Landing Operation Calculations... i.e. I Want To Land At XYZ - Can We Do It?

[NeoMorph]

Now I know that Mechjeb can land you on a dime but what about things like returning from the Mun, aerobraking and then landing in the sea.

There has to be a way of doing it.

I did find this awesome Apollo tutorial video about how they steered the capsule to do the skip manoeuvre. I never figured out how spinning the capsule could make the craft climb or dive... but this vid makes it easy to understand.

I just want to know how to be able to calculate the impact point... without MJ doing most of the work.

Oh and yeah, I'm running DennyTX's Apollo along with Deadly re-entry so the return from the moon, hitting the atmo and then managing to get it into the sea is a VERY tough thing to do I've found.

[KvickFlygarn87]

As in calculating it manually? Well, MJ does it, so it has to be possible. It's likely to be hard though! Check the source code

[Pecan]

Actually MJ doesn't do it. It'll do your return burn, usually being quite a way off on the resultant Kerbin orbit, it'll do your plane change and circularisation, quite well, and it'll do your deorbit burn very well. It certainly won't do all of them at once. As I understand it neither did/do NASA - mid-course correction and orbital stabilisation burns are normal, aren't they?

[Taki117]

The Awesome thing about Kerb in is its mostly water. Now, if you are trying to land in the ocean off of KSC that takes a little more work. Mechjeb will take into account atmospheric drag if and only if you are using stock aerodynamics. (Turn on landing guidance and then turn on the aero brake calculator)

[cantab]

KSP's aerodynamics doesn't allow a bare capsule to control its re-entry. You'll have to add aerodynamic control surfaces.

[architeuthis]

Now I know that Mechjeb can land you on a dime but what about things like returning from the Mun, aerobraking and then landing in the sea.

There has to be a way of doing it.

The Drawing Boards in the tutorial forum has an extremely helpful series of links. You don't even to have to use the forum search! Here are several pertinent ones I found there:

Kerbin Landing Chart: Land at KSC consistently from your stations.

Atmospheric Landing Charts: Pinpoint landings! [NEW UPDATE: No Protractor Required!]

KSP's aerodynamics doesn't allow a bare capsule to control its re-entry. You'll have to add aerodynamic control surfaces.

Or use FAR. Blunt bodies can produce small amounts of lift.

[zarakon]

I can usually eyeball it well enough to land near KSC from low orbit. In general I do my deorbit burn above the desert, and aim for the overshoot of the arc past KSC to be about double the height of the arc at the point above KSC

Planning a return from the Mun, or especially anywhere farther away than that, is much harder because Kerbin is going to rotate a lot. You have to figure out how long it will take you to reach your re-entry point, figure out how much Kerbin will have rotated by then, and see if your target and your entry point match up. If they don't, make adjustments and recalculations until they're correct.

[Rokker]

See below post, accidentally double posted.

Edited April 19, 2014 by Rokker

[Rokker]

Now I know that Mechjeb can land you on a dime but what about things like returning from the Mun, aerobraking and then landing in the sea.

There has to be a way of doing it.

I did find this awesome Apollo tutorial video about how they steered the capsule to do the skip manoeuvre. I never figured out how spinning the capsule could make the craft climb or dive... but this vid makes it easy to understand.

I just want to know how to be able to calculate the impact point... without MJ doing most of the work.

Oh and yeah, I'm running DennyTX's Apollo along with Deadly re-entry so the return from the moon, hitting the atmo and then managing to get it into the sea is a VERY tough thing to do I've found.

Well, just look at the mechjeb source code and see what calculations are used. This prediction will not work well with FAR. However, if you want to do skipping, FAR will be required. This is because KSP's aerodynamics are, as many people know, very, very basic. This means that the capsule's shape doesnt allow it to produce lift like the capsules can in real life since KSP hasnt given it a lift value.

[Arsonik]

If you have FAR... (otherwise skip this)

One easy way to half-ass it would be to just put your return Pe at around 38-40km, this should capture you into around a 1,000km-30km orbit. Then depending on your return vehicle, and how much re-entry heat you can tolerate, you can land on second approach with a much higher degree of accuracy (being captured at this point). Alternatively, raise your Pe back to 36-40km when you reach Ap for second pass. This will bring your Ap down closer to 300km once you hit the atomosphere again. You can safely deorbit without a heat shield attached on a Mk1 pod from an orbit roughly along those lines. Once again adjust your Pe to around 35km for third and final approach though or you perhaps might need a heat shield.

This process take a very long time as opposed to a single pass re-entry, but I use it often. Especially early on in the tech tree when I often forget to strap on a heat shield... Oops. Once you're coming in for final approach though it can be very pleasant. Hit F2 and enjoy the ride. This kind of return trajectory tends to give you almost a full orbit while in the atmosphere. You will hover along at 40-20km altitude while slowly losing your orbital velocity. Probably catch a sunrise or sunset. Good time for pictures and snacks. Don't forget to decouple all of your hardware from the pod before you come in to final approach. And do make sure to keep your velocity vector aimed at retrograde... Your capsule will survive but your parachutes might not. The stock node attach parachute will probably burn up if you lose control. If you have Real Chutes mod, they seem a bit more resilient. I tend to use 2 radials (mod) as well as a node attached chute (stock) on the top just in case something like that happens.

Also of note, it takes awhile in real-time, but Kerbin orbits are very short. So even with life support this is viable if you are just doing a quick Mun-and-back. 3 Orbits should happen in roughly 1 kerbal day I believe. I used this technique in a new game last night and the whole mission time was less then 3 days IIRC. That was a burn from the pad straight to the Mun. Science and return. No dicking around on the surface of the Mun.

Edited April 19, 2014 by Arsonik

[NeoMorph]

Yeah, Arsonik... that's what I currently do... The fun part begins when you add in Life Support to the mix too. Hit too deep and you burn up, hit too shallow and your capsule runs out of air, miss the lottery and end up on land and it gets a bit painful for the astrokerbs as the capsule goes boom.

For the Apollo capsule I decouple the forward heat shield after the temp comes down and I don't ditch the bottom heat shield at all... for some reason it makes the capsule float a bit better lol.

Regarding FAR, I didn't think it affected non-stock models.

The hard part about Apollo landings is they don't go into a circular orbit after returning from the Mun. As soon as you return to Kerbin you do the re-entry... and choosing the landing site after the first skip is what is driving me bonkers.

Edited April 19, 2014 by NeoMorph

[Rokker]

Yeah, Arsonik... that's what I currently do... The fun part begins when you add in Life Support to the mix too. Hit too deep and you burn up, hit too shallow and your capsule runs out of air, miss the lottery and end up on land and it gets a bit painful for the astrokerbs as the capsule goes boom.

For the Apollo capsule I decouple the forward heat shield after the temp comes down and I don't ditch the bottom heat shield at all... for some reason it makes the capsule float a bit better lol.

Regarding FAR, I didn't think it affected non-stock models.

The hard part about Apollo landings is they don't go into a circular orbit after returning from the Mun. As soon as you return to Kerbin you do the re-entry... and choosing the landing site after the first skip is what is driving me bonkers.

http://www.collectspace.com/images/news-041714c-lg.jpg

Apollo never actually ended up using skip reentry, the only vehicles I know of that ever actually used skip reentry were Zond 6 7 and 8.

[NeoMorph]

Well I finally figured out how to land where I want... I will have to try it out a few times to see if I can replicate it but I landed in the bay outside of the spaceport. Well chuffed. Entered the atmo about 90 degrees from the spaceport and did it with Deadly re-entry too. Well happy.

I did use MechJeb to give me landing estimations though...