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#526 Re: Planetary transportation » Best propulsion for a long range rover » 2014-03-12 06:57:48
Congress has gotten over it's irrational fear. It's time for you to do so as well.
I dont fear nuclear: I fear people who fear nuclear.
I like this stuff.
#527 Re: Human missions » Phobos ISRU based LOX-LH2 mission architecture » 2014-03-12 06:52:31
Hi Quaoar:
Glad you liked my "landing boat" design.
I was very impressed by your site: is a source of very interesting ideas and innovative concepts.
I didn't look at the benefits of mining water on Phobos (or Deimos), but you are correct. Anything not in a gravity well is easier to do. If you have right equipment with you.
Even without use Mars moons for ISRU (at the first mission we cannot have the groud thrue to realy on it), it may be convenient to use the modular spaceship "Johnson Express" to travel from Earth-Moon L2 to Deimos orbit, for saving propellant.
Your landers, with dead end propellent tanks, may travel from Deimos orbit to low Mars orbit, leave there one or two fuel tank for the return, and landing on Mars. When the surface missions are finished, the landers will ascent to LMO, rendez-vous with the tanks, refuel and trasfer to Deimos for the rendez-vous with the mother spaceship.
Starting from Deimos orbit, the mother spaceship will change plane, low the pericenter at LMO altitude, fire the rockets when is close to Mars and insert in a Earth transfer orbit in economy.
So in one mission we can explore Deimos and Phobos for prospection and 6 surface sites on Mars: if water has been found on the moons, the next mission will bring the equipment for LOX-LH2 production and storage.
#528 Re: Planetary transportation » Best propulsion for a long range rover » 2014-03-12 04:49:42
Quaoar wrote:But a semi-direct mission with an orbital ERV and a little MAV can relay on solar panel to produce 6-8 tons of ascent propellant or has to bring it from Earth?
Semi-Direct brought return propellant all the way from Earth. But still required ISPP anyway; the MAV used ISPP to produce propellant for ascent to Mars orbit. So hauling return propellant from Earth dramatically increases cost without increasing safety. Really bad idea.
If free return is required, an express trajectory (6 month transit), can use Mars gravity to loop around the far side and head back to Earth. Only RCS thrusters are required to tweek trajectory. So no return propellant is required for "free return". That's why it's called "free". Apollo 13 did this with the Moon.
My mission plan uses an orbital ERV, but uses the MAV as the TEI stage. So requires full propellant load.
The trouble is that is higly improbable that politicians will allow a mission plan with a nuclear reactor. So I guessed if it's possible to produce the ascent propellant for a little MAV only with solar panels.
For the ERV, we cannot use ISRU, but we can save a lot of propellant sending it unmanned in Earth-Moon L2 with a solar electric space tug: L2-MTO delta-V is less than 1 km/s. Using L2 as a starting point, plus aerocapture at Mars and Earth, the total mission delta-V will be not prohibitive.
#529 Re: Planetary transportation » Best propulsion for a long range rover » 2014-03-11 17:26:49
It's theoretically possible to maintain soft cryogenics on Mars, such as LOX and LCH4. But to produce propellants, liquefy them, and maintain them as liquid, you really need so much power that a nuclear reactor is required. I don't have any figures, but Mars Direct estimated 85kW for the ERV.
But a semi-direct mission with an orbital ERV and a little MAV can relay on solar panel to produce 6-8 tons of ascent propellant or has to bring it from Earth?
#530 Human missions » Phobos ISRU based LOX-LH2 mission architecture » 2014-03-11 10:45:16
- Quaoar
- Replies: 8
Many evidence suggest that Phobos and Deimos are rich of water in the form of buried ice protected by water rich clay permafrost
http://www.uapress.arizona.edu/onlinebk … rces31.pdf
If these evidences will be confirmed, it will be more simple to refuel on Phobos an orbit-orbit vehicle than to land on Mars the whoole spaceship, refuel it with local produced LOX-LCH4 and bring it back to Earth, like in Mars Direct.
