Flight Question Flight to mars HELP

[ben bradford]

Hi all,
i'm fairly new to orbiter (3-4 months) and have been so far successful with my flight to mars. However, i have come accross a slight question that cant really be answered in the tutorials i have seen.

I was just wondering:
Whilst in cruise you have to do inflight corrections (with transx)
But how do you no when to carry them out ? My inc. is matched with mars's inc so is that all you have to correct every now and then?

If anyone has any feedback, it will be appreciated,
Ben

 

[TSPenguin]

In theory, corrections are most efficient when done as early as possible. Up to the point that you don't need them because your initial burn put you on a perfect trajectory.

When using an inaccurate tool such as TransX, it is a good idea to do them once your trip length halves. So you start with the mid course correction (MCC), which is exactly half the way from your target. Then do the next when you are 3/4th the way and so on.
Given that you need to make them.

Happy Orbiting

 

[ben bradford]

how do i no though when to make these burns? on transX's targeting view(manouver plan) it says something like 'T to manouver' and then the relative v. t manouver keeps going down (-216.56, -216.57 and so on) this is the only bit i dont get. As i said at the beginning, how do i no if burns are neccessary and when do i make them.....

 

[PaulG]

First, try using IMFD, it is much easier to use than TransX, once you get the hang of it. With that, you'll find your course corrections will be minimal. I generally do the first about 1/2 way there, and then again 1/2 the remainder of the distance. I watch the dV needed for target to make sure it doesn't go very high and correct as needed. Corrections should really should be minimal.

 

[TSPenguin]

You as a pilot have to set the date for the maneuver. Enter maneuver mode and switch through the variables, there is a date one. That is what the time to maneuver and time to burn refer to.

 

[MetalMania]

I just completed my first successful flight to Mars following one of the TransX tutorials. Even the tutorial I followed just basically said "it's up to you to decide when to do your corrections". I made the first one after I had completely escaped Earth's gravity (G=0.0 in the Orbit MFD with Ref set to Earth, you will also know when you're at this point when TransX drops the initial Earth escape stage of the flight plan). Other than the final orbit insertion burn, this first correction was the biggest one with a Dv of around 270. After that I just waited until a couple of months had passed to make my next one. Using the 1/2 distance guide given above is probably better but I just "eyeballed it". The subsequent corrections were really small, like Dv of less than 2 each time. I used my RCS thrusters for them since a short main engine burst could easily be too much.

Here's a couple of things I noticed that might help you. When you go into maneuver mode and set up your variables, be careful not to change the "man date" to a time before the current sim MJD or the time to maneuver will be negative when you go into the target view - basically telling you that you're already past the maneuver time that you set up. Also, the Cl. Approach value represents the radius from the planet's center, NOT distance above the surface. I failed to recognize this on my first approach since I usually have the Orbit MFD PeA/ApA/Alt set to display as altitude from the surface. So instead of setting up a nice tight low Mars orbit I had set a course for deep inside the core of the planet! Set your Cl Approach to be higher than the Maj Rad value shown in the Encounter View, and get your estimated altitude above the surface from the Min Alt value shown on the same screen. If that value is negative, make a correction burn to raise the Cl Approach! I made most of these adjustments well outside of Mars' sphere of influence (G value in Orbit MFD was still 0), and the required Dv to make significant changes to my approach was ridiculously small, like I said - only required small linear RCS bursts.

I'm sure on my next try I could do it better, and I have some other questions that I'll probably make a separate post for, but most importantly I made it and TransX makes more sense to me!

 

[atuhalpa]

I've learned through experience to watch my closest approach readout carefully. As long as it is decreasing I don't even make a correction. Once it stops decreasing and just starts to increase is when I do my first correction. This seems to save me quite a bit of dV. Of course I always tweak my injection burn to be as accurate as possible first.