How to reach the moon from Baikonur? (RSS/RP-1)

[this_Tessa]

I am playing an RP-1 install from Baikonur and am at a point where I have the launch capability of reaching the moon. I already accepted a flyby contract to do so, but I'm struggling to find a way to actually get the encounter in simulations due to the limited ignitions.

My booster has ~7.4km/s, second stage has 4km/s and the final kickstage has 2.5km/s, so dV is not a problem, I just need to time it right. But since Baikonur is at 46° inclination to the equator, while the moon is only at 20°, I struggle with getting into the same plane. A solution I thought off would be to launch just at the right time so my initial trajectory after booster cutoff would intersect the descending node, so I could match the inclination with the second stage burn. But since the DN only appears after liftoff, I can't seem to find the right timing.

Is there something I'm missing? How do I get the timing right? Or is this approach inefficient/wrong?

[Curveball Anders]

Moved from Tutorials to Gameplay Questions.

[Leganeski]

I don't have experience with RSS specifically, but what I personally do to get to moons orbiting the home planet at a lower inclination than the launch site's latitude (for example, Iota from GPP) is to estimate the launch timing as best as I can, but then launch into orbit without worrying much about inclination. Once in low orbit, I wait until the moon is 65-70 degrees behind a relative node, and eject entirely prograde at the previous node in order to meet the moon there. It's certainly slower in terms of total mission duration, but is more efficient for achieving a flyby than changing inclination during ascent. Also, at least for me, it's a lot easier to perform.

[king of nowhere]

as far as getting into the same plane, you can easily just reach the moon when it passes through the orbital node. just wait in earth orbit until the moon is in the right place to reach by burning on a node. like this

as you can see, i'm in an equatorial orbit, I'm just reaching the moon while it crosses the equator.

you'll be coming to it with a high inclination, meaning higher intercept speed, but the moon is in high orbit, so fixing inclination is going to be cheap - and it is included in the intercept deltaV. I got 150 m/s intercept speed, so it wasn't expensive. and it doesn't require any additional ignition that you wouldn't have to perform already.

it's not the most elegant solution, but it does work.

Edited September 15, 2022 by king of nowhere

[this_Tessa]

4 hours ago, king of nowhere said:

as far as getting into the same plane, you can easily just reach the moon when it passes through the orbital node. just wait in earth orbit until the moon is in the right place to reach by burning on a node. like this

as you can see, i'm in an equatorial orbit, I'm just reaching the moon while it crosses the equator.

you'll be coming to it with a high inclination, meaning higher intercept speed, but the moon is in high orbit, so fixing inclination is going to be cheap - and it is included in the intercept deltaV. I got 150 m/s intercept speed, so it wasn't expensive. and it doesn't require any additional ignition that you wouldn't have to perform already.

it's not the most elegant solution, but it does work.

Alright, but how do I time this? With my Chronos rocket, I can't launch into a parking orbit, I need to take over some of the second stages dV for the kickstage to reach the moon and I can only light it once. This singular ignition is needed to achieve orbit in the first place, so it needs to be a direct ascent flight profile. Without eyeballing it, how do I determine when to launch?

[king of nowhere]

35 minutes ago, this_Tessa said:

Alright, but how do I time this? With my Chronos rocket, I can't launch into a parking orbit, I need to take over some of the second stages dV for the kickstage to reach the moon and I can only light it once. This singular ignition is needed to achieve orbit in the first place, so it needs to be a direct ascent flight profile. Without eyeballing it, how do I determine when to launch?

oh. i thought you had at least enough ignitions to reach a parking orbit, then launch for the moon. this complicates matters.

I still see a couple of possibilities;

1) if your last stage has many ignitions, you can just eject into a high elliptic orbit - any high elliptic orbit - and once there, use your extra deltaV (you have some 500 m/s more than strictly needed) to fix. take advantage of inclination being cheap to adjust in a slow, high apoapsis. I show an example on how to reach Gilly from high elliptic eve orbit, because it's a very similar condition - reaching a moon with high inclination and eccentricity from a constrained orbit

you can see on the bottom left I visualized the components of the maneuver. it's made in the high, slow part of the orbit because it's got a lot of radial and normal component, which are cheaper to do when the vessel is moving slow, close to apoapsis. the point is, just fling your vessel in the right direction as the moon is passing by, and use radial/normal components liberally to adjust the encounter. the whole point of this maneuver is that you can use those components and they're relatively cheap when close to apoapsis. in this case I got a gilly intercept with 160 m/s, in rss things are roughly 3 times more expensive, meaning you should be able to get your moon flyby with your 500 m/s.

 

2) the second option is a lot more professional, but perhaps more boring. it basically involves trial and error.

launch many times, at different times, trying to get a repeatable ascent profile to always get into the same inclination. do it until you manage to find the right time to launch to meet the moon at a planar node.

then check how long it would take for the moon to pass there. say you see that your lunar injection trajectory takes 3 days; time warp forward, see that the moon passes at the node 6 days later, then reload the game and launch three days later. you have enough freedom with your trans lunar injection that you can fix a difference of a few hours.

once you manage to hit a moon planar node at apoapsis, you can also drift for a few orbits until you pass sufficiently close to the moon.

