Flight Question Need help with my first slingshot

[RogerWilco]

I am orbiting the Earth in the Perseus spacecraft (which I downloaded) and I've set up a slingshot past Jupiter to get to Saturn. I used Celestia to determine when Saturn and Jupiter would be in reasonable proximity to each other and set my MJD to 64940. I am looking at a September launch.

According to TransX, my Closest Approach to Jupiter will be 2.04G, and am expected to come within 527M of Saturn.

Looking at stage 1 of my plan (escape from Earth orbit) I see my incl. Value is 55.61, LAN is 158.6, Rel Inc is 53.53, DeltaV is 9.402k, T to Pe is 2.597k and counting down, begin burn is 202 and Ang to Pe is 159

I have tried doing my ejection burn at periapsis, I've tried it when the Begin Burn value hits zero, and I've tried it when the date precisely coincides my my eject date I set up, and my orbit either extends out the wrong direction, or wobbles around and doesn't appear to get far enough from Earth to reach my hypothetical orbit that I need. Or, it does some combination of both!

I have done transfers before in both the Delta Glider and Perseus and never had this issue before, so I am wondering what I am doing wrong.

Another question I have is how the variables for the Sling Direct view actually get put into practice. Outward angle is at 70.5432' and Inc. Angle is -3.4816.

Do I have to do anything else besides enter these values in order to get them to do what they say they will do? If so, how do I know when to do it, and how do I tell if I did it right?

This is my first attempt at a slingshot like this, so all advice and help will be warmly welcomed!

Thanks!

 

[dgatsoulis]

Can you post the scenario? (between

 tags).

From a first glance, your Injection dV and R.Inc are huge. 

In order to fly the plan you have setup on stage 2, you need to have a R.Inc as close as you can to 0 in stage 1.

You also have a huge burntime. The time to periapsis is 2597 and TransX says that you need to start the burn in 202 seconds. That means 2395 seconds (~40 minutes!) before periapsis. If you are starting from LEO, that is almost half an orbit away from periapsis, which is close to the apoapsis.

Have a look at flytandem's tutorial [URL="http://orbiter-forum.com/showthread.php?t=16990"]videos[/URL] and also search at David Courtney's [URL="http://www.youtube.com/user/DavidWCourtney"]YouTube channel[/URL] for slingshot videos.

 

[RogerWilco]

I haven't posted a scenario before so I am not clear on how to do that. I did read that the Orbiter master code from the .cfg file can be copy/pasted in the manner you specified. Is that the code you need, or am I after something else?

Out of curiosity, what defines DeltaV as huge? What is a typical value for my kind of trip?

 

[Ripley]

- Close Orbiter;
- Open with notepad (or any plain text editor) the scenario you usually launch in Orbiter (folder: Orbiter\Scenarios);
- Copy the whole text and paste it here, between a pair of "CODE" tags, like this:

[open_tag]some text goes here[/close_tag]

Keep also in mind that every time you exit Launchpad (without a CTD, that is) the latest scenario state is saved in the "(Current state).scn" scenario, so if you need to post an "in-between" situation, just fly the scenario until you can, exit from Orbiter, and copy-paste the "(Current state).scn" content.

 

[dgatsoulis]

Out of curiosity, what defines DeltaV as huge? What is a typical value for my kind of trip?

Somewhere in the 6.8 km/s region.
Trans-Jupiter Injection burns are big ones. I can see it going to ~7km/s depending on the kind of transfer you are flying, but 9.4 km/s is huge.

Even with a 6.8 km/s burn, in order to be efficient, you should brake it into a couple (or more) periapsis kicks, depending on what kind of acceleration your ship has.

For posting the scenario, follow what Ripley said.
Run the scenario, set up your TransX plan and exit. Then go to the Orbiter\Scenarios\(Current State).scn and open it with a text editor.
Select everything, copy and paste it in your post here.
Then select the whole text of the scenario and press the "Wrap

 tags around selected text" button, which is above the text space when you write a post. It's the grey button that says "CODE" on it.

