Author Topic: RLV expectations: from light to heavy  (Read 17823 times)

Offline jongoff

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Re: RLV expectations: from light to heavy
« Reply #20 on: 01/27/2017 06:56 pm »
Space tourism would be the high flight rate market that would justify RLV. Seat price is critical, this where larger is better. See aeroplane industry.

At $10m seat F9/Dragon might be viable at $70m launch. With NG a 20 seat vehicle should be possible at $200m launch.

I think flight rate of the vehicle is a bigger driver for seat price than vehicle scale. But agree that space tourism is one of the potential RLV markets (along with propellant, provisions, raw materials for orbital construction, etc).

~Jon
But this really depends, doesn't it?

Is 50 flights of Pegasus cheaper per pound than 15 flights of Falcon 9?

Scale is super important, as is flight rate. Scale is most important on the low end. You probably start getting diminishing returns as you go bigger.

As I said, for realistic near-to-medium term flight demand levels, I still think a fully-reusable 1mT to LEO full RLV is going to be cheaper in $/kg than a partially-reusable F9 or Falcon Heavy. Yes, in full expendable mode, that 1mT to LEO LV would be much more expensive per kg than F9 or FH based on hardware efficiencies of scale. But with the kind of flight rates we're talking about, I think flight rate efficiencies of scale will more than win out.

Note, by "realistic near-to-medium term flight demand levels", I'm skeptical SpaceX is going to launch their full 4000 spacecraft megaconstellation, and I'm skeptical they'll get Mars colonization off the ground. I could see things getting busy enough that a fleet of 1mT full RLVs RLVs combined with less frequent launches of semi-reusable EELV-class vehicles (F9/FH, Vulcan/ACES, etc) starts feeling cramped and you start having demand for full RLVs in the 5-10mT to LEO scale.

I just think that multi-SaturnV-scale RLVs flying multiple flights per vehicle per day to orbit is fantasy.

~Jon

Offline AncientU

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Re: RLV expectations: from light to heavy
« Reply #21 on: 01/27/2017 07:01 pm »
Aren't you assuming that the only things we will be doing in space are the things we have been doing?

Nope. RLVs of any size only make sense if we're doing new things that require a lot higher flight rate.

Next question?

~Jon

So, if we're doing new things, how can you be certain that small RLVs make sense while large ones don't?

Flight rate and payload per flight are two parameters in the space that pertain to launch cost($/kg to orbit).  Where this optimizes is highly dependent on what the new things are... some could be beyond the capability of a 1t launcher entirely(like space tourism).  Others that are infinitely divisible like propellants will achieve an optimum between the two parameters; depending on quantities of propellants needed, orbit(s), etc.
« Last Edit: 01/27/2017 07:02 pm by AncientU »
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Offline Robotbeat

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Re: RLV expectations: from light to heavy
« Reply #22 on: 01/27/2017 07:04 pm »
I don't think we need to be doing new things to justify any kind of RLV. Existing things with existing modest growth rates is enough to justify F9 partly reusable.
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Offline jongoff

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Re: RLV expectations: from light to heavy
« Reply #23 on: 01/27/2017 07:35 pm »
Aren't you assuming that the only things we will be doing in space are the things we have been doing?

Nope. RLVs of any size only make sense if we're doing new things that require a lot higher flight rate.

Next question?

~Jon

So, if we're doing new things, how can you be certain that small RLVs make sense while large ones don't?

By being realistic about what new things might actually happen? Maybe I'm wrong, and we'll really see a 3-4 order of magnitude increase in flight demand. I'd be happy to be wrong. But assuming more modest evolution of new markets, I'm skeptical that ITS/NewGlenn class RLVs make any real sense.

Quote
Flight rate and payload per flight are two parameters in the space that pertain to launch cost($/kg to orbit).  Where this optimizes is highly dependent on what the new things are... some could be beyond the capability of a 1t launcher entirely(like space tourism).

A 1mT to LEO capability might be just fine for tourism. Remember, most of the functionality of a capsule are required to have a full RLV. Which is why full RLVs have lower payload per GLOW than an ELV or semi-RLV. If you really have a reliable full RLV, the 1mT of payload should suffice for at least 1-3 passengers if you're smart about things.

