Size of the ship that would go to Mars.

Ian · 2003-06-18 16:15:41

How big would the ship that will eventually go to mars be? I think that the ships that eventaully go to mars should be small at first so that they would accelerate faster when a lot of force is applied to the ship like nuclear propulsion so that the ship could get to mars in a much shorter time. How big does anyone think that the ship that would go to mars have to be?

Gennaro · 2003-06-21 12:47:00

I would prefer a ship with a cylinder type artificial g hab section to use during coast periods (the easy way would otherwise be to tumble the entire craft through space with the crew compartment at the far end).
With a cylinder however, minimum comfort criteria predicts a diameter of at least 44 m. Concievably, the ship could use a gas core nuclear engine for high initial thrust (why launch from space if you don't have too?).
If someone could get around to building a nuclear pulse propulsion spaceship on the other hand - that is a ship that flies on atomic bombs - (doesn't have to be America as, judging from the discussions on this subject, she appears quite sensitive to all things nuclear), the 1950's plans for a 10,000 ton "Orion" called for a diameter of 56 m (185 ft) and a height of 85 m (280 ft).
Yes, I know, it will never see the light of day.
:;):

Article on artificial gravity:
http://www.spacefuture.com/archive....s.shtml

Palomar · 2003-06-21 13:33:49

How big would the ship that will eventually go to mars be? I think that the ships that eventaully go to mars should be small at first so that they would accelerate faster when a lot of force is applied to the ship like nuclear propulsion so that the ship could get to mars in a much shorter time. How big does anyone think that the ship that would go to mars have to be?

*Have you read _The Case for Mars_ by Robert Zubrin?

Regardless, specifications regarding the craft have been discussed previously here. Conversation at these message boards picked up dramatically in 5/2002...there is loads of information for new-comers to sift through, if you take the time to go through the old threads. You might be missing out, otherwise.

Just a suggestion.

--Cindy

RobS · 2003-06-22 00:27:26

The Case for Mars by Zubrin assumes a 25.2 tonne hab flies to Mars in six months with the crew on board and lands on Mars, and a 28.6 tonne Earth Return Vehicle flies to Mars on a Hohmann orbit (260 days on average) unmanned and lands there two years earlier, with a back-up Earth Return Vehicle (which otherwise is the ERV for the next mission in the future) flying out about the same time as the crew. One hab and one ERV total 53.8 tonnes on the Martian surface.

NASA seems to have thought Zubrin was a bit optimistic in proposing such masses. But the last decade has probably improved the situation. The hab could be made of plastic and be inflatable, like the Transhab. The reactor can be more efficient in converting heat to electricity and therefore need not weigh 3.5 tonnes; 2 tonnes might be enough.

The Mars-24 project I posted on the list in the fall (which I am still working on) proposed a 16 tonne interplanetary "semicycler" habitat that would fly from Earth orbit to Mars orbit; a reusable one stage "Mars shuttle" that would weigh 17 tonnes empty (but had to be accompanied by 8 tonnes of liquid hydrogen and could also land 8 tonnes of cargo on the surface); and automated cargo landers that could land about 16 tonnes of cargo on Mars at a time. Establishment of a Mars outpost required three such landers with three more for redundancy that otherwisewould be the supplies for the next mission. So I assumed a landing mass per mission of about 76 tonnes, which may have been generous.

The trick is getting everything to Mars. If you are using chemical rockets alone, Zubin is assuming a 140 tonne to low earth orbit launcher is needed for his 25 and 28 tonne payloads, respectively (the lighter payload is flow at a higher velocity and thus needs more fuel). He says (p. 105) that a solid core nuclear engine increases your landing payload sixty percent; in other words, the 140 tonnes in low Earth orbit can get about 40-45 tonnes on the Martian surface, or you can get 25-28 tonnes on Mars using a launcher that puts 90 tonnes in low Earth orbit.

If you assume solar thermal propulsion to "kick" the payload into a highly elliptical orbit, then chemical to send it to Mars, you get about a 40 to 50% improvement over chemical alone, so the 140 tonne launcher can put 35 to 42 tonnes on the Martian surface, or you can get 25-28 tonnes there with a 100-tonne to low earth orbit launcher. Solar thermal propulsion involves a large pair of mirrors focusing intense sunlight onto a graphite block, through which you run liquid hydrogen; it can give a specific impulse probably as high as 900 seconds, but the thrust can't get over 100 pounds or so. Better than an ion engine, but it would require a series of perigee "kicks" over several months to launch a craft to Mars.

