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Comment by paul | Hacker News Reader

Apparently the Saturn V could lift 119 metric tons to LEO.

The Falcon XX is planned to have a 140 metric ton to LEO capacity, but that comes later, for when we need to ship cargo to Mars colony without requiring a space station stop.

http://news.discovery.com/space/will-a-commercial-flight-be-...

Unless you extract fuel from the environment on your stop, it's a very bad idea to make a stop when you are shipping cargo to space. Any change in trajectory spends fuel. If you absolutely have to send the vehicle in pieces, you'd better send them to the lowest energy orbit, assemble them there and blast off. The ISS is not on a particularly useful orbit for this and the only reason I imagine to stop by would be to use the extra helping hands of the resident crew to do the required assembly.

And shipping cargo to Mars doesn't need to be very expensive if you are patient - you send the cargo towards a low-perihelion trajectory and deploy a solar sail closest to the Sun. It may take a good couple years for the shipment to get to Mars, but the delta-V on the way up will be free. If you send the shipments well ahead of the landing crews, they'll have lots of toys when they arrive.

But I agree with the SpaceX folks. Nuclear is the way to go if we are to even go back to the Moon.

> The ISS is not on a particularly useful orbit for this and the only reason I imagine to stop by would be to use the extra helping hands of the resident crew to do the required assembly.

That, and the living quarters. If it's going to take a couple months to put stuff together and test, you don't want to be living out of an Apollo-sized capsule.

I didn't mean to suggest the ISS in any way. I am talking about the various plans such as von Braun's Das Marsprojekt, where you assemble a fleet of (for example) 3720 ton Mars ships in orbit: http://www.thelivingmoon.com/41pegasus/01archives/Von_Braun_...

It's not possible to launch a 3720 ton ship to Mars from the surface in one shot, it has to be assembled in space from parts and fuel shipped up in multiple launches.

Von Braun's plan, while spectacular, was never particularly feasible - it's more like colonizing Mars on the first trip than anything else. You don't need to send your crew in a 3000+ ton spacecraft towards Mars - you can send the crew on a smaller craft and send habitats, vehicles, supplies and all other stuff in advance in low-energy orbits (because food is less sensitive to radiation than astronauts). Von Braun's plan did not rely on automation (we can land a robot on Mars) and thus required every supply ship to be manned.

Yeah I'm aware of that. Above I pointed out that the XX was possibly coming and would have Saturn V level payload capability. The Saturn V is a giant rocket and needed to be that big to ship a bunch of stuff in one launch in order to beat the Russians rather than longer term plans involving using smaller rockets with smaller payloads and assembling things in orbit. Right now there is less point to going to the moon again rather than Mars but there is still the issue of assemble a big payload in orbit from small parts sent in modest ships or send a medium payload in one big giant freaking rocket. The Mars rovers and such were very tiny lightweight payloads compared to sending a human contingent to Mars, and even with the XX's payload, it is still barely enough to send a Mars crew and ship. So the issue remains. I only mentioned "without a space station stop" because I thought that people were going to otherwise jump on me with commentary about "yes but what about a space station stop then you can have smaller rockets". By mentioning "without" I had hoped to avoid needed to have that debate. I was not expecting to have the opposite debate and sorely wish I had said nothing at all and kept the link to the XX to myself now.

But now that we are having to have this talk, personally I think multiple ships assembled are still the way to go. A one-shot XX launch means not enough weight for proper radiation shielding, and enough food and spare parts to make it all the way there is a problem, and enough space to prevent the astronauts from killing each other is also an issue. We still have to have enough fuel to get there and land even if there is a bunch of fuel on site waiting in pods both in orbit and on the surface. The Dragon capsule is not really big enough to prevent mission failure from mass homicide en route, something considerable larger, and larger than the XX can lift in one go with fuel and food and water is needed to avoid this.

The space assembly step doesn't have to be something done in a giant station over a period of months. It can be send 4 modules up one after another, dock them together and go. We assembled two space ships together en route to Luna using this method on the Apollo mission. Adding a few more modules isn't a big deal, if we could assemble (not build from scratch) stuff in space 40 years ago, we can do it again now.

At $1.11 billion per launch, though. SpaceX is promising $80-$125 million for half the payload.

