Orbiter-Forum [Challenge] Rescue in Antartica (paper, pencil and a calculator)
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 12-06-2011, 01:54 AM #16 dgatsoulis Orbinaut Quote: Originally Posted by Tommy  BTW, how did you get the ascent autopilot to accept a heading with over 2 digits? I'm sorry, I probably didn't understand the question very well, in my previous reply. The PRO904SPECxxx (hover take-off) and the PRO903... (normal take-off) autopilots, accept a 3 digit format for the heading. Writing PRO904SPEC090 is the same as PRO904SPEC90. Quote: then i waited untill the speed was over 500 m/s My comment was about the slight correction that was needed after the take off. Quote: Originally Posted by Tommy  It would be interesting to know how long it took you to complete this, I took 1:45, with 7 minutes on the ground at the crash site. With a bit of practice I could easily shorten that up with more aggressive braking. Very similar to yours. I think it was about 97 minutes, with 3 minutes on the ground at Antartica. Quote: Originally Posted by Tommy  There will be a couple of "tricks" in my pdf, ways of using MFD's in ways they weren't really designed for, that will help you with that. The first flight is still pretty tricky. This will be very interesting to see. I have tried to use IMFD for suborbital flights, but my results were not very good. The way I go about it, is to try and make a relatively accurate estimate of how much time the flight will take me (in minutes) and then multiply that with 0.25 to see how many degrees to the east my target will "move", by the time I get there. (360 degrees/day ~ 0.25 degrees/minute). Then I add the result to the target's longitude and find the bearing for the new coordinates.
 12-06-2011, 02:19 AM #17 Tommy Orbinaut When I tried to use the AP for the ascent it didn't seem to accept more than 2 digits - it's possible I have a different release of the DG-IV, or just don't know how to use it! My "trick" with IMFD didn't work as well as I'd hoped - but another MFD from the same guy (hint, hint) proved very useful for directional corrections. My launch heading adjustments were "seat of the pants", based on experience - and the heading was fudged "to the right" on both ascents! I also used a lower altitude "skimming" flight so minor corrections were possible. Should be posting the files in this week sometime.
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01-03-2012, 05:04 AM   #19
dgatsoulis
Orbinaut

Great job Tommy!

As the maths go, we did pretty much the same thing. Starting location and bearing were straightforward to find, but distance was trickier. I also used the pythagorean theorem, first finding half the angle and then doubling it to find the true distance. Any difference in our calculations is from roundoff errors and nothing else.

Once you have starting point-bearing-distance, it's not too difficult to calculate the target's coordinates. (link with the equations and shortcuts on post #1 of this thread).

For the launch azimuth, I tried to make a good estimate for my TOF and then see how much my target will move, by the time i get there. (Everything moves to the East at 0.25 degrees/min)
On the PDF attached here, I explain my reasoning and also give some examples of different ships and different departure/arrival sites. The first part may seem a little complicated at first, but with that equation, one can make a somewhat accurate estimate of how long the flight will take.

For the TOF, I got 50.67 minutes, multiplied it with 0.25 and added the result to my target's longitude. Then I calculated the bearing for the "new" coordinates. This would be my launch azimuth. The result was 204.25 degrees.

As for the flight, I took off with the PRO904SPEC204 autopilot and after reaching 500 m/s, I made a small correction to try and get that 0.25 degrees to the "right". - Important note: Must have the correct azimuth, before the ship reaches ~800-900 m/s speed.

I already knew the coordinates of my target and had a pretty good idea where it was on the map. I trusted my launch azimuth calculation so I let the AP burn the engines untill the groundtrack on MapMFD was above it. Then I pitched the ship to about 40 degrees AoA and used AerobrakeMFD to see if i needed more or less thrust to get to my target. The difficulty here is that there is no base to target.
I used the "map" page of AerobrakeMFD to see on what coordinates i was going to land and made the slight adjustments that were needed. DockMFD was on the other panel and after the reentry, I landed a few hundreds of meters away from the disabled DGIV.

The journey home was easier. I used the same method to calculate the launch azimuth, but this time, there was a base to target. Fuel was tight but enough to make it. To my surprise the same AP that I had used to get here, got me to a higher ApA than before, making my reentry more aggressive at first, but the DGIV could easily handle it.

I hope that the ones that tried this challenge enjoyed it, even if they were not successfull.

Playback attached. Remember to raise your gear right after the take offs and press "Backspace" to engage the turbo-pumps, ~40-50 secs later. Also lower the gears before the landings.

Have fun, happy (sub)orbiting
Attached Thumbnails

Attached Files
 RescueDisabledDGIV.zip (112.2 KB, 17 views)

Last edited by dgatsoulis; 01-03-2012 at 06:30 AM.

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 02-18-2012, 10:18 AM #20 Gr_Chris_pilot DGIV Captain I think this PDF can be really useful! http://www.freelancepilot.nl/ATPL%20summary.pdf Page 3 General navigation
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