares is the new upper stage with a new engine. It's hard to justify a new stage that size unless you have multiple missions for it, and a new engine? The alternative was 7 RL10 derived engines. It also used the Advanced SRB, which was cancelled.
http://www.marssociety.org/images/full/lv.jpg]Ares from Mars Society
http://www.astronautix.com/lvs/ares.htm]Ares from Encyclopedia Astronautica

C M Edwards · 2004-12-10 12:26:08

It's important to separate "Mars Direct, The Design" from "Mars Direct, The Mission Architecture".

The current design won't work, but design may be too strong a word for a collection of sketches and manufacturer's specifications gestimated together into a glorified Powerpoint presentation. Though advanced beyond the vaporware stage, it's an unfinished product, no more able to fly to Mars than a model ship is meant to sail to Hawaii.

However, the design is just a sample of how to use the design approach. The important innovation isn't some sketchy, unfinished mass estimates that don't even provide a means for the crew to avoid appearing naked on international television. (The analysis of Mars Direct only ran so deep. If fuel wasn't accounted for, clothes weren't either.) It's the combination of in situ propellant production, a separate ERV and other approaches that, if used in a properly designed system, could produce the kind of mass savings necessary to make a Mars mission possible for less than a tenth of previous estimates.

Anyone who says that Mars Direct provides no useful inspiration is as crazy as someone who expects to run out and hop in the working model tomorrow.

GCNRevenger · 2004-12-10 13:47:27

Upon a little more research about the SP-100, I have found that even reducing the fuel won't help. Only 140kg of the reactor is actual fuel, the rest is cooling, conversion, etc. There is no way to signifigantly reduce this mass and still use thermoelectric conversion. Switching to a dynamic brayton cycle like JIMO's SAFE-300 system will let you get away with a slightly smaller reactor, but the cooling systems won't be any lighter plus conversion system probobly heavier.

Just look at it Robert... that little picture of yours. Put yourself in it. Clearly only one deck on that HAB module would be too cramped for six solid months! The crew would need double that kind of volume. You may also overestimate the practical volume delta of an "inflatable" module too, that such a module doesn't nearly tuck down to a washing-machine box. TransHab can only double in diameter or so and the walls are the better part of a foot thick.

Orbital circulization is a small enough delta that it isn't a signifigant problem, and this expense is well worth the option to abort the mission if something goes wrong during launch, or if the HAB fails after deployment (solar panel torn off, inflatable module leak). Have a CEV ready on the pad to go up and get the crew if there is a problem... Or for that matter, don't launch the crew with the HAB at all, and put the vehicle on orbit and bring up the crew later.

The cost for orbital assembly with a total of 200-240MT worth of vehicle instead of a single one in the 120MT range is pretty obvious, giving you 66-100% more payload mass for the price of docking hardware. In that respect, its a great deal...

As far as not being able to afford to lift the rover as some token concession that MarsDirect won't work, thats only a drop in the bucket, a mere few percent of vehicle mass. Plus, that kills one of the major safety features in the event of a landing miss.

The advantages of Super Ares (we need to come up with a name for it) are that it can use the same factory, same VAB, same crawler, same pad, and so on too. It would just be fatter and a little taller with more boosters. Using the SSME for an HLLV is a terrible idea given their very high cost ($40-50M each) and when the RS-68R would be a relativly easy swap and the 5-segment SRB has been test fired.

As far as MarsDirect only being a throught experiment Edwards, you could have fooled me. It would be awfully nice if Zubrin actually stated this his idea as written didn't have a prayer so that it would be easier to take him seriously.

RobertDyck · 2004-12-10 14:04:28

Could I stand being an astronaut in Zubrin's Hab for the 6 month journey to Mars? Sure! I see myself alternating between working on maintenance, writing science papers, computer games on my laptop, and just bouncing on my bunk with excitement. Imagine seriously being part of the first manned mission to Mars! Of course, upon arrival on Mars the first thing is to get the hell outside. I again argue that spacesuits for Mars must be designed to let every crew member go outside once per sol every sol for the entire surface stay. Even if it's to just throw around a football. (Hmm, pressure. Nerf football?)

