## Kerbal Space Program

Of the Tabletop, and other, lesser varieties.

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Carlington
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### Re: Kerbal Space Program

So, the most recent What-If (the one about golf ball rockets) caused me to realise that I can take the rocket equation, and re-arrange it to solve for fuel mass needed for a given delta-v. I feel reeeeeeeeealllllly dumb for not thinking of that before now, I've just been putting together different combinations of fuel tanks and payloads and engines and then solving for delta-v each time to see whether it's enough. So this should speed up my rocket design process a little, hopefully.

Also, I wanted to ask you guys, when (if) you do actual calculations to work out the delta-v of your rockets, do you do it stage-by-stage and add it up at the end, or do you work out the combined specific impulses of your engines and do it all as one big sum? Is there even a difference between the two methods?
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SecondTalon
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### Re: Kerbal Space Program

Cal..cu..lations?

Yeah, I just eyeball things because I never learned that part of physics. If I did, though, I'd do it by stages in reverse order as ... well, I'm assuming that the delta-v would change based on the payload and the power of the thrust, so calculating engines that aren't firing as anything but payload seems... odd.

But I'm probably missing something.
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Suzaku
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### Re: Kerbal Space Program

If I understand correctly (and it's possible of course that I don't), you have to do it per-stage-and-sum. And for each stage you should consider the entire mass of all stages above it as 'dry' mass.

So if you have a 10-ton launch stage with 8 tons of fuel lifting a 1-ton payload, you need to use 11 tons as the initial (fueled) mass and 3 tons as the dry mass, even if the payload is 80% fuel as well. The reason being that the payload engines aren't helping in the launch phase, so they and their fuel are just dead weight.

TBH, though, I use the Kerbal Engineer Redux mod to calculate mass and dV, because while I wouldn't mind doing the Isp and dV calculations myself, I really could not be arsed to add up the individual masses of all the parts on my ship, and I haven't found an in-game total mass display accessible from the VAB.

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Carlington
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### Re: Kerbal Space Program

Doing it stage-by-stage does make the most sense - the rockets that aren't firing are just dead weight, not sure why I didn't realise that. I enjoy doing the calculations out by hand usually - aside from which, I don't know how much more hardware-intensive modding the game would make it, and it runs slowly enough as it is.
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Suzaku
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### Re: Kerbal Space Program

I only use KER, and only in the VAB, not in flight. It can clunk a bit if you make radical staging changes on a big ship with a high part count, but other than that it's very non-intrusive. There is a Flight Engineer component that displays in-flight data, but I've never tried it so I don't know how hardware intensive it is.
As I say, though, if I could easily get the total mass of the ship without using it, I'd do the calculations myself.

I've never tried any other mods, but I am thinking of putting in Kerbal Alarm Clock to remind me of key events coming up on long-term missions. Maybe just getting into the habit of checking the tracking center first and last in each game session will be enough, though.

EDIT: In other news - and the reason I'm thinking about KAC - I just sent my first probe to Duna. Just a simple probe to do some basic preliminary analysis (Temperature, Pressure, Seismic Activity). Unfortunately, there was just a touch too little aerobraking, and it wasn't ruggedised sufficiently to withstand the subsequent lithobraking phase Still, I got the atmospheric data back.
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yurell
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### Re: Kerbal Space Program

Carlington wrote:Doing it stage-by-stage does make the most sense - the rockets that aren't firing are just dead weight, not sure why I didn't realise that. I enjoy doing the calculations out by hand usually - aside from which, I don't know how much more hardware-intensive modding the game would make it, and it runs slowly enough as it is.

You definitely do it stage by stage and then add. Your dry mass for each stage is the dry mass of the items in that stage itself plus the mass of the rest of the ship. If you tried to lump all the stages at once into the equation, you would find absolutely no difference between staging and not.
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SecondTalon
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### Re: Kerbal Space Program

And, I imagine, an enormous surprise when your eight stage craft doesn't even wiggle off the launchpad on full power.
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Will
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### Re: Kerbal Space Program

Yeah, KER is pretty much indespensable for me, because doing dv calculations otherwise is such a pain. It also gives you the (full) mass of each of your stages, which makes it a lot easier to do dv calculations when you need to (e.g. when building a craft in orbit)
Carlington makes a good point about solving the rocket equation for m0. That can be really really useful.

SecondTalon wrote:Cal..cu..lations?

Yeah, I just eyeball things because I never learned that part of physics.

The rocket equation is ridiculously simple for something that is literally rocket science. There's not a lot you actually have to learn.
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Suzaku
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### Re: Kerbal Space Program

So, turns out that Kerbal Alarm Clock rocks.

Great Thing 1: Automatic alarms triggered when planets line up for a transfer window, with configurable lead time. Want to go to Eve, want to do other stuff in the meantime, but don't want to miss the transfer? Just set up an alarm and it will tell you when you need to pay attention.

