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Re: Mars Is a Hellhole

Fri May 07, 2021 9:55 am

jlv wrote:
Fri May 07, 2021 8:48 am
WetEV wrote:
Fri May 07, 2021 8:39 am
jlv wrote:
Thu May 06, 2021 1:19 pm
What SpaceX is working on down there is another massive sea change in space transportation.
Rocket equation hasn't changed.
Yes, that's why Starship/Superheavy remains a TSTO system. But a fully reusable TSTO system.
Which isn't another massive sea change in space transportation. It still takes massive amounts of chemical propellants just to get to orbit. Rockets are terribly inefficient and expensive. Reusable might or might not reduce the cost, but will increase the amount of propellants needed.
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Re: Mars Is a Hellhole

Fri May 07, 2021 10:15 am

Yes, Mars is still a (bitterly cold, desiccated, extraordinarily hostile to human life) hellhole, and will be for generations to come. No changing that barring completely unforeseeable changes in technology, on a scale commensurate with friendly Vulcans arriving and obviating several hundred years of future development.

But fully reusable TSTO (2-stage to orbit) super-heavy-scale launch vehicles will change the economics and practical possibilities by several orders of magnitude. That's no small potatoes either.

SLS is dead on arrival. Surpassed before it even flew in so many ways, it's hard to count them all. The Raptor engine is itself a game-changer, for those of us who are paying attention, and can appreciate the step-change that's being implemented.

None of which means that human colonization of Mars is anywhere on our near horizon. Color me skeptical on that point. Nor do I find the arguments in favor particularly compelling, frankly. There is no planet B. Not in our lifetimes, nor in our great-grandchildren's lifetimes, should we be lucky enough to have any such children.

In the timeframes we can usefully contemplate, the most we'll do is establish a more or less permanent scientific outpost on Mars. Which would be quite an accomplishment in itself, albeit perhaps a self-defeating one if the goal is seeking proof of a second abiotic genesis in our solar system.

Musk doesn't give a flying eff about scientific progress for the sake of scientific progress. His kind will likely win out. Like it or not. That's how I read our history, anyway. I do think we'll put humans on Mars, probably in my son's lifetime if not in mine. There are other more pressing issues today, though. Much more pressing in my mind.
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Re: Mars Is a Hellhole

Fri May 07, 2021 10:51 am

frontrangeleaf wrote:
Fri May 07, 2021 10:15 am
But fully reusable TSTO (2-stage to orbit) super-heavy-scale launch vehicles will change the economics and practical possibilities by several orders of magnitude. That's no small potatoes either.
Sounds just like the Space Shuttle. Which had better engines than the Raptor.
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Re: Mars Is a Hellhole

Fri May 07, 2021 11:38 am

WetEV wrote:
Fri May 07, 2021 10:51 am
Sounds just like the Space Shuttle. Which had better engines than the Raptor.
Except the Space Shuttle wasn't a fully reusable TSTO. It was only a partially reusable system, and only after a huge amount of costly refurbishment between flights. They stopped flying it because of the massive cost of keeping it running.

I also fail to see how the RS-25 engine is better than the Raptor. The numbers in these tables are 2 years old, and the Raptor has improved since this was created (e.g., ISP is up 10%).

(Source https://everydayastronaut.com/raptor-engine/)
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Re: Mars Is a Hellhole

Fri May 07, 2021 12:12 pm

WetEV wrote:
Fri May 07, 2021 10:51 am
frontrangeleaf wrote:
Fri May 07, 2021 10:15 am
But fully reusable TSTO (2-stage to orbit) super-heavy-scale launch vehicles will change the economics and practical possibilities by several orders of magnitude. That's no small potatoes either.
Sounds just like the Space Shuttle. Which had better engines than the Raptor.
Uh, no. Not even remotely close. Better how?

The RS-25 is a dual fuel-rich staged combustion engine running hydrolox. It is nominally reusable, but more accurately refurbishable. Every engine is torn down and rebuilt after every flight.

Raptor is a full-flow gas-gas staged combustion design running methalox capable of extracting a much higher percentage of available energy from the prop load on board than RS-25 ever will. Main combustion chamber pressures on the RS-25 don't begin to approach what Raptor runs. Higher MCC drives thrust and specific impulse. No full-flow gas-gas design has ever progressed to flight testing, ever, in the history of the world. The design has only ever been attempted 3 times. To claim that the RS-25 was somehow the "better" engine is to ignore the fundamental differences in them.

And let's not even get into cost. The latest contract has new RS-25s for a cool $146M per copy. This is being bandied about as "cheaper" somehow. That's a bald-faced lie. Sorry. Not cheaper. Not by any rational standard. More like triple the old cost. The worst kind of political pork.

The only advantage the RS-25 has over Raptor is in specific impulse, which is entirely a matter of the fuel it burns. RS-25 was a fine engine - in the 70's. Today it's been surpassed. I would argue there are Russian designs that also better the RS-25 as well. We conceded world leadership in liquid rocket engine design to the Russians for decades. Until Raptor. Merlin also holds some impressive new world records of its own, namely around thrust to weight ratio, previously held by the Russians.

As to the space shuttle, as we all know, it was no where near fully reusable. Certainly not compatible with fast turnaround. Starship is being built to be fully reusable, and with heretofore unheard of short turnaround times. Days, not weeks, not months. Care to compare useful payloads?

You can't be serious. Starship doesn't "sound" anything like Space Shuttle. We retired Space Shuttle a decade ago and for good reason. Belongs to history now.

