Idea "Man on the Earth" project.

[Linguofreak]

I was thinking it might be interesting to design an addon for a mission that involves landing a lunar inhabitant on the Earth and returning him safely to the moon with approximately 1960's or 70's technology. (Before the decade is out, if possible. )

The challenge of this is that it would involve finding some way to soft-land a surface to LEO launcher (Something about the size of a Mercury-Atlas for one man to Earth, or Gemini-Titan for two men) on an unprepared field (thus ruling out "airplane style" landings) on Earth. We'll probably have to ignore/handwave the logistics aspect, since such a launcher would require a pretty massive crew to prepare for launch, and just landing it and getting it up again should be a pretty big challenge without worrying about whether our surface team could actually prepare the rocket for launch.

Our tech assumptions:

The empty mass of each stage/vehicle involved is equal to engine+structure+crew quarters (if that stage has any)

Crew quarters mass 1000 kg of life support + living space + occupant per person carried.

Engine mass is determined by power/mass ratio, with the limit being somewhere around 3 Megawatts per kilogram. (Power is equal to isp*thrust). The J-2 is 3.024 MW/kg, so that high is fine, but don't push it too much higher.

Structure is 5% of crew quarters + engine mass + fuel. This is subject to review by those with more engineering experience than myself. Structural mass will probably be a fairly high percentage for Earth stages (since they have to withstand 1 g on the surface, and more than that during launch, as well as a bit of a jolt during landing), and a fairly low percentage for space stages and lunar liftoff and landing stages.

Engine types should be limited to nuclear thermal and chemical. ISP's and propellant densities should be within reason for the engine type selected (propellant density should probably have some effect on structural mass, but I'm not exactly sure what effect). For nuclear thermal, the ISP limit is 10000 m/s for hydrogen, 7800 m/s for methane, and 6300 m/s for ammonia.

Anybody interested in trying?

 

[Andy44]

I once proposed a similar project involving Martians of human size rather than Lunar people (Lunians?). I'm interested.

We all agreed that the hardest part is getting the visitors off the surface and back into LEO. Nobody ever settled on a solution. My idea was to send in the launch vehicle in segments with solid fuel, and assemble them on the ground. Spares would have to be sent as well, in case some are damaged in transit. Others proposed sending empty liquid stages and using ISRU to make your own propellant on the surface.

We all agreed that it would be best to restrict your landing party to two individuals and use a small capsule made for only those two and a small sample of rocks, flora, fauna, etc. The capsule doesn't need a heat shield since it only needs to get to LEO and meet up with the return-home vehicle.

About ruling out a winged vehicle, why? A lifting body would be quite nice for variety of landing sites, and you can use a parafoil for a short-field landings. Might be a bit rough, but if it's a one-time use expendable vehicle, should be managable.

Are we to assume that our Lunians can withstand the same G-force as humans for simplicity? If not, just standing on Earth would be all but impossible.

 

[wehaveaproblem]

What about considering a rotary landing/takeoff vessel? I know the Roton, or whatever it was called, didn't pan out too well, but the theory is fairly sound. Controlled vertical decent would be a real asset for landing, and it could feasibly be a one-stage to LEO vessel on the way back up to LEO?

 

[Unstung]

Getting Lunatics to the Earth? Sorry, had to bring that up. Although, I have almost no add-on experience.
The only related add-on I made was for YSFLIGHT and did not come out so well.
But, there would be no point if these Lunatics could not survive in Earth's gravity. I was thinking we could make the capsule could be similar to the Russian's and land on, well, land in Florida. An aircraft-like space vehicle such as the shuttle would not make sense since there would be no way any aircraft could fly on the moon. That means parachutes will not work on the moon either, right? So, how would the Lunatics know? They would need quite a bit of thrust to get back into orbit to dock with a command module or just be able to fly back to the moon.
I am nowhere near a rocket-scientist, so I will leave that to the others.