Quote
Others that are infinitely divisible like propellants will achieve an optimum between the two parameters; depending on quantities of propellants needed, orbit(s), etc.

Agreed. I personally think the optimal RLV size is one where you can have 2-3 healthy competing RLV companies, each with enough vehicles that they can afford to lose any one vehicle without having to stand down for half a year. If you need 30-50 flights per year per vehicle to be "healthy", that's saying a minimum of 180-750 flights per year for a healthy RLV industry. To get to the really nice price levels, you probably want to be pushing more in the 200-250flts/yr/vehicle. So multiplied out over an industry, that is more like 1200-3750 flights per year globally from the healthy RLV industry. And that's not counting bigger launches from semi-reusable vehicles of large unitary payloads.

That kind of flight rate and launch demand is already a huge increase over what we have today, and would require some significant new markets to become realistic.

~Jon

Offline jongoff

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Re: RLV expectations: from light to heavy
« Reply #24 on: 01/27/2017 07:38 pm »
I don't think we need to be doing new things to justify any kind of RLV. Existing things with existing modest growth rates is enough to justify F9 partly reusable.

Partial reusability is justified with current markets, I agree. But fully-reusable vehicles flying often enough to get into the RLV price ranges people talk about are going to require much bigger markets, or new ways of doing things.

Dave Salt actually made an interesting case that with a ~5mT to LEO full RLV, you could support most GEO launches using distributed launch. And even if you only snagged 1/4 of the global GEO market with that RLV, you'd still be up in the flight range necessary to start justifying a full RLV.

But once you start talking gargantuan RLVs, the only way they're going to be cheaper than small RLVs is if the demand gets big enough to justify it. And that's going to be a huge increase in demand compared to today.

~Jon

Offline A_M_Swallow

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Re: RLV expectations: from light to heavy
« Reply #25 on: 01/29/2017 02:51 am »
I don't think we need to be doing new things to justify any kind of RLV. Existing things with existing modest growth rates is enough to justify F9 partly reusable.

Partial reusability is justified with current markets, I agree. But fully-reusable vehicles flying often enough to get into the RLV price ranges people talk about are going to require much bigger markets, or new ways of doing things.

Dave Salt actually made an interesting case that with a ~5mT to LEO full RLV, you could support most GEO launches using distributed launch. And even if you only snagged 1/4 of the global GEO market with that RLV, you'd still be up in the flight range necessary to start justifying a full RLV.

But once you start talking gargantuan RLVs, the only way they're going to be cheaper than small RLVs is if the demand gets big enough to justify it. And that's going to be a huge increase in demand compared to today.

~Jon

At ~5mT the RLV capsule would be in the same size range as small passenger aircraft.

For example see the Cessna Turbo Skyhawk
http://cessna.txtav.com/en/piston/cessna-turbo-skyhawk-jt-a

A few weight saving messages would be needed. For example do the capsules need both a door on the side and a docking port on the top?
Passengers could enter by climbing down a ladder from the launch tower's white room.

Offline Pipcard

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Re: RLV expectations: from light to heavy
« Reply #26 on: 07/23/2017 08:01 am »
Are the current ideas for 7-9 m fully reusable rockets (ITSy, maybe New Glenn if it gets upgraded) going too far?

Should they have just gone for smaller rockets just to test the markets? Something with F9's expendable capacity when fully reusable? Are the markets just not going to be big enough and they should just develop 1-5 t full RLVs?
« Last Edit: 07/23/2017 08:17 am by Pipcard »

Offline Nilof

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Re: RLV expectations: from light to heavy
« Reply #27 on: 07/23/2017 03:46 pm »
That depends on the payloads. Both Elon and Bezos have large-scale colonization of space in mind, so they want a vehicle capable of lifting big HSF payloads.

1-5t RLV's can just barely lift a capsule to LEO. They can't lift space station modules. They'd require something on the order of a hundred flights to fuel a mars transfer stage.

Reusable super heavy launchers enable much larger scale operations than smaller RLV's do. In particular, they offer a credible beyond-LEO capability.
« Last Edit: 07/23/2017 03:47 pm by Nilof »
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline TrevorMonty

Re: RLV expectations: from light to heavy
« Reply #28 on: 07/23/2017 04:56 pm »
1-5t RLVs are better for satellite delivery to LEO. With LEO fuel supplied by large RLs, OTVs can deliver satellites to higher orbits.

