Author Topic: Skepticism about reusability  (Read 23762 times)

Online Lars-J

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Re: Skepticism about reusability
« Reply #40 on: 12/12/2015 11:42 PM »

IOW: The fact that chemical fuel is used is not the cause of current high launch costs. It is responsible for ~1% of these costs.

Bingo. People can moan about chemical propulsion holding us back from spreading off this rock, but it ISN'T. It is an *insignificant* part of launch costs, and the REAL cause of our launch costs being high is that we keep throwing away hardware - not chemical propulsion.

Offline Lee Jay

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Re: Skepticism about reusability
« Reply #41 on: 12/13/2015 12:08 AM »
We aren't going to expand beyond Earth on chemical rockets.  Period.

Why not? Question mark.

2-3% of glow gets to LEO.  Way less beyond that.

Way too much material usage, way too expensive (factor of 10,000).

97% of launcher's mass is not making orbit, true.

95% of the mass which isn't making orbit is fuel. Yes, it is irrevocably spent, but it is less than 1% of launch cost.

IOW: The fact that chemical fuel is used is not the cause of current high launch costs. It is responsible for ~1% of these costs.

It's not the fuel cost, it's the extremely expensive storage and users of that fuel that are the problem.  And the root cause of that is that chemical reactions just aren't energetic enough for this application to be economical and practical in wide usage.

Look at it this way.  A jet engine on a modern commercial airliner costs around the same as a modern rocket engine but lasts 1,000 times longer and produces an ISP of around 3,000, doing a job that requires a lot less energy.

To make chemical rockets as widely practical as airliners are, they'd need to have rocket engines that last 10,000 hours and produce an ISP of 1,000 or more.  Only problem is, the fuel itself is incapable of that.

Offline Lee Jay

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Re: Skepticism about reusability
« Reply #42 on: 12/13/2015 12:17 AM »
By the way, the fuel cost of a 7-person Dragon launched on F9FT is about $70k per person (I'm using round numbers for LOX and RP1).  So, that's how much it would cost if the entire system were free, fully-reusable, didn't require any ground personnel to assemble or fuel it for launch, and lasted forever.

Still kind of pricey if you want to make a new civilization on a new planet, and that doesn't include the cost of getting from LEO to that planet, getting from planetary orbit to the surface, or the cost of the infrastructure on that planet (which could well be in the billions per person).

Offline meekGee

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Re: Skepticism about reusability
« Reply #43 on: 12/13/2015 12:27 AM »
We aren't going to expand beyond Earth on chemical rockets.  Period.
That's a pretty odd use of the word "period".

You assertion is supported by what exactly?

And since achieving LEO is by far the most difficult part, do you have any idea on non-chemical means of getting to orbit?

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Offline meekGee

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Re: Skepticism about reusability
« Reply #44 on: 12/13/2015 12:35 AM »
On one hand, I've seen people talk about reusability as a major "game-changer" that will revolutionize everything about space access, leaving everyone who still has expendable systems in the dust.

On the other hand, I've seen people who are skeptical, saying that reusability might end up with high refurbishment and labor costs, higher unit costs due to decreased production, low market elasticity, "not enough demand for high flight rates," and it not mattering because the launch costs are only a small part of a total mission.

Is there any truth to these doubts?

You need to look at the reasons why the previous reusable system (Shuttle) was so expensive.

If you don't, then you're just basically extrapolating on the blind... "Well Shuttle was expensive, so we can't say anything about F9".  It's an empty logical step.  One does not follow from the other.

Shuttle was expensive because:
- It threw away the solids, or rather, it recovered only a small portion of them.
- The main engines were extremely expensive to refurbrish
- It threw away the fuel tank
- The orbiter was 110 tons, and could only carry 20 tons of payload.  That's a 5x cost multiplier right there if you consider STS merely as a launch system
- ...

None of these applies to F9.

If F9 launches, and the first stages touches down with good reliability, and given what SpaceX must already know about the lifetime costs of a Merlin, then there's just no way that you can hide major costs in there.

Once they get the first stage back, they'll realized they need to beef up some components, but also that they can lighten up others.  They'll also probably have to tweak the Merlin so they will come out with an M1E.

But from an engineering viewpoint, SpaceX is the first group to field a reusable system that's designed to be low cost and not a flagship.