 

[RogerWilco]

Okay here is my attempt. I had the scenario in a quicksave file, and I opened it with notepad.

I'm very excited to see what advice more experienced pilots will have based on this:

BEGIN_DESC
Orbiter saved state at T = 18569
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 64940.9694056658
END_ENVIRONMENT

BEGIN_FOCUS
  Ship perseus
END_FOCUS

BEGIN_CAMERA
  TARGET perseus
  MODE Cockpit
  FOV 50.00
END_CAMERA

BEGIN_HUD
  TYPE Docking
  NAV 0
END_HUD

BEGIN_MFD Left
  TYPE User
  MODE TransX
  Ship  perseus
  FNumber 5
  Int 1
  Orbit True
  Vector  -4929765.16357 4506225.36724 -1485216.15291
  Vector  4767.55426155 3740.67525908 -4612.73678816
  Double  3.98600439969e+014
  Double  64940.9694014
  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
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0 0
Prograde vel.
 0  0
Man. date
 0  64940.969401
Outward vel.
 0  0
Ch. plane vel.
 0  0
Intercept with
0 0
Orbits to Icept
0 0
Graph projection
0 2
Scale to view
0 0
Advanced
0 0
Pe Distance
 0  7645212
Ej Orientation
 0  0
Equatorial view
0 0
Finvars
  Finish BaseFunction
  Int 2
  Orbit False
  Handle Sun
  Handle Earth
  Handle Jupiter
Select Target
 0 Jupiter
Autoplan
0 0
Plan type
0 2
Plan
0 0
Plan
0 0
Plan
0 1
Select Minor
 0 None
Manoeuvre mode
0 0
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0 1
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 0  0
Man. date
 0  64940.969401
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.
 0  7420.46165277
Eject date
 0  64940.7644291
Outward vel.
 0  591.831877731
Ch. plane vel.
 0  10871.9148326
Finvars
  Finish BaseFunction
  Int 4
  Orbit True
  Vector  -213641800073 -144045078353 -391718875399
  Vector  2815.42618045 1875.83866441 5108.04618095
  Double  1.26686534397e+017
  Double  65210.9671493
  Handle Jupiter
  Handle NULL
  Handle NULL
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 0 Escape
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0 0
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0 1
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0 0
Plan
0 1
Plan
0 0
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 0 None
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0 0
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0 0
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 0  0
Man. date
 0  64940.8097398
Outward vel.
 0  0
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0 0
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0 0
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0 0
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0 0
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  Finish BaseFunction
  Int 3
  Orbit True
  Vector  -795634923763 20231709636.8 222651542259
  Vector  -9719.55246524 557.920188237 -12215.4314722
  Double  1.32839126489e+020
  Double  66074.0201677
  Handle Sun
  Handle Jupiter
  Handle Saturn
Select Target
 0 Saturn
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0 0
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0 0
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 0  0
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 0  64940.8092553
Outward vel.
 0  0
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 0  0
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0 0
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0 0
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0 0
Scale to view
0 0
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0 0
Velocity.
 0  0
Outward angle
 0  1.23121110489
Inc. angle
 0  -0.0607653832374
Inherit Vel.
0 0
Eject date
 0  66074.0201677
Finvars
  Finish BaseFunction
  Int 5
  Orbit True
  Vector  468290502628 -30642771404.7 237178536408
  Vector  -5220.99481463 343.317182999 -2650.96048971
  Double  3.79311866084e+016
  Double  66169.3482649
  Handle Saturn
  Handle NULL
  Handle NULL
Select Target
 0 None
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0 0
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0 1
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0 0
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0 0
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0 0
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0 0
Prograde vel.
 0  0
Man. date
 0  64940.1803748
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
ISS:ProjectAlpha_ISS
  STATUS Orbiting Earth
  RPOS 6392214.63 1288695.60 -1603404.51
  RVEL 1897.134 -7280.830 1688.389
  AROT 109.61 -8.53 80.06
  AFCMODE 7
  PRPLEVEL 0:1.000000
  IDS 0:588 100 1:586 100 2:584 100 3:582 100 4:580 100
  NAVFREQ 0 0
  XPDR 466
END
Mir:Mir
  STATUS Orbiting Earth
  RPOS 5741512.83 209953.45 3379868.60
  RVEL -3927.697 402.313 6647.835
  AROT 0.00 -45.00 90.00
  AFCMODE 7
  IDS 0:540 100 1:542 100 2:544 100
  XPDR 482
END
Luna-OB1:Wheel
  STATUS Orbiting Moon
  RPOS -1236230.36 -1864570.07 -519.38
  RVEL 1234.040 -817.911 -1.135
  AROT 0.00 -0.00 -113.71
  VROT 0.00 0.00 10.00
  AFCMODE 7
  IDS 0:560 100 1:564 100
  XPDR 494
END
perseus:Spacecraft\Spacecraft3
  STATUS Orbiting Earth
  RPOS -4927988.89 4507618.33 -1486934.21
  RVEL 4769.839 3738.586 -4612.048
  AROT 140.85 -38.54 158.12
  VROT -0.00 0.06 -0.01
  AFCMODE 7
  PRPLEVEL 0:0.998000
  IDS 0:482 100
  NAVFREQ 484 482
  RCS 1
  CTRL_SURFACE 1
  CONFIGURATION 1
  CURRENT_PAYLOAD 0
END
END_SHIPS

