Someone asked me to sanitize some ancient comments on the blog today, and in the process of doing so, I perused some other posts from that era, and ran across this.
It wasn’t obvious at the time, but it was an historic post in this blog, because it led to all of my essays at The New Atlantis. I don’t know (or at least don’t remember) how Adam found out about it, but he contacted me to argue about/discuss the topic, and he ended up asking me for an essay, which resulted in this (not sure why it’s 404ing and I had to go the Wayback Machine, but I’ll tell the current editor about it).
I wonder if LH2 & LOX first stage rocket would ever work?
Well, I mean from Earth. I think they could work fine and perhaps, best, if launching from Mars or the Moon.
LH2 from Earth, no. Low density, requiring enormous tanks and difficult to handle, and ultimately not needed if you use liquid CH4. Out in HEO or CIS lunar orbits, maybe. But I’d argue you’d be better off with nuclear thermal and either just use the moon water as is (steam jets) or work on a reactor design that can dissociate H2 from O and then recombine them chemically to get both therm and chemical ISP assist, perhaps as a re-burner, like a jet afterburner. But if you have NTR maybe you’re getting all the ISP you need from cooling the nuclear reaction thus recombination/combustion, even though chemically the most efficient known, isn’t needed?
I think assisted launch is only way to get really cheap launch from Earth, break the less than $100 per kg to LEO {or Musk’s $60 per kg to LEO}. So with assisted launch the first stage of rocket could be H2 and LOX if launched fast enough.
And for suborbital the assisted launch vehicle doesn’t need to be boosted as fast as compared to
orbital or escape velocity.
So, for assisted launched suborbital vehicle, it’s first stage might be H2 & LOX.
So, I am still crazy enough to think Mothership and my pipelauncher would work. But my pipelauncher is most just a launchpad, a cheap launchpad used in the ocean. And I think launching from the ocean is required to get near $100 per kg to orbit.
I also think infrastructure in above atmosphere in LEO can be used to boost a suborbital trajectory to get into space, transforming the require of 10 km/sec delta-v velocity Earth, into 5 km/sec Earth, boosted at LEO, planet.
But that is pretty far into the future.
I also think low Earth launch cost depends on whether the Moon has mineable water or not AND NASA not being stuck on the Moon, but quickly starting Mars exploration {which at this point is entirely dependent on Starship}.
The other pathway, is suborbital travel. Both would be better. Though Space Power Satellites
is also possible, I tend to think SPS, follows, Lunar and Mars exploration. But either or all three may be separate and all at once.
The more I think about the thermodynamics of trying to build a recombinant NTR the more I realize this is upside down with no propulsive advantage. Obviously if you’re at dissociative temperatures to start with you now how to cool it to get it back to combustion and what you’ll get from that won’t make up for the energy you lost. Nope, keep the exhaust gas at high temperatures/pressures through your nozzle. Rocket 101.
…Assuming there *IS* abundant moon water to be had as propellant….
Wasn’t there a booster-formerly-known-as-Delta IV that had an LH2 & LOX first stage?
OK, OK, alright already, there were different versions of the thing, including the “single-stick” Medium version that had small strap-on solid-fuel rockets, but the Heavy using strap-on core stages was all cryogenic, at least for the first stage?
Not saying that the Delta IV was ever an economic proposition, but there was a moment in history when it was “a thing.”
I have a soft spot in my heart for the Delta-IV Heavy.
Not in my wallet mind you…
There’s also the Japanese H2 and H3 rockets with LH/LOX first stages. I recall reading that the H3 can use zero, two, or four strap-on solids depending on the payload. These rockets are outliers.
I’m strictly an amateur at this, but I think LH2/LOX is considered a bit too energetic for first stage – it makes more sense when the vehicle velocity is higher. For first stage I think you want mass flow more than velocity as such. Which is why the first stages we’ve seen tend to use heavier things like kerosene.
