Low Power Flight ( and I'm Back! )

[NewtSoup]

I have been away.  Had an intense and torrid love affair with Elite Dangerous - which will only run in Windows.  Most of my games are installed in Linux which meant I didn't play anything else but ED for a few months!

Having had Windows force an update while I was playing ED ( and in combat no less, the digital rug was firmly pulled from under my feet) my system, set up as it is, defaulted to Linux on reboot  so Here I am again! 

To get back into KSP I thought I'd try something in Sandbox before getting back into my proper career mode game  and after killing Jeb on re-entry after a Mun Orbit or 3 using an example ship ( I really should have done some breaking maneuvers, I just didn't realise I had no heat shield ) I decided to see what ion thrusters were all about.  They say they can go anywhere so I built the "Go Anywhere Seat".  It has 19,600 m/s DV.  Enough RTG's to run both ion engines at 50% power indefinitely the solar panels should make up the rest ( I hope )  even so the 1k battery can recharge off the RTG's in deep space if the  sunlight is too little.. here it is in all it's glory with Valentina on the nose in the seat!

 

Now, the thing is, it only has 4kn of thrust.  I thought KER said 0.4 TWR when building which would have been fine and dandy.  However it's only 0.04.  Now I know this thing CAN fly anywhere.  Just how to do it.  For example a minmus transfer orbit is a 46 minute burn.  So I know I'll need to do several burns to increase AP to the desired distance.  What I want to know most though is how do I get encounters when navigating using multiple burns like that?

[Dfthu]

40 minutes ago, NewtSoup said:

  What I want to know most though is how do I get encounters when navigating using multiple burns like that?

I'd guess you would just have to make a couple small maneuvers, slowly moving your orbit.

[Cerberus738]

There is a mod out there that lets you split a large burn into multiple maneuvers. I can't remember what it's called right now. So you plan your encounter with one large burn and then can split it into multiple burns and your encounter should stay the same at the end.

Otherwise you would have to figure out the math yourself.

[NewtSoup]

I guess I shall just have to try it and see.  Because the ship is such low power I'm having to make a number of 5 minute burns at periapsis.  This means maneuver nodes are useless.  My plan is to simply  AP to ~Minmus orbit and then simply wait for an encounter and try to capture into minmus orbit from there.

[IncongruousGoat]

For interplanetary transfer burns, it's usually possible to set up a burn that'll work if done in one go, burn part of it, and then set up a new burn that'll work with your adjusted orbit. For other time-sensitive maneuvers, one way to do it is to work out how long you'll be spending coasting between burns, and account for that when planning. Moving the AP to the orbit of wherever you're trying to go and then getting an encounter from there also works just fine, if delta-V and/or time are not major concerns.

[NewtSoup]

dV is not a concern  I have about 19km/s of it..  I do think however that I should have fitted more than 2 ion engines to a 12 ton vehicle - as I say, I was fooled by a miss read on the amount of power it actually had.

[nathan1]

1 hour ago, Cerberus738 said:

There is a mod out there that lets you split a large burn into multiple maneuvers. I can't remember what it's called right now. So you plan your encounter with one large burn and then can split it into multiple burns and your encounter should stay the same at the end.

Otherwise you would have to figure out the math yourself.

Maneuver Node Splitter

[Wcmille]

I find it easy to burn my way up to a higher orbit where my orbital period is longer. When you get to a spot where 20 minutes isn't a significant arc of the orbit anymore, the burn works normally. You lose some dV this way, but I've been OK with it.

[NewtSoup]

2 minutes ago, Wcmille said:

I find it easy to burn my way up to a higher orbit where my orbital period is longer. When you get to a spot where 20 minutes isn't a significant arc of the orbit anymore, the burn works normally. You lose some dV this way, but I've been OK with it.

Yeah I've just worked this out  to start with my orbital period was just 34 minutes in orbit around Kerbin so I was stuck to 4 minute burns.. 2 mins either side of PE but as the orbit increased I was able to burn for longer.  I think it took 5 burns in total to reach minmus orbital distance and by happy chance a 56m/s burn in 1 day's time will give me a minmus encounter at 1600km, so I will just capture there and decide what to do next then.

The ship does actually have a docking port jr on the rear, so in theory it woulnd't be that hard to cart up a couple more engines, rendezvous in minmus orbit and attach them via the docking port.  Running them at full power WILL overload the solar pannels and RTG's and drain the battery, but that's just part of the fun I guess  the total dV shouldn't change that much for adding 2 more engines a docking port and enough metal work to hold them.

