General Question Tutorials you would like to see

[PhantomCruiser]

Perhaps you refer to this.
When I see it, it seems like reading russian to me.
Completely unfamiliar to me.

Yes, it makes my head hurt...
I'm currently working on http://www.orbiterwiki.org/wiki/Vessel_Tutorial_1
but work progress is slow due to real life.

 

[flytandem]

Earth to mars from earth orbit. All the tutorials I've seen are from the ground. Been wanting one of these a while now.

Interesting idea.

Going to Mars efficiently, starting from the ground on Earth is far simpler generally than if you are already in Earth orbit.

Now if all you want to do is go regardless of fuel usage, then you just randomly escape Earth with a prograde burn at any time you like. Then wait a few days until you are no longer within Earth influence. Now you are orbiting the Sun and you just plan a burn to go to Mars much like you would do orbiting Earth to go to the moon.

But if trying to minimize fuel used and you are starting from Earth orbit, it's a complicated problem. You are probably not in an alignment around the Earth to do a single eject burn to take you to Mars. What follows therefore is a trade-off of trying to combine a plane change with the eject burn which is inefficient for the plane change but efficient for doing the eject burn in Earth's gravity well. So the most efficient way might be a hybrid of doing a bit of plane change and most of the eject burn with additional plane change with respect to orbiting the sun when part way to Mars.

I would tackle the problem probably using the maneuver function in TransX. Plan an eject maneuver and then in the stage going to mars plan another maneuver to do any necessary plane change and additional transfer dv. Write down the total dv for this pair of maneuvers and then try a different pair of maneuvers, and so on, repeating several times until I get close to what I think is the least fuel used for the trip. It would be both random and gut feel for what maneuvers to try.

Is this the sort of flight planning you are thinking of for a tutorial?

 

[Andy44]

I've found heliocentric plane changes to require much more delta-V, since you sun-centered velocity is high. I think it's best to take care of any major plane changes while still in Earth's SOI. Should be interesting to see how it works out. You could do this on paper using patched-conic approach, I think.

 

[flytandem]

Actually just a second after posting the previous, I changed my mind on how I would start from random Earth orbit. I would instead definitely consider a free return of the moon using a "prograde only" burn. Then use the swing around the moon to accomplish the plane change w.r.t. Earth that has me arriving in a perfect alignment for a gravity well burn back in low earth orbit to go efficiently to Mars. This way I get all my eject burn done in the gravity well as purely prograde and the plane change would be free.

I could easily make a tutorial for that but it would involve using a surrogate as a target for the free return. It would be considered an advanced use of TransX IMO.

 

[dgatsoulis]

Flytandem's idea was quite interesting, but i must agree with Andy44 on this one. Heliocentric plane changes cost you in fuel. I know this only through my experience in Orbiter and nothing else.

Depending on the craft and the amount of fuel at my disposal, here is what i would do to make this trip (LEO-Mars, at any given date) as much fuel efficient as possible: (without any slingshots)

Plan the trip on IMFD "off plane" when the Dv reaches a minimum, related to Time to Intersect (TIn) (this might take several hours, but when a pound in mass costs about 1M$...)

From this i'd have a Plane change value in degrees.

Depending on my Orbital altitude (LEO: 160Km - 2000Km) i'd set the time to ejection to match the time it would take me to reach Earth's "thick" atmosphere (after a series of retrograde apoapsis "kicks") and make an "aerobrake" plane change.

When my plane is aligned with the "off plane" trajectory of IMFD i'd either make a "raise periapsis" burn at apoapsis... or if the timing was right burn all the way to Mars.

EDIT: Sorry, i posted this after flytandem's post about approaching the Moon first, which is a very interesting approach!

 

[flytandem]

or a third option other than a combination of burns or using the moon (it may not be in the correct position to be of use) is to start with a prograde burn to raise the Ap above the moon's orbit so a plane change could manually be done with minimal dv.

I guess it would all depend on the initial orbit as to what the best way to Mars would be.

 

[dgatsoulis]

How about making this a "worst case" scenario? Our ship is on a 2000Km (outer limit for LEO) polar orbit around Earth.