 

[dgatsoulis]

You posted that the R.inc was 53.53°, but in the scenario it was less than 0.6°. That amount of relative inclination to the hypothetical injection trajectory of the plan is still big, but manageable. And surely nowhere near the 53.53° that you mentioned.
I think you probably wrote that value before adjusting the eject orientation?

It is better to try and make the Injection burn with the R.Inc as low/close to zero as possible.

The main "problem" of your plan was the very high amount of plane-change it had, in order to arrive on Jupiter at that date. It was even higher than the prograde velocity.

The total tranfer dV is = sqrt(Prograde²+Ch.Plane²+Outward²).
High plane change = high total transfer dV = high injection burn dV

Depending on what kind of accelaration the ship has, a high injection burn delta velocity can lead to a long burn time. In this case the burn time was so long that it was unmanageable, with TransX asking you to start the burn almost 1/2 orbit away from periapsis.

That said, there was nothing else wrong with the plan.
The sling was very nicely set up and everything was ready to go.
If your ship had an accelaration more than 2.5g, you would have no problems flying that plan with a couple of MCCs later on.

I do not have the perseus addon installed, so I copied the plan, replaced the perseus with a DeltaGlider and re-replaced the perseus before posting the plan here:

BEGIN_DESC
Contains the latest simulation state.
END_DESC

BEGIN_ENVIRONMENT
  System Sol
  Date MJD 64134.0321784596
END_ENVIRONMENT

BEGIN_FOCUS
  Ship perseus
END_FOCUS

BEGIN_CAMERA
  TARGET perseus
  MODE Cockpit
  FOV 50.00
END_CAMERA

BEGIN_HUD
  TYPE Surface
END_HUD

BEGIN_MFD Left
  TYPE User
  MODE TransX
  Ship  perseus
  FNumber 5
  Int 1
  Orbit True
  Vector  -6412385.97579 -1808361.40604 334418.750671
  Vector  -2045.51814825 6627.49608846 -3414.26449719
  Double  3.98600439969e+014
  Double  64134.0321785
  Handle Earth
  Handle NULL
  Handle NULL
Select Target
 0 Escape
Autoplan
0 0
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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  64134.0321785
Outward vel.
 0  0
Ch. plane vel.
 0  0
Intercept with
0 0
Orbits to Icept
0 0
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0 2
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0 0
Advanced
0 0
Pe Distance
 0  6671010
Ej Orientation
 0  1.11725506737
Equatorial view
0 0
Finvars
  Finish BaseFunction
  Int 2
  Orbit False
  Handle Sun
  Handle Earth
  Handle Jupiter
Select Target
 0 Jupiter
Autoplan
0 0
Plan type
0 2
Plan
0 0
Plan
0 0
Plan
0 1
Select Minor
 0 None
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0 0
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0 1
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 0  0
Man. date
 0  64134.0321785
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0 0
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0 0
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 0  8920.9263216
Eject date
 0  64138.8475
Outward vel.
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 0  -377.798
Finvars
  Finish BaseFunction
  Int 4
  Orbit True
  Vector  -450394904422 28430913871.2 87123711440.1
  Vector  5862.24815789 -370.968535102 -1115.69865351
  Double  1.26686534397e+017
  Double  64359.9861852
  Handle Jupiter
  Handle NULL
  Handle NULL
Select Target
 0 Escape
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0 0