If I was a betting man, I'd be giving them very very good odds.
« Last Edit: 12/13/2015 12:37 AM by meekGee »
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Offline Dante80

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Re: Skepticism about reusability
« Reply #45 on: 12/13/2015 03:21 AM »
Elon Musk said that the Falcon Heavy can lift 7 tonnes to GTO "with full reusability of the all three boost stages. I think he means that all three cores return to the launch site (for faster turnaround).

Musk/SpaceX intends to reuse their launchers, that is their short-term goal. If it works, it would be better to launch heavy satellites to GTO individually instead of using a SYLDA/SPELTRA-like system on the Falcon Heavy, especially to satisfy "higher flight rates."

Yes, I know the quote, its from 2014 and before we knew about the exact upgrade FT brought. In that article, Elon talked only about densification, and some minor weight shedding. In the end, FT got a bigger interstange, bigger second stage, and different tank lengths. As well as more engine power via unlocking the M1-D.
I believe that Mr. Musk knew precisely what Falcon 9 v1.1 Full Thrust was being designed to do when he said that Heavy will lift 7 tonnes to GTO with all boost stages recovered.   He had to know, given the timing of the development.  7 tonnes meshes with SpaceX's 6.4 tonne listing, with some buffer.  In addition, I've spent far too much time trying to model what SpaceX has been and will be doing.  The answers I see match more or less with what Mr. Musk said, and with what SpaceX advertises.  Reuse takes a hammer to GTO performance, dropping the capability by a factor or three or more. 

Falcon 9 v1.1 could not do, and did not do, landing attempts on GTO missions.  It didn't even carry legs on those missions.  Full Thrust might be an attempt to do recoveries on some GTO missions, but I'm not sure it will be able to do it on the heavier GTO payloads.  My estimate is that Full Thrust in expendable mode would lift about the same to GTO as Falcon Heavy in recoverable mode.

 - Ed Kyle

Thanks for the answer. I do agree with you that re-usability cuts heavily into GTO missions, especially since the Falcon family lacks a high energy/efficiency second stage to compensate.

The reason I am not ready to believe the 6.4t quote for FH (with the FT changes in it) is that it seems like the F9 FT could be more capable than previously thought. We will have to see how it unfolds.

The original plan for SES-9 on v1.1 was for Falcon to place the sat into a sub-synchronous orbit , and then have onboard propulsion raise perigee, change plane and circularize (more than 1,800ms needed). SES-9 weighs around 5,330kg, and that was deemed to be more than what v1.1 could do for a typical GTO mission (even in expendable mode).

From what we hear, v1.1 FT might attempt a barge landing on the mission. There have been some clues for that.

Quote
"SES CTO: We've asked SpaceX if recovered 1st stage from our SES-9 launch this summer could be sold to us for lower-cost future launch. TBD."

https://twitter.com/pbdes/status/611199719864410112

We also don't know whether the mission plan has changed. If I were SES, I would take advantage of the higher cap to place the sat closer to home (since it would both go online quicker, and boost station keeping dv / orbit life). This might mean that the SES-9 mission could be a GTO 1,800ms re-usable attempt with a 5,330kg payload.

So, to conclude. If SES-9 really does a barge landing, wouldn't this help us extrapolate that FH would be able to do more than 6,4tons with all three cores returning?
« Last Edit: 12/13/2015 03:48 AM by Dante80 »

Offline KelvinZero

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Re: Skepticism about reusability
« Reply #46 on: 12/13/2015 04:57 AM »
Thanks for the answer. I do agree with you that re-usability cuts heavily into GTO missions, especially since the Falcon family lacks a high energy/efficiency second stage to compensate.

This is uninformed speculation on my part but I wonder if reusable SEP tugs will one day make only the LEO capability important for chemical stages.

There are also quite different possibilities like solar thermal and rotovators. In any case a reusable vehicle from LEO to GTO feels technically easier than reuse from ground to LEO. I imagine the problem is more that the trajectory itself may not be reusable. You might not want to throw anything in that particular direction again for a while.

Offline llanitedave

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Re: Skepticism about reusability
« Reply #47 on: 12/13/2015 06:20 AM »
We aren't going to expand beyond Earth on chemical rockets.  Period.

Er, Apollo? Pretty sure that was chemical, prety sure it made it to the moon. That's expansion, albeit in a very minor way, but it proved it could be done with chemical rockets. Recent images of Pluto - chemical rockets only got New Horizons there (plus Jupiter gravity assist). There is a lot that can be done with chemical propulsion. What cannot be done with it yet, is replace it with something better.

