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#426 Interplanetary transportation » Plasma magnetoshell areocapture and entry system » 2014-05-01 12:59:42
- Quaoar
- Replies: 3
Using a magnetic shield for entry is an old idea of Von Braun, who thinked to a fictional (at his times) light weight high temperature superconductive coil.
The device proposed by this NASA study dosn't use superconducting coil, but a Rotating Magnetic Field (RMF) to generate a fully ionized high temperature magnetized plasma, that form a shield in front of the spaceship increasing drag.
http://www.nasa.gov/offices/oct/early_s … rtley.html
https://s3-us-west-2.amazonaws.com/pnwm … _final.pdf
If it works, a magnetoshell may be very interesting, because drag may be increased or reduced simply tuning the magnetic field, resulting less critical entry angles and very easy and safe aerocapture maneuvers, even in planets with high atmospheric variability like Mars.
P.S.
I ask myself if such device can be also used douring the trip as a cosmic ray deflector like Winglee's mini-magnetospere.
#427 Re: Interplanetary transportation » Sodium Vapour Thermal Propulsion » 2014-04-30 01:17:43
Is it an in-space only propulsion?
#428 Re: Human missions » What if te next major planet out was a brown dwarf? » 2014-04-28 15:36:45
A Dyson sphere or a supramundane habitat is very farr from our actual capability. But we can imagine a planet in the brown dwarf habitable zone, tidally locked, heated by infrared radiation and by tidal vulcan activity, with an almost black alien vegatation that use infrared radiation for photosynthesis.
We can use a laser driven photonic sail for acceleration and a nuclear pulse for deceleration in the outward voyage and nuclear pulse for acceleration and a laser photonic sail for deceleration for the inward voyage.
#429 Re: Interplanetary transportation » Storing LOX-LH2 as water » 2014-04-28 15:16:40
The only downside I see to this would be the electric power. You'll need a much larger solar-electric rig to handle both the electrolysis rig and the electric thruster at the same time during the long transit.
I'm not sure about 40-day trips to Mars, but 60-90 days would be a lot better than 6-9 months.
Nicest thing is every bit of this is essentially off-the-shelf technology.
GW
I think a copule of 15-20 m radius Megaflex solar array, that can be easly fitted in a Falcon launced module can easly support both, electrolysis and electric propulsion.
If the ship has to go in the asteroid belt or beyond we can add one or two SAFE-400.
#430 Re: Interplanetary transportation » Storing LOX-LH2 as water » 2014-04-28 15:04:29
Of course, there is still the question of engine mass. Doing the burns at separate times doesn't change the fundamental power issues with electric propulsion, namely that it is incapable of shortening transit times that much.
This work is about a still experimental but very promising advanced electric propulsion, where propellant is not used directly for thrusting, but to generate a plasma sail that deflect solar wind protons, gaining almost 1N/KWe. The ship depart and arrive with chemical rockets, but douring the transfer use electric propulsion to add energy to the transfer orbit, shortening transit time.
#431 Re: Interplanetary transportation » Storing LOX-LH2 as water » 2014-04-28 08:10:47
Ice buried deep in a asteroid would be under greater pressure than in a vacuum. Now the surface exposed to the vacuum would be ice free, but if you go under the crust, especially in large asteroids, I am sure ice can be found, and other hydrogen compounds as well. As for a rocket motor, they can be delivered a part of the rocket vehicle that arrives at the asteroid. NASA has yet to use a mass driver for anything. One idea has been to mount a space shuttle main engine to an asteroid, then feed it hydrogen and oxygen separated from compounds within the asteroid Most asteroids just need a little nudge in their orbits to be useful, and the space shuttle main engine can run for hours to get the job done.
If ice is present as a pack (even buried under some meters of regolith) melting, extraction and propellant production can be easly done with on board hardware (I imagine some kind of specialized lander-tanker). But if ice is diffused between regolith grains it may be very difficoult to get it in useful amount, without having a permanent base on the asteroid, with all the extraction and processing hardware.
