Starship, how many decades did we loose?

[StrandedonEarth]

2 hours ago, Dragon01 said:

Wet workshop require too much effort to convert into anything usable

I believe wet workshop is doable if it is designed to be converted. Features like standardized equipment mounting rails, in parallel to double as channels for running cables, tubes, and conduits would go a long way towards being able to convert an emptied tank to habitable space.

Alternately, designing a habitable space to handle storing propellants is another potential path.

Where there's a will, there's a way. The only way to determine if an idea is truly viable is to try it, a method employed by both Thomas Edison and Elon Musk, among others

[Guest]

7 minutes ago, tater said:

Every single aspect of flight is easier with 2 stages, because the vehicles can be more optimized for their flight regimes, whereas an SSTO has to do all of the flight regimes.

Except that by going back into atmosphere the 2nd stage has to deal with much of the same conditions that the 1st stage dealt with on ascent. So your only gain is in the engines. TSTO only makes sense if you split into the part that goes into space and the part that doesn't.

Edited May 17, 2019 by Guest

[StrandedonEarth]

The problem with SSTO's is that the payload fraction is minuscule. And requires a high level of thermal protection over a much larger area.

Edited May 17, 2019 by StrandedonEarth

[Guest]

That is the problem with chemical rocket engines (and why Skylon uses LH2 and bothers with airbreathing mode) not SSTOs as a whole. Staging is a crutch that we need to overcome our crappy propulsion tech.

Edited May 17, 2019 by Guest

[StrandedonEarth]

2 minutes ago, Dragon01 said:

the 2nd stage has to deal with much of the same conditions that the 1st stage dealt with on ascent

A re-entering stage has nearly full orbital velocity going into the atmosphere. An ascending vehicle does a significant portion of its acceleration above the atmosphere.

[tater]

9 minutes ago, Dragon01 said:

Except that by going back into atmosphere the 2nd stage has to deal with much of the same conditions that the 1st stage dealt with on ascent. So your only gain is in the engines. TSTO only makes sense if you split into the part that goes into space and the part that doesn't.

Not "space" but orbital velocity. Boosters separate at substantially lower velocities than stage 2, and also carry the large majority of the propellant. The aim for air breathers is specifically to use the ambient air as propellant they don't have to carry. This necessitates achieving higher velocities (and for longer time spans) while in the useful atmosphere, which significantly increases stress on the vehicle, vs getting past the bulk of the air as quickly as possible.

Your statement about stage 2 dealing with the stresses of stage 1 is bizarre. Stage 2 deals with the same stresses of launch (it's attached), and in fact deals with substantially greater stresses on reentry at orbital velocity than Stage 1 does with a mere 2 km/s. There's a reason we don't have SSTOs yet, they're substantially harder (and even when they work, the payload mass fraction will be low).

10 minutes ago, Dragon01 said:

That is the problem with chemical rocket engines (and why Skylon uses LH2 and bothers with airbreathing mode) not SSTOs as a whole. Staging is a crutch that we need to overcome our crappy propulsion tech.

Are you suggesting a nuclear SSTO, because hydrolox is chemical propulsion?

Staging is not a crutch, it's an acknowledgement of physics.

Edited May 17, 2019 by tater

[Bill Phil]

12 minutes ago, Dragon01 said:

Except that by going back into atmosphere the 2nd stage has to deal with much of the same conditions that the 1st stage dealt with on ascent. So your only gain is in the engines. TSTO only makes sense if you split into the part that goes into space and the part that doesn't.

Well with concepts like ballutes and other reentry augmentations like direct insertion of a neutral gas that may be less of a problem than one would first believe.

A ballute could drastically reduce the stress on the vehicle, though we don’t know the performance numbers yet.

[tater]

The larger the vehicle, the less need for solutions like ballutes since the ballistic coefficient is better (big and fluffy is good).

Chances are we will have rapidly reusable second stages long before any would-be SSTO even has taxi tests, much less space flights.

[Lisias]

15 hours ago, ZooNamedGames said:

NASA wouldn't have attempted a reusable booster like SpaceX designed, yes. As it's extremely costly and NASA is in the business of innovation and discovery and reusable boosters is more of a cost saver than anything new. We were reusing plenty of hardware thanks to the Space Shuttle program, so it didn't discover much and wouldn't innovate enough to keep NASA's interest. It's why NASA has always been focused on efforts above and beyond that of LEO since the end of the space shuttle- NASA doesn't tread where others can do it more cheaply and despite what others claim- so far only NASA has the ability to send crew BEO. 

IMHO the problem is not the cost of development, but the potential savings themselves.

NASA budget is approved by the Congress, and congressmen get elected by bringing the pork home.

