Kerbal Space Simulator: Starlink

It seems that we will all have low latency, high bandwidth internet soon, regardless of where we are on the earth, all courtesy of SpaceX and Starlink. It seemed like a good idea at the time to make a Kerbal representation of the constellation just for shiggles over the xmas lockdown.

Step 1 – Design the bird
Rather than start from scratch, I had a search around (similar to a customer looking for a satellite bus format) and found this video from Gameplay review UK. After some messing about we end up with a lovely flatsat layout with a gigantor array and xenon power.

Our bird is designed flat so we can launch a stack of them. we base it on the OKTO2 and add mechjeb2 for additional control plus a reaction wheel for in service orientation (our normal orientation is radial out).

Launch weight is not too much of an issue so we have a full xenon tank and around 1200 delta v – enough for many years of faithful service and orbit raising.

We simulate the Starlink service with a pair of antennas – the Communotron 16-S for C&C and the folding SG-5 for the user internet traffic.

We put a Z100 battery pack on board so that small DV adjustments (<10 m/s) can be made even on the dark side of Kerbin. A couple of flat solar panels each side of the sat give us emergency power to deploy the gigantor.

Considerable tweaking is needed to get the COG aligned with the xenon engine.

Starlink satellite based on the Gameplay Review UK design. Constructed with stock parts with the addition of MechJeb2

Step 2 – Testing the bird
I built a SSTO rocket and fixed one satellite to it – we’ll call this the TinTinA launch. Launched to a nice low 100km orbit, the satellite works great – it’s controllable and maintains power throughout it’s orbit and has enough electricity for small DV changes. we have just enough DV in the booster to deorbit and our orbital debris is zero.

TinTinA prior to deployment. The booster and bird both have OKTO2 and Mechjeb2 controllers so they can both be deorbited to mitigate orbital debris.

Step 3 – Orbital Parameters
Starlink orbits at 350km and at an inclination of 53°. Our constellation will use identical parameters even though that’s a much higher relative orbit. Looking at the offsets around Kerbin, we need to launch at around 7 minutes 30 offsets – this gives us about 49 separate orbital planes to fill, or around 2500 separate satellites (EEK)!

Step 4 – Extended orbital test programme
Extending the TinTinA launch, we send up 48 further single sat launches to test the concept and test the coverage. Again, we set these launches low, but to the correct inclination. This is successful and after the testing is complete, all test artefacts are deorbited.

Testing the planes with further TinTin launches.

Step 5 – Testing the stack
The first stack design is built and tested as a two stage to orbit dispenser. We release all the sats at once and deorbit the dispenser. This first attempt of 24 birds is messy – using the SpaceX technique of allowing the set to jostle a bit results in a few damaged birds – typically the gigantor array. it takes quite a while to deorbit the failed satellites using only the tiny fixed panel. Another problem with the all-at-once dispenser is that the satellites disperse too unevenly. Because they have to be individually positioned, they drift a long way in the orbit it takes to position each one.

The SpaceX technique to release all at once and let them spread is pretty messy

Deorbiting the failed birds gives us a chance to test that they burn up completely in the atmosphere. They don’t, but it’s a bit late to do anything about this. As we have lot’s of delta V, we’ll try to controlled deorbit them into the ocean. Luckily Kerbin seems to be very sparsely populated.

The stack is redesigned slightly to release them individually and we try again. Now we have a stack of 38 on a two stage configuration.

Testing the stack configuration with an SSTO configuration.

It turns out that this is still a very messy configuration – the dispenser is aligned to prograde prior to sat deployment and then the idea is that the satellite can boost away from the 330 deployment orbit to the 350km operational orbit, but the stack is upside down and so there is considerable delay while the bird clears the stack far enough to invert it and deploy the antenna and solar array.

There is also a problem with the supports: many support struts were needed to prevent the stack flopping around and these were not all applied from the dispenser to the satellite. On separation, any bird with the strut base is unstable under thrust.