If the atmosphere’s resistance is a large enough factor then maybe for lifting off in thin/no atmosphere then hydrogen makes sense.
But then you also have to consider things like how hard it is to make/use the fuel at your point of liftoff. Shipping fuel from Earth makes your rocket enormously larger.
“Work” as in function? Sure. Been there, done that, got the T-shirt. NASA, the Euros and the Japanese are all still mucking about with hydrolox boosters. But David Spain accurately points out the intrinsic hydrolox tankage mass problem. And, at sea level, hydrolox gives away nearly all of its vacuum Isp advantage over other common props.
Hydrolox gives away its vacuum ISP advantage?
Not if you use a high enough chamber pressure (cough, SSME, cough).
The RS-25 produces only 80% of its vacuum Isp at sea level. Raptor produces 90% of its vacuum Isp at sea level.
Speaking of blasts from the past, an adjacent post to the one you linked has a link to Musk’s unveiling of “Falcon 5” not quite 20 years ago, and back when “falcon heavy” meant three Falcon 1s strapped together.
Who’da thunk that we’d ACTUALLY be watching multiple launches of a FH with nine times as many engines, RTLS, and reused boosters less than 20 years later?
Short time or long time? I think it shows how timelines for space based activities don’t conform very well to how humans usually conceive time. It is an interesting dichotomy between Musk’s daily drive and how long fruition takes.
On your first New Atlantis piece, it is remarkable how NASA has ignored basic economics for more than 50 years. I wonder where we would be now, if we had done something sane instead? It wasn’t even a path not taken. More excluding a sea of universally better options.
Like what they say about the public school system, if this had been imposed by a foreign power, we would consider it an act of war.
SpaceX wasn’t successful just from doing things differently with existing technology but because advancements made in other industries and an economy that allowed them attract funding. Imaginings of alternate pasts must take things like this into consideration and not just rely on creativity and wishful thinking.
In the end, it is a pointless, but perhaps enjoyable to some, exercise and that energy would be better spent on what could be done next month or next year.
SpaceX wasn’t successful just from doing things differently with existing technology but because advancements made in other industries and an economy that allowed them attract funding.
I believe we had enough of all that in 1975. One of Rand’s key observations (also echoed in previous works like A Rocket a Day Keeps the High Costs Away) was that over the past 50 years the economics of the launch vehicle was far more important than the technology choices available in manufacture, vehicle design, and payload innovation.
Read both of the links including comments. Still relevant today. Shuttle development problems as you describe seems relevant to Starship development. Falcon9 demonstrating flight rate being the key to affordability. I also thought, perhaps with your influence, that suborbital vehicles would be on the road to affordable orbital vehicles.
In comments, Phobos direct was proposed. If Phobos has a readily available source of volatiles, that may be worth a look.
Good reads, thank you.
John Hare: ” Falcon9 demonstrating flight rate being the key to affordability.”
Musk must have read Simberg (among others) Lacking a customer for frequent launches, Musk built his own. Starlink fills the schedule, and the cargo space, on any SpaceX launch with any capacity going otherwise unsold.
Teddy Roosevelt would have called this a “Horizonal Trust” and would have tried to make it illegal.
Hi Rand,
Given how history has shown (is showing) its solutions:
– F9, two-stage, orbital with propulsive landing.
– COTS / Commercial Cargo & Crew
– LEO constellation (i.e. Starlink)
– Starship
Would you be willing to self-critique your seven recommendations?
– Prizes for suborbital to orbital.
– Tech prizes: Orbital assembly, EVA equipment, ISRU.
– Redirect reusability from NASA to privates.
– Limit regulation
– Offer to buy thousands of seats at low price and auction off excess. Offer to pay for thousands of tons of water in orbit.
– Withdrawal from OST Re: Private property rights.
– NASA switch from Ares-1 to Commercial Crew
That could be an interesting read.
Left out one: Millions in bribes to politicians to keep regulators at bay.
Well, we now know where the RLVs are finally. Thank God!