SpaceX Tests Its Raptor Engine For Future Mars Flights (techcrunch.com)

Thelasko writes: Elon Musk is preparing to unveil his plans to colonize Mars at the 67th annual International Astronautical Congress tomorrow. As a tease to his lecture, he has released some details about the Raptor engine on Twitter, including pictures. Mr. Musk states that, "Production Raptor coal is specific impulse of 382 seconds and thrust of 3 MN (~310 metric tons) at 300 bar." He goes on to note that the specific impulse spec is at Mars ambient pressure. The Raptor interplanetary engine is designed for use with Space X's Mars Colonial Transporter craft. Musk notes that the "chamber pressure runs three times what's present in the Merlin engine currently used to power Falcon 9," according to TechCrunch. "Merlin has specific impulse of 282 seconds (311 seconds in the vacuum of space), and a relatively paltry 654 kilonewton (0.6 MN) at sea level, or 716 kN (0.7 MN) in a vacuum. You can view a picture of the "Mach diamonds" here, which are visible in the engine's exhaust.

Comments

Human missions = funding

[saibot834]

Before someone comments that we don't need humans on Mars if robots can do the same cheaper: that's beside the point. I mean, robots are no where near performing on the same level as humans when it comes to ingenuity and ability to come up with and implement ad hoc fixes to problems that no one could even imagine before launch of the mission. But putting that question aside, the problem with robotic missions is that they will never get the same sort of funding as human missions. A human mission automatically has to have a certain size, e.g. has to develop capabilities to land payloads in the ballpark of 10 tons or more on Mars. Once we have this capability, we can easily send lots of robotic and scientific payload along with humans -- it amounts to simply using the same payload delivery system that we are developing for humans anyway.

On the other side, if there is no ambition to fly humans to Mars, then no one will develop these capabilities. There is simply no funding for a system that delivers 10 tons of cargo onto the surface of Mars, unless it can also deliver humans, and bring them back safely. So we cannot send big robotic missions to Mars.

Human missions generate lots of excitement, lots of excitement leads to lots of funding. Robotic missions can never be on par with human missions in terms of how much excitement, and thus funding they can raise.

Re:Human missions = funding

[Rei]

How much excitement did that ever generate? The mars rovers landed in 2004 and NASA's budget (in constant dollars) has only gone down since.

Yes, nothing since to Mars since 2004! Excepting of course MRO, Curiosity, MAVEN, InSight, and the upcoming Mars 2020 Rover. Some of those being much more expensive than the MERs.

. There's no reason for the government to throw money at Musk that they wouldn't throw at NASA

Nor is there any expectation nor plan of such. SpaceX and NASA have a no-cost arrangement, where NASA provides free consultancy, access to the DSN, and sterilization assistance, while SpaceX will provide any data they collect.

and Musk certainly can't afford to do this on his own.

The opinions of experts interviewed on the subject are almost in universal disagreement with you on this, at least concerning Red Dragon. SpaceX already shoots things up to GEO; the energy required to get to a Mars Transfer Orbit is not much more. SpaceX already decelerates capsules with an aeroshell facing an entry load similar to that needed for aerocapture at Mars. And Dragon is already designed for automated vertical powered landing. Red Dragon is not some super-ambitious mission, it is quite doable without any radical advancements.

Actual colonization, boots on the ground, is of course a much bigger challenge. This will be many years in development. But SpaceX was specifically founded for this purpose. Just like how Tesla was founded when Musk found that he couldn't pay anyone to build him a clone of the tzero, SpaceX was founded when Musk found that nobody could launch him payloads to Mars for an affordable price. Ultimately getting humans to Mars is a founding principle of SpaceX. All of its investors are aware of this. SpaceX will continue to work towards this so long as they are an operating entity. And unlike NASA, they're not burdened with massive mandated costs and constantly changing mandated missions, both of which have utterly crippled it over the past decades.

Re:Haha no.

[Rei]

Indeed. Part of the reason that satellites are so expensive is how light you have to make everything; there's a huge amount of engineering that has to be done in order to achieve mass goals, as well as make use of the most expensive materials on the planet. An example is the use of things like top-end Spectrolab multi-junction solar cells, which get the highest efficiencies, but since they're basically lab-scale production hardware they cost two orders of magnitude more than what slightly less efficient panels on Earth cost (about $400/W).

Beyond the simple cost effect on engineering, there's the size effect. Look at James Webb and the massive expense they had to try to make it "origami" itself to fit into smaller launch vehicles. Or how many parts ISS had to be built out of in space, dramatically escalating both ground engineering / production costs and in-space assembly costs (the latter costing nearly $10m per man-day). There are serious expenses to trying to compensate for a lack of space or payload capacity when you really need it.

Then there's the size of the market. As launch costs have been dropping, the number of companies looking to launch payloads has skyrocketed. The skyrocketing launch demand has been reducing average payload development costs, as designs get more reuse. Both of these trends will continue as costs continue to decline. Meanwhile, new markets will continue to open up. Space tourism has always been hindered by the absurdly high launch costs, limiting it to only the wealthiest individuals. While it will remain a "small" market for the forseeable future, it can expand by orders of magnitude with reduced launch costs. Which again makes more demand..

Lastly, there's economies of scale. It's generally recognized in the rocketry world that - at least up to a point - larger rockets get a better cost per kilogram than smaller rockets. So wherein you can launch a lot at once - multi-satellite launches, large geo launches, large interplanetary probes, fuel depots for tugs/boost stages, shielding mass for manned missions, etc - you tend to save a lot of money by going big rather than using multiple smaller launches. The caveat is that just simply going big is no guarantee of a price reduction. Just like you can make an absurdly-expensive smaller craft, you can also make an absurdly expensive large craft. And even a "moderately priced" large craft isn't generally a "win" - if you can sell payload space for $5k/kg on a 10 tonne payload rocket and for the same price per kilogram on a 100 tonne payload, the vast majority of customers will choose the former. But if you're a company like SpaceX that's been delivering cost reductions on the small scale, and you can carry it over to the large scale, it gives you the potential to take the cost reductions even further.

If you can pull it off.