Ariane 6: solid vs. liquid

[woods170]

One issue with Araine 5 it's now too small for double GTO launches as a typical geostationary satellite today is nearly twice the mass one was back in the 80s but overkill for a single comsat.

Yeah, same problem that killed Ariane 4. For Ariane 5 it will be (temporarily) solved by the arrival of Ariane 5 ME. But that's it. After that they will have to revert back to single payload launches. Hence the main driver for Ariane 6.

[bobthemonkey]

Apparently insurers have been assigning lower risk and therefore premiums to single launches, compared to dual setups.

There was also some debate about finding suitable payloads for a dual manifest flight.

[spacediver]

The most interesting result is that all modular concepts, using a common core approach or strap-on-boosters, are not competitive to the “clean” inline designs.

Competitive is in the eye of the beholder. You can tweak your assumptions to get the outcome you want.

No, competitive is a matter of cost! If a certain configuration has 25% higher RC cost than another it will not be competitive vs. that other concept!

The three most promising concepts KH (kerolox first stage with NK-33 engines), HH (cryogenic first stage with Vulcain 3) and PPH (solid first and second stage in-line) have practically the same recurrent cost.

What about fixed vs variable costs?

Share of fixed cost is a bit higher for the liquid concepts, giving the solids a small advantage at low launch rates.

The small differences are well within the accuracy of our cost estimates.
Therefore, no economic justification for a solid Ariane-6 design can be derived from these results!   

Or against it.

Yes, but if cost can not drive the decision, I normally would choose the technology with the better future prospects. And that is definitely LOX/hydrogen!

BTW, no concept is able to meet the 70M Euro benchmark for 6,5t to GTO.

Interesting.

Taking into account the loss of crucial technology, for me the clear winner is a HH concept using 3 Vulcain-3 engines in the first stage for the large payloads (up to 6,5 t) and two engines on the same first stage with a 35% propellant offload for the small payloads (up to 3,5 t).

Do you work on liquid engines yourself?

No, not anymore.

The development cost for the HH concept are in the same range as for the solid concepts, but the development risk is much lower as the Vulcain engines are well understood and the V3 is directly derived from the V2. Also the main stage tank is nothing but a stretched version (with different wall thickness of course) of the existing EPC stage.

Did the study look at a triple Vulcain 2 variant?

No, the Vulcain 2 as used today has too low lift of thrust as it is optimized for altitude operation. You'd need at least 4-5 Vulcain 2 to get off the pad.

BTW: the Vulcain 3 I refer to is a low cost version of the Vulcain 2 with simplified components. Optimized for sea level operation with a much lower expansion ratio, lower ROF, slightly increased combustion pressure but still GG cycle.

[pippin]

Apparently insurers have been assigning lower risk and therefore premiums to single launches, compared to dual setups.

Source? Arianespace claims that Ariane 5 has the lowest insurance premiums in the business and they always do dual launches for commercial launches.

[spacediver]

The most interesting result is that all modular concepts, using a common core approach or strap-on-boosters, are not competitive to the “clean” inline designs.

The three most promising concepts KH (kerolox first stage with NK-33 engines), HH (cryogenic first stage with Vulcain 3) and PPH (solid first and second stage in-line) have practically the same recurrent cost. The small differences are well within the accuracy of our cost estimates.
Therefore, no economic justification for a solid Ariane-6 design can be derived from these results!   

BTW, no concept is able to meet the 70M Euro benchmark for 6,5t to GTO.

Taking into account the loss of crucial technology, for me the clear winner is a HH concept using 3 Vulcain-3 engines in the first stage for the large payloads (up to 6,5 t) and two engines on the same first stage with a 35% propellant offload for the small payloads (up to 3,5 t).

Interesting, can you provide us with a cost breakdown, core stage, vulcains, upper stage?

Have you also looked at the P7C design?

Of course I have all that data available, but I can not post it here. We made cost and mass breakdowns with 50 to 70 line items per launcher configuration. The cost estimates are based on information from external partners (e.g. engine manufacturers) and common cost estimation tools. That tools were calibrated to known cost breakdowns of existing launchers.

Yes, we also investigated a similar design like P7C.
It's RC cost is about 2% higher than for HH. It was one of the most expensive solid configurations that we investigated due to the high number (5) of propulsive modules.

[spacediver]

results from the NELS study

Thanks very much for providing this overview!

In addition to the questions from others:

for me the clear winner is a HH concept using 3 Vulcain-3 engines in the first stage for the large payloads (up to 6,5 t) and two engines on the same first stage with a 35% propellant offload for the small payloads (up to 3,5 t).

On other threads people have suggested propellant offload approaches like this, and had their ideas shot down by assertions from professionals that first stage propellant offloading just isn't done. (It came up most prominently in the AJAX thread, if I remember correctly. But also in discussions of other cores that might use 3 or 4 engines depending on the mission.) So, is this concept considered to be "low risk" in general? Or were there specific aspects of the core using Vulcain-3 engines that made it possible?

