Author Topic: Raptor Upper Stage consolidated thread  (Read 58968 times)

Online punder

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Re: Raptor Upper Stage consolidated thread
« Reply #340 on: 07/02/2017 08:15 PM »

Yes, I think the FH needs a heavier upper stage, because the payload capability with 3-core reuse is too low, probably only 8 tons to GTO.  Which is less than Ariane V at 10t, and Delt 4H at 13t.

Of course 3-core reuse is ideal, but what is the payload with full expendable? That is the valid comparison.

Offline AncientU

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Re: Raptor Upper Stage consolidated thread
« Reply #341 on: 07/02/2017 08:23 PM »

Yes, I think the FH needs a heavier upper stage, because the payload capability with 3-core reuse is too low, probably only 8 tons to GTO.  Which is less than Ariane V at 10t, and Delt 4H at 13t.

Of course 3-core reuse is ideal, but what is the payload with full expendable? That is the valid comparison.

26.7 tonnes per SpaceX site, or a bit over 3x F9 expendable (8.3t) which makes sense.
F9 reusable with ASDS landing is around 5.5-6.0t, so FH should get 16-18t with boosters RTLS and core downrange recovery.  Definitely will outperform Ariane 5 and Delta Heavy.
« Last Edit: 07/02/2017 08:24 PM by AncientU »
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Offline MATTBLAK

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Re: Raptor Upper Stage consolidated thread
« Reply #342 on: 07/02/2017 10:17 PM »
There is actually little need for a Raptor powered upper stage for Falcon Heavy - though obviously that would be 'cool' in terms of performance etc. If they just stretched the upper stage propellant tanks a bit more and upgraded the Merlin vacuum engine again - most of the same benefits could be achieved. In fully expendable mode; FH could then get almost 70 metric tons into low Earth orbit, nearly 20 tons on Trans-Mars Injection and nearly 30 tons to GTO. Pretty darn good.

But this would probably be the best, 'bleeding edge' of FH performance. Anything more would likely require major redesign or a whole new design.
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Offline TomH

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Re: Raptor Upper Stage consolidated thread
« Reply #343 on: 07/02/2017 11:37 PM »
If they just stretched the upper stage propellant tanks a bit more and upgraded the Merlin vacuum engine again - most of the same benefits could be achieved. In fully expendable mode; FH could then get almost 70 metric tons into low Earth orbit, nearly 20 tons on Trans-Mars Injection and nearly 30 tons to GTO. Pretty darn good.

And a dual launch architecture of that could make a very robust and economic manned lunar program.

Offline MATTBLAK

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Re: Raptor Upper Stage consolidated thread
« Reply #344 on: 07/03/2017 12:05 AM »
If they just stretched the upper stage propellant tanks a bit more and upgraded the Merlin vacuum engine again - most of the same benefits could be achieved. In fully expendable mode; FH could then get almost 70 metric tons into low Earth orbit, nearly 20 tons on Trans-Mars Injection and nearly 30 tons to GTO. Pretty darn good.

And a dual launch architecture of that could make a very robust and economic manned lunar program.
Oh yes! We have a good thread about that somewhere round here - Dragon derivatives as the Command Module and Descent/Ascent vehicles etc ;)
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Offline Nathan2go

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Re: Raptor Upper Stage consolidated thread
« Reply #345 on: 07/03/2017 09:31 PM »

Yes, I think the FH needs a heavier upper stage, because the payload capability with 3-core reuse is too low, probably only 8 tons to GTO.  Which is less than Ariane V at 10t, and Delt 4H at 13t.

Of course 3-core reuse is ideal, but what is the payload with full expendable? That is the valid comparison.

26.7 tonnes per SpaceX site, or a bit over 3x F9 expendable (8.3t) which makes sense.
F9 reusable with ASDS landing is around 5.5-6.0t, so FH should get 16-18t with boosters RTLS and core downrange recovery.  Definitely will outperform Ariane 5 and Delta Heavy.
That calculation ignores the fact that you tripled the first stage, but are keeping the second stage the same.  Bringing back the first stage while maintaining good payload capability depends on keeping the staging velocity low, under Mach 7 for Falcon 9.  Landing a core downrange helps a bit, say Mach 9 single-core. 

Carrying a payload of 16t and a 4t vehicle to GTO, using 120t of propellant gives a Mr of  7.  This means that you have to stage at Mach 12...

Ok, I ran the calculations again, and I think you are correct.  With 3 core re-use, and the existing Falcon upper stage, I think the GTO payload will be about 15 tons.  For LEO, staging is around Mach 13, and payload will be about 40t.  These are rough calculations.