On orbit assembly has benefits? Sure. Remember I argued for assembly using existing launch vehicles, and delivering crew with a reusable space taxi. It also has the benefit that the ITV can also be reusable, creating a "highway in space" for subsequent missions to Mars.

Super Ares: be careful what you change. If you add SRBs or move main engine location you have to cut new exhaust holes in the Mobile Launcher. Make sure you don't cut so many holes the ML looses structural integrity. Changing something as big as an ML is expensive, and Shuttle managers may not let you cut up one of their MLs.

Mars Direct just a thought experiment: I believe Robert Zubrin and his partner seriously pitched the mission plan to NASA after Battlestar Galactica was shot down. Now with new technological advances and Shuttle becoming old, serious modifications are necessary.

BWhite · 2004-12-10 14:24:03

The cost for orbital assembly with a total of 200-240MT worth of vehicle instead of a single one in the 120MT range is pretty obvious, giving you 66-100% more payload mass for the price of docking hardware. In that respect, its a great deal...

I agree and I believe this proves a slightly modified Mars Direct is really rather easy with 2 shuttle B/C per ERV and crew transit hab.

Since only 20% of the total mass lifted to LEO lands on Mars, the crew hab and the ERV can both be launched without the need for on orbit assembly, correct? The "docking hardware" can be positioned smack dab along the axis of thrust so that the engine burn will press the two pieces together rather than pull them apart.

Two shuttle B/Cs (with 5 segment SRBs and perhaps a larger Michoud made tank to push that 77K kg payload closer to 90k kg) and a Kliper class crew transport and there you go with 200 MT, correct?

ERV launches from Pad 39A and the Mars injection engine and fuel from Pad 39B perhaps a week apart. Line them up end to end and go for Mars.

23 months later, the back up ERV launches from Pad 39A and the Mars injection engine and fuel from Pad 39B perhaps a week apart. Line them up end to end and go for Mars on a slower Hohman trajectory. Less fuel.

Another 3 months later, MarsOne launches from Pad 39A and the Mars injection engine and fuel from Pad 39B a week after that with CEV from the Delta pad or Vandenberg or Kouru once MarsOne has docked.

This saves the Ares development cost and save the cost of any new clean sheet HLLV.

= = =

Edit: How much extra room would a Delta IV CEV have to carry up additional clothes, food, and personal gear? Could that add a few MT to the overall mass budget as well as the roughly 1000 pounds of human payload (0.5 MT)?

Edited By BWhite on 1102710912

John Creighton · 2004-12-10 14:55:22

It's important to separate "Mars Direct, The Design" from "Mars Direct, The Mission Architecture".
The current design won't work, but design may be too strong a word for a collection of sketches and manufacturer's specifications gestimated together into a glorified Powerpoint presentation. Though advanced beyond the vaporware stage, it's an unfinished product, no more able to fly to Mars than a model ship is meant to sail to Hawaii.
However, the design is just a sample of how to use the design approach. The important innovation isn't some sketchy, unfinished mass estimates that don't even provide a means for the crew to avoid appearing naked on international television. (The analysis of Mars Direct only ran so deep. If fuel wasn't accounted for, clothes weren't either.) It's the combination of in situ propellant production, a separate ERV and other approaches that, if used in a properly designed system, could produce the kind of mass savings necessary to make a Mars mission possible for less than a tenth of previous estimates.
Anyone who says that Mars Direct provides no useful inspiration is as crazy as someone who expects to run out and hop in the working model tomorrow.

I think we can all agree with that. In such a case I am not clear which would be better a fully worked out Mars Direct or Mars Semi direct. I think they are probably both about the same but NASA took more time to work out all the details of mars semi direct (A.K.A NASA’s reference mission)

GCNRevenger · 2004-12-10 15:04:35

Oh I imagine that would last for a month or two... but after that. Doubtful. Even your eyes would stop being able to focus over long distances in such a cramped tin can.

The staterooms are about the right size, but the "main hall" and lab need to be about double that size minimum. Combine the excersize room with the main hall too... That lab is silly, you couldn't even fit a glove box in there.

