Ambitious space program relying on medium payload carriers - Practical?

[Kerbin Dallas Multipass]

I was asking myself how practical, how technically feasible and how economically viable a space program would be if it completely relied on existing medium payload launch technologies.

Let's say I want to put a man on the moon and do the other things, namely having a lunar base, putting a man on mars and such fancy stuff.

Can this realistically be done with the current (soon available) fleets of Delta Heavies,Falcons, Arianes and so on? We are talking payload capacities of perhaps 15-35t, so how challenging would it be to design and assemble larger space ships in orbit from these smaller modules?

-Are there technical problems that would have to be solved?

-Would such modular designs be much more complex to plan and lay out compared to larger chunks of payload (120+t)

-Would it be cheaper than a dedicated heavy lifter system such as the SLS or would the increased complexity and logistics (all that docking and EVAs to attach struts!) eat up most of the economic advantages?

-Other limitations that would make a heavy lift system a "must have"? What would you regard as a minimum payload capacity required for a manned moon or mars mission?

Edited May 7, 2014 by Kerbin Dallas Multipass
Added an "a"

[jwenting]

You'd need to construct the mission craft in orbit, which in real life is rather more complicated than it is in some game featuring little green men.

You'd probably need several launches just for the crew compartment, several more for supplies, several more for fuel, a few for pieces to build the lander(s), then a few for the engines and other stuff needed to bolt those on to the ship. And that doesn't even include the nuts and bolts to hold it all together, the living quarters on orbit for the construction crew, their food and drink, air, the people doing the construction work, etc. etc.

So instead of a single Apollo launch or 2 part launch with Geminis or Soyuz (both had planned lunar mission profiles) you're soon looking at several dozen launches.

And with the launch failure rate of those rockets, that's an almost certainty that at least one and probably several of them are going to go BOOM.

[R0cketC0der]

Two falcon heavy launches actually get almost the same to LEO as one Saturn V launch, so if you are able to save a bit of weight by using modernized components, you should have a little extra margin to bring the dV and RCS fuel needed for docking.

On the other hand, the falcon heavy isn't planned to get man-rated, so you either would need an extra launch to get the crew up or need to spend more money for man-rating the falcon heavy.

[KSK]

I don't think it would be feasible with medium lifters. Some rough figures (in metric tons)

Apollo CSM: 30.3

Apollo LM: 14.7

Dragon: 6

So you're need about 45 tons of payload capacity to get an Apollo style orbiter and lander into orbit, or a modern day equivalent based on Dragon. Apollo Command Module weighed about 5 tons, so Dragon is slightly heavier but a modern Service Module could potentially be a bit lighter (?) I don't have the numbers for Orion but it was billed as an Apollo-plus level of mission, so I'm assuming it's going to be heavier than 45 tons.

Next, you need an Earth Departure Stage (EDS) of some kind to get all that from LEO to Lunar orbit. Extremely rough weight for that is 73 tons based on the Saturn V payload difference to LEO (118 tons) vs TMI (45 tons). Take into account that a) the Saturn V SIVB stage also did some of the lifting to LEO and you could probably get away with a lighter EDS if you launched it separately (rather than making it sturdy enough to stick a CSM/LM on top of) and you could maybe (handwave handwave) get that 73 tons down to 50-55. Which coincidentally (or probably not) is about the projected payload for the Falcon Heavy.

This is assuming an Earth orbit rendezvous of CSM/LM and EDS. Building a moonship out of more than two parts would be challenging, for the reasons that jwenting points out and also because your fuel only has a limited lifespan on-orbit before it either boils off or corrodes the spacecraft plumbing. Orbital refueling would get around that of course but that is yet another layer of complexity.

Summary: not going to happen with medium lift, unless we figure out orbital refueling or get really good at building spacecraft in orbit from relatively small parts. Could happen with a heavy lift vehicle of around 50-55 ton payload capacity.

Possibly.

[astropapi1]

Two falcon heavy launches actually get almost the same to LEO as one Saturn V launch, so if you are able to save a bit of weight by using modernized components, you should have a little extra margin to bring the dV and RCS fuel needed for docking.

On the other hand, the falcon heavy isn't planned to get man-rated, so you either would need an extra launch to get the crew up or need to spend more money for man-rating the falcon heavy.

And you would need to launch a rocket stage for the TLI burn...

[Red Fang]

Ninjaed by KSK who gives a better example, and I mostly agree with his points. My post goes for a Mars mission and is jumled as I am typing from a tablet. TLDR. :-)

Let us suppose that our upper limit for launching structural elements to LEO is Proton's 20t and for fuel and supplies is Falcon 9R - 13 tonnes (say, we can use 10 while 3t are the delivery craft itself). All of the systems assembled in orbit have to be developed and fall into two categories: propulsion and mission systems.

Propulsion

A single type of autonomously docking booster must be used, with integrated engines, RCS, guidance, communication systems etc... Given the modular nature of the system, we will be using UDMH and N2O4 for fuel, to reduce compexity of the engines, cut down fuel boiloff and weight of the tanks. Assembly of such ship may take a while. Please correct me, but to transfer from LEO to LMO, including correction burns and capture, one needs some 6 km/s of delta-v.* Therefore, if we are to launvh and return some 50t of empty craft, we need about 300t of fuel and oxidizer. That would be in a single stage configuration. Four boosters that can carry up to 80 tonnes of fuel each, would be launched by four Proton rockets, mostly emmpty. That would require 32 sucsessfull F9R launches. ( round it up to 40, to compensate for high failiure rate of fueling craft).

Mission Systems

Than add two part habitat - one would be a TKS derived, or similar 20t vehicle; the other, a partialy fueled lander/Mars hab. Both would be laaunched aboard Proton rockets.

