Reusable Lunar Lander [idea]

[deadman1204]

I suppose this thread is as good as any to pose a question.

Why are landers almost always designed/depicted with the cargo sitting atop the propulsion and tankage ??  Is there any technical or engineering reason for this ??

IMO this configuration will always necessitate the inclusion of a crane or davit of some kind and therefore introducing some level of instability when lifting weighty cargo down the side of the craft, especially in the case of Starship.

Would it not be better to have the cargo, whatever it be, attached underneath a framework that holds the engines, tanks, avionics and everything else ??  This way the cargo is placed directly on the ground.

Think Thunderbird 2 touching down, releasing a pod and flying off.

This doesn't really work. Putting aside top heavy concerns (engines and fuel are very heavy), the engines need to fire down, which means they cannot be firing into the cargo. Its not different than why are wheels on the bottom of cars? The wheels need to push off the ground. Engines need to push prop out the bottom of the rocket.

[AS-503]

I suppose this thread is as good as any to pose a question.

Why are landers almost always designed/depicted with the cargo sitting atop the propulsion and tankage ??  Is there any technical or engineering reason for this ??

IMO this configuration will always necessitate the inclusion of a crane or davit of some kind and therefore introducing some level of instability when lifting weighty cargo down the side of the craft, especially in the case of Starship.

Would it not be better to have the cargo, whatever it be, attached underneath a framework that holds the engines, tanks, avionics and everything else ??  This way the cargo is placed directly on the ground.

Think Thunderbird 2 touching down, releasing a pod and flying off.

This doesn't really work. Putting aside top heavy concerns (engines and fuel are very heavy), the engines need to fire down, which means they cannot be firing into the cargo. Its not different than why are wheels on the bottom of cars? The wheels need to push off the ground. Engines need to push prop out the bottom of the rocket.

Seems the JPL Sky Crane did a good job with having the propulsion above the cargo.

[MickQ]

Yes.  Skycrane is part way to what I’m thinking of.

Obviously you would not have the engines firing down on to the top of the cargo but have the cargo positioned in between the engines.  In the final 50 or so meters of the descent the engines start to gimbal outwards to blow most debris away from the lander.

At touchdown either the engines shut down or the cargo pod is released and the lander returns directly to orbit for re use.  Another advantage of this configuration would be that if a problem occurs during descent, such as an engine out, the cargo can be dropped and the lander aborts to orbit.

[tbellman]

Yes.  Skycrane is part way to what I’m thinking of.

Obviously you would not have the engines firing down on to the top of the cargo but have the cargo positioned in between the engines.  In the final 50 or so meters of the descent the engines start to gimbal outwards to blow most debris away from the lander.

At touchdown either the engines shut down or the cargo pod is released and the lander returns directly to orbit for re use.  Another advantage of this configuration would be that if a problem occurs during descent, such as an engine out, the cargo can be dropped and the lander aborts to orbit.

Dynetics' ALPACA lander seems to be fairly close to what you are thinking of.  A frame with the cargo (cabin) in the center, and propellant tanks and engines on each side.

As for why so few have been designing landers that way, I can only speculate, but here are some possible reasons:

• Needs to be launched on its side, to fit inside launch vehicle fairings.  That gives different load paths than when it is landing and/or launching on its own on the Moon.

• You need 2, 4, 6 or 8 engines, not just a single engine.  Often, having multiple smaller engines is less mass efficient than having a single engine.

• Likewise, you need two sets of propellant tanks, one set on each side, which increases mass.

• Some payloads don't care much if they are directly on the surface, or if the are a meter or two up.  An instrument that investigates the lunar "atmosphere" may be perfectly OK with sitting on top of the lander.  Even something that drills or digs into the regolith for analysing, might need an arm anyway, and it might not matter that much if it needs to be a bit longer.  (This point of course only applies to the case where the payload is fixed to the lander and uses it as a platform.)

• (For the case where you disconnect the cargo from the lander and put it on its own on the surface.)  You probably need some mechanism for carefully lowering the cargo to the surface anyway.  You will most likely have landing legs, so after landing the cargo might be half a meter or more from the surface, and you might not want to just drop it and let it fall.  That mechanism may be easier and more lightweight than one that has to take the payload down from the top of the lander, but the difference might not make up for other complications.

• A payload that is a rover, can sometimes drive itself down from the top of the lander.  The only mechanism needed on the lander is a ramp that the rover can drive down.

• "It's not how Apollo did it."  Once you have seen one working solution, it is very easy for your brain to "lock on" to that, and it can be difficult to imagine other solutions.

