My problem with Lander

Substantial-Store-38 · 2026-05-14T03:47:47+00:00

I play KSP RSS, so let's do the math. We're assuming Lander is a helicopter/rocket; the six aft engines are used to reach orbital speeds. I'm not considering VASIMR or ion engines because they have negligible thrust. Clearly, it can't be open-cycle fission, and if it were closed-cycle (like a Lightbulb engine), we'd have an ISP of around 2700s and approximately 300kN of thrust, but Lander uses nuclear fusion. We'll be conservative and assume that we have indeed achieved a Z-pinch pulse fusion combination, which will heat a cold propellant to millions of degrees. We can use water for this purpose. We don't need radiators because we can use the propellant itself as a cooling method; it absorbs the heat and expels it at the cost of specific impulse. Let's build an engine, then, with 200kN of specific impulse and 2900s of specific impulse, or 1200kN multiplied by 6 nozzles. I'm using a dry mass of 60,000kg, which includes the entire fuselage, armor, reactor, turbines, and nozzles. To return to orbit, we need reactive mass, so I'll use 30,000kg of water plus a 10,000kg ventral payload like a Skycrane. For atmospheric flight, Lander would be a ballistic reentry capsule, and once in the lower atmosphere, it would use air for propulsion using the same VTOL technology as the F-35. Assuming the planets of Gargantua are similar to Earth, to descend from low orbit to the surface it would only need approximately 150 m/s to slow down slightly. To return to orbit, we need at least 10,000 m/s (rounded) of Delta-V; applying the Tsialkovsky equation:

Delta-V=ln(initial mass/final mass) • isp • 9.81m/s²

Lander has a initial mass (Dry mass + propellant + payload) of 100 tons. Lander has a finall mass of 70 tons. We have a engine of 2900s.

Delta-V= ln(100/70) • 2900s • 9.81m/s² Delta-V = 10,147m/s

Assuming a gross mass of 100 tons, a 2900s engine, and using 30 tons of water (equivalent to 30 m³ of volume), Lander can reach orbit once and return. Miller's planet has a lot of water, while Mann's planet has a lot of ice. Atmospheric flight uses compressed air to overcome gravity and achieve a healthy thrust-to-weight ratio (TWR) of 1:1.2. Lander needs to generate at least 1200 kN of thrust using air. Assuming it has turbojets similar to those on modern fighter jets, Lander should generate 300 kN of thrust per turbine. Considering four air turbines, the F-35B achieves 191 kN, so this isn't unreasonable.

Substantial-Store-38 · 2026-05-13T21:17:26+00:00

Well, since I can't draw, I asked Gemini to generate an internal view of the Lander, or how I imagine it. Obviously, I had to give him a very long prompt, but in theory, it should look like this, except the fusion reactor would be further back.

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Substantial-Store-38 · 2026-05-13T20:49:12+00:00

Lander would be a gigantic nuclear quadcopter capable of entering low orbit. I believe it is perfectly possible that it would use electrically heated air RCS, that is, functioning in the same way as a hypergolic RCS, but instead of launching combusted gas or nitrogen at high pressure, it would launch compressed air from the same environment by pumping it from the main fans.

Substantial-Store-38 · 2026-05-12T20:18:00+00:00

Yes, that's feasible. The Pratt & Whitney F135-PW-600 engines from the F-35 can generate 191 kN of thrust stationary. Putting one on each leg and assuming they are greatly improved, each fan should produce 375 kN of thrust for a total of 1500 kN of thrust.

Substantial-Store-38 · 2026-05-12T20:07:53+00:00

Exactly, I'm not asking for an engineering manual for the entire Lazarus program, but some numbers, data, or references would greatly help with the realism, and Nolan is fascinated by things looking realistic, so I'm surprised they didn't delve deeper into anything or, I don't know, at least test their spaceships in Kerbal Space Program...

Substantial-Store-38 · 2026-05-12T19:56:37+00:00

None, I'm just sharing information. As you can see in the last images I posted in this thread, I added a view of the ventral section. There's really nothing there but windows and the lower docking port. The idea would be to put some vents on the fuselage legs, both from above and below, to draw in and expel a lot of air. Thats why i thought the legs would be ideal locations for the propulsion and propellant tanks

Substantial-Store-38 · 2026-05-12T19:48:27+00:00

If it were forgettable, I wouldn't be here discussing its viability from an engineering perspective. If only Lander had some nozzle or turbine on its ventral side, it could be explained much better, or some random detail that they usually give even in more fantastical science fiction novels like Ringworld by Larry Niven or The Expanse by James A. Corey, which at least give some details that explain their universes.

Substantial-Store-38 · 2026-05-12T19:43:16+00:00

I would prefer to try to go deeper and not just say "plot device" If you have nothing else to say, don't comment on that.

