Joolian Relay Network

[Ouega]

Hi everyone !

I'm not used to post here, but i got a problem. I played my career a long time and it's gonna be the time to set some relays around Jool to prepare future missions.

I used to place a cheap but efficient 2x relay method around Kerbin, Eve and Duna, as shown below.

Spoiler

2 sats placed on approx. polar orbit.

 

Quick look at the Perispsis of each relay.

Well, it worked fine for those 3 planets. But now, im encountering Jool with my ship carriing 2 relay sats, and I just can't reproduce this pattern. Let's take a look at my ship's current trajectory :

 

Spoiler

This is my carrier for those 2 simple relays.

Current path of the ship.

 

Here's my current approach trajectory. Quite polar as you can see.

Every time i try to tweak the periapsis down, i end up with my Pe in front or the equator. In this situation, my signal will be blocked by all the joolian moons.

 

So, here's my question : How do I do to set my Peri-Jool above North or South Pole, and how to have it as low as possible ?
Second question : I got 1600dV left on my carrier (without the sats fuel). Do you think i can actually set my sats as those orbiting Duna ?

I seached all around the Web, and I just can find some Relay tutorials, show how to put 2/3/5 relays on a equatorial trajectory, everytime done on Sandbox mode.

Remember that I'm playing Career mode, so I like tiny and efficient solutions ! I won't use any "Space Titanic".

Do you think I can reach It ? Shall I change my design that might be too light for Jool ?

Any help will be lovely !

Edited July 23, 2017 by Ouega

[Cpt Kerbalkrunch]

Unfortunately, the kind of maneuver you need should have been done long ago. I'm on my phone, so it's a crappy picture, but it looks like you're already at Jool. The farther away from an encounter you are, the easier and (more importantly) cheaper it is. Once your Jool encounter is set, you need to set a maneuver node at the An or Dn (I forget which one you hit on the way to Jool). Here, use your normal/anti normal dials to flatten out your orbit until it's even with Jool. Then you can use the radial in/out or the prograde/retrograde dials to change your path until you're actually going to hit Jool. Then use normal/anti normal again until your path is just above or just below the planet (not very technical terms, but you get what I mean). Notice how Jool's enormous gravity well bends your path around the planet. This makes your capture extremely easy. Note that you could actually capture for free if you hit Tylo or even Laythe. However, this will require some finagling afterward to put yourself in a polar orbit. Might be best to wait until you have maneuvers down a bit better.

For your current predicament, maneuvers are going to cost a lot more inside Jool's powerful gravity, but you should still be able to bring your Pe down a bit. However, the cost of moving your Pe and then attempting to capture may end up costing more than just hitting the brakes at your current Pe and capturing higher up. It's just a sat, so you should be pretty light. I would make a quicksave from where you are and attempt it both ways to see which one costs you less. For the maneuver itself, your angle of approach can change which direction dial you need to use to move your path the way you want. What I mean is, what you usually use normal/anti normal for, may now require the radial in/out or prograde/retrograde to achieve the same effect, because of the angle at which you're approaching the planet.

Not sure if this is making sense or not. Bottom line is, it'd be best to go back, but you can still stick it out and accomplish your mission. If you're like me, you probably hate to give up. Sometimes though (maybe most times) it's the smart thing to do. Best of luck.

[OhioBob]

On ‎7‎/‎23‎/‎2017 at 6:09 AM, Ouega said:

So, here's my question : How do I do to set my Peri-Jool above North or South Pole, and how to have it as low as possible ?

I suggest that you try to get the Pe as close to where you want it to be as possible.  If it's ends up near the equator, don't worry about it.  Then just wait until you cross into Jool's sphere-of-influence.  Immediately after crossing into Jool's space, set up a maneuver node and adjust your trajectory, moving the Pe over one of the poles.  When you are that far away out near the edge of the SOI, it should take only a small adjustment to alter the trajectory to something that satisfies your needs.

On ‎7‎/‎23‎/‎2017 at 6:09 AM, Ouega said:

Second question : I got 1600dV left on my carrier (without the sats fuel). Do you think i can actually set my sats as those orbiting Duna ?