 

[Arrowstar]

Well, one could argue that we don't live on the Moon, yet we came up with and developed a perfectly usable LEM in the Apollo days. I'm sure their scientists/engineers are capable of that sort of thought.

 

[SiberianTiger]

I believe it might seem quite useful for a visitors from another world to value ocean landing over firm land landing on Earth. Because of that, they might also employ a floating platform design as a launch pad for their return rocket, this would give them some advantages: keeping the structure more intact than after a firm land landings; possibility to move the platform around for exploration and for picking the best launch spot; guaranteed access to water that can be electrically split into propellant components (given they are in no shortage of energy). The pltaform itself might look buoy-like.

 

[Linguofreak]

I once proposed a similar project involving Martians of human size rather than Lunar people (Lunians?). I'm interested.

We all agreed that the hardest part is getting the visitors off the surface and back into LEO. Nobody ever settled on a solution. My idea was to send in the launch vehicle in segments with solid fuel, and assemble them on the ground. Spares would have to be sent as well, in case some are damaged in transit. Others proposed sending empty liquid stages and using ISRU to make your own propellant on the surface.

This is why I said we should probably gloss over the logistics aspect.

The problem of assembling and fueling the rocket if we don't gloss over the logistics is such that you'd probably have to set up a permanent base before you could send anybody back, or else you'd have to land ten times the mass of your rocket in highly automated equipment.

I figure for simplicity's sake we can drop a whole fully fueled rocket. Designing a system to drop that should be challenging enough, if not 100% realistic. If people don't like that, we can drop it in full liquid stages, with some extra mass on the landing vehicle for reinforcement. The solid stages could also be a way of doing it, though they might be a bit slim on the ISP side.

We all agreed that it would be best to restrict your landing party to two individuals and use a small capsule made for only those two and a small sample of rocks, flora, fauna, etc. The capsule doesn't need a heat shield since it only needs to get to LEO and meet up with the return-home vehicle.

Which still makes the capsule+launcher the size of Gemini-Titan or so...

About ruling out a winged vehicle, why? A lifting body would be quite nice for variety of landing sites, and you can use a parafoil for a short-field landings. Might be a bit rough, but if it's a one-time use expendable vehicle, should be managable.

I suppose, but even dropping it in stages or segments we're talking pretty heavy landing vehicles. Would you be able to find a stretch of terrain that was level, hard, and long enough to support even a short-field vehicle of that size? Then again, I suppose size would make it hard to land vertically as well.

I guess we can take winged vehicles, but we'll have to set an upper limit for landing distance.

Or, another idea, land the crew and a bulldozer in a capsule or two, and have them prepare a dirt field of a few thousand feet onto which the rest of the launcher is dropped. Although I'm not sure that such a dirt field would support the weight of your landers...

Are we to assume that our Lunians can withstand the same G-force as humans for simplicity? If not, just standing on Earth would be all but impossible.

I'd forgotten about that, but yes, it makes a good simplifying assumption.


-----Post Added-----

I believe it might seem quite useful for a visitors from another world to value ocean landing over firm land landing on Earth. Because of that, they might also employ a floating platform design as a launch pad for their return rocket, this would give them some advantages: keeping the structure more intact than after a firm land landings; possibility to move the platform around for exploration and for picking the best launch spot; guaranteed access to water that can be electrically split into propellant components (given they are in no shortage of energy). The pltaform itself might look buoy-like.

I thought of that, and it does present some advantages, but the Lunatics probably wouldn't be able to land the infrastructure neccesary to stabilize it against wave action.

 

[astrosammy]

And what is with us, the humans? Are we existing in this scenario or not? If yes, we need to think about what the humans would do with the selenites, maybe they could help them to get back to the moon.

 

[Andy44]

To simplify, no, there should be no sentient Earthling species involved, no humans. Otherwise the Lunians could just land at Canaveral Runway 33 and hop on the next STS ride back to LEO. That's cheating.

I think the important thing is to drop your return-to-LEO equipment, as well as whatever hab equipment you need for camping out on the surface, before you ever land any people.