So there is still a significant benefit to payload capacity with upsizing the 2nd stage, but the existing stage is useful for FH.  I'm not sure why the SpaceX pricing table calls out 8t to GTO.
« Last Edit: 07/03/2017 09:32 PM by Nathan2go »

Offline Robotbeat

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Re: Raptor Upper Stage consolidated thread
« Reply #346 on: 07/03/2017 10:16 PM »
...market segmentation. Also allows them to perform upper stage reuse experiments, allow more margin for stage recovery, and maybe even secondary payloads.

Additionally, there's a good chance they think block 5 can do 8t, so that gives them the flexibility of two different configurations for launch.
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Offline Jim

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Re: Raptor Upper Stage consolidated thread
« Reply #347 on: 07/03/2017 10:27 PM »

Additionally, there's a good chance they think block 5 can do 8t, so that gives them the flexibility of two different configurations for launch.

that exactly opposite of what Spacex does

Offline Robotbeat

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Re: Raptor Upper Stage consolidated thread
« Reply #348 on: 07/03/2017 11:37 PM »

Additionally, there's a good chance they think block 5 can do 8t, so that gives them the flexibility of two different configurations for launch.

that exactly opposite of what Spacex does
If FH is unavailable for whatever reason, they could launch reusable FH payloads on expendable F9.

For instance, if LC39a is booked, they could launch from LC40 (which can only handle single stick) instead.

Intelsat 35e was originally FH, wasn't it?
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Online guckyfan

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Re: Raptor Upper Stage consolidated thread
« Reply #349 on: 07/06/2017 07:23 AM »
...market segmentation.

Been thinking about this. One thing you could do as a novel market segment might be effectively an ACES like concept as an unmanned high C3 missions "tug".

IMO ability to land a stage and lower cost of launch make an ACES like concept obsolete.

Offline R.Simko

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Re: Raptor Upper Stage consolidated thread
« Reply #350 on: 07/25/2017 02:58 PM »
I had an idea of how SpaceX can increase the wt of a payload a Falcon rocket can launch, or save fuel for second stage recovery.  My idea is to put springs on the second stage, that would launch the payload, like the shuttle use to do when launching satellites. 

The spring could give the payload extra delta-v, while acting to slow the second stage at the same time, thereby saving fuel for recovery.  I don't know if this is practical because of the extra wt of the springs or other considerations.

Offline Bynaus

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Re: Raptor Upper Stage consolidated thread
« Reply #351 on: 07/25/2017 03:02 PM »
I had an idea of how SpaceX can increase the wt of a payload a Falcon rocket can launch, or save fuel for second stage recovery.  My idea is to put springs on the second stage, that would launch the payload, like the shuttle use to do when launching satellites. 

The spring could give the payload extra delta-v, while acting to slow the second stage at the same time, thereby saving fuel for recovery.  I don't know if this is practical because of the extra wt of the springs or other considerations.

The energy density of a spring is very low compared to the fuel it would replace. So as you suspect, its not practical.

Offline R.Simko

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Re: Raptor Upper Stage consolidated thread
« Reply #352 on: 07/25/2017 03:10 PM »
I had an idea of how SpaceX can increase the wt of a payload a Falcon rocket can launch, or save fuel for second stage recovery.  My idea is to put springs on the second stage, that would launch the payload, like the shuttle use to do when launching satellites. 

The spring could give the payload extra delta-v, while acting to slow the second stage at the same time, thereby saving fuel for recovery.  I don't know if this is practical because of the extra wt of the springs or other considerations.

The energy density of a spring is very low compared to the fuel it would replace. So as you suspect, its not practical.

Thanks Bynaus, I thought that might be the case.

Offline ZachF

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Re: Raptor Upper Stage consolidated thread
« Reply #353 on: 09/11/2017 12:31 PM »
"Despite describing the Block 5 as the final version of the Falcon 9, Shotwell hinted at the possibility of a future version of the rocket that could use the Raptor engines designed for transportation to Mars. Shotwell said Raptor, a liquid methane and oxygen engine for SpaceX’s interplanetary spaceship, has undergone “many dozens of tests” and is progressing well.

“The original idea for those engines were to serve as a propulsion system for the big Mars system, but we are looking at the utility of it on the Falcon program,” she said."

I think of of the reasons why they are changing their mind about using raptor in falcon rocket is that originally they thought they cannot land raptor-based falcon first stage because of too high minimum T/W, but now they are getting confident that they can do it, and they already proved the minimum T/W is not too high by landing the bulgariasat booster with 3 merlin 1d engines.

We have not had any evidence to show they are chaining their mind about a Raptor US. We have one off the cuff comment that they might take a look at it. That's all. Their investigation may be as simple as "We reckon this is a stupid idea, just go and confirm it is"

I've with Jim on this one, it just doesn't seem to have any real reason for existence. Test bed for Raptor? Nah. Not needed. Makes the stage reusable? Nah, too expensive to implement and would never make the cash back. Need for bigger payloads? Nah, not enough payloads to make it pay.

The only thing I can think of that might make a Raptor engined stage on top of an F9 even vaguely useful would be a custom combined stage/satellite dispenser for the constellation. That might be cost effective if they are able to make it reusable.

What a Raptor US +B5 would allow, is launching the average sized GEO satellite to GTO and having the booster RTLS. 

It's not hard, with a faster launch cadence, to see the slow-moving ASDS ship as a potential bottleneck. Raptor US may be unlikely, but this fact with the fact that they have been testing MiniRaptor probably makes this less unlikely than some think.

I personally think they are going to develop 2 Raptors, one 3MN sea level version and a ~1.4MN vac verson based off the ~1MN test version. 18 Raptor3Ss fit perfectly in a 9m frame for the first stage, and 6 ~1.4MN vacuums with one SL in the middle fit well enough to even increase the vacuum version's expansion ratio slighty and perhaps get a few more seconds of ISP. 18 3MN Raptors would also give a BFR 42% of the GTOW of ITS2016 a slightly better liftoff TWR (1.47vs1.38). With a slighty higher liftoff TWR and slightly higher second stage ISp, SpaceX might be able to meet their performance goals with less aggressive materials development.

Online MikeAtkinson

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Re: Raptor Upper Stage consolidated thread
« Reply #354 on: 09/11/2017 01:47 PM »
What a Raptor US +B5 would allow, is launching the average sized GEO satellite to GTO and having the booster RTLS. 

It's not hard, with a faster launch cadence, to see the slow-moving ASDS ship as a potential bottleneck. Raptor US may be unlikely, but this fact with the fact that they have been testing MiniRaptor probably makes this less unlikely than some think.

There are only about 20 GEO satellites a year maximum that SpaceX could launch, that is not enough for launch cadence with ASDS return to be a limiting factor.

There are perhaps good reasons for Raptor US + B5 but launch cadence for GEO sats is not one of them.

Offline wannamoonbase

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Re: Raptor Upper Stage consolidated thread
« Reply #355 on: 09/11/2017 03:02 PM »
There are perhaps good reasons for Raptor US + B5 but launch cadence for GEO sats is not one of them.

Enabling US recovery is about the most powerful reason I can think of, but is it needed or can it wait for ITSy?

The Block 5 F9 could easily dominate the global launch market with disposable US. 

A change in the launch market is needed to justify further development.
Excited to be finally into the first Falcon Heavy flow, we are getting so close!

Offline Nomadd

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Re: Raptor Upper Stage consolidated thread
« Reply #356 on: 09/11/2017 04:40 PM »
What a Raptor US +B5 would allow, is launching the average sized GEO satellite to GTO and having the booster RTLS. 

It's not hard, with a faster launch cadence, to see the slow-moving ASDS ship as a potential bottleneck. Raptor US may be unlikely, but this fact with the fact that they have been testing MiniRaptor probably makes this less unlikely than some think.

There are only about 20 GEO satellites a year maximum that SpaceX could launch, that is not enough for launch cadence with ASDS return to be a limiting factor.

There are perhaps good reasons for Raptor US + B5 but launch cadence for GEO sats is not one of them.
ASDS can be a limiting factor no matter what. It can break, need upgrades, spend two months getting through an ABS inspection for stupid reasons or be unavailable for lots of reasons. Any one of which could wind up putting $30 million in 1st stage hardware on the bottom.

Online guckyfan

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Re: Raptor Upper Stage consolidated thread
« Reply #357 on: 09/11/2017 04:51 PM »
What a Raptor US +B5 would allow, is launching the average sized GEO satellite to GTO and having the booster RTLS. 

It's not hard, with a faster launch cadence, to see the slow-moving ASDS ship as a potential bottleneck. Raptor US may be unlikely, but this fact with the fact that they have been testing MiniRaptor probably makes this less unlikely than some think.

A Raptor upper stage would be more expensive than a Merlin upper stage. Not worth it unless it is reusable. First stage RTLS is desirable but not nearly enough to justify expending a Raptor upper stage.

Offline titusou

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Re: Raptor Upper Stage consolidated thread
« Reply #358 on: 09/30/2017 01:50 AM »
Based on IAC 2017 info on BFR, Raptor now seems down-sized from 3000kN class to 1700kN class.
That's closer to Merline1D(Vac)'s 900kN class.

Maybe that make the Falcon9 with Raptor upper more likely to happen?

Titus

Offline octavo

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Re: Raptor Upper Stage consolidated thread
« Reply #359 on: 09/30/2017 06:43 AM »


Based on IAC 2017 info on BFR, Raptor now seems down-sized from 3000kN class to 1700kN class.
That's closer to Merline1D(Vac)'s 900kN class.

Maybe that make the Falcon9 with Raptor upper more likely to happen?

Titus

Since Musk explicitly said that they're trying to make f9 and FH redundant, I think if anything we can now categorically put this to bed. There will be no raptor US for any Falcon rocket. Their focus now is FH and dragon 2, then straight on to BFR/BFS

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