- Status
rockett":186qt8wv said:
The problem I see with this reactor is not direct heat to electrical current as RTG do it they uses steam turbines.
We would not use steam in outer space. also you have to get rid of 70 mgawats of Heat.
from there web site
What is Hyperion's output?
Approximately 70 megawatts (MW) of heat (thermal energy) and 25 megawatts (MW) of electrical power via steam turbine
Hyperion can be scaled down so if Chang-Diaz's 10-12 MWe mission could in principle be powered by a smaller one. It's developers LANL page says down to 10 MWe.
What with the new thin film PV solar techs might be time to look at nuclear fluorescence generation: a layered film consisting of an emitter, a fluorescent layer, a semi-transparent PV layer and a reflector (so the photons can get a 2nd bite at the PV layer). These have been played with for a while, but without thin film PV techs weren't too practical. Lets you carry your PV systems "sun" around with you with all components tuned to a particular wavelength for max efficiency. Such a film could in principle be rolled up to save space.
What with the new thin film PV solar techs might be time to look at nuclear fluorescence generation: a layered film consisting of an emitter, a fluorescent layer, a semi-transparent PV layer and a reflector (so the photons can get a 2nd bite at the PV layer). These have been played with for a while, but without thin film PV techs weren't too practical. Lets you carry your PV systems "sun" around with you with all components tuned to a particular wavelength for max efficiency. Such a film could in principle be rolled up to save space.
HEY! Where's VASIMR?
NASA Funds New Research Into Novel Space Engines
http://www.space.com/news/nasa-propulsion-contracts-100326.html
I thought NASA was talking about novel engine system designs!
Far as I know, these guys are just more of the same old stuff...
NASA Funds New Research Into Novel Space Engines
http://www.space.com/news/nasa-propulsion-contracts-100326.html
I thought NASA was talking about novel engine system designs!
Far as I know, these guys are just more of the same old stuff...
Sounds like a program with separate funding for modernizing chemical rockets, jets and using biofuels in same, not deep space propulsion.
Some information on Vasimr I hadn't seen before, although it's dated August, 2009, <http://www.adastrarocket.com/Ben-JPC=AIAA-2009-5359-704.pdf>
Basically, states that efficiencies are now calculated to be about 5-10% greater than originally thought, especially at high thrust. I'm no rocket scientist, so some parts of the article are over my head, but it also sounds like this increase in exhaust velocities should continue even when constructing much larger engines.
Basically, states that efficiencies are now calculated to be about 5-10% greater than originally thought, especially at high thrust. I'm no rocket scientist, so some parts of the article are over my head, but it also sounds like this increase in exhaust velocities should continue even when constructing much larger engines.
moreandless":uw0ab7vc said:
Chang-Diaz says 'only' 400 tonnes (http://biography.jrank.org/pages/3309/C ... -Mars.html), but I found another source saying 660 tonnes (with the 60 tonnes of payload included).
I see the potential development of VASIMR, but for Mars missions, it just doesn't make any sense! You'd get better efficiency on chemical/NERVA engines, and a 6 month flight as proposed by Mars Direct, or even the 9 month flight of any minimum-energy transfer, are not outside the experience of human astronauts. VASIMR has potential for missions to Jupiter, or Saturn, where a manned mission would, without VASIMR, require hundreds of tonnes of life-support payload, so it evens out. But for Mars, it's not needed.
Polishguy":3p7b4u7l said:
I am no expert but can give you some pointers on the advantages and disadvantages of NERVA vs. Vasmir vs. chemical.
The rocket equation is a brutal one. There are two big things in terms of rocketry thrust and ISP (or fuel efficiency). The greater your ISP the less propellant you need to get to a certain change in velocity. The greater your thrust the faster you can get there. The downside is that is it almost impossible to get both at the same time.
Rockets wither chemical, thermal, or electric work by throwing mass in the opposite direction of flight. To get good fuel efficiency, a rocket must throw mass out at high speed. The higher the speed you throw the mass out the more speed can be imparted to the rocket. Imagine sitting on a rolling office chair throwing baseballs to move. The faster you throw the baseball the faster you roll in the opposite direction.