If we stick to the above assumptions, we need a capsule of Gemini size, or better yet, a Soyuz capsule with no heatshield, no mission module, and minimal maneuvering requirements. To get such a vehicle into LEO requires something with more throw weight than an Atlas D, but a little less than a Titan II. This can probably be done with solid-fueled Minuteman III-style staged rocket.

Pros of solids are that they are pre-loaded and easy to assemble on site, but the cons are that they are heavy, bigger than equivalent liquid stages, harder to soft-land, and, if the Minuteman III is any indicator, will result in very high g-forces during ascent.

Pros of liquids are the opposite, but the cons are that fuel is harder to handle, may have to be obtained from the local environment, which is NOT easy, and they are more mechanically complicated.

But if the Lunies figure it out ahead of time, they can land a fuel processor plant ahead of time near a water source and telemetry will tell them if it's working right before they commit to a manned landing.

I was leaning towards solids, but I think I'm liking liquids the more I think about it. Earth is practically made of rocket fuel. Might as well use it.

 

[Linguofreak]

One advantage we do have is that the lunatics will be able to build a very big launcher for their initial ascent from the moon. The moon's 1/6th g of surface gravity and lower escape velocity would mean that the Saturn V's five F-1 engines could loft alot more. So they'll be able to ferry alot more mass to Earth than we were able to send to the moon. Of course, they'll also be leaving a whole bunch of that behind on Earth.

 

[T.Neo]

Sounds interesting.

Can anybody work out how much a Saturn V could loft from the lunar surface to a 50km orbit?

From there, the payload could be boosted towards Earth, where it would perform an aerocapture to a LEO type orbit. An Atlas style rocket would reenter and land, where it might use some of the local rescources as fuel. It would then launch back, and perform a rendezvous with the rest of the payload. It would then be boosted back to the Moon. The one man mercury style capsule would break into lunar orbit and dock with a orbiting landing vehicle.

Oh, and give the Lunatic a gun. The fauna might find him tasty.

 

[Linguofreak]

So.

If we're actually gonna do this, we need to figure out what exactly we need to have on our Earth liftoff capsule and our Lunar return vehicle. The weight of the ELC will determine the weight of our Earth launcher, which will determine the weight of our Earth drop vehicle. The weights of the EDV and the LRV together will determine the weight we actually need to start with from the moon:

So, for the ELC: We need 2000 kg to support two crew members. What else do we need? We don't need heat shielding, because it won't be re-entering (at least not with a crew on board), but we probably need engines and propellant for rendevous with the LRV. How much weight needs to go to engines and propellant, and do we need anything else?

For the LRV: 3000 kg for 3 crew. Also needs enough thrust and propellant to get back to the moon from Earth, and to land on the moon, plus a reserve for maneuvers in Earth orbit, rendezvous with the ELC, emergencies, etc. I'm thinking somewhere around 7 or 8 km/s. (I think it's about 3 or 4 km/s from Earth orbit to the moon, then around 2 or 2.5 to land, and then we leave ourselves a km/s or two as a reserve). A rough BOTE calculation says that this can be done with an Apollo CSM type vehicle where the service module is a cross between the S-IVB and the Apollo service module. I'm also thinking a nuclear thermal design might be interesting. (Not having an atmosphere to carry fallout over long distances, the Lunatics aren't quite as sqeamish about things nuclear as we are ).

 

[T.Neo]

:goodposting:

Does the ERV (Or MRV, is it?) have to land? I thought it could rendezvous with a craft in lunar orbit. Maybe that pushes things, but how about it's feasibility?

This would make a cool addon. I'd love to mesh this if all the parameters were worked out.

 

[Linguofreak]

:goodposting:

Does the ERV (Or MRV, is it?)

Oops. That should be Moon Return or Lunar Return vehicle, MRV or LRV, yes. I will edit that as soon as I finish this post.

have to land? I thought it could rendezvous with a craft in lunar orbit. Maybe that pushes things, but how about it's feasibility?

