Best propellant & stuff for a Mars spaceship and lander

GW Johnson · 2018-07-22 09:34:57

Chemical for crew, electric for cargo.

That is EXACTLY what I proposed over at my "exrocketman" site for Mars Mission 2016.

GW

SpaceNut · 2018-07-22 10:36:34

To which this is the mass equation that is in support of the crew in chemical and not so much for electric as life and or its support are not part of its equation. It is also why we look at the legs of a mission for doing different propulsion methods as mass matters for each.

kbd512 · 2018-07-24 22:09:04

Quaoar,

These aren't normal arrays. They're plastic films with the active material and electrical connections printed on them. The arrays should be wrapped around a cylinder (with the rest of the electrical system in it) and deployed using centripetal force. Gravity is the best deployment system. The use of counter-rotation can provide artificial gravity for a SEP powered ITV. A chemical kick stage would be useful for the SEP powered ITV to have.

spacetechsforum · 2018-09-22 13:59:23

I do not think that electric propulsion is of any use in cargo transportation. I cannot give a specific figure, but last time i checked the amount of electrical power needed to generate enough thrust and dv to push heavy cargo (250t+ for payload and ship) to Mars cannot be provided in any feasible way.

My choice is LH2/LOX as it gives the best Isp and I am not a specialist to evaluate the cons of this propellant, although I am currently trying to do so, which brings me to the topic.

Although many NASA publications I found suggest the technology needed for long time LH2 storage seems to be almost ready, I find myself unable to scale provided systems to suit the needs for Mars mission. My first though on this subject was: "Is that not simple? Why not to put a big refrigerator into ship and we are done". Now, as I do not consider NASA scientist to be fools, my understanding is that there must be a serious problem with this approach, yet the thing must be very obvious, since I cannot find any good source that can explain it. I hope someone in this forum will enlighten me.

I did some calculations to comprehend the problem, below the numbers in case i did mistake and so my perspective is flawed.

Model - external shell (const temperature calculated from heat equilibrium - Th=262.15K ), insulation (2xMLI blankets, 22 layers each - E=0.001 ), LH2 tank(Tc=18K). Stefan-Boltzman cost: sigma=5.67E-08

LH2 tank: volume: 464.218m3, surface area: A=353.320m2

Heat Leak: sigma*E*(Th^4 - Tc^4)*A = 94.62W

To remove this amount of heat from tank using Helium as working medium would require a heat pump capable of generating dT=282 with COP=0,03.
That means that we need a little more than 3kW electric power (this much can be provided with 2x18m2 solar panels). If i am correct the 8m2 radiator working at 300K would remove 3,3kW of heat generated by system summed with heat from tank.

The heat pump proposed is 100% theory. The subject of efficiency of cryogenic heat pumps capable of working in space does not seem to be popular on the internet.

Terraformer · 2018-09-22 14:46:33

I cannot give a specific figure, but last time i checked the amount of electrical power needed to generate enough thrust and dv to push heavy cargo (250t+ for payload and ship) to Mars cannot be provided in any feasible way.

Well, it all depends on how fast you want to get there. If you can spare a year, then it's a lot easier than trying to get there in 39 days.

SpaceNut · 2018-09-22 15:32:36

Ion engine could one day power 39-day trips to Mars with a new engine, called VASIMR (Variable Specific Impulse Magnetoplasma Rocket).however, the engine would need 1000 times more power than solar energy could provide. For that, VASIMR would need an onboard nuclear reactor. Early versions of the reactor technology were used from the 1960s to the 1980s by the Soviet Union, but have not been used in space since and would take time to develop.

NASA thinks there's a way to get to Mars in three days

part of the problem is not just what you use to get there but will be used to get back.

Which is a Better ISRU Propellant on Venus/Mars–LOX/LH2 or LOX/CH4?