To get good thrust a rocket must throw more mass out in a given time. Imagine two people of equal mass sitting on two office chairs each with 15 baseballs. The person throwing 3 baseballs a minute will accelerate faster than the person throwing 1 baseball a minute even if he is throwing that one baseball a minute a twice as fast. However the person throwing three baseballs a minute will run out of baseballs before the person throwing one baseball a minute and might not achieve a higher speed because he is plum out of baseballs. Anyway here is how it relates to chemical, NTR (NERVA), and vasmir (electric propulsion).
In terms of thrust (in theory):Chemical>NTR>>>Electric (Vasmir).
In terms of Fuel efficiency (ISP):Electric>>>NTR>Chemical
Electric and chemical\NTR also work differently. With chemical rockets all the force needed to push the payload to its final velocity is delivered in short burst. The burn that took Apollo to the moon lasted 10 minutes or less. NTR work the same as chemical, but have longer burns due to having lower thrust than chemical. Electric on the other hand slowly accelerates it’s payload over a period of hour, days, weeks, months, even years.
This has several implications. On short trips like say to the moon a chemical rocket will take more proplent per amount of payload mass to get to the moon, but will also get there faster than NTR or VASMIR. 3 days vs. 4 days vs. months.
NTR and VASMIR while slower would allow you to take more payload(NTR) to much more payload(VASMIR) with an equal amount of proplent.
NTR and VASMIR can take equal masses to any desitnation with less propelent than to much less propellant(VASMIR) chemical.
Vasmir and other electric propulsions are so fuel efficient that carrying enough propellent for a return trip to LEO from lunar Orbit is possible. With NTR you would need more proplent for the return trip and have to deal with a hot reactor in LEO and radioactive ehuast plume when it returned! With chemical it is highly impractical to carry enough propellent for a return to LEO.
On longer trips like to mars Electic propulsion can beat chemical and NTR in terms of time. Like the turtle and the hare. The electric rocket slowly keeps on going getting faster and faster while the chemical rocket\NTR burned most of it fuel at once.
However if your goal is to get into Orbit at your destination, Electric propulsion’s low thrust can be a cruse. You have to begin to decelerate into Orbit which can take a long time due to less thrust. A chemical rocket would coast then decelerate much latter in the flight.
One of the things that makes vamir more attractive than many other forms of electric rocket is that it has a greater ability to trade ISP and Thrust with it. You won’t get chemical like thrust, but you can get much more thrust out of vasmir than a typical electric rocket. ISP is nice, but taking way too long to get somewhere is not practical.
Anyway if you want to get to mars in 39 days then yes you would use vasmir in the “petal to the metal” mode, Max thrust, 660 tons of fuel, no slowing to get into orbit(direct decent). If you allowed Vasmir to take an equal amount of time as chemical, you it would need ten times less propellant than chemical. And you can do something in between(get there faster than chemical but slower than the max. possible speed but still need less propellant than chemical or NTR).
I personally don’t think NTR are worth it. They are not reusable. They can fire 1-3 time, but you can’t refuel them like chemical and electric. They emit radioactive exhaust (one more thing to deal with).
The only reason why NERVA was developed was because they thought they would need it to land on the moon, but the change from direct landing to lunar orbit rendezvous eliminated its need. I support nuclear power in space, but would prefer it in the form of a reactor driving a rocket via electricity generation than by controlled meltdown
Polishguy":2wxaox9c said:
Anyway there are three ways to use vasmir to get to mars.
- 1. As Main propulsion
The low ISP “petal to the metal” method would get you there in 39 days but require 660 tons of fuel. Another trip method would take 3-4 months but only use 80 tons of propellant for the crew’s outbound trip. And only need 202 tons of mass total(craft+ propellant) for the round trip. A similar mission for a NTR is mention in the link, and it would require 282 tons total (a savings). If you were to take as long as a chemical rocket 6 months it would require even less propellant.
2. To decelerate into orbit after using a chemical or nuclear thermal rocket
An electric rocket would need less propellant to slow the craft down into mars orbit. This could be a savings.
3. As a tug to move propellant and cargo.
Not carrying all the propellant at the start of a mission can result in big mass savings. Propelent that is not being used to move the craft at the moment counts as mass too. Vasmir could move propellant and cargo from LEO to EML 1 and mars. An electric rocket’s great ISP can allow it to move payload with a lot less propellant than a chemical one. You launch the propelent into LEO using EELV and have the tug move it to EML1 and mars. Your outbound chemical mars craft now only needs to be able to carry enough propelent to get from an LEO depot to EML 1. Where it refuels and goes on to an high mars orbit refuels gets into Low mars orbit ect. A craft that can hold enough propelant to get to EML 1 from LEO has more than enough tankage to make the whole trip. The slow trip times are no problem for cargo.