In Mars-24 I assume solar powered ion engines based on Michael Duke's "Lunar Reference Strategy" which is discussed on the "Romance to Reality" website. Duke assumes the space shuttle as the primary launch vehicle, so he based his entire plan to return to the moon on the assumption you could put only 24-25 tonnes in low earth orbit at a time. I used this mass assumption as well, but assumed that the Delta, Atlas, Angara, Ariane, or H-1 (existing commercial rockets) would be used instead and that 24 tonnes to low earth orbit would be the baseline. Duke says that a solar ion vehicle with a total mass of 8 to 9 tonnes, including the xenon propellant, could push 16 tonnes to the lagrange point between the earth and moon (L1) in six months. Of the sixteen tonnes, half (8 tonnes) could be payload to land on the moon, and the other half (8 tonnes) would be a vehicle (including hydrogen/oxygen fuel) to land the payload on the moon. In other words, every tonne going to the moon requires three tonnes launched from the Earth. It turns out the same rule pretty much applies to Mars; the delta vee for landing is a bit less, but you need a heat shield and parachute, so the mass ratio ends up being about the same. Solar ion propulsion already exists but would have to be scaled up about 100 fold to produce a vehicle of the sort Duke assumes.

Robert Dyck, who is on this list, is very interested in an all-ion vehicle to Mars. I don't know how we would estimate the ratio of mass launched from Earth to the mass landed on the Martian surface; maybe 2.5 to 1 or 2.75 to 1.

To summarize and set all these proposals in the same format:

All chemical: 140:25 is 5.6:1, launch mass to landing mass
Nuclear thermal: 140:40 is 3.5:1
Solar thermal/chemical: 140:35 is 4:1
Solar Ion/chemical: 140:47 is 3:1
All solar ion: 140:50? is 2.8:1
I suspect with gaseous fission you get a ratio closer to 2:1.

I should add that if you assume solar-ion to the lagrange point and lunar-manufactured hydrogen and oxygen for trans-Mars injection and Mars landing, the *Earth launch mass* to Mars landing mass gets closer to 2.5 to 1.

So it's a question of what technology you think is likely to be available or reasonable to develop in terms of technological and political costs (and nuclear involves a lot of both). My guess is the following, for what it is worth:

1. We will return to the moon before going to Mars. This delays the Mars mission, but there is a strong moon lobby out there and there is a good argument to be made that the moon provides a safe destination to develop *some* of the technology needed to go to Mars.

2. We will develop a transportation system to the moon using lunar water from the lunar south pole. This system will require a docking and vehicle transfer point at the lagrange point, most likely. This was proposed by a NASA team last fall and was called "Gateway" Station. Gateway would be a transportation node for Mars missions and for sending radio telescopes to the Earth-Sun L2 point as well.

3. We can use lunar hydrogen and oxygen for trans-Mars injection. If lunar fuel is cheap enough, we could launch Mars cargo just as far as low Earth orbit and use lunar fuel for the entire rest of the trip, yielding a launch to landing mass ratio close to 1:1.

4. That solar ion propulsion will be used to lift cargo to Gateway. This dovetails fairly well with Project Prometheus, which will develop nuclear reactors for space use for ion engines, but the reactors will probably be 100 kilowatts or less. Solar-ion engines to lift cargo to Gateway of the sort proposed by Duke would need more like 400 kilowatts. Thus ion engines that could be used by either power source will be developed, but solar power would be used in the inner solar system.

But all these guesses are just that; guesses. If there is a breakthrough with VASIMR propulsion, it would be used instead. Tethers will almost certainly be undergoing development by the time we're ready to fly to Mars. So there are many other possible futures.

-- RobS

Bill White · 2003-06-23 10:21:53

Questions:

<1>

Duke assumes the space shuttle as the primary launch vehicle, so he based his entire plan to return to the moon on the assumption you could put only 24-25 tonnes in low earth orbit at a time.

