IFMD 5 Base Approach Question

[FordPrefect]

Flying the Apollo 17 mission (was IMFD 5 base approach Q)

Hello experts,

I was wondering, when using the base approach program and adjust NUM to 0.000 I end up over the previously defined target base right at my very first revolution after orbit insertion, which is fine so far. However, is there a way I can also tell IFMD several hours before orbit insertion (planet approach phase), to have my orbit not only pass right over the target base but also that the apex* of the orbit will be over the target base as well?

*with apex I mean the point of the orbit with the highest latitude (halfway between the ascending node and descending node), here in my case it is a retrograde lunar orbit and at the apex my velocity vector would be pointing to heading of exactly 270°.

Any feedback appreciated.

 

[Bullethead]

However, is there a way I can also tell IFMD several hours before orbit insertion (planet approach phase), to have my orbit not only pass right over the target base but also that the apex* of the orbit will be over the target base as well?

*with apex I mean the point of the orbit with the highest latitude (halfway between the ascending node and descending node)

I'm just figuring out IMFD5 myself, but I can help a little.....

When lined up as described, your orbit would have the following key parameters:

• Inclination = target base's latitude
• LAN = target base's longitude +/- 90^, adjusted for 360^ as needed.

The 1st part of this can be done easily in Planet Approach. In that screen, the top variable in the left column, just below the words "Planet Approach", is EqI. This is the desired inclination of the orbit you want to achieve as a result of Planet Approach and Orbit Insert burns. Set this to equal the base's latitude and you've got the 1st part of the problem solved.

I'm afraid I can't help you with the 2nd part. There doesn't seem to be a way to do this in Planet Approach.

 

[tblaxland]

The LAN for a given inclination is essentially defined by your arrival time.
You could adjust your LAN over a small range by adjusting your trajectory
to arrive at a different time but you would need to do this a long way out and the amount of variation in your LAN would be restricted.

 

[Bullethead]

The LAN for a given inclination is essentially defined by your arrival time.

Kinda what I thought. Which would mean you'd either have to do some homework before flight to figure the best launch time to arrive with the desired LAN, or you'd have to wait after orbit until the planet's rotation moved the base under your "apex". But the moon doesn't rotate very fast....

 

[FordPrefect]

Thanks guys for the input.

Well, that is interesting. The thing is, I was trying to fly the Apollo 17 mission very close to the actual timings. As it turned out I even arrived 3 hours early for LOI.
I've got to explain a bit more so the problem gets more obvious. I have a copy of a part of the Apollo 17 ALO chart (Apollo Lunar Orbit chart), which has the ground tracks of several orbits (as they have been planned) painted on it. Shown ground tracks include Rev1, 10, 13, 20, 30, 40, 47, 49, 60, 70 and 75. As you all know, Apollo 17 had a launch delay of 2 hours 40 min, which was compensated by a modified TLI burn, which shortened the overall translunar coast time by that 160 minutes, so in the end they arrived at LOI at the actual planned UTC time.
Now, on the ALO chart it is clearly visible that the first orbit (Rev 1) has its apex ( = point of highest latitude, halfway between ascending and descending node) pretty exactly over LON 42.27° East. This is because the Moon's rotation (0.5° per hour to the east) is taken into account, as Apollo 17 was to remain in lunar orbit for 23 hours after LOI until the scheduled landing time. That means during Rev 13, the apex was located nearly directly over the landing site.
Now, as I was flying this mission in Orbiter, I was targeting for a surface base located at LAT 20.1908° N and LON 42.27° E, which is the point the apex of the real mission's first revolution was located. Curiously enough, I arrived 3 hours early for LOI and the apex of my first Rev still ended up even west of my targeted base about over the landing site! (with an orbital inclination about 3 deg higher than the landing site latitude).

I'll try it once more, since I wasn't aware of being able to adjust the inclination during the planet or base approach phase in IFMD, thanks for pointing that out! However I remember encountering the same problem earlier.

 

[NukeET]

I've got to explain a bit more so the problem gets more obvious. I have a copy of a part of the Apollo 17 ALO chart (Apollo Lunar Orbit chart), which has the ground tracks of several orbits (as they have been planned) painted on it.

:threadjacked:

Sorry for that, but at least I've warned you.

Googled this chart you mentioned above and couldn't locate it. I would appreciate it if I could get the same for all flights. The "Apollo by the Numbers" site is fantastic, but the plotted ground tracks would help target the right orbital plan at roughly the right time in Orbiter.

 

[FordPrefect]

Sorry NukeET, I only have a hard copy for personal use. It was printed in the book Mapping of the moon : past and present by Zdenek Kopal and Robert W. Carder, 1974. You may find it in a public library. A friend of mine has a scanner, if time permits I'll try to scan it for you.

The only ALO chart I am aware of being available online is the one of Apollo 12:

http://www.hq.nasa.gov/alsj/a12/A12_smobtl.JPG

I too would sure love to have similar scans of the ALO charts for the other Apollo lunar missions! :mellow:

BTW I posted a video of the Apollo 17 landing site fly-over, recorded one orbit prior landing:

 

[Bullethead]

I wasn't aware of being able to adjust the inclination during the planet or base approach phase in IFMD, thanks for pointing that out!

No problem. You can also set the desired orbit's altitude the same way. That's in the variable just below EqI, 2nd down in the left column. I forget offhand whether this is listed as PeA or ApA, but since IMFD puts you in a circular orbit, it doesn't really matter . To set them, select with the Prv and Nxt buttons, then use the SET button and type in the desired value. Using the + and - buttons instead is a pain if you're looking for an exact number with multiple decimal places.

 

[NukeET]

Sorry NukeET, I only have a hard copy for personal use. It was printed in the book Mapping of the moon : past and present by Zdenek Kopal and Robert W. Carder, 1974. You may find it in a public library. A friend of mine has a scanner, if time permits I'll try to scan it for you.

The only ALO chart I am aware of being available online is the one of Apollo 12:

http://www.hq.nasa.gov/alsj/a12/A12_smobtl.JPG

I too would sure love to have similar scans of the ALO charts for the other Apollo lunar missions! :mellow:

BTW I posted a video of the Apollo 17 landing site fly-over, recorded one orbit prior landing:

http://youtube.com/watch?v=_mFkJv7sXwA

Thanks FordPrefect! For now, all I needed was Apollo 12.

I'll see if I can locate that book in the local public library.

I'm guessing you have one for Apollo 17.