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Old 04-07-2015, 08:31 PM   #16
boogabooga
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Well, I didn't take the fancy aerocapture challenge, but here is how to do a burn capture/intercept from Delta glider's first scenario.


First of all, your intercept delta-V was large because you were approaching Mars in a roughly polar trajectory. You need to set up your periapsis to just outside the orbit of Phobos with a minimum RIn. Notice the offsets in the Target Intercept program, and the RIn of only ~13 degrees:



I needed ~156 m/s to set this up. The correction delta-V will be much lower if you set this up MUCH sooner. Perhaps even half way to Mars is good to start. Use the power of the map.

Be sure to turn off your offsets.
From then on, it is just a matter of varying TIn and TEj to optimize the Enroute Tot.



Notice that the the burn starts just after periasis.

Notice also that the Enroute delta-V of 2717 m/s (the delta-V of the upcoming burn) is very close to the circularization velocity (Cir in the Map in the 1st picture). This indicates the the burn is mostly retrograde, and inefficient out-of-plane components are fairly small.

I would suspect that the iV of 419 m/s is a fair estimate for you actual Phobos rendezvous burn since Phobos does not have a gravity well. So, It appears you can do the entire rest of the mission in about 3300 m/s, which is a substantial savings over 5000+ m/s you were getting before, but obviously not as good as free aerocapture.

Here is the set up:
Code:
BEGIN_DESC
Contains the latest simulation state.
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 63872.4776146498
END_ENVIRONMENT

BEGIN_FOCUS
  Ship GL-01
END_FOCUS

BEGIN_CAMERA
  TARGET GL-01
  MODE Cockpit
  FOV 45.96
END_CAMERA

BEGIN_HUD
  TYPE Docking
  NAV 0
END_HUD

BEGIN_MFD Left
  TYPE User
  MODE Interplanetary
  Scenario Old2
  MapMFD V5
  Reference mars
  Target phobos
  Center mars
  Data 0 1 5.806695707009294e-006 0 0 1 1 3 1 0 0 0
  MassLimit 1e+020
  CMode 0
  Config 1 1 1 1 140000 0
  ExtMode 2
  Periapis Phobos
  END 
  CorMFD V4
  Reference Mars
  Target Phobos
  Source GL-01
  ActiveProg 1 1
  DataA 0 3 1 0 0 0
  DataB 0.6666666666666666 10 63873.6109070411 0 0 2.316856233053694 0 63874.09535039974 0
  DVProg 0 0 0 1
  AdvConf 0 0 1 0 0
  Guidance 0
  END 
  EjectMFD V5
  Reference Auto
  Data 0 1 3 0 1 63872.45420881501 10
  Guidance 0
  END 
  BaseAprMFD V2
  Reference Auto
  Target none
  Source none
  DataA 0 0 120000 0.10821 0.366519 1 1 63872.45420881501 63872.45420881501 0
  DataB 0 3 0 1 0 1
  END 
  SlingMFD V4
  Reference Auto
  Source none
  Data 0 1 1 3 0 1 63872.45420881501 0
  END 
  LaunchMFD V4
  Target None
  Data 0 1 1 3 0 1 0
  END 
  CF1_DataA 0 0
  CF1_DataB 0 10 120000 2 20 150000
  CF1_SecTgt 
  mfdShare -1
  mfdProgram 2
END_MFD

