Rakaydos

Why is everyone trying to make the landing engine run on cryogenic fuel? You want the landing engine to be reliable after a week out and back on GTO, and cryo fuels just dont work that way. Separate, storable fuel in an optional module you can remove if you want to fly expendable.

They've already designed the Superdraco. Part commonality saves cost. If it ends up weighing an extra half ton for separate tanks, that just comes out of the reuse mass budget. The Falcon Heavy, especially, can afford the cost.

you may notice that Raptor isnt flying yet. neither is BE4, or the SLS engines. Designing a new engine is not a lesser evil compared to adding more tanks. especially if the extra tanks add flexibility by being removable if you arnt landing on a mission.

The merlin is too powerful, and the Kestrel isnt in production. Also a GTO return may involve a longer wait time than LOX can handle. The Superdraco, on the other hand, is just the right power and already in production. SpaceX has more to worry about than a kerbal player.

The dry mass of the upper stage, according to wikipedia, is about 4000 kilos. (4 tons) Thrust of a single SuperDraco, same source, is 71 kilonewtons. 4 of them are enough to land a 6.4 ton (dry) Dragon 2 (though it carries 8 superdracos for redundancy) with 1.4 tons of hypergolic fuel, enough for 25 seconds of operation. Wolfram Alpha calculates 4 superdracos would land a drymass dragon 2 at just over 4 g (clearly, it's gong to be a bit less because there's still fuel it's burning, but that's the ballpark for landing speed) Lets assume a worst case, where stripping the Dragon's pressure vessel and all the draco maneuver thrusters saves no mass at all, and everything else is exactly the same as the dragon 2. That gives a 7.8 ton "landing module" to take out of Falcon 9 FT's 10.8 ton reusable LEO mass, or 7.8 tons from Falcon heavy's 63.8 tons to LEO or 26.7 tons GTO. Assuming these worst case numbers, an off the shelf (read as- Cheap) recovery system is marginally useful for Falcon 9 FT (though Block 5 has better LEO numbers, I didnt see them on wikipedia), but amazing on Falcon Heavy.

Current speculation on NSF is a nose landing, to protect the (non retracting) vac bell from supersonic winds. Basically fitting a "landing module" secondary payload between the second stage and the payload adapter. The (entirely optional) landing module has the primary heat shield, superdraco landing thrusters, and landing legs, bringing the center of gravity foreward of the center of pressure. Any mission small enough can get a rebate for allowing 2nd stage recovery. those that are too heavy, go with the stock falcon9/heavy

SLS is currently demonstrating one of the problems with that approach- namely that if your rocket construction rate is slower than your workforce turnover... every rocket is your first rocket, and you have to go through the learning process and dumb mistakes all over agai each time.

I'd actually like to see something like the ARCA linear aerospike smallsat launcher design, but as a 1.5 stage with disposable solids.

"As god and Heinlen intended."

What about rail-launched scramjets? We can build "cars" that break the sound barrier- how hard would it be to build a track designed to bring a large scramjet (and it's non-airbreathing upperstange) to operational speed at ground level?

A single big satelite can only be in one place at a time. Lower altitudes have better latency, and more managable signal strengths, but limit individual satelite "uptime" where the ground can see the satelite. The answer is more satelites.

It's more a problem at, ironically, the higher altitudes. At low altitudes the dangerous schrapnel that sustanes a kessler cascade has too much drag to stay in orbit, and falls back to earth. And the satelites arnt actually that close together. Imagine if there were only 40,000 cars in the entire world, roughly equally far apart.

There's been a model floating around for years that says that the solar system formed with an extra planet between jupiter and saturn, and that the orbits were unstable and kicked this extra planet out of the solar system. This model predicts the planets current orbits far better than a straight 8 planet simulation, which give something like a 90% chance of kicking saturn out of the solar system. One of the factors being protoplanetary disk drag, pushing towards circularizing orbits, I wonder if planet 9 could be that ejected (recaptured?) gas giant.

What do you do if the LAS engines blow up?' I seem to recall some famus person reportedly saying "you can put all your eggs in one basket, as long as you make DAMN sure you protect that basket." That is the ITS's escape strat- a reliable second stage that doesnt blow up.

I wouldnt say there's no way to solve that problem, but you are right in that an alternate heat source is something that needs to be engineered around.

Actually, i think a scaled down ITS might work, but not with Raptors or Merlins. The ITS also has planned a set of methane-gas thrusters it uses for RCS- we have no specs for this, it may not even be designed yet, but as a smaller thruster using meth/ox, it could run the same combination of sealevel/orbital nozzles that the larger ITS would run.

The problem with that, is that the shuttle's unique cabability is it's hybrid nature- bringing crew and cargo up in the same load to do things together. But with rendevous perfected over the ISS years, a single hybrid vehical can be out performed with a pair of dedicated vehicals that can match the individual performance. If Falcon Heavy can lift any thing that fit in the shuttle bay, and a crew dragon can meet it to do space-work, then the shuttle doesnt have a unique selling point anymore.

The upcoming circomlunar mission is 2 people for a week. I think it's unlikely to be consumable-limited (more like 2 adventurers paying through the nose for a private flight) but if we DO take that as a limit, then you might need to launch additional resupply dragons to match the shuttle's endurance. And at the Falcon's price per Kg, STILL be cheaper than the shuttle.

So by next year, what could the shuttle have done that couldnt be done by a fleet of 2 crew dragons and a Falcon Heavy, for the cost of 3 upperstages and possibly a center core? The shuttle sucked at space stations too. Skylab was a single module, bigger than anything the shuttle could deliver, for cheaper than any given shuttle flight. They ran out of Saturn 5s before they could try assembling anything bigger though. THAT's not an issue wiith Falcon.

How about cost per kg of astronaut?

Not everest. Chimborazo Factoring in equatorial bulge, it's farther from earths center than everest, even though everest is technically taller. And it IS in the equator, with all the DV bonuses that gives.

At least for any varient that actually launches crew. A hypothetical lunar lander varient of Dragon 2 (White dragon) that goes up unmanned for a 1-way landing on the moon has less need for a launch abort system.

Yea, at that point you might as well make it the Falcon/Raptor Upperstage people have been speculating about since the AF contract was bandied about.

Presumably he means "Not using russian rocket engines on their american rockets"

Falcon heavy is finally, officially, going to launch in FIVE months!