I know we have discussed shuttle variants meaning SRBs + main engine without the orbiter. Shuttle C and Zubrin's Ares are two examples. Are these ideas feasible within a reasonable time frame and budget?

<2>

Duke says that a solar ion vehicle with a total mass of 8 to 9 tonnes, including the xenon propellant, could push 16 tonnes. . .

I recall someone somewhere posting about world-wide limitations on supplies of xenon gas or other gases suitable for electric ion propulsion (whether nuclear electric or solar electric) - - yet I have not been able to confirm this anywhere. Supposedly an all ion drive mission to Mars would consume more propellant gas than could be reasonably manuafactured in a short period of time. Am I merely passing on a spurious rumor or is there some truth to this?

<3>

Solar thermal? What is the propellant gas? Can you concentrate sunlight sufficiently to generate adequate ISP?

I understand nuclear thermal (in a vague layman sort of way) yet never really heard about solar thermal.

I will hang up now and listen for any reply. :-)

RobS · 2003-06-23 23:21:56

These are very good questions, and may not have good answers!

Heavy-lift variants of the space shuttle: They will cost several billion dollars to develop. Post-Challenger they are even less likely to see the light of day because one is essentially rearranging old technology. The big issues about a a heavy lift shuttle variant are political and commercial. There is no commercial need for them; just for lunar and Martian manned flights. Politically, developing a heavy-lift shuttle variant may be seen as "dejustifying" a bunch of decisions NASA made years ago. For example, it would have been cheaper to develop a heavy-lift cargo shuttle and lift the International Space Station into orbit using two or three flights instead of a few dozen. But that would have "dejustified" the manned shuttle, which would have been reduced to a very big and expensive vehicle for flying crews and cargo to ISS. Now, building a cargo shuttle would dejustify those decisions. In other words, NASA would have to imply that it was wrong. Something all of us have to do in our lives from time to time, but which government agencies prefer not to do.

It might be easier rebuilding Energia construction and assembly facilities. Energia variants can lift 100-200 tonnes into low orbit. The Angara can lift 29 tonnes, if I recall.

Ion engine propellant: I have no idea what the answer to this is, but while xenon is the current ion propellant of choice, it is not the only possibility. In the 60s they used cesium, and I am sure it could be used again. You can use anything you can ionize, and that's just about everything, though obviously you want to use something that ionizes easily. I suspect argon can be used as well.

Solar thermal: It uses hydrogen, just like nuclear thermal. But solid-core nuclear reactors put out many megawatts--thousands of kilowatts--of heat energy. A thousand kilowatts of solar energy requires about a thousand square meters of mirror, all precisely focused on a small target. Furthermore, the heat comes from the outside, and the hydrogen circulates inside, whereas a nuclear core has the heat inside as well as the hydrogen. If you use Google on "solar thermal rocket" I think, you will find references to the current NASA research. It is a very promising engine concept.

-- RobS

RobertDyck · 2003-06-24 07:49:29

I recall someone somewhere posting about world-wide limitations on supplies of xenon gas or other gases suitable for electric ion propulsion (whether nuclear electric or solar electric) - - yet I have not been able to confirm this anywhere.

Christopher Hirata told me that he thought there was insufficient supply of xenon gas for a manned Mars mission. That was in a telephone conversation, and I think I mentioned it once on these boards. I haven't been able to verify it, but xenon is currently produced as a by-product of liquid air. Cryogenically cooling air produces xenon and other trace gasses from the atmosphere. Christopher thought the entire world-wide production of liquid air would not produce enough xenon as a byproduct. However, I suppose we could build a very large liquid air plant specifically to extract enough xenon.

Bill White · 2003-06-24 09:57:46

Heavy-lift variants of the space shuttle: They will cost several billion dollars to develop.

As an engineering matter (to ignore the politics of it all) it seems to me that it shouldn't be too difficult to design a cargo pod having the mass distribution profile of the current orbiter, with a disposable fairing to provide the aerodynamic profile (more or less) of the curent orbiter.

If cargo mass (payload) were distributed in close approximation to the current launch stack configuration and if a disposable fairing gave a comparable aerodynamic shape during launch, it would seem that the engineering needed to certify the design goes way, way down.