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0 1
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0 0
Plan
0 1
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 0  64134.0320918
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  Finish BaseFunction
  Int 3
  Orbit True
  Vector  -98787877256.4 211149614.409 754134424446
  Vector  -18177.7004293 819.766047554 -3976.298871
  Double  1.32839126489e+020
  Double  65225.1678054
  Handle Sun
  Handle Jupiter
  Handle Saturn
Select Target
 0 Saturn
Autoplan
0 0
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0 2
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Plan
0 2
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0 0
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 0  0
Man. date
 0  64134.0320666
Outward vel.
 0  0
Ch. plane vel.
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Intercept with
0 0
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0 0
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0 0
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0 0
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 0  -0.507206643264
Inc. angle
 0  -0.0645508278521
Inherit Vel.
0 0
Eject date
 0  65225.1678054
Finvars
  Finish BaseFunction
  Int 5
  Orbit True
  Vector  493082275282 -15197968392.5 156216669801
  Vector  -8283.26717262 253.530490655 -2637.6491052
  Double  3.79311866084e+016
  Double  65799.161534
  Handle Saturn
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  Handle NULL
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  Finish BaseFunction
END_MFD

BEGIN_MFD Right
  TYPE User
  MODE TransX
END_MFD

BEGIN_SHIPS
perseus:Spacecraft\Spacecraft3
  STATUS Orbiting Earth
  RPOS -6412385.98 -1808361.41 334418.75
  RVEL -2045.518 6627.496 -3414.264
  AROT 117.87 16.03 -175.28
  VROT -0.01 0.06 -0.00
  AFCMODE 7
  PRPLEVEL 0:0.998000
  IDS 0:482 100
  NAVFREQ 484 482
  RCS 1
  CTRL_SURFACE 1
  CONFIGURATION 1
  CURRENT_PAYLOAD 0
END
ISS:ProjectAlpha_ISS
  STATUS Orbiting Earth
  RPOS 6392214.63 1288695.60 -1603404.51
  RVEL 1897.134 -7280.830 1688.389
  AROT 109.61 -8.53 80.06
  AFCMODE 7
  PRPLEVEL 0:1.000000
  IDS 0:588 100 1:586 100 2:584 100 3:582 100 4:580 100
  NAVFREQ 0 0
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Mir:Mir
  STATUS Orbiting Earth
  RPOS 5741512.83 209953.45 3379868.60
  RVEL -3927.697 402.313 6647.835
  AROT 0.00 -45.00 90.00
  AFCMODE 7
  IDS 0:540 100 1:542 100 2:544 100
  XPDR 482
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  VROT 0.00 0.00 10.00
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BEGIN_ExtMFD
END

Trans Jupiter Injection Delta V: 6384 m/s and from there a fast sling to Saturn.
I have set the date to ~5 days before the burn. This way you can make a ~3050 m/s burn at the periapsis to extend your apoapsis to ~2.5 days away and then return to periapsis to complete the burn on time. At the apoapsis you can take care of any remaining R.Inc.
These are known as "Periapsis Kicks" and they are used when there is a long injection burn. For a LEO starting orbit, a periapis kick must have less dV than the escape velocity, otherwise you will not fall back to Earth for a second burn.
The "secret" is to time Orbital period of the "kick" orbit with an arrival at periapsis, in time with the date of the departure on TransX stage2. But you don't have to worry too much about that, especially for a target like Jupiter.