MAV should require two more proton launches. One for the Mav itself, the other for a booster. Than add 8 (10) more F9R missions for fueling.

To sum it up, you are looking at about

- 50 Falcon 9R launches - 500M

- and 8 Protons. - 450M

- 50 expendable fuel tugs - 50M each

- 5 reusable boosters - 100M each

- 1 Mars ascend vehicle - irrelevant

- 1 transfer habitat -irrelevant

- 1 lanser/habitat -irreleevant

- at least 5 crewed missions to check up on systems while the thingbn is built on orbit and to crew it. let us say you will be usiing Dragon mk2 for that. Say mission cost iss about 200M each.

So, you are lookingat about 4.95BN $ in launch and craft costs alone. And that does not include developement of fuel tugs and boosters, as well as mission payload (habitats, lander, ascend vehicle). Thee same could be donee with 5 heavy launchers and change, for similaar amount of money.

Heavy vs meedium launchers approach:

Same:

-Mars payload

-Orbital boosters

-total mass in LEO

Different

-MLV Optimistic launch and R&D costs for booster fueling systems

- MLV Optimisstic F9R launch costs and frequency

- HLV mission architecture does not beneefit from economics of scale,

- HLV develeopement cost is not included and may offset benefits of fewer launches

- HLV launch rates would probably be too low to assemble everything in LEO within 3 years

- MLV - Unreasonaable number of launches for reasonaable time of craft compleeteon

- MLV - developement is finished, no new funds needed.

Therefore, IMHO, MLV mission architecture could be feasible if:

a- We want to go to Mars NOW and assume that building a fleet of expendable fuel tugs will pay of in the long run.

b- We relay on F9R becoming what Musk claaims it will be.

HLV mission architecture sound smore viablee, but i doubt that anyone will be launching enough of those to make such a mission a possibility.

So in essence, we are stranded in Earth/Moon system regarding human space flight. If somebody manages to make Mars Direct work, than we might have a fighting chance, with al laater version of SLS or similar system and hydrolox stage for TMI.

*https://www.google.rs/url?sa=t&source=web&rct=j&ei=8lJpU7zTDcTY0QWW34HIBw&url=http://trajbrowser.arc.nasa.gov/pdfs/FosterDaniels-HumanExplorationOfNearbyPlanetaryBodies.pdf&cd=1&ved=0CCUQFjAA&usg=AFQjCNHmm5rw4Xe9j7K8VEVJIExuYrbmpg&sig2=zKXoN-ZcJB7Spy6GFH67xg

[Nuke]

Let's say I want to put a man on the moon and do the other things...

"the other things" in kennedy's speech was 'smash communists'. i suppose medium launchers can do that (anything is possible with nukes).

[deadshot462]

And you would need to launch a rocket stage for the TLI burn...

RocketCoder may have included that. After all, a Saturn V put the TLI stage into LEO.

[R0cketC0der]

RocketCoder may have included that. After all, a Saturn V put the TLI stage into LEO.

Yep, that was with the TLI stage included.

[KSK]

Ninjaed by KSK who gives a better example, and I mostly agree with his points. My post goes for a Mars mission and is jumled as I am typing from a tablet. TLDR. :-)

Let us suppose that our upper limit for launching structural elements to LEO is Proton's 20t and for fuel and supplies is Falcon 9R - 13 tonnes (say, we can use 10 while 3t are the delivery craft itself). All of the systems assembled in orbit have to be developed and fall into two categories: propulsion and mission systems.

Propulsion

A single type of autonomously docking booster must be used, with integrated engines, RCS, guidance, communication systems etc... Given the modular nature of the system, we will be using UDMH and N2O4 for fuel, to reduce compexity of the engines, cut down fuel boiloff and weight of the tanks. Assembly of such ship may take a while. Please correct me, but to transfer from LEO to LMO, including correction burns and capture, one needs some 6 km/s of delta-v.*

*snip*

Wikipedia has a nice (but approximate) delta-v chart for Earth-Moon-Mars missions. 6km/s looks about right to me from LEO to Mars orbit. I have trouble reading TMI as anything other than Trans-Munar Injection though.

Edited May 7, 2014 by KSK

[sgt_flyer]

One of the problems you'll have, is the increased weight of the various docking systems you'll need (plus, their complexity is going to add risks) they spend a lot of time on ISS checking the docking went well each time a spacecraft docks. (Especially if you need to use various electric and fuel connections across modules - each single one of these connections needs to work)

They spent a lot of time working around the soyuz's and ATV automatic docking systems. Everything else is still docked by canadarm.

Imagine one of the modules rams and damages the docking system of another module because one of it's rcs thrusters failed (they don't have magic magnetic docking ports )

So, if it's possible to minimize the required amount of dockings, you'll minimize the risks and the weights of the systems. Afterwards, from decreased weights, tsiolkovsky is your friend

[Nibb31]

A moon mission could probably be done with two or three launches. One for the crew on Orion, one for the lander, and one for the EDS, which could be an ACES stage (the successor to Centaur that ULA has been proposing).

The biggest problem with multiple launch architectures is the loitering period between the launches. Cryo propellant boils off pretty rapidly, which means that you would need to launch your crew and your EDS within a couple of days of each other. If either of those launches is scrubbed due to weather or anything else, you risk losing the whole mission.

This is why a multiple launch architecture pretty much requires an orbital propellant depot. The depot would combine active and passive boiloff mitigation (sun shades and solar-powered cryo equipment) and would be replenished with tankers (there is a proposal for an ACES-derived tanker). It gives you a place to store propellant for several missions, to assemble your vehicle, and can be run as a commercial service.