Step 6 – Testing one orbital plane
Testing the deployment of one entire orbital plane is hard work – we are working with a version one stack and so they are all upside down. Some of them have the detritus from the support struts and this means that they don’t produce thrust through the CoG. It takes about 8 hours (real time!) to deploy and we hit another snag: The last two birds are not on separation rigs and so are permanently attached to the dispenser. Another redesign!

Deployment process
Checklists for the win! It’s really easy to miss a step in the deployment for each satellite and as there will eventually be 2500 of them, probably important for a repeatable list.

Launch dispenser to 330km
Check and adjust plane and offset from
Tune Apo and Peri to 330 exactly

Planning a train
The deployment process for each train needs careful timing and coordination – satellite spacing in the plane is determined by timed release of each sat. Once you have the apoapsis and periapsis well sorted and the inclination is solid, you need to warp to ‘dawn’ from the dispenser point of view: You are going to release the bird, boost it’s apoapsis and then circularize half an orbit later when it reaches apoapsis. you want to make sure bot of these happen in sunlight. After circularizing, you will flip back to the dispenser and repeat the exercise and so it should all be happening in daylight. If you screw this up, the whole train will be launched at night and the power budget is very tight!

The UT between each deployment is 30 minutes. That gives you time to release, align, raise Apo, wait for apo, circularize, rinse and repeat. Just. Every few launches, you will want to adjust the dispenser apoapsis back to 330 – those constant prograde sat deployments cause the dispenser to slow down!

Hints, tricks and tips
Creative use of the different ship type icons can help finds ways to declutter the screen *ahem* when in Tracking station and Map view. Perhaps use one for the dispenser, one for birds that have been deployed but not fine tuned, another for fine tuned, Another for on-orbit spares and another for the head of each train.

Name each satellite according to the launch, the plane and a unique number. I use starlink 430-33 where 430 is the launch time UT and 33 is the position in the train. I add ‘HEAD’ to the reference bird in each train and give it a different icon.

Each Starlink Sat Deployment
Point dispenser prograde
Select Sat
Deploy solar panel
Deploy Sat
Switch to Sat
Check naming
Unfold antenna
Activate engine
Switch on attitude hold
Align prograde
Change the Engine Max thrust to 50%
Use Mechjeb manoeuvre planner
Select ‘Change Apoapsis’
Select 350km (or whatever this train operation altitude is)
Select ‘After a fixed time’
At the appropriate time, hit ‘create and execute’
After the burn, use Mechjeb manoeuvre planner
Select ‘Circularize’
Select ‘at the next apoapsis’
Select ‘Create and execute’
Select 5% max engine power after the circularization burn
Minor apo/peri adjustment (no warp!) – Leave this until later!
After circularization complete orient ‘radial out’
Switch back to the stack and repeat.

Post Deployment Dispenser decommissioning
The empty dispenser is now useless. If you have not needed all the birds, keep the dispenser on orbit to keep them together. If keeping the dispenser, probably raise it’s orbit to that of the main plane for collision mitigation.

To deorbit it, you have choices. If you included chutes, you may want to go for a land return at KSC. It does have enough DV for alignment but not a powered landing. The dispenser is unlikely to survive re-entry unless designed quite carefully – it’s as aerodynamic as a house brick. Conduct your own risk assessment! Otherwise use Mechjeb and pick a nice uninhabited spot in the ocean. Bear in mind that a return to KSC from a 53° inclination may require a long warp.

You could of course boost the dispenser into deep space or go for a graveyard orbit. You may have the DV for either of these, but they are not very SpaceX!

Deployment Fine Tuning
Change the engine power to 5%
Orient prograde or retrograde as required
Warp to apoapsis -10 seconds or periapsis as required
Tweak orbit to 350km x 350km exactly. A couple of meters is acceptable. you may decide, based on your own collision avoidance measures to put each train at a slight different height, say 100 meters separation on each orbital plane. This would be the right time to chose that number and start tweaking.
Deactivate unused equipment (engine) to prevent any power drains and accidents. You may be able to deactivate mechjeb and other systems.

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This bird does not seem to be burning up on re-entry