But then Energia with strap on boosters may be an even better solution (to really ignore the politics of it all).

prometheusunbound · 2003-07-03 09:35:48

I do not believe a heavy lift shuttle to be feasable simply b/c it is designed to return to earth. . .that is a lot of extra weight that goes up into orbit, weight that costs fuel and payload. It would be more economically feasible in my eyes to revert to saturn five (which launched skylab in one launch, which is larger than ISS according to my knowledge). Unfortantly, all the blueprints were destroyed by the government, but I believe it could be found if pressured hard enough. Even if it is not found, a more powerful and efficient heavy lifter could be created with new materials techologies and CAD programs

RobertDyck · 2003-07-03 10:34:15

I read in one book that the author attempted to locate the blueprints for the Saturn V. He found that one complete set of blueprints had been given to the Boy Scouts for a paper drive. One copy was supposed to be permanently kept at a government archive, however, when he asked a librarian there to locate the blueprints for him, the librarian was unable to find them. As far as the author could tell the only remaining copy of Saturn V blueprints that were not destroyed were supposed to be in that archive, but librarians who work there can find no trace.

As a contrary claim, employees of NASA who I talked to at science conferences claim the blueprints to still exist and NASA has them. They don't know exactly where, but they think NASA still has them "somewhere". You tell me who is right.

However, there are designs using more modern vehicles. There are proposals for Shuttle-C or Ares.

Shaun Barrett · 2003-07-06 06:55:44

Can anyone think of a nice conspiracy theory to account for the apparent scarcity of Saturn V blueprints?
I mean is there any reason (e.g. the perennial national security angle) why NASA and/or the U.S. government might prefer such blueprints to remain conveniently 'misfiled' and difficult to locate?
:;):

RobertDyck · 2003-07-06 14:55:08

Can anyone think of a nice conspiracy theory to account for the apparent scarcity of Saturn V blueprints?
I mean is there any reason (e.g. the perennial national security angle) why NASA and/or the U.S. government might prefer such blueprints to remain conveniently 'misfiled' and difficult to locate?
:;):

That one is obvious. In the 1970s there was a strong push to complete the Space Shuttle before it also became a project that was started only to be cancelled by the next administration. The "misfiling" of Saturn V blueprints were to force a focus on the Shuttle. Until its first flight, NASA directed all funds into it at the expense of all else.

Today it makes little difference. The factory that manufactured the first stage of the Saturn V is now producing Shuttle external tanks. Three complete Saturn V launch vehicles were left outdoors exposed to the elements so their rust makes then unusable. The interstages for all thee vehicle were used as storage sheds, but even those sheds have disappeared. The two launch pads have been converted to service the Shuttle. The service structure on two of the Mobile Launchers has been converted to the Stationary Service Structure on the launch pads. All three Mobile Launchers have been converted to Mobile Launch Platforms for the Shuttle. The service structure for the third ML has been cut in pieces and is sitting in a field rusting, just in case someone wants to convert it into a museum piece. They could have maintained the third ML in an Apollo configuration, and protected the three Saturn V launch vehicles from the elements; that would have maintained heavy launch capability. In fact a backup Skylab was constructed in case something happened to Skylab 1. Something did happen; it fell out of the sky. But since Saturn V launch capability was scuttled, they couldn't launch Skylab 2. If it had been maintained they could have launched Skylab 2 at the cost of fuel and the salaries of launch staff for a single launch. Aren't those staff members paid anyway, even if they aren't working? The backup Skylab is now in a museum.

So at the expense of scuttling Saturn V, we now have a Space Shuttle.

RobertDyck · 2003-07-06 15:34:34

Perhaps this is redundant, and covered in other threads, but since the issue of the shuttle came up I thought I should mention...

Much of the launch cost is fixed cost for a manned space capability. For example, the Johnson Space Center with its mission control, zero buoyancy tank, and other astronaut training facilities. All of that will be required regardless of what launch system is used. Just slightly less than half the fixed cost of Shuttle is JSC, so the hardware cost of Shuttle is actually not as high as it first appears.