Great Thing 2: Can store manouver nodes with the alarms. Have a node set up for the perfect Minmus escape burn in 15 minutes, but want to EVA to get more science? No worries, just set up an alarm 30 seconds before the node, do the EVA or whatever, and when the alarm triggers select 'Restore Manouver Node'. Also works with switching ships, going back to the space center, etc.

Great Thing 3: Inter-dimensional (Earth Real Time) alarms. Need to go to bed at a reasonable time? Just set an alarm and it will automatically pause the game and tell you to pack it in! Brilliant!

I'm sure there are other Great Things as well, but I haven't discovered them yet
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Wnderer
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### Re: Kerbal Space Program

Is there a use for IVA?

yurell
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### Re: Kerbal Space Program

Immersion and screenshots. That's about it, though; it doesn't actually offer any gameplay or UI enhancement.
cemper93 wrote:Dude, I just presented an elaborate multiple fraction in Comic Sans. Who are you to question me?

Wnderer
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### Re: Kerbal Space Program

yurell wrote:Immersion and screenshots. That's about it, though; it doesn't actually offer any gameplay or UI enhancement.

That's what I thought but I always seem to be finding new features I should be using, so I thought I'd check.

SlyReaper
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### Re: Kerbal Space Program

You can actually click drag a lever in the cockpit to throttle up and down.

What would Baron Harkonnen do?

Suzaku
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### Re: Kerbal Space Program

There is a radar altimeter in IVA that shows your altitude above the ground, as opposed to the altitude above datum the main (top-of-screen) altimeter shows.

It's ... somewhat useful ... when landing under power.

There are mods that show the AGL altitude on the main screen, of course, but IVA is the only way to get it in vanilla.
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jotun
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### Re: Kerbal Space Program

The IVA radar altimeter is quite useful if you're doing a landing in the dark, especially if you don't have lights on your lander

It's also pretty cool to fly planes and drive rovers in IVA, though the stock cockpits don't provide very good views, if any at all. The cone-shaped plane cockpit is decent if you angle it downward, but then your navball orientation is screwy, so you'd probably want to add a probe core to "control from"

Will
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### Re: Kerbal Space Program

I do a lot of IVA-only missions, because I find it an interesting challenge. I usually use mods that give me a lot more data in-cockpit, though, like RasterPropMonitor
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Suzaku
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### Re: Kerbal Space Program

Suzaku wrote:It's ... somewhat useful ... when landing under power.

By which I meant "absolutely essential and can't be done without."
Looks like I need to work on my understatement-fu.
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Wnderer
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### Re: Kerbal Space Program

I use kdata for the radar.

http://kerbalspaceport.com/kdata/

Suzaku
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### Re: Kerbal Space Program

Interesting looking (nice and simple) mod.

I use KER for VAB stats, and have recently started adding the Flight Engineer component for in-flight data. It also gives a height above terrain, but with an interesting bug; over water, it actually gives the altitude over the sea floor, not the sea surface.

Does kdata have the same problem? The IVA radar altimeter doesn't, I don't think.
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Wnderer
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### Re: Kerbal Space Program

I haven't noticed if there is bug over water, but then I don't pay that much attention to splash down. I used kdata before I found KER and got used to the kdata format.

Suzaku
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### Re: Kerbal Space Program

Yeah, it's not critical; use whichever value is lower.

It's just that I only figured out that's what it was doing yesterday, because I don't usually land under power on Kerbin, I just use parachutes, so I don't care about AGL altitude. Landing on Minmus, on the other hand...

Speaking of which, I was going for a high-southern-latitude Minmus landing the other day to hit the 'Highlands' biome. Discovered that the mesa I was aiming for is high enough above datum that the nav ball doesn't automatically switch to surface mode. Made the landing interesting, as I thought I was going straight down but actually had a lateral velocity relative to the ground equal to Minmus' rotational speed. Good thing it was near the pole, as equatorial rotation speed would probably have killed me.

*Note to self* Add "Nav Ball to Surface Mode" to the descent and landing check list.
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Carlington
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### Re: Kerbal Space Program

I am not sure whether this counts as boasting (I don't want to be boasting), but I've never used IVA or any kind of mods for any of my landings, under power or otherwise. I generally land on the lit side of a body anyway, because I'm using solar panels a lot, and I usually just eyeball it and do fine. I've only crashed once - the first time. Landing on slopes is tricky, granted, but often if I'm landing on a flat enough surface I don't even need solar panels - they're only useful for keeping RTS and...the other thingy turned on to keep it stable. I mean, I've only visited Mun and Minmus so far, I'm in career mode and I don't have tech high enough to go further out than that yet. So yeah, when you say "impossible", is that impossible impossible, or just kinda tricky?
Kewangji: Posdy zwei tosdy osdy oady. Bork bork bork, hoppity syphilis bork.

Eebster the Great: What specifically is moving faster than light in these examples?
doogly: Hands waving furiously.

Please use he/him/his pronouns when referring to me.