I suppose it could rendezvous with a surface to orbit shuttle once it got to the moon. Or it could be two stage, with a return stage and a lander stage. I was thinking that it would be easier to make it reusable if it could actually make a lunar return, since that's where the infrastructure would be. Then again, it would be easier to lift repair and refurbishment infrastructure into orbit on the moon, and the reduced delta V of an orbit only vehicle might save some design hassles. But I still like the idea of the whole LRV landing.

This would make a cool addon. I'd love to mesh this if all the parameters were worked out.

Well, let's see what other people say about weight requirements. We can use that to estimate size, as well as how much fuel tankage we'll need, and that will give you a starting point for meshwork.

 

[T.Neo]

I just tried to take a Velcro Saturn V into low lunar orbit from Brighton Beach. She seems quite overpowered, but I think she would be able to make lunar orbit and the Earth injection burn. That leaves a fully loaded S-II and S-IVB on top, or, in this case, their weight equivalent.

 

[Andy44]

For the LRV: 3000 kg for 3 crew. Also needs enough thrust and propellant to get back to the moon from Earth, and to land on the moon, plus a reserve for maneuvers in Earth orbit, rendezvous with the ELC, emergencies, etc. I'm thinking somewhere around 7 or 8 km/s. (I think it's about 3 or 4 km/s from Earth orbit to the moon, then around 2 or 2.5 to land, and then we leave ourselves a km/s or two as a reserve). A rough BOTE calculation says that this can be done with an Apollo CSM type vehicle where the service module is a cross between the S-IVB and the Apollo service module. I'm also thinking a nuclear thermal design might be interesting. (Not having an atmosphere to carry fallout over long distances, the Lunatics aren't quite as sqeamish about things nuclear as we are ).

If we're going nuclear, something like the Ares ship from 2001: A Space Odyssey should do, the one that Floyd lands on the Moon in. It was nuclear powered, and had enough delta-V and thrust to operate from the lunar surface and fly to the Earth-orbiting station and back. If you reduce the creature comforts and cut back on the mass, you can probably get more performance out of it.

I also like the idea of a direct landing on the Moon. Makes the mission simpler, and the Moon's low grav and lack of atmo don't make this so difficult like Earth does.

 

[Linguofreak]

If we're going nuclear, something like the Ares ship from 2001: A Space Odyssey should do, the one that Floyd lands on the Moon in. It was nuclear powered, and had enough delta-V and thrust to operate from the lunar surface and fly to the Earth-orbiting station and back. If you reduce the creature comforts and cut back on the mass, you can probably get more performance out of it.

That's the general idea, though I don't find the 2001 Ares very aesthetically appealing.

Right now, though, I'm trying to work out a good weight for the non-propulsion part of the ship so we can figure out the propulsion part. Right now I have 3000 kg for crew and accomadations. The Apollo CM, built for the same crew, was 5000 kg, for which the mass over the 1000 kg/person mark, looking at the mass breakdown on Wikipedia, seems to be mostly heat shield and recovery system mass, which we don't need, and navigation equipment mass, which we need, but might be able to be hacked away by Moore's Law, depending on how strict we want to be with applying our "60's/70's" tech limit to our electronics. The service module's non propulsion mass is 3110 kg, 1910 of which is structure, and 1200 of which is electrical equipment (I think primarily the fuel cells). If we go nuke thermal, we can use the reactor for power, so we don't need the fuel cells, which should save us quite a bit of mass. (Although we will need to take into account reduced thrust/weight ratio of the engine, as well as the mass of shielding, which might lose us some of what we gain).