Prop offload was done with Ariane 40. the version without boosters. It could not lift off fully fueled.

If you look on the small launcher version isolated from the overall concept, it would be a bad design to use a too large fuel tank that you do not need, but regarding the fact that only 20% of the expected payloads are in the bandwidth of the "small" launcher it would not justify the development and production of a shorter tank version.
You'd need to run a separate production line, even if there is a high comonality in components, and you need to know very early in the production process if you need a standard or small launcher.

The cost saving is only one engine for the small launcher, but you can decide very late in the stage production process (only a few weeks prior to delivery of the stage) if you need to mount 2 or 3 engines.

The only real risk I see is some base heating problem when the center engine is missing, but this could be addressed by proper thermal protection design.

[mmeijeri]

No, competitive is a matter of cost! If a certain configuration has 25% higher RC cost than another it will not be competitive vs. that other concept!

You didn't respond to my main argument: you can tweak your assumptions to get the outcome you want. Just try a long list of slightly different assumptions, and see which makes your preferred solution come out best, then set that as your official goal. I'm sure that happens all the time. I've seen amusing examples of this relating defence spending of NATO countries to GDP, population, area, total length of borders, GDP/capita etc etc. Almost every country could point to a statistic that showed they were spending more than others. Remember, there are lies, damned lies and statistics!

Yes, but if cost can not drive the decision, I normally would choose the technology with the better future prospects.

Bear in mind the official goal of Ariane 6 is assured access to space for institutional payloads, not having state of the art propulsion technology. Also, the solids have commonality with ballistic missiles.

And that is definitely LOX/hydrogen!

I'm not so sure about that, neither LOX/LH2 nor solids are ideal as a first stage. They were meant to be used together, that doesn't mean either is good alone.

No, the Vulcain 2 as used today has too low lift of thrust as it is optimized for altitude operation. You'd need at least 4-5 Vulcain 2 to get off the pad.

Hmm, that does not match the numbers I've seen. You could also use a shorter EPC of course.

[Oli]

@spacediver

So did they give your team any reasons why your preferred design was not selected? How many different teams at different institutions/companies were doing such studies anyway?

Regarding the HH concept, how would the first stage compare to the A5 first stage? Propellant load, tank diameter etc.? Is there reason to believe it would be significantly cheaper? You know as a layman it just seems that about the only thing you save from A5 are the 2 boosters, which, to my limited knowledge, don't even remotely make up 40% of A5 launch costs...

Yes, we also investigated a similar design like P7C.
It's RC cost is about 2% higher than for HH. It was one of the most expensive solid configurations that we investigated due to the high number (5) of propulsive modules.

So how would you judge their 70m/launch target? Delusional? Maybe they're just trying to shoot down the whole ariane 6 program 

[spacediver]

You didn't respond to my main argument: you can tweak your assumptions to get the outcome you want. Just try a long list of slightly different assumptions, and see which makes your preferred solution come out best, then set that as your official goal. I'm sure that happens all the time. I've seen amusing examples of this relating defence spending of NATO countries to GDP, population, area, total length of borders, GDP/capita etc etc. Almost every country could point to a statistic that showed they were spending more than others. Remember, there are lies, damned lies and statistics!

So you accuse me, the whole team from different companies, our external partners, our ESA client and our supervising external experts from DLR and other institutions that we manipulated the study results according to our biases?
It is that really what you want to say?

BTW: There was hardly any room for assumptions. We had a bunch of hard requirements from ESA that we had to follow!

One of these requirements was first launch 2020 which threw any reusable or partly reusable solutions out of the scope.

[mmeijeri]

So you accuse me, the whole team from different companies, our external partners, our ESA client and our supervising external experts from DLR and other institutions that we manipulated the study results according to our biases?
It is that really what you want to say?

I didn't accuse anyone of anything. I said competitive is in the eye of the beholder. But yes, everyone is vulnerable to biases. Ask a solid propulsion expert for an answer, and you'll likely get one biased towards solids. If we ask a liquid propulsion person like yourself, we're more likely to get an answer that is biased towards liquids.

BTW: There was hardly any room for assumptions. We had a bunch of hard requirements from ESA that we had to follow!

Perhaps, and I'm happy to believe that's your opinion, but from here it's hard to agree or disagree without seeing the studies in question.

[mmeijeri]

As an aside, are you accusing decision makers of being biased towards solids?

[spacediver]

@spacediver

So did they give your team any reasons why your preferred design was not selected? How many different teams at different institutions/companies were doing such studies anyway?

No. The order came from highest ESA ranks. Even the ESA people that were our direct contacts were not happy with this decision.

For me it is clear that A6 had to be all solid no matter what the results of the studies would be. This is purely politically driven.

For me as a German tax payer it is a nightmare that my money will be used to subsidize french military missiles while our own technological capabilities will decline. I hope that our government will refuse to go that way but I doubt that they really will...