BEGIN_MFD Right
  TYPE User
  MODE Interplanetary
  Scenario Old2
  MapMFD V5
  Reference mars
  Target phobos
  Center mars
  Data 0 1 5.806695707009294e-006 0 0 1 1 3 1 0 0 0
  MassLimit 1e+020
  CMode 0
  Config 1 1 1 1 140000 0
  ExtMode 2
  Periapis Phobos
  END 
  CorMFD V4
  Reference Mars
  Target Phobos
  Source GL-01
  ActiveProg 1 1
  DataA 0 3 1 0 0 0
  DataB 0.6666666666666666 10 63873.6109070411 0 0 2.316856233053694 0 63874.09535039974 0
  DVProg 0 0 0 1
  AdvConf 0 0 1 0 0
  Guidance 0
  END 
  EjectMFD V5
  Reference Auto
  Data 0 1 3 0 1 63872.45420881501 10
  Guidance 0
  END 
  BaseAprMFD V2
  Reference Auto
  Target none
  Source none
  DataA 0 0 120000 0.10821 0.366519 1 1 63872.45420881501 63872.45420881501 0
  DataB 0 3 0 1 0 1
  END 
  SlingMFD V4
  Reference Auto
  Source none
  Data 0 1 1 3 0 1 63872.45420881501 0
  END 
  LaunchMFD V4
  Target None
  Data 0 1 1 3 0 1 0
  END 
  CF1_DataA 0 0
  CF1_DataB 0 10 120000 2 20 150000
  CF1_SecTgt 
  mfdShare 0
  mfdProgram 4
END_MFD

BEGIN_PANEL
END_PANEL

BEGIN_SHIPS
GL-01:DeltaGlider
  STATUS Orbiting Sun
  RPOS 188062498372.01 -6442314701.60 -84858159322.94
  RVEL 11431.242 761.069 20325.662
  AROT 148.37 62.33 173.27
  AFCMODE 7
  PRPLEVEL 0:0.404874 1:0.941436
  NAVFREQ 434 524 84 114
  XPDR 124
  PSNGR 2
  AAP 0:0 0:0 0:0
END
GL-02:DeltaGlider
  STATUS Landed Mars
  BASE Olympus:3
  POS -135.4299999 12.7366195
  HEADING 0.00
  AFCMODE 7
  PRPLEVEL 0:1.000000 1:1.000000
  NAVFREQ 484 0 0 0
  XPDR 124
  GEAR 1 1.0000
  PSNGR 3 4
  AAP 0:0 0:0 0:0
END
END_SHIPS

BEGIN_ExtMFD
END
As you approach Mars, the Target Intercept solution will change a little, so you will need to stay on top of it. You can use offsets plus the map to maximize accuracy when you get to about 10-15 minutes before the main burn.


Last edited by boogabooga; 04-07-2015 at 08:35 PM.
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Old 04-07-2015, 08:56 PM   #17
Delta glider
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No, I was alinged with Phobos - I used planet approach to get my inclination to Phobos' s but I was not adjusting TEJ as I thought that had to be the time to periapsis.
HALF WAY TO MARS?

You can tell how much velocity in which directions by opening the burn vector and looking at thenthe DV required values. DVf means prograde -retrograde is negative DVf. DVp is plane change and DVI is inward - outward veloocity ie pitch up relative to prograde to do outward and pitch down for inward.

But !
And thank to dgatsoulsis as well.
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Old 04-08-2015, 05:10 AM   #18
Tommy
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The easiest way to do this is to use Map along with target offsetting or Delta-V during the course correction burns. If you are going to Phobos I recommend using a target plane transfer because that will leave you with the lowest plane change at arrival. For a trip to Titan you don't need to be in plane, since you can aerocapture at Titan. Just make sure that the node is at your Titan periapsis.

Map displays the node as a box on the trajectory plot, when using INT mode. Map's reference should be the planet (ie Mars) and CNT should be the moon Pe (ie "p-phobos").

If I can get my PC working again I will be posting some supplements to the IMFD Full Manual/Playbacks, and targeting a moon directly is one of the subjects. It includes a flight from KSC to Titan via a Jupiter slingshot, Titan, using Delta-V and Map.
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Old 04-08-2015, 06:44 PM   #19
Delta glider
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Quote:
Originally Posted by Tommy View Post
 The easiest way to do this is to use Map along with target offsetting or Delta-V during the course correction burns. If you are going to Phobos I recommend using a target plane transfer because that will leave you with the lowest plane change at arrival. For a trip to Titan you don't need to be in plane, since you can aerocapture at Titan. Just make sure that the node is at your Titan periapsis.

