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We all know what the Mars Direct mission architecture looks like.
And we know that Mars Semi-Direct is similiar except that it requjres a minimum of three launches instead of two because it splits the job of the Earth Return Vehicle (ERV) into two parts. With a Mars Ascent Vehicle on the surface and an Earth Return Vehicle in orbit that the Ascent vehicle docks with and the astronauts transfer to.
Now, one of the big problems seems to be the Mars Direct ERV. It has to do too much within its mass budget and ends up being pretty cramped for a six month trip back to Earth.
My change is this:
Why not make the Mars Ascent Vehicle REUSABLE?
That is, after it docks with the ERV in Mars Orbit, deorbit the MAV and send it to the projected site of the next Hab landing.
Now, the MAV would have to be a single stage to orbit vehicle, and would have to carry much more hydrogen feedstock to produce methane for subsequent missions, but I assume this is doable. Remember the MAV wouldn't need near the equipment that a full up ERV launched from the surface would.
And this MAV could probably be used as the ERV for long duration lunar missions.
Anyway, I would only make the MAV so it would be used twice.
By the time two manned Mars missions are complete (about five years) I would send a newer MAV with a small nuclear thermal rocket engine. All it would have to do would be to suck in a tankfull of CO2 to heat with the reactor and use as rocket fuel.
This way, after the first missions that emplaces the MAV (and one later that brings the nuclear power MAV), your Mars Semi-Direct Missions will require only two launches. One for the Hab. One for the orbiting ERV.
Is anyone going to read this?
Does Dr. Zubrin ever come online?
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It is been though of here before and I am sure Zubrin has thought of it. This is one of those technological improvements that can be done to mars direct to make the program more affordable. Zubrin based his proposal on current technology and said as technological advances come along they can be used to improve the plan. As for only using the MAV for two launches why? Use it for as many as it is safe to do so. The only question is do we invest in the development of a reusable mars accent vehicle or do we go right away. I am in favor of the technological development but some people are in a hurry. As long as we get there I will be happy.
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It is been though of here before and I am sure Zubrin has thought of it. This is one of those technological improvements that can be done to mars direct to make the program more affordable. Zubrin based his proposal on current technology and said as technological advances come along they can be used to improve the plan. As for only using the MAV for two launches why? Use it for as many as it is safe to do so. The only question is do we invest in the development of a reusable mars accent vehicle or do we go right away. I am in favor of the technological development but some people are in a hurry. As long as we get there I will be happy.
The reason I suggested using the MAV for two launches only was because I figured it would have to carry along the hydrogen feedstock to manufacture all the methane it will use for ascent (and landing) during its original trip to Mars and I (not being an engineer) didn't know how many tons of hydrogen feedstock the MAV could carry to the Mars surface.
I figured that sometime in the first two mission time frame we would either have discovered ice on Mars to use or a small NTR would become available.
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Well if we discover ice on Mars then there is our hydrogen feed stock. Otherwise we just bring the hydrogen feedstock along with the next crew. Even if a NTR was developed they get more thrust if they use an oxidizer for the nuclear thermal part and a fuel for an afterburner. Triton would not have enough trust to get off mars. That doesn’t mean a NTR with enough trust couldn’t be built but it won’t be the triton design. I know you didn’t mention triton but it is the only NTR design I know of. I am sure there are lots of other ones but I am not an expert in these things.
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What about propellant for return to Earth. To use a buzz word, Trans-Earth Insertion (TEI). NASA's Design Reference Mission calls for bringing propellant for the return trip all the way from Earth. The great advantages of Mars Direct are aerocapture, and in-situ propellant production. That's why I suggested using the MAV as the TEI stage; giant propellant tanks so it would have enough fuel in Mars orbit to push the Interplanetary Transit Vehicle into Trans-Earth trajectory. Of course that would leave the MAV heading to Earth with the ITV. With a reusable MAV, are you counting on TEI propellant from Earth?
I don't know if Robert Zubrin reads this message board, but I know Maggie Zubrin does. Neither one of them ever post.
