Tylo reusable ship surface to low orbit

[kerbonaut23452345]

Hello,

Im trying to design a reusable system to bring kerbal to explore Tylo. I tried to make an SSTO with ISRU that would get from surface to low orbit and down and realised it is not possible.

My goal is to have a ship that can carry 3 kerbals (1 lander can + 2 external seat), that can go up to a station in orbit and down to the surface without refueling. I tried a 2 two stage solution, first one with the ISRU and 2nd one that goes to the station and back down again. I cant find a design where i dont crash the 1st stage. Is there a solution for a 2-stage reusable rocket? Would a fixed refueling base on the ground be better? Is there an optimal altitude for the station in low orbit (equatorial orbit)? At the lowest possible orbit, it seems I dont have enough time to decelerate the 1st stage.

[bigcalm]

You should be able to make a lander that can get to the surface in a single stage, refuel itself on the ground using ISRU, and then return to Tylo orbit.  However, you will likely have to top up the fuel that's in it when it reaches orbit in order to reuse it again.

Use a large engine - I used the Rhino, but mainsail should do it too.

A fixed refuelling base is a reasonable idea, but accurate enough landings are likely to be challenging.  Do you have a backup plan for when you're not accurate enough?

I would start from equatorial orbit, because of the likely need to rendezvous with it, and I think I normally start descent at about 100km circular orbit.

[Lt_Duckweed]

1 hour ago, kerbonaut23452345 said:

At the lowest possible orbit, it seems I dont have enough time to decelerate the 1st stage.

When descending to the surface from a low orbit, you should not be doing a pure retrograde hold descent (aka a suicide burn).

Instead, you burn at an angle between retrograde and vertical, so that retrograde is always pointing directly at the horizon (ie, near 0 vertical speed) and only let the craft start to descend when you are nearing the end of the burn and are approaching your landing site.  This is called a constant altitude descent.  Ideally you start it at the lowest possible altitude that does not result in you smashing into the terrain surrounding your target landing site, and come screaming in just above the hilltops.  Done correctly, this actually uses even less fuel than a suicide burn.

[king of nowhere]

7 hours ago, kerbonaut23452345 said:

Hello,

Im trying to design a reusable system to bring kerbal to explore Tylo. I tried to make an SSTO with ISRU that would get from surface to low orbit and down and realised it is not possible.

 

why wouldn't it be possible? It's not complicated at all. You just need a ship with a drill, a convert-o-tron, 3 km/s of deltaV (2.5 km/s are enough, but you can stay safe), and TWR >1.5 (kerbin), possibly >2. Those are not particularly harsh requirements. One of my rovers did it, with enough spare mass for all the rover parts.

And it's certainly much easier to do than doing it in one stage

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My goal is to have a ship that can carry 3 kerbals (1 lander can + 2 external seat), that can go up to a station in orbit and down to the surface without refueling.

Again, perfectly doable. You need 5 km/s and a TWR>1.5. You can do it if you use a large, powerful engine with an appropriately-sized fuel tank. As long as your crew pod is very light compared to everything else, it will work. Even just a crew pod, a couple large reaction wheels, an RTG, and 50 tons of fuel with an appropriately sized engine (a rhino could do the trick with this mass, but you'd have to check) would be enough.

Quote

I tried a 2 two stage solution, first one with the ISRU and 2nd one that goes to the station and back down again. I cant find a design where i dont crash the 1st stage. Is there a solution for a 2-stage reusable rocket? Would a fixed refueling base on the ground be better? Is there an optimal altitude for the station in low orbit (equatorial orbit)? At the lowest possible orbit, it seems I dont have enough time to decelerate the 1st stage.

Oh, so it appears your problem is not deltaV or thrust, but trajectory. You've done a lot of other landings on other moons, and you learned techniques, but on tylo they don't work anymore. Indeed, on tylo the suicide burn is much longer than everywhere else, so the manuever that will result in a perfect mun landing will crash you down on tylo.