 

[flytandem]

A polar orbit could be either a worst or best case. It's possible the polar orbit could be oriented (LAN) to allow a single prograde burn to go to Mars and it could be 90 degrees misaligned. So the worst case would have to be the polar orbit 90 degrees incorrect LAN. ??

 

[dgatsoulis]

A polar orbit could be either a worst or best case. It's possible the polar orbit could be oriented (LAN) to allow a single prograde burn to go to Mars and it could be 90 degrees misaligned. So the worst case would have to be the polar orbit 90 degrees incorrect LAN. ??

All orbits can be either a worst or a best case scenario, depending on the time of departure and the time of arrival. (I think)

How about today? 5/1/2010 ? (It would be far from a Hoffman Transfer, no?)
A DG orbiting Earth on a 2000k polar, circular orbit.

 

[flytandem]

Here's an easy transfer to Mars from the 2000Km orbit suggested. It's polar and leaves today. Less than 4000 m/s dv.

BEGIN_DESC

END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 55317.7949996759
END_ENVIRONMENT

BEGIN_FOCUS
  Ship 3
END_FOCUS

BEGIN_CAMERA
  TARGET 3
  MODE Cockpit
  FOV 60.00
END_CAMERA

BEGIN_MFD Left
  TYPE User
  MODE TransX
  Ship  3
  FNumber 3
  Int 1
  Orbit True
  Vector  603744.372864 -7477199.97964 -3908031.68756
  Vector  -4805.2244435 -2570.01481963 4174.8350114
  Double  3.98600439969e+014
  Double  55317.7949991
  Handle Earth
  Handle NULL
  Handle NULL
Select Target
 0 Escape
Autoplan
0 0
Plan type
0 0
Plan
0 1
Plan
0 0
Plan
0 0
Select Minor
 0 None
Manoeuvre mode
0 0
Base Orbit
0 0
Prograde vel.
 0  0
Man. date
 0  55317.7949989
Outward vel.
 0  0
Ch. plane vel.
 0  0
Intercept with
0 0
Orbits to Icept
0 0
Graph projection
0 3
Scale to view
0 0
Advanced
0 0
Pe Distance
 1  8458490.85271
Ej Orientation
 2  1.85407373637
Equatorial view
0 0
Finvars
  Finish BaseFunction
  Int 2
  Orbit False
  Handle Sun
  Handle Earth
  Handle Mars
Select Target
 0 Mars
Autoplan
0 0
Plan type
0 2
Plan
0 0
Plan
0 0
Plan
0 1
Select Minor
 0 None
Manoeuvre mode
0 0
Base Orbit
0 1
Prograde vel.
 0  0
Man. date
 0  55317.7949989
Outward vel.
 0  0
Ch. plane vel.
 0  0
Intercept with
0 0
Orbits to Icept
0 0
Graph projection
0 0
Scale to view
0 0
Advanced
0 0
Prograde vel.
 3  4742.96724432
Eject date
 3  55317.8874994
Outward vel.
 0  0
Ch. plane vel.
 1  1001.59465047
Finvars
  Finish BaseFunction
  Int 5
  Orbit True
  Vector  -1957587109.47 246958854.677 5974822608.15
  Vector  2999.59435801 -382.384620934 -9163.45981921
  Double  4.28282991638e+013
  Double  55841.9649766
  Handle Mars
  Handle NULL
  Handle NULL
Select Target
 0 None
Autoplan
0 0
Plan type
0 1
Plan
0 0
Plan
0 2
Plan
0 0
Select Minor
 0 None
Manoeuvre mode
0 0
Base Orbit
0 0
Prograde vel.
 0  0
Man. date
 0  55317.7920696
Outward vel.
 0  0
Ch. plane vel.
 0  0
Intercept with
0 0
Orbits to Icept
0 0
Graph projection
0 0
Scale to view
0 0
Advanced
0 0
Draw Base
0 0
Finvars
  Finish BaseFunction
END_MFD

