Update Deepstar development

[Urwumpe]

Coward! :lol:

 

[Axel]

@Izack
Grrr here is a small disagreement. I didn't mean to use the hab module complet for RCS, i would it want only for killrot, without changing rotation achses to the ship. Due to tts physical nature its an stabilizer itself, better would be a stable connection to the ship and let rotate the complet ship along the z-achsis, after main engine burns. This would be technically mutch easier and would save fuel/energy. Without this we have permanent to prevent a complet rotating of the whole ship, with magnetic anti-fields, motors ect. However, ANY rotating part of a ship, will stabilize its achsis physically itself, because its physically not possible to remove it from the rest of the system, so you have to handle it when you want to accelerate or rotate the ship!
But orbiter simulates this not yet, only complet roating structures are self stabilized!

 

[Izack]

Ah, now I see what you mean! I'll look into this, and see how to model it, although I wonder if the effect is even very noticeable with such a slow rotation speed.

I wonder, though, about accelerations on the hab, I was thinking either starting/stopping the centrifuge would create torque on the ship, or we could assume there's a counter-rotating assembly inside that section which counteracts the change in angular momentum.

 

[80mileshigh]

Given the discussion in this thread so far, is this RCS design altogether too conventional, or can we use it? I'm presupposing the hab rotation would be stopped to use the forward RCS.

 

[Frogisis]

This has always been one of my favorites and now it's looking really, really cool.

But I think yeah, the old school RCS clusters seem a little out of place, especially at that scale next to a person, because you'd kinda expect there to be so many more sub-details. Something like a truncated white cone with a hole on the end, and four holes around the axis, with silvered insides, would fit the overall look a lot better and provide hypothetical design space for any extra mechanisms or even propellant they could later be discovered to need. That's the cool thing about simulating hypothetical technology - You can give some extra priority to style because anything that could theoretically be more drab can be declared to actually be a necessary engineering compromise by author fiat. We'd be able to build it already if only we knew it actually required all these awesome looking parts.
I propose "That actually saves mass" as the Hard SF ship design equivalent of "because I said so."

 

[MaverickSawyer]

:hesaid:
If you put a leetle more detail into the thrusters, like bell nozzles, maybe a fifth port coming straight out to assist the (I presume) yaw rotation and movement sideways, etc. The little details that make it come alive.

 

[Axel]

@80mileshigh
It's looking good! Yeah, maybe only a little bit more details, like the other posters sayed, some silver look and some extra rings around the nozzles and it will be great! And it's not to conventional, i can't see any other reasonable solution than a chemical RCS design for fast interactions, proven and simple!
MHD thrusters are to weak and to heavy. Chemical design needs more fuel, but it seems that we have enough fuel at the Deepstar - 13500mT, and the most RCS action at the long travels drifting in space will be the killrot command done by the hab centrifuge :thumbup:!

But here my question, what is your idea to fuel/to refuel the ship?
13500mT is alot, the biggest value i know for semi-real near future ships!
Normal rockets or heavy lift rockets are weak, with 150mT payload like the new NASA SLS it would need 90 launches of it OMG. A space elevator, if it works, will carry about 20mT in few days for only one lift - we would need 675 lifts to fuel Deepstar completly :facepalm:.
I have two ideas:
1) the first is to fuel Deepstar from the moon. A base at the moon produces hydrogen or helium3 and fires the fuel tanks per magnetic catapult to a low moon orbit. There is a big tank depot station, small shuttles and/or space tugs are permanently busy in refuelling the station and fly back empty tanks. Maybe we combine it by a moon space elevator. A tank station would be very usefull for other ships too, the gate to the solar system! But it would be a immense effort and costs to install the 2 bases, at moons surface and orbit!
2) A more elegant solution is to use hydrogen from the gas giants, the targets for what Deepstar has been made for!
For that job we can use a tank station, with a magnetic scoop system, positioned in a low orbit near the higher atmosphere of a gas giant. For a scooping manover the station lowers the orbit to the upper egde of the atmosphere, where it's able to catch hydrogen parcticles, but high enough that it doesn't fall into the gas giant from the atmospheric drag. Turbo compressors, liquidizers and coolers saving the fuel. For long time saving we change the hydrogene to methanol. The station itself has although a small fusion engine for altitude control.
The other solution is my favorite, you model for Deepstar itself a scooping device at its front part or at the front of every tank. Then we would be independent and could fly 200km/s with refueling at target instead 100km/s without it (dV of Deepstar is 400 km/s at the moment with fixed Isp/thrust, possible are mutch more with thrust curves). The idea is from the awesome "Perseus" deep space ship, from "Salvador Tega". This ship scoopes nitrogene from earth atmosphere for an ion engine and a nuclear thermal engine. The second nice and important thing of the scoop is cosmic radiation shilding by it's magnetic field.