A more extreme example with a ship that required 11 periapsis kicks to be able to leave Earth can be found here.

In general, try to use the line of nodes (the grey line on stage2) as the point of departure and arrival. It is the place where the planes of the departure and arrival orbits "naturally" intersect, without having to apply a lot of plane-change velocity.

Hope this helps.

 

[RogerWilco]

Thanks for the analysis!

I am not sure why the R Inc value changed. I used the same scenario to list the values to begin with, but I must have done something I don't remember to increase it, or I was looking at the wrong item or something.

Is there something I need to watch out for in my initial setup of the scenario and my plan that I can use to avoid this issue where it takes a massive plane change?

I want to be as proper and accurate as I can. (Which means some day I'll turn fuel consumption on.)

In the meantime, what is the proper way to going about setting up a periapsis kick? Do I just eyeball my orbit as I perform the kick and cut off the engines when my t to pe value shows 2.5 days? (Assuming clock is set to 5 days before the eject date I'm my plan.)

This would give me about two orbits around the earth to get my plan finalized, and then do ejection burn on my second pass by periapsis, correct?

Is there a formula for figuring these kicks?

What is happening with these kicks that fixes my plane change issue?

 

[dgatsoulis]

Thanks for the analysis!

I am not sure why the R Inc value changed. I used the same scenario to list the values to begin with, but I must have done something I don't remember to increase it, or I was looking at the wrong item or something.

Is there something I need to watch out for in my initial setup of the scenario and my plan that I can use to avoid this issue where it takes a massive plane change?


I want to be as proper and accurate as I can. (Which means some day I'll turn fuel consumption on.)

That day has come.
Instead of trying to setup a slingshot with unlimited fuel, set up a "simpler" plan to Mars or Venus with limited fuel.
The standard DeltaGlider is an excellent ship to help you learn with lots of extra fuel if something goes wrong. If you want to make things more difficult later on, all you have to do is to cut back on the fuel.

Find and watch as many tutorials and videos you can find, to see how others do it.

BTW, if you are flying with unlimited fuel, it's the main reason your ship has such poor acceleration. The spacecraft doesn't become lighter by the use of the fuel.

In the meantime, what is the proper way to going about setting up a periapsis kick? Do I just eyeball my orbit as I perform the kick and cut off the engines when my t to pe value shows 2.5 days? (Assuming clock is set to 5 days before the eject date I'm my plan.)
This would give me about two orbits around the earth to get my plan finalized, and then do ejection burn on my second pass by periapsis, correct?

No, you want to be back at periapsis in 5 days, not 2.5. So you need your time to apoapsis to be 2.5 days. (ApT ~ 200k. in Orbit MFD).
This would give you 1 orbit around Earth.

Is there a formula for figuring these kicks?

A formula? You could write one down depending on the ship you fly, but in general I use this: If the burn takes more than 6-7 minutes in a low Earth parking orbit, I brake it into two (or more) kicks.

What is happening with these kicks that fixes my plane change issue?

The best time to change your plane is when the spacecraft is moving slower and that happens at the apoapsis of its orbit. So if you have some amount of R.Inc, you can get rid of it when you reach the apoapsis of the "kick" orbit.

 

[blixel]

In the meantime, what is the proper way to going about setting up a periapsis kick? Do I just eyeball my orbit as I perform the kick...

This is a good question in my opinion. I was trying to envision how this works myself. If I have a TransX plan to go to Mars, it's going to look like this:

Here we can see that the burn time is 207 seconds (about 3 1/2 minutes.) But suppose we were using a craft that turned this into a 9 minute burn instead. Would I still burn at the Eject point for the periapsis kick burn?

If I'm not going to be back around to periapsis for 5 days, I'm wondering if the target planet (Mars in this case) will have moved far enough along in its orbit around the sun that my Eject point is no longer valid by the time I get back to periapsis? Especially if there are multiple kicks involved.