SpaceX Mars Plans In-Space Refueling: Elon’s plan is built around the idea of refueling his ITS (Interplanetary Transport Ship) in LEO prior to Mars departure.

section 9.3.2. LOX/LH2

The chemical propulsion option considered in the DRA for the MTV is LOX/LH2. This bipropellant is often favoured for two main reasons:
Highest specific impulse for liquid bipropellant (~450 seconds).
Availability of existing engines.
Non-toxic.
Unlike hydrocarbon fuels, combustion of LH2 doesn’t produce any pollution — only water. (Although, for in-space propulsion this is not an issue.)
Available throughout the Solar System, and, indeed, the Universe.
However, for Adeona, or indeed any Mars mission, LOX/LH2 is probably not the ideal choice as it has a number of nontrivial drawbacks.
LH2 is notoriously difficult to store for long periods, especially in the vacuum of space. Because of the very small molecule size, it tends to leak away, or “boils off”. Even with a boil-off rate of only 1%, it would still be necessary for Adeona arrive at Mars with a surplus of at least 20% of the fuel needed for TEI. Note, however, that zero boil-off tanks and densified liquid hydrogen have been developed to address this problem.
LH2 has very low density (71 kg/m3 compared with 424 kg/m3 for LCH4 or 810 kg/m3 for RP-1), and therefore requires larger storage tanks compared with other fuels. The tank size becomes yet larger when accounting for the boil-off margin. Larger tanks are obviously heavier, and thus more expensive to launch.
LH2 is highly cryogenic, with a boiling point of just 20 K, and therefore requires active cooling. This additional power requirement means additional mass for solar panels or other power system hardware, thereby further increasing IMLEO and launch costs. The need for active cooling means that LH2 is not generally considered space storable. This makes it unsuitable for Adeona, which must wait 1.5 years on Mars orbit.
Because LH2 must be stored at such low temperatures, its tank must be kept separate from the LOX tank, otherwise the LOX could freeze. This increases the mass of tankage and other parts of the propellant system.
LH2 causes metal to become brittle, which means associated engines and tankage require advanced metallurgy. This also drives up the cost of the vehicle.
LH2 is more expensive than either RP-1 or LCH4.
LH2 is highly explosive and difficult to work with, and can cause invisible high-temperature fires.
Because of its low temperature, LH2 fuel lines can only be purged with expensive helium.
These drawbacks arguably outweigh any advantages of LH2 attributable to its high Isp.
Advancements such as the new composite cryotanks developed by Boeing and NASA may produce strong, lightweight LH2 tanks that greatly reduce boil-off rates, possibly to zero when combined with MLI (Multi-Layer Insulation). However, even if this technology becomes available, considering the other disadvantages of hydrogen there is probably a better choice for MTV propellant.

The other combinations are on the page as well.

SpaceNut · 2018-09-22 16:17:45

Nasa has been on the nuclear power will solve everything kick for quite some time now... NASA's Mars Design Reference Mission Goes Nuclear (2001)

Of course its hard to solve a problem for landing if all you know is the payload that you want to land as its not just a payload that does the landing but the rest of the dry mass that remains which contains it.

So 1999 space ship design

kbd512 · 2018-09-22 16:24:56

SpaceNut,

Thanks to the hard work done by Ascent Solar, the claim that solar power could not possibly provide the type of energy required for VASIMR to get a craft to Mars in 39 days is simply not true. Dr. Zubrin made the assertion that a 1kW/kg power source simply didn't exist and at the time he made that assertion he was correct. Ascent Solar has since had 2kW/kg (about 2.45kW/kg, actually) thin film photovoltaic arrays in testing as I write this and their 1.25kW/kg photovoltaic arrays are current production technology, slated to power Japan's Jupiter-bound solar sail-powered probe, and actually powering long duration lighter-than-air drones made by Airbus Defense. Even after you factor PMAD and propulsion hardware into the equation, you arrive at a completely realistic power-to-weight ratio (PWR) for the complete system. I don't think VASIMR is the optional propulsion solution, given recent developments with solid-fueled (Iodine crystal) plasma thrusters with better thrust-to-weight ratios (TWR), but that takes nothing away from the fact that VASIMR would actually perform as advertised. At the time that Dr. Chang-Diaz made his assertion about his propulsion system, it was utterly fantastic because no such solar or nuclear propulsion system with the requisite PWR existed. Such is no longer the case. Time marched on and technology advanced.