BEGIN_MFD Right
  TYPE User
  MODE TransX
END_MFD


BEGIN_SHIPS
3:DeltaGlider
  STATUS Orbiting Earth
  RPOS 603513.72 -7477323.33 -3907831.29
  RVEL -4805.244 -2569.778 4174.959
  AROT -71.46 -12.66 49.18
  RCSMODE 0
  PRPLEVEL 0:1.000 1:1.000
  NAVFREQ 0 524 84 114
  XPDR 6
  GEAR 1 1.0000
  PSNGR 2 3 4
  TRIM 1.000
END
END_SHIPS

BEGIN_ExtMFD
END

BEGIN_VistaBoost
END

 

[dgatsoulis]

How much fuel did you have when you reached Mars' SOI?

 

[flytandem]

81.7% in the main and didn't really use much RCS, maybe a couple kilos just rotating for the main engine burn. This was a best case. I just made a worst (or at least not very good) case scenario. It's the same general plan to get to Mars but the initial orbit is sitting normal to the eject direction making it a 90 degree change of plane no matter how you orient the ejection. Will play with it a bit to see how it fares. Many times one thinks they have a particular situation but in fact it's not really very tough if approached from a different basic plan.

---------- Post added at 10:07 PM ---------- Previous post was at 05:47 PM ----------

OK here it is... a fun (challenging) starting orbit. (scenario below) The task is to arrive at Mars before the end of 2011. The starting date is May 1st 2010. Hint: you are looking at a Type 2 where you create an Ap a fair bit further out than Mars where Mars catches up to you as you meet it on the way back in toward the sun.

I did 3 ways with the following results.

1. Just tried to do a simple prograde burn from this orbit at some future date and played with various amounts and dates to get a surprisingly efficient solution using 8580 m/s dv. Try Pro= 8,579 on 55317.8074

2. Next I tried a prograde burn to barely escape Earth leaving relatively slow wrt earth. Then just after leaving Earth's SOI, I did the required prograde and plane change to complete the journey. Result was a savings of 1500 m/s (using only 7042 m/s). Specifically I did a Pro=2847 on 55317.8095 then a Pro=4149, Plane=620, on 55321.5797

3. The third way was even more savings using just 6540. But it was complicated. I set up a plan to depart in about 8 days. In that time I did a prograde burn when crossing the plane of the planned departing orbit (raising the Ap out to about 75% the height of the moon). At the Ap I did a plane change to match the plan also making the orbit circular. Then I floated around this orbit until I was exactly opposite the Pe of the Plan. I did a retrograde burn to lower my Pe to just above the atmosphere. Fell into the gravity well and did a burn near the Pe as per the initial plan. Even with these 2 major maneuvers of about 1200 m/s each, that it had the least total dv.

The following scenario has enough fuel to do any of the methods above.

BEGIN_DESC
Transfer to arrive at Mars before the end of 2011. No re-fuelling. 
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 55317.8031126967
END_ENVIRONMENT

BEGIN_FOCUS
  Ship 3
END_FOCUS

BEGIN_CAMERA
  TARGET 3
  MODE Cockpit
  FOV 60.00
END_CAMERA

BEGIN_PANEL
END_PANEL


BEGIN_SHIPS
3:DeltaGlider
  STATUS Orbiting Earth
  RPOS 6570835.61 1714348.62 5042902.18
  RVEL -217.392 6577.520 -1952.786
  AROT -71.46 -12.66 49.18
  RCSMODE 0
  PRPLEVEL 0:0.213 1:0.133
  NAVFREQ 0 524 84 114
  XPDR 6
  GEAR 1 1.0000
  PSNGR 2 3 4
  TRIM 1.000
END
END_SHIPS

BEGIN_ExtMFD
END

BEGIN_VistaBoost
END

 

[flytandem]

I have no knowledge of the mission planning function of IMFD. Maybe someone with this ability could take the scenario above and see what IMFD is able to do. ??

 

[ar81]

flytandem, you have made tutorials to fly making the most efficient use of fuel.
What happens with low thrust-high ISP vessels like a ship that uses VASIMR engine?
Trajectories will be a spiral.

Have you ever thought of that?
What would be the main differences in nav planning?