Trouble is, you need to make a HAB/Lander anyway for each mission, then its not worth the trouble of making a reuseable transfer vehicle. You'd need to launch a new TMI stage every time anyway.

If the mobile launcher is a show-stopper, then NASA is beyond help and should be eliminated... Please, its just a metal box with treads and large diesel engines.

If Doc Zubrin was pushing his original design back in the SEI days, then he must be crazy or up to somthing, since it definatly wasn't going to be any lighter back then.

Something a little bigger... except TransHab based: http://exploration.jsc.nasa.gov/marsref … tents.html

Design the HAB with two main decks, a "bilge" half deck, and a cylendrical airlock "basement" running across the bottom between the external landing fuel tanks and surface payload stowage, just as on p.111 of the 1997 DRM section three. One end of the airlock deck would house the Mars airlock with room for three, and the other end would hold the docking port for CEV access or HAB-HAB mating. The basement may have its walls lined with extra radiation shielding in the event of a solar storm. The upper deck would house the crew staterooms, hygene facilities, and control room w/ storage and the lower deck the lab(s), the galley/living room, and refrigerated stowage/equipment space. The "bilge" would house equipment, extra storage, and perhaps limited hydroponics/aquaculture.

The main two decks should have inflatable walls with a nominal diamter increase from 8m ID to 12m ID but not the bilge deck, though this may make the aerobrake shield tricky. The "central core" would house the ladder along one side between both main decks and the airlock basement along with the toilette/hygene facilities, control equipment, and some sensitive materials storage. The core would be wrapped with water tankage, and staterooms would extend into the core by about a meter so the crew could sleep upright in zero-gravity within this additional shielding. A perminant "partition" that divides the room in two, near the front door with a break in one side to enter the rest of the room. The idea being, the crew could live for extended periods in only the core section and airlock basement during a serious solar event and limit sleep-period radiation exposure during transit.

GCNRevenger · 2004-12-10 15:16:03

ERV launches from Pad 39A and the Mars injection engine and fuel from Pad 39B perhaps a week apart. Line them up end to end and go for Mars.
Another 3 months later, MarsOne launches from Pad 39A and the Mars injection engine and fuel from Pad 39B a week after that with CEV from the Delta pad or Vandenberg or Kouru once MarsOne has docked.
This saves the Ares development cost and save the cost of any new clean sheet HLLV.

I don't think its practical to operate two shuttle pads concurrently. Pack extra seed hydrogen and leave the ERV/HAB/MAV/whatever in orbit while you prepare the TMI stage on the same pad.

Send up the HAB, then the crew, then the TMI module. The crew will have time to ensure the HAB works, and will help with docking if manual assistance is required. If nessesarry, the crew could even perform an EVA to ensure the TMI stage is in working order and properly mated. The crew should have a little time in orbit to prepare and check and not pressed to "beat the clock" of LH2 boiloff, where delays would cost fuel margin.

I think you misunderstand a little bit about Ares Bill... Ares IS Shuttle-Z, for intents and purposes, it just has a slightly different engine arrangement and booster selection. It will not be in any way cheap or easy to develop given the more radical changes made, particularly versus Shuttle-C, but it does extend payload by 20-40MT. If such a vehicle is selected, I think it should be asked if its worth the trouble to save any of the Shuttle arcitecture and if we should go clean sheet or not. Launching one large rocket will obviously be easier and cheaper then two smaller ones, and will save the trouble of orbital rendevous. Not to mention give you the option of superheavy payloads down the road.

RobertDyck · 2004-12-10 15:24:21

Don't forget I said later designs move the lab, EVA prep room and airlock to the lower deck. Replace the airlock with a very steep stairway, almost a ladder. That gives you what was lab space for expanded galley/lounge/library or exercise/health room. The staircase has to be moved to one side so there's room in the lower deck for the rover. However, the FMARS design put a radiation shelter walled with food storage shelves in the centre. You can't do that if the rover is there. I'll let you play with floorplan details. After all, I favour Hybrid Direct.

Actually, the Mobile Launcher is just a metal box with fixed legs. The crawler is a separate vehicle that is the treds, diesel engines, and hydralic jack to lift up the ML or set it down. The crawler is parked safely beside the VAB when Shuttle launches.