The very Space Shuttle Program was constrained by this: a lot of technical decisions were taken on political criteria - as the booster's width!

Once the program was running, savings would need to be achieved indirectly (as not painting anymore the external fuel tank, did only once on the first flight of Columbia) as trying to really optimize the vehicle would reduce the "pork going home". That would hinder NASA funding next year.

Pure research and development are easier to fund on a new Space Race - that commandment from Trump to lay feet on the Moon in 5 years would probably keep NASA somewhat shielded from Pork Politics, as anything hindering this program would face direct presidential backslash.

But then someone else would need to fulfil now mundane tasks, as provisioning the ISS. Again, relying on a foreign (and not necessarily friendly) nation to provide such critical role is terribly problematic on a strategic point of view, but also on a finantial one: the Pork is going overseas, no congressmen wants to be responsible to this!

I expect that at least some SpaceX decisions end up having to secure some Pork to someone - but  not to the point of undermine the profitability of the enterprise.

 

[RocketSquid]

3 hours ago, Dragon01 said:

Except reusing the upper stage in orbit is not viable. Wet workshop require too much effort to convert into anything usable (if you need volume, use inflatables) and we have absolutely no use for raw material in orbit. We'll have Skylon way before we have an orbital foundry capable of recycling an upper stage.

SSTO is the only way you're getting realistic 100% reusability. The only other way is to reuse the first stage and only launch payloads with enough dV to serve as their own upper stage. The real trap is anything that requires building a new pump-fed rocket engine for each flight.

We don’t know how much effort a wet workshop would take because we’ve never tried it. And “downcycling” an upper stage into micrometeorite shielding or the like would really only require cutting the stage apart and bolting it to the hull. 

Plus, recovering a second stage is not that difficult as rockets go. Adding more thrust than strictly necessary, or a set of small, solid-fueled soft landing thrusters, is sufficient for the landing. A shield or the like will be necessary, but the engine can be used as a shield if it’s designed with a plug nozzle instead of a de laval nozzle, and a ballute or inflatable shield could also be used. Retaining a bit of extra fuel would allow use of active cooling. 

 

[mikegarrison]

We know from the math that two stages will always have a huge advantage over one stage. The only offsets for single stage are reduced complexity and cost -- if you can achieve them, which no one ever has. This two-stage advantage only gets bigger as staging technology improves with experience.

[Guest]

31 minutes ago, mikegarrison said:

We know from the math that two stages will always have a huge advantage over one stage. The only offsets for single stage are reduced complexity and cost -- if you can achieve them, which no one ever has. This two-stage advantage only gets bigger as staging technology improves with experience.

This reasoning only applies to expandable LVs. If you want to reuse the entire vehicle, staging forces you to use multiple counts of various landing systems. And we're not talking small solid braking motors. If what you're trying to land is bigger than a solid kick motor (which, judging from pictures of one PAM that fell in Saudi Arabia, could do just with a parachute and a small air cushion), you need a Falcon 9-style landing equipment. Which you're going to carry to orbit, and then back down. Of course, an SSTO has to do that, too, but it's only carrying one set of landing gear.

2 hours ago, tater said:

Are you suggesting a nuclear SSTO, because hydrolox is chemical propulsion?

It's the only way you're going to get airplane-like reuse with a decent payload fraction.  Ultimately, what you need for economical SSTO is specific impulse coupled with good thrust for liftoff. In other words, thrust power. NTRs would allow you to dispense with hydrogen and use methane as propellant, which could give you kerolox-like density and decent thrust with Isp in excess of hydrolox. 

[mikegarrison]

16 minutes ago, Dragon01 said:

This reasoning only applies to expandable LVs. If you want to reuse the entire vehicle, staging forces you to use multiple counts of various landing systems. And we're not talking small solid braking motors. If what you're trying to land is bigger than a solid kick motor (which, judging from pictures of one PAM that fell in Saudi Arabia, could do just with a parachute and a small air cushion), you need a Falcon 9-style landing equipment. Which you're going to carry to orbit, and then back down. Of course, an SSTO has to do that, too, but it's only carrying one set of landing gear.

Apparently I was unclear ... I was assuming all of that when I said "staging technology" and referred to "cost and complexity".

Yes, the second stage of a two-stage reuseable lifter has to carry everything needed to land from orbit -- but an SSTO has to carry everything needed to land from orbit AND everything needed to do what a first stage does, which actually means it's even harder (more weight) to safely land it from orbit.

The math still works out -- two stages are the way to go. The only (to date) reuseable orbital spacecraft have used two stages (space shuttle, OK, technically "stage and a half") or have been the payload stage of two-stage launchers (X-37, Dragon, upcoming: Dreamchaser, Crew Dragon, CST-100).

