Double gravity assist

[Matte]

How is it possible to obtain a gravity assist twice from the same planet, as should happen in cassini addon with
Venus, or in Galileo one with Earth?
i know i need to use trans X, but is it possible to program a double assist one after the other by the same planet?
ty

[Elington]

Hello Matte

It's just that there's an additional Deep Space Maneuver between the 2 Venus swing-bys on the Cassini flight plan.
Sorry I don't have more details but you may find more data on the web.

Best regards,
David

[Matte]

so u mean i have to do:
1)escape earth plan
2)sun centred plan
3)sling venus
4)sun centred plan direction venus
5)sling venus
6)sun centred direction Earth
7)earth sling
8)sun centre direction jupiter
9)sling jupiter
10)sun centred direction Saturn
11)saturn centred encounter                          ?????????????????????????

is it right?????

[Elington]

Sorry I don't speak "TransX" !
Yet I think you lack an engine burn sequence between steps #4 and #5. Apart from that it looks like the Cassini flight
plan

[Matte]

i'll try.
but what "language" do u speak?
what do u use for flight plans? for interplanetery travels^

[Elington]

I'm currently coding NavMFD3.0
http://monsite.wanadoo.fr/navmfd-3x

[Matte]

And how is it??

[DocHoliday]

hehe, if you ask the author you know what the answer will be

Say, Elington, does NavMFD predict the case where you are in Lunar orbit and wish to use Earth for gravity assist to
push on to Mars?

So you start in lunar orbit, go back to Earth (TEI) and at perigee, burn for Mars?

TransX is currently short on that, only support the other way around... IMFD I believe also.

You're my only hope, Obi Van Elington

[canadave]

Good questions, which raise another question that just occurred to me:

Would it be possible for any of the nav MFD's (NavMFD, TransX, TransferMFD, etc) to use more than one MFD screen
to display output/information?  In other words, for instance: when calculating a trip to Mars from Earth, focus on the
Earth orbit in one MFD (showing the ejection point, delta-V, etc) and hijack the other MFD to show a zoomed-out view
of the orbit in terms of the inner solar system?

[Elington]

DocHoliday wrote:
hehe, if you ask the author you know what the answer will be

The answer of the author is "will I ever complete that damn buggy thing ?"

The answers are yes and yes (you know what, I'm happy )

The trajectory computation routines can navigate up and down within the solar system tree without any restriction.
In your example DocHoliday, the whole computed trajectory would be composed of several "legs":
- the first one from LEO to the encounter with the Moon's SOI (sphere of influence),
- then an hyperbolic part around the Moon (or more complicated with another burn sequence),
- once again in the Earth reference frame, from the Moon, to the exit of the Earth's SOI
- around the Sun until the encounter with Mars
and so on...
Actually there will be more legs because vessel maneuvers also "cut" the trajectory into smaller parts.

What's funny is that this flight was used as a tutorial for navmfd2.3 two years ago ! The main difference with the
coming navmfd3 is that now it's not necessary to define targets anymore. The engine takes into account all existing
objects. Also thanks to the numerical engine, multiple gravity fields are taken into account simultaneously, I mean
a moon has an influence on the trajectory even if you're not in its sphere of influence, you just have to be "close"
enough (perturbation computation).

And yes at any time you can use two mfds to optimize different parts of the trajectory (also already available with the
older versions).

Well everything's not that nice: at the moment there's a bug reading the vessel configs of the NASSP5...
Back to the compiler

[DocHoliday]

Hm..

Yes, I tried the tutorial again. It's been a while since I used NavMFD so I went exactly as instructed. Now, I don't
know why, but the burn to Moon was too short. After the first burn (Man0) DG was still in a higly elliptical orbit around
Earth... I thought this might be okay, so I let it proceed. Man1 (formerly AAOP) also took place and I was still in orbit
of Earth... The funny thing is I went EXACTLY by the numbers in the .pdf. I had a FPS of 100 all the time and I didn't
switch views to external, nor did I use time acceleration, so miscalculation is probably not an option. Now I either did
something wrong, there is a bug, or the tutorial is somehow out-of-date...

Could you test the tutorial yourself? I have a feeling that SOMETHING must have changed since you created the
tutorial and the current release of orbiter. For example the DG itself. In your .pdf you predict that DG has a maximum
dV of about 40km/s, while the current DG only has around 34... Now I'm sure this isn't the problem, NavMFD probably
takes into account ISP and vessel mass, so the calculations should compensate for the burns...

I tried several times, I even tried a simple Earth-Moon flight and it still came up short on the burn. I tried different
vessels and all that.. I'm really frustrated....

About my question: I mean this scenario.. Moon-> Earth -> Mars... (not Earth-Moon-Mars) You start in orbit around
Moon and then slingshot around Earth towards Mars.. The way I see it, NavMFD should be able to do that (while
IMFD and TransX cannot, heh), I just need you to confirm that.


PS: NavMFD 2.5 crashes when I try to use it... Do I need anything else to run it? The readme mentiones collision
detection. Is there a module that I need to get somewhere for that or is it included? I am using the NavMFD2.5 pack
that's available on orbithangar.com....

[Elington]

Hello Doc,

Sorry for the inconvenience, the 2.3 and 2.5 versions are obsolete ! I gave the example of the 2.3 tutorial to answer
your question, I didn't think you would actually try to fly it . These plugins use the former thruster interface of
Orbiter and the engine data they get back from the sdk is erroneous, that's why your burn was too short. And that's
also why they're not on AVSIM anymore

I misread your initial question (Earth-Moon-Mars instead of Moon-Earth-Mars). Anyway that makes no difference for
the mfd.  The current 3.0 dll can already handle such a flight (at least with most existing vessels). So if you need a
tool for this trip right now, I can send it to you. However this version is more complex than the former ones and the
doc is very thin at the time so...

Best regards,
David

[DocHoliday]

Hello,

Ah, good, I thought I was the ONLY one in the world who can't use these nav tools.   I also discovered that the
accuracy of the calculation depends on the MFD update rate. E.g. I had 0.2 seconds and then I put it up to 0.5 and 1
update/second and every time the burn lasted a little longer... So I thought the calculations were somehow tied to
the update rate of Orbiter (at least I think you mentioned something like that in the docs)..

Well, there is also an issue with the sound. If you fly in DGIII for example, the engines sound is replaced by one of
the countdown sounds. There is a way to circumvent this by setting the "soundbase" variable to a value from 0-60.
The higher the safer. 60 being the last acceptable value, so (60-total_number_of_NavMFD_sounds).

Yes, I would love the 3.0 dll. No problem about the documentation, I think I can figure it out. NavMFD is IMO the most
intuitive of the three (TransX, IMFD), so if you didn't change the whole concept I should get from Earth to Moon at
least

Cheers,

[Elington]

Sent !

The concept is the only part that has not changed ! I hope you'll still find it intuitive.

Regards,
David

[DocHoliday]

Yes, yes I was actually at a point where I would use NavMFD for the planning and then manually execute the
maneuvers, because math itself seems very accurate to me only the autoburn

Will be in touch.