Here is a link that can give some info on the things you can do with vasmir:
http://www.adastrarocket.com/VASIMR_for_flexible_space_exploration.pdf
edit: fixed a math error
pathfinder_01":20hhkwbl said:
It would make more sense to use chemical or NERVA and aerobrake into Mars orbit, or directly to the surface, and generate all your fuel on the surface (for chemical, methane/oxygen or possibly hydrogen/oxygen. For NERVA, if the hydrogen shows itself, H2, if not, then methane propellant is a better deal than CO2, if more complex to make. The aerobraking would mean absolutely no fuel besides RCS is used to brake into Mars orbit. But yes, VASIMR as a cargo booster from LEO to Mars is a good idea. For crew, I'll take a look at that link.
Polishguy":ua34iy2d said:
Not quite. Vasmir has two advantages over chemical and Nuclear. It is more fuel efficient. It can attain a higher final velocity. It disadvantage is low thrust(low acceleration).You can also generate argon on the surface of mars.
The higher fuel efficiency means that if allowed to a take an equal amount of time as chemical or Nuclear it would need less propellant. This translates into a possible cost savings as you would need to put up less argon gas in LEO than you would chemical or nuclear propellant. You will still require chemical(or nuclear) for aerobraking and landing, but you would only need to carry the amount of propellant needed for those maneuvers. In addition like a chemical rocket Vasmir is refuel able. It is possible to use the same rocket for multiple trips to mars.
If allowed to go faster, then vasmir can beat a chemical or nuclear rocket to mars allowing for shorter trip time but consume more propellant than it would if it took the slow route.
Basically Vasmir isn't warp drive(more techincaly it is a plasma rocket) and more akin the star trek's impulse drive. Vasmir can get more delta V per killogram propelant than nuclear or chemical.
You still need chemical to take off or land on a planet. However, instead of generating all the chemical propellant to return to earth, you would just generate enough chemical propellant to get to Low mars orbit. This could result in a mass savings as your mars landing craft could be smaller than an earth return vehicle. If you choose to generate argon gas on mars(this part is debatable due to the extreme fuel efficiency of vasmir) it would mass less than the amount of chemical or nuclear propellant needed to return to earth. Again a mass savings.
Polishguy":setf8ktj said:
Anyway if you are wondering what advantage a Zurbin approach would have over a using vasmir as the main propulsion I would say two.
The chemical approach has fewer unknowns. Vasmir requires large amounts of power and light weight structures. If you are unable to reach the required Kg/Kw the trip time can balloon from “Warp 10” to “Granny can get there faster in her rocking chair” The 3 month trip is the most doable, the 39 day trip is very theoretical. If the President and Congress caught mars fever and wanted to land on mars in ten years, I would lean toward the Zurbin approach. The Zurbin approach could turn out to be less doable than it seems at the on set (like direct landing vs. lunar orbit rendezvous for Apollo). The Zurbin approach just has bigger known obstacles (need a big earth return craft) while the Vasmir approach has bigger question marks but more payback.
The other advantage comes if the vasmir trip takes as long as the nuclear or chemical one. An electric rocket can spend a lot of time spiraling out from a planet till it has escaped. If you take 6 months to spiral out from mars that is 6 months you could have spent on the ground. However the advantage of needing less mass for propellant and needing only to carry(or produce) enough chemical get into orbit could more than make up for it. The smaller the mass you need to land on mars and the smaller the mass you need to take off again, the easier the whole problem becomes. Vasmir gets around the long spiral times by trading ISP for thrust but if you are lacking kw,your available thrust will also be low.
The questions for vasmir are how much Kg/Kw can be achieved and what is the lifetime of the engine. Kg\Kw determines how this technology will be used. The lifetime of the engine in the space environment is unknown unlike a chemical engine an electric one has to work for days, months, even years. There are no known reasons why a vasmir engine should not last a long time, but it is critical that it does. This is a "we need to fire one up in orbit and see how it performs" type task.