[Coastal Ron]

I suppose this thread is as good as any to pose a question.
...
Would it not be better to have the cargo, whatever it be, attached underneath a framework that holds the engines, tanks, avionics and everything else ??  This way the cargo is placed directly on the ground.

Think Thunderbird 2 touching down, releasing a pod and flying off.

ULA, many years ago, proposed their Dual Thrust Axis Lander (DTAL), which is based on their Advanced Common Evolved Stage (ACES) platform. You can find the study here:

Robust Lunar Exploration Using an Efficient Lunar Lander Derived from Existing Upper Stages - United Launch Alliance

Their proposed lander looks like current "rockets with cargo on top", but lands horizontally. A pretty neat concept, that I always thought had possibilities, but no one else had proposed similar concepts for the Artemis program.

BTW, ULA used to have a dedicated section on their website called Papers and Presentations, but now it has been moved to their "Explore" section, and the link no longer works (hopefully this is temporary). Which means ULA is no longer promoting their ideas for space exploration, including those that were going to use ACES. Sad to see, and I wonder if that will change when/if someone buys them...

[MickQ]

ALPACA is basically the closest configuration to what I’m thinking of.  The difference being that the payload section ( payload meaning hab module, rover, cargo pod etc )  is quickly and easily detachable from the rest of the lander.  At touchdown the lander’s legs adjust to place the payload on the ground.  The attachment mechanism unlocks and the lander then returns to orbit for refueling and another load.

[chopsticks]

I'm surprised no one has mentioned Blue Origin's HLS. Tanks are on the top and the people are underneath.

[Asteroza]

ALPACA is basically the closest configuration to what I’m thinking of.  The difference being that the payload section ( payload meaning hab module, rover, cargo pod etc )  is quickly and easily detachable from the rest of the lander.  At touchdown the lander’s legs adjust to place the payload on the ground.  The attachment mechanism unlocks and the lander then returns to orbit for refueling and another load.

A straddle frame style lander with at least a pair of rockets, at first glance at least, seemed like a decent choice in the past, but with increasing worries about plume impingement digging a hole, is the current consensus moving towards landers with high mount rockets (effectively a puller rather than pusher configuration?)

Starship HLS is that weird one where it might be a classed as a pusher config due to waist mount rockets simply by convenience of size of lower tankage, whereas some other bottom loaders really are a puller/tractor config. Tractor style bottom loader rigs do face the long leg issue though (true long legs, or a lower structure that extends leg reach)

[DanClemmensen]

Starship HLS has landing thrusters in addition to its main Raptor engines. The landing thrusters have enough thrust to perform the last 100 meters or so of the landing (i.e., they can hover the HLS in a 0.16 g field) and they point down at an angle, ("cosine thrusters") instead of pointing straight down.

Consider an HLS that lands with the raptors pointing up, using landing thrusters near the raptors but pointing down. This would put the crew or payload section near the surface. landing legs would be at the "lunar down" end. The ogive would be discarded after the HLS was launched, so the "lunar down" end would be flat.

The lunar landing trajectory would be nearly horizontal as the raptors brought HLS near the surface. When HLS was about 100 meters above the landing point at zero velocity, raptors would flip it to lunar vertical and the landing thruster would take it down. Ascent wouhd be the reverse: landing thruster take it up to 100 meters and flip it, and raptors take over.

Presumably the crew couches would be gimballed.

[deadman1204]

I suppose this thread is as good as any to pose a question.

Why are landers almost always designed/depicted with the cargo sitting atop the propulsion and tankage ??  Is there any technical or engineering reason for this ??

IMO this configuration will always necessitate the inclusion of a crane or davit of some kind and therefore introducing some level of instability when lifting weighty cargo down the side of the craft, especially in the case of Starship.

Would it not be better to have the cargo, whatever it be, attached underneath a framework that holds the engines, tanks, avionics and everything else ??  This way the cargo is placed directly on the ground.

Think Thunderbird 2 touching down, releasing a pod and flying off.

This doesn't really work. Putting aside top heavy concerns (engines and fuel are very heavy), the engines need to fire down, which means they cannot be firing into the cargo. Its not different than why are wheels on the bottom of cars? The wheels need to push off the ground. Engines need to push prop out the bottom of the rocket.

Seems the JPL Sky Crane did a good job with having the propulsion above the cargo.

This is quite missleading. 99% of the slowing down was done before the skycrane happened. As well, it can only work for lighter payloads because its incredibly inefficient. The engines all point away instead of directly down. Add to that the damage the rovers have taken from this. For example curiosity's weather package got ruined from this.
There are alot of thnigs that are "possible", but we were talking about rockets, not 1 off landing systems that exclude 99% of the deceleration