You have 2 solutions: the first is the one mentioned by @Lt_Duckweed. It is the most efficient, fuel-wise, especially if you have low thrust. It is also extremely difficult to pull off correctly, unless you have a bunch of mods to help you do exactly that.

The second solution is less efficient, but much easier: just pack an additional 500 m/s and start the suicide burn higher. on tylo, i've started suicide burns as high as 40 km.

 

Have faith: to land on tylo you only need 2 things: 2500 m/s of deltaV, and 1.5 TWR. If you have higher thrust and you are good, you can go as low as 2300 m/s, but I don't recommend it. For a comfortable landing, I suggest 2700 m/s and TWR 2. If you have those, then your ship CAN and WILL land on Tylo, if piloted correctly.

 

[18Watt]

Your design goals, as I understand them, should be achievable.

• A vessel with ISRU equipment on board.
• Can refuel on the surface of Tylo,
• Then get to orbit of Tylo (with 3 passengers)
• Then return to Tylo’s surface, without refueling in orbit.

I have never actually accomplished what you are describing.  The vessels I use can refuel on Tylo’s surface, but to return back to the surface they always need additional fuel.  However, I do not believe it is impossible, I just haven’t optimized my vessels for that task.

I think you will need to figure out how to get to the surface efficiently, which is not easy at Tylo.   Your descent profile is going to make a very big difference in how much fuel you use.   I would not consider this a trivial challenge, I suspect it will take a lot of trial and error to make it work.

Good Luck!

[kerbonaut23452345]

On 8/31/2021 at 10:23 PM, bigcalm said:

A fixed refuelling base is a reasonable idea, but accurate enough landings are likely to be challenging.  Do you have a backup plan for when you're not accurate enough?

The refueling base would be on wheels, i could always drive it to the ship

On 9/1/2021 at 4:17 AM, king of nowhere said:

Oh, so it appears your problem is not deltaV or thrust, but trajectory. You've done a lot of other landings on other moons, and you learned techniques, but on tylo they don't work anymore. Indeed, on tylo the suicide burn is much longer than everywhere else, so the manuever that will result in a perfect mun landing will crash you down on tylo.

yes there less margin of error, with more powerful engine it is easier, but it also adds more weight to the ship.

 

I think I will go with the refueling base and a 6km/s single stage ship. I have also a related question, how much delta V does it take to make a trip from equator to pole and back? Is it more or less than the surface->low orbit-> surface trip?

[king of nowhere]

2 hours ago, kerbonaut23452345 said:

yes there less margin of error, with more powerful engine it is easier, but it also adds more weight to the ship.

A 6 km/s ship won't have enough thrust to land on tylo.

Let's make some calculations. To land/orbit on tylo you need 2300 m/s. Make it 2500 for safety. you want 5000 m/s for the two-way trip. You also want a TWR of 2.

Let's take the most efficient vacuum engine, the wolfhound (i experimented with higher thrust engines, but the advantage in thrust does not compensate the loss of Isp). The wolfhound has a thrust of 375 KN, or 37.5 tons (it's easier to think the thrust in tons). To have TWR 2, you can lift 18.75 tons. 3.3 tons are the engine itself, so you have room for 15.45 tons of fuel. Of course 1/9^th of that will be the weight of the fuel tanks, so 1.72 tons of fuel tanks. Your ship will have a dry weight of 3.3+1.72=5.02 tons, and a wet mass of 18.75 tons. Apply the rocket equation, 380*9,81*ln(18.75/5.02) = 4912 m/s.

Close enough to make it viable. You see there's no way you can reach 6 km/s; to do that, you'd have to cut too much on engine mass.

You can content yourself with a lesser thrust; after all, when you will land you will have mostly empty tanks and your thrust will be higher, that's important. You can take off from tylo with a lower thrust without losing too much efficiency.