[this_Tessa]

2 hours ago, king of nowhere said:

oh. i thought you had at least enough ignitions to reach a parking orbit, then launch for the moon. this complicates matters.

I still see a couple of possibilities;

1) if your last stage has many ignitions, you can just eject into a high elliptic orbit - any high elliptic orbit - and once there, use your extra deltaV (you have some 500 m/s more than strictly needed) to fix. take advantage of inclination being cheap to adjust in a slow, high apoapsis. I show an example on how to reach Gilly from high elliptic eve orbit, because it's a very similar condition - reaching a moon with high inclination and eccentricity from a constrained orbit

you can see on the bottom left I visualized the components of the maneuver. it's made in the high, slow part of the orbit because it's got a lot of radial and normal component, which are cheaper to do when the vessel is moving slow, close to apoapsis. the point is, just fling your vessel in the right direction as the moon is passing by, and use radial/normal components liberally to adjust the encounter. the whole point of this maneuver is that you can use those components and they're relatively cheap when close to apoapsis. in this case I got a gilly intercept with 160 m/s, in rss things are roughly 3 times more expensive, meaning you should be able to get your moon flyby with your 500 m/s.

 

2) the second option is a lot more professional, but perhaps more boring. it basically involves trial and error.

launch many times, at different times, trying to get a repeatable ascent profile to always get into the same inclination. do it until you manage to find the right time to launch to meet the moon at a planar node.

then check how long it would take for the moon to pass there. say you see that your lunar injection trajectory takes 3 days; time warp forward, see that the moon passes at the node 6 days later, then reload the game and launch three days later. you have enough freedom with your trans lunar injection that you can fix a difference of a few hours.

once you manage to hit a moon planar node at apoapsis, you can also drift for a few orbits until you pass sufficiently close to the moon.

Thank you, that helps out a lot. I'd still like to do some maths for it, since I'll probably need a few lunar missions with those limited ignitions, but I guess trial and error is better than not doing it at all lol

2 hours ago, king of nowhere said:

oh. i thought you had at least enough ignitions to reach a parking orbit, then launch for the moon. this complicates matters.

I still see a couple of possibilities;

1) if your last stage has many ignitions, you can just eject into a high elliptic orbit - any high elliptic orbit - and once there, use your extra deltaV (you have some 500 m/s more than strictly needed) to fix. take advantage of inclination being cheap to adjust in a slow, high apoapsis. I show an example on how to reach Gilly from high elliptic eve orbit, because it's a very similar condition - reaching a moon with high inclination and eccentricity from a constrained orbit

you can see on the bottom left I visualized the components of the maneuver. it's made in the high, slow part of the orbit because it's got a lot of radial and normal component, which are cheaper to do when the vessel is moving slow, close to apoapsis. the point is, just fling your vessel in the right direction as the moon is passing by, and use radial/normal components liberally to adjust the encounter. the whole point of this maneuver is that you can use those components and they're relatively cheap when close to apoapsis. in this case I got a gilly intercept with 160 m/s, in rss things are roughly 3 times more expensive, meaning you should be able to get your moon flyby with your 500 m/s.

 

2) the second option is a lot more professional, but perhaps more boring. it basically involves trial and error.

launch many times, at different times, trying to get a repeatable ascent profile to always get into the same inclination. do it until you manage to find the right time to launch to meet the moon at a planar node.

then check how long it would take for the moon to pass there. say you see that your lunar injection trajectory takes 3 days; time warp forward, see that the moon passes at the node 6 days later, then reload the game and launch three days later. you have enough freedom with your trans lunar injection that you can fix a difference of a few hours.

once you manage to hit a moon planar node at apoapsis, you can also drift for a few orbits until you pass sufficiently close to the moon.

Thank you, that helps out a lot. I'd still like to do some maths for it, since I'll probably need a few lunar missions with those limited ignitions, but I guess trial and error is better than not doing it at all lol

[jimmymcgoochie]

Judging by the delta-V you've listed, your rocket is actually overkill for a lunar flyby- it takes about 9km/s to launch into LEO (call it 9.5 for ascent inefficiencies and the higher inclination) and another ~3.2km/s to get a lunar intercept, so about 12.8 in total. Make the second stage smaller and the third stage larger so that the third stage does all of the trans-lunar injection (TLI) burn on its own and the second stage merely has to put the third stage in orbit and you might find it a lot easier to get there.

You could try launching to the same LAN as the Moon which would mean your relative ascending and descending nodes would be aligned and so an intercept would be easier, or launch polar so that your apoapsis meets the Moon's orbit. Either way it'll require a lot of careful timing and a little bit of luck to get a good encounter with the Moon. Doing so without a parking orbit will be doubly difficult.