Flexible architecture paths for human spaceflight


SA 2010 Soccermaniac
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Jun 22, 2008
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Or: why NASA does not need systems like the MPCV or SLS and how human spaceflight can be achieved in an optimal manner instead of being turned into problematic and suboptimal politically motivated and money-draining programs.

This is an example of a lunar mission with SpaceX hardware. It is not intended to be a SpaceX lunar mission nor is it intended to solely use SpaceX hardware. It is, however, based upon the SpaceX Falcon 9 and Falcon Heavy rockets, and Dragon spacecraft.

Falcon Heavy is advertised as being capable of lifting up to 53 metric tons to a 200x200km, 28.5 degree orbit. This would make it the heaviest US launch vehicle since the Shuttle, the first Super Heavy Lift launch vehicle since the Soviet Energia, and the first US SHLLV since the Saturn V (or more accurately, since the Saturn V 2 used to launch Skylab).

However, projects like Mir and the International Space Station have demonstrated that super-heavy launch vehicles are not required to place large structures in orbit. The ISS suffered from delays and high costs, but this was only because the main construction vehicle was the Space Shuttle, which was in fact a suboptimal launch vehicle for the task.

In addition, because of their large size, Super Heavy launch vehicles would only fly a few times per year at best. Low flight rates and low production rates would drive up costs. A smaller vehicle however has a higher flight-rate, which thus drives costs down, in a similar manner to how a larger production run of anything will drive cost per item down.

In addition, SpaceX advertises far lower launch costs than for competing vehicles; $54-60 million for Falcon 9, and $80-125 million for Falcon Heavy. By comparison, the cost for the 10 300 kilogram capable Delta IV Medium + has been estimated at $100 million, and the cost for the 20 500 kilogram capable Delta IV Heavy has been estimated at $140 million.

As always, extraordinary claims must be treated with skepticism, but SpaceX already has deals with NASA and private companies at these prices.

While Falcon Heavy would not fly as often as a Delta IV Heavy-sized launch vehicle, it would fly more often than a very large vehicle such as the Saturn V, the cancelled Ares V rocket, or the currently proposed Space Launch System. In addition, by using common components repeatedly, it would still increase production runs.

Larger payloads also simplify orbital construction, and while this is likely not absolutely required, it could make development and testing easier.

So, we can imagine in the capability of three 53 ton capable vehicles:

- A moon lander, along with a specially designed service module with docking ports at both ends, a pressurised transfer tunnel, and propellant tanks and possibly engines.

- A large propellant tank filled with liquid hydrogen and liquid oxygen, with docking/attachment systems to link up with other items, and fuel cross-feed piping.

- A similar propellant tank, but with a high-performance engine as well. The J-2X engine intended for the Constellation program would be ideal for this task.

We can also fly a crew to orbit in Dragon using the Falcon 9 rocket. A few modifications would be needed on the Dragon capsule, however its heatshield is already capable of withstanding reentry from the Moon.

First, the Falcon Heavy rockets would launch in succession. The lander might be first; it can stay in space the longest because it could use storable hypergolic propellants. In addition since it has its own manuvering system, it can act as a "space tug" to connect the parts of the Departure Stage. Mounted atop the lander, already connected to its docking port, would be the service module. This service module is vital to the mission. The Dragon capsule does not have to launch with it, nor does it have to physically accomodate it.

The propellant tanks would then launch. They would not need their own manuvering systems since the lander would perform rendezvous and docking to connect the first tank to it, and then to connect the second tank to the first. The tanks can be mass-optimised using the latest technology, and can be insulated against solar radiation to decrease cryogenic propellant boiloff. Electrical power to the tanks can be provided by solar panels on the lunar lander, which will be used later in the mission to support the crew during their mission on the lunar surface.

The Dragon arrives within a certain timeframe, and performs rendesvous with the stack using its own manuvering engines, just as it would do to dock with the ISS. It would dock, using an iLIDS port, to the Service Module.

The stack would then perform Translunar Injection (TLI) and break out of LEO. After the propellants in the tanks have been depleted, the tanks are discarded, and can be manuvered into a solar orbit, or deliberately crashed into the Moon to gather seismic data.

One the stack has arrived at the Moon, the lander would perform Lunar Orbit Injection with its main engines. The crew, having used the lander as their main living space for the transit, would undock from the Dragon and Service Module and begin their descent to the lunar surface.

After their stay on the lunar surface, the crew would then fly back into orbit in the lander using its redundant engines. Instead of using a two-stage system similar to the Apollo LM, the lander could simply leave empty propellant tanks and landing legs on the surface (which would also act as a launch pad) and ascend using the same engines used for descent.