See here for suggestions: [ame="http://www.orbithangar.com/searchid.php?ID=3629"]Perseus Deep Space Ship[/ame]

 

[80mileshigh]

Here are some RCS shots from GMAX. I've tried to incorporate a bit of each suggestion here. Looking better?

EDIT: Added some shots of the same design in-sim.

 

[Axel]

@80mileshigh
Yes it's looking mutch better! Only a last thing, try to make the inside of the rcs nozzles flat and silver, the rings only at outside.

 

[80mileshigh]

@80mileshigh
Yes it's looking mutch better! Only a last thing, try to make the inside of the rcs nozzles flat and silver, the rings only at outside.

Thanks! Have a look here (also experimenting with specularity on the tanks and habs - I'll reduce the glossiness you see here).

 

[Izack]

Hello again! Sorry for the delay; many things slipped my mind over the holiday.

The RCS system looks good! I had something else in mind, with thrusters embedded more smoothly into the structure, instead of being outrigged. I determined a way which both reduces the number of thruster hardpoints, and allows more snug-fit thruster placement, usually thrusting in a direction orthogonal to the local surface of the hull. I can illustrate it, but my artistic ability is lacking. On top of that, I don't want to suggest undoing your work if you prefer the way you've already used. :tiphat:

 

[80mileshigh]

Hello again! Sorry for the delay; many things slipped my mind over the holiday.

The RCS system looks good! I had something else in mind, with thrusters embedded more smoothly into the structure, instead of being outrigged. I determined a way which both reduces the number of thruster hardpoints, and allows more snug-fit thruster placement, usually thrusting in a direction orthogonal to the local surface of the hull. I can illustrate it, but my artistic ability is lacking. On top of that, I don't want to suggest undoing your work if you prefer the way you've already used. :tiphat:

No problem at all, I understand what you're suggesting and it's a better idea. I can scale these ones down and put them on the landers.

 

[kamaz]

But here my question, what is your idea to fuel/to refuel the ship?
13500mT is alot, the biggest value i know for semi-real near future ships!

Build a fuel station.

The station sits in a low Earth orbit, and lowers a scoop down on tether. The scoop collects water vapor. The station then electrolyzes water into hydrogen, using power from solar cells. Deepstar docks with the station and refuels.

For more mobility, put similar stations (fission/fusion powered, converting methane into hydrogen) on gas giants.

 

[Axel]

@Kamaz
The upper earth atmosphere has no water! The most water is in the troposphere from 0-12 km, the stratosphere from 12-50 km altitude has no water vapor. We can only scoop nitrogen and oxygen in the upper atmosphere, when the breaking effect to the tethered scoop in the atmosphere is small enough, that we need less fuel for the altitude holding than we can scoop. The best area is betwenn 90-120 km altitude, depends on the efficience level of the used propulsion system. Nitrogen in a nuclear thermal rocket solid core fission gives Isp of 2300 m/s. As propellant for a fusion engine mutch more, but i guess not more than a quarter of the value of hydrogen (up to 1 000 000 m/s) at a given energy level of the reactor.

But ofcourse we could use the nitrogen for lower speed transits to a gas giant for scooping/refueling hydrogen there.
A nuclear rocket, fission/fusion can nearly use the gas whatever you can find. But gases with oxygen are corrosive, so we have to build engines of corrosion-resistance materials.

 

[kamaz]

Ah, such a nice idea goes to waste...

I'm not sure how it is with fusion drives, but with NTRs, the Isp goes down with molecular mass of the fuel. Running on anything else than LH2 is not economical. Although if you are really pressed out there...

 

[Izack]

I'm new at and terrible with Illustrator, but here's a diagram of what I'd meant before:

Top:

Side cutaway:

Essentially, a raised, flattened, bevelled cylinder containing four inset nozzles, located in 12 locations across the vessel (the top, bottom and sides of the fore end of the main habitation cylinder, four in outriggers protruding from the rear of that cylinder, facing the sides, two on the top, two on the bottom, and on the top, bottom, and sides of the beam the fusion drives are placed on), along with four translation-forward thrusters near the fusion drive, for fine-tuning and perhaps for ullage burning.

Edit: The locations are given literally here:

	th_mpdt[ 0] = CreateThruster(_V(  0.00, 13.51, 131.59),_V( 0,-1, 0),mpdt_thrust,prop_acs,mpdt_isp); //FRONT TOP
	th_mpdt[ 1] = CreateThruster(_V(  0.00,-13.51, 131.59),_V( 0, 1, 0),mpdt_thrust,prop_acs,mpdt_isp); //FRONT BOTTOM
	th_mpdt[ 2] = CreateThruster(_V( 13.51,  0.00, 131.59),_V(-1, 0, 0),mpdt_thrust,prop_acs,mpdt_isp); //FRONT RIGHT alternate pos: 13.49,1.01,131.59
	th_mpdt[ 3] = CreateThruster(_V(-13.51,  0.00, 131.59),_V( 1, 0, 0),mpdt_thrust,prop_acs,mpdt_isp); //FRONT LEFT

	th_mpdt[ 4] = CreateThruster(_V(  0.00,  3.14,-181.38),_V( 0,-1, 0),mpdt_thrust,prop_acs,mpdt_isp); //BACK TOP
	th_mpdt[ 5] = CreateThruster(_V(  0.00, -3.14,-181.38),_V( 0, 1, 0),mpdt_thrust,prop_acs,mpdt_isp); //BACK BOTTOM
	th_mpdt[ 6] = CreateThruster(_V(  3.14,  0.00,-181.38),_V(-1, 0, 0),mpdt_thrust,prop_acs,mpdt_isp); //BACK RIGHT
	th_mpdt[ 7] = CreateThruster(_V( -3.14,  0.00,-181.38),_V( 1, 0, 0),mpdt_thrust,prop_acs,mpdt_isp); //BACK LEFT

	th_mpdt[ 8] = CreateThruster(_V(  0.00, 13.33,  74.12),_V(-1, 0, 0),mpdt_thrust,prop_acs,mpdt_isp); //MIDDLE TOP pointing RIGHT
	th_mpdt[ 9] = CreateThruster(_V(  0.00, 13.33,  74.12),_V( 1, 0, 0),mpdt_thrust,prop_acs,mpdt_isp); //MIDDLE TOP pointing LEFT
	th_mpdt[10] = CreateThruster(_V(  0.00,-13.33,  74.12),_V(-1, 0, 0),mpdt_thrust,prop_acs,mpdt_isp); //MIDDLE BOTTOM pointing RIGHT
	th_mpdt[11] = CreateThruster(_V(  0.00,-13.33,  74.12),_V( 1, 0, 0),mpdt_thrust,prop_acs,mpdt_isp); //MIDDLE BOTTOM pointing LEFT

 

[Axel]

@Kamaz
It's pure physic and not a case of decision. Nitrogen is about 4 times heavier than hydrogen, so Isp is 4 times lower than the value of hydrogen for NTR and fusion drives. I repeat: nitrogen NTR = 2300 m/s, nitrogen fusion up to 250 000 m/s, thats alot i find and conforms the actual Deepstar value! For ion drives is better to use heavier propellants like xenon or mercury, there hydrogen would be the worst fuel ever :lol:.
But nitrogen IS FOR FREE, thats the big advantage when we want to start from LEO, with whatever kind of drive. And it's density is mutch higher, we can save more of it in the same tank, so we should have maybe deltaVelocitis with similar values to hydrogen for fusion (maybe somebody can calculate it) and we can storage it easy for a very very long time. Hydrogen to store in it's pure form is only possible for short time, because it's impossible to prevent leaving of the very small atoms from the tank. We have to transform it to methanol and retransform that amount of hydrogen we need short time before we pump it in the fusion drive. This is an official planed method of NASA for long time missions, which will using hydrogen.

 

[80mileshigh]

here's a diagram of what I'd meant before

Thanks! I did have a go at meshing somthing based on your first suggestion. Pretty similar:

 

[Axel]

Hello 80mileshigh and Izack!