 

[dgatsoulis]

I have no knowledge of the mission planning function of IMFD. Maybe someone with this ability could take the scenario above and see what IMFD is able to do. ??

Ok, that was fun!

1st attempt:
Nothing fancy just open imfd, select course program, set target Mars (off plane), set time to intercept MJD 55926 (31 Dec 2011), switch to Orbit-eject program (course), Autoburn. Total burn time 330.5 seconds
Main fuel left after ejection burn 0.5%, RCS only used one kg for orientation.

1st MCC at MJD 55710 (29 May 2011) Total burn time: 1.526 seconds
2nd MCC at MJD 55848 (14 Oct 2011) Total burn time: 0.126 seconds
3rd MCC at MJD 55924.1 (29 Dec 2011) Orbit MFD ref Mars G=0.01 Total burn time: 0.326 seconds

Entered Martian SOI on 55925.8327 (30 Dec 2011 19:59) and started to plan a landing. I wanted to land on Olympus base so i opened the base approach program on IMFD and used the orbit insert function to plan a trajectory that would bring me inside the Martian atmosphere on the planet's opposite side of Olympus base (Olympus base: 135.43W 12.74N - Opposite side: 44.57E 12.74S) to aerobrake and then land at the base. Total burn time: 9.519 seconds. I run out of Main fuel with still 3.5 seconds of burn time needed, which i completed with a linear RCS burn. Fuel left after the burn 19kg of RCS

Unfortunately i miscalculated the altitude of the aerobrake (30km) and ended up back in space flying away from Mars.

Mission: Partial success. I did make it to Mars with the fuel at my disposal but didn't manage to land.

For my second attempt i'll try to make a plane alignment first with a series of aerobrakes on Earth and then make the ejection burn. I suspect that this will cost me more in dV but i'll give it a try.

Thanks for the scenario flytandem.

 

[flytandem]

Awesome! I was a bit surprised to see that IMFD managed to complete the mission on the given fuel but it did appear to be fairly close with not too much fuel left.With 0.5% remaining it appears that the dv for that burn was about 8450 m/s. That's roughly about the same as the 1st method I used using TransX.

You wouldn't happen to have a scenario save just a few seconds before the autoburn would you? I am curious exactly when and what combination of directions it chose to get you there. Maybe I could sort of reverse engineer that situation to get TransX to duplicate the pro, out and plane vectors so that it has the same direction and amount of burn.

I don't have much experience with constant microthrust like with ion engines. Sure seems to me that it would be a lot of trial end error. The new Orbiter beta with it's faster integration rate could be useful for interplanetary trial runs.

 

[dgatsoulis]

You wouldn't happen to have a scenario save just a few seconds before the autoburn would you? I am curious exactly when and what combination of directions it chose to get you there. Maybe I could sort of reverse engineer that situation to get TransX to duplicate the pro, out and plane vectors so that it has the same direction and amount of burn.

Here it is: 90 seconds to autoburn. this is with IMFD 5.3
Remember to hit the AB button as soon as the scenario starts.

BEGIN_DESC
Contains the latest simulation state.
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 55317.8625321643
END_ENVIRONMENT

BEGIN_FOCUS
  Ship 3
END_FOCUS

BEGIN_CAMERA
  TARGET 3
  MODE Cockpit
  FOV 60.00
END_CAMERA

BEGIN_MFD Left
  TYPE User
  MODE Interplanetary
  Scenario Old2
  MapMFD V5
  Reference Auto
  Target none
  Center GravityRef
  Data 0 1 1e-006 1 0 0 0 0 1 0 0 0
  MassLimit 1e+020
  CMode 0
  Config 1 1 1 1 0 0
  ExtMode 0
  Periapis none
  END 
  CorMFD V4
  Reference Sun
  Target Mars
  Source Earth
  ActiveProg 1 1
  DataA 0 3 0 0 0 0
  DataB 1 1 55317.86253142356 0 0 2.364814592968294 0 55926 0
  DVProg 0 0 0 1
  AdvConf 0 0 1 0 0
  Guidance 0
  END 
  EjectMFD V5
  Reference Auto
  Data 1 1 3 0 0 55317.86356693826 7664.84
  Guidance 0
  END 
  BaseAprMFD V2
  Reference Auto
  Target none
  Source none
  DataA 0 0 120000 0.10821 0.366519 1 1 55317.80327314809 55317.80327314809 0
  DataB 0 3 0 1 0 1
  END 
  SlingMFD V4
  Reference Auto
  Source none
  Data 0 1 1 3 0 1 55317.80327314809 0
  END 
  LaunchMFD V4
  Target None
  Data 0 1 1 3 0 1 0
  END 
  CF1_DataA 0 0
  CF1_DataB 55317.8031126967 10 120000 2 20 150000
  CF1_SecTgt 
  mfdShare -1
  mfdProgram 3
END_MFD