It's not expansion unless we stay, reproduce, and expand the civilization.  Flags and footprints isn't expansion of the species beyond Earth anymore than a weekend vacation to the beach is the same as moving your family to the beach and living there permanently.


Methane and LOX are cheap.
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Offline llanitedave

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Re: Skepticism about reusability
« Reply #48 on: 12/13/2015 06:25 AM »
By the way, the fuel cost of a 7-person Dragon launched on F9FT is about $70k per person (I'm using round numbers for LOX and RP1).  So, that's how much it would cost if the entire system were free, fully-reusable, didn't require any ground personnel to assemble or fuel it for launch, and lasted forever.

Still kind of pricey if you want to make a new civilization on a new planet, and that doesn't include the cost of getting from LEO to that planet, getting from planetary orbit to the surface, or the cost of the infrastructure on that planet (which could well be in the billions per person).


But those other costs have little or nothing to do with whether the vehicle is chemical or not.  So essentially your argument boils down to "Humans will never expand beyond Earth.  Period."
"I've just abducted an alien -- now what?"

Offline MP99

Re: Skepticism about reusability
« Reply #49 on: 12/13/2015 07:24 AM »
It isn't just the cost of refurbishment.  It is the loss of capability.  Falcon 9 v1.1, for example, could not do useful GTO missions if first stage recovery was attempted.  Falcon Heavy will only lift 6.5 tonnes to GTO (GEO-1800 m/s) with full recovery while weighing perhaps 1,400 tonnes at lifoff - nearly 70% as much as STS.  Compare that with Atlas 521, which can lift about as much while weighing only 429 tonnes at liftoff.  Or Ariane 64, which will lift 11 tonnes to GEO-1500 m/s while weighing 800 tonnes.  Or Proton M, which can lift nearly as much to GEO-1500 m/s for half the liftoff mass despite launching from 46 degrees latitude.

 - Ed Kyle

I would expect SpaceX to be pretty cautious about extending the number of flights per core, but ISTM there is a learning curve and risks to be retired.

Hopefully the benefits of using proven hardware will outweigh those risks, but that's not a given until demonstrated. IE failure rate on reflights is lower than failure rate on first flights.

Cheers, Martin

Offline MP99

Re: Skepticism about reusability
« Reply #50 on: 12/13/2015 07:27 AM »
We aren't going to expand beyond Earth on chemical rockets.  Period.

Why not? Question mark.

2-3% of glow gets to LEO.  Way less beyond that.

Way too much material usage, way too expensive (factor of 10,000).

You give a relative statements without providing an alternative to compare them to. Your words do not make sense to me.

Also, what does this has to do with reusability?
It is a statement that even reusability is insufficient for his goals.

Cheers, Martin

Offline TrevorMonty

Re: Skepticism about reusability
« Reply #51 on: 12/13/2015 09:57 AM »
Thanks for the answer. I do agree with you that re-usability cuts heavily into GTO missions, especially since the Falcon family lacks a high energy/efficiency second stage to compensate.

This is uninformed speculation on my part but I wonder if reusable SEP tugs will one day make only the LEO capability important for chemical stages.

There are also quite different possibilities like solar thermal and rotovators. In any case a reusable vehicle from LEO to GTO feels technically easier than reuse from ground to LEO. I imagine the problem is more that the trajectory itself may not be reusable. You might not want to throw anything in that particular direction again for a while.

Reusable chemical LEO to GEO space tugs could enable small RLVs to launch GEO satellites. The SES 9 is 5330kg, of which approx 2800kg is made up of chemical engines, tanks and fuel to get it from GTO to GEO. The actual satellite and its station keeping SEP + fuel only weigh approx 2500kg.
 For 4 launches (3 fuel + 1 satellite) a 2500kg RLV could deliver an SES 9 satellite direct to GEO and return the to LEO for next mission. The satellite would also be cheaper as there is no need for the GTO-GEO chemical propulsion system.

What is need is a orbit refueling of tug 460 ISP LOX/LH, long endurance of tug eg ULA IVF and ability to transfer payload from upper stage to tug.


Offline DarkenedOne

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Re: Skepticism about reusability
« Reply #52 on: 12/13/2015 12:06 PM »
We aren't going to expand beyond Earth on chemical rockets.  Period.