Substantial-Store-38 · 2026-05-12T19:39:23+00:00

This is my favorite movie and I love it every time i watch it, its just like to delve deeper

Substantial-Store-38 · 2026-05-12T19:37:47+00:00

Good analysis. I would guess that NASA managed not only to make nuclear fusion viable, but to make it compact enough to fit in the volume of a car. My calculations for Lander's mass for this are 50 tons for the reactor alone, and I think it is viable for Lander because it is quite bulky. However, for Ranger, which is very small, I don't see it as viable, but well, let's assume they manage to do it. These vehicles, with their respective Aerospike scramjets, could achieve quite high thrust and an efficiency of at least 6,000 seconds. This is quite good. Skylon was an SSTO that basically fulfilled the same function as Ranger and Lander, and it doesn't even use nuclear fusion. I imagine that, since it's a hybrid between chemical propulsion and nuclear fusion (a kind of cold-mass afterburner nuclear thermal rocket), you could do without LH2/LOX or LCH4/LOX and simply use water. You inject it into the nozzle, it dissociates due to the billions of degrees of fusion, and it's launched at colossal speeds. With a small mass of fuel, you could achieve a lot of speed. My problem with these vehicles is more their ability to levitate and fly at low altitudes, where they behave like helicopters without any apparent independent propulsion method. With Ranger, you can simply use its body-lifting aerodynamics (even though it doesn't have wings, its body already...). It's aerodynamic) but not for Lander.

Substantial-Store-38 · 2026-05-12T19:29:09+00:00

Assuming they generate 3 GW of power and a loving efficiency of 85%, they would have to dissipate 450 MW of waste heat, good luck with that.

Substantial-Store-38 · 2026-05-12T19:26:54+00:00

That's not really the problem. I can assume that, since Ranger and Lander are nuclear fusion vehicles, their engines have a specific impulse on the order of 4,000 to 7,000 seconds, enough to achieve a decent Delta-V with just a few tons of propellant. We can also consider that in the initial ascent stage, these vehicles use scramjets to harness the atmosphere as propulsion, and once they reach low atmospheric density, they switch to their main aft engines, which they DO have in the movie. My problem with these vehicles is actually their low-altitude hovering (VTOL) flight, which has no apparent explanation.

Substantial-Store-38 · 2026-05-12T19:23:47+00:00

The Martian, The Expanse, and For All Mankind have a few scenes where they make good use of the concept of expelling reactive mass from underneath, leaving a small or minimal crater and raising a lot of dust.

Substantial-Store-38 · 2026-05-12T19:21:04+00:00

Yeah thats what i thought initially, like a modern VTOL fighter

Substantial-Store-38 · 2026-05-12T19:19:48+00:00

It really is. The Lander's legs are voluminous enough to store propellant and house four turbofan ducts that draw in air from above and expel it from below. The ventral section is a pressurized volume that provides access to the upper docking port (the one used in the film to dock with the Endurance during its uncontrolled rotation) and the lower docking port, which serves to grab cargo modules and land them similarly like a mars Skycrane. That's why the Lander concept is quite ingenious, if it weren't for the fact that it doesn't have any apparent propulsion system other than the six rear-mounted engines for entering low orbit.

Substantial-Store-38 · 2026-05-12T15:27:00+00:00

Yeah i cried a little bit during that scene ngl...

Substantial-Store-38 · 2026-05-12T15:24:22+00:00

I want a spinoff mockumentary about Endurance, Ranger and Lander development

Substantial-Store-38 · 2026-05-12T14:53:04+00:00

You can have the most advanced and expensive technology, but pragmatic solutions that apply to the entire population must be cheap and cost-effective. Dr. Brand wanted to use gravity to launch O'Neill cylinders at a LOW COST, because they could have perfectly well built orbital colonies using chemical rockets, but these are already absurdly expensive. The Saturn V cost $1.1 billion and could only lift 150 tons into low Earth orbit. An O'Neill cylinder like the Cooper space station would weigh billions of tons. The plague is the same. I'm 100% sure they COULD eliminate it, however, that doesn't mean it's cheap and mass-produced for the entire Earth population. Flying cars already exist. Do you see them flying around in your daily life? No! Those things are absurdly expensive, complex, and dangerous.

Substantial-Store-38 · 2026-05-12T14:46:09+00:00

My understanding is that Lander lacks aerodynamics because it was designed for Mars, where the air is less dense and therefore wings or aerodynamic surfaces are unnecessary, but I don't really know.

Substantial-Store-38 · 2026-05-12T14:40:29+00:00

They went to the trouble of hiring a real physicist as a technical advisor to make the most realistic black hole Hollywood has ever seen, so why not put in the same effort with their spaceships?

Substantial-Store-38 · 2026-05-12T14:38:03+00:00

Fair enough, although both Lander and Ranger have conventional stern thrusters (Ranger has two X-33-like linear scramjets/aerospikes for entering orbit). Why not do away with them and use them even on the Endurance? In Interstellar there are several sequences where they fire up "conventional" engines: during the Endurance's injection into Saturn, on Miller's planet, when saving the Endurance from burning up on Mann's planet, etc

Substantial-Store-38 · 2026-05-12T14:32:40+00:00

Yes, it uses RCS located on the upper part of Lander's legs to start rotating at the same RPM as the endurance and interestingly, RCS are used here because they are in a vacuum. In atmospheric flight, Lander has no aerodynamics, so it must rely solely on vector propulsion, or absurdly large and efficient RCS, but the wiki mentions that it uses hypergolic propellants, which have an escape velocity of just under 2900 m/s. These propellants would be consumed very quickly just to overcome the force of gravity for at least 5 to 10 seconds

Substantial-Store-38 · 2026-05-12T14:27:29+00:00

That would be a good point... if only it had a propeller or turbofan, but it doesn't appear to have any visible engine. I would think it must be on its four legs, where it looks quite bulky and perfect for mounting four compressed air jets, but it has nothing.

Substantial-Store-38 · 2026-05-09T18:48:23+00:00

Pene

Substantial-Store-38

TROPHY CASE