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Old 01-03-2015, 11:19 PM   #1
RAF Blackace
Orbinaut
Post Flying the Rosetta Mission.

I used version 3D of BrianJs mission edited and improved by flug. I also used TransX-2, so you need this if you use the scenarios attached if you want to see the TransX plans.

I promised BrianJ and Flug I would post some hints and tips for others who want to do it once I had successfully completed it myself.

This has got to be the hardest mission I have ever tried in Orbiter, but well worth the effort when you eventually get it completed.

First note. Use the rosetta markers, the file can be edited to have any marker active. Obviously the first marker is used for orbit ejection. So make sure it is active in the config file Rosetta_Marker.cfg

The file has several markers, just comment out the ones you are not using at that moment. The file also gives you the target MJD dates that you use in IMFD. You need these because this mission is extremely fuel tight, and any unnecessary course adjustments will waste valuable fuel. As BrianJ has already stated, the Earth is pulled all over the place by the Moon so it is very difficult to keep on course without using the markers when doing Earth flybys.

Read the read me for a better understanding of how to use the markers. You need about 800Kg (or more if your lucky) in the the tank by the time you do the 21 Lutetia flyby. Any less, and you are probably not going to make it.

First issue was the Launch azimuth, no idea why but for me it left a Ein of about 12 degrees for departure, not very good for fuel consumption. So I adjusted the Launch Azimuth to 90 degrees in the file guidance158.txt.

File is located here..\Config\Vessels\Ariane5Rosetta

Roll Line should read 12=roll(3,89,90,85.7,1)

This leaves you with less than 0.2 degree Ein for Earth departure if you target the first rosetta marker on MJD53249.

Ejection burn I found was best commenced 600 seconds before IMFD Tig, burn prograde until you are about 250km altitude, then line up the cross hairs and complete the burn. This should set you off on your journey quite nicely.

As with all trips, after orbit ejection, do not do any more course adjustment burns until the Dv has dropped to its minimum in IMFD.

Keep targeting the rosetta marker until you are about 50 days away from the first Earth fly by. Then switch to TransX and plot the course for the flyby. Be aware that the flyby has to be very accurate to save fuel. Any burn more than about 70dv for a course correction after a flyby will burn too much fuel and your probably not going to make it.

Especially important are the Earth Flybys. I found the usual method of adjusting the flyby to Pe ratio 1, angle 0 in TransX until I was within the SOI kept the sudden jump once inside the SOI reasonable. Then point the spacecraft either prograde/retrograde/90 degees left, right, up, or down to do small manual burns to keep the Pe ratio and Angle as close to 1 and 0 as possible until you are past periapsis. You may seem like your using fuel, but if you don't do this you will use far more making a large course correction after the flyby and your probably not going to make the rest of the trip.

You must use TransX as well as IMFD for this mission, either one on its own will just not do it for you. I used IMFD for the cruises, then switched to TransX when 100 or 150 days out to plot the flybys.

Stick to the actual mission flyby dates, do not try to let them wander to save fuel, the dates are very important and if you change one, the rest of the flight is thrown out meaning it may no longer be possible to get to the comet.

Above everything else, think fuel. Save as much as you possibly can.

Once past 21 Lutetia, you need a very large burn of about 800Dv to target the comet, wait for the required Dv to drop to its lowest value before making the burn.

Documentation is wrong for the comet target date, it says 66818, it should read 56818.

Comet approach...

I found the best method (providing you on a course to hit the comet using IMFD) was to point prograde (view is reversed, so prograde is actually retrograde for any burn) from about 10,000Km out. Then point the ship directly away from the comet and do some long burns to reduce the approach speed gradually. You can use the surface MFD to make sure you are pointing directly away from the comet. You need about 450Kg of fuel for the approach or your not going to make it. Using IMFD map keep an eye on the Pe distance. Keep moving the direction of the burn around slightly to keep the Pe very low, ideally to aim to hit the comet. This takes a long time and is quite hard to do, but take your time.

Once your down to about 50 m/s you should be within 100Km of the comet, when your about 10Km away come to a complete stop, then simply do a puff of a burn at a tangent to the comet to enter orbit.

Any other questions, feel free to ask.

As a help, I have attached my full mission scenarios. I made it into orbit with just 30Kg of fuel left. This was my third attempt, the other two I aborted due to no fuel left.