Ad Astra · 2004-12-10 17:37:01

Robert Zubrin's Mars Direct calls for the http://www.marssociety.org/images/direc … .gif]Earth Return Vehicle to launch from Mars surface directly to Earth.

Maybe somebody can help me understand the numbers on this drawing. Initially, it says the dry masses of stages 1 and 2 are 6.33 and 1.77 tonnes, but later it says that the inert masses for stage 1 and 2 are 8.85 and 2.56 tonnes. Aren't these terms descibing the same thing? Is something extra included in the inert mass that isn't in the dry mass?

(BTW, his mass fractions for the stages are a bit optimistic but still in the acceptable range.)

RobertDyck · 2004-12-10 18:10:33

Inert mass includes unburned residual propellant, dry mass is with completely empty tanks. Notice it also has usable propellant, residual propellant has to be produced but isn't usable. If only everything were 100% efficient.

Mad Grad Student · 2004-12-10 18:14:51

Why exactly are the mass estimates so off the mark? Zubrin estimates that the hab and ERV will each be about 60,000 pounds, that seems logical to me. If you look at the estimates, everything is accounted for, along with a 16% margin for mass gain. Even if they're still too heavy for a single Ares launch we can up the size of the launcher or instead split it into two parts for Earth orbit rendezvous. Keep in mind that a mission for, say, ten astonauts (is this what you're asking for GCN?) would be far more massive and even more difficult to launch.

Any humans-to-Mars mission is going to be an extremely difficult sale for NASA (or any space agency) to make. But telling the politicians "let's sidestep starting small and just start with a big, more expensive mission type" isn't going to help you. Mars direct could lead to a Martian Apollo, but at least it would be more likely to get us to that point in the first place. Besides, there would still be money in the bank for bigger missions once the MD ones are done.

That drawing of the Mars Society hab would be perfectly acceptible for a mission with a crew of four, IMHO of course. Compared to the U-boats that operated in WW2, that would look positively spacious, and many of the enlisted men on the crew would never see daylight in tours as long as a mission to Mars. Those guys were also waging war and had no form of communication at all with the outside world. Human factors is blown way out of proportion by the doom/gloom naysayers who claim that we need massive crews and palace like habs. We don't.

GraemeSkinner · 2004-12-10 22:41:57

Any humans-to-Mars mission is going to be an extremely difficult sale for NASA (or any space agency) to make. But telling the politicians "let's sidestep starting small and just start with a big, more expensive mission type" isn't going to help you. Mars direct could lead to a Martian Apollo, but at least it would be more likely to get us to that point in the first place. Besides, there would still be money in the bank for bigger missions once the MD ones are done.

I can imagine that sales pitch, "hi, rather than just spend a few billion on a small manned mission to Mars to test the theories and equipment, we propose spending ten times that on the same risky mission." And the response from any sane government "hmm, security".

Although I'd like a full on, all singing, all dancing manned mission, the chances are that the governments involved would want to go for a cheaper option to test the water.

Graeme

Euler · 2004-12-11 02:58:39

Why exactly are the mass estimates so off the mark? Zubrin estimates that the hab and ERV will each be about 60,000 pounds, that seems logical to me. If you look at the estimates, everything is accounted for, along with a 16% margin for mass gain.

60,000 lbs for a four-person hab is smallish, but may be workable. However, I think that the habitable part of the ERV needs to be about the same size as the hab because it provides essentially the same function. In the Mars Direct scheme, the ERV must also include some big rocket stages, hydrogen feedstock, a nuclear reactor, etc. so that the habitable part of the ERV ends up being much smaller. The Mars Direct scheme gives the ERV a mass which compares unfavorably with small real life 3-person space vehicles such as Soyuz, Shenzhou, and the Apollo Command/Service modules, despite the fact that is must carry 4 people on a much more difficult mission. There are also some other objections to Mars Direct, but I think that this is the one 100% irrefutable reason why the current Mars Direct plan would not work.

That drawing of the Mars Society hab would be perfectly acceptible for a mission with a crew of four, IMHO of course. Compared to the U-boats that operated in WW2, that would look positively spacious, and many of the enlisted men on the crew would never see daylight in tours as long as a mission to Mars.

