Review: The Wolverine

Pretty good for a comic book movie. Not knowing the cannon made it easier to follow without guessing what will come next. Plot holes can be handwaved away with the "its a comic book" excuse. The credits teaser had problems.


Ionic Mk.3 Arrives At Dres

Mission log:

(MET Day:Hour:Minute; IB=Ion Burn #)

285:06:24 IB17  +2h11m Match orbital speed with Dres 1693m/s

  • Gigantor performance at 35.5Gm: 14.79 -- so a single one is sufficient to drive an ion engine at least out to Dres.
  • We are 500Mm away from Dres.  I think this means we pooched the Hohman intercept.  On the other hand that's like a 1.3% miss.

351:12:50 IB18: +3m15s 45m/s adjust intercept orbit

  • Closest approach will now be 7Mm in 1y 12d.

594:18:04 IB19: 7m 35s, 99.9m/s Set up for Dres encounter

  • Encounter Periapsis currently at 700Km.

The tiny dot just above the probe is Dres

992:14:28 Dres encounter. Encounter periapsis set for 580km.

Orbital Insertion

994:10:10 IB20: 5m52s, 78m/s -- insertion into 600x10000km orbit around Dres

994:10:17 Engine shutdown, welcome to Dres.

Engine shutdown, welcome to Dres

So aside from there being a lot of waiting for ion burns and for planets to get into the right position, that was an interesting exercise.

Now I have to decide what to do next. Probes are interesting, but I have a desire to do a lander again.

On the other hand, we still have 4800m/s of delta-v available in the Mk.3.  Maybe we should try to push it out to fly past Jool.


Isn't it Ionic?

...just a bit.

So with the wrapping taken off of 0.21, I decided to play around with ion engines this time around.  Why?  Well, I still have a mental block about killing Kerbals, so I'm reluctant to play with "manned" missions.  This does rule out a lot of the potentially fun stuff.  So being the contrary so-and-so you all know, I decided that I'd pick something that I don't read about much in the G+ group.  I'd like to do something new, rather than trying to repeat what others have already done.

And so: probes with ion engines.

The original title of this article was Ionic Mk.3, from which you can infer there was a Mk 1:
Mk 1: Fancy girders.
...which got sent on a deep space mission to Eeloo for the usual no good reason that I'd watched a video about someone going there.  Somehow the upper stage of the rocket I assembled had the Delta-V required to inject into a transfer orbit and to circularize out there.  Once an intercept was set up, the upper stage was discarded, and I discovered that the solar panels I had put on were insufficient for the task of powering the ion engine way out there.  After the Eeloo flyby, I set up an intercept with Jool, but I only get about seven seconds of ion run time out of the batteries before I have to charge, and a quick back-of-the-envelope calculation showed I'd need about 50 of these to get the required five minute burn needed effect the Joolian intercept.  Now JPL can do this, but I estimated this would take three or four of my real hours to do this since there doesn't appear to be a programmable automation system -- what I'd need would be "fire engines until charge is down to 10 units, then turn engines off until fully recharged.  Repeat all that until the required delta-V was effected."  This didn't seem that interesting to me, and I abandoned it.

So it is still floating out there, but unused.

And of course there was a Mk.2:
Flashy flashy.
This time I exploited a clipping problem to stack two ion fuel tanks inside the battery pack, and attached the ion motor to the base of that.  So it is a lot more compact than it might otherwise be.

And, being an inquisitive KSPer, I've watched the Kickstart video for the micro-ion satellite kickstart.  And that animation showed how you gain escape velocity with an ion engine: very slowly.   As you pass your periapsis, you burn the ion engine briefly to push the apoapsis out a bit more.  And you repeat on the next orbit.  And the next. And the next. And (you get the idea) the next.

I picked a three minute burn for the usual no good reason.  That gives me a burn at 1m30s on either side of periapsis; I'm sure some detailed math would show what the ideal burn length time was, but I don't know how to do it.

So, for ten or eleven times, I did this:

A bit more this time, please
I flew the first three or four totally manually.  I tried to just point the probe in the direction of travel for the whole burn, eyeballing the MET clock.  Probably not the most efficient way to get around.

After doing this a few times I did figure out how to get MechJeb to help -- I set up the maneuver node manually, adjusting the thrust so that I had three minutes of burn time.  Then I told MechJeb to fly the next node.  So MechJeb would warp to the node, orient the probe, do the burn, then return control to me.  So it was tedious, but doable.

Then eventually the elongated orbit (I'm sure there's a fancy name for this type of operation) crossed the Munar orbit, and something wonderful happened:

Step up and claim your free ejection. 
The Mk.2 return's swing back to Kerbin brought it past the Mun, and suddenly we got a free ejection from the Kerbin sphere of influence.

Well I'm not one to say no to a free ejection... but as you can see the trip past the Mun was actually through the Mun.  Fortunately a lateral ion burn corrected that problem.

Making a close approach a little less close.
...and just to show off, I made the closest approach 10km from Munar datum.  (I didn't have the nerve to make it any closer.)