Regarding the HH concept, how would the first stage compare to the A5 first stage? Propellant load, tank diameter etc.? Is there reason to believe it would be significantly cheaper? You know as a layman it just seems that about the only thing you save from A5 are the 2 boosters, which, to my limited knowledge, don't even remotely make up 40% of A5 launch costs...

The first stage tank would be a stretched version (with thicker wall of course) of the A5 EPC. Same tank dome shape, same diameter. Could be made on existing tooling.
The cost reduction would come from the use of only one propellant trechnology (no more solid furl factory in Kourou necessary), less infrastructure cost, horizontal integration etc...

Nevertheless, as all the other concepts, it will never meet the 70M€ target

Yes, we also investigated a similar design like P7C.
It's RC cost is about 2% higher than for HH. It was one of the most expensive solid configurations that we investigated due to the high number (5) of propulsive modules.

So how would you judge their 70m/launch target? Delusional? Maybe they're just trying to shoot down the whole ariane 6 program 

No f***** way that any of the concepts will ever meet the 70M€ target. Not with the current political / industrial landscape.

Maybe it would be  better to stick with A5ME and take more time to develop a partly reusable system until 2030...

[spacediver]

As an aside, are you accusing decision makers of being biased towards solids?

Yes I do, and that is no secret!

Anyone in the European space community knows that ESA and CNES are pushing toward concepts that can subsidize the french military applications.
The Italians are pushing towards solids because of their VEGA which is, at least, something one could understand.

[spacediver]

So you accuse me, the whole team from different companies, our external partners, our ESA client and our supervising external experts from DLR and other institutions that we manipulated the study results according to our biases?
It is that really what you want to say?

I didn't accuse anyone of anything. I said competitive is in the eye of the beholder. But yes, everyone is vulnerable to biases. Ask a solid propulsion expert for an answer, and you'll likely get one biased towards solids. If we ask a liquid propulsion person like yourself, we're more likely to get an answer that is biased towards liquids.

We had external partners from both sides in our team.
And It's not so that all our team members have the same point of view that I have.
Within our team there are lots of colleagues that are quite fine with the solids...

[woods170]

The first stage tank would be a stretched version (with thicker wall of course) of the A5 EPC. Same tank dome shape, same diameter. Could be made on existing tooling.
The cost reduction would come from the use of only one propellant trechnology (no more solid furl factory in Kourou necessary), less infrastructure cost, horizontal integration etc...

Nevertheless, as all the other concepts, it will never meet the 70M€ target

Emphasis mine. That argument does not apply as long as Vega keeps flying.

No f***** way that any of the concepts will ever meet the 70M€ target. Not with the current political / industrial landscape.

Had you actually expected anything else? No single version of Ariane has ever met the predicted cost target. All versions turned out to be (in some occasions much) more expensive then advertised. That's why I don't buy the crap coming from Astrium that the Ariane-5 ME won't need any subsidies. And clearly, that has been recognized by ESA top-brass as well, because they openly questioned that claim.

Maybe it would be  better to stick with A5ME and take more time to develop a partly reusable system until 2030...

The benefits (regardless of them being financial or technical) of (partial) reusability are highly over-rated. IMO that is something a certain new-space company from Hawthorne will discover as well if and when they take reusability of their launchers to the full level. And that is a commercial effort. I don't give anything for (partial) reusable efforts when it's being paid for by an intergovernmental agency like ESA.

[edkyle99]

Anyone in the European space community knows that ESA and CNES are pushing toward concepts that can subsidize the french military applications.

I've wondered about such assertions, in the U.S. too when it comes to ATK and Aerojet.  How does pouring solid motors in Kourou (or SLS SRBs in Promontory) really help French (or U.S.) defense needs?  Military missiles usually use a different, more potent blend of propellant, for example.  Large numbers of military missile motors are needed for the arsenal, while only a relative handful of Ariane 6 or SLS motors would be poured.  No military missiles use any of the space launch tooling.  And so on.

 - Ed Kyle

[arkaska]

Anyone in the European space community knows that ESA and CNES are pushing toward concepts that can subsidize the french military applications.

I've wondered about such assertions, in the U.S. too when it comes to ATK and Aerojet.  How does pouring solid motors in Kourou (or SLS SRBs in Promontory) really help French (or U.S.) defense needs?  Military missiles usually use a different, more potent blend of propellant, for example.  Large numbers of military missile motors are needed for the arsenal, while only a relative handful of Ariane 6 or SLS motors would be poured.  No military missiles use any of the space launch tooling.  And so on.

 - Ed Kyle

R&D?

[Patchouli]

Would it even be possible to manrate the all solid Ariane 6?

[R7]

Would it even be possible to manrate the all solid Ariane 6?

Or 'comsat-rate' for that matter? All solids is going to be a rough ride.

[Lars_J]

Would it even be possible to manrate the all solid Ariane 6?

There really is no such thing as a "man rating". You make it as safe as you can.

The only question is how much risk you are willing to accept.