![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
Moho Launch Window
Mar. 20th, 2024 05:44 pmThe next job from Mission Control is to go to Duna, but before that, a launch window to Moho will open up. I will send a probe there to get some science and, if I do it right, put a satellite in orbit to use the Orbital Survey mod to begin mapping the planet.
I know this launch window is coming up because the Alarm Clock mod will apparently reach out to Alexmoon’s Launch Window Planner to tell you when those windows will be. The mod predicts the window for Year 1, Day 154.
Wanting the detailed information about Ejection Angles, Ejection Inclination, and the delta-V required, I went to the Launch Window Planner website and it gave me conflicting information. There was a not-so-good window back on Day 94 and a good window coming up on Day 269. Day 154 was pretty much the worst time to try to get to Moho.
I wasn’t sure why the dates were so different but using the protractor on the screen method of judging the 108.2 degree transfer window, it looks like the year 1, day 154 information from the Alarm Clock mod is the correct one
That doesn’t tell me the Ejection Inclination, so there may be an inclination change maneuver node needed.
It also doesn’t tell me the specific delta-V requirements. According to the KSP delta-V map:
(930 transfer + 760 capture + 2,400 low orbit) + 20% = 4,908 m/s
The KSP delta-V map suggests a possible 2,520 m/s might be necessary for an inclination change but that assumes you are going to be burning at an ascending ot descending node to match inclinations. You probably don’t need to do that but, even so, Moho is a challenge for being so deep in the sun’s gravity well and you will probably use more delta-V than even Launch Window Planner would predict. Even with the 20% I threw in there as Standard Operating Procedure, I will build with more.
As the plan is to have a single satellite perform both the visual and region orbital surveys, I add two antennas, the Communotron DTS-M1 and the RA-15 Relay Antenna because they work with the Orbital Survey map to provide Region and Visual mapping respectively. I also need to make sure I can communicate with the probe. The RA-15 is rated with a maximum range of 86 Gm. The maximum distance to Moho (semimajor axis 5.3 Gm) from Kerbin (semimajor axis 13.6 Gm) is about 18.9 Gm, so it is well within the capabilities of the antenna. In fact, before the Duna window, there is a launch window to Jool (semimajor axis 68.8 Gm) so the RA-15 should be good out to there as well.
To that satellite, I add some solar panels, two X200-64 fuel tanks, and an RE-L10 “Poodle” engine. Altogether, this works out to 6,117 m/s of delta-V, almost 50% over the predicted requirements.
There is another online application I like to use called the KSP Optimal Rocket Calculator. It’s for an older version of KSP1 and hasn’t been updated since before Making History but it is a great way to build a rocket. You enter the specifics of what parts you have available, the mass you want to lift, what planet you are lifting that mass from, and the program starts building rockets. It will build hundreds and compare the efficiency of them against one another and, in a few moments, will spit out a list of rockets, starting with what it thinks is the best.
They aren’t necessary the most usable designs but if you tweak the settings (such as excluding non-launcher engines) you will get something that works.
In this case, my 57 t craft is launched with a unexpectedly short Mainsail core, a pair of short boosters with Skipper engines, and then two more tall boosters with Mainsails, asparagus staged into the previous ones. Because I don’t have the the large nose cones yet, I use RS-AD-SL 800 Fuel Tanks to get a more aerodynamic profile, and downsize some of the other fuel tanks because of it. It’s a bit weird looking, but should work.
Mission Designation : SCAN-4
Rocket Model : ScanSat M-II
Total delta-V (to orbit) : 10,212 m/s (6,117 m/s)
Surface TWR : 1.16
Total Mass (to orbit) : 361.17 t (57.12 t)
Dry Mass : 59.69 t
Part Count : 53
Height : 31.51 m
Width : 3.94 m
Length : 8.02 m
Mission Objectives : ScanSat into Moho orbit
The first launch tore itself apart on launch because I forgot struts.
The second launch failed because, in the reload to VAB, the fuel ducts disappeared for some reason, so the staging discarded the two long tanks still mostly full of fuel.
I double and triple checked everything and the third launch was successful. . . except that I did not see the line showing my trajectory. But, though it wasn’t the most efficient burn, lacking a maneuver node at apoapsis, the craft was in orbit.
I switched to the Tracking Station to maybe get the display to reset and when I return, my craft is suddenly on a deorbiting trajectory.
So, the fourth launch goes like the third, with the trajectory disappearing, but I close out of the session and reload. The craft is still in orbit properly but it is still not showing the orbit. Closing KSP2 altogether and relaunching has the same missing trajectories but at least it’s still in orbit. Only after a reboot can I see the orbital trajectory and create a maneuver node to try my transfer.
Remember, KSP2 is in Early Access.