I can see this being less of a problem with Jupiter since it has a large gravity well.

I understand that you would need to leave 5 days ahead of the scheduled Eject burn to give yourself time to do the periapsis kick, but it still seems to me like you would be burning at the "wrong point" of the orbit. Like the periapsis kick would need to be done 10 degrees before the Eject point or something like that?

Hopefully that question is worded well enough to make sense. I apologize if it's not clear.

 

[dgatsoulis]

No need to offset the burn. But don't start the burn when "Begin Burn = 0" either.

Here is an example:

You have a plan on stage2 with a date X.
You calculate the injection dV for stage1 and you find it to be somewhere in the 6.5 km/s region.

This is where you decide how to split the burn. Obviously, you cannot split it into 4 km/s on the first pass and 2.5 km/s on the second pass, because you would never return to Earth after the first burn.

I usually have the first burn in the 3000 - 3100 region, because it is close to the dV of Moon journey and I know how long that takes.

So the "5 day" rule is a bit arbitrary. It can easily be 10 days or 3 days if you want. After you pass 3000 m/s on the first burn, the period of the orbit becomes big quickly, with using only little dV.

Back to the example.
You launch 5 days before the date X shown on stage2 and get into a parking orbit with R.Inc 0 relative to the plan. Remember that the hypothetical injection trajectory on stage1 is for the date you selected on stage2.

Looking at the T to Pe (NOT the begin burn time), you open BTC and plug in the dV for a 3000 m/s burn and see how long it takes.
For the sake of this example, let's say that it takes 100 seconds.
When T to Pe = 50 seconds, begin burning with the prograde autopilot on and stop the burn when the ApT in orbit MFD is ~200k-215k (~2.5 days).
So the burn will not be exactly 3000 m/s but ~3050 or 3060, depending on the altitude of your parking orbit.
At any rate, the difference is negligable and your burntime will be very close to the burntime you saw in BTC.

So now, you will be back at periapsis (without an offset) in ~5 days. For the second burn, you can follow the "Begin burn:" on TransX or set it up as a manoeuvre.

 

[RogerWilco]

No need to offset the burn. But don't start the burn when "Begin Burn = 0" either.

Here is an example:

You have a plan on stage2 with a date X.
You calculate the injection dV for stage1 and you find it to be somewhere in the 6.5 km/s region.

This is where you decide how to split the burn. Obviously, you cannot split it into 4 km/s on the first pass and 2.5 km/s on the second pass, because you would never return to Earth after the first burn.

I usually have the first burn in the 3000 - 3100 region, because it is close to the dV of Moon journey and I know how long that takes.

So I should expect my orbit to extend out near the moon?

So the "5 day" rule is a bit arbitrary. It can easily be 10 days or 3 days if you want. After you pass 3000 m/s on the first burn, the period of the orbit becomes big quickly, with using only little dV.

3000 m/s is meters a second, yes? Where do I find that readout?

Looking at the T to Pe (NOT the begin burn time), you open BTC and plug in the dV for a 3000 m/s burn and see how long it takes.
For the sake of this example, let's say that it takes 100 seconds.
When T to Pe = 50 seconds, begin burning with the prograde autopilot on and stop the burn when the ApT in orbit MFD is ~200k-215k (~2.5 days).
So the burn will not be exactly 3000 m/s but ~3050 or 3060, depending on the altitude of your parking orbit.
At any rate, the difference is negligable and your burntime will be very close to the burntime you saw in BTC.

So now, you will be back at periapsis (without an offset) in ~5 days. For the second burn, you can follow the "Begin burn:" on TransX or set it up as a manoeuvre.

What is BTC? Sorry about my ignorance, I just want to make sure I'm doing this right.

 

[dgatsoulis]

So I should expect my orbit to extend out near the moon?

Near the orbit of the moon. In fact it is going to be less than that, since journeys to the Moon cost slightly more than 3100 m/s, when you start from a LEO (Low Earth Orbit).

3000 m/s is meters a second, yes? Where do I find that readout?