BEGIN_PANEL
END_PANEL


BEGIN_SHIPS
3:DeltaGlider
  STATUS Orbiting Earth
  RPOS -3176745.91 -7813949.91 -555082.27
  RVEL 4665.402 -2218.128 4521.676
  AROT -131.27 -44.52 -61.25
  RCSMODE 0
  PRPLEVEL 0:0.213 1:0.132
  NAVFREQ 0 524 84 114
  XPDR 6
  GEAR 1 1.0000
  PSNGR 2 3 4
  TRIM 1.000
END
END_SHIPS

BEGIN_ExtMFD
END

BEGIN_VistaBoost
END

 

[ar81]

I don't have much experience with constant microthrust like with ion engines. Sure seems to me that it would be a lot of trial end error. The new Orbiter beta with it's faster integration rate could be useful for interplanetary trial runs.

I have been thinking that ion engine changes the way of thinking.
We do not think anymore about burns near apoapsis and periapsis and cruising, but about constant modification of a circular orbit. How could it be made more fuel efficient?

You are the master of fuel efficiency here. I think it would be very interesting.

 

[Tommy]

I don't have time to work out an efficient method using IMFD, but for those that want a simple method it's not hard. You would use the same method to set up the transfer that you do when leaving from the ground. (For best results, don't forget to set the "Parking Orbit Alt" in IMFD's config page.) Obviously, you would skip surface launch and go straight to Orbit Eject. That will display the nodes with the ejection plane and EIn is the relative inclination you currently have. It will also display a dV for the plane change - positive numbers mean burn normal, and negative mean burn anti-normal. After the plane change check TEj in Orbit Eject (a stock DG tends to alter it's Ap and Pe during planechanges) and adjust for smallest dV.

 

[flytandem]

I hit AB and sure enough ti start at Tej=0. I used external camera to see it had a fair amount of plane change built into the burn.
Just after the burn stopped I went to warp 0.1 and opened up TransX. In about a minutes I had the plan up that matched the current orbit and rotating the eject orientation to offplane amount to zero I had it in effect like a TransX plan. But the plan would have been quite a bit offplane from prior to the burn. What is needed is to get the maneuver figured out that places the before burn to the after burn. Will play more later when my honeydoo list drops to zero again. fun stuff.

---------- Post added at 07:48 PM ---------- Previous post was at 06:53 PM ----------

ok, couldn't help myself, I snuck back to play a bit. (obsessed)
I found the mix of TransX maneuver values (Prograde, Plane and Date) that matches those of the AB in IMFD. Pretty much matched the overall burn amount. It had a pro of 6564 and a plane change of -5444. You figure the date.

So I reduced the plane change to about -800 and played with pro and date and found a solution that got there several months earlier with a MCC necessary part way there. It had something like 7860 initial eject and 136 m/s several months later. Overall savings of 500 m/s. As I suspected in the beginning, a light mix of plane and pro with a maneuver half way to Mars is a savings of quite a bit over no mix.

But the option of just prograde to barely eject Earth was even better than that and the best of all was the complicated high Ap plane change around the Earth. Personally given the best efficiency and the challenge of the complication makes this my favorite. If I were making an advanced challenge scenario out of the initial scenario I would have supplied only 6900 m/s dv leaving the only option for completion probably that last option which would still have had about 400 m/s to spare. I know, cruel. :lol: