Author Topic: Possible role of fully reusable Raptor-based F9/H 2nd stage for accelerating MCT  (Read 15896 times)

Online Robotbeat

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If a Raptor-based upper stage is developed for Falcon 9 and Heavy, I expect it will be intended to be reusable. Here is a progression I see as making sense and accelerating the MCT architecture:

1) 5 meter Raptor US on Falcon 9 and Heavy. 2018-2019 timeframe. High enough performance that they can put PICA-X and maybe Superdracos on it to attempt recovery very soon. But like booster recovery, it will be designed to be affordable even if upper stage reuse isn't initially successful.

2) After full reuse is then demonstrated, they can then build the full BFR launch pad somewhere. Might be hard to find a good place, so first launch in 2021, however it'll use the same 5meter Raptor upper stage as has already flown on the Falcons.

3) Falcon Heavy is phased out once BFR is successfully introduced, 2023.

4) At around the same time, the full BFS is tested. This dramatically expands capability, but many commercial launches will still use the much smaller upper stage.

First missions to Mars would occur on the upgraded Falcon Heavy in the 2018-2020 timeframe. Like a Red Dragon or something. Validates full BFS going around 2022/2024.
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Online Robotbeat

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The advantage of this approach is that it allows Raptor to be used for paying customers ASAP, thus paying for further development. It also gets SpaceX to full reuse ASAP while significantly reducing the development/cost/schedule risk of 2nd stage reuse, since you're developing it at like a 1/5th or 1/10th scale and can use paying customer launches to test the recovery methods, just like SpaceX did with F1 and F9 (all versions), without losing a lot of expensive hardware each time recovery fails.

And for small payloads, it probably makes more sense to use a fully reusable F9 (even if you still have kerosene first stage) than it does to use a whole BFR/BFS launch.

According to Shotwell, a fully reusable F9 was supposed to cost around $7 million (+/- 50%) per launch. I doubt a fully BFR launch would ever get that low, but this way it doesn't have to. But I do think that a fully reusable BFR+5mRaptor stage would be cheaper than a fully reusable Falcon Heavy, and refurbing the smaller stage would be cheaper. So this allows SpaceX the ability to service the full commercial market for very cheap while also accelerating the MCT-relevant development feedback loop and reducing business case risk.

It would further strengthen the moat that SpaceX is building around its affordable launch business using reuse to the point of being virtually unassailable for over a decade, even with great effort. Even if the enormously expensive (and overly technically ambitious... making X-33 engineers blush) Skylon project were successful, it wouldn't likely be able to compete with that.

If instead SpaceX did BFR/BFS and only BFR/BFS, they'd be leaving a big gap in cost per launch that smaller RLVs could fit through and end up out-flying SpaceX, thus undermining SpaceX's business plan.
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Offline sanman

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Makes sense - reminds me of the late 90s, when Intel focused on developing their next-generation 64-bit Itanium chip, only to be undercut by AMD which developed its 64-bit Athlon chip on existing x86 technology, thus penetrating the gap left open by Intel.

What aspects of MCT/BFS could be tested out on the F9H upper stage? Which technologies, subsystems, or components would F9H Raptor stage be best suited to flight-test? What might the evolutionary upgrade path for this upper stage look like?


Online Robotbeat

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The whole upper stage recovery problem is actually harder than first stage recovery.
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Offline docmordrid

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>
What aspects of MCT/BFS could be tested out on the F9H upper stage? Which technologies, subsystems, or components would F9H Raptor stage be best suited to flight-test? What might the evolutionary upgrade path for this upper stage look like?

ISTM an ACES like reusable stage allows you to test S2 reusability (duh), autogenous lox and methane systems, tanker and prop transfer technologies etc. in a subscale (vs BFS) platform. Iterate upwards in size.
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Offline sanman

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What launch markets could this stage be particularly enabling for?

Bigger/better platforms in Earth orbit?
Bigelow habs?
Orbital depots?
SLS-comparable payloads?
Lunar missions?

Would it compete with SLS?

If you consider that the Moon might likewise be a nearer testing ground for some Mars-bound technologies, then would this F9H Raptor upper stage then facilitate lunar missions?

Offline sdsds

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Now that SpaceX has demonstrated hypersonic retropropulsion the natural question is, "Well, what can you do with that?"

The notion that there's any amount of propellant that can get a rocket stage from orbit to hovering is mind-boggling. Figuring out if some added heat shielding or aerostructural mass could reduce the required amount of propellant could take a fair bit of experimenting. The Raptor second stage on Falcon seems like it could provide the needed opportunities for that.
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Offline xanmarus

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What about transportation of 5m second stage?

Offline john smith 19

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Musk has stated there will be no development of upper stage reusability on either F9 or FH hardware.

Why would you not take his words at face value?
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Online RotoSequence

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I don't have more than a gut feeling for this, but I'd push the timeline back five years for the introduction of the MCT, towards 2028 or so. It ultimately took SpaceX almost ten years to get where they wanted to be with the Merlin, so I'd expect them to take a few years to get the Raptor where they want it to be. Raptor flight engineering would probably keep the design of the MCT in some degree of flux as well.
« Last Edit: 01/19/2016 09:37 AM by RotoSequence »

Offline Hauerg

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Musk has stated there will be no development of upper stage reusability on either F9 or FH hardware.

Why would you not take his words at face value?
Because then was then and now is now.
The context may have changed enough.

Offline The Amazing Catstronaut

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I don't have more than a gut feeling for this, but I'd push the timeline back five years for the introduction of the MCT, towards 2028 or so. It ultimately took SpaceX almost ten years to get where they wanted to be with the Merlin, so I'd expect them to take a few years to get the Raptor where they want it to be. Raptor flight engineering would probably keep the design of the MCT in some degree of flux as well.

