Asteroid Deceleration

[warm jolt]

I've got a huge asteroid that I got into Kerbin's SOI, but I don't know how to slow it down enough for it to stay in an orbit around Kerbin. I've got 2 vessels attached to it and I managed to get it to aerobrake through the atmosphere. The problem is that the aerobraking does basically nothing to the speed, and actually increases it like a gravity assist. I tried aerobraking at 45km and then again at 10km, but it got vaporized at around 15km. I really don't know how to slow it down at this point.

[sacred glen]

maybe use engines? also an asteroid ISRU module on it helps to refuel your asteroid tug

[warm jolt]

The craft attached to the asteroid has the ability to mine and convert the asteroid into liquid fuel for my engines.

This is the craft btw

[sacred glen]

are those LF/Ox tanks?

[warm jolt]

Yeah but full of LF, no Ox

[sacred glen]

the LF/ox tanks have a much worse dry mass than the LF only tanks. its essentially like carrying liquid fuel tanks with empty oxidizer tanks, which is dry mass thats not being used, which can reduce the delta v, and in this case probably mean you will need to mine more asteroid to capture it into an orbit

[warm jolt]

But this asteroid is huge enough that I don't think a few fuel tanks make that much of a difference

It's like maximum maybe 5% of the weight or something

Maybe less

[sacred glen]

i mean yea, it will probably not be that much worse, but overall like for new designs /vessels you havent launched yet its a good idea (to use liquid fuel tanks only while using the nerv)

[warm jolt]

I don't think I have any similar parts that are only LF. Only the plane parts are, but they're not the same. Are you talking about a mod?

[sacred glen]

no, i mean like either using mk3 liquid fuel tanks, or clustering the mk1 liquid fuel tanks together

though there is probably a mod that does that better, like having any size/diameter liquid fuel only tank

[sturdy sphinx]

moar boosters

if you try aerobraking, have some radiators

[scarlet tartan]

(radiators wont help and even if they did you would need a staggerly large number of them to help cool an E class asteroid)

just use more inflatable heatshields

[scarlet tartan]

those are hardcoded to not work in reentry

[swift zealot]

it must be a staggeringly massive asteroid for aerobraking not to affect it, that seems odd

if aerobraking really is not helping my best suggestion is to revert back to when you are attached far away from kerbin and just begin braking back there. your only goal is to capture the asteroid no matter what in so long as it is captured in the same inclination you want to be in

you can have an AP right at the edge and it won't matter

I also don't see a crew compartment, you should know drills harvesting asteroids without an engineer are bugged and will overheat eventually so you will have to babysit it as you timewarp

[keen crown]

that's kinda realistic

the drag to weight ratio of an asteroid is very low

what i mean by that is that yes you have a big surface, but the thing you are towing is insanely heavy that aerodynamic forces are ridiculous compared to this monster

[keen crown]

Not sure how it increases your speed tho lol

you're always supposed to lose mechanical energy in an aerobrake, not gain any

[warm jolt]

Idk maybe it decreased it but it really didn't feel like it

The path didn't shrink visibly at all

[keen crown]

ever so slightly it did

it's not viable

and you can also accidently increase your periapsis during the process lol

costing you a lot of fuel to then lower it back again using fuel

you need to farm fuel and burn with the asteroid retrograde until your peri is really in the dense atmosphere

like 10k meters

then spam parachutes to bring it down then idk

how much? you'd need to do math

[scarlet tartan]

ehh idk if I would say that

[warm jolt]

It blew up at around 15km

[scarlet tartan]

asteroids are as dense as styrofoam

a fraction of normal spacecraft density, and an even smaller fraction of the super-osmium planets in stock ksp

even lh2 tanks are way denser

[keen crown]

try the inflatable heatshield solution they offered

[keen crown]

IRL or in KSP?

[warm jolt]

Bring it down to orbit or landing?