Map displays the node as a box on the trajectory plot, when using INT mode. Map's reference should be the planet (ie Mars) and CNT should be the moon Pe (ie "p-phobos").

If I can get my PC working again I will be posting some supplements to the IMFD Full Manual/Playbacks, and targeting a moon directly is one of the subjects. It includes a flight from KSC to Titan via a Jupiter slingshot, Titan, using Delta-V and Map.




---------- Post added at 06:57 AM ---------- Previous post was at 06:55 AM ----------

But map program is not good enough for Phobos though - it moves too fast.

---------- Post added at 07:51 AM ---------- Previous post was at 06:57 AM ----------

Well Tommy you are saying that want to do a direct approach to Phobos and that would be allot of IV. I got dgatsousis method to work (kind of) - I alinged planes after aerocapture because I don't know how to during aerocapture and IMFD wanted 500m/s DV.

---------- Post added at 06:44 PM ---------- Previous post was at 07:51 AM ----------

Quote:
Originally Posted by dgatsoulis View Post
 From that starting point, I'd make a small burn to arrive at a low Mars periapsis altitude (~25 k) as much in plane with Phobos as possible. Even more important than that is to get the node (the intersection between your plane and Phobos' plane) exactly at periapsis.

Then perform an aerocapture and also take care of the plane-alignment with Phobos, using the atmosphere. Exit the atmosphere at the right time and coast to apoapsis where you'll encounter Phobos either directly or in subsequent orbits.

Unfortunately, I don't have time to go into the details right now, I'll try to make a more detailed post tomorrow.
I don't want to be like a 4 year old child pleading you, but could you explain now.

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Old 04-08-2015, 07:37 PM   #20
dgatsoulis
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Using the scenario you provided as a starting point:

First, open Orbit MFD on the left side, set the reference to Mars, target Phobos and select the equatorial frame. You'll also need to switch the distance to altitude. Make a mental (or physical) note of Phobos' inclination and average orbital altitude [(PeA+ApA)/2]. While you are at it, also press the HUD button to view your orientation relative to Mars on the hud.
On the other side, select IMFD→Course→Planet Approach and set the reference to Mars.



On the side you had Orbit MFD, Open IMFD, connect it to the IMFD on the other side and open the Map program. Set the reference to Mars and target "l" (letter l for equatoria'l').
Enter Phobos' inclination on the Planet Approach program and the altitude you want to perform the aerocapture. With this periapsis velocity, I'd go for ~25km. Notice that the EqI value on the Planet approach program cannot go below a certain value.That's because the starting point of the scenario is too close to the periapsis arrival. Doesn't matter though, it will just cost a few m/s of dv more to fix it.



On the Map side, press Plan to view the result of the maneuver. The blue dashed line that ends with a small box is the line of nodes relative to Mar's equator. (you targeted "l" remember?). That's where the plane of your trajectory (after the maneuver) and the equatorial plane of Mars intersect.

On the side with the Planet approach program, adjust the EqI and PeA values, until the periapsis altitude on the Map program is where you want it (~25k) and the line of nodes passes exactly over the periapsis.



Now that you know exactly what the result of the burn will be, go ahead and autoburn the Planet Approach program.
Remove the "Plan" from the Map, so that you can see the actual trajectory. Notice that so far, we haven't target Phobos in IMFD.
After the burn is completed (cost ~80 m/s), coast until you are near the Martian atmosphere (alt ~150k) and open Align Planes MFD→Target Phobos.
On the other side open Surface MFD. Also switch the hud to Surface mode and press Ctrl-/ to switch off the attitude RCS. (No need to waste fuel, the atmosphere and the dynamic surfaces of the Deltaglider are enough to help you orient the spacecraft).



Once you are deep inside the atmosphere that you can control the bank of the spacecraft, full trim up and bank to the side that gives you a negative rate in the Align Planes MFD, so that the RInc is getting smaller. You need to watch 4 things. Vertical vel and vertical acceleration on one side, RInc and Rate on the other.
Your goal is to get the RInc as close as you can to 0 on Align planes MFD and to get the vertical acceleration to ~0 when the vertical velocity is close to 0.