I advanced my knowledge about NTR and LANTR drives/enignes last weeks strongly and I did some recalculation for the Deepstar landers! The old values are wrong, i don't know an engine which could rund with the old settings at the given tank size. But don't worry, my recalculations give good dV too, but we have to increase the tank fuel mass a little! Why this? For simplification the landers and Deepstar should use the same kind of propellant. I calculated the complet volume of all tanks of one lander with 88.735m³ (for the 8 cylinders AND the 4 spheric ones).
At given density for liquid hydrogen of 71kg/m³ we get:
88.735m³ x 71kg/m³=6300.185kg fuel. At Isp of 8800m/s for solid core NTR we get only dV of 2,520km/s with hydrogen. Thats to less. The biggest airless world at Sol system is Ganymed (mercury to hot) with an escape velocity of 2,7km/s! If the landers should be able to make a landing and fly back to orbit, they need dV of 5,4km/s minimum, logically.
We can reach this target without remeshing of bigger tanks/landers ect.
We use insteed pure LH2 a combination of LH2 and LOX at a ratio of 1:6.
At first we pump pure LH2 to the solid reactor core (sitting in the burning chamber), it will be accelerated there to 8740m/s. But at step two we inject LOX inside the nozzle, this is interacts like a big afterburner then, named LANTR, "liquid oxygen augmented NTR"!
The hydrogen begins really to burn and increases the thrust at a factor of 8,1 !!! But on the other side the Isp will decrease from 8740m/s to 5346m/s. But thats no big problem, because the density of liquid oxygen is so big (1141kg/m³) that we can store alot of it (26.622mT) at our given lander tanks. For our 1:6 ratio need 4,43 mT LH2 at 66,55m³, and 26.622mT LOX at 22,185m³, both together 31 mT fuel. The dV is then 5,172km/s, but we need for Ganymed 5,4 minimum! So i prefer to increase the values a little, for some extra manovers, tank volume to 35mT, that gives us dV of 5,584km/s. Thrust in LANTR 1620000 N.

But there is another maybe better method, better for long time missions and more Isp, if we use pure methane (CH4). Because the high density we can store it for very long time. We got then 88.735m³ x 420kg/m³ = 37268.7kg = 37.27mT fuel mass. Isp for methan at solid core NTR is 6318m/s!!! That gives us dV 6,830km/s. The thrust is 200000-250000N, without Lox LANTR.

You can decide know! But im at travel next 2 weeks, after that i can recalculate CH4-LOX variants allthough. But dont release a update of Deepstar, before we set values for landers new!

my sources:
http://www.nss.org/settlement/moon/LANTR.html
http://www.projectrho.com/public_html/rocket/enginelist.php#Gaseous_Core_Nuclear_Thermal_Rocket_

---------- Post added at 04:06 PM ---------- Previous post was at 02:49 PM ----------

I did new calculations for a pure chemical engine. If we want to use LH2 and LOX, the tanks has to be 1,4 times larger for 47mT fuel -> this would need remeshing.
But if we use methane-LOX, we can store in the given tanks 75,37mT without remeshing and reach about 6km/s dV !!! Thrust would be huge about 1-1,2MN. I think thats maybe the best way? We don't need a nuclear reactor then.
But with an reactor CH4-LOX in LANTR-mode at ratio 1:4 would give Isp of 4304m/s with dV of 6,9km/s, thrust 1288508N.

I prefer the pure methane-LOX chemical mode, but this needs 38,37mT more total mass of the lander against the pure CH4-NTR-variant, but we would prevent extra radioactivity (a NTR would be more and more radioactiv after hours of working, the reactor core has to change then).

What do you think is the best?

 

[Urwumpe]

I would recommend the Methane-LOX version as well - also you save a lot of engine mass there, since the NTR engine as much heavier than a comparable chemical engine. And its doubtful that you can throttle an NTR deep enough for landing - at least not without risks.

An nice alternative fuel is the Ammonia-Etylen mixture, that the Russians currently research. Using LOX as oxidizer, this mixture would be close to LH2/LOX in performance (Lots of hydrogen bound in the molecules, low activation energy), but with only LOX as cryogen liquid, and the fuel would also have a density that is even higher than liquid methane.

Disadvantage would be, that the long-term stability of the fuel is currently unknown. While etylen become pretty tame when mixed with nitrogen-based material (like ammonia), it is pretty nasty and likes to decompose explosively when heated or overpressurized.