[tater]

Lol, relevant to this thread:

 

[Guest]

1 hour ago, mikegarrison said:

The math still works out -- two stages are the way to go. The only (to date) reuseable orbital spacecraft have used two stages (space shuttle, OK, technically "stage and a half") or have been the payload stage of two-stage launchers (X-37, Dragon, upcoming: Dreamchaser, Crew Dragon, CST-100).

Space Shuttle wasn't efficient. Also, the discussion is about reusable LVs. None of the systems you mention were 100% reusable (as flown. The Shuttle was meant to be). Once you compromise reuseability of a part of the spacecraft, then TSTO does edge out ahead. Again, usually at the cost of throwing away an expensive, pump-fed engine, and adding a whole lot of maintenance overhead. All an SSTO needs over a reusable second stage is a bigger fuel tank and more powerful engine, essentially. Of course, the landing gear also gets bigger, but not as big as if you wanted to slap two sets of it on a rocket.

You may be able to beat reusable SSTOs by "big dumb booster"-style fully expandable TSTOs, but that's assuming you can get by on economics of scale. And of course, nuclear engines blow anything chemical out of water, and you don't want to put them on anything expandable for multiple reasons.

38 minutes ago, tater said:

Lol, relevant to this thread:

Great, now let's wait for Musk to build enough public/government confidence in the thing so he can slap a bunch of high-tech NTRs on it.  

Edited May 17, 2019 by Guest

[mikegarrison]

2 minutes ago, Dragon01 said:

Space Shuttle wasn't efficient.

Yes it was. It lifted a MASSIVE amount of payload to orbit. Technically it was extremely efficient for its time. As for cost, no, not super cost-efficient. But people forget that the space shuttle was not really an orbital delivery vehicle (even if it was sold as one). It was really a space station that had a week+ endurance in space, science labs, crew life support for more than half a dozen people, etc. Of course it was going to be costly to launch something like that up to space over and over again.

6 minutes ago, Dragon01 said:

Once you compromise reuseability of a part of the spacecraft, then TSTO does edge out ahead.

You miss the point. Look at Falcon 9. What's non-reuseable? The second stage. Compare the technical difficulty of making the second stage capable of controlled orbital re-entry v. making an entire SSTO capable of controlled orbital re-entry. The latter is much harder because the craft's mass is so much bigger, but you seem to think it would be easier.

[tater]

6 minutes ago, Dragon01 said:

You may be able to beat reusable SSTOs by "big dumb booster"-style fully expandable TSTOs, but that's assuming you can get by on economics of scale. And of course, nuclear engines blow anything chemical out of water, and you don't want to put them on anything expandable for multiple reasons.

This is again, untrue. Starship, or indeed ANY TSTO spacecraft, where Stage 2 is reusable beats an SSTO. No compromise is required.

Vehicle cost, amortized by the number of reuses, plus operational costs (propellants, turn around, loading, etc) all times the payload mass total, divided by the number of flights.

SSTOs are not magic, they sacrifice payload mass for losing a stage.

[mikegarrison]

11 minutes ago, Dragon01 said:

All an SSTO needs over a reusable second stage is a bigger fuel tank and more powerful engine, essentially.

This betrays a fundamental lack of understanding of the rocket equation. Yes, "a bigger fuel tank and more powerful engine", but it's SO MUCH bigger, because the mass goes up exponentially. What it really needs is a higher ISP engine. Much higher ISP. Thus the idea of using an air-breathing engine, but now you either carry an air-breathing engine around with you or you need a bimodal engine that is a huge increase in cost, complexity, etc. -- everything you were trying to decrease by going SSTO.

Edited May 17, 2019 by mikegarrison

[tater]

Also, while I really want to see NTR spacecraft, an NTR spaceplane is not likely to be a thing.

[mikegarrison]

2 minutes ago, tater said:

Also, while I really want to see NTR spacecraft, an NTR spaceplane is not likely to be a thing.

Gods yes. Save us from this: https://en.wikipedia.org/wiki/Convair_NB-36H

[magnemoe]

6 hours ago, Dragon01 said:

Except reusing the upper stage in orbit is not viable. Wet workshop require too much effort to convert into anything usable (if you need volume, use inflatables) and we have absolutely no use for raw material in orbit. We'll have Skylon way before we have an orbital foundry capable of recycling an upper stage.

SSTO is the only way you're getting realistic 100% reusability. The only other way is to reuse the first stage and only launch payloads with enough dV to serve as their own upper stage. The real trap is anything that requires building a new pump-fed rocket engine for each flight.

