VTOL SSTO 6km/s dv 3 kerbal pod

[Endolf]

Just playing around with ideas. I'm trying to increase the capabilities of my SSTO VTOL lander. It's a 3 kerbal lander. The idea is I can put it in orbit somewhere, brim the tanks, land it (powered or not depending on destination), collect science on the surface (4 goo, 4 materials, 1 temp, 1 pressure, 2 seismic and 2 gravity, plus the crew reports, surface samples and EVA reports), then return the whole lot to orbit, ready to offload the science to a lab, brim the tanks and reuse it.

By the time I've added batteries etc it's dV is down to 4.8km/s. This requires parachutes to land on kerbin and can only get to around 80k orbit. I'd like to be able to stick it on top of my heavy launcher, put it in 125k orbit, powered landing on kerbin (mostly aerobraked so should be doable), then return to the mother ship launcher.

I don't want to use nuclear engines in kerbin atmosphere, happy to use them for interplanetary transfer, but that's not the problem here.

Am I trying for the impossible?, I've struggled with this before and never quite managed it. I'm guessing I need around 5.5k to 6k dV, with a kerbin surface TWR of >=1.3, am I asking too much of the stock engines?

Thanks

Endolf

[linkxsc]

Craft file? Easier to test out for you if we got the exact same (though this looks easy enough to build)

[Endolf]

Craft file

Only mod it needs is MechJeb.

Endolf

[undercoveryankee]

Tavert's optimal-engine charts show that 6 km/s single-stage with 1.3 G TWR is possible.

Best engine choices for 6 km/s in vacuum would be 48-7S cluster or NASA KR-2L, depending on payload size. The aerospikes are decent if you expect to burn most of your delta-v in low atmosphere on Kerbin or Laythe, but for a multi-mission lander, vacuum performance is more important.

Unfortunately, 6 km/s is close enough to the theoretical limit that your vehicle may end up a lot bigger than what you've been working with.

[Taki117]

Might I suggest a redesign? You have a lab so you don't need multiple goo and science jr experiments, same goes for the other experiments as well. Also, why have a 3 kerbal pod if you are only ever going to use it for one kerbal? (And if you are using it for 3 Kerbals, why are you taking 3 on your lander mission when 2 are going to sit inside the capsule). This may sound counter-intuitive, but Build only what you need for exactly what you need it for, don't build what you want and then try to make it do what you want it to.

[Andrew Hansen]

I take it you're trying to gather science from around Kerbin. If that's the case, I think an airplane plane would suit you a lot better.

[Armchair Rocket Scientist]

I take it you're trying to gather science from around Kerbin. If that's the case, I think an airplane plane would suit you a lot better.

This. Going to orbit and back with just rocket fuel is HARD.

Using 48-7S engines (30 kn thrust, ISP 350 s vacuum, 0.1 t), to get a dV of 6 km/s (vac) 82.6% of your vehicle mass must be fuel. An additional 1/8th of the fuel mass must be tankage, so fuel + tanks will equal 92.9% of your vehicle's mass. With a fully fueled TWR of 1.25, the engines must be 4.1% of the mass.

This means that everything but engines and fuel tanks on your vehicle must be only 3% of its mass. Your pod and scientific payloads add up to 5.4 tons, but that's not counting docking ports, RCS tanks/fuel/thrusters, parachutes, landing gear, solar panels, batteries, ladders, and anything else you need. For example, I see 8 parachutes on your vehicle. That's another 1.2 t. already. I'll assume your "payload" ends up at around 8 tons. That means your vehicle must weigh 267 tons fully fueled (and need 109 Rockomas 48-7S engines). With aerospikes, it's even worse.

Fortunately, even allowing 5000 m/s to get into orbit and 500 m/s to dock, deorbit, and land, you only need 5.5 km/s of dV. That extra 500 m/s DOUBLES your payload fraction to 6%, but that still gives you a very fat, unwieldy vehicle.

You'd be much better off using jet engines, whether on a spaceplane or a VTOL. If you airhog, payload fractions can reach 30%, and that might be without counting the command pod and structural mass.

You might also want to consider not going all the way to orbit. I don't know how much dV you need to perform a suborbital hop between antipodal points on Kerbin, but it's possible that doing that twice is still easier than going to orbit. This is especially true for spaceplanes. A mach 5 circumnavigation would take about 40 minutes, but depending on the design it should be possible to pop up out of the atmosphere so you can use timewarp.

[Endolf]

Thanks for all the feedback. Let's not get hung up on kerbin, I was intending this to be a build once use anywhere type lander, all but eve anyway. According to the dV maps I've seen tylo requires 3070 to get in to orbit, and the same to land, so in a vacuum I would need this lander to have 6140m/s dV minimum to do a tylo reusable lander, I'd also like to use it as the rentry vehicle to kerbin and use it on duna, laythe etc.

