Question The Moon to Earth (specific orbit)

[SiberianTiger]

Rare thing, but here I am, asking for some guidance. My goal is to fly from the Moon (an XR2 parked at a pad) to some spaceport on Earth. I agree to end my planning at an orbit with known Pe, Inc and time of Perigee passage, - having that, i would have planned further steps to capture, make a base approach and land.

My problem, however, is that, when I'm using TransX to plan my lunar Escape, I cannot make it to show Encounter view for Earth approach, and therefore I don't know what my Earth-referenced elements will be after I take off and do my Moon departure burn.

I had an idea that TransX should enable specific encounter stage automatically when the plan trajectory is near any celestial body, but it turns out, flights from a planet satellite to another specific orbit of the major planet is not handled like this.

What's the best thing to do in this case?

 

[blixel]

I think Lunar Transfer MFD will help with what you're trying to do.

 

[Tommy]

Yes, LTMFD will work. Use the TEI program in periapsis mode (not re-entry mode) and adjust the TIn so that your Pe is about 90 degrees west of the target base. Once you enter the Earth's SOI you'll make a correction burn (I prefer IMFD's Delta-V program with IMFD's Map program - set the landing target on the main config. Then, in Map, hit the mode button so that the base is shown and reduce the Ang to as close to zero as you can) and plan for a PeA of about 67k. You'll re-enter on a path that will take you over the base - and have enough distance to aerobrake and land.

 

[Cras]

Awesome. I was just thinking about how to do this. Quick question, how do you know the periapsis is 90 degrees west of the base, whilst I am adjusting the TIn?

 

[SiberianTiger]

Thank you, I'll study the MFD and try the recommended method out. By the way, does an XR2 survive translunar reentry at 67k altitude?

 

[n72.75]

Thank you, I'll study the MFD and try the recommended method out. By the way, does an XR2 survive translunar reentry at 67k altitude?

Aim for ~75 and do an inverted reentry, that way you can keep vs=0 with the radiator still open.

With the XR2 it's a balance between overheating the systems and overheating the hull.

This landing video(poor quality), was taken after performing a trans-lunar reentry:

[ame="http://www.youtube.com/watch?v=ROBchMN-HrE"]Orbiter 2010 XR-2 landing at Jarvis Island. - YouTube[/ame]

 

[Luke Skywalker]

Aim for ~75 and do an inverted reentry, that way you can keep vs=0 with the radiator still open.

With the XR2 it's a balance between overheating the systems and overheating the hull.

This landing video(poor quality), was taken after performing a trans-lunar reentry:

Orbiter 2010 XR-2 landing at Jarvis Island. - YouTube

I'd aim around 69-76 km, though i fine 64 more challenging.

and you should do an inverted landing as well. :rofl:

 

[orbekler]

I'd aim around 69-76 km, though i fine 64 more challenging.

and you should do an inverted landing as well. :rofl:

I found 65km PeA target optimal, even with XR-1 and XR-5 inverted reentry:

[ame="http://vimeo.com/33098669"]Orbiter 2010: Direct / Inverted reentry - XR-2 Moon to Earth on Vimeo[/ame]

[ame="http://vimeo.com/33339062"]Orbiter 2010: XR-1 & XR-5 Inverted Reentry on Vimeo[/ame]

 

[SiberianTiger]

When I do BaseApproach planning with IMFD 5.5 as shown in orbekler's vid 1, I'm getting "No Data from BaseApproach program" sign in the right MFD set to Surface Launch program. I had correctly linked two instances with OpShare before trying that.

Any idea why this might be happening?

EDIT: I have just tried IMFD 5.1 and sharing with Surface launch have worked like charm! :thumbup:

 

[Tommy]

Awesome. I was just thinking about how to do this. Quick question, how do you know the periapsis is 90 degrees west of the base, whilst I am adjusting the TIn?

Use object info to get the longitude of the target base, then check the longitude of the periapsis in LTMFD. Just set the Pe longitude 90 degrees west of the base's longitude. That's not perfect, of course, but unless you have an unusually high inclination (over 50 degrees) it will be close enough.

Thank you, I'll study the MFD and try the recommended method out. By the way, does an XR2 survive translunar reentry at 67k altitude?

In Orbiter 2010, it can easily survive ate 67km. In Orbiter 2006, I'd aim a bit higher - around 70km to 72 km.


If I can ever find the time, I've been wanting to do an update to my Home Direct tutorial using the "new" method of flight planning with LTMFD. The original tutorial uses IMFD for the TEI, and requires a "magic number" to set the TIn.

 

[orbekler]

...The original tutorial uses IMFD for the TEI, and requires a "magic number" to set the TIn.