The Ejection Angle (where in Kerbin’s orbit you place the maneuver node) for Moho is 61.3 degrees. I use the protractor on the screen method of trying to line it up and start working on an encounter. Given the 7 degree inclination of Moho’s orbit, it is not ideal. The best case scenerio would be to use prograde only to intersect with Moho’s orbit at the craft’s periapsis. That would require Moho’s orbit to have its ascending/descending node line up with the craft’s periapsis. For this encounter, the ascending node is earlier, maybe 50 degrees. So, you have to shift the orbit using the Normal vector to pull the encounter towards that node. Prograde, normal, prograde, normal, you walk those three things together; the marker for Moho, the market for the craft, and the node. When they all come together you get an encounter.
And with a little fiddling, I get a nice polar flyby at 68 km altitude for a 10 and a half minute burn.
After burning 2/3 of the fuel, I have my encounter with 3,625 m/s of dV remaining.
Is 3,625 m/s going to be enough to get into orbit? According to the Delta-V Map. . . probably. 760 m/s for the capture and then 2,410 m/s for low orbit totals 3,170 m/s. I’m not going into a low orbit but instead am going to get into a 400 km polar orbit to do an Orbital Survey. Will less than a 500 m/s buffer be enough?
I won’t know for sure until I actually enter Moho’s sphere of influence because KSP2 doesn’t allow you to make maneuver nodes outside of the SOE you are in.
At worst, I’ll have a close flyby to get the Low and High Orbit science. Not bad, considering the first real world missions to Mercury were flybys.
And that encounter will be on Year 1, Day 254. Before that, though, the Alarm Clock predicts a launch windows for Jool (Day 199) and then the Duna window (Day 229) that Mission Control wants.
Why is the online Launch Window Planner off when the Alarm Clock, using the same data, appears correct?
I looked in the forums and found out that the problem appears to be that Year 1, Day 1 in KSP1 calculates to Year 0, Day 1 in KSP2, even though the game calendar SAYS Year 1. You can’t enter Year 0 into the Launch Window Planner website so, for the first year of game play, I will need to use the protractor method. After that, I will always need to subtrtact 1 year from the in-game calendar to use in the website.
And another thing I thought of only after the launch, is timing the launch to the Ejection Angle. This is especially important when you want an inclination to your ejection, as I think it would have helped me on this launch. So, to work this out in the case of Moho, the Ejection Angle is 61.3 degrees. With a 6 hour Kerbin day, this works to a convenient 1 minute per degree. 61.3 degrees retrograde would be 1 hour, 1 minute past sunrise which, at the Space Center, is 04:14. Launch at 05:15 at the appropriate inclination and, on the next orbit, eject at the now ascending or descending node to get the correct ejection inclination.
But I won’t be able to get that information from the Launch Window Planner until Year 2.
I know this launch window is coming up because the Alarm Clock mod will apparently reach out to Alexmoon’s Launch Window Planner to tell you when those windows will be. The mod predicts the window for Year 1, Day 154.
Wanting the detailed information about Ejection Angles, Ejection Inclination, and the delta-V required, I went to the Launch Window Planner website and it gave me conflicting information. There was a not-so-good window back on Day 94 and a good window coming up on Day 269. Day 154 was pretty much the worst time to try to get to Moho.
I wasn’t sure why the dates were so different but using the protractor on the screen method of judging the 108.2 degree transfer window, it looks like the year 1, day 154 information from the Alarm Clock mod is the correct one
That doesn’t tell me the Ejection Inclination, so there may be an inclination change maneuver node needed.
It also doesn’t tell me the specific delta-V requirements. According to the KSP delta-V map:
(930 transfer + 760 capture + 2,400 low orbit) + 20% = 4,908 m/s
The KSP delta-V map suggests a possible 2,520 m/s might be necessary for an inclination change but that assumes you are going to be burning at an ascending ot descending node to match inclinations. You probably don’t need to do that but, even so, Moho is a challenge for being so deep in the sun’s gravity well and you will probably use more delta-V than even Launch Window Planner would predict. Even with the 20% I threw in there as Standard Operating Procedure, I will build with more.
As the plan is to have a single satellite perform both the visual and region orbital surveys, I add two antennas, the Communotron DTS-M1 and the RA-15 Relay Antenna because they work with the Orbital Survey map to provide Region and Visual mapping respectively. I also need to make sure I can communicate with the probe. The RA-15 is rated with a maximum range of 86 Gm. The maximum distance to Moho (semimajor axis 5.3 Gm) from Kerbin (semimajor axis 13.6 Gm) is about 18.9 Gm, so it is well within the capabilities of the antenna. In fact, before the Duna window, there is a launch window to Jool (semimajor axis 68.8 Gm) so the RA-15 should be good out to there as well.
To that satellite, I add some solar panels, two X200-64 fuel tanks, and an RE-L10 “Poodle” engine. Altogether, this works out to 6,117 m/s of delta-V, almost 50% over the predicted requirements.