We have to know more about asteroid structure, before relaying on local resources.
#432 Re: Interplanetary transportation » Storing LOX-LH2 as water » 2014-04-28 07:41:59
In general, I think that the idea of storing your H2/LOX rocket fuel as water for as long as possible before electrolyzing is a good one. Water is much denser, much easier to handle, and much warmer than its component elements.
However, it's well worth noting that certain things are either impossible or unreasonable. For example, you can't electrolyze as you burn. It's simply unfeasible. Even if you are keeping the fuel as water for the transit from, say, the Moon to LEO, you will reap significant gains by leaving it in the form of Water for that time.
I know "real time electrolysis" is impossible unless having a multi GW range nuclear reactor. I imagine a big modular orbit-to-orbit reusable spaceship, with 100-200 KW of solar (or nuclear) electric power, who has to spend hundreds days in low planetary orbit waiting for the launch window: it can be safer to store propellant as water and electrolyze it in LOX-LH2 2-3 months before living, even if the spacehip has a good cryogenic cooling system.
If in a future we will discover ice on Phobos or Deimos, this ship can be also refueled melting it.
If the ship has an hybrid chemical-electric propulsion system (like in option 3) and the electrolysis is done only douring orbital stay, the ship will be free to use all her power for electric propulsion douring the transfer.
Another option may be to envoy the return water to low mars orbit using a solar electric space-tug. Then the manned spaceship docks the water tank and start electrolysis 3-2 month before leaving.
#433 Interplanetary transportation » Storing LOX-LH2 as water » 2014-04-27 15:02:36
- Quaoar
- Replies: 24
Storing hydrogen as a liquid at 20°K is very nasty, so there are many study on storing water and electrolyzing it on demand to produce liquid hydrogen and oxygen.
https://ia600603.us.archive.org/10/item … 026039.pdf
According to the study above, a 500 ton/year hardware needs almost 100 KW of electric power.
I like the idea of using water: in a precedent post I have explored the possibility of a water propelled nuclear spaceship: it seem possible, but there are still many technologies to develop. On the contrary, we can build until now a solar powered LOX-LH2 chemical rockets propelled spaceship that gets her propellant from water electrolysis.
like the nuclear steam spaceship, or water electrolyzing LOX-LH2 spaceship can be a very versatile vehicle that can find the return propellant from Mercury pole to Jovian satellites. Water is also a very good cosmic ray shielding material: so we can imagine a multiple shells propellant tank that surround the habitat, solving another nasty issue. Using the same substance for propulsion and for life support is also very safe: imagine a Ship returning to Earth that fail orbital insertion burn for rockets failure: the unused water can keep astronauts alive for years, giving time to set-up a rescue mission.
Power is not a problem, there are many very large deployable solar arrays on the market (http://www.nasa.gov/offices/oct/home/feature_sas.html#.U1voz6KG-M0 ), and water is a very cheep propellant. The only issue is the oxygen/hydrogen ratio of 8:1 that doesn’t match the 6:1 ratio of chemical rocket. Burning LOX and LH2 at 8:1, would result in a slightly lower specific impulse (almost 10 seconds) but a too high combustion temperature that can damage rocket chamber.
Surfing on Internet, I found 3 possible solution:
1) fixing the oxidizer/fuel ratio adding at the mixture 6% LCH4 or 8% of RP1: the result is a tri-propellant rocket like Russian RD-171 (http://www.astronautix.com/engines/rd701.htm ). We can avoid the complicated turbo-pump machinery having it pressure feed: for a in-space propulsion a high expansion ratio is more important than pressure chamber, so we can regain the specific impulse loss with a very high expansion ratio nozzle 1:250 or more.
2) burning LH2 with 75% of LOX inside the chamber in the classical ratio of 6:1 and using the remaining 25% in the nozzle as a LOX afterburner (something like the LOX afterburner of a LANTR). Specific impulse will be slightly lower, but we can use all the propellant without risking chamber damage.