You should be able to get the first commsat into position, but I don't know about the second.  1600 m/s should be plenty to capture into an elliptical orbit.  Let's say you come in low over the north pole.  You can perform a burn and capture into an elliptical orbit with the Ap high over the south pole.  You've effectively already put the first satellite into its final orbit, so you should be able to detach it without having to perform much if any further adjustment.  But now you have the other satellite in an orbit exactly opposite of the way you want it.  You have to circularize the orbit by dropping the Ap all the way down to just over the south pole, and then raise a new Ap on the opposite side high over the north pole.  That will take a very large amount of dV (about 5500 m/s) and I doubt you have enough based on what I see.

The other thing you can try doing in separating the two commsats while out at the edge of the SOI and fly them in on separate trajectories, one with a Pe over the north pole and the other with a Pe over the south pole.  You then perform two separate insertions burns.  I don't know if each individual commsat has enough dV to do that or not.*  The other potential problem is that you need to make sure the commsats arrive at their insertion points at different enough times that you'll be able to control them both.  While you're focused on one, the other is on rails, so I don't think it's possible to have both burning at the same time (though I've never tried it).  I believe you'll need to start and complete one burn, then switch vessels and perform the second burn.

*  Working to your advantage is that you just need to perform enough of a burn to capture and get the Ap inside Jool's SOI.  You want the commsats in highly elliptical orbits, which is good.  That may not take more than few hundred m/s.  If you had to circularize into a low orbit, that would take a few thousand m/s, which clearly you don't have.

Another possibility to consider for the future is aerocapture.  However, that's not a possibility in this case because you don't have a heat shield(s).  Heat shields are essential at Jool because the entry speeds are so high that you'll overheat and explode without them.

Hopefully you'll get some other (i.e. better) suggests.
 

Edited July 24, 2017 by OhioBob

[Kryxal]

Worst case, put them in the same, highly-eccentric orbit, but have them about half an orbit apart.  That should give good coverage for mostly everything in equatorial orbits

[OhioBob]

@Ouega, I just played around with the scenario a little bit and I think you have enough delta-v in each satellite to put them on separate trajectories if you want to give that a try.  But I couldn't get their Pe to be directly over the poles.  I don't know the exact conditions of your approach, so I couldn't reproduce it.  So I just assumed I was coming in along Jool's equatorial plane.  I ended up with one commsat with its Pe at about 45 N latitude, and the other with its Pe at about 45 S latitude.  Although that's not exactly what you want, it ought to still work fine.

@Kryxal's suggestion also works.  Start out with them in essentially the same orbit, but with one satellite having a lower Ap.  The one with the smaller orbit will have shorter period and will start to move ahead in its orbit compared to the slower one.  Just monitor them until one satellite has moved 180 degrees ahead of the other.  Then perform a burn (doesn't matter which satellite) to equalize their orbital periods.  From that point forward, when one satellite is moving through Pe, the other will be near Ap.  They don't have to have their Ap on opposite sides on the planet.

 

[Spricigo]

On 23/07/2017 at 7:09 AM, Ouega said:

 

 

....my current approach trajectory. Quite polar as you can see.

Every time i try to tweak the periapsis down, i end up with my Pe in front or the equator. In this situation, my signal will be blocked by all the joolian moons.

The solution seems simple to me.

1. Capture in a high elliptical orbit with apoapsis equal to the desired final apoapsis.

2.Circularize at apoapsis.

3.Wait until you are over a pole, release one of the satellites and lower the periapsis to the desired heigh.

4.Same for the other satellite at the other pole.

5.Tweak the orbit to get same orbital period but while one is at periapsis the other is at apoapsis.

Notice that I didn’t considered what would be the 'ideal' height of the periapsis at capture time. That depends on your actual situation and desired final orbit.

Probably too late by now, but I'd go with ant engine, no decoupler between the batteries and fuel tank, and a single Z-100 instead of 2x z-1k. That would be enough to squeeze an extra 200m/s out of each satellite. For further mass saving using TR-2V instead of TR-18A and putting the satellite in-line inside the fairing and getting rid of the adapter is 130kg less, the fairing itself will be bigger, but if you will be using it only during the launch from Kerbin (and use a 1,25m fairing that, depending on how you build it, may be lighter {-100kg the base, -2kg/m²}) maybe the end result is also a little extra deltaV.