I found your tutorial fundamental to get past an inverted reentry and how to stay in the safe atmospheric corridor, but, regarding the magic number, I never cared about it.

On Base Approach, I just set Cape Canaveral, pushed Hint until a solution was visible, set Alt (Reference altitude) to 145k that would bring about 65k of periapsis (checked on IMFD Map), Ant to 90°, and go.

I also tried setting Alt to 65k and ReA (Reentry angle) to 0° (tangent to Reference altitude?), it works in anyway.
Perfectly aligned with KSC.

 

[SiberianTiger]

On Base Approach, I just set Cape Canaveral, pushed Hint until a solution was visible, set Alt (Reference altitude) to 145k that would bring about 65k of periapsis (checked on IMFD Map), Ant to 90°, and go.

Why does 145k set initially plays out to 65k periapsis altitude in the end? What will happen if I just aim to 65k in the beginning and during a midcourse correction?

 

[Tommy]

Why does 145k set initially plays out to 65k periapsis altitude in the end? What will happen if I just aim to 65k in the beginning and during a midcourse correction?

IMFD has a hard time calculating the Pe at Earth when you are still within the Moon's SOI. Remember - most IMFD programs use two body solutions, and only Map considers more than one gravity source. A TEI requires a four body (Vessel, Moon, Sun, Earth) solution.

You CAN set a Pe of 65k right from the start - but only if Map's Plan mode shows a Pe of 65k (and there will still be SOME error). Setting a Pe of 65k in Base Approach will NOT result in an actual Pe of 65k - at least until you are well within the Earth's SOI. It just works out that initially setting the Pe to about 145k ends up with a Pe of somewhere around 65k.

The true skill of a craftsman is in knowing the limitations of his tools - and adjusting his method to allow for those limitations.

 

[orbekler]

Why does 145k set initially plays out to 65k periapsis altitude in the end? What will happen if I just aim to 65k in the beginning and during a midcourse correction?

At the time, setting 65k didn't work, but I could have missed something.

However, as I said in the previous post, with later tries, even with different settings it worked in anyway.

You'll have to perform several mccs (at least 3) to get PeA on 65k, but in case this value it's too high or too low, use Delta Velocity Program and adjust dVf to fine adjust 65k PeA.

I suppose ReA has a key role about how successful your reentry will be, so, if you're setting 0°, will be the roundest and smoothest you could get (to me, it worked).
If you set, absurd, 80°, you'll pearce through (and burn), but it's just a guess. :lol:

At the end, inverted reentry is all about staying in the safe corridor (60k-68k Alt) until you can flip-over at sub-orbital speed (~7.3k m/s).

Let's experiment!

 

[SiberianTiger]

I must be completely safe about reentry this time, because my daughter will sit behind and look. If the cutely painted XR2 burns up, she will cry. :hmm:

Does it make sense to mind some upper limit for the mass at reentry?

 

[orbekler]

I must be completely safe about reentry this time, because my daughter will sit behind and look. If the cutely painted XR2 burns up, she will cry. :hmm:

Does it make sense to mind some upper limit for the mass at reentry?

Of course, but usually I never mind too much: as you could see from my clip, even a (whale) XR-5 Vanguard can make it! :thumbup:
In case you feel too heavy, drop fuel!

 

[Tommy]

You'll have to perform several mccs (at least 3) to get PeA on 65k, but in case this value it's too high or too low, use Delta Velocity Program and adjust dVf to fine adjust 65k PeA.

I find I only need one MCC, made shortly after I enter the Earth's SOI. I use Delta Velocity program, and ensure that Map program is set to max accuraccy

At the end, inverted reentry is all about staying in the safe corridor (60k-68k Alt) until you can flip-over at sub-orbital speed (~7.3k m/s).

Couldn't have said it better! :tiphat:

 

[Cras]

Man, a lot of good information here. I hope to have time to attempt a direct entry with LTMFD soon.

 

[Tommy]

Using LTMFD is more accurate (and seems to be a bit more efficient) for the TEI, but a bit more difficult than using IMFD. Go to Return mode, then go to the TEI page. Once you figure out your TEj and TIn, you'll have to go back to the launch page (you need the TIn to be able to figure out the launch heading). Guesstimate your launch time (around 6400 seconds before TEj seems to work well) and take off. Once in LLO, go to the TEI page - and you'll have to reset all the data (LTMFD will now use your current orbit to make it's calcs).

I find the best time for the MCC is when OrbitMFD shows the Earth's influence at about 52%.

 

[markweasal]

the dgiv

will it work for the dgiv?