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What about propellant for return to Earth. To use a buzz word, Trans-Earth Insertion (TEI). NASA's Design Reference Mission calls for bringing propellant for the return trip all the way from Earth.
It’s not obvious to me which is better. Isn’t the majority of the propellant used to get off mars. The mars accent vehicle could perhaps transfer some fuel to the transfer vehicle it could even do multiple flights to bring up fuel perhaps even stopping at a fuel depot on one of the Martian moons. I don’t think much is gained though by refueling the transfer vehicle at mars. Also if the transfer vehicle is a triton it can’t be launched off mars anyway. If the transfer vehicle can carry enough fuel for both ways then it will be much more versatile and there will be less chances of failure.
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What about propellant for return to Earth. To use a buzz word, Trans-Earth Insertion (TEI). NASA's Design Reference Mission calls for bringing propellant for the return trip all the way from Earth. The great advantages of Mars Direct are aerocapture, and in-situ propellant production. That's why I suggested using the MAV as the TEI stage; giant propellant tanks so it would have enough fuel in Mars orbit to push the Interplanetary Transit Vehicle into Trans-Earth trajectory. Of course that would leave the MAV heading to Earth with the ITV. With a reusable MAV, are you counting on TEI propellant from Earth?
I don't know if Robert Zubrin reads this message board, but I know Maggie Zubrin does. Neither one of them ever post.
I figured on bringing the TEI propellant from Earth. Because I thought the whole point of Semi-Direct was to only have to produce enough fuel in situ for Ascent to orbit. So that if propellant production failed, then the mission could still be saved by launching a fully fueled Ascent vehicle from Earth to the Martian surface.
I would've thought the Zubrins would post somewhere given that Mars Direct has seemed to have been very must a "grassroots" effort.
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Good point on the refueling of just what ever is considered the lander portion for Mars for relaunch to orbit.
I also like the safety net approach to the ITV or what I consider orbit to orbit vehicle but that would require using the Iss as the means to return to earth and an orbiting station around Mars as well to make this work for reusuability of vehicles.
If one considers the size of the ITV as being able to provide the resources for half the trip and the rest for half the duration of being on the planet, then I think we can achieve this with out much hardship to the financial side of things.
Basically the apollo capsule/ CM on steroids link to another for the trip to start to mars.
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I would like to note that the Apollo 17 geologist, Harrison Schmidt I believe, in a recent issue of Popular Mechanics estimated that a heavy lift launch vehicle derived from the Saturn V could be developed with a few years for only five billion dollars with twice the lift capacity of the Saturn V.
I assume he was referring to the Comet design.
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If you want to go the reuseable route, it isn't going to be easy. The amount of fuel that the MAV would have to be able to haul is pretty big, and I don't think that such a vehicle would be practical early on (especially with importing H2) or all that bennefical. The Semi-Direct scheme relies on alot of the surface payload being sent with the MAV/Cargo lander, and the scheme won't be workable without that. Plus, Semi-Direct scheme relies on keeping the MAV mass as light as possible, which clearly demands expendability and absolute minimum capability (just crew and rocks, maybe not even pressurized).
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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I don't think its practical to make any of the direct arcitectures have reuseable componets... what I do see eventually though goes somthing like this:
-Earth/LEO spaceplane RLV with medium payload capabilities is built, able to deliver payloads up to ~25MT to orbit regularly.
-Small-ish LEO/LMO cycler vehicle, powerd by NERVA style NTR engines that, with aerobraking, could deliver 1-2 cargoes (conjunction) or 2-3 cargoes (opposition) and return without refueling. The manned version would accomodate the crew in lieu of a payload.
Later on, when supplies of Martian water are secured, the cycler would leave Earth with multiple payloads instead of carrying the return fuel with it.
-Item #3, medium Martian RLV, probobly modeled on the DC-I concept, powerd by Methane/LOX and able to carry a single modular cargo from LMO to the surface with accuracy and 100+ flight reliability. Manned version would come equipped with emergency reentry capsule with extended LSS capacity.