So we can imagine a colonization plan driven by a Phobos base, connected to Mars sufrace via LOX-LH2 reusable shuttle landers (like the above GW Johnson's design).
#531 Re: Planetary transportation » Best propulsion for a long range rover » 2014-03-11 09:58:08
Storing liquid oxygen in the Mars Ascent Vehicle, or Earth Return Vehicle, will require refrigeration. Mars has very thin atmosphere, so it will heat much more slowly than it would on Earth. Yet, it will boil. That oxygen gas has to be refrigerated to turn it back into liquid. That requires power, so again that requires the nuclear reactor. You don't want to carry an operating reactor on a vehicle that carries humans.
To keep mass down, reactors designed for space don't have radiation shielding. Uranium is safe to handle before it goes into a reactor. However, the fission fragments (nuclear waste) is very radioactive. Mars Direct deals with that by putting the reactor on a light truck, and parking it in the bottom of a crater some distance from the ERV. With a power cable trailing back.
So, a Mars mission architecture that only relies on solar panels cannot use ISRU and has to bring a minimal MAV with storable propellant rocket, something like 3-4 tons of dry mass and 7.5-10 tons of N2O4-MMH?
How much power/kg is needed to keep LOX-LCH4 liquid with good multilayer insulated tanks?
#532 Re: Planetary transportation » Best propulsion for a long range rover » 2014-03-11 06:22:00
If it's so difficoult to store liquid oxigen, how can we preserve it for more than two years in the tanks of the Mars Ascent Vehicle?
#533 Re: Interplanetary transportation » Pit stop in L2? » 2014-03-10 04:47:02
One solution is to use a high temperature ceramic, heat it up with sunlight over a long period of time, then use all that heat over a short period of time. You can probably get more thrust that way, but your engine gets heavy; maybe half a tonne or a tonne to store the heat. If you heat the ceramic first, then heat the hydrogen effluent with the sunlight, maybe you can get an Isp of 1200. So it has a lot of potential. Someone does need to develop it.
It may be a very good solution: the engine may store energy douring the whoole orbiting and fire only at pergee, so the mirrors have not to be so huge.
One problem with solar electric; you can't store your energy, so you thrust contunuously. When you do that, you can't just thrust at perigee, so you spiral away from Earth, and that doubles your delta-v!
Solar electric become interesting with specific impulse over 3000 s and 100-300 KW (or more) electric power, so the gravity loss are compensed by the engine efficiency. Another option may be bimodal nuclear like Pratt & Whitney Triton: a 3 rocket pod may produce up to 300 KW of electric power: so the spaceship can spiral unmanned in L1 or L2 with a NEXT engine and then leave manned for Mars with NTR rockets, saving a lot of propellant.
#534 Re: Human missions » Mini magnetosphere radiation shielding for a manned mission » 2014-03-10 02:51:15
But you need a means to conduct the charge that creates the umbrella of protection and mars does not have the moisture in the air to make it happen or free ions that make up the van allen belts that allows for the charge to make up the shield.
Mini-mag is only for space travel, where the charged particles interact with the solenoid field: it seems not possible to use it on the surface of a planet with atmosphere like Mars. There, the best thing to do is using local water or regolith to screen the habitat.
#535 Re: Interplanetary transportation » Pit stop in L2? » 2014-03-09 15:18:32
The delta-v to L1 is something like 3.6 km/sec and it would be the same for a solar thermal engine as for chemical propulsion. You'd only fire the solar thermal engine at perigee and perform a series of kicks to raise apogee. You could probably circularize the orbit by using a lunar pass, too. With an ion engine the delta-v is about 7 km/sec because you have to raise the apogee and circularize continuously.
I'm sorry I've misunderstood: your solar-thermal spaceship will use multiple perigee burns, to minimize the gravity loss, so the delta-V is the same as using a single impulsive burn with a more powerfull rocket.
#536 Re: Interplanetary transportation » Pit stop in L2? » 2014-03-09 13:57:54
L1 is also a possibility; there are a lot of studies of the "L1 Gateway" station, as it is called. L1 may be more convenient because it is closer and faster to reach, but it takes 300 meters per second more delta-v. Either way, trans-Earth injection has to be done deep in Earth's gravity well, so you have to go back to Earth to head to Mars. L1 is closer and more convenient.
Yes: from L1 or L2 we have to low the perigee to LEO to make the burn near the Earth utilizing Oberth Effect.
You could also save time and propellant using a solar electric or solar thermal engine to move most of your assets into a very large elliptical orbit, then move the people and the earth return capsule there quickly, rendezvous above the Van Allen Belts, loop back in, and perform trans-Earth injection.
Personally, I rather like solar thermal propulsion. You can only generate about 100 pounds of thrust at a time, but you can heat up a transfer medium for many hours and choose when to perform your burn--at perigee--so it is efficient. It can generate specific impulses of 900 seconds, maybe more; so it is comparable to a nuclear thermal engine. But you can't use it to move people; they'd loop through the Van Allen Radiation Belts repeatedly.
I'm not sure solar thermal may work for a space tug: non impulsive trasfer to L1 have a delta-V of 7, so with only 8.8 km/s of exaust velocity we have almost the same mass ratio of a LOX-LH2 chemical rocket tug, that make an impulsive trasfer in L1 with a delta-V of 3.77 (consider that solar thermal use only LH2 that is difficoult to send in LEO, instead of 85% LOX and 15% LH2 used by chemical rocket).
#537 Interplanetary transportation » Pit stop in L2? » 2014-03-09 11:10:12
- Quaoar
- Replies: 36
A trans mars injection is almost 4 km/s starting from LEO and less than 1 km/s starting from Earth-Moon L2.
So why not consider to send the spaceship unmanned in L2, with a slow spiraling solar-electric space tug, one year before departure?
When is time to depart, the astronaut can rendez-vous the spaceship in L2 with a less massive vehicle like an Orion or a Dragon Rider.
In a future, we can put LOX propellant depot obtained from lunar regolith in L2, by now we have some very interesting electric thruster like NEXT ( http://en.wikipedia.org/wiki/NEXT_%28ion_thruster%29 ), that can do the job with a good solar array.
#538 Re: Planetary transportation » Best propulsion for a long range rover » 2014-03-09 10:57:02
The hydrogen-oxygen fuel cells used since Gemini in space are just that: bottled gas feeds to the unit. Those work fine in vacuum. You could just as easily use liquified gas sources, and they did on Apollo, at least for the oxygen.
GW
So we can imagine some sort of hybrid rover, with a dual powered electric motor: H2-O2 (or O2 CH4) fuel cells plus solar arrays and bacteries: when the Sun is high it uses solar arrays saving fuel an when it goes downhill, the wheels recharge the bacteries, like in the hybrid vehicles.
The rove may have also a drilling hardware to find water, so it can exted the exporation range to almost 1000-2000 km.
#539 Re: Planetary transportation » Best propulsion for a long range rover » 2014-03-09 10:44:49
Even in Elysium Planitia (5°N 150°E) there is probably a very big buried glacier:
It's only 5° above the equator and it may be a perfect landing site for a manned mission, but I don't know how difficoult may be for an unmanned lander-tanker to drill and extract water. It may be simpler to land it northen on a well known ice pack, so it will have only to melt ice, electrolize water, liquefie LOX and LH2 and take off to fill orbital depot.
#540 Re: Human missions » Mini magnetosphere radiation shielding for a manned mission » 2014-03-09 10:14:01
Good news for mini-magnetosphere: Ruth Bamford's team of Rutherford Appleton Laboratory has found that the model used by Robert Winglee is incorrect, because it is based only on ion gyroradius ( http://en.wikipedia.org/wiki/Larmor_radius ), giving on order of magnitude overstimate power compsuntion (almost 100 KW according to Winglee http://earthweb.ess.washington.edu/space...elding.pdf ) for GCR deflection.
According to RAL's model, wich is based on electron gyroradius, 10-20 KW may be enough to create a weaker magnetic field, that can deflect electrons creating a charged separation in the bow shock region of the mini-mag, resulting a strong electrostatic gradient that deflect GCR.
#541 Re: Planetary transportation » Best propulsion for a long range rover » 2014-03-08 16:22:12
Liquifying hydrogen is now a very well-known technology here on Earth, unlike 1960. I suspect (engineering experience and intuition) that coming up with hydrogen-liquifying equipment suitable for robot operation on Mars would be easier, faster, and cheaper than coming up with a new IC or turbine engine technology capable of handling fuel-oxygen flame temperatures.
But at least folks are looking at these ideas. That's good.
If liquifying hydrogen is quite simple, why limiting it only for rover fuel cells?
Why not reconsidering the whole mission, sending an unmanned lander tanker with a stak of empty modular propellant depot?
The lander tanker can land on summers at high norten latitudes, where there are well known ice packs, melt the ice, electrolize water and bring LOX and LH2 to the orbital propellant depot, to refuel an orbit to orbit manned trasfer vehicle.
#542 Re: Planetary transportation » Best propulsion for a long range rover » 2014-03-08 04:32:06
To GW: it's possible to bring on mars surface sam kind of light weight cryogenic hardware for H2 liquefaction and active cooling?
To Robert Dycke: an hybrid vehicle with LOX-LCH4 internal combustion engine plus bacteries electric motors and solar array seems a very interesting and intrinsecally safe option. Probably it can have an exploration range up to 1000-2000 km.
#543 Re: Human missions » Mini magnetosphere radiation shielding for a manned mission » 2014-03-07 07:54:12
Well earth seems to have a bit of defences for when the sun kicks up a storm....
Earth raises a plasma shield to battle solar storms
Earth can raise shields to protect itself against solar storms. For the first time, satellites and ground-based detectors have watched as the planet sends out a tendril of plasma to fight off blasts of charged solar matter. The discovery confirms a long-standing theory about Earth's magnetic surroundings and offers us a way to keep track of the planet's defences.
If i've understood correctly, it's some kind of natural feedback: douring solar storms magnetic reconnection broke Earth magnetosphere and solar protons hit high atmpsphere. Ionized plasma formed in high atmosphere enflates again Earth magnetic field, reforming a new magnetosphere that counteract solar wind pressure and deflect incoming solar particles.
There is another very interest work by Robert Winglee, about Earth magnetosphere: in the model proposed, Earth magnetic tail shields the Moon from cosmic ray for almost seven days a month: so it's possible to plan manned moon mission in these safe periods.
#544 Re: Human missions » Yet another Mars architecture » 2014-03-03 05:01:46
Quaoar:
Thanks, I had never seen that NASA report before. Amazing how they came to the same conclusions I did: 4 rpm, 1 full gee, and an end-over-end spinning baton as both stable and (at least a bit) maneuverable while spinning.
The truss they used is an artifact of the nuclear-electric propulsion they assumed. There's not a plethora of propellant tanks, but you need connecting structure to make the baton shape.
If instead you use chemical propulsion, then you have a plethora of propellant tanks, and that stack of tanks can serve the function of the truss, without a need for any truss at all. If you are clever with your stack-up of those tanks, you can stage-off empties and still maintain overall length, just at reduced mass and (to a much lesser extent) mass moment of inertia.
This kind of thing just does not integrate hardly at all with direct-landing or aerocapture designs. Unfortunately. But, I think it solves so many other problems, that it's worth the extra propellant. Just my opinion.
GW
Why not send every module of your ship in Earth-Moon L2, by a solar-electric space-tug?
It's almost a year spiral trip with two 40 meter diameter 790 KW mega-flex solar array and 50 km/s electric propulsion (all the tug can be stoved in a 5 x 25 m cylindrical module). When your ship is assembled, the crew can reach it with an Orion or a Dragon Rider: starting from L2, the inserction in a Mars trasfer orbit is less than 1 km/s of delta-V.
Another option may be to protect the belly of every module and reinforce the docking joints to support aerobraking: starting from L2 your ship is shorter (it's also possible to have one full gee with 35 m radius and 5 rpm: not very comfortable but astronauts can adapt) and I think it's factible. Protecting the belly will add almost 14% of mass but it will save a much more propellant.
#545 Re: Human missions » Yet another Mars architecture » 2014-03-02 15:37:39
To Robert Dycke:
This NASA study is proposes a very lightweight (3 Kg/m) graphite-epoxy coilable boom for artificial gravity, that can fit very well with your mission architecture.
http://www.artificial-gravity.com/NASA-JSC-EX-02-50.pdf
There is also an apparently similar commercial product of ATK ( http://www.atk.com/products-services/co … m-systems/ ): it is projected for light loads but I think they can build a sturdy version hor high loads on demand.
#546 Re: Interplanetary transportation » Uranium Arc afterburner for NERVA » 2014-03-01 09:06:07
Something like a magnetic nozzle?
Even a gas core engine needs a magnetic nozzle or it can goes with a traditional nozzle?
#547 Re: Human missions » Yet another Mars architecture » 2014-02-28 08:45:44
Yea yea. You said that before. But the over arching engineering requirement you must always think about is cost control. The 90-day report asked for $450 Billion in 1989 dollars. If you deduct the price of ISS, then apply inflation to the remainder to today's dollars, the result is $750 Billion. There are individuals who seriously expect Congress to authorize that, and corporate executives of "Old Space" companies seriously attempt to manipulate any space effort to become that expensive, but there is no way in Hell that Congress will ever do that. They will authorize NASA's current budget. That's all. That includes all space centres that serviced the Shuttle. That includes work on SLS and Orion. Once they're finished, funds will be available for something else about the same price. That's all. That's what you have to work with.
So your options are either zero-G, or get a tether to work.
If we want to cut cost, instead of cut artificial gravity, number of rovers, and habitat volume, why not to cut propellent mass using a 9 km/s exaust velocity NTR?
#548 Interplanetary transportation » Uranium Arc afterburner for NERVA » 2014-02-28 08:04:39
- Quaoar
- Replies: 3
Uranium Arc is an uranium plasma core confined in electric arc, where fission reactions rise temperature up to 9000°K.
It is proposed as an afterburner for a classical solid core nuclear thermal rocket.
http://www.google.it/url?sa=t&rct=j&q=& … 5928,d.bGQ
Teorically a 9000°K gas core afterburner, can rise the exaust velocity of a classic NERVA to 18 km/s using hydrogen, 8.3 using ammonia and 7.3 km/s using water. The last can be a very interesting option for wild refueling.
#549 Re: Human missions » Yet another Mars architecture » 2014-02-26 10:05:28
If both, hab and TMI, use opposit firing outed canted rockets to keep the cable in tension while manuvering, and all the manuvers are assisted by a specific software that controls allineament and tension, I think they can do spinning, despinning and course corrections easly.
At the times of Gemini 11 and Agena computer and software were at the stone age. Now we can do it better.
Why not to start manuvering tests with two little satellites?
#550 Re: Human missions » Light weight nuclear reactor, updating Mars Direct » 2014-02-20 15:04:34
A Mars Direct Hab would only have room for one pressurized rover. In fact, even Robert Zubrin's slides only include one rover, the open rovers are deleted. The table on the first post of this thread is from his book "The Case for Mars".
But if there will be an engine failure when the rover is 100-150 km far from the habitat the crew will be doomed. With only one rover astronatus cannot go out of a walking return range.