SpaceX Fires Mars-Bound Raptor Engine (extremetech.com)

Elon Musk took to Twitter Sunday evening to announce the "first firing of Starship Raptor flight engine." While SpaceX has fired individual components before and experimented with various designs, this is the first time the now-completed design has been assembled and fired in its intended spaceflight configuration. ExtremeTech reports: Raptor has gone through a number of design changes -- originally, SpaceX planned to mount it to the ITS launch vehicle back in 2016 (powered by 42 Raptor engines), before changing gears and unveiling its BFR rocket concept (officially known as "Super Heavy" for the first stage, and Starship for the second). The Super Heavy mounts 31 Raptor engines, while the Starship has seven. The engine has been designed with a priority on lowering overall wear and tear and removing failure points that could limit its reusability or increase long-term operating costs. Unlike SpaceX's Merlin engine, which runs on a mixture of RP-1 and LOX, the Raptor engine is fueled by cryogenic liquid methane and LOX. The Raptor uses subcooled methane (subcooling refers to keeping the temperature of the liquid well below its boiling point). Subcooling the methane allows SpaceX to increase the amount of propellant stored in the rocket. It increases specific impulse and reduces cavitation.

The actual test burn only goes on for a few seconds, but yields tremendously valuable information about the actual performance of the rocket and its ability to ignite in a controlled fashion. The green glow in the exhaust near the end of the firing indicates the copper liner in the engine chamber burned by accident. While this should not have happened, it's precisely to find these pain points that engineers conduct test firings in the first place. There is no substitute for this kind of test-firing and, as Ars Technica notes, "any 'first' test firing of a new, full-scale rocket engine that doesn't end in an uncontrolled explosion is a good thing." Ars also states that this specific engine may be deployed for "hopper" flights this year when SpaceX attempts to fly the Starship roughly 5km high, then land it again.

Comments

Moon-Bound at Least

[mentil]

The new plan is to send the BFR on trips to the moon, early on. Later, they'll send it to Mars; this may only happen after they build their next-gen Raptor engines.
There is some sense to this. If they can cram 100 space tourists into Starship, then send it to orbit the Moon for a day (7 day space vacation), they could make LOTS of money. $10 million per ticket x 100 seats = $1beeelion per launch (prior launch of fuel into orbit required, however), and they'd only pay the cost of fuel, probably less than $1million. After a few years, once they get more super heavies/starships built, they could bring the price down to $1 million for a ticket, still make massive profits, and it'd hugely increase the number of people who would pay to go to the moon. Only a few dedicated people would be willing to spend a few years of their life to go to Mars, wait a while for a launch window to arrive, then come back. Of course, they could also offer moon landings, maybe build a moon hotel. Maybe put some Starlink satellites in lunar orbit for lunar internet connectivity, although the 1,250ms latency would be killer.

Internet access on Mars would suck (due to the half-hour latency). Bet there's a business opportunity for an orbiting data center that'd host mirrors of various sites.

Re:Moon-Bound at Least

[Kjella]

Nobody is going to the moon or Mars on a tourist trip in your lifetime, try to stop being an idiot before you die.

You underestimate how much money some people have.
Jeff Bezos: Net worth $142 billion (before divorce)
Apollo program: $125 billion in today's dollars

Jeff Bezos could single-handedly fund the Apollo program. In fact, that should now be the new unit when describing how just how rich they are. Is there a market for $10 million joyrides to the moon? Well we know 7 tourists went to the ISS on the Soyuz when the Russians were selling seats for $20-40 million and that was a very limited opportunity. The moon sounds grander and cheaper.

Of course to normal people spending millions of dollars on this is crazy talk. But I remember passing by a TV show that was selling crazy stuff to the super rich, the store had made a gold plated $200k bicycle that was actually just intended for show. A Sheik's buyer came in, thought that was cool and that was it. That's $0.2 million for a bicycle, that sounds like the type of guy who could hire an entire flight just to throw a destination wedding.

Basically, don't underestimate what can happen when billionaire wants something.

Re:Moon-Bound at Least

[Kjella]

There is some sense to this. If they can cram 100 space tourists into Starship, then send it to orbit the Moon for a day (7 day space vacation), they could make LOTS of money.

The budget version would be a free return trajectory where you're never in orbit, you do one flyby around the moon at a fairly long distance because you have so high relative velocity and that's it. If you first do lunar orbit, that'd probably be the two week option where you spend a week orbiting the Moon. Then neat thing is that with no atmosphere you can get real close, the LM was normally at a 110 km circular orbit but went down to 15 km for Descent Orbit Insertion, like you could get an airplane-like closeup view. That'd take at least one more tanker mission though, maybe more.

P.S. Even with some degree of re-usability it's silly to assume just the cost of fuel. There will be wear and tear parts, there will be parts that must be deprecated over 10 or 100 flights, there will be launch range/mission control operation costs and they'll never come free. Fuel is just a lower bound on how cheap it could get.