I still think expendable launch vehicles should be used for delivering heavy cargo to orbit; cargo such as ISS modules. We don't have Saturn V any more, but we now have EELVs such has Delta IV and Atlas V. The argument against it is that manoeuvring engines, their fuel tanks, radar, autopilot, electric power supply all are heavy equipment that is used only once for docking. I argue that a reusable space tug that is designed to stay on orbit, with a small grappling arm, could grab the modules after they are thrown into LEO then carried to ISS and attached. Such a tug would not require heat shields, aerodynamic shape, or any landing systems. Such a tug could be simply a single seat capsule for a pilot, a small grappling arm (a small copy of the Space Station Remote Manipulator System), manoeuvring rockets, and the main engine would have to provide orbital changes for the tug and ISS module. Since the maximum Shuttle lift to ISS is 16 tonnes, but the orbiter masses 104.3 tonnes itself, that means the orbiter OMS is capable of orbital changes for a total of 120.3 tonnes. This tug would only require an OMS capable of 16 tonnes plus the mass of the tug itself; that tug should mass somewhere between 3 and 4 tonnes. An advanced option would be unmanned operation of the tug: remote piloted or autonomous. It should be easy to keep an unmanned tug down to 3 tonnes.

In addition to an EELV fleet and on-orbit tug, a comprehensive space system would include a small Orbital Space Plane to act as a crew taxi. The OSP should be sized to be launched to ISS with an EELV that has only one common core module, such as an Atlas V 401. For safety, the launch vehicle to lift the OSP should not have any solid rockets; I think Challenger proved that. The OSP could be configured to carry 4 astronauts, or one or more seats removed to carry ISS equipment drawers. The current shuttle could be maintained in case a mission requires a big-ass orbiter complete with large RMS robot arm. Off hand I can't think of a single mission that couldn't replace the orbiter with a combination of EELV, on-orbit tug, and OSP.

For the long term, skip the second generation shuttle and use the above fleet until a third generation shuttle is ready. A third generation shuttle would be a Single Stage To Orbit, Reusable Launch Vehicle, with Rocket Based Combined Cycle engines that can operate in SCRAM jet mode.

GCNRevenger · 2003-10-15 11:29:43

As far as flight two and from LEO and the ISS, this is a perfictly sensable strategy. Russia (and perhaps the USAF...) were thinking about designing an unmanned nuclear/ion tug that would perform that sort of function but be able to do it many times or with very heavy payloads rather than having to refuel or risk a crewman in a manned chemical tug.

But for anything beyond low earth orbit of signifigant mass, like a Mars ship or pieces for a Lunar city, even the Boeing-daydreamed "Delta V" 5-CCB rocket or the 7-CCB+Mega-Upper-Stage Russian Angara simply can't launch large enough payloads to be practical. The weight, complexity, and safety penalty of on orbit construction of a large craft with many smaller launchers should be Jay Leno grade material, proven by the insane trouble of building ISS compared to Skylab.

What isn't really clear is if the EELV fleet could make efficenct-enough supply/fuel launchers for already assembled bases or beyond-earth-orbit ships.

As far as the next shuttle or the next-next shuttle, I think that a shuttle replacement based on current rockets or engines just isn't worthwhile. Why? We are pushing the limits of practical efficency for fuel/oxidizer chemical propellants, the SSME engines on Shuttle are already running at 6000F and above 90% efficency, we just can't make it that much better. So, we skip the next-generation craft entirely since it would be limited to "classic" rocket propellants and go directly to air-breathing rockets to cast off the mass penalty of oxidizer entirely, which makes staging of rockets a nessessity.

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#1 2003-06-18 16:15:41

Re: Size of the ship that would go to Mars.

#2 2003-06-21 12:47:00

Re: Size of the ship that would go to Mars.

#3 2003-06-21 13:33:49

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#4 2003-06-22 00:27:26

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#5 2003-06-23 10:21:53

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#6 2003-06-23 23:21:56

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#7 2003-06-24 07:49:29

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#8 2003-06-24 09:57:46

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#9 2003-07-03 09:35:48

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#10 2003-07-03 10:34:15

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#11 2003-07-06 06:55:44

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#12 2003-07-06 14:55:08

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#13 2003-07-06 15:34:34

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#14 2003-10-15 11:29:43

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