Even if you are unable to use it for main propulsion it could be of great aid for a chemical approach. You could use it to move your mars departure craft and propellant into a high earth orbit. This would reduce the amount of chemical propellant needed and your mars transfer craft could probably be lofted by existing EELV.
You could establish propellant depots in high mars orbit and low mars orbit. This could reduce the amount of mass you need to carry. You could move equipment, supplies even a Lander. For instance if you had depots in high and low mars orbit, then your earth return vehicle craft would only need enough propellant to reach the low mars orbit depot. This could result in a smaller easier to land earth return vehicle.
You could use it to return used spacecraft from mars and high earth orbit to LEO for refurbishing (if moving it is deemed worth it).
pathfinder_01":2xme4rd4 said:
Thank you for clearing that up. Perhaps the Zubrin approach could be used for the first expeditions, with VASIMR taking over a bit later. But it seems the main question is how big the nuke for VASIMR would need to be. So far, humans have flown a 5 kilowatt device (TOPAZ) and tested a stronger one (hundred kilowatts for SP-100). How big are we talking for the 6 month VASIMR plan?
Perhaps there's a solution for that problem of VASIMR needing 6 months to spiral around Mars. Maybe our Mars Ascent Vehicle, on Methane/Oxygen, can just approach Mars escape velocity and dock with the VASIMR just as the latter is concluding the spiral.
Why is there talk of competing VASIMR or nuclear propulsion technologies? What I've read about VASIMR is that it will require a nuclear reactor to get the electricity it is going to need.
Some say nuclear is much more effective and faster, but how is the nuclear option supposed to work just by itself? Nuclear just generates power, its not an actual propulsion technology. Am I misunderstanding something?
Some say nuclear is much more effective and faster, but how is the nuclear option supposed to work just by itself? Nuclear just generates power, its not an actual propulsion technology. Am I misunderstanding something?
There are two different uses of nuclear power here.Booban":gex7r57e said:
A nuclear thermal rocket is a type of propulsion just as chemical, solar thermal and electric propulsion. Nuclear thermal rockets work by heating their propellant up using a nuclear reactor. The result is that they are about twice as fuel efficient as chemical rockets (in theory). In reality, there is no material known that can withstand the heat and so a nuclear thermal rocket work by a controlled melt down leaving a radioactive exhaust plume and require heavy shielding. In my opinion it is unlikely that a nuclear thermal rocket will ever be used in space. Too much hassle and not enough gain.
All electric propulsion systems (vasmir) need a power source which given current technology looks like a nuclear reactor would be the best power source for a manned mission although solar panels could work for cargo esp. light cargo. The trouble here in the case of manned systems in the need for megawatts worth of power yet not mass too much. This causes problems because the nuclear reactor must be shielded from the crew(mass) and needs radiators to get rid of excess heat(more mass) and the kind of reactor needed in space is very different from the ones needed on the ground.
However again an electric rocket does not care where the electricity comes from. All that is required is that there is enough of it and that the power system does not mass too much. Solar panels, radio thermal generators even beamed power can be used. An electric rocket can be ten times (or more) fuel efficient than a chemical one but its low thrust can doom it to long trips. No one cares if cargo takes 1-2 years to get to mars. However a 1-2 year trip with people would be inappropriate. However if you have enough power then the fuel efficiency of the electric system can allow you to carry enough propellant to attain a higher velocity than a chemical or nuclear thermal one. Hence the 39 days to mars.
Polishguy":2ro879uf said:
Here is the thing as much as I hate the term "game changing technology" vasmir is. The availability and capabilities of electric propulsion change everything. Even if it is not the main propulsion the Zurbin Approach would be silly not using it. It is like being single, having a wife or having a pregnant wife. It impacts a lot of other decisions (i.e. How big a house\car do you need? Do you even need a car? Can you risk being without health insurance? Do you need life insurance?).
It does not have to be a nuke. It is just that nuclear power is the best known way to get megawatts worth of power. I guessing that most other things being equal about 10MW worth of power would be needed for the slow route since that is the lowest level of power they considered for a human trip. The trouble with vasmir is that things don’t scale linearly and the trajectories that a electric rocket would take are different than the ones a chemical one would take. Given the fact that they mentioned using a 4MW engine as an abort return option the amount of power needed to return from mars is less than the amount of power needed to get from earth.