Sorry, Ghostrider, the pattern is full.
So now I've got it ejected from Kerbin.  I didn't want to go into deep space because Mk.1 showed me that the ion engine might not work well out there -- even though the Mk.2 has way more in the way of solar power collectors.  So I tried to go down instead of up.  Eve is the next target, so I settled on getting into an equivalent orbit.

Problem is I'm totally in the wrong place.  What I need to do is change one of my -psis'es a Gm or so and then wait for an appropriate encounter.  Well that'll take time, so I've pretty much left that one as is as well.

So for today's exercise I decided to add lots of Ion Fuel, just to see if it would be usable.  So this is the Mk.3, which only has one light, and has eight Xenon tanks instead of one or two:

Beauty shot.
Navlight for the usual stupid reason that if I have to look
at this for hours, I want it to be visually interesting.
Eight ion fuel tanks, one ion engine.
Lots of waiting.
The Mk.3 reaches orbit with about 10300m/s available Delta-V from the ion engine.

The launch process is pretty straight forward too -- fire the first stage more or less straight up as high as it will go, then circularize with the second stage at apoapsis.

Also interesting is that I've been flying these launches manually again rather than letting MechJeb do it for me. I've gotten to the point where I can get these things into orbit pretty much every time, and pretty much with an inclination of less than a couple of degrees.

This time I was more rigorous about the flight process, and wrote a log of the maneuvers and events encountered. I also changed the ion burn time to five minutes and used MechJeb for all of them. I threw away the launch upper stage after circularization -- everything after that has been done with the Ion engine.

Each Ion Burn was five minutes, and each time was 61.8m/s in Delta-V.

So I can say with authority that this was Ion Burn #14, that started at MET+2d8h44m, and lasted 1m20s:

Planning our escape.

This time the Munar periapsis was a more head-room friendly 124km.

Munar Periapsis, or thereabouts.
Kerbin rises for the last time.
And presto, we have escape at MET5d9h20m.  Doing the math from the recorded ion burns, I used up 760m/s to escape Kerbin from an initial orbit altitude of 197km.  We end up in good position, too, with the solar periapsis less than three days away.

So, having spent a couple hours of real time doing that, what should I do with my 9400m/s of available Delta-V?  I try some example nodes to estimate what the cost would be to go to Duna, Dres, and Jool.  

My back-of-the-envelope calculations have Duna costing 1500m/s; Dres costing 5000m/s (including the plane change); and Jool costing at least 5500m/s plus a plane change.  After considering these factors, I decide for Dres because:

  • Everyone goes to Duna, it is a cliche -- a well done cliche, don't get me wrong, but I want to do something different.  And most people go there with Kerbals, me flying by with a probe isn't likely to impress anyone, not even me.
  • Encountering Jool will be harder because of Jool's increased gravity and complex moon system.  Things happen faster in a high gravity field, and an ion engine is pretty slow.  Also we're getting out in the sticks again where the ion engine might not work well in the first place.  Put it all together and there is a good chance of a catastrophe.
  • I can't remember anyone doing a mission to Dres.  So it will be new to me.
Dres it is!
Therefore, we'll do a Dres flyby and see what targets offer themselves afterwards.  If we do it right we might get a gravity assist to Jool or back to Eve.

And that's where I've left it for now.  I set up a 1h10m change-of-plane burn while I was writing this monster post up, and so I'll probably let that finish and then stop for today.

So, a couple things I've learned, in no particular order:

  • The ionic burn point (periapsis, but can be anywhere on the circular initial orbit) should be either at orbital dusk or orbital mid-day.  Mine was orbital dawn, and dawn kept getting closer and closer to the burn time.  On ion burn 11, it was about 90 seconds before the burn started, rather close when you need the sun to burn.
  • The MechJeb doofus seems to want to be placed on the right (starboard) side of the craft with the antenna pointed in the desired direction of travel.  Otherwise, the gimbal won't match reality.  (I thought I had a screenshot showing the gimbal level and the solar panels at 90 degrees, but I don't.)  My first try for the Mk.3 had the MechJeb on the top/front of the probe; but the gimbal was totally out of whack so I moved it back to the belly (opposite the radio dish), which is where it was on the Mk.2.  During one of the long periods between burns I played with the Mk.3's physical orientation to figure out where MechJeb really wanted to be.  We'll have to try that next time.
  • When doing long burns, check in on the non-map view periodically to make sure your solar panels are still getting good sun exposure.  Otherwise, the engine might stop.
Oh, the change-of-plane burn finished.  The Hohman intercept burn will take almost two and a half hours to make the 1700m/s velocity change.  I'll set that up and let it run.


Review: Elysium

A little excessively violent and gory at times. A bit too much "District Nine" for me, but that is probably because we'd just watched that the night before. Worth watching, but not a DVD buy.


Review: District Nine

Slide between faux documentary and drama was jarring. High on the violence/gore spectrum for me. Interesting ideas, especially since they were not really explored.