Yes. It is known as Delta-v, which means "change in velocity". You can find it in the first stage of your TransX plan and also BTC (BurnTimeCalculator, see next answer).

In general, delta-v is a type of "currency" which tells you how much umph you can get out of your fuel. It depends on the weight of the ship, the engines and the amount of fuel that you are carrying.

What is BTC? Sorry about my ignorance, I just want to make sure I'm doing this right.

[ame="http://orbithangar.com/searchid.php?ID=4530"]BurnTimeCalc[/ame]. It is an MFD that helps you find out how much change in velocity (Delta-v) you can get from your fuel and how much time you can burn your engines before you run out of fuel.

 

[RogerWilco]

Okay, I have BTC up and running. I input 3.000 m/s as my targetDV and it says estimated burn time is 1.557 seconds and total burn time is 17.060ks. Estimated total dV is 74.556.

Am I supposed to like at t to pe in transx or BTC? What about time to apoapsis?

I'm a little fuzzy on what the goal is I am trying to reach. To do part of my total burn but remain in Earth orbit? And then do the second half on my projected launch date? (Assuming I set up my timing and orbit right)

What am I trying to discover with BTC?

I'm sorry for all the questions, I'm still trying to learn everything I can.

 

[downloaderfan]

Thanks a lot dgat,i was trying to figure out a way to get to mars or venus with MainfuelISP=0 of the XR2(from the surface of the earth),but as the ISS(to refuel) is in a highly inclined orbit with the ecliptic,i didnt have enough fuel to make it there.

Perhaps by using this 'Periapsis kick' technique,i was able to do it.The only thing i had to care of,was to adjust the eject orientation such that my point of ejection and the node were very close,so that my other node was at 180 degrees,which would allow me to change planes with minimum amount of fuel.(At the apoapsis)

I was able to get to venus with a dv of about 4.1k,plane change consumed a dv of 465.(Rinc according to transX was 85 degrees)

Aerosurfing is another option,but that would be boring. :hmm:

---------- Post added at 01:22 PM ---------- Previous post was at 12:33 PM ----------

Okay, I have BTC up and running. I input 3.000 m/s as my targetDV and it says estimated burn time is 1.557 seconds and total burn time is 17.060ks. Estimated total dV is 74.556.

You have to input 3000 m/s as u mentioned earlier and not 3m/s,the total burn time is the time that would take to burn all the fuel u have,but thats only when u have limited fuel on.

Am I supposed to like at t to pe in transx or BTC? What about time to apoapsis?

You have to look at t to pe in transX,i think u have misunderstood t to pe as time to periapsis,but it is actually the time that you have left before u arrive at ur point of ejection.

I'm a little fuzzy on what the goal is I am trying to reach. To do part of my total burn but remain in Earth orbit? And then do the second half on my projected launch date? (Assuming I set up my timing and orbit right)

I have never used the ship that u have mentioned but it seems like the ship that u are using doesn't have engines powerful enough to complete the ejection burn in one go,so u are doing it in steps,as u do the burn,u slowly raise ur apoapsis,but if u increase it beyond a certain altitude,the sun's gravity takes over and u are no longer in an earth orbit.As the engines are not powerful,u finish some part of the burn and raise ur apoapsis just enough that u dont escape earth,then u come back again at ur earth's periapsis and finish rest of the burn.

What am I trying to discover with BTC?

The t to pe refers to the point of ejection,but is valid only if the entire burn takes place in an instant.Thats why time to burn and t to pe are different.

In ur first burn,u are not planning to escape earth but planning to raise ur apoapsis to a certain extent,so with BTC,u are finding the time to burn for ur first burn,rather than for the entire burn as shown by transX.As the burn takes some time,u have to start the burn before the point of ejection so that u can evenly distribute it about the point of ejection.

 

[RogerWilco]

When I plug in 3000 into BTC it displays 3000 k/s instead of 3000 m/s. Is that normal?

So the goal of BTC is to figure out how long it would take to do the first half of my burn? Then I take that number and figure up how long before t to pe I should initiate the burn.