These engines could be derivatives of the AJ10 engine. Derivatives of the AJ-10 were used in the Apollo CSM, and these engines have been flying for decades in the Delta-K upper stage of the Delta II rocket. The OMS engines on the Space Shuttle were AJ-10 derivatives (AJ10-190 or OME) and exhibited exceptional reliability. For landing however, the engines would have to be throttled through quite a wide range- I am not sure if this is possible.

Once ascent was complete, the crew would re-dock with the unmanned Dragon (either using their own propellant, or by having the Dragon rendezvous with them automatically, using its own thrusters). The lander can either be seperated and left to crash into the lunar surface with engines on the service module performing the TEI burn, or propellants in the service module can be fed to the lander (this is not unknown technology, as it has been a staple on Russian space stations for decades) which could then use its own engines for the TEI burn (this would be the fourth firing of the engines on the lander).

One of the advantages to Lunar Orbit Rendezvous (apart from having to carry a heavy capsule down to the lunar surface and the back up again) is the elimination of the requirement to land the TEI propellant on the surface, when it can instead stay in orbit.

After TEI, the stack would coast back to Earth. By keeping the lander attached, the crew has a very large volume within which to live in during the return trip.

The Dragon would then undock from the lander and service module, discard its 'trunk', reenter Earth's atmosphere, and return to Earth. The lander and service module could be destructively reentered into the Earth's atmosphere.

By using this mission architecture, all the criticisms of Dragon over the MPCV are answered. MPCV is simply not needed. Here Dragon is nothing more than a launch and return vehicle, that is taken along for the ride. The lander is the main habitation unit for the astronauts, and can be shielded against radiation (which is important both in transit and while being landed on the Moon). The lander would obviously have many redundant systems and would be heavily ruggedised. There would be a lessened chance of catastrophic failure, and more abort options than in Apollo (for example, no chance of engine failure during lunar ascent or TEI).

Dragon has been developed up to now, for a fraction of the cost of the MPCV. It is clear that the development methods of the MPCV are highly inefficient in terms of economics and its high cost is clearly primarily because of political reasons.

The Space Launch System would only reach its full incarnation in over 20 years. Falcon Heavy could launch in just three or four. Falcon Heavy would also be far cheaper and far more justifiable- it could be used to launch some commercial and USAF payloads, for example. It is clear that SLS is not only unecessary, but suboptimal as well. Since there is no more STS, commonality with it does not make much sense. Since SLS would first launch in 2017 (?), it is likely that many people in the much spoken of Shuttle workforce would have retired or moved on to other things, and thus the oft cited "Keep the workforce" idiom actually destroys itself. I don't see how you can keep thousands of people employed for 6 years doing... nothing.

In addition, there is the "reuse the hardware" debate. Again since the Shuttle is no longer flying, there is no real impetus to keep hardware commonality. Indeed much of it would have to be changed for SLS anyway. And of course, if there are cheaper ways of doing things (and Falcon Heavy looks like a cheaper way), why is there any reason to reuse the Shuttle infrastructure? You could almost call it... ungainly.

Nobody cries that NASA still doesn't keep Saturn V infrastructure in working condition after some 40 years of inactivity. And the workforce can move on- they will need to move on, because STS has stopped flying. They can't just hang waiting for a job that might come in five or six years. These people will retire or go elsewhere. They will go into the aerospace industry, where they will work on other launch vehicles- such as Atlas, Delta, or even Falcon. They will work on satellites, or aircraft, or high-end military or civillian applications.

Good luck rehiring what's left of that workforce in 2017.

In addition, SLS has been scheduled to launch at a very low rate- only one flight per year- which will incur very large costs. Without a viable mission architecture and billions of dollars in expenditure, the MPCV and SLS make no sense and there are clearly no logical reasons to continue funding them. They should be cancelled. You can try to defend the MPCV, I suppose. But SLS is just absolutely unexcusable.

That said, pretty much everything I have described here would have to be developed, built, and tested first. But it can use a lot of existing hardware. And if it can be done in the way SpaceX has done Dragon and Falcon up to now- and I am not saying done by SpaceX itself, then it could be ready in a shockingly short timeframe and for a shockingly low cost. The first BEO missions could take place before 2020.

I think it is very clear that political reasons drive costs up pretty high in spaceflight. If things can be cost-optimised, and not pork-optimised, then things could be done far more efficiently. Obviously it would be pretty difficult to combat bad politics, but I think that if enough Americans shout loud enough, it could be done.

EDIT: Falcon graphic derived from here.
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Clueless developer
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Sep 12, 2010
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What are current projections of launch campaign duration for F9H? I recall it was touted as part of Responsive space infrastructure or sth. like that.