In other words not a simple answer. The thing is there are too many variables to even give a simple answer. For instance Vasmir’s isp can be throttled from 3,000s to 30,000s. Zurbins would be a constant 376s. This means that the vasmir could take anywhere from 4 days to months to spiral away from mars depending on how much power is available and how much isp you want to trade for thrust and how much propellant is on hand and what is your total mass.
In other words if your craft mass heavy you will accelerate slower. The amount of power limits the amount of propellant that can be processed in a given time(i.e. thrust).If your trade isp for thrust you will accelerate quicker, but if you trade too much isp for thrust you will run out of propellant. Not simple.
Your approach of meeting the vasmir in high mars orbit can work. In fact it is how you would do it from earth to reduce the crews in space time.
VASIMR,
en.wikipedia.org : Variable Specific Impulse Magnetoplasma Rocket
not vasmir.
email from aarcinfo ( at ) adastrarocket dot com, 1.Sep.2009 :
This seams to be related :
http://www.adastrarocket.com : A Survey of Missions using VASIMR for Flexible Space Exploration
page 8 ( 3 of 24 ) :
Some other sections, related to the above discussion :
en.wikipedia.org : Variable Specific Impulse Magnetoplasma Rocket
not vasmir.
email from aarcinfo ( at ) adastrarocket dot com, 1.Sep.2009 :
This seams to be related :
http://www.adastrarocket.com : A Survey of Missions using VASIMR for Flexible Space Exploration
page 8 ( 3 of 24 ) :
:
Some other sections, related to the above discussion :
Polishguy":e5ooe3nv said:
Even as a tug electric propusion can be of great use. Using mars direct information Here is how.
From http://www.marssociety.org/portal/c/soc ... rect2/view and and using http://en.wikipedia.org/wiki/Delta-v_budget and using a bad javascript version of the rocket equation.
The mass of the ERV that needs to go to mars is about 29.67MT. If he used a J2 from the Saturn V. He would need 45 tons of lox\H2 in low earth orbit at an isp of 421 and a delta V of around 3.81 km\s to get to mars. That is not counting additional propellant needed for the mass of the stage and structure and addition propellant needed incase of a shortfall in performance of the rocket. The total in LEO must exceed 74MT and he is forced to use\develop an HLV. In fact the HLV he calls for needs to be able to lift 121 tons to leo and push 47MT to mars. Even worse this rocket would only be used twice every two years.
The total mass of this craft is about 29.67MT. An EELV can lift this to LEO. A upgraded lunar tug or two ad astra lunar tugs can move this to EML1 using about 14MT of aragon. As the lunar tug does not have to brake into LLO to reach EML1, I would expect better performance than what I calculated here.
From EML 1 the delta V to mars is .74 km\s. This drops the amount of proplent needed to reach mars to about 7MT of methane\oxygen at an isp of 373. I am using methane\oxygen due to the boil off problem.
With a solar electric tug I can send the ERV to mars with no more than two launches of exsisting rockets. One for the ERV and one for all three propellants needed. The tug can be used for other missions. It could take months to move the craft to EML 1 but as it is unmanned and mars windows open up about every 2 years this is not a problem. Even taking 1.5 years to reach EML1 could be acceptable depending.
This represents a big cost savings.
If I did it like Zurbin, On the next window, I would launch the habitate module and another ERV. The habitation unit masses 28.4MT I can use the same process to get it into EML 1 ready to go to mars. I would then launch the crew in a separate craft to join it at EML1. This would take 6 launches. Two of exsisting can get the hab to EML 1. I would need two of slightly uprated exsisting EELV to get the crew to EML1.
If I do this in a different, more tug friendly manner I would do it this way. Assuming it takes 6 months for each tug to move it’s cargo and 1 month to return to LEO. These 6 launches could be spread over time depending on how long it takes for the last tug to reach EML1. In the first year I could launch the aragon, the ERV and the hab. In the next the lox\methane in an Mars depature stage, in one launch (well before the window opened) and the crew in two(when the window opened). A single tug could it all to EML1 while the aragon needed for the mission would stay in a LEO depot.
As you can see just having this ability means that you either don’t need an HLV to get to mars or you need a much smaller one. The whole mission can be done with a 2-3 HLVs capable of 60-80mt . Instead of needing two capable of 121 tons launched in short order every two years. You can spread the launches over time. Three EELV lauches every year is not extreme or 1-2 HLV launches a year makes better use of fix costs than two every other year. This is a game changing ability.
