Author Topic: Advancements in Electric Thrusters  (Read 104512 times)

Offline tea monster

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Re: Advancements in Electric Thrusters
« Reply #140 on: 04/22/2015 10:33 pm »
I've given her 8 double-length megaROSA arrays, that should be able to deliver about 250Kw.

Offline Robotbeat

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Re: Advancements in Electric Thrusters
« Reply #141 on: 04/22/2015 11:48 pm »
I've given her 8 double-length megaROSA arrays, that should be able to deliver about 250Kw.
That's what I'm talking about.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Offline tea monster

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Re: Advancements in Electric Thrusters
« Reply #142 on: 05/05/2015 08:34 pm »
Got a rough out of the ion drive ship. The Bigelow module is complete. I've roughed out a logisitics/docking/airlock module. I've morphed the base of the probe into a propulsion module.

I may have over-loaded her on propellant and consumables :D.

Texures, apart from the hab, are all WIP.

Offline RonM

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Re: Advancements in Electric Thrusters
« Reply #143 on: 05/05/2015 08:40 pm »
Got a rough out of the ion drive ship. The Bigelow module is complete. I've roughed out a logisitics/docking/airlock module. I've morphed the base of the probe into a propulsion module.

That's great! Looks like a practical design to me.

I may have over-loaded her on propellant and consumables :D.

Forget Mars, we're going to Titan.  :)

Offline tea monster

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Re: Advancements in Electric Thrusters
« Reply #144 on: 05/16/2015 09:26 pm »
I realised that for Titan, I'd need a different power source - I'll be getting to that, and I'll probably do a few renders!

Just for now, here she is en-route for Mars.

Offline tea monster

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Re: Advancements in Electric Thrusters
« Reply #145 on: 07/17/2015 04:06 pm »
I've finished up the ship. I've given the SEP module some radiators.

Offline Impaler

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Re: Advancements in Electric Thrusters
« Reply #146 on: 07/17/2015 05:02 pm »
I think you drew a bit too much from.. dun, dun, dun, duun, dunn, DUUNN...




The long central tank section makes no sense (in 2001 the aft drive section is nuclear so they are keeping the crew as far away as possible), the tanks are volumetric inefficient and their is tons of structure which can be omitted, no to mention it is too long to fit in any kind of payload fairing.  A short plump tank segment (it can be a cluster of multiple long lozenge tanks rather then a monolithic tank) would make much more sense.

Also I don't think the solar panel area is remotely large enough given the number of thrusters present and mass being moved, as thouse look like the X3 nested Hall thruster, each one would be 200 kW, you would need MW of power for that many thrusters.

The landers are just simple cones and look like placeholders, if this is your intent then fine but I think significant improvement would be needed to get the final look.

Solar panels should be rotated to point to the rear, the thrust of a SEP vehicle is always in the plane of travel which is on the elliptic (the plane of the planets around the sun), this means you would never get the 90 degree angle between the thrusters and panels you have depicted.  Conversely the radiator SHOULD be at 90 (as you have it) to minimize the light hitting it.

I have some concept designs for a large SEP cargo hauling vehicle if your interested in taking a stab at illustrating it.
« Last Edit: 07/17/2015 05:13 pm by Impaler »

Offline Paul451

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Re: Advancements in Electric Thrusters
« Reply #147 on: 07/17/2015 07:19 pm »
Solar panels should be rotated to point to the rear,

Solar arrays on a SEP would never be pointing directly to the rear. A SEP'd ship is never thrusting directly away from the sun, it is always thrusting tangentially to its current orbit, hence they'll have the orientation Tea Monster has. (Well, I say "never", but during orbital manoeuvres, the orbit is centred on the planet, so the drive may sometimes be coincidentally pointing away from the sun.)

However...

Tea Monster,
The whole ship should be rotated 90° around its thrust axis. If you look at Mars, the angle of the sun is obvious. The panels should therefore be facing to the right of screen in image "01a". (Or the background image should be rotated 90° left, which is probably easier from your point of view.) And I'd put the two radiators on the same side, one running off each panel. That way they're always in the shadow of the arrays. With your arrangement, one of the radiators is always on the sun-side.

Also, the scale of the capsules doesn't gel with the rest of the vessel. Capsules are never wider than the width of their launch vehicle. The SEP drive module is also wider that the obvious launch vehicle used for the rest of the components, although not as bad as the capsules.

Since a Bigelow module's rigid core is roughly the width of its launcher's payload shroud, minus a bit of clearance, that sets your typical component width.

The fuel tanks would likewise be the same width, but probably individually longer. Similar length to the Bigelow. (Probably three cylinders in a cluster, rather than six spheres in a line.)

Of course, it gets more complex than that once you start trying to put together a realistic launch/mission narrative. Does the launcher have a flared payload shroud or a straight one? Are the tanks part of a larger non-aerodynamic assembly (so launched inside a payload shroud), or are they built from the launcher's second-stage mold-lines (so launched without a payload shroud, full width of the launcher), or are they built to maximise volume (the external width of the flared payload shroud, wider than the launcher, thus the widest part of the SEP-vessel)...? Are the parts all launched on the same launcher? Are all parts bespoke for this mission, or are they LEGO'd from other designs. For example, is the SEP section a pre-existing SEP-tug repurposed for the mission, or custom-built for this mission? Is each major component launched intact, or are they launched as sub-assemblies and built in LEO?