3) burning LH2 with 75% of LOX inside the chamber in the classical ratio of 6:1 and divert the remaining 25% of O2 to feed an electric thruster, resulting a chemical-electric hybrid spaceship, that can be very useful for interplanetary exploration.
Oxygen has a first ionization energy of 1313.9 KJ/mol, higher than 1170 KJ/mol of xenon but lower than 1350.8 KJ/mol of Krypton. Hall effect thrusters and ion thrusters have been adapted to run with oxygen, that is less and less expensive than xenon and krypton and can be extracted from Lunar regolith ( http://arc.aiaa.org/doi/abs/10.2514/6.1998-3994 http://dspace.mit.edu/handle/1721.1/74748 )
#434 Re: Interplanetary transportation » Steam nuclear rocket » 2014-04-26 09:09:08
Compare that to simply firing out in the open vacuum every single time on the moon, and not having to do anything to clean up the radioactive residues afterward, since Vex exceeds lunar escape.
GW
I think you are right, but unfortunatly, by the moment, we have not a lunar test facility. I guessed if it may be possible to simulate a gas core NTR on Earth, with a very safe and cheep argon vortex core, heated with some kind of microwave device (something like VASIMR ion-cyclotron resonance heater) at 10-20k °K and use it to study all the issues of core-propellant heat transfer, core confinement, chamber cooling, plume contamination and multi-propellant use.
When all the issues are solved, we can go to the Moon to perform the final tests with a real gas core prototype, saving a lot of money.
A solid core NTR can be designed for a reducing propellant like hydrogen or an oxydizing propellant like water, but not for both. A gas core has not these problems and can work with any kind of propellant. It can do the departure burn with hydrogen at very high specific impulse of 2500 s, then switch for easy storable water and use it for arrive burn at a lower specific impulse of 1000 s.
I imagine a very verastile ship with a small habitat surrounded by a multiple shells water tank and a bigger "habitank" holding the departure burn LH2, that is vented after departure and used as an habitat extention douring coasting.
After the burn, instead to be vented out, the gas core can be aspired in a bigger tank, where it adiabatically cools, and used as a gas core reactor for generating electrical power.
#435 Re: Human missions » Cheep simulation of low gee environment » 2014-04-26 07:43:33
The only problem with an extreme gee gradient is fainting from reduced blood flow to the head, when sitting up or standing. Putting on a gee suit to counter this screws up the deal for experimenting with artificial gravity.
Douring 20-30 RPM cicle, if not a gee-suit, astronaut will surely need some kind of elastic garmet to counteract fluid shift in the lower limbs. But I guess a short arm-centrifuge will be used at high RPM high gee for multiple short periods to mantain bones and muscle and low RPM low gee for longer period in order to avoid microgravity body fluid shift. Optimal centrifugation protocol has to be determinated.
Large-radius artificial gee avoids this, as the gradient is essentially negligible. For 56 m at 4 rpm, I had a rather low number for the gradient, one not much different from sitting vs standing, in terms of cranial blood pressure change. And 4 rpm should be tolerable even to untrained civilians.
Your spinning spaceship is the top, but I think even with her, a short arm centrifuge may be useful as an auxiliary artificial gravity devicie: there are still situations where your ship cannot spin. For example, if you want to couple chemical rockets with electric propulsion, it may be difficoult to spin when ion thrusters are firing.
You get a much better experiment with a big rig, even if it has to be cable-connected, which is a real bitch to start and stop spinning. Sounds like something we should be building in LEO. Maybe something we should have built instead of the ISS that we did build.
Hindsight is always 20-20, ain't it?
GW
If spin and despin operations are computer controlled and done with RCS perfectly syncronized and cable kept in tension by canted outward retrorockets, it may be not such a bitch... Or not?