Man this is worse than I thought it'd be

[keen crown]

down to landing

[warm jolt]

I don't want to land it

Endgoal is minmus orbit

[keen crown]

💀

oh my god good luck with that

by the time you get to minmus orbit you'll have drilled the entire asteroid

it will become smaller than your spacecraft 💀

[scarlet tartan]

minmus is cheap to capture around

[warm jolt]

I've drilled it so far and gotten half a percent lower

From 80 to 79.5

[scarlet tartan]

you only need a couple hundred m/s to capture around minmus

[keen crown]

depends

[scarlet tartan]

you just need to aerobrake into an orbit with an apoapsis at minmus height first

[keen crown]

how you capture it

[scarlet tartan]

normal hohmann from lko

which is essentially what you have after aerobraking to minmus altitude

or you could even just straight capture at minmus

no aerobraking

just time the encounter

so you are going the same way as minmus around kerbin when you encounter it

[keen crown]

what's the speed of minus?

[scarlet tartan]

from the screenshots the relative velocity didnt seem that bad

it looked like you were only just about going kerbin escape vel

[scarlet tartan]

about 300

[keen crown]

274m/s, so yeah you need about 200-300m/s to capture it

[scarlet tartan]

and again from the shown screenshots it looked like the rel-v to kerbin was very low

[keen crown]

or actually less thanks to gravity assist

but it's minor

[scarlet tartan]

you could also just capture with the mun

that would be easier than aerobrake

and since you have such low rel-v, the mun is more than enough

gravity assist off the mun to an orbit with apoapsis at minmus altitude

[warm jolt]

I'm still relatively new to this so I'll have to see

But maybe I'll try that moon thing

I actually managed to get it to pass by kerbin at 500 meters but ended up deciding to change it to 10km

Still vaporized

I didn't know they can even vaporize

[keen crown]

I didn't know either lol

https://tenor.com/view/thanos-vanish-gif-20470261

epic embed fail

[warm jolt]

Wait so how do I do the mun gravity assist? Do I need to approach it from a specific direction and then burn retrograde?

I actually landed my first asteroid but it was class B

[keen crown]

show your orbit

[scarlet tartan]

no

[keen crown]

you want to park in mun or minmus orbit?

[warm jolt]

Then people told me it's supposed to be something really difficult that people do for a challenge

Okay I'll explain my goal

[warm jolt]

I have a space station I'm building around minmus

I found this asteroid and decided to add it to the station

[scarlet tartan]

you want to pass in front of the mun

[keen crown]

so you want to approach the mun from behind

to gain velocity

[warm jolt]

But I want to slow down

[scarlet tartan]

???

[keen crown]

idk where his orbit is that's the thing

[warm jolt]

Tomorrow morning I'll send whatever screenshots you guys need

[keen crown]

he hasn't shown me

[scarlet tartan]

that doesnt matter lol

in no situation would you pass behind to lose velocity

definitely not here

[warm jolt]

What do you mean by "where my orbit is"

[keen crown]

what does it look like

[scarlet tartan]

he is trying to lose velocity

not gain

[keen crown]

what apo, peri

[scarlet tartan]

why would you suggest gaining velocity lol

[warm jolt]

Circular, similar to kerbin

[keen crown]

is there an inclination?

[warm jolt]

Yeah

[keen crown]

important details you know

[warm jolt]

I had to go normal to rendezvous eith kerbin

[keen crown]

if he wants raise his orbit to minmus orbit maybe???

[warm jolt]

Or anti

[keen crown]

in the case that his orbit is lower???