Now I could go on exactly like Zurbin and launch a new habitat with each earth return vechile each time you go to mars, but what if I used my tugs to move propellant to mars. The delta V from EML1 to Low mars orbit is 3.04km/s. I would need about 36MT of propelant to get the mars habitat to and from low mars orbit. If instead of a habitat it were a lander+in space habitat I could leave the habitat in orbit and land on mars.
They considered using a 4MW tug to move 202 tons of cargo for the human mission, so I expect you could move it with much less esp, as this does not have to be moved from LEO by the same tug. A solar electric tug could probably do it.
With the propellant in mars orbit I could simply return to EML1, decrew the ship then tug it down to a LEO station for serving. This could be cheaper than building/lauching a new craft every time. Another game changer.
In addition I would need only need to generate enough propellant to get to LMO instead of earth. This would be a big savings. I could also export aragon from mars for the tugs.
pathfinder_01":2bdyvjw3 said:
I'm not quite sure I understand what you're saying. Can you please explain this again? From what I understood, you have a habitat and Mars Ascent Vehicle on the surface. The MAV, powered by Methane/Oxygen, docks with a Transfer Hab in Mars Orbit, and they go on to Earth. But I don't understand the rest.
Also, given that Argon has a higher atomic weight than methane or oxygen, might it not make more sense to power a VASIMR with those fuels? Or am I missing something?
Polishguy":1z5poxoz said:
Sorry lost my train of thought there.
I was trying to explain how even if you can’t use vasmir as the main propulsion system for a manned expedition it could be of great use. If you can only generate 500kw-4mw, that is too little for a manned mars mission using vasmir directly but could still be very useful. I was also trying to point out how using vasmir or another form of electric propulsion like arc jets and Hall effect thrusters as a tug would be operationally different than the Zurbin approach.
One way electric propulsion could be helpful is by reducing or eliminating the need for heavy lift. If you explore mars Zurbin style you need a rocket able to push 45 tons from leo to mars which in turn requires a rocket able to life about 121 tons to leo. If you have tugs on hand all you need to do is be able to lift your spacecraft to LEO. Current rockets could lift Zurbin's crafts to low earth orbit. Due to the extreme fuel efficiency of electric propulsion the required amount of Aragon to get the craft to a high earth orbit and bring the tug back, would mass less than the payload . That is why the lunar tug they mention can deliver 67% of the required mass in LEO to LLO as payload. In short if you are willing to wait 6 months to even 1.5 years for the tug to move your craft to a high earth orbit, you would reduce the amount of chemical propellant needed to get to mars dramatically. This could allow you to stage mars missions with current rockets or perhaps slightly up rated ones. If you decide you need heavy lift, you could easily do with heavy lift that is much less than 121 tons to leo.
The Zurbin approach requires two heavy lift launches while the mars window is open. The tug approach spreads the required launches over more time. You are only limited by how long it takes for the tug to move the craft to high earth orbit.
Zurbin saves mass by aero capture and\or direct landing. This requires less propellant than attempting to brake into mars orbit using your engines. While you can do the same by only using your tugs to make up for the lack of heavy lift, having a mars capable tug opens up new possibilities.
Aero capture and direct landing make reuse difficult. If you just could go back and forward between earth orbit and mars orbit reuse would be easier. While you could generate the required chemical propellant on mars, doing so is less attractive than just generating enough to come directly back to earth. It would take more propellant to get between low mars orbit and high earth orbit than it would just to get to low mars orbit, escape mars and directly reenter earth. In addition the extra mass of this propellant requires even more propellant to get to low mars orbit. It would further complicate a complicated mission.
If you try to carry it with you from earth the extra mass is going to require a bigger rocket than what Zurbin mentioned.
On the other hand if you tried to send the propellant required to return to a high mars orbit from earth by a chemical rocket tug, it would mass much more than the payload. Even if you could tolerate it, it could require even more heavy lift than Zurbin mentioned or require bigger more expensive rockets in general.
If you use an electric tug the amount of propellant needing to be sent could possibly be within current rocket lifting capability, although this is probably a job for a 60-80ton heavy lift. The amount argon in this case would mass more than the payload but still could be manageable. This makes sending propellant and other cargo to mars for resupply more attractive.