[Wcmille]

7 minutes ago, NewtSoup said:

Yeah I've just worked this out  to start with my orbital period was just 34 minutes in orbit around Kerbin so I was stuck to 4 minute burns.. 2 mins either side of PE but as the orbit increased I was able to burn for longer.  I think it took 5 burns in total to reach minmus orbital distance and by happy chance a 56m/s burn in 1 day's time will give me a minmus encounter at 1600km, so I will just capture there and decide what to do next then.

The ship does actually have a docking port jr on the rear, so in theory it woulnd't be that hard to cart up a couple more engines, rendezvous in minmus orbit and attach them via the docking port.  Running them at full power WILL overload the solar pannels and RTG's and drain the battery, but that's just part of the fun I guess  the total dV shouldn't change that much for adding 2 more engines a docking port and enough metal work to hold them.

I think you'll get the same Isp at partial power, just (even) lower thrust.

[NewtSoup]

15 minutes ago, Wcmille said:

I think you'll get the same Isp at partial power, just (even) lower thrust.

I can check the effect in the VAB.  Just reduce the fuel I have left and add the modifications. See what it does to the dV, It's how NASA would do it.

** Edit, 20 minute burn to capture @ 1000 km,  I'd rather capture wide and be sure of doing it in a single burn than risk going closer and failing to get an orbit.

Edited January 15, 2018 by NewtSoup

[NewtSoup]

I made it to Minmus, captured, burned for a solar orbit and in 163 days I'll be making an 800m/s burn out to Duna.  My first ever Duna trip!  On 2 Ion Engines and a Command Chair!.

[NewtSoup]

just over halfway through a 40 minute capture burn into Duna Orbit.  I may try for Ike too.

 

[NewtSoup]

If I'm reading this correctly -

Will this burn of 19 m/s result in periapsis around Duna @ 174km and then one around Ike at 426km (or Vice Versa )?

 

I mean I can't lose anything by trying it.  I just want to know if my reading is correct.

[qzgy]

1 hour ago, NewtSoup said:

Will this burn of 19 m/s result in periapsis around Duna @ 174km and then one around Ike at 426km (or Vice Versa )?

As I read it, you get an Ike fly-by, PE 426 km which will put you into the Duna orbit, PE 174 km

[NewtSoup]

Ahh of course because the patched conic shows a dotted ellipse around Duna so that can't happen first.  Has to be the Ike Flyby first. 

I shall make that burn. Shortly

[NewtSoup]

I like Ike

 

And Duna Orbit,  Highly eliptical, almost reaching Ike at AP, I've not circularised as I'm still not sure what I want to do next.  Orbit Ike for a bit or get closer to Duna.


 

Edited January 15, 2018 by NewtSoup

[NewtSoup]

I think this is as far as I will take this.  As interesting as the Anywhere Seat is to me.  It's time for Sandbox Valentina to be supplanted by Empress Valentina.  SB will remain in vigilant repose around the planet known as Duna.

[NewtSoup]

And with some final vanity pictres we bid farwell to brave Valentina, courageous Valentina:

 

Who as, she moves into an IkeClipse, can't help feeling that something is also watching her!

Edited January 15, 2018 by NewtSoup

[Fearless Son]

I just wish there was a mod for planning ion engine continuous-thrust trips, but that would involve so many entanglements with the point-thrust transfer planning system and weird interactions with the time-warp feature that I am not sure it could be done in the engine as its stands.  

Because it would be the fastest way to go interplanetary (via direct burns with a halfway flip for breaking instead of long coasting transfers) even if the specific impulse is low.  Which is what ion engines are (theoretically) actually for.

[Kerbal pancake]

On 1/15/2018 at 6:41 PM, Fearless Son said:

I just wish there was a mod for planning ion engine continuous-thrust trips, but that would involve so many entanglements with the point-thrust transfer planning system and weird interactions with the time-warp feature that I am not sure it could be done in the engine as its stands.  

Because it would be the fastest way to go interplanetary (via direct burns with a halfway flip for breaking instead of long coasting transfers) even if the specific impulse is low.  Which is what ion engines are (theoretically) actually for.

skiddle skidish i have granted your wish

https://spacedock.info/mod/961/MechVal

is is for 1.1.3 though but it might work

 

Edited January 17, 2018 by Kerbal pancake