Edit: See JLV's post above for the numbers. Didn't have that handy.
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Re: Mars Is a Hellhole

Fri May 07, 2021 3:07 pm

jlv wrote:
Fri May 07, 2021 11:38 am
WetEV wrote:
Fri May 07, 2021 10:51 am
Sounds just like the Space Shuttle. Which had better engines than the Raptor.
Except the Space Shuttle wasn't a fully reusable TSTO. It was only a partially reusable system, and only after a huge amount of costly refurbishment between flights. They stopped flying it because of the massive cost of keeping it running.
That's reality. Promise was that it was going to be massively cheaper.

jlv wrote:
Fri May 07, 2021 11:38 am
I also fail to see how the RS-25 engine is better than the Raptor. The numbers in these tables are 2 years old, and the Raptor has improved since this was created (e.g., ISP is up 10%).
Higher ISP. Or has that changed?

Less CO2 (hydrogen vs methane).
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Re: Mars Is a Hellhole

Fri May 07, 2021 3:19 pm

frontrangeleaf wrote:
Fri May 07, 2021 12:12 pm
As to the space shuttle, as we all know, it was no where near fully reusable.
Space Shuttle was promised to be mostly reusable, other than the external tank. Turn around in less than a week, so 50+ launches per year.

Promised $118 per pound to LEO.

Actual? $27,000 per pound to LEO.

I'd bet even Elon Musk can get a better promise to actual ratio. But I wouldn't count on 1:1.
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Re: Mars Is a Hellhole

Fri May 07, 2021 7:10 pm

WetEV wrote:
Fri May 07, 2021 3:19 pm
frontrangeleaf wrote:
Fri May 07, 2021 12:12 pm
As to the space shuttle, as we all know, it was no where near fully reusable.
Space Shuttle was promised to be mostly reusable, other than the external tank. Turn around in less than a week, so 50+ launches per year.

Promised $118 per pound to LEO.

Actual? $27,000 per pound to LEO.

I'd bet even Elon Musk can get a better promise to actual ratio. But I wouldn't count on 1:1.
Time will tell. Musk has totally changed the game with Falcon 9, after delay. His timelines are known fantasies. His accomplishments are not.

Falcon 9 is an absolute workhorse. They have now *recovered* almost as many first stages as ULA has ever flown Atlas V, the previous American launch vehicle record holder. That doesn't mean that Starship will be as successful. It is even more ambitious on a lot of levels. But the physics suggest that they have a decent shot at coming close. Their iterative "hardware rich" approach certainly has its advantages. Being willing to turn the engineers loose and give them free rein to try new approaches experimentally will make the difference. It's agile software development theory applied to aerospace manufacturing. There is no reason to believe they won't succeed using that approach based on what we know today.

Shuttle was *never* going to be anything near what was promised. Way too much complexity. Way too much dry mass. It would have had to have flown like an airliner, but they never got the main engines or the TMS to work without significant refurbishment. The program assumptions were ridiculous from the get go. The propulsion backbone is a mix of hydrolox sustainer engines (high impulse, mediocre thrust/weight ratio, medium thrust) and solids (crappy impulse, crappy thrust/weight ratio, lots of thrust). A bizarre set of engineering trades driven by political agendas. It ended up being an incredible machine, but unfortunately also a deadly one. Not to mention stupid expensive. SLS repeats almost all of these mistakes, again for purely political reasons. Congress doesn't actually care if it ever flies as long as the money flows.

Saturn V was a far more rational design. Use kerolox on the first stage to get it off the ground, switch to high impulse hydrolox in the upper stages. Stage enough, but not too much. For its day, an absolute tour de force. Also stupid expensive, but vastly more capable for the money. SLS advertises as the "most powerful" based on launch thrust, but it's a far cry from as capable in terms of useful payload to any orbit. Because of the bizarro world propulsion backbone.

NASA did a bunch of engineering studies prior to choosing the design direction, one of which drew directly from the Saturn V approach. That team thought they'd won the competition, and by rights, they should have, but the Senate wrote the 2010 bill to exclude other approaches and that was that. $20B and a decade later and it still hasn't flown. Forecasts of $1.5 - 2B per flight. A flight cadence of 1x per year at that investment level. You've got to be kidding me. Why is this not criminal? What might we have accomplished had we invested those funds and all the associated effort into a more sound plan this time around?
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Re: Mars Is a Hellhole

Sat May 08, 2021 12:10 pm

frontrangeleaf wrote:
Fri May 07, 2021 7:10 pm
Time will tell.
Yes.

frontrangeleaf wrote:
Fri May 07, 2021 7:10 pm
Shuttle was *never* going to be anything near what was promised.
As for "*never*", that's easy hindsight. If Musk had two weeks less funding for Tesla, Model S launch would have run out of money. According to Musk. Hindsight is 20 20. Musk skated close to the edge, on the thin ice, and got away with it. The Shuttle didn't.

TMS? Perhaps referring the APU issues?
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Re: Mars Is a Hellhole

Mon May 10, 2021 7:15 am

frontrangeleaf wrote:
Fri May 07, 2021 7:10 pm
Shuttle was *never* going to be anything near what was promised.
As for "*never*", that's easy hindsight.
No, it was pretty early on. NASA promised everything for everybody for the Shuttle (the whole "pickup truck to space") -- and it quickly became clear that they were never going to meet most of those promises at anywhere near the cost and cadence NASA promised. Much like the Constellation and SLS, which were promised to be the time and cost effective ways "back to space" and "back to the moon" because they were re-using existing Shuttle hardware, but instead being neither.
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