Landing an upper stage for reuse is again way easier than an SSTO.
The upper stage is much lighter and smaller typically 1/4 of first stage or less in wet weight and length, lighter engines as less mass and less need for even 1g trust then full. 
Less structural mass as it don't have to carry so much weight 
So its far less mass you need to reenter and land. Every kg you add to be able to land is directly subtracted from the payload mass but the same is true for an SSTO. 
But on an upper stage you only need to heat shield an fraction of the total size and an vehicle of far less mass. 

Two other factors rockets scales up very well, design something like New Glenn and you can take 40 ton into LEO, increasing the upper stage mass by 10 ton and you can only take 30 even 20 is fine for most missions. On the other hand for an small upper stage it might be so light you can do stuff like helicopter catch of parachutes  
And you have the option to go disposable. 

That do you loose? yes you have to stack the parts anyway, But you also need to integrate the payload. 

Yes Skylon might work but its far more challenging to build than starship, engines has not been tested at hypersonic speed for one. 

Complexity again so back to the original question could they build SS / SH back in 69 or 79, no don't need 100 ton to orbit 40 is enough. 

[StrandedonEarth]

12 minutes ago, Dragon01 said:

All an SSTO needs over a reusable second stage is a bigger fuel tank and more powerful engine, essentially.

Okay, so you don't need a second stage engine. For that savings, you need to bring the equivalent of an entire first stage to orbit, which is a LOT of mass. The rocket equation exacts a stiff penalty for accelerating all of that extra mass an extra few km/s, bringing your useful payload down by an order of magnitude or so.

As an aside, NASA contracted private contractors to supply rockets on a cost-plus basis. There was no incentive for those contractors to develop, or help develop, re-usable vehicles, as it was much more profitable to build new rockets for each launch. Even Shuttle required a huge new tank each launch, and refurbishing the SRB's cost nearly as much as making new ones. And the army required to turn the Orbiters around for the next launch kept the pork flowing.

[Guest]

10 minutes ago, magnemoe said:

The upper stage is much lighter and smaller typically 1/4 of first stage or less in wet weight and length, lighter engines as less mass and less need for even 1g trust then full. 

Except you need 1G for reuse, anyway, unless you're not doing propulsive landing. Things like helicopter catch are risky and very involved to set up. If it's going to be anything like an airplane, the least you can do is a single stage suborbital booster with a reusable spacecraft. 

9 minutes ago, mikegarrison said:

This betrays a fundamental lack of understanding of the rocket equation. Yes, "a bigger fuel tank and more powerful engine", but it's SO MUCH bigger, because the mass goes up exponentially. What it really needs is a higher ISP engine. Much higher ISP. Thus the idea of using an air-breathing engine, but now you either carry an air-breathing engine around with you or you need a bimodal engine that is a huge increase in cost, complexity, etc. -- everything you were trying to decrease by going SSTO.

Or an NTR. It has high Isp, and running on methane can allow you to actually save mass on tankage over LH2. An airbreather is the next best thing, but it pretty much requires hydrogen as fuel, with all the problems that entails. 

No need for nuclear spaceplanes, either, you could have a VTVL SSTO with methane. Ultimately, every chemical attempt at reuseability will have similar problems to Space Shuttle.

[tater]

8 minutes ago, Dragon01 said:

Except you need 1G for reuse, anyway, unless you're not doing propulsive landing. Things like helicopter catch are risky and very involved to set up. If it's going to be anything like an airplane, the least you can do is a single stage suborbital booster with a reusable spacecraft. 

It doesn't need to hover, it needs to reach low velocity at h=0.

Regardless, engines on upper stages need to push the full vehicle (mostly propellant), and only need to propulsively land a time % of that (dry mass plus any return payload. Something like Starship is 1300 tonnes wet, and with landing props, 100-something. Thrust is not really an issue.

Even TSTO with horizontal landing is better.

Take any SSTO spaceplane you envision. Lower the propellant tankage, and/or increase the payload. Put it on top of a similar, but much larger vehicle that accelerates it up to the speed where it would just about go full rocket and head to space. You now have a 100% reusable vehicle with better payload. It adds the complexity of staging, but eliminates the complexity of dual modes for the spacecraft, and allows the 2 stages to be optimized for their respective tasks.

[magnemoe]

 

29 minutes ago, mikegarrison said:

Gods yes. Save us from this: https://en.wikipedia.org/wiki/Convair_NB-36H

This, I'm very pro nuclear but using an NTR launch vehicle is insane even if an pebble bed will not have radioactive exhaust at start it will be radioactive after long use ruling out reuse, and the damage of an failed launch or very hard landing could be an small Chernobyl. As an 3rd stage who did circulation and then ejection burn, yes that work