This makes reusing your mars habitat for many crews and building a reusable earth\mars shuttle attractive. The Zurbin approach pretty much requires a new hab and a new earth return vehicle every time you go to mars. This approach reuses both. In addition not needing to make all the propellant to get home is an advantage. Now all I need to do is just generate enough to get to low mars orbit. You could also use it to send the habitat module or additional habitat modules to mars or perhaps a back up supply of methane\oxygen from earth.
In the future it would be advantageous to generate both the methane and the Aragon on mars instead of sending it from earth, but your first missions are not forced to do so.
Nice post, but please, VASIMR.
There is a problem with electrical charge accumulating on the spaceship when using gridded Ion propulsion, and i think Hall thrusters too, which limits how much power you can use. I don't remember this being solved.
VASIMR doesn't have that problem, and achieves much higher Isp, with about the same power conversion efficiency (about 60%).
There is a problem with electrical charge accumulating on the spaceship when using gridded Ion propulsion, and i think Hall thrusters too, which limits how much power you can use. I don't remember this being solved.
VASIMR doesn't have that problem, and achieves much higher Isp, with about the same power conversion efficiency (about 60%).
Polishguy":3kondp1r said:
The higher atomic weight is desired. The problem with vasimr and electric propulsion is the low thrust. With all rockets the more mass you throw out in a given time the faster you accelerate. This is why a lox\kerosene rocket has more thrust than a lox\hydrogen one. Imagine two spacecraft of equal mass in orbit. In both spacecraft, you have a person throwing mass out the rear end to move the craft. However one is filled with lead bricks and the other Styrofoam bricks.Each person is throwing one brick out a minute. The person throwing lead bricks out is going to accelerate faster than the person throwing Styrofoam bricks out. The most fuel efficient propellant for both chemical and electric rockets is hydrogen but for electric propulsion using hydrogen results in even lower thrust! Fuel efficiency is nice, but taking 6 years to get to moon is not.
The other reason is due to the way electric rockets or more speficifcly plasma rockets work. Plasma rockets work by heating propellant all the way until it becomes plasma. Then using electromagnets they accelerate the plasma out the end of the rocket at high speed. Since a rocket’s velocity is determined by exhaust speed this allows them to be faster than a chemical rocket. The exhaust velocity of an electric or even a nuclear rocket is higher than a chemical rocket’s exhust speed. This is why those rockets are more fuel efficient than a chemical one. The more energy it takes to turn your propellant into plasma, the less you have for actually moving the craft. I suspect that it would take more enengy to turn methane to plasma due to having to break the CH bonds.
As for oxygen. Oxygen is a very reactive chemical, I suspect that having such a reactive chemical as plasma would create bigger engineering challenges. Aragon was selected because it is cheap, reasonably easy to turn to plasma and has a high atomic weight. Xenon, krypton and lots of other things can be used by an electric rocket.
Forgot to add the Martian atmosphere is 1.6% Aragon while Earth’s is .96%. Aragon gas on earth is extracted from the atmosphere so getting it on mars might not be much of a problem. In fact it would take equipment similar to that needed to liquefy oxygen.
Good idea but I would imagine it would be significantly more challenging getting Argon out of the martian atmosphere, perhaps a hundred times harder?! (martian atmosphere averages 7-10ppm, about 1% of the earths!) ...or am I missing something?
Can't wait for the first test of VASIMR on ISS btw!!
Isn't this an update thread? I saw a bunch of new post & got excited. Then I read them & there wasn't a single update. Maybe you guys need to start a discussion thread?
Boris_Badenov":28t9a6lv said:
It reminds me a bit of a SpaceX launch thread ..
Anyway, there are updates, just covered under the discussion. At least these two are new, i think :
http://www.adastrarocket.com/aarc/Publications
before mentioned :
http://www.adastrarocket.com : A Survey of Missions using VASIMR for Flexible Space Exploration
http://www.adastrarocket.com : Observations of single-pass ion cyclotron heating in a trans-sonic flowing plasma
www.adastrarocket.com : Ambipolar Ion Acceleration in the Expanding Magnetic Nozzle of the VASIMR VX-200i
The rest is in various NASA budget discussion threads, but as far as i know, currently 'go'.
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