The new engines are so much lighter and more efficient than the old ones, they are a good spot. I like to have a large docking port adapter centrally on the rear of the ship so I can dock to transfer stages etc. The new engines offer so much thrust that I end up with 4 orange tanks worth or more of fuel, but I can get near 7km/s dV with a similar (but larger) craft. The LFB KR-1x2 is good, but still too power full, I'd like one 1/4 of that power and weight, then I could stick them on rockomax tanks on the existing launcher and be much closer to what I'm after I think.

I've not had much time to play around with the configuration yet, but it looks interesting. Just have to figure out where to put my 3 man pod and rockomax docking port if I have to have my main engine in the centre.

Endolf

[undercoveryankee]

You have a lab so you don't need multiple goo and science jr experiments, same goes for the other experiments as well.

When you're landing on a body with an atmosphere (Duna or Laythe), it's nice to be able to get upper atmosphere, lower atmosphere, and landed with one landing. That's why I put three full sets of experiments on my Duna lander even though I also have a lab in orbit.

[Armchair Rocket Scientist]

Thanks for all the feedback. Let's not get hung up on kerbin, I was intending this to be a build once use anywhere type lander, all but eve anyway. According to the dV maps I've seen tylo requires 3070 to get in to orbit, and the same to land, so in a vacuum I would need this lander to have 6140m/s dV minimum to do a tylo reusable lander, I'd also like to use it as the rentry vehicle to kerbin and use it on duna, laythe etc.

The new engines are so much lighter and more efficient than the old ones, they are a good spot. I like to have a large docking port adapter centrally on the rear of the ship so I can dock to transfer stages etc. The new engines offer so much thrust that I end up with 4 orange tanks worth or more of fuel, but I can get near 7km/s dV with a similar (but larger) craft. The LFB KR-1x2 is good, but still too power full, I'd like one 1/4 of that power and weight, then I could stick them on rockomax tanks on the existing launcher and be much closer to what I'm after I think.

I've not had much time to play around with the configuration yet, but it looks interesting. Just have to figure out where to put my 3 man pod and rockomax docking port if I have to have my main engine in the centre.

Endolf

Landing on Kerbin and landing on Tylo are totally different.

Landing on Kerbin is essentially free in terms of delta-V. If you use parachutes, all you need is 100 m/s or less for deorbiting, but even with a propulsive landing, 90% of your dV will be used during the ascent back to orbit. On the other hand, a Tylo lander will use nearly the same dV for landing and launch. This means that your Kerbin lander will be basically fully fueled on takeoff. On the other hand, with a dV of 5500 m/s and an ISP of 575 (you'll see why I used such a high number later), will have the following properties:

mass (fully fueled) = 2.65 * dry mass

mass (half the dV left) = 1.63 * dry mass

This means that by the time it lands, the vehicle will have decreased to 61.5% of its original mass. Obviously to land safely your TWR should exceed 1 a bit before that, but it's fine if you start out with it a tiny bit less than 1.

The other thing that makes Tylo different from Kerbin is that because Tylo has no atmosphere, your engines will be at their vacuum ISP the entire journey. This means, among other things, that there's no point in using aerospikes on Tylo. The nuclear engines, on the other hand, become viable.

To illustrate:

A Tylo lander powered by sixteen 48-7S engines, with a starting TWR of 0.8 and a dV of 5500 m/s, will have a total mass of 60 tons. 48 tons will be fuel, 6 tons will be tankage, and 1.6 tons will be engines, giving a payload of 4.4 t.

A Tylo lander powered by eight 48-7S engines and 4 nuclear engines (mean ISP of 575), with the same dV requirements and starting TWR, will still have a total mass of 60 tons. Now, though, 37.4 t will be fuel, 4.67 t will be tankage, and 9.8 t will be engines, giving a payload of 8.1 t, almost double what it was previously.

A Tylo lander powered by eight nuclear engines, with the starting TWR raised to 1 to account for the mass decreasing less during the landing, will have 24 t of fuel, 3 t of tankage, and 18 t of engines, giving a payload of 3 t. Not so good, but still technically functional.

This indicates that the best design for a single-stage Tylo lander is a nuclear-chemical hybrid. On the other hand, nuclear rockets are a horrible choice for launching from Kerbin due to their 200s atmospheric ISP.