Compared to the ERV, it would definitely be the U-boats that look spacious.

RobS · 2004-12-11 10:07:56

It might be helpful to add some precision here. The hab is 8 meters/25 feet in diameter, has two levels each with about 50 square meters/500 square feet, and has a TOTAL mass of 25 tonnes, but that includes supplies, furniture, a pressurized rover, and scientific equipment. The structure is given as 5 tonnes, the life support system as 3 tonnes. The aeroshield and landing system are not included in the 8 tonnes or the 25 tonnes, because the 25 tonnes is the total that is landed on the surface. No fuel is landed on the surface,so it isn't in the 25 tonnes. it isn't clear to me whether engines and tanks are included in the 25 tonnes.

The ERV cabin has a 3 tonne mass with a 1-tonne life support system. Dimensions are not given, but when one looks at drawings it apears to be 2 stories and about 6 meters/20 feet in diameter. That would give the ERV 27 square meters/270 square feet per floor. In other words, the two floors of the ERV have about the same surface area as thre top floor of the Hab. The bottom floor of the Hab is used as cargo storage on the flight out, so the living space during both voyages is about the same.

This is much larger than a Soyuz in terms of area and volume (multiply by about 2.4 meters/8 feet to convert surface area to volume), yet the mass is comparable. I suspect that's one reason people think the Mars Direct mass estimates are too low.

Somewhere NASA has a chart showing how much volume a person needs per length of voyage. It is a graph and I have seen it somewhere, maybe in the Reference Mission. What would NASA require for a six-month voyage? What would NASA require for an 18-month surface mission?

-- RobS

GCNRevenger · 2004-12-11 14:14:34

"The ERV cabin has a 3 tonne mass with a 1-tonne life support system...

...This is much larger than a Soyuz in terms of area and volume (multiply by about 2.4 meters/8 feet to convert surface area to volume), yet the mass is comparable. I suspect that's one reason people think the Mars Direct mass estimates are too low."

And there would be good reason to suspect. I don't see hows it is possible to make the ERV so light and still be of practical size. One floor of the HAB module is already too small in my opinion for 3-4 crewmen, module contiguous area is a psychological concern not simply square footage too, but the ERV probobly cannot even reach this.

There is also the reactor which is about 2-3MT over budget, the ISRU plant is still a question mark, the hydrogen boiloff must be held to quite low levels, the Earth entry mechanism, and allowances for sample return - which will require a substantial increase in ERV capacity.

"..."hi, rather than just spend a few billion on a small manned mission to Mars to test the theories and equipment, we propose spending ten times that on the same risky mission." And the response from any sane government "hmm, security".

Although I'd like a full on, all singing, all dancing manned mission, the chances are that the governments involved would want to go for a cheaper option to test the water."

And so when you are done "testing equipment," you have to throw away every single penny in development for that whimpy and underpowerd hardware. You just sealed NASA's fate and ensured that we're stuck here for another generation or two, way to go! Its really quite simple...

1: If we go to Mars without looking ahead to the next phase beyond exploration, then the program will become Martian Apollo, and end as soon as we get bored again.

2: "Just enough" exploration hardware cannot be anything more. Ever. Its cost may be lower to actually reach Mars, but it will all be worthless and you'll have to pay for bigger hardware later on anyway to go to stay.

3: Hardware with enough capability to establish a human presence on Mars is not unaffordable given minimal single-digit budget increases, and could also be used to more effectively carry out the exploration phase as well. MarsDirect is not enough, but what we would need is not beyond our reach.

How much would Ares cost? How much MORE would something bigger cost? Or splitting payload and TMI? A bigger HAB versus a smaller one? Six crew instead of four? Spend a few billion to make an EELV "Martian Progress?"

NASA DRM in the late 90's would have cost ~$60Bn and thats with double HABs and heavier equipment, with DRM-III the cost may be substantially lower while still offering about double the capability of MarsDirect. We could count on $90-100Bn over a decade today given NASA's budget sans-Shuttle/ISS, and heck we've spent that much on the ISS.

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