Suzaku
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### Re: Kerbal Space Program

I tend to come in quite fast, and it's a rude shock to find that I'm only 500m AGL instead of the 5000m I thought I was. I can decelerate from 150 to < 10 m/s pretty easily in 5000m, usually not in 500.

This is more a problem on the Mun than Minmus, simply because the gravity's stronger there.
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Kulantan
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### Re: Kerbal Space Program

Suzaku wrote:I can decelerate from 150 to < 10 m/s pretty easily in 5000m, usually not in 500.

More engines. Its the only Kerbal thing to do.
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Wnderer
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### Re: Kerbal Space Program

I used to land on Minmus and Mun without the radar. Looked for the shadow of the craft to know when to really slow down. The radar really helps avoiding getting neffed (not enough fucking fuel).

SecondTalon
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### Re: Kerbal Space Program

..... Yeah, I just drop a stage as I descend and track when it blows up. Then I know I have 4km or whatever to the surface.
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Izawwlgood
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### Re: Kerbal Space Program

Real Kerbalnauts land with Separatrons.
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yurell
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### Re: Kerbal Space Program

Izawwlgood wrote:Real Kerbalnauts land with Separatrons.

Real Kerbalnauts land with EVA packs
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Will
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### Re: Kerbal Space Program

Real Kerbalnauts land horizontally, like an airplane ...on Minmus.
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Izawwlgood
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### Re: Kerbal Space Program

... with gigantic melancholies and gigantic mirth, to tread the jeweled thrones of the Earth under his sandalled feet.

Steax
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### Re: Kerbal Space Program

Quick question - what's the most fuel-efficient way to dock 2 spacecraft sharing the same orbit?
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SlyReaper
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### Re: Kerbal Space Program

Steax wrote:Quick question - what's the most fuel-efficient way to dock 2 spacecraft sharing the same orbit?

A very tiny burn prograde or retrograde, then wait a few thousand years for the two craft to drift together.

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Steax
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### Re: Kerbal Space Program

I dunno, I think my kerbals wouldn't enjoy sitting around for a dozen thousand years or so. Any faster methods? :p
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SlyReaper
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### Re: Kerbal Space Program

Yeah, a slightly bigger prograde or retrograde burn. But you asked for the most efficient, and in orbital mechanics, "most efficient" is usually equivalent to "slowest".

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Steax
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### Re: Kerbal Space Program

I was fiddling with the burns, and even with me trying my best to hit either prograde/retrograde exactly on the spot I always end up veering off course slightly in some way or another. I could just keep going and do more correction burns as I get closer, But it's touchy and slow, so I was wondering if there was some of crazy method to deal with this. I'd like to set up a bunch of tugships that share an orbit, so I can send up a rocket at any time and latch on to the closest tug. I also want to be able to be able to move components between the tugs, so I could merge two tugs together and so forth.

And yeah, I know my mistake. I'd say KSP is one of the few environments where answering stuff literally could be a good idea, though; I foresee some situations where I would opt for a millenial docking operation. ... Well, more like I've already done them before.
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Izawwlgood
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### Re: Kerbal Space Program

It depends how you're spreading the burn over the exact point. If you need to, say, put out 300m/s delta-v at the 1m mark, and can only generate 10m/s delta-v per second, you want to start your burn 15s before the mark, and continue it 15s after the mark. depending on how precise you're trying to me, this will throw your maneuver off a scoch, as you're not getting slammed with 300m/s delta-v exactly at the 1m mark.
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Wnderer
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### Re: Kerbal Space Program

I haven't tried docking yet, but I use the ion engines to make small adjustments to my orbital approaches. It's hard to find a place to put it because they don't mount radially. My most successful configuration has the ion engine on the bottom of a central liquid fuel tank. This fuel tank has four other fuel tanks with four liquid engines mounted radially. I then use fuel ducts to connect the center tank to the radial ones. I then hit the 'corners' of the ball (N, 90, 180, 270, blue, brown) to adjust the planetary encounter PE.

Steax
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### Re: Kerbal Space Program

In my attempts to shove orbiting satellites around, I may have reenacted Gravity.

Whoops.
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Suzaku
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### Re: Kerbal Space Program

Fortunately you can't cause a full-blown Kessler Syndrome in KSP; the physics range isn't big enough.
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Izawwlgood
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### Re: Kerbal Space Program

Wnderer wrote:I haven't tried docking yet, but I use the ion engines to make small adjustments to my orbital approaches. It's hard to find a place to put it because they don't mount radially. My most successful configuration has the ion engine on the bottom of a central liquid fuel tank. This fuel tank has four other fuel tanks with four liquid engines mounted radially. I then use fuel ducts to connect the center tank to the radial ones. I then hit the 'corners' of the ball (N, 90, 180, 270, blue, brown) to adjust the planetary encounter PE.
I've forgotten to put RCS on ion satellites before and just flipped the satellite around to dock it. That said, this definitely only works with very very small satellites.
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