I want to mention I did make it to Saturn with the scenario DG posted, but I had to refuel my engines along the way, and got stuck at Jupiter first.

But still, I had never made it to Saturn before!

 

[downloaderfan]

When I plug in 3000 into BTC it displays 3000 k/s instead of 3000 m/s. Is that normal?

When u type in 3000,it should say 3.000k,meaning 3km/s,a burn time of 1.557s isn't a valid one.

So the goal of BTC is to figure out how long it would take to do the first half of my burn? Then I take that number and figure up how long before t to pe I should initiate the burn.

Yes,u subtract half of ur burn time(as shown by BTC) with t to pe as shown by transX,that is ur time to burn.

I want to mention I did make it to Saturn with the scenario DG posted, but I had to refuel my engines along the way, and got stuck at Jupiter first.

But still, I had never made it to Saturn before!

I really can't comment about that scenario since i don't have that ship but since u earlier asked,

Another question I have is how the variables for the Sling Direct view actually get put into practice. Outward angle is at 70.5432' and Inc. Angle is -3.4816.

Do I have to do anything else besides enter these values in order to get them to do what they say they will do? If so, how do I know when to do it, and how do I tell if I did it right?

Are u setting the plan such that the Pe/pl ratio is 1 and Rinc is 0 in the second stage of transX?If ur not,then u should watch David*blixel*Courtney's mars to venus to earth video,that's where i learn't how to execute slingshots.

 

[RogerWilco]

Okay I think I am getting the hang of figuring out my BTC numbers. I am assuming that my ship needs to be as close to the Earth as possible on the second half of my burn. Correct?

One issue I am facing now is what exactly I should do at apoapsis to lower my rel inc. value. I tried some basic RCS stuff and could only get it down to 30 something, which is probably not low enough at all.

 

[dgatsoulis]

Okay I think I am getting the hang of figuring out my BTC numbers. I am assuming that my ship needs to be as close to the Earth as possible on the second half of my burn. Correct?

Yes, but don't go inside the atmosphere. Go for a minimum altitude of 150 km.

One issue I am facing now is what exactly I should do at apoapsis to lower my rel inc. value. I tried some basic RCS stuff and could only get it down to 30 something, which is probably not low enough at all.

When the ship is at the node (the grey line that shows where your trajectory and the hypothetical trajectory of the TransX plan intersect), you need to burn either "NML+" or "NML-".

But this is confusing. As I mentioned on post #7 of this thread, in the scenario you posted, the ship is has a R.Inc of ~0.6°. How did that turn into "30 something"?

Let's start from the beginning.

You mentioned that you had performed transfers to other planets on post #1, but later you said that you have only flown those with unlimited fuel.

I have done transfers before in both the Delta Glider and Perseus and never had this issue before, so I am wondering what I am doing wrong.

I want to be as proper and accurate as I can. (Which means some day I'll turn fuel consumption on.)

Have you ever performed a flight from Earth to Mars, with the default DeltaGlider AND with limited fuel?

If the answer is no, go and see the links I posted on post #2.

It seems to me that you are trying to perform a more advanced flight without having a good grasp of the basics. Now, there is nothing wrong with "jumping in the deep" and learning from there, but it will be much easier for you, if take the time to learn with an easier combination of ship/flight-plan and then try something more advanced.

 

[RogerWilco]

My mistake for the confusion. I started a new scenario with the Delta Glider to try again with the Jupiter to Saturn thing. So that is why my rel inc value is so different now.

Yes, I have flown to Mars, Venus, Mercury, the moon, Jupiter and recently, Saturn. (Though I had to refuel multiple times to get to Saturn.)

Most of those trips were with unlimited fuel, save for a few moonshots and a trip to Mars at your recommendation.

I have been using orbiter on and off for years, and I can set up a transfer anywhere and move the lines around and get a good approach. The issue is that I am just changing a lot of variables without understanding what some of them actually do in detail, and I know there has got to be a better technique. I want to understand what I'm doing as I am doing it.