There is another online application I like to use called the KSP Optimal Rocket Calculator. It’s for an older version of KSP1 and hasn’t been updated since before Making History but it is a great way to build a rocket. You enter the specifics of what parts you have available, the mass you want to lift, what planet you are lifting that mass from, and the program starts building rockets. It will build hundreds and compare the efficiency of them against one another and, in a few moments, will spit out a list of rockets, starting with what it thinks is the best.
They aren’t necessary the most usable designs but if you tweak the settings (such as excluding non-launcher engines) you will get something that works.
In this case, my 57 t craft is launched with a unexpectedly short Mainsail core, a pair of short boosters with Skipper engines, and then two more tall boosters with Mainsails, asparagus staged into the previous ones. Because I don’t have the the large nose cones yet, I use RS-AD-SL 800 Fuel Tanks to get a more aerodynamic profile, and downsize some of the other fuel tanks because of it. It’s a bit weird looking, but should work.
Mission Designation : SCAN-4
Rocket Model : ScanSat M-II
Total delta-V (to orbit) : 10,212 m/s (6,117 m/s)
Surface TWR : 1.16
Total Mass (to orbit) : 361.17 t (57.12 t)
Dry Mass : 59.69 t
Part Count : 53
Height : 31.51 m
Width : 3.94 m
Length : 8.02 m
Mission Objectives : ScanSat into Moho orbit
The first launch tore itself apart on launch because I forgot struts.
The second launch failed because, in the reload to VAB, the fuel ducts disappeared for some reason, so the staging discarded the two long tanks still mostly full of fuel.
I double and triple checked everything and the third launch was successful. . . except that I did not see the line showing my trajectory. But, though it wasn’t the most efficient burn, lacking a maneuver node at apoapsis, the craft was in orbit.
I switched to the Tracking Station to maybe get the display to reset and when I return, my craft is suddenly on a deorbiting trajectory.
So, the fourth launch goes like the third, with the trajectory disappearing, but I close out of the session and reload. The craft is still in orbit properly but it is still not showing the orbit. Closing KSP2 altogether and relaunching has the same missing trajectories but at least it’s still in orbit. Only after a reboot can I see the orbital trajectory and create a maneuver node to try my transfer.
Remember, KSP2 is in Early Access.
The Ejection Angle (where in Kerbin’s orbit you place the maneuver node) for Moho is 61.3 degrees. I use the protractor on the screen method of trying to line it up and start working on an encounter. Given the 7 degree inclination of Moho’s orbit, it is not ideal. The best case scenerio would be to use prograde only to intersect with Moho’s orbit at the craft’s periapsis. That would require Moho’s orbit to have its ascending/descending node line up with the craft’s periapsis. For this encounter, the ascending node is earlier, maybe 50 degrees. So, you have to shift the orbit using the Normal vector to pull the encounter towards that node. Prograde, normal, prograde, normal, you walk those three things together; the marker for Moho, the market for the craft, and the node. When they all come together you get an encounter.
And with a little fiddling, I get a nice polar flyby at 68 km altitude for a 10 and a half minute burn.
After burning 2/3 of the fuel, I have my encounter with 3,625 m/s of dV remaining.
Is 3,625 m/s going to be enough to get into orbit? According to the Delta-V Map. . . probably. 760 m/s for the capture and then 2,410 m/s for low orbit totals 3,170 m/s. I’m not going into a low orbit but instead am going to get into a 400 km polar orbit to do an Orbital Survey. Will less than a 500 m/s buffer be enough?
I won’t know for sure until I actually enter Moho’s sphere of influence because KSP2 doesn’t allow you to make maneuver nodes outside of the SOE you are in.
At worst, I’ll have a close flyby to get the Low and High Orbit science. Not bad, considering the first real world missions to Mercury were flybys.
And that encounter will be on Year 1, Day 254. Before that, though, the Alarm Clock predicts a launch windows for Jool (Day 199) and then the Duna window (Day 229) that Mission Control wants.
Why is the online Launch Window Planner off when the Alarm Clock, using the same data, appears correct?
I looked in the forums and found out that the problem appears to be that Year 1, Day 1 in KSP1 calculates to Year 0, Day 1 in KSP2, even though the game calendar SAYS Year 1. You can’t enter Year 0 into the Launch Window Planner website so, for the first year of game play, I will need to use the protractor method. After that, I will always need to subtrtact 1 year from the in-game calendar to use in the website.
And another thing I thought of only after the launch, is timing the launch to the Ejection Angle. This is especially important when you want an inclination to your ejection, as I think it would have helped me on this launch. So, to work this out in the case of Moho, the Ejection Angle is 61.3 degrees. With a 6 hour Kerbin day, this works to a convenient 1 minute per degree. 61.3 degrees retrograde would be 1 hour, 1 minute past sunrise which, at the Space Center, is 04:14. Launch at 05:15 at the appropriate inclination and, on the next orbit, eject at the now ascending or descending node to get the correct ejection inclination.
But I won’t be able to get that information from the Launch Window Planner until Year 2.
