2-stage lander designs: seperate thrusters vs droptanks

[Jestersage]

While researching about Russian Lunar Landers, I noticed that except for LEK-based landers, russians seems to favor a deorbit/crasher stage, follow by a lander that use droptanks (or just landing legs in the case of LK and LK700)

The Americans on the other hand, both NASA and private, seems to favor seperate landing thrusters, with descent stage handling the deorbit and landing (and may even include orbital insertion)

What is the reason for that (not interms of staging, but in terms of using droptank type vs each-stage-has-own-thrusters)? And if there are benefits, does that translate to KSP?

(Also please move to spaceflight... properly more relevant on that)

Edited August 30, 2019 by Jestersage

[Gordon Fecyk]

Remember that KSP's considerably scaled down compared to reality. A direct-ascent mission, like what the Kerbal X stock craft and the Soviet LK-700 were designed for, is much simpler but only works reliably in the 1/10 scale ultra-dense system we play in. But even in this system you'll see a lot of multi-stage Tylo landers because of the sheer amount of delta-v needed to land on Tylo and get back to orbit.

Try playing in JNSQ if you are up to it and can make it work. Even modestly scaling the system up to 2.7 x stock will start demanding multi-stage landers to the Mun.

[Gordon Fecyk]

2 hours ago, Jestersage said:

(but in terms of using droptank type vs each-stage-has-own-thrusters)

(After re-reading the question, silly me) Drop tanks could work better to save on parts and on mass, getting you more delta-v with fewer engines. But if you need those separate engines for thrust-to-weight (such as for Tylo landings) then use those instead. I suppose it depends more on whether you can keep TWR above one or not.

[Empiro]

3 hours ago, Jestersage said:

While researching about Russian Lunar Landers, I noticed that except for LEK-based landers, russians seems to favor a deorbit/crasher stage, follow by a lander that use droptanks (or just landing legs in the case of LK and LK700)

The Americans on the other hand, both NASA and private, seems to favor seperate landing thrusters, with descent stage handling the deorbit and landing (and may even include orbital insertion)

What is the reason for that (not interms of staging, but in terms of using droptank type vs each-stage-has-own-thrusters)? And if there are benefits, does that translate to KSP?

(Also please move to spaceflight... properly more relevant on that)

It's mostly about the TWR you need. Dropping tanks reduces your mass be a small amount while dropping engines reduces your mass by a large amount, but also reduces your TWR. Drop tanks are useful for something like a Tylo lander, since TWR matters the most toward the end.

If you use stack staging set ups, it does mean that some of your engines aren't firing the whole time, which means that they're basically dead weight. Asparagus staging kind of gets the best of both worlds -- all your engines are firing at all times.

[Jestersage]

9 hours ago, Empiro said:

It's mostly about the TWR you need. Dropping tanks reduces your mass be a small amount while dropping engines reduces your mass by a large amount, but also reduces your TWR. Drop tanks are useful for something like a Tylo lander, since TWR matters the most toward the end.

If you use stack staging set ups, it does mean that some of your engines aren't firing the whole time, which means that they're basically dead weight. Asparagus staging kind of gets the best of both worlds -- all your engines are firing at all times.

I had reread about LK1, and found out Russians go with the drop tank method for redundency (there are actually two sets of thrusters)

Edited August 31, 2019 by Jestersage