Hope it helps anyone else struggling with this fantastic mission.

Fly Safe.
Attached Files
File Type: zip Mission-3.zip (71.1 KB, 29 views)

Last edited by RAF Blackace; 01-03-2015 at 11:22 PM.
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Old 08-01-2019, 01:22 AM   #2
djidji
Orbinaut
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i'm trying to get this mission done but i can't seem to find the proper way with the rosetta_marker. on the Rosetta_marker_elements.txt the fisrt one says

;MJD 54131 (pre-Mars GA)

Epoch = 2007.0841889117
SemiMajorAxis = 204784643176.766
Eccentricity = .276401941430808
Inclination = 2.45975487541973E-02
LongAscNode = 6.00361433238406
LongPerihelion = 9.04040307032215
MeanLongitude = 10.2853040170719

as the 1st one.. but it makes no sense to target this at MJD 53249, both IMFD and trans-x give me a stupidly high delta V to eject from earth.

is this the marker for the way to mars after the first earth flyby??..

if so how do i find the info for the proper eject burn.

thanks if anyone can help
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Old 08-01-2019, 12:44 PM   #3
BrianJ
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Hi,
it's been a long time since I had a go at Rosetta. Just the number of Earth gravity assists make it pretty difficult. You also need to handle the long Earth escape burn due to low powered Ariane5 upper stage.

IIRC, I included the "marker" as a help for Earth escape burn planning (and also later navigation). The marker orbital elements are taken from the JPL Horizons trajectory data for the Rosetta spacecraft. If you match the marker position and velocity at the given date, you "should" be on course.

Since I understand how to use TransX better these days, I would probably ignore the "marker" and just plan using TransX, if tried the mission again.

If you want to post your scenario, maybe I can take a look.

Cheers,
Brian

P.S.
Quote:
;MJD 54131 (pre-Mars GA)

Epoch = 2007.0841889117
SemiMajorAxis = 204784643176.766
Eccentricity = .276401941430808
Inclination = 2.45975487541973E-02
LongAscNode = 6.00361433238406
LongPerihelion = 9.04040307032215
MeanLongitude = 10.2853040170719

as the 1st one.. but it makes no sense to target this at MJD 53249, both IMFD and trans-x give me a stupidly high delta V to eject from earth.
If you use these elements, you should target the given date of MJD54131, assuming you are already past the 1st Earth Gravity Assist.

Last edited by BrianJ; 08-01-2019 at 12:51 PM.
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Old 08-02-2019, 01:40 AM   #4
djidji
Orbinaut
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Quote:
Originally Posted by BrianJ View Post
 Hi,


If you use these elements, you should target the given date of MJD54131, assuming you are already past the 1st Earth Gravity Assist.
the part i'm mostly wondering about is the marker for the initial eject burn.

it seems to me that the default scenario has the one loaded for the mars flyby, but i have a really hard time doing the eject burn without needing 130 Dv right after i leave earth SOI.

tx for the response.
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Old 08-02-2019, 01:54 PM   #5
BrianJ
Addon Developer
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Hi,
Quote:
it seems to me that the default scenario has the one loaded for the mars flyby, but i have a really hard time doing the eject burn without needing 130 Dv right after i leave earth SOI.
The orbital elements for the "marker" are set by the Rosetta_marker.cfg file, not the scenario. The default orbit elements in Rosetta_marker.cfg are for MJD53249 (~6 months pre 1st Earth GA)

The eject burn must be done efficiently, otherwise you won't have sufficient dV in the Ariane5 upper stage. You need to start the burn well before the IMFD/TransX indicated burn time. I think I put some info about that in the flight notes.

Cheers,
Brian
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Old 08-04-2019, 07:58 PM   #6
djidji
Orbinaut
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The default orbit elements in Rosetta_marker.cfg are for MJD53249 (~6 months pre 1st Earth GA)


_______________\

that's the part that got me mixed up. the default for me is the one for mars. i cannot find the orbital element for the first pass to earth (the one i should target at MJD 53249...

don't know why

---------- Post added at 07:58 PM ---------- Previous post was at 07:46 PM ----------

never mind found why when i reloaded the whole file, i already messed with the .cfg files and found the 53249 in the .zip, will reinstall and retry
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