In my opinion, a "one-size fits all" lander isn't a great idea, mostly because of Tylo. I'd prefer to have multiple classes of lander:

Class I: Minmus, Gilly, Bop, Pol. 600 m/s of dV is plenty, and TWR requirements are miniscule. You could use a larger lander, and use the extra fuel for transfer burns, though.

Class II: Mun, Ike, Moho, Dres, Vall, Eeloo, Duna. 2250 m/s needed, and TWR of 0.3-0.4 is sufficient.

Class III: Kerbin and Laythe: rocket-only single-stage landers are HARD. Use jets instead.

Tylo and Eve have unique challenges that require purpose-built landers.

[Jouni]

In my opinion, a "one-size fits all" lander isn't a great idea, mostly because of Tylo. I'd prefer to have multiple classes of lander:

Class I: Minmus, Gilly, Bop, Pol. 600 m/s of dV is plenty, and TWR requirements are miniscule. You could use a larger lander, and use the extra fuel for transfer burns, though.

Class II: Mun, Ike, Moho, Dres, Vall, Eeloo, Duna. 2250 m/s needed, and TWR of 0.3-0.4 is sufficient.

Class III: Kerbin and Laythe: rocket-only single-stage landers are HARD. Use jets instead.

Tylo and Eve have unique challenges that require purpose-built landers.

Kerbin, Laythe, and Eve require something different, but an one-size-fits-all lander works well with the rest of the planets. The trick is not building a lander at all, but using the transfer stage instead. On Tylo, you'll have to leave all unnecessary modules in orbit, but elsewhere you can carry them to surface as well.

If you make many repeated landings on Class I and Class II planets, the high dry mass of the Tylo lander may be wasteful. On the other hand, you'll save a lot of fuel by not hauling a separate lander around.

[magnemoe]

Landing on Kerbin and landing on Tylo are totally different.

Landing on Kerbin is essentially free in terms of delta-V. If you use parachutes, all you need is 100 m/s or less for deorbiting, but even with a propulsive landing, 90% of your dV will be used during the ascent back to orbit. On the other hand, a Tylo lander will use nearly the same dV for landing and launch. This means that your Kerbin lander will be basically fully fueled on takeoff. On the other hand, with a dV of 5500 m/s and an ISP of 575 (you'll see why I used such a high number later), will have the following properties:

mass (fully fueled) = 2.65 * dry mass

mass (half the dV left) = 1.63 * dry mass

This means that by the time it lands, the vehicle will have decreased to 61.5% of its original mass. Obviously to land safely your TWR should exceed 1 a bit before that, but it's fine if you start out with it a tiny bit less than 1.

The other thing that makes Tylo different from Kerbin is that because Tylo has no atmosphere, your engines will be at their vacuum ISP the entire journey. This means, among other things, that there's no point in using aerospikes on Tylo. The nuclear engines, on the other hand, become viable.

To illustrate:

A Tylo lander powered by sixteen 48-7S engines, with a starting TWR of 0.8 and a dV of 5500 m/s, will have a total mass of 60 tons. 48 tons will be fuel, 6 tons will be tankage, and 1.6 tons will be engines, giving a payload of 4.4 t.

A Tylo lander powered by eight 48-7S engines and 4 nuclear engines (mean ISP of 575), with the same dV requirements and starting TWR, will still have a total mass of 60 tons. Now, though, 37.4 t will be fuel, 4.67 t will be tankage, and 9.8 t will be engines, giving a payload of 8.1 t, almost double what it was previously.

A Tylo lander powered by eight nuclear engines, with the starting TWR raised to 1 to account for the mass decreasing less during the landing, will have 24 t of fuel, 3 t of tankage, and 18 t of engines, giving a payload of 3 t. Not so good, but still technically functional.

This indicates that the best design for a single-stage Tylo lander is a nuclear-chemical hybrid. On the other hand, nuclear rockets are a horrible choice for launching from Kerbin due to their 200s atmospheric ISP.

In my opinion, a "one-size fits all" lander isn't a great idea, mostly because of Tylo. I'd prefer to have multiple classes of lander:

Class I: Minmus, Gilly, Bop, Pol. 600 m/s of dV is plenty, and TWR requirements are miniscule. You could use a larger lander, and use the extra fuel for transfer burns, though.

Class II: Mun, Ike, Moho, Dres, Vall, Eeloo, Duna. 2250 m/s needed, and TWR of 0.3-0.4 is sufficient.

Class III: Kerbin and Laythe: rocket-only single-stage landers are HARD. Use jets instead.

Tylo and Eve have unique challenges that require purpose-built landers.

You can increase the Tylo SSTO performance by only using the LV-N during deorbit and first part of the braking burn, also during circulate.

If you use the lander on Val, Bop or Pol you only use nuclear.