[scarlet tartan]

he is on an escape trajectory lol

[warm jolt]

Hyperbolic orbit

[scarlet tartan]

last time i checked im pretty sure an escape velocity is higher energy than an orbit lmao

[keen crown]

i didn't read the original post how am i supposed to know that e > 1

[scarlet tartan]

you didnt read the original post

skill issue

[scarlet tartan]

you didnt even read the title apparently

[keen crown]

so how are you going to plan out a gravity assist with the mun if you are literally on an escape trajectory

[scarlet tartan]

he is coming in from solar orbit

[keen crown]

i thought he wanted to make it land through aerobraking as evidenced by my other messages

[scarlet tartan]

you enter kerbin soi, then use the mun to capture

[scarlet tartan]

now he wants to get it on minmus

keep up

[keen crown]

no crap 😭

[warm jolt]

I wanted to aerobrake to shrink my speed so that I no longer escape kerbin soi

[keen crown]

anyways

[scarlet tartan]

again skill issue

[warm jolt]

Tried 45km and then 10km

[keen crown]

yeah as if the mun is a paid actor and is already set up for that

[scarlet tartan]

you just use a maneuver node to time it

buddy doesnt know how to mun assist

burn retrograde, prograde and radially to help time and position the encounter

[warm jolt]

I could probably target mun

[scarlet tartan]

make sure to target the mun in mapview

[warm jolt]

Yeah

[keen crown]

he needs a proper orbit in order to do so 😭

[warm jolt]

No I know how to intercept well

[scarlet tartan]

he is in solar orbit

not kerbin soi

[warm jolt]

Just kinda new to gravity assists

[keen crown]

and how far from kerbin are you?

[scarlet tartan]

far enough to significantly change his kerbin periapsis

[warm jolt]

I have several saves from different points

One of them is a year before interception

[scarlet tartan]

so likely far enough to capture with mun assist, you dont need to offset the time that much to get a usable mun assist for capture

[warm jolt]

When I'm above kerbin in the solar orbit

Yeah I don't think it'll be difficult to get into mun soi

The issue is maybe getting into it in the right way

And then going retrograde at the right time

Cause this asteroid is a nightmare to rotate

And my ship starts bouncing when I rotate it

[scarlet tartan]

do you need an example of a mun assist to capture

[warm jolt]

Maybe

[scarlet tartan]

ok one minute

[keen crown]

connect to this asteroid off center of gravity

this is kinda a wacky solution

but it works

for maximum torque

[warm jolt]

I also run out of monoprop really fast for some reason, which is really annoying

I keep having to make more

[keen crown]

if you need to use them for 2 minutes just to rotate to prograde not surprised it goes down quickly

RCS is kinda slow in the first place for spacecraft, an asteroid is an entire new metric

[warm jolt]

What I did instead is use RCS to get it spinning and then turned off SAS

Let it spin and then turn it on to stop

[keen crown]

yep that works

[warm jolt]

Still difficult

Also the asteroid spins hard when I use thrust, even though I targeted center of mass. Someone told me to make the arm pivot and then target it again

[sacred glen]

i think making the arm pivioting might make it a bit unstable, idk though.
also, might be worth setting control from here on the grabbing unit

[warm jolt]

I did

I think they meant to make it pivot, aim at CoM and then turn off pivot

That way I don't have to detach

[keen crown]

whitedwarf is cooking an example but basically you just want to get a simple mun encounter, then adjust the sliders so that your trajectory is ahead of the mun (orbiting counterclockwise) and so you have to lower your periapsis the closest as possible to surface to maximize the gravity assist

[keen crown]

now the catch is that you need to do it at the right position of mun in its orbit (called true anomaly)

[warm jolt]

I'm trying to understand what I'm seeing 😅

Oh there's more

Is yellow your planned path

Like you're coming from solar

[scarlet tartan]

(with ui)

[keen crown]

it's his current trajectory

[scarlet tartan]

yellow is my path through kerbin's soi, green is my orbit after encountering the mun

[keen crown]

purple is maneuver node, and red is his orbit after the mun encounter gravity assist

[warm jolt]

So I still need to get into kerbin's soi, and then find a way so that after I go around kerbin, I pass in front of the mun

[scarlet tartan]

after the assist, make sure to raise your periapsis to not hit kerbin's atmosphere again, but from that point its just a matter of waiting for a minmus encounter

there is one tricky part though, if you cant meet minmus' orbit easily from a normal mun assist, you may need to use the mun to slightly incline your orbit