On 23/07/2017 at 4:24 PM, Kryxal said:

Worst case, put them in the same, highly-eccentric orbit, but have them about half an orbit apart.  That should give good coverage for mostly everything in equatorial orbits

Instead I’d  settle for not so eccentric  orbit with apoapsis in opposite directions and same orbital period. The point is that in the same orbit there is a considerable time the area below the periapsis will be in communication shadow and the distance between the satellite can be much shorter, increasing the likelihood of both being out of LoS.

23 hours ago, OhioBob said:

I ended up with one commsat with its Pe at about 45 N latitude, and the other with its Pe at about 45 S latitude.  Although that's not exactly what you want, it ought to still work fine.

Yes, this probably works very well. Most of the time the satellite will be high in the orbit (a result predicted by Kepler's 2nd law) and the moons of Jool will be conveniently out of the way. OTOH you ended in this configuration after a capture in equatorial orbit, approaching in a 'quite polar' means less change of inclination and even more deltaV available to place the periapsis over higher latitudes.

[OhioBob]

31 minutes ago, Spricigo said:

OTOH you ended in this configuration after a capture in equatorial orbit, approaching in a 'quite polar' means less change of inclination and even more deltaV available to place the periapsis over higher latitudes.

I started out in an equatorial orbit on initial approach.  But while near the edge of the SOI I transitioned each satellite into a trajectory that took it over the poles, one north and one south.  Although the orbits were polar, the periapsides were not over the poles.  The satellites passed over the poles and reached periapsis when over a latitude of about 45 degrees.  That's how I ended up the configuration I described.  Roughly what I got is,

Commsat #1 (northern trajectory)
inclination =  90^o
longitude of ascending node* = 0^o
argument of periapsis = 135^o

Commsat #2 (southern trajectory)
inclination =  270^o
longitude of ascending node* = 180^o
argument of periapsis = 315^o

*  These numbers are just for illustrations purposes; I don't know what the real longitudes were.

[Spricigo]

12 minutes ago, OhioBob said:

 But while near the edge of the SOI I transitioned each satellite into a trajectory that took it over the poles, one north and one south.

well, maybe you used like 2m/s to change inclination..that is 2m/s extra deltaV for the OP..

I guess, Chip and Dale (my two neurons) were fighting  by the time I reached the conclusion that the change of inclination would have a significant cost.

[Ouega]

Hi everyone ! Thanks for the all the advice you gave me. I thought about my problem all day long and i decided to keep on my mission.

Since I know that my approach wasn't perfect (I remembered I placed one of the AN/DN at the exact location of Jool's intercept which is WRONG if you want to spend as low Dv as possible), I decided to keep going, and see if I actually could do it another way.

I usually use the flight plan @OhioBob described for any other planet : coming in polar, decouple the sats from the carrier, pick one sat and make it burn 'radial In' to make it pass on the other side of the planet, and then perform a capture burn for both sats.

 

 

WARNING : This path might not be optimized at all in terms of Dv, but i tried to see if I had enough to actually do something with this ship.

This time, i decided perform a little course correction (radially out) before encountering Jool. I came in quite equatorial, with a Periapsis close to 800.000 km. Then, I did a retro-burn (1300m/s) to enter orbit and i kept my Apoapsis as far as I could (things like 2.438.000 km). With that trajectory, I waited my Ap to do a inclination change. At Ap, it only took 328m/s, to reach 90° inclination. Then, i decoupled my sats, and did some fine tuning (1.5m/s) to get my Ap / Pe in front of the poles.

Last maneuver : burn retrograde till i hit Periapsis at 210.000 m with each sat.

They're now secured from any Joolian Moons encounter, as you can see :

Spoiler

Mission is now a success, with some Dv left ! Thanks for your help, and see you around ! I may post a thread for my next Jool / Eve mission. Stay tuned !