True, but most merlin iteration was done on F9s, not F1s. Proof of concept + initial tweaking on F9 and FH, then straight on to the second generation raptor on BFR, with most of the optimisation done on BFR. All doable by the early 2020s.
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Offline JamesH

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Musk has stated there will be no development of upper stage reusability on either F9 or FH hardware.

Why would you not take his words at face value?

I generally do take his words at face value, but the reason for not having a F9/h second stage return was money. And the money situation is something that CAN change, it not being an immutable law of physics,  as shown by the Air Force Raptor contract.

Whether they do it? Up to them of course, I'm thinking they won't.

Online Robotbeat

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I've come to the realization that SpaceX changes plans quite a lot, and sometimes rapidly. I can point to several examples here, but I think you're all aware of them.

There's no reason for SpaceX to develop a new stage for Falcon 9/ Heavy unless it's reusable. Falcon Heavy can already launch everything while recovering the booster stages. Adding an expendable Raptor would make the per launch more expensive. They originally planned a reusable upper stage, but kerolox is not quite hi enough performance to be worthwhile. Methane is.
« Last Edit: 01/19/2016 11:53 AM by Robotbeat »
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Offline john smith 19

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I generally do take his words at face value, but the reason for not having a F9/h second stage return was money.
A curious way to put it. IIRC Musk called it "uneconomic" to do upper stage reuse due to the limited performance of LOX/RP1. Exactly why it is inadequate remains extremely vague.
Quote
And the money situation is something that CAN change, it not being an immutable law of physics,  as shown by the Air Force Raptor contract.

Whether they do it? Up to them of course, I'm thinking they won't.
No I don't think they will either.
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline The Amazing Catstronaut

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I've come to the realization that SpaceX changes plans quite a lot, and sometimes rapidly. I can point to several examples here, but I think you're all aware of them.



Which is a good thing. Situations change ridiculously quickly.

I wonder if raptor stage 2 is a response to ACES?
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Offline docmordrid

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My bet is that it's an ACES-X with a built-in path to reusability and tankers, testing techs for BFS while giving USAF a redundant ACES class functionality.
« Last Edit: 01/19/2016 12:50 PM by docmordrid »
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Offline dkovacic

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I generally do take his words at face value, but the reason for not having a F9/h second stage return was money.
A curious way to put it. IIRC Musk called it "uneconomic" to do upper stage reuse due to the limited performance of LOX/RP1. Exactly why it is inadequate remains extremely vague.
Quote
And the money situation is something that CAN change, it not being an immutable law of physics,  as shown by the Air Force Raptor contract.

Whether they do it? Up to them of course, I'm thinking they won't.
No I don't think they will either.
Whole upper stage reuse might be "uneconomic" for a different reason. F9 upper stage could be made reusable from both LEO and GEO, perhaps even easier than the first stage technically. For upper stage, you don't need main engine relight or supersonic retropropulsion at all. You need new set of engines (such as SuperDracos), fuel/propellant for 200-300m/s delta-v, heat shield and landing legs or helicopter mid-air recovery.

If we estimate performance hit of 2000kg for upper stage landing kit (note - dragon has estimated dry mass of 4200kg, so that is not unreasonable assumption), that is LESS than estimated performance hit for 1st stage re-usability (15% to 33% of LEO mass). Since main propulsion engine and propellants (Merlin using RP-1/LOX) is not used during reentry, landing kit can be easily operational for days and possibly weeks after launch without any passive or active cooling. Therefore the same barge could be used for reentry event when using Draco/SuperDraco with MMH/NTO.

So I think the real reason for "uneconomic" upper stage reuse is not technological, but business oriented:

1. Upper stage is not 35% of the cost, but much lower. It has 9x engine costs, and roughly 4x-5x smaller mass, using the same components as first stage. So it should be at least 3x times expensive than the first stage
2. SpaceX simply does not have enough resources to address reusability of the upper stage in parallel with Dragon development (matter of priorities)
3. Once both F9 stages are reusable, there would be significant pricing pressure for SpaceX to lower their launch prices, without significant increase of launch opportunities. That would lead to significant reduction of future revenues OR put them in the same position of market monopoly enjoyed previously by ULA. Even with just first stage reuse, we already see commercial customer pressure to lower their launch price (an example is SES request/offer/expectation to be the first customer for first stage reflight)

So pushing reusability to Raptor based upper stage enables SpaceX to focus on their weak spot (high energy trajectories) and develop a stage similar to ACES. So I think that the Raptor upper stage will be designed to enable reusability through modifications but will not support it initially, much like for the first stage. It will be added mainly to offer cost effective tests of MCT technologies.

EDIT: spelling corrections
« Last Edit: 01/19/2016 02:31 PM by dkovacic »

Online guckyfan

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So pushing reusability to Raptor based upper stage enables SpaceX to focus on their weak spot (high energy trajectories) and develop a stage similar to ACES. So I think that the Raptor upper stage will be designed to enable reusability through modifications but will not support it initially, much like for the first stage. It will be added mainly to offer cost effective tests of MCT technologies.

You assume a performance gap. I think there is none, at least not with Falcon Heavy coming. They can do anything up to Mars. The only gap they may have compared to ULA would be NASA missions beyond Mars and that can be helped with a kickstage as part of the payload.

To me reusability is the only conceivable reason to build a new methane upper stage for the Falcon family beside doing it for early experience with methane before BFR/MCT final design. And even there reentry for reuse would be the most valuable knowledge gained.

Offline ArbitraryConstant

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A curious way to put it. IIRC Musk called it "uneconomic" to do upper stage reuse due to the limited performance of LOX/RP1.
This is why the contract to work on a Raptor upper stage suggests reexamining this.

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