Flieger, grüß' mir die Sonne, grüß' mir die Sterne und grüß' mir den Mond. Dein Leben, das ist ein Schweben, durch die Ferne, die keiner bewohnt! - Hans Albers, F.P.1 antwortet nicht (Adaptation in the 80s: Extrabreit)

Friday, 17 July 2015

Some more Minmus launches

For some time, I read a bit about the mathematical background of rocketeering. In an earlier blog entry back in April, I already tried to get a grasp what the figure of "deltaV" is about. During my extensive design, I always wondered, how can I eyeball a bit better what engines and the amount of fuel is needed in order to reach a given target with a given payload.

I took some of my questions into the game forum and got some helpful tips, which I translated into a spreadsheet. I also got the hint that a somewhat interesting youtube-gamer made a very nice video to connect the player of Kerbal Space Programme back to good old school physics. Basically, it is about being able to roughly plan which engines and how much fuel you have to take with you if you want to bring a certain payload mass to somewhere else, the distance to be covered being expressed in a deltaV figure (because, if I understand this stuff correctly, in space, traversing a distance is more about achieving a different level of kinetic energy or speed, in relation to the local dominating gravity wells i.e. big chunks of matter i.e. planets and moons and rocks).

After having found the correct formulas and playing around with the spreadsheet, I find that it gives me a good idea about relations, but I am not playing that precise enough to really design a ship by a spreadsheet.
I guess the most useful aspect for me is going to be to estimate when a switch from a conventional engine to a nuclear or ion engine, once I have them available, would make sense. In all other cases, I do not really need a precise calculation; my main "fault" so far has been that I misestimated the deltaV requirements, so I try now to overengineer my vessels, anyways.

Back to Kerbin. It is t-2 days towards "busy day". And again, I have discovered plenty of additional occasions, so again nono to timewarp, and here is a little picture story instead, which is mainly about the launch of some Minmus focused operations.

- the Münbus docked with the White Goose for refuel, then with the Tripol, and is now burning for Minmus (forgot to refill the monopropellant, but still 50% capacity will hopefully do)

- an eternal burn for Minmus of 8 minutes, due to only 0.25 TWR of the combined vessel; there is probably not enough dV left, so it is better to just do a flyby and drop off the Tripod

 - the White Goose V2 has taken over some science points from the Tripol (the LKO gravity measurements)

It is now time to try to get the White Goose V2 back on Kerbin; the problem still is that I forgot to install airbrakes. In order to compensate, I pump all fuel to the frontal tanks. I want to try to brake by flying an upward angle of attack, but this requires a forward center of mass, lest the plane would easily flip over at those high speeds.

re-entry without airbrakes thankfully works out

The re-entry works out in the end, but still not as planned or anticipated. My electricity runs out while I try to keep an air-braking angle of attack ("AoA", a cautious +10 degrees to prevent it from flipping over). Thanks to my forward center of mass, the plane continues to fly prograde all by itself. Then, thankfully, the turbo engines kick back online without needing charge and they produce sufficient electricity to regain control. So, in the end, the plane survived the high re-entry speed even without needing airbrakes or my "high angle of attack" steering. I guess I am lucky that the Kerbal Space Programm goes very easy on the player rooky with its atmosphere flight mechanics.

A second tense situation arises during the final landing approach. I almost crashed when I approached too high and dipped my AoA to -25 degrees; the control surface could not handle re-aligning to 0 degrees. During the last seconds, I remembered and managed to pump all fuel from the front tanks to the aft tanks; this kind of trimming shifted the center of mass backwards enough for my control surfaces to get a grip again.

- very glad to have made it; bringing back 108 science points and some unused fuel

My science point account now alows me to unlock the 300-point tech node for the ore scanner. I feel that I should test that thing and probably bring it then along to my Duna mission. Which means that I should quickly prepare according missions, lest the launch window to Duna is gone. So, I construct a satelite with that hughe dish on it. There is no good way to maintain an upwards mounted docking port, so I will have to think about a different way to transport this satelite. But for now, I only want to launch and test a basic setup.

- the Ore Scan Sat fits barely into the Cargo Shuttle´s bay...

With no more room for docking clamps, ejection is going to be done via a small separator, even when there is no room to really get pushed foward. I hope that the game mechanics will be forgiving. As a sideline, I also adapt the Cargo Shuttle´s engines and wings to patch 1.03´s modified atmospheric model. It flew well already, but it had still the old 150-fuel tanks instead of the revamped 400-fuel tanks.

 - moment before the moment of truth


Thankfully, the ScanSat survives the harsh forces and clips harmlessly out of the Cargo Shuttle.

- cannot scan unless in polar orbit; good that I tested this and found out before plotting an orbit for Minmus

The ScanSat is ready to leave for Minmus... until I discover that I forgot to put a regular antenna on it, too (that big dish is only for ore scanning, after all!). Reloading the whole launch (which I find myself doing quote too often it seems!), then finally the emptied Cargo Shuttle is ready for re-entry and the ScanSat burns for Minmus.


- ready to leave the scene

This ends a very Kerbal typical game session, a lucky one, because only one re-load was needed for that forgotten antenna, and I even avoided a near-crash of the White Goose V2.

Next session, I hope to complete and to detail a bit more my new ideas concerning the Minmus missions.

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