#436 Re: Human missions » Cheep simulation of low gee environment » 2014-04-26 07:13:04
Sounds like a good idea to me. My feeling is that if astronauts can adapt to microgravity, they can also probably adapt to high spin rates over time. Either way, with modern medicine as it is I bet the process of adaptation (if for whatever reason we can't simply stick to spinning habitats with larger radii) won't be as bad as the effects of space sickness upon astronauts in the past.
If you go in a marina and observe desembarking yachtsmen, you can see single hull sailors waiving left and right while walking and catamaran sailors raising and crouching like kangaroos. This beacuse douring cruise, theiy have developed some kind of motor program to minimize the roll of a single hull sailboat or the up-down motion of a catamaran. And now that they are programmed to cancel boat motion, after disembarking they may experience "ground sikness", because now the not moving ground gives them discordant sensorial inputs.
I guess for astronaut will be the same. Douring a 6 month cruise on a 25 meter of radius, 6 RMP spinning spaceship (slightly shorter than GW's modular spaceship), astronauts will learn how to move in a way to compensate Coriolis accelerations: automatically shifting their barycenter anti-spinward when they rise to not fall spinward or shifting barycenter spinward when they crouch to not fall anti-spinward. When they return to Earth, having spent the criuse in artificial gravity, their bones and muscles would be perfect but their brains would be still programmed to neutralize Coriolis acceleration and would need some days to change program. Douring this days, they probably would have "Earth sickness".
To help astronauts enproving adaptation in artificial gravity, it may be useful some kind of google glass, that sligly distort their vision to compensate Coriolis acceleration.
But there is another consideration about differences between individuals: there are people who can read in a mooving car without problems and people who have motion sickness if not looking outside. People that never experienced sea sickness even in a gale and people who start to vomit just when they board a boat in a harbor. I guess the cause may be in the connections between vestibular nuclei and dorsal nucleus of the vagus nerve: people with many connections would experience dizziness very easly and people with few connections would be very resistant.
#437 Re: Interplanetary transportation » Landing a flying saucer on Mars » 2014-04-24 09:47:35
Hi Quaoar:
On my landing boat design, I had 4 engines near the center, inside a room sealed to the backside of the heat shield structure. That design would only need to gimbal a little in the engine-out condition, where only two diametrically opposite are running. Or you could rely on attitude control thrusters for steering (as in the 1960's-vintage Scout launcher).
With all 4 engines running, differential thrust among the engines will provide steering about as well as gimballing would. For engines nearer the periphery, the differential thrust moment is even larger, but so is the disturbing moment when one engine quits, but before you can shut the diametrically-opposite one down to compensate. So, maybe 8 smaller engines is even better. I don't know, really.
As for off-center but axially-oriented engines having stable plumes, I don't know. I'd cant around 10 degrees in a first design, just to be sure. Cosine(10 deg) is a number fairly close to unity, so there's not any really significant loss of thrust and Isp at low cant like that. It'll take some flight experience with this, in more than one vehicle, to really know the art of doing it.
GW
Your landing boat has 4 rocket: let's call them R1, R2, R3, and R4: in case of R3 out, we have to shut down R1 or we can pivoting it to align its thrust to the center of mass and run with three rockets?
#438 Re: Human missions » Cheep simulation of low gee environment » 2014-04-24 09:29:21
Quaoar, as a doctor what is your opinion on the notion that slow spin-up and anti-nausea medication can be used to ease adaptation to high-spin rate environments?
I think it may be work very well: starting with low spin rate, some scopolamine if needed, and gradually spinning-up, I guess astronauts will quickly adapt to Coriolis accelerations, almost like sailors adapts to pitch and roll motion sikness. But I also think we can enhance their comfort in the first days using some kind of augmented reality sofware, to minimize discordant sensorial input
#439 Re: Human missions » Cheep simulation of low gee environment » 2014-04-24 09:02:05
Oh I appologize, I did not get what you were proposing. Clever. Of course it is not the same, as the head would experience significantly less synthetic gravity than the legs, but never-the-less, some data similar to an actual artificial spinning world in space. If the person does not get sick.