As far as heavy launchers go, Comet would probobly be too expensive... Saturn was horribly expensive. Somthing more like an American Energia, jumbo sized Shuttle tankage with five RS-68R engines and 4-6 Shuttle SRBs and a single RS-68R for upper stage... real heavy lift with 6 engines instead of 16, and you get to save the boosters.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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what I do see eventually though goes somthing like this:
I see the same three vehicles developing, but all three are built almost exclusively around transporting humans. Bulk cargo mostly goes one way- from Earth to Mars. There just isn't much on Mars that would be valuable enough to send back in the early human missions to Mars. All the non-human cargo can just be sent direct using an HLLV.
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The idea is to ultimatly rely on the superior economics of medium RLV launches to haul cargo in bulk, like shipping containers on Earth, and to minimize HLLV launches except for when they are needed.
Edit: I think it would provide more scaleability then parallel HLV shots. The smaller cargo containers would also be a more appropriate size for an electric engine tug of some sort.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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If you try to rely on an small or medium RLV for launching cargo, you will run into the same problems that have been plaguing the ISS. Experience with STS also seems to indicate that reusable are not yet ready to compete with expendables for launching cargo.
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Right now of course, but this will not always be the case. The Shuttle never was nor ever will be a "reuseable" vehicle, I am talking somthing that can fly 50 times a year and be entirely reuseable, which will be able to best heavy lift vehicles in the long run. This is definatly a later-term concept when bulk transport to Mars is nessesarry.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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I like the idea of a re-useable MAV, but I think it is probably a little to ambitious for the first mission. Making the MAV reusable adds alot of mass, as there is the whole re-entery thing to worry about. Also shipping enough hydrogen feed-stock for multiple assents is just impractical.
However, a reusable MAV should be way high up on the priority list for cargo to deploy at a developing martin base. I like the idea of using a stripdown/bulked up NTR/CO2 hopper. Such a vehicle could provide both continental mobility and re-usable access to orbit.
The main thing that worries me is, will it ever be practical to build a reliable reusable MAV? Most rocket engines have to be heavily serviced every couple of launches to ensure their continued opperation, and most have to be retired after only a smaller number of missions. The heat shield will also probably need heavy servicing and replacment. A NTR would be even more difficult in this respect as servicing it's engine would be both difficult and dangerous.
He who refuses to do arithmetic is doomed to talk nonsense.
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The main thing that worries me is, will it ever be practical to build a reliable reusable MAV? Most rocket engines have to be heavily serviced every couple of launches to ensure their continued opperation, and most have to be retired after only a smaller number of missions. The heat shield will also probably need heavy servicing and replacment. A NTR would be even more difficult in this respect as servicing it's engine would be both difficult and dangerous.
I am optimistic about the solving the technical hurdles associated with a reusable MAV. There has been a lot of improvement in engine reliability and reusability in recent years, and reentry from low Mars orbit should be easier than reentry from LEO due to the lower velocities involved.
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I don't think I like the idea of an NTR RLV MAV (wow three acronyms in a row)... the reactor will be pretty heavy, especially if it has minimal shielding, and if it operates with CO2 and modest temperatures to prolong life, it will have lousy Isp.
I think that an RLV can be built that could fly about ten times between engine overhauls without too much trouble, and that would probobly be enough if the engines could be easily disconnected and brought inside for servicing.
[i]"The power of accurate observation is often called cynicism by those that do not have it." - George Bernard Shaw[/i]
[i]The glass is at 50% of capacity[/i]
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Packing so much stuff into any vehicle will make it tough for us to go so any weigh reduction can help. That include solar cells as well.
Solar cell doubles as battery
The researchers' photocapacitor is also efficient at capturing energy from weak light sources like sunlight on cloudy or rainy days and indoor lighting.
Solar energy system usually includes solar cells that convert light to electricity and batteries that store the energy for later use.
We succeeded in incorporating both photovoltaic and storage functions in a single cell with a thin, sandwich-type structure.
The researchers are working on boosting the cell's capacity and making a flexible, lightweight plastic version of the device.
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