Oldfart1939 · 2018-09-22 18:05:13

This discussion is slowly moving towards an eclectic solution of many of these problems. I'm not yet convinced that ion drive will be fruitful for some time. But my thought is we may see some resurrection of the Nerva type propulsion system. Nerva using H2 as the propellant would be ideal for deep space missions from LEO, and we are moving towards having adequate lift capacity with BFR and New Glenn. Utilization of orbital assembly and modular designs would allow lifting a Nerva-style EDS (Earth departure stage) to orbit, in addition to ferrying large quantities of liq H2 as well. With an Isp of 850-900 seconds, the EDS should be able to achieve Mars orbit with ease. Using a chemically powered descent/ascent stage would be carried as payload. With on-Mars orbit refueling, the outer solar system becomes accessible--at least the asteroids and Jovian moons.

SpaceNut · 2018-09-22 18:42:29

spacetechsforum

We talk all the time about issues in specific topics and then we seem to forget them just as fast

Zero boiloff and active cooling
https://ntrs.nasa.gov/archive/nasa/casi … 023073.pdf

http://newmars.com/forums/viewtopic.php?id=7004

spacetechsforum · 2018-09-23 03:22:52

Thanks for the link. I am moving my question with numbers to that topic (somehow i missed it when searching earlier).
As for the electric propulsion, I cannot find any up to date article, so does anyone know if they even completed this 100 hour constant work test?
Also even if they did, to generate 400N of thrust one would need a 200 engines and 20MW reactor (one engine seem to generate 2N of thrust with 100kW power). The reactor design seems to be pursued, so this part may be doable. Still there is problem of heat dissipation - my best guess is that just the radiators array would weight around 50t. (btw. why people write "metric tons" and not just "t"? ).
The lower thrust does not only donates longer travel time. Some maneuvers must be completed within time frame (like hyperbolic to eclipse orbit change near Mars), so to weak engine is not an option.

elderflower · 2018-09-27 04:33:04

The abbreviation for a metric tonne (1000kg) is "te". This distinguishes it from other sorts of tons (eg 2240 lbs) and short tons (2000 lbs).

Quaoar · 2018-09-27 05:41:44

kbd512 wrote:

SpaceNut,
Thanks to the hard work done by Ascent Solar, the claim that solar power could not possibly provide the type of energy required for VASIMR to get a craft to Mars in 39 days is simply not true. Dr. Zubrin made the assertion that a 1kW/kg power source simply didn't exist and at the time he made that assertion he was correct. Ascent Solar has since had 2kW/kg (about 2.45kW/kg, actually) thin film photovoltaic arrays in testing as I write this and their 1.25kW/kg photovoltaic arrays are current production technology, slated to power Japan's Jupiter-bound solar sail-powered probe, and actually powering long duration lighter-than-air drones made by Airbus Defense. Even after you factor PMAD and propulsion hardware into the equation, you arrive at a completely realistic power-to-weight ratio (PWR) for the complete system. I don't think VASIMR is the optional propulsion solution, given recent developments with solid-fueled (Iodine crystal) plasma thrusters with better thrust-to-weight ratios (TWR), but that takes nothing away from the fact that VASIMR would actually perform as advertised. At the time that Dr. Chang-Diaz made his assertion about his propulsion system, it was utterly fantastic because no such solar or nuclear propulsion system with the requisite PWR existed. Such is no longer the case. Time marched on and technology advanced.

I've seen their site:

http://www.ascentsolar.com/custom-solutions.html#wide

They claim 1100 W/kg for bare modules (without the supporting structure), 200 W/kg for the superlight solar blanket and 30 W/kg for the extreme blanket, but I couldn't find anything about 2450 W/kg

kbd512 · 2018-10-02 16:07:35

Quaoar,

I saw it in a press briefing regarding what they're working on several months back, but I can't seem to find it now. Maybe it was a typo or maybe my memory is going, but I'm almost certain I saw that 2450W/kg figure cited in a press release document. I'll attribute that to "brain not working". Even so, 1,100W/kg is most impressive. Obviously mass for support structure has to be included, but technology development isn't standing still there, either.

Mars_B4_Moon · 2022-07-30 17:34:18

I still believe some kind of Ion drive would be best for keeping some A.I Mars Station in Orbit.

Hopefully we live to see colonization of Mars, but what culture will dominate?

Russians seem out of the game now with their Wars and Battles and Sanctions. However as horrible as Putin is and as imperialist as the dictator government is I would say many of the Russians themselves are not Putin and they will be missed for their unique ideas.

Russians still are launching satellites but may not stay with the ISS

https://www.globaltimes.cn/page/202207/1271534.shtml

https://www.space.com/lightweight-angar … ite-launch

What I found interesting about the Russians were their unique designs and the influence they had on commerical space flight and Ukraine sciences when relations with the international community were better. I liked how before other guys like Space-X got into the launch business it was Russians trying to new ideas to make space flight cheaper or look at old ideas in new ways, Hydrazine is simply organic substance consisting of two molecules of nitrogen and four molecules of hydrogen but with ts derivative one hydrogen molecule is replaced with a more complex compound. Naphthalene is now used as Thruster in Sat Propellant it is a compound with formula C ₁₀H ₈. it has a risk and causes kidney damage, cancer and neurotoxic effects. Hydrazine supplies would have been used fuel European ExoMars spacecraft and Rover lander joint Russian programs with the European Space Agency. These missions have now be suspended, hydrazine is a liquid at 0 degrees C at the pressure of 1 atmosphere, the fuel becomes more efficient and it produces more energy per kilogram of weight, many compounds of hydrazine family hypergolics combust spontaneously however if UDMH/N2O4 is used then Mars will need a Hazmat suit, it is extremely toxic, the thrust would be more than enough to move a spacecraft around an Asteroid, push the ISS, send supply to the Moon, change the course of Mars bound craft or other spacecraft, around.

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#51 2018-07-22 09:34:57

Re: Best propellant & stuff for a Mars spaceship and lander

#52 2018-07-22 10:36:34

Re: Best propellant & stuff for a Mars spaceship and lander

#53 2018-07-24 22:09:04

Re: Best propellant & stuff for a Mars spaceship and lander

#54 2018-09-22 13:59:23

Re: Best propellant & stuff for a Mars spaceship and lander

#55 2018-09-22 14:46:33

Re: Best propellant & stuff for a Mars spaceship and lander

#56 2018-09-22 15:32:36

Re: Best propellant & stuff for a Mars spaceship and lander

#57 2018-09-22 16:17:45

Re: Best propellant & stuff for a Mars spaceship and lander

#58 2018-09-22 16:24:56

Re: Best propellant & stuff for a Mars spaceship and lander

#59 2018-09-22 18:05:13

Re: Best propellant & stuff for a Mars spaceship and lander

#60 2018-09-22 18:42:29

Re: Best propellant & stuff for a Mars spaceship and lander

#61 2018-09-23 03:22:52

Re: Best propellant & stuff for a Mars spaceship and lander

#62 2018-09-27 04:33:04

Re: Best propellant & stuff for a Mars spaceship and lander

#63 2018-09-27 05:41:44

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#64 2018-10-02 16:07:35

Re: Best propellant & stuff for a Mars spaceship and lander

#65 2022-07-30 17:34:18

Re: Best propellant & stuff for a Mars spaceship and lander

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