Offline Lars-J

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Re: RLV expectations: from light to heavy
« Reply #29 on: 07/24/2017 12:08 am »
Many people seem to suggest that RLVs don't scale up well... I would rather suggest that the opposite may be true. RLVs may actually not scale down well at all. At least from an economic and practical perspective.

Of course the existing RLVs number exactly ZERO, so we can't use any current launch vehicle(s) to prove either case... but that's what my gut is telling me.


« Last Edit: 07/24/2017 03:09 am by Lars-J »

Offline Propylox

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Re: RLV expectations: from light to heavy
« Reply #30 on: 07/24/2017 02:35 am »
Many people seem to suggest that RLVs don't scale up well... I would rather suggest that the opposite may be true. RLVs may actually not scale down well at all. At least from an economic and practical perspective.
That's true of any rocket. Larger tanks hold more propellant per lb and larger engines produce more thrust per lb - so as rockets grow they become more efficient. Falling from the sky as a RLV, a larger rocket will also be less dense, decelerate more and be easier to control.
While there may be a market for small launchers and/or RLVs, the economics will favor larger ones - which is why so many small-launch proposals fail long before testing is complete. Even Falcon1 died this way and I wouldn't expect current proposals to fair any better.

Offline Lars-J

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Re: RLV expectations: from light to heavy
« Reply #31 on: 07/24/2017 03:04 am »
Many people seem to suggest that RLVs don't scale up well... I would rather suggest that the opposite may be true. RLVs may actually not scale down well at all. At least from an economic and practical perspective.
That's true of any rocket. Larger tanks hold more propellant per lb and larger engines produce more thrust per lb - so as rockets grow they become more efficient. Falling from the sky as a RLV, a larger rocket will also be less dense, decelerate more and be easier to control.
While there may be a market for small launchers and/or RLVs, the economics will favor larger ones - which is why so many small-launch proposals fail long before testing is complete. Even Falcon1 died this way and I wouldn't expect current proposals to fair any better.

Exactly... You phrased it much better than I tried to. This is why I don't see any RLV's in the 1-5t to LEO payload range really coming to fruition until the technology is much more mature... And even then, the larger ones will become even more efficient as well.

The question is more what the optimum size is for a RLV. This is where market forces (trending small) will be balanced by physics and practicality. (trending large)

Jon seems to think it is around 5t. (unless I am misunderstanding you, Jon!) I suspect 10x (50t)of that may be more likely. But what do I know?  ;)
« Last Edit: 07/24/2017 03:20 am by Lars-J »

Offline Robotbeat

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Re: RLV expectations: from light to heavy
« Reply #32 on: 07/24/2017 04:07 am »
They scale in both directions, but the cost/benefit ratio is not very attractive when you get really small. Most of the market is somewhere between Soyuz and Ariane 5, as far as total revenue goes.
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Offline TrevorMonty

Re: RLV expectations: from light to heavy
« Reply #33 on: 07/24/2017 04:38 am »
Smaller RLV may only reuse booster while using expendable US. Alot of smallsat LV companies are aiming for high production rates to drive LV cost down, making RLV less viable. We will have to see where cross over point is eg 0-250kg ELV, 250-2t partially RLV,  >2t fully RLV.
« Last Edit: 07/24/2017 04:39 am by TrevorMonty »

Offline Propylox

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Re: RLV expectations: from light to heavy
« Reply #34 on: 07/27/2017 06:13 am »
Many people seem to suggest that RLVs don't scale up well... I would rather suggest that the opposite may be true. RLVs may actually not scale down well at all. At least from an economic and practical perspective.
Smaller RLV may only reuse booster while using expendable US. Alot of smallsat LV companies are aiming for high production rates to drive LV cost down, making RLV less viable. ...
If scaling down isn't economically viable without high production rates that negate RLVs, what about using cheap, expendable 1st stages and focusing on a reusable upper? Just a thought and here's a paper-rocket mash-up to explain the idea;

 - Begin with a Minotaur's 1st/2nd stage solids, its 300kg payload fairing and avionics/thruster/payload adapter package (20kg?).
 - US is 2x 5,000lbf Propylox engines and tankage from Vector Space, vacuum optimized to around 350s(?) with 4,500kg propellant and 350kg dry.
 = That's around 906kg to 185km LEO and under 3.5g from the Cape. Surrounding the US is 126kg of IREV-2 that would deploy for a payload adapter-first re-entry and splashdown. Powered descent could be used instead, but with IREV-2 payload to LEO drops to 780kg.