[keen crown]

you lowered the mun periapsis here?

the horizontal velocity here is so low that you hit kerbin after the assist

[scarlet tartan]

yes, you can just do an inexpensive periapsis raise after the mun encounter

also the rel-v to kerbin is very high in this example

based on his screenshots, he can probably capture much more easily without needing to do a periapsis raise

[warm jolt]

We'll see

I'll try to check tomorrow morning and I'll ping you guys with screenshots of it

[keen crown]

well ur asteroids trajectory or whatever is still curved despite the close distance

my asteroids that fly by just zoom past by lmao

straight barely curved line

[scarlet tartan]

thats cause they are coming in from highly elliptical orbits

with very high relative-v

he looks like hes only barely going kerbin escape velocity

[keen crown]

can i get normal asteroids 🙏🏻

[scarlet tartan]

ie. the asteroid has a very similar orbit to kerbin

[keen crown]

soon in minmusian orbit

[scarlet tartan]

now ive changed it to move my inclination as well

only 3.7 m/s to raise periapsis out of atmo

after that it can be very relaxed since you are already in orbit and just need to change your orbit to eventually encounter minmus

[warm jolt]

The reason I picked this asteroid in the first place was because it was E and it also went into kerbin soi on its own and had a curved path

So I was like oh hey neat, makes my life easy

I grabbed it and then I think I couldn't even move it much. Tried catching up to it inside kerbin soi with my other ship but couldn't

[swift zealot]

you really wont lose or gain any energy using the mun or minmus, you need kerbin-dense objects to significantly alter a trajectory

[scarlet tartan]

not if hes only trying to capture from an orbit similar to kerbin's around kerbol

a mun assist is enough to turn what would be a highly eccentric kerbin orbit into an escape trajectory on the way to duna

and so the same can be done in reverse

[swift zealot]

yes but you're talking VERY close, like nearly captured already

[scarlet tartan]

also ppl have used mun and minmus assists to help go to eve

they just do it repeatedly

like 10-30 times

[swift zealot]

10-30 yeah because what little it has adds up

[scarlet tartan]

it takes a lot but it saves on inclination changes when margins are thin

[scarlet tartan]

in the kerbin soi a mun assist is a lot

[swift zealot]

yeah those wild videos definitely use everything

[scarlet tartan]

its not even that little

you can get a few hundred m/s from a mun assist

especially if you are just going to duna

it can reduce the 1100 m/s transfer to 800-900

[swift zealot]

it's not really, because at the height the mun is at you're basically 90% of the way to escape. For reference it's ~800 m/s to raise your orbit to the mun and then another 200 to escape

[scarlet tartan]

he isnt trying to lower his orbit that much lmao

just look at my posted examples

[swift zealot]

people use it on crazy min max journeys to do exactly that, min max

[scarlet tartan]

my solar periapsis is already halfway to eve

and yet im able to capture with the mun

and raise periapsis with only 3.7 m/s to a minmus waiting orbit

[swift zealot]

ok fair enough, yeah apparently it does help enough

I wouldnt really use it to escape but apparently it helps for that little push to capture

[warm jolt]

@scarlet tartan@keen crown
This is my current orbit

This is my orbit after changing it to pass in front of the mun

[scarlet tartan]

Turn patched conics slider up in settings

[warm jolt]

uh oh

[scarlet tartan]

Can you try making a maneuver node at mun periapsis and see how much it costs to not escape kerbin soi

Also you can get a tiny bit closer

[warm jolt]

oh hey this works

I got it closer to mun

[scarlet tartan]

nice

[warm jolt]

It's gonna be 2 mun encounters in a row

[warm jolt]

Okay this is impossible

I make a good plan, I rotate the asteroid in the maneuver's direction, I wait until the time to burn is 0

and then I thrust and the maneuver node moves away almost immediately

yo

[swift zealot]

nice! guess we all learned something today

I will have to try mun assists on my returns