So let's assume that 3000 kg is a good figure for the non-propulsion, non structure mass of the LRV. Assuming that we want at least 2 lunar gravities of acceleration, we'll need about 10000 newtons, which will take about 80 megawatts assuming an ISP of 8000 m/s. Which will take a 25 kg engine assuming our 3 MW/kg power/mass ratio. With an ISP of 8 km/s, we'll need a mass ratio of e (about 2.7) if we want a total delta v of 8 km/s, which adds about 5150 kg of propellant, which will then require a 70 kg engine to propell the entire spacecraft at 2 lunar gravities. In the end we get about 8225 kg, and then add 5% structural weight, and come out to a bit over 8600 kg. Making various allowances for shielding, miscalculation, and systems we may have forgotten, let's say the entire LRV weighs 9 or 10 metric tons, of which about 37 percent is spacecraft and 63 percent is propellant. What propellant do we want to use?

EDIT: Also, please do comment on the mass of the ELC. How much maneuvering fuel do we need for rendezvous with the LRV? Is a 2250 kg total mass good? 2500? 3000?

 

[T.Neo]

What propellant do we want to use?

For the LRV?

My batteries are low at the moment, but:

Chemical: Depends on stay on Earth surface. Shorter stay, one might be able to use cryo propellants, longer stay, hypergolics might be necessary.

Nuke thermal: I heard somewhere that ammonia might be good for nuke thermal, and is relatively easy to store.

Me, I'm a bit unsure of nuke thermal. Sure, it might have been possible with 60's/70's tech, but it has not been used in spaceflight. I think sticking to lower Isp could impose more of a challenge on the design.

Also, any idea of landing sites?

The landing site might just define the mission.

 

[Linguofreak]

For the LRV?

My batteries are low at the moment, but:

Chemical: Depends on stay on Earth surface. Shorter stay, one might be able to use cryo propellants, longer stay, hypergolics might be necessary.

Nuke thermal: I heard somewhere that ammonia might be good for nuke thermal, and is relatively easy to store.

I was thinking methane would be better, though it might have the problem of leaving sooty deposits in the reactor that could cause problems.

The problem with ammonia is that the heavier your molecular mass, the lower of an ISP you get for a given reactor temperature. Even methane is only really good because it dissasociates into carbon and hydrogen at high temperatures, which boosts the ISP a bit. The same thing happens to ammonia, but there's less hydrogen in it, and nitrogen is heavier than carbon, so it ends up with a lower ISP. It may still be workable, but if it is, it's about the worst propellant you can use in an NTR and still have any advantages over a chemfuel rocket.

Even with methane, it might not quite be possible with a 60's/70's style NTR, at least without ending up with an unacceptably low ISP.

So probably methane or hydrogen, I'm thinking.

Me, I'm a bit unsure of nuke thermal. Sure, it might have been possible with 60's/70's tech, but it has not been used in spaceflight. I think sticking to lower Isp could impose more of a challenge on the design.

Also, any idea of landing sites?

The landing site might just define the mission.

Your point here, and the ones I made in discussing propellant choice, make me really uncertain about whether an NTR is workable.

But still... I do like NTR's, and alot of their disadvantages (fallout spreading on the winds if it breaks up on launch, low thrust to weight ratio) aren't so bad for a ship that will never touch down on Earth, so the Lunatics might well have more advanced NTR technology at an otherwise "1960's" tech level.

I don't know. NTR/chemfuel is a really tough choice.

As for landing site, the plains in Colorado strike me as a somewhat nostalgic choice. Anywhere flat with hard ground will do. It might have to be a desert to avoid starting a grass fire on landing, since I get the feeling our landing vehicle will need braking rockets as well as parachutes for the last few feet.

 

[Andy44]

For NTR propellant I say hydrogen. I think you can get H2 from lunar soil, and the big drawback of H2, which is a large volume tank, doesn't mean as much since it doesn't have to be launched through an atmosphere.

Landing on dry terrain is nice, but for both mission science and ISRU reasons I think someplace with nearby water and abundant life is best. This shouldn't be hard to find provided you do good landing site recon mapping before launching the mission. Although I'm partial to North America for obvious reasons, a site near the equator in South America or Africa would have more diverse life to study, and be easier to plan orbit-wise.