Best Orbit for Mun Survey Missions?

[reedjos]

I've found survey contracts to be a good way to raise cash in .90 (on moderate), but now I've gone and done something sort of rash. I accepted 3 survey contracts on the mun (I need to stay between 10,000m and 12,000m). I've put a lander into orbit with plenty of fuel (3500 delta v) with the intent of surveying all 12 locations with one vehicle.

My question is somewhat theoretical, but what orbit type would give me full coverage of the mun? Originally I was thinking a skewed polar orbit would be best, but then I realized the mun doesn't rotate like kerbin allowing for 100% coverage of the planet. I probably do not have enough delta v for 12 separate alignment burns, plus I need to do two ground measurements to complete the contracts.

Edited December 22, 2014 by reedjos

[Anquietas314]

A polar orbit is the best for coverage. Mun does rotate, but it's tidally locked to Kerbin - it takes a full orbit to rotate once.

[Rusty6899]

It rotates every month. The slow rotation actually helps you here as it means that you will catch every survey site without altering your orbit (apart from your height depending on the contract requirements). Stay in an exact polar orbit and you'll be fine.

[Anquietas314]

It rotates every month

It's a bit less than that. Mun's orbit doesn't take a month to complete; it's orbit (in this case, the same as the rotational period) is 6 days 2 hours and 36 minutes, according to the in-game knowledge base. Also remember that's Kerbin days - 6 hours each.

[Rusty6899]

It's a bit less than that. Mun's orbit doesn't take a month to complete; it's orbit (in this case, the same as the rotational period) is 6 days 2 hours and 36 minutes, according to the in-game knowledge base. Also remember that's Kerbin days - 6 hours each.

I suppose I consider a kerbin month to be defined as the orbital period of the Mun, maybe a Munth would be a better word for it. Although, you would then have Minmus months as well.

According to Wikipedia "A month is a unit of time, used with calendars, which is approximately as long as a natural period related to the motion of the Moon; month and Moon are cognates."

[reedjos]

Thanks for the help it should work great!

[Anquietas314]

According to Wikipedia "A month is a unit of time, used with calendars, which is approximately as long as a natural period related to the motion of the Moon; month and Moon are cognates."

Sure, that's where it comes from, however... why should we assume the Kerbals have the same construct? 6 days is pretty much their equivalent of a "week".

(We also know better now that a month isn't actually very close to the Moon's orbital period at all - it's a few days off, never mind the fact month lengths are all over the place. February is closest at 28 days - the Moon orbits in ~27 days according to google).

Edited December 22, 2014 by armagheddonsgw

[Rusty6899]

Sure, that's where it comes from, however... why should we assume the Kerbals have the same construct? 6 days is pretty much their equivalent of a "week".

(We also know better now that a month isn't actually very close to the Moon's orbital period at all - it's a few days off, never mind the fact month lengths are all over the place. February is closest at 28 days - the Moon orbits in ~27 days according to google).

I'm not one to back down from a pedantic internet argument. From the KSP Wiki;

"A sidereal Kerbin day is 6 hours long, the Mun has an orbital period of 38.6 hours which defines a Kerbin month, and Kerbin has an orbital period of 2556.5 hours which defines a Kerbin year."

http://wiki.kerbalspaceprogram.com/wiki/Time

[Anquietas314]

Rusty6899: remember the wiki is almost entirely community-managed. As a technical definition, sure you can define a Kerbin month as 38.6 hours... but that's not a useful unit of time given a week is just under a day longer. Granted the whole idea of a week originates mostly from religion, and maybe the Kerbals don't have any religions on their planet, but that doesn't really matter.

EDIT:

Although, you would then have Minmus months as well.

Shouldn't those be called "minths"?

Edited December 22, 2014 by armagheddonsgw

[Tex_NL]

...

Shouldn't those be called "minths"?

Could that be the explanation of the minty colour?

[Anquietas314]

Could that be the explanation of the minty colour?

I think that's probably unrelated lol

[OhioBob]

(We also know better now that a month isn't actually very close to the Moon's orbital period at all - it's a few days off, never mind the fact month lengths are all over the place. February is closest at 28 days - the Moon orbits in ~27 days according to google).

The Moon's sidereal period is 27.3 days, but it's synodic period is 29.5 days. Sidereal period is referenced to the stars while synodic period is referenced to the Sun. The synodic period is the time between phases of the moon and is much closer to the duration of a month on Earth.

[Anquietas314]

OhioBob: I am going to blame Google for it not bothering to mention it was referencing the sidereal period, but 29.5 days is still neither 30 or 31, the two main month lengths (cue comment regarding our arbitrary calendars )

[LethalDose]

My question is somewhat theoretical, but what orbit type would give me full coverage of the mun? Originally I was thinking a skewed polar orbit would be best, but then I realized the mun doesn't rotate like kerbin allowing for 100% coverage of the planet. I probably do not have enough delta v for 12 separate alignment burns, plus I need to do two ground measurements to complete the contracts.

In my view, this is a question that doesn't have a single correct answer.

A polar orbit will eventually get you full coverage of the entire planet, but it will take the most time to do it, largely because it will take more orbits to cover the entire equator of the planet, where the orbital tracks are furthest apart.

It's also possible that you may miss some some sites on one munar rotation, and not be able to hit them again until the next semi-rotation, so in practice, it may take a while to hit everything.

An inclined orbit will cover it's ground track faster, but will never cover sites with latitude above it's inclination (e.g. a satellite with an inclination of 40 degrees will never cover a site at Lat 50 degrees).

So if all your sites are near the equator, you'll more reliably get them covered quickly with an orbit with it's inclination greater than the latitude of the northern- or southern-most survey point.

If your sites are all over the place, just use a polar orbit, but you'll have a longer wait to hit everything.

So, two answers, just conditional on exactly what you're trying to do.

Edited December 23, 2014 by LethalDose

[Kryxal]

You could always compromise ... a mapping orbit, then ONE plane-change to pick up a missed site or two.

[reedjos]

I came in equatorial and landed at a ground survey site. Then took off on a polar orbit at 90 deg inclination and mapped all of my sites. Various altitude changes to speed up warp, but I still had over 1300 delta v to return home. I had a fourth contract to plant a flag on the mun, but I was so excited by sticking my landing in the dark on a steep slope that I completely forgot about it.

Survey 13 sites for 3 contracts

Revenue: 1,017,000 (including advances)

Vehicle Cost: 49,499 Gross, 43,372 Net after recovery

Profit: 973,628

Science Center Level 2: Priceless

[CrazyJebGuy]

Rusty6899: remember the wiki is almost entirely community-managed. As a technical definition, sure you can define a Kerbin month as 38.6 hours... but that's not a useful unit of time given a week is just under a day longer. Granted the whole idea of a week originates mostly from religion, and maybe the Kerbals don't have any religions on their planet, but that doesn't really matter.

EDIT:

Shouldn't those be called "minths"?

Kerbals are christian. They are smart enough to invent computers and space travel, anyone that smart must surely be wise enough to be christian.

[Pecan]

Kerbals are christian. They are smart enough to invent computers and space travel, anyone that smart must surely be wise enough to be christian.

Thank you for that crazy message. Certainly told me how thick I must be.

Still, I managed to find 4 Kerbal computers, having never seen any evidence of one before, so now I know. Pity they have no game effect though.