Why not? Question mark.

2-3% of glow gets to LEO.  Way less beyond that.

Way too much material usage, way too expensive (factor of 10,000).

You give a relative statements without providing an alternative to compare them to. Your words do not make sense to me.

Also, what does this has to do with reusability?
It is a statement that even reusability is insufficient for his goals.

Cheers, Martin

Ultimately I agree that the days of chemical power in spaceflight are limited.  Eventually nuclear rockets will be used for launch because their payload ratios are significantly better due to much high ISP, but the capital costs of the rocket will likely be significantly higher then chemical.  Such rockets must be fully reusable to make any sense.

Reusability can potentially drive down costs to a bit over a million dollars per flight for a rocket the size of a Falcon 9. 

Offline DarkenedOne

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Re: Skepticism about reusability
« Reply #53 on: 12/13/2015 12:09 PM »

IOW: The fact that chemical fuel is used is not the cause of current high launch costs. It is responsible for ~1% of these costs.

Bingo. People can moan about chemical propulsion holding us back from spreading off this rock, but it ISN'T. It is an *insignificant* part of launch costs, and the REAL cause of our launch costs being high is that we keep throwing away hardware - not chemical propulsion.

That is definitely true at the moment.  Cost of the hardware expended in each launch dwarfs practically all other costs, but once we have fully reusable rockets then increasing payload ratios will be the next frontier for space launch improvement. 

Offline dror

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Re: Skepticism about reusability
« Reply #54 on: 12/13/2015 12:18 PM »
Thanks for the answer. I do agree with you that re-usability cuts heavily into GTO missions, especially since the Falcon family lacks a high energy/efficiency second stage to compensate.

This is uninformed speculation on my part but I wonder if reusable SEP tugs will one day make only the LEO capability important for chemical stages.

There are also quite different possibilities like solar thermal and rotovators. In any case a reusable vehicle from LEO to GTO feels technically easier than reuse from ground to LEO. I imagine the problem is more that the trajectory itself may not be reusable. You might not want to throw anything in that particular direction again for a while.

Reusable chemical LEO to GEO space tugs could enable small RLVs to launch GEO satellites. The SES 9 is 5330kg, of which approx 2800kg is made up of chemical engines, tanks and fuel to get it from GTO to GEO. The actual satellite and its station keeping SEP + fuel only weigh approx 2500kg.
 For 4 launches (3 fuel + 1 satellite) a 2500kg RLV could deliver an SES 9 satellite direct to GEO and return the to LEO for next mission. The satellite would also be cheaper as there is no need for the GTO-GEO chemical propulsion system.

What is need is a orbit refueling of tug 460 ISP LOX/LH, long endurance of tug eg ULA IVF and ability to transfer payload from upper stage to tug.
Now that's reusability!
Not only the LV needs to be reuesd but also the inspace propulsion and the design. The most important factor of this architecture is the reduction of the satellite's price because that will drive the market's elasticity.
That's why I'm a keen supporter of Jupiter for CRS2.
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Offline Lee Jay

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Re: Skepticism about reusability
« Reply #55 on: 12/13/2015 01:12 PM »
By the way, the fuel cost of a 7-person Dragon launched on F9FT is about $70k per person (I'm using round numbers for LOX and RP1).  So, that's how much it would cost if the entire system were free, fully-reusable, didn't require any ground personnel to assemble or fuel it for launch, and lasted forever.

Still kind of pricey if you want to make a new civilization on a new planet, and that doesn't include the cost of getting from LEO to that planet, getting from planetary orbit to the surface, or the cost of the infrastructure on that planet (which could well be in the billions per person).


But those other costs have little or nothing to do with whether the vehicle is chemical or not.  So essentially your argument boils down to "Humans will never expand beyond Earth.  Period."

They have everything to do with the fuel being chemical.  If we had some sort of safe, reliable fusion rocket, we might be able to take it from Earth's surface to Mars' surface numerous times without refueling or refurbishing, and that's what it's going to take to create an off planet civilization.

Offline Remes

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Re: Skepticism about reusability
« Reply #56 on: 12/13/2015 01:24 PM »

IOW: The fact that chemical fuel is used is not the cause of current high launch costs. It is responsible for ~1% of these costs.

