RCgothic

The more I think about this the more I just don't understand why this is a good idea. The full scale 100m diameter centrifuge will have an instantaneous acceleration of 10,000Gs when launching at 8000kph (2222m/s). If they simply built a 100m linear accelerator the acceleration drops to 2500Gs. Plus it's a lot easier to imagine a 500m (500Gs) or 1km long (250Gs) linear accelerator than it is to imagine centrifuges at that scale. Ok, the instantaneous power requirements of a linear accelerator are a lot higher, but there are multiple ways that can be achieved. I'm suddenly reminded that Mount Chimborazo is within 1 degree of the equator and goes to an elevation of ~6200m. its prominence is ~4km and its slopes are ~30-40deg. So with a little tunnelling you could build an 8km linear accelerator up its flanks and the acceleration required would only be about 30Gs, which is actually getting towards survivable for humans. Plus as it would emerge roughly 6km above sea level the air pressure would be reduced to 50%, much better than launching from a centrifuge at Spaceport America.

(ノ｀Д´)ノ彡┻━┻ Good catch, thanks.

My mistake, this contract is for 6 pairs of boosters up to Artemis XIII and including development for BOLE boosters for Artemis IX+, but not actual production. So that's effectively $530m per pair of boosters. Add $396m for the RS25s. Ouch. ("But that includes development costs!" "Yes, and we include development costs when talking about the CRS, CCS and HLS contracts as well.")

AKA at least $350m per flight on SRBs basically in perpetuity.

Looks reasonable. Same as F9 and Superheavy basically.

A few more thoughts. So this is a Falcon 9 competitor. Neutron weighs 480t and can put 15t in LEO expendable or 8t RTLS. That's a payload mass fraction of 1/32 or 1/60th depending. Falcon 9 weighs 550t and can put 22.8t in LEO expendable or 11t RTLS. That's a payload mass fraction of 1/24 or 1/50. So F9's quite a bit better in terms of propellant to payload, despite Neutron's higher energy propellants and ultra-lightweight construction. That surprised me. I think I was expecting a little more. Methane's cheaper than RP1, so that's definitely a point in Neutron's favour. Expendable second stage - F9US is a significant proportion of an F9 flight. But it uses the same tooling as F9 1st stage. Neutron's ultra-lightweight upper stage doesn't really scream "low cost", and avionics won't be cheaper. Doesn't obviously share tooling with the 1st stage. Unclear how Neutron US would be cheaper TBH. Do we have any idea on cost, Archimedes Vs Merlin?

But dissimilar propellants and the thrust division doesn't work out well. 7MN on the 1st stage to ~1/40thMN (26kN) on the second stage doesn't seem right.

I like the tension upper stage and petal fairing idea. I do wonder how they get it to attach though. A few digs at SpaceX, but I consider that by disposing of the upper stage they're not really solving the same problem, so they didn't really land for me. Let's see that carbon fibre test again at cryo temperatures and then again during the heat of re-entry.

https://arstechnica.com/science/2021/12/planetary-scientists-are-starting-to-get-stirred-up-by-starships-potential/ Not sure why this isn't embedding. Hmmm.

Possible static fire tomorrow.

Bit of an explanation:

This made me lol

Cursed:

I meant it the other way round. (-_-;) SLS is way wider than Orion. It needs to be adapted down via ICPS, and EUS is needs adapting just as much. For Superheavy it wouldn't be much more.

SLS is already way wider than Orion and requires a ridiculous adaptor. Starship's only 50cm extra each side. And when we say "expendable starship", really, what we mean is take a stainless steel tube and stick a raptor on the back of it. Knocking together an expendable raptor upper stage would be ridiculously easy. "Starship" may never be deliberately expended, but it's not really not difficult to conceive a version with an upper stage for special payloads. 15m diameter payloads. Deep space missions. Things that require launch escape systems. Those sorts of things, even after they've got orbital refuelling down

They're really only good on a sustainer architecture. They're only *really* good on a reusable sustainer architecture.

Kerbiloid is being facetious, but if that's really a problem there's no reason they can't start it on the arm at an angle so that it's traveling nose forward on exposure to air.

I'm saying Two Stage To Surface And Back (TSTAB) isn't desirable for orbital shuttles where the mothership is exploring unknown planets. Despite SSTSAB having much lower payload than the two stage solution, it's preferable to get all the pieces of your infrastructure back. They may not be replaceable.

At Mach 6 in 33ms the projectile will have travelled nearly 70m, which is many body-lengths. It will stabilise.

Yes, the projectile will have an initial rotation when released, but it's aerodynamically stable and the aerodynamic forces are extreme. It won't get far off-axis before getting corrected.

One thing I've recalled about TSTO though - it only works if your industrial base and recovery infrastructure are on planet. If you're coming down from orbit and then need to return to orbit without servicing, SSTO becomes extremely desirable. It's not really workable with TSTO because you have to leave something behind and that makes it not fully reusable. Landing sites for a nearly-fully laden spaceplane on unprepared surfaces would be pretty limited though. A conventional VTVL SSTO would have a lot fewer difficulties.

Maybe a hypersonic version of Virgin Orbit's launcher might make sense for launching an upper stage. However. Hypersonic air breathing is an extremely exotic regime. I suspect any hypersonic air breathing engine and airframe is always going to be much more stressed than a conventional rocket which does most of its work outside the atmosphere. So what does a spaceplane first stage get you as opposed to a conventional first stage? You trade additional wear and stress, a dual axis loading of the payload as gravity's not in the same direction as thrust, more expensive engines, higher dry mass, and a lower takeoff and landing gross weight limit, all of that for reduced fuel consumption and lower required thrust. With cheap rocket propellant and a very reusable conventional TSTO I suspect the trade offs are not really going to be particularly worth it. With an extremely capable spaceplane launcher, if the drawbacks and wear become negligible, then perhaps it might be more worth it. Perhaps Earth isn't the right planet. Somewhere with a denser, higher atmosphere and lower gravity. Maybe somewhere like Titan might be ideal. Except that would be more fuel-breathing than oxidiser breathing.

Any SSTO will always be outperformed by a TSTO. Any fully reusable SSTO will always be outperformed by a fully reusable TSTO. The margins of a TSTO are just bigger, so it has to use fewer compromises, doesn't have to shave as many grams, and so it will just be more robust and carry larger payloads than an equivalent SSTO.