Impaler,
When you start asking these kinds of questions, Discovery One is also a pretty rubbish resign.

[not] to mention it is too long to fit in any kind of payload fairing.

The truss implies on-orbit assembly. (Although that's inconsistent with the length of the Bigelow module. You aren't going to launch multiple individual fuel tanks smaller than the Bigelow.)

Offline tea monster

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Re: Advancements in Electric Thrusters
« Reply #148 on: 07/17/2015 09:14 pm »
LOL, it does kind of look a bit like the Discovery! I wasn't aiming for that look though.

Some of my thoughts for this design are:

1. Bigelow modules would be much more nicer to live in than some of the hab concepts I've seen (apart from SLS stage-derived modules). If I were going to Mars and it was going to take around 8 months, I'd want at least some elbow room. Spending 3 years in something the size of a camper van is just not something I want to think about. This is ignoring whether NASA would actually use a Bigelow module.

2. A lot of designs I've seen don't have any kind of logistics module. If you look at the inside of the ISS, it's incredibly cluttered. Stuff is just everywhere. You are going to need to have room for a lot of equipment for a trip to Mars. Especially EVA equipment. Suits are very bulky and you may need to take certain equipment into the ship for possible repairs. This is going to require a fair sized airlock. Also, you will need docking collars for the landers. It would make sense to incorporate these into one large 'space garage'. You could also put the spare parts, 3D printer, stores etc. into this module and have more living room in the living quarters.

3. The fuel tanks are within a modular truss structure. My mathematical skills aren't great, so I have guestimated how much propellant and other consumables will be required for a mission to Mars. This could be wildly out. It also depends on how fast you want to get there. If you are happy to spend 8 months in transit, then you would probably need a lot less propellant. If you are impatient like myself and your pilot will seriously consider putting you out the airlock after 1 month of asking "Are we there yet?", then you will want more propellant so that you can shift your Halls into high gear and get there faster. Again, I am hopeless with such calculations so I have guestimated the amounts required.

The 'back story' is that the modules are kept at a Lunar Lagrange point station. A mechanical arm on the station would assemble the different sections into one ship. That way you don't have to do the long spiral thing from LEO and you can mix and match modules depending on what sort of mission you are doing. Tanks can be refilled with arms and balky modules can be put into a repair airlock. The idea is that you would build your ship out of these components, sort of like a train being constructed from different carriages. If you wanted to shift more cargo, or wanted to travel to Jupiter instead, you could slot in a few more modular tank units. That way, you could have an established infrastructure for exploring not just Mars, but other interesting places in the Solar System. It was only after doing those illustrations for Redilox that I was introduced to the idea of a SEP tug, which sounds like a better idea generally.

4. You are right on the sizes of different objects. As a graphic artist, I've varied the sizes of the modules for visual effect. The SEP module is offered here as a custom unit.

5. The solars are based on MegaROSA units that are under development currently. Someone else earlier in the thread came up with the figure of about 200Kw to power that amount of 3X Hall thrusters. I worked out (I was very proud of myself!!!) that with the power to area ratio of those arrays, that the units on the model ship should give you about 360 Kw.

6. The landers are based on the old MEM design. A lot of Mars lander designs seem to have that same basic conical shape. I have done some more detailed ones for Redilox, but I didn't want to crib them here. Also, my focus was on the ship itself. I wasn't sure what lander design to go for either.

Impaler - Yes, I would be interested in seeing those designs.

Thanks for the input guys!

Offline tea monster

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Re: Advancements in Electric Thrusters
« Reply #149 on: 07/17/2015 09:28 pm »
As to the general design. I kind of followed this template. I've seen several NASA concepts of various space vehicles that follow this general theme.

Offline Paul451

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Re: Advancements in Electric Thrusters
« Reply #150 on: 07/18/2015 12:19 am »
As to the general design. I kind of followed this template. I've seen several NASA concepts of various space vehicles that follow this general theme.

The lack of solar panels suggests they're using a nuclear reactor for electricity. Hence the need for a truss to distance the crew from the reactor. (The lack of radiators is less explicable.) Although the engines look chemical, so it's neither NEP nor NTR.

However, notice the relative width of the capsule and the Bigelow in that image? That's much more realistic, IMO.

Offline A_M_Swallow

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Re: Advancements in Electric Thrusters
« Reply #151 on: 07/18/2015 12:28 am »
For a human rated system the Federal Aviation Authority (FAA) will almost certainly want the critical systems duplicated. That covers air tanks, water tanks, fuel tanks, thrusters, valves, solar panels and radiators. Like the ISS these are subject to frozen pipes and micrometeorite damage.