Yeah, SpaceX is super-cool. I was just curious how it compared with the most powerful rocket ever built.

I'm actually surprised things haven't gotten cheaper by more than a factor of 5 in half a century. (If anyone's wondering, $1.11 Billion is in 2011 dollars.) Does anyone know what the primary costs are? People, construction, raw materials, etc.?

I've heard it's people to make sure nothing goes wrong.

Fixed costs are usually the biggies, especially R&D and the infrastructure for supporting production.

Probably the biggest impediment to lowering launch prices over that time period was the existence of the Shuttle. It was sold with promises of capabilities (especially in terms of flight rate) that it would never have, and that disrupted a lot of other launch vehicle development at the time. Worse yet, it kept billions per year of NASA funds locked up maintaining jobs for the standing army of Shuttle engineers instead of being spent on improving launch systems.

One interesting thing I read Elon Musk saying the other day is that it's definitely not fuel -- the cost of fuelling a Falcon 9 is actually only about the same as the cost of fuelling a Boeing 747.

The problem is that the cost of building a Falcon 9 is still similar to the cost of building a 747, and you throw it away after one flight. So if you could recover and re-use the booster rocket then you'd be looking at a serious cost reduction.

> So if you could recover and re-use the booster rocket then you'd be looking at a serious cost reduction.

This was the logic behind the space shuttle. But unfortunately, they have to survive to high stresses that inspecting and repairing them between launches costs more than building a simpler disposable launch vehicles.

I honestly believe that as long as we will be using rockets, the best cost savings will not come from reuse, but from increasing the launch volumes to the point where launch vehicles stop being hand-built boutique items and start being mass-produced commodities.

This announcement gives me hope that this might happen during my lifetime.

The Shuttle is an excellent example of how an initially good idea (reusable launch vehicles) can become twisted and perverted by excessive compromises and congressional meddling. The Shuttle as it was built was actually a step backward from previous generations. Not only was it not properly reusable (it was at best refurbishable and partially reusable), it's unusual characteristics caused it to require a huge standing army of engineers to keep the program going, regardless of flight rate. As the true limits to the flight-rate of the Shuttle came to light it became obvious that no matter what the Shuttle system was capable of it wasn't capable of lowering launch costs over conventional expendable boosters.

It's a good case study in the downfalls of a waterfall type process and of committing too early to a system before it's true character is known.

I'm not sure that economies of scale can get you that far when you're talking something as complicated as a rocket. How many jet engines does Rolls Royce make every year? Rolls-Royce and GE make many hundreds (thousands?) of jet engines per year, but they still cost a crapload of money each.

You might be right, maybe fully-recoverable rockets aren't possible. On the other hand, being personally unqualified to judge, if I've got some random piscinymous internet commenter telling me that it's not possible on one hand, and Elon Musk telling me that it is possible on the other, I'm more inclined to believe the dude who owns a rocket company.

Hm, if fuel is so cheap then why not bring enough fuel with you to decelerate before de-orbiting? Then you don't have to worry about reentry heat.

Because if you want to take fuel with you, that's a lot of extra mass you have to lift. Which requires bigger engines and even more fuel.

53 metric tons worth of fuel?

The fuel requirements to decelerate are much lower than the requirements to reach orbit, for multiple reasons. You aren't fighting against gravity, your weight is greatly reduced (having burnt the fuel to get to orbit), and you also don't need to fully decelerate, only decelerate sufficiently to avoid burn-up upon reentry.

The original comment said that fuel was very cheap, and the primary expense was constructing the launch vehicle. Suppose it required five times as much fuel to be able to launch a rocket with sufficient additional fuel to be able to decelerate out of orbit. Wouldn't this still be much more economical if it meant the ability to easily reuse the launch vehicle after reentry?

Aside from what's already been mentioned, no real competition. You had NASA or nothing for decades.

I'm actually surprised things haven't gotten cheaper by more than a factor of 5 in half a century.

We're used to electronics getting cheaper as we find ways to make smaller and faster chips. We get change driven by Moore's law.

Getting to orbit is governed by simple lifting against gravity, and that hasn't changed at all. ( It's still 9.8 m/s^2 ) A Falcon rocket looks a lot like a Saturn rocket, so desipite a lot of ideas, a radically different and better design hasn't been commericialised yet.

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