All the Orbital/ATK bits are disposable while the Vector US is reused. Not sure about IREV-2.

Offline Lars-J

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Re: RLV expectations: from light to heavy
« Reply #35 on: 07/27/2017 06:16 am »
Keep in mind that upper stage reuse is a lot more difficult than first stage reuse. So why start from the top down? All current RLV efforts start from the bottom up (F9, New Glenn, XS-1), so either they learned something from the Shuttle experience, or they are all mistaken.

Offline spacenut

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Re: RLV expectations: from light to heavy
« Reply #36 on: 07/27/2017 12:47 pm »
The shuttle was supposed to be reusable.  It could only get 20 tons to LEO.  It cost as much to refurbish the solids as it cost to manufacture new ones. 

So, lesson learned, solids are expensive and heavy for the thrust they produce.  They are good only for boosters and then monolithic expendables. 

The shuttle with its 20 ton payload weighed about 100 tons to orbit, but the wings can't be used in orbit.  Lesson learned, a winged craft is heavy for payload to orbit. 

SpaceX has shown that about 70% of the total rocket expense is the booster (more engines, more mass).  You save the booster and cut launch costs with reuse.  Their base price for a new rocket is $62 million, reuse price is about $40 million.  Right of the bat, it is about 1/3 cheaper to get tonnage to orbit.  The F9 is a small rocket compared to others but has a high thrust to weight ratio so it can meet Delta IV's payloads a lot less expensively.  SpaceX can't get 20 tons to orbit without expedibility, but still is cheaper than Shuttle due to no solids and no wings. 



Now, Blue Origin is going to build a 7m reusable booster, and with reuse can get 45 tons to orbit. 

With FH and reuse of boosters, they will be able to get 40 tons to orbit.  This and being cheaper than Shuttle. 

Scale up to ITS and you get even more payload probably more expensive than FH, but cheaper/lb or kg than FH. 

Same with aircraft.  A 747 is cheaper/passenger mile than a 1920's Ford Tri-motor.  Bigger is cheaper/lb.  SpaceX is going for the ITS in a reduced scale from the original 12m to 9m because of infrastructure, tooling, and manufacturing capability, not because it would deliver cost/lb or kg to orbit cheaper.  They are at least being pragmatic.  Larger will come, probably within 10 years of ITS being operational by another company or country. 

Offline rayleighscatter

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Re: RLV expectations: from light to heavy
« Reply #37 on: 07/28/2017 10:47 pm »

Same with aircraft.  A 747 is cheaper/passenger mile than a 1920's Ford Tri-motor.  Bigger is cheaper/lb. 
Assuming a full load. If the market won't bear a large size it will look for a smaller size. It's why the big efficient widebody jets sell worse than the little inefficient regional jets.

Offline Nilof

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Re: RLV expectations: from light to heavy
« Reply #38 on: 07/28/2017 11:36 pm »

Same with aircraft.  A 747 is cheaper/passenger mile than a 1920's Ford Tri-motor.  Bigger is cheaper/lb. 
Assuming a full load. If the market won't bear a large size it will look for a smaller size. It's why the big efficient widebody jets sell worse than the little inefficient regional jets.

...While on the other hand, we see the reverse trend for cargo ships due to containerization.
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline Stan-1967

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Re: RLV expectations: from light to heavy
« Reply #39 on: 07/29/2017 12:10 am »

Same with aircraft.  A 747 is cheaper/passenger mile than a 1920's Ford Tri-motor.  Bigger is cheaper/lb. 
Assuming a full load. If the market won't bear a large size it will look for a smaller size. It's why the big efficient widebody jets sell worse than the little inefficient regional jets.

I think this analogy is of very marginal utility.   Route density & airspace issues also affect the market for the commercial aviation fleet.  Try flying LAX to Auckland NZ with 737's, or routing all domestic traffic into busy international destinations like Chicago, Frankfurt, Amserdam, etc. at peak hours.


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