Bingo. People can moan about chemical propulsion holding us back from spreading off this rock, but it ISN'T. It is an *insignificant* part of launch costs, and the REAL cause of our launch costs being high is that we keep throwing away hardware - not chemical propulsion.
You are right saying fuel is inexpensive. But somehow the conclusion is wrong, because the fact that we need so much of this inexpensive liquid means that we need really big tanks (5m dia, 8m dia, ...). Lot of (very light weight, very reliable and therefore expensive) material, lot of expensive tooling and machines, lot of handling,...

The fact that there is so much inexpensive liquid means, that there is lot of weight which must be lifted. So we need lot of powerful engines (very light weight, very reliable, very much tested, ...). Because of the powerful engines all components are much bigger (valves which deliver hundreds of liter per second rather than hundred of liters per minute, tvc, pressurization, launch pad, ...).

And so on.

----

Yep, I also doubt the economical part of reuse. To much rocket equation to make wall street work here.

But on the other hand: when SpaceX figures out that reuse doesn't work economically: cut off the legs, strip down the fins, strip down the first stage landing electronics/mechanics (imu, computer, thrusters, thermal...) and voila: a very inexpensive, very versatile and cheap family of rockets for a wide range of payloads (F9 + F9 heavy). Perfectly suited for LEO and GTSO. Perfect crew transporter, because enhancements can be tested on cargo variant and due to gas generator cycle rather medium complexity and risk.

Online Johnnyhinbos

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Re: Skepticism about reusability
« Reply #57 on: 12/13/2015 01:41 PM »
Sorry, but some of the posts here amaze me. I feel that people are stuck in the past and have lost all ability to understand creativity and thinking (ugh, hate this term) out of the box.

Talking about reuse while using the past as your measuring stick just doesn't work. Why did reuse fail in the past? How is what SpaceX is working towards different? The differences are night and day.

For example, SpaceX isn't ditching boosters in the ocean (and obviously not using SRBs at all), F9Rs aren't covered with finicky TPS tiles that require huge human resources to refurbish and QA. SpaceX isn't using ablative nozzles on their motors. The list goes on - point being, you have to be forward thinking instead of dogmatic. It's that kind of thinking which is the real reason humans will never got off this planet.
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Offline Remes

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Re: Skepticism about reusability
« Reply #58 on: 12/13/2015 02:02 PM »
I feel that people are stuck in the past
Past rocket physics is still current rocket phsics. :)

Edit: Or to say it in different words: it's very much useless to claim that "some people" are stuck in the past. You can discuss the topic or you can discuss "meta-things" like beeing stuck in the past or lacking any creativity. To discuss the topic: point out to what physical law/material science/economical issue from the past people are stuck to and what is new nowadays. If there is a lack of creativity: what creative measure has SpaceX taken not to add a tremendous amount of weight to the first stage, to loose a lot of payload capability and still only recovering (if at all) the first stage (which is only one part of the total cost) and what measures are taken to keep refurbishment costs down?
« Last Edit: 12/13/2015 02:23 PM by Remes »

Offline Dante80

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Re: Skepticism about reusability
« Reply #59 on: 12/13/2015 02:10 PM »

IOW: The fact that chemical fuel is used is not the cause of current high launch costs. It is responsible for ~1% of these costs.

Bingo. People can moan about chemical propulsion holding us back from spreading off this rock, but it ISN'T. It is an *insignificant* part of launch costs, and the REAL cause of our launch costs being high is that we keep throwing away hardware - not chemical propulsion.
You are right saying fuel is inexpensive. But somehow the conclusion is wrong, because the fact that we need so much of this inexpensive liquid means that we need really big tanks (5m dia, 8m dia, ...). Lot of (very light weight, very reliable and therefore expensive) material, lot of expensive tooling and machines, lot of handling,...

The fact that there is so much inexpensive liquid means, that there is lot of weight which must be lifted. So we need lot of powerful engines (very light weight, very reliable, very much tested, ...). Because of the powerful engines all components are much bigger (valves which deliver hundreds of liter per second rather than hundred of liters per minute, tvc, pressurization, launch pad, ...).

And so on.

Yep, thats how it works. And thats one of the main reasons to strive for re-usability too. Fuel is cheap, but the hardware is expensive. If you can re-use the hardware reliably, then you are better off.

And SpaceX is not the only one striving for re-usability.
« Last Edit: 12/13/2015 02:11 PM by Dante80 »

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