Once you get the Rinc as close to 0 as you can, bank inverted and focus on keeping the vertical velocity close to 0 by adjusting the trim.



Switch the side with AlignPlanes MFD to OrbitMFD and keep an eye on the eccenticity. Remind yourself of Phobos' average orbital altitude (~6M meters).



Wait until you get captured (ecc < 1) and switch the side with Orbit MFD to Aerobrake MFD. You will find a very useful value there; the Apo Alt. This tells you what your apoapsis altitude will be after the aerocapture. If you don't see that value, it means that you are going to hit the planet's surface. No need to worry though; just adjust your trim until you see it.



Bank the spacecraft upright (in one quick smooth motion, so that you don't mess up your RInc to Phobos) and adjust your trim while looking at the Apo Alt value in Aerobrake MFD. You want to get it to ~6M. If neccessary, also pitch up or down the spacecraft a little bit.



Stay on top of the Apo Alt value, keeping it close to 6 - 6.1 M, until you are on your way out of the Martian atmosphere.



Time to set up the intercept to Phobos. Use IMFD's Course→Target Intercept program and target Phobos. Adjust the Tej, Tin values until you have a minimum Total dV. Once you have it, go ahead and AutoBurn it.



After the burn is completed it's good to have TransX targeting Phobos on the other side, . This way you'll be able to see the closest approach to Phobos, something that IMFD's map program can't do. This way, instead of setting up MCCs, you can easily use a little bit of linear RCS to fix your approach to Phobos if it strays too far. You'll probably need to do this once or twice, depending on whether you are flying with non-spherical gravity turned on or off. Or you can re-adjust the TIn in IMFD's Course program until you get a new minimum dV solution and AB than one; whichever suits you best.



After the MCC, all that remains is to match your velocity to Phobos. You already know the dV you'll need from the Target Intercept program (iV on the bottom left) but at which distance from Phobos do you need to start the burn? you can use IMFD to find out.
Wait until you are close to Phobos (alt ~200km on the hud) and open Orbital→Match Velocity program. Target Phobos.
Multiply the burn-time with the dV and divide by two. This will give you a very good approximation at which distance from Phobos' surface to begin the burn.



In this example the dV is 674 and the BT is 35.28. 674x35.28/2 = 11889.36 meters. Round it up to 12k. Orient the spacecraft to get the cross in IMFD's Vel match program centered and repeat the calculation when you are closer (~50 km).



674.5x35.3/2 = 11904.925, round it to 12k. Very IMPORTANT: That's the ALTITUDE when you'll begin the burn, NOT the distance shown in IMFD,



All done, go ahead and land it.

Delta-V used:
--------------------------------------------
80 m/s (Pic 3 Planet approach)
8.0 m/s (Pic11 Target Intercept)
~5 m/s MCC
675 m/s Phobos velocity match

Total: 768 m/s.

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Old 04-08-2015, 07:50 PM   #21
Delta glider
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Thank you!


---------- Post added at 07:42 PM ---------- Previous post was at 07:40 PM ----------

Some parts like the matching velocity's I do under my own preference though - you are too mathematic!

---------- Post added at 07:50 PM ---------- Previous post was at 07:42 PM ----------

I do it in steps - first slowing down until like 30 m/s vertical speed, then a burn that gets me over my landing site (your amazing Hall base), and then a burn to stop most of my velocity until vertical speed = 5m/s, and finally using linear thrusters to get my vessel landed on Phobos.
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Old 04-08-2015, 07:58 PM   #22
dgatsoulis
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Your way is more realistic than mine. But there is something appealing in making a single burn timed in such a way that you end up a few meters above the surface with 0 velocity.

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Old 04-09-2015, 06:50 AM   #23
Delta glider
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Yeah, it feels cool.
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