I imagine a 2.4 m radius centrifuge that can be fitted in a Falcon 9 or Delta IV launced module: astronauts will live in microgravity (if the study is performed on Earth, "ground astronauts" will float head-up in a swiming pool douring the day and stay at bed douring the night) and willl periodically exercise in high gee environment, following a training protocol to be determinated.
At 25 RPM a 1.8 m tall astronaut will experience almost 1.6 gee at the feet, 0.8 gee at the belly, 0.4 gee at the head. At 30 RPM our astronaut will have 2.4 gee at the feet (elastic sox will be needed), 1.2 gee at the belly and 0.6 gee at the head.
They will experience drizzines, but we can try to fix it using augmented reality.
Dizziness is mostly due to disagreement between visual and vestibular inputs, that cause an overstimulation of vestibular nuclei, extended to the dorsal nucleus of the vagus nerve. It can also be experienced reading a book on a moving car: the book doesn’t move but the car does, so there is discordant inputs that may cause dizziness. The same happen in a short arm high spin centrifuge, where dizziness is due of vestibular stimulation by strong Coriolis acceleration, but I think it's possible to correct the discordant sensorial input using some device like google glass and a proper software.
#440 Re: Human missions » Cheep simulation of low gee environment » 2014-04-24 08:13:58
http://www.popsci.com/scitech/article/2 … ates-mouse
I don't know what the results were, or whether they managed to achieve partial effective gravity.
This is diamagnetic levitation: animal and human body is composed mostly of water, that is diamagnetic and can be repelled by a very strong magnetic field of almost 16 Tesla (1-2 Tesla is the field of a NMR devicie).
If you put a big superconductive coil on the roof of an ISS module, you can repell the astronauts on the floor, simulating a 1 gee gravity environment, and have also a very good cosmic ray magnetic shielding, both with the same devicie. It sounds fantastic?
But there are four little issues:
1) the coils and the cooling hardware are very massive
2) there are no data on health effect of long term exposition to 10-20 Tesla range magnetic fields
3) in case of cooling failure, the superconductive coils become resistive and will explode like a bomb, realeasing all the energy stored inside (see magnetic quench http://en.wikipedia.org/wiki/Supercondu … net_quench )
4) every ferromagnetic object inside such a field is turned in a bullet.
#441 Re: Interplanetary transportation » Steam nuclear rocket » 2014-04-24 07:37:33
Thanks Quaoar. Nice to know my hunch was about right.
I think the steam NTR would be even more attractive, and practical, done as an open-cycle gas core design: somewhere between 1500 and 4000+ s Isp, depending on achieved T/W. Too bad nobody ever tested such a thing, other than a couple of academic bench tests of a couple of principles, about half a century ago.
GW
With a solid core NTR steam rocket we can add an arc-jet afterburner, like the hybrid electro*thermal MITEE, that super heat propellant at 4000 °K, reaching an Isp of 800-850 s, but I guess we are reached the limit.
Gas-core is very interesting: I read that the most promising type is a toroidal counterflow vortex in a spherical chamber. With core temperature of 15-20k °K, hydrogen is almost transparent to radiation, I read, and it needs to be seaded to have a good heat transfer. So water may be probably a better propellant, reaching an Isp of 1200-1500 s.
UF2 gas is stored at low pressure in big tanks, to not be critical. Before start-up it is pressurized and injected in the vortex inside the chanber. When the burn is finished, the chamber is vented and all the trouble are finished: very safe.
Even if may be dangerous to test it on Earth, why not to study all the issues of core confinement with some heavy not radioactive gas at high temperature?
#442 Re: Interplanetary transportation » Non-Space Uses for Rocket Engines » 2014-04-23 10:48:53
I'm with Tom on this one, actually. If your nuclear warhead were small enough it would be fairly trivial to smuggle it into any city with, for example, a truck.
Beyond that, New York and Los Angeles are both American cities. Likewise I would expect that there wouldn't be an issue for any European cities within the Shengen Zone.
I was thinking that smelting would be the only use of the rocket engine. This would mean that the thrust beverages would be a negative rather than a positive. I suppose this would make it more of a large blow torch.
It's true (and may be interesting to note how useful can be spending a lot of money in anti missile defence, when a nuke can be delivered on an anonymous cargo ship, but this is another story) but what worths is not reality but perception of reality. In people mind, rocket is more and more impressive than a cargo ship.
#443 Re: Human missions » Cheep simulation of low gee environment » 2014-04-23 04:39:45
It's very interesting but a bit expensive and very difficoult to do, because you need to lobby politician of many states. My stuff is very cheep and can be done now with less than 50000 $.
#444 Re: Interplanetary transportation » Non-Space Uses for Rocket Engines » 2014-04-23 04:36:20
One that springs to mind is rapid package delivery. The delta-V to go from New York to Los Angeles (4000 km) is 6.5 km/s if done as one hop (13 km/s if you use rockets to slow down), but could also be done in two smaller hops of 4.5 km/s (9 km/s), or four hops of 3.5 km/s (7 km/s). One hop would have a travel time of 900 s, 15 minutes. Two hops would involve 1300 s spent in transit, about 21 minutes. Four hops would be about 1800 s spent in transit, about 30 minutes. Either way, if there were cargo that had to arrive as close to immediately as possible sending it by rocket might be feasible.
I think no state would accept foreiner rockets in their air space, because may be impossible to distinguish a speed cargo or passengers rocket from a militry rocket armed with nuclear warhead.
Then there's also the potential for the use of liquid rocket engines as blowtorches on a massive scale. One could imagine a rocket with significant amounts of extra hydrogen burning its way through iron rich rock by smelting it.
This may be interesting: we can image some special launchpad, where the exaust of the rockets is channeled over something to melt.
#445 Interplanetary transportation » Steam nuclear rocket » 2014-04-22 13:46:53
- Quaoar
- Replies: 11
As a steam punk passionate, I love the idea of a steam Spaceship, but there are also other reasons to love her: unlike hydrogen, water is very easy to store and can be found everywhere in the Solar System. A water propelled Spaceship can find the return propellant from Mercury poles to Jovian moons. Water is also a very good cosmic ray shielding material: we can imagine a multiple shells propellant tank that surrounds the habitat, solving another nasty issue. Using the same substance for propulsion and for life support is also very safe: imagine a Ship returning to Earth that fails orbital insertion burn for rockets failure: the unused water can keep astronauts alive for years, giving time to set-up a rescue mission.
A water propelled Spaceship may be strategic for future human space exploration, but surfing on Internet I found no serious work about steam NTR: the web is full of very interesting LH2 NTR study, but completely empty about water NTR.
The only study I found is this ( http://www.permanent.com/space-transpor … ckets.html ) but it propose a ridiculous specific impulse of 190 s: it would be wiser using nuclear energy to split water in LOX and LH2 and burn them in a good chemical rocket (adding a small percentage of RP1 or LCH4 to fix oxidizer/fuel ratio; but this is another story: I’m here to talk about steam NTR).
Even if water has an higher molecular weight than hydrogen, I found hard to believe that a NTR can do anything better than 190 miserable seconds. But there are no works on the issue. So I wanna try to imagine how a steam NTR can be and what kind of performance can reach (it’s to note that an experienced rocket man like GW Johnson talks about 600 s or more for water NTR in his blog).
I’m not an expert, only an amateur, so I beg the engineers of this forum to correct my (many) mistakes.
Let’s start from a basic design: a classical Pratt & Whitney with a cermet W/UO2 core, derived from the Rover Pewee.
Core temperature 3000 °K
chamber pressure 136 atm
Isp 940 s with LH2
First of all, we have to note that the cermet core is conceived to run with LH2, so if we want to adapt it to run with an oxidizer propellant like water, we have to protect it with some kind of coating: I guess Thorium dioxide, because it’s the oxide with the highest melting point (3660 °K, very near to tungsten). Let’s imagine it works and go on.
Now let’s calculate the specific impulse, that is proportional to the square root of the temperature/propellant molecular weight ratio. Hydrogen has a molecular weight of 2, water of 18, so 940 s with LH2 will become almost 313 s using water: more than 190s, just enough for a MAV, but to low for an orbit to orbit Spaceship.
If we want more, we have to rise the temperature: just bring it to 3500 °K, like the Russian Superraket Block B ammonia NTR ( http://www.astronautix.com/stages/suplockb.htm ).
Working at 3500 °K, our steam NTR reach 338 s of specific impulse, quite better, but not very useful for interplanetary travels.
At this point, we are just 195 °K below tungsten melting point, very near the temperature limit of a solid core NTR. If we want to enhance Isp, we can only lower propellant molecular weight. At 3500 °K and 136 atm, water is almost integer and to dissociate needs temperature higher than reactor melting point.
So, if we think 338 s are not enough, we have to build a different kind of rocket, working at very low chamber pressure (1 atm or even below), for achieving water dissociation at sustainable temperature.
A very promising high temperature-low pressure NTR is the pressure feed MITEE monoatomic H, designed by the same guys the Timberwind. It may be a good candidate to be adapted for water.
http://web.archive.org/web/200503071638 … mitee.html
http://web.archive.org/web/200503171455 … /PUR-8.PDF
Let’s start with this MITEE:
core temperature 3000 °K
chamber pressure 1 atm
Isp 1270 s with LH2
At 3000 °K and 1 atm, water is partially dissociated in a mix of: H2O, H2, O2, HO, H, O. To
calculate the possible specific impulse of a hypothetical water version of MITEE, we need to know the fraction of every component of the cocktail. I used this curve, that show the dissociation of water at 1 atmosphere of pressure:
According to the graphic, at 3000°K and 1 atm the mixture is composed of: 40% H2O, 18% H2; 16% H, 14% HO, 6% O, 6% O2 and the mean molecular weight is 12.98. So the specific impulse will be 429 s: slightly less than a good LOX-LH2 rocket, but quite good.
Now let’s rise core temperature at 3400 °K: we have 34% H, 16% H2, 16% O, 15% H2O, 14% HO, 5% O2, with a mean molecular weight of 9.9. Now the specific impulse rises to 530 s: better than any chemical rocket, and near GW’s 600 s target.
Rising core temperature at 3500°K, we have 40% H, 20% O, 14% H2 13% HO, 9% H2O, 4% O2, with a mean molecular weight of 8.99. The specific impulse is now 565 s.
If we want to obtain more, now we can only lower the pressure: let’s put it to 0.4 atmosphere. Unfortunately, I have not a curve for 0.4 atmosphere, so I move slightly to the right side and guess that dissociation at 3500 °K and 0.4 atm would be almost like 3750°K and 1 atm. It’s the best I can do, and I beg you to correct me if you have better data.
At 3500°K and 0.4 atm, I guess: 51% H, 26% O, 10% H2, 8% HO, 3% O2, 2% H2O. With a mean molecular weight of 7.55, the specific impulse would be now 616 s (GW was right!), more than 6 km/s of exaust velocity!
With this rocket we can build a completely reusable and versatile spaceship, that can be used from Mercury to Jovian moons, without all the nasy trouble of storing cryogenics. Isn't she lovely?
#446 Re: Interplanetary transportation » SpaceX Falcon 9R launch » 2014-04-21 03:37:13
I'm excited to find out what the telemetry from the landing said, with regards to how quickly the stage was moving when it hit the water, and what SpaceX has to say regarding how fast is slow enough.
Having landing legs, Falcon 9R will not need launchpad: is it correct?
If so, another big cost will be cut.
#447 Re: Interplanetary transportation » Landing a flying saucer on Mars » 2014-04-20 14:43:43
There's no data to support or deny this, but my engineering intuition suggests that 10 to 15 degrees of cant would more than suffice to ensure plume stability for supersonic retropropulsion. That remains to be seen in testing, but could be verified in flight at about 100,000 feet right here at home.