Offline Nilof

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Re: Advancements in Electric Thrusters
« Reply #152 on: 07/18/2015 09:41 am »
As to the general design. I kind of followed this template. I've seen several NASA concepts of various space vehicles that follow this general theme.

This looks like the NTR stage that was proposed as the NTR option in the DRM 5. It has a liquid hydrogen drop tank, the truss between the payload and the back tank is its framing, which also gives some extra distance from the NTR engines and allows the thing to be spun up while coasting.

A SEP craft would have much denser fuels and does not have any dangerous components that it needs to keep the astronauts away from. Spinning up the ship for artificial gravity is most likely not an option with large solar arrays, so if AG is used it would be with a Nautilus-like centrifuge.
« Last Edit: 07/18/2015 09:48 am by Nilof »
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline Impaler

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Re: Advancements in Electric Thrusters
« Reply #153 on: 07/18/2015 05:20 pm »
Solar panels should be rotated to point to the rear,

Solar arrays on a SEP would never be pointing directly to the rear. A SEP'd ship is never thrusting directly away from the sun, it is always thrusting tangentially to its current orbit, hence they'll have the orientation Tea Monster has. (Well, I say "never", but during orbital manoeuvres, the orbit is centred on the planet, so the drive may sometimes be coincidentally pointing away from the sun.)

Impaler,
When you start asking these kinds of questions, Discovery One is also a pretty rubbish resign.

The inappropriateness of Discovery One was my point.

As for orientation of solar your thinking mainly about the spiraling around planets in which yes the thrust is always tangent to the expanding circular orbit.  But I was assuming his vehicle was in heliocentric phase of the journey which dose not obey this rule.  That thrust vector will swings through an arc from towards the sun to away from it as the vehicle brakes into Mars orbit (this assumes a high speed trajectory).  The arc remains in the plane of travel so relative to the thruster the panels should be on rotational joints that allow the panels to remain pointed towards the sun as the thruster 'spins' in an equatorial fashion.

Offline tea monster

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Re: Advancements in Electric Thrusters
« Reply #154 on: 07/18/2015 05:53 pm »
I can crank them back a bit. You are right, they wouldn't be pointing directly upwards.

That was an NTR design, but there are loads of different ships with generally the same plan design, even though they are using different power sources/propellants/drives.

I found this one of Boeings latest SEP tug. I'm not an engineer, but does it really need all that trunking? Wouldn't it be better to extend the arms and then bring the SEP module and the hab together?

The reason mine has a longish trunk is that I've filled it with fuel and consumables.
« Last Edit: 07/18/2015 05:53 pm by tea monster »

Offline A_M_Swallow

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Re: Advancements in Electric Thrusters
« Reply #155 on: 07/18/2015 07:51 pm »
{snip}
A SEP craft would have much denser fuels and does not have any dangerous components that it needs to keep the astronauts away from. Spinning up the ship for artificial gravity is most likely not an option with large solar arrays, so if AG is used it would be with a Nautilus-like centrifuge.

Alternatively put the solar arrays on a slip ring. Generate gravity by spinning the engine and fuel module in one direction whilst spinning the crew compartment in the other direction. Each of the 3 sections may need its own radiators.

Offline A_M_Swallow

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Re: Advancements in Electric Thrusters
« Reply #156 on: 07/18/2015 08:01 pm »
{snip}
I found this one of Boeings latest SEP tug. I'm not an engineer, but does it really need all that trunking? Wouldn't it be better to extend the arms and then bring the SEP module and the hab together?

The reason mine has a longish trunk is that I've filled it with fuel and consumables.

If you can think of a way of getting rid of the trunking please show it.

Limitations:
To follow the sun the solar panels need to rotate through 360 degrees without hitting anything.
The hot exhaust plumes from the thrusters must not hit anything, especially the solar panels.
For maximum power the solar panels should not be in shadow.
Where as for maximum cooling the radiators should be in permanent shadow.

Offline tea monster

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Re: Advancements in Electric Thrusters
« Reply #157 on: 07/18/2015 08:42 pm »
Extend the arms for the solars out farther on booms so that they clear the mass of the Hab and lander.

You are putting your solars out on longer arms, but you are saving the mass of all that thick, heavy trunking.

How much propellant would you need to get that much mass to Mars? Say you want to make a fairly fast transit.

Offline Archer

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Re: Advancements in Electric Thrusters
« Reply #158 on: 07/18/2015 09:28 pm »
Put the thrusters in front of the ship, so they would pull the ship (like a train locomotive) instead of pushing. You can save a lot of weight by avoiding making the ship rigid.

Like this:
« Last Edit: 07/18/2015 09:31 pm by Archer »
The future is better than the past. Despite the crepehangers, romanticists, and anti-intellectuals, the world steadily grows better because the human mind, applying itself to environment, makes it better. With hands...with tools...with horse sense and science and engineering. (c) R. A. Heinlein

Offline Hanelyp

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Re: Advancements in Electric Thrusters
« Reply #159 on: 07/18/2015 10:13 pm »
Putting thruster up front you also have some cosine losses from not pointing directly aft.

 

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