Let's try some other figure; 2 wolfhounds, 36 tons of fuel + 4.5 tons of tanks, 2 tons of assorted payload. total dry mass 13.1 tons, wet mass 49.1 tons. 4925 m/s, starting TWR 1.53. It's up to specifications. If you want more dry mass, you have to add proportionally more wolfhounds and fuel. Yes, the weight escalates quite fast. For example, if you want a large convert-o-tron and 2 drills, that's 7 tons. 10 rtgs to use it with some speed, a couple large reaction wheels to have some manueverability, and a Mk3 command pod, that's close to a 10 tons payload. So you will need 10 wolfhounds and 200 tons of fuel tanks to bring that mass up and down from orbit.

 

You could go refuel on Pol. Low tylo orbit to Pol surface is something like 1500 m/s, so you'd only need 4 km/s for your ship. It would increase your payload fraction considerably.

 

[jimmymcgoochie]

There are two ways of doing this- there's the "mine fuel on Tylo with a dedicated mining base, truck it around Tylo on dedicated fuel tankers to the lander(s) whenever they land and then battle with gravity losses by lifting off a high-gravity body with a full load of fuel" way, and then there's the "mine fuel somewhere else, bring it to Tylo and fuel the lander in space" way.

Mining elsewhere is probably the better option in my opinion- Vall's the closest available mining spot and getting from Tylo to Vall and back is pretty trivial, but Bop and Pol have really low gravity and could be better options for hauling large quantities of fuel off their surfaces and all the way to Tylo orbit. Getting off of Tylo is difficult enough that you want to be lifting off with as little weight as possible- including fuel- and filling up with fuel in orbit means you'd be landing with the majority of your fuel already burnt, increasing your TWR and making things much easier for yourself.

[kerbonaut23452345]

So after trying to make several tylo ships, i could finally get to my original goal. This ship has 3 seats and ISRU, it can go to low orbit (18km) and back to surface with even up to few hundreds spare deltaV. With starting TWR >2, there is not much losses due to and 5374 m/s is enough to go up and down.

The design could certainly be improved, but i dont know if there is way to have a lighter ship with the same TWR and deltaV.

 

 

[18Watt]

On 9/2/2021 at 5:19 PM, king of nowhere said:

Let's try some other figure; 2 wolfhounds, 36 tons of fuel + 4.5 tons of tanks, 2 tons of assorted payload. total dry mass 13.1 tons, wet mass 49.1 tons. 4925 m/s, starting TWR 1.53. It's up to specifications. If you want more dry mass, you have to add proportionally more wolfhounds and fuel. Yes, the weight escalates quite fast. For example, if you want a large convert-o-tron and 2 drills, that's 7 tons. 10 rtgs to use it with some speed, a couple large reaction wheels to have some manueverability, and a Mk3 command pod, that's close to a 10 tons payload. So you will need 10 wolfhounds and 200 tons of fuel tanks to bring that mass up and down from orbit.

I would take a similar approach to this.

However, first I would not power the ISRU equipment with RTGs.  They cost too much, for too little power.  I’d use fuel cells.  The only time you need the electricity is when you’re on the surface, and fuel is infinite.  Fuel cells are cheap, don’t weight much, and produce lots of power.  
 

Also, you don’t need a TWR of 2, or even 1.5.  A TWR of 1 will work fine.  The critical (difficult to fly) part will be landing.  This ship will be landing essentially empty, so the landing TWR will be quite high, even if the takeoff TWR is at or near 1.0.  Saving in engine mass really helps, if you don’t truly need the high TWR.

I miscalculated on my last Tylo lander.  It actually had a TWR of about 0.9 fully fueled on the surface.  Still worked fine.  I just ran the engines until the TWR reached 1.0, then slowly climbed to orbit.  My vessel was loaded with extra payload, so was not able to return to the surface without refueling in orbit.  I had to bring fuel over from Bop or Pol to get back to the surface.