I think you are right. If you put the rokets nearer the outer perimeter, is it possible to have them fire perfectly vertical and let the atmospheric flow cant the plumes outward douring descent?
The remaining question is how many engines and where in the heat shield do you put them? Opinions vary. I'd guess 4 to 8, nearer the center to restrict engine-out torque transients that might destabilize attitude. Others prefer a ring nearer the outer perimeter of the heat shield. My guess is that either, or anything in between, could be made to work. Something else will constrain that choice.
Do these need ports through the heat shield with doors that close when the engines are not firing? Again, opinions vary. I'd say that no, doors are not necessary, if-and-only-if you can reliably seal the engine compartment to prevent all throughflow. There is no better insulator than a static gas column, even against entry plasma.
A question about your landing boat design: do the nozzles open in fixed holes in the center of the heatshell, or in a bigger sealed compartment where they are free to pivoting for thrust vectoring control?
#448 Re: Human missions » LOX/CO2-Diborane rocket for reusable landing boats » 2014-04-20 14:24:59
Sure using CO2 would be less energy intensive since there is no electrolysis or RGWS used to create the LOX that we would use for Methane or other such fuels. Then if we need to use a canted hypergolic fuel such as in the Draco design then we have more problems for when we create fuels from insitu than we first had thought. In either case we need power to make this all happen. That said we should bump the topic of power and which forms can we ship and or create on mars for fuel creation.
My hypothetical diborane rockets use LOX for descent and CO2 only for ascent: diborane is very reactive with LOX and probably ignition will be easy. If not we can start it with hybergolic, like in Russian school rockets.
#449 Re: Interplanetary transportation » Landing a flying saucer on Mars » 2014-04-20 13:10:09
So by solving entry descent for larger payload mass we now have a secondary problem of ascent is not achievable.
One way to solve is if the engines are detachable to allow for them to be relocated would the hypregolic fueled engines have the launch power to achieve orbit. Which on a guess would be a no but I will leave that up to others that can compute the values. This also does cause an issue if we are wanting to use methane created fuels for return in the same vehicle that we land in. It is starting to sound like we need a multiple engine system for landing and take off.
Detachtable enigine may be a solution, but I imagine pivoting pods that stay 45° canted outward for descent and will be extrofletted and pointed straight downward for orbital ascent.
Propellant issue may be solved using hypergolics only for ignition, like almost every Russian's rockets do, then burning other propellant like LOX-CH4, LOX-RP1 or LOX-LH2. It's a very well proven technology.
#450 Re: Human missions » LOX/CO2-Diborane rocket for reusable landing boats » 2014-04-20 10:46:22
Yeah, borane and borax are not the same. There used to be a laundry detergent with borax in it, so that form of boron is fairly plentiful. I think it was "Twenty-Mule Team", and I think Ronald Reagan was its TV pitch man. This was 1955 stuff.
I know diborane is toxic. I propose it as a possible propellant because is the only I know that can react with atmospheric CO2. Storing atmpspheric CO2 and use it directly as an oxidizer may be a very practical and reliable form of ISRU, because it needs few energy and few time than chemical processing. Using it on your landing boat will save almost 16 tons that can be used for payload.
I think Quaoar likes my Mars landing boat designs. He's looking for better propellants for it. I did take a look over in the other thread at that organo-metallic stuff with the lithium in it. Isp-wise, it does look pretty good. Lithium-poisoning-wise, maybe not so good. Peroxide stability-wise, not good at all.
GW
Yes, I like very much your landing boat. I'm only concerned about storing LH2 for long periods on Mars surface: multi-layered insulation doesn't work in atmosphere and we have to use other matherials like aerogel. Is it possible, with some kind of very efficient active cooling, to keep your landing boat on Mars for months without losing ascent propellant for boil-off?
Happy Easter for all!