# [UNOFFICIAL/FANMADE] 0.17 Discussion Thread 3

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I like the Idea of the NERVA.

So much energy we can bring up in orbit now.

(Energy = Total Movement Change / Fuel) (ms^2/kg)

So ISP 800 m/s means 800 Ns/kg or 800 Newtonseconds per kg fuel)

A Newtonsecond is about 1 meter and 1 kg per second movement.

If we apply that to TMC (weigth assumed= 1kg) we get 800 meters per second

So the small tanks have about 300 units of fuel (300 kg assumed)

Applied to Fuel and Calced: 8/3 ms^2/kg ~ 3 ms^2/kg

Means this engine would move 1kg (hope its right) at a velocity of 3 m/sÃ‚Â² per kg fuel.

I think that is good.

Your formulas are correct,but remember that 1t = 200l of fuel

So so 1l = 0,005t = 5kg

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How bad will that high ISP of the NTR be offset by the low TWR for interplanetary transfers? It does have a bit worried. I certainly wouldn't use those engines for landing though, especially not in an atmosphere.

Low TWR isn't a problem for on-orbit maneuvers. In fact, I kind of prefer it, as it's easier to hold the craft on-course for a longer burn... which seems counter-intuitive, but it does make sense if you think about it. Yes, you have to control the craft's attitude longer, but the effect of any errors are minimized because you have more time to react and compensate for them. A powerful but short burn may be over before you realize you are just a little bit off your intended trajectory, necessitating a second correction burn.

The only time you really need a high TWR is take-off. And I wouldn't use NTRs for a lander, either, unless on a small, low-gravity object with minimal or no atmosphere.

Edited by RoboRay

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How bad will that high ISP of the NTR be offset by the low TWR for interplanetary transfers? It does have a bit worried. I certainly wouldn't use those engines for landing though, especially not in an atmosphere.

I'm not sure if your question makes sense. The TWR is not dependent on the ISP.

We already know the thrust and the ISP of the NTR, and the TWR will be directly dependent on the weight of your ship. The lighter the ship, the higher the TWR.

But you're right, the low atmospheric ISP makes it unsuitable for atmospheric use. However, if you're landing a small ship on a moon without air, it might still be a viable option, given you have enough thrust.

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Wait a second! What's that down in the right, behind the created by bar?

It's a weight icon, similar to <a href="http://www.ergotron.com/Portals/0/Products/icon_weight.jpg">this</a> one, but with a circle in the middle of it patterned like an attachment node. I'm guessing toggles the visibility of the centre of mass indicators.

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Has it been announced what the new part on the left is? I don't recognise it.

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Has it been announced what the new part on the left is? I don't recognise it.

It's probably a 2 meter RCS tank.

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I personally wouldn't use it on a lander stage. To develop a similair thrust to the large lander engine would require you to use two Nuclear engines giving you 0.5 more tons and 15 less thrust on your lander stage. This will translate to more fuel being needed in your earlier stages. If the amount of fuel you save by going with the nuclear engines to land is less than that you gained in your earlier stages then you are actually losing in efficiency.

That being said, I believe that the nuclear engines have fit into a niche which was really needed, inter-planetary engines.

Personally I think for no atmosphere landings we will need no more than what we have as landers right now. For atmospheric entries, I plan to use a mixture of aerobraking, parachutes, and mini SRB's with an lv-45 engine for control when landing. And maybe that same engine plus the non-gimballing ones for take off.

I think a second ship, piloted by one kerbal will be waiting in orbit to get our Duna heroes back home.

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I find it harder to pilot a ship with a low accelaration: for instance, at 0,3 m/s^2 (medium sized ship with 1 ion thruster from mmi satellite pack), the munar injection burn has to start before the launch phase angle is reached: if you don't, the ship takes so much time to accelerate you miss the mun.

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I cant wait to compare my current design for an interplanetary orbiter to a new one with these NTRs. I'm sure the NTRs will allow for a lot more variation in design.

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Wait a second! What's that down in the right, behind the created by bar?

It appears to be a purchase button. Shopping bag symbol. I guess we need to start making spacecraft budgets!

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2 qustions, will there be a new (bigger) tri-coupler?

And whats so special about the new atomic engine, is it extremely powerful or something?

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It's probably a 2 meter RCS tank.

You're probably right.

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2 qustions, will there be a new (bigger) tri-coupler?

And whats so special about the new atomic engine, is it extremely powerful or something?

The NERVA uses thermal energy, generated by radioactive decay, to increase the exhaust gas velocity of the engine. The long and short of it: these engines can use less fuel for the same amount of work. The downside is that they are heavy, and inefficient in atmospheric conditions. Plus, they are a radiation hazard.

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Wait a second! What's that down in the right, behind the created by bar?

It looks like a weight-symbol for me... Maybe a button for switching between showing CoW, CoD, CoT,... ?

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If you zoom in really close, it's a weight symbol. On it is a circle with opposite quarters coloured yellow.

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If you zoom in really close, it's a weight symbol. On it is a circle with opposite quarters coloured yellow.

You are right! there are three buttons, one on top of the other. Must be to turn on the CG, CD, CT representations.

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You are right! there are three buttons, one on top of the other. Must be to turn on the CG, CD, CT representations.

I only noticed the bottom one, thanks for pointing that out. Yes, it must be something like that.

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It's probably a 2 meter RCS tank.

It's part of the Deep Space pack, actually.

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In that latest map of the stellar system, it looks like Moho's orbit is nowhere near circular. Does that mean that it won't be tidally locked? Realistically you need circular orbit to be locked.

The idea of having it molten over one entire side would be a bit silly if the magma sea kept drifting over to the cold side.

No, that should just mean, if it is true, that it would librate like our moon does (wobble back and forth, exposing a bit more than half of its surface area to the scorching rays of Kerbol).

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When the update comes out, which body will be the easiest to land on, other than Kerbin (+moons)?

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I'm going to guess that it'll be Ike (moon of Duna) or Gilly ("moon" of Eve). The lower gravity and lack of atmosphere or both will make the landings easier...there is probably a problem with getting to them. Whether or not you want to try a direct approach or enter orbit around the parent and then translate to them. But that's orbital issues.

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Gilly will probably be the easiest to land on, getting there however will be more difficult, especially as that moons soi will be pretty small

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Which is smaller, Bob or Gilly? I cant tell from the diagrams but I am exited about the small one as it will likley be oddly shaped like phobos.

Edited by zpox357

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I actually think Ike is easier to land on than Gilly, as Gilly's gravitational force is to weak to hold your vehicle on the ground securely. It will be quite easy to propel yourself out of Gilly's SOI accidently.

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I'm going to guess that it'll be Ike (moon of Duna) or Gilly ("moon" of Eve). The lower gravity and lack of atmosphere or both will make the landings easier

I feel that atmospheres will make landings far easier. Parachute-assisted powered descents seem trivial, from my experimenting on Kerbin... the chutes hold you in a proper attitude and you only need to burn to keep your decent-rate down to a safe level. You sacrifice some precision on picking your exact touchdown point, but unless you are trying to set down right next to a specific object it's no big deal. And you save a lot of propellant.

Edited by RoboRay

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