Author Topic: SpaceX advances drive for Mars rocket via Raptor power  (Read 666791 times)

Offline Lobo

  • Senior Member
  • *****
  • Posts: 6915
  • Spokane, WA
  • Liked: 672
  • Likes Given: 437
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #860 on: 04/13/2015 07:03 pm »
 
Unsure about the cause of the one that destroyed the pad (but I think that was the one where one engine shutdown right after liftoff, and so the computer shut the opposite engines down as they didnt' gimbal, and it lost thrust and fell back to the pad). 
 

From what I remember, but I don't have a source that one blew up before launch during fueling, killing many people who were near the pad. I may be confusing it with another accident.

Reading a little farther down the Wikipedia page (which I should have done at first):

Quote
Just before liftoff, the LOX turbopump in the #8 engine exploded (the pump was recovered from the debris and found to have signs of fire and melting), the shock wave severing surrounding propellant lines and starting a fire from leaking fuel. The fire damaged various components in the thrust section[41] leading to engine shutdown. The KORD computer intentionally shut off the opposing #7 and #19 engines after detecting abnormal pressure and turbopump speeds. Telemetry did not provide any explanation as to what shut off the other engines. Engine #18, which had caused the booster to lean over 45 degrees, continued operating until impact, something engineers were never able to satisfactorily explain. It could not be determined exactly why the #8 turbopump had exploded. Working theories were that either a piece of a pressure sensor had broken off and lodged in the pump, or that its impeller blades had rubbed against the metal casing, creating a friction spark that ignited the LOX.

After the accident, Vladimir Barmin, who was in overall charge of the launch facilities at Baikonour, demanded that a feature be installed in the KORD computer to prevent the engines from being cut off until at least 50 seconds into launch to prevent the vehicle from coming down on or around the pad again. [42] [43] The destroyed complex was photographed by American satellites, disclosing that the Soviet Union was building a Moon rocket.[37] The rescue system saved the spacecraft again. After this flight, fuel filters were installed in later models.[37] It also took 18 months to rebuild the launch pad and delayed launches. This was one of the largest artificial non-nuclear explosions in human history and was visible that evening 22 miles (35 kilometres) away at Leninsk (See Tyuratam).[44]
]


Online Robotbeat

  • Senior Member
  • *****
  • Posts: 39271
  • Minnesota
  • Liked: 25242
  • Likes Given: 12115
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #861 on: 04/13/2015 07:15 pm »

It's quite likely the Soviets simply couldn't afford a test stand to do these sorts of tests on (plus they were single-use, although they did do batch testing), but it meant the end of the program.

As I understood, it wasn't so much that they -couldn't- have built a stand for the N-1 1st stage (or maybe it was), but that that wasn't really that big of a deal to the Soviets.  Their methodology was to launch, and if it failed, analyzed the reason, fix it, and launch again.  Wash, rinse, repeat until successful.  I'd read somewhere that they'd planned 7 test launches to work out the issues.  That was normal for Soviet development and any failures were kept secret per Soviet poltics.  Only successes were let be known.

Politics, rather than engineering then killed off N-1 after we beat them to the moon.

Were the first D4 and AV boosters fully tested prior to their first flights?
Delta IV booster was fully test fired before its first flight (may not have been the same booster but instead a qualification booster). I don't know about Atlas V, but it was an evolution of the Atlas III (same basic engines).

And really, both vehicles had extensive development history before launch. A better analogy if you're talking a new rocket would be early rockets like Saturn V which were not mere evolutionary steps of previous rockets.
« Last Edit: 04/13/2015 07:22 pm by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Lobo

  • Senior Member
  • *****
  • Posts: 6915
  • Spokane, WA
  • Liked: 672
  • Likes Given: 437
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #862 on: 04/13/2015 07:32 pm »
If you read musks quote carefully (the one stated 2 pages back) he neverer  said that raptor changed in thrust, he simply stated where th. T/W optimum is. He just evaded to answer that question...

Yea, but I think that's a bit of a reach.  He was asked about an "official" power of Raptor at 1.5Mlbf, and responded that it looks like the optimum looks to be around 500klbs. 
Yes, it's possible he said that without meaning anything by it, but that would be fairly intentionally deceitful.  Why?  That doesn't realy seem like his style.  Vague, yes.  But deliberately deceitful?

I don't think he brings it up if there wasn't a reason for it...IMHO.
Please bear in mind that the cost of developing a rocket engine is roughly proportional to the thrust squared. Thus, a 500klbf Raptor could be as much as 10 times cheaper than a 1.6Mlbf one.

And as the first iteration in the Raptor brand, would make sense for 2018. considering cash flow between then and now! Then further iterations would benefit from the added cash flow of the first Raptor and SpaceX projects over the following 15 years  ;D

my half pound worth (inflation folks  :( )

Gramps

Yes, that would make a certain sense.  Start with a smaller Raptor and then build a larger one when you have a lot of real world telemetry on it.
However, two issues with that, IMO.

1)  Elon said recently in his Reddit comments:
Quote
Emily Shanklin indicated in late 2013 that the Raptor would be the first of a "family of engines" designed for the exploration and colonization of Mars. Could you elaborate on her wording, i.e. was she simply referring to a vacuum version and standard version, or do you plan on building multiple methane-based engines with significantly different thrust and size specifications?

[–]ElonMuskOfficial
Default plan is to have a sea level and vacuum version of Raptor, much like Merlin. Since the booster and spaceship will both have multiple engines, we don't have to have fundamentally different designs.

This plan might change.


2)  In Elon's recent Reddit comments, and has Robotbeat and others have pointed out, Elon mentions 500klbs as a target with the best T/W ratio. 
Quote
Thrust to weight is optimizing for a surprisingly low thrust level, even when accounting for the added mass of plumbing and structure for many engines. Looks like a little over 230 metric tons (~500 klbf) of thrust per engine, but we will have a lot of them :)

So a larger "Raptor 2" would get away from that, as would a high thrust "Block 2" version of the initial 500klb Raptor.  Why mention 500klbs as an efficient target when the plan is to blow that up wtih a much higher thrust new engine, or much higher trust version of the same engine?

Not saying you aren't right, but those would be my two sticking points with your speculation.

:-)


Offline Lobo

  • Senior Member
  • *****
  • Posts: 6915
  • Spokane, WA
  • Liked: 672
  • Likes Given: 437
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #863 on: 04/13/2015 07:56 pm »
Delta IV booster was fully test fired before its first flight (may not have been the same booster but instead a qualification booster). I don't know about Atlas V, but it was an evolution of the Atlas III (same basic engines).

And really, both vehicles had extensive development history before launch. A better analogy if you're talking a new rocket would be early rockets like Saturn V which were not mere evolutionary steps of previous rockets.

Yes, good point.  Thanks for the info there Robot.  :-)

So then was that Atlas III core fully tested on a test stand then, as it was quote a different core than the MA-5 powered Atlas II?
« Last Edit: 04/13/2015 07:57 pm by Lobo »

Offline Lobo

  • Senior Member
  • *****
  • Posts: 6915
  • Spokane, WA
  • Liked: 672
  • Likes Given: 437
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #864 on: 04/13/2015 08:14 pm »
Really?  I thought Elon and SpaceX typically talked about a 30% penalty for reuse, not a 100% penalty?
I think a 130mt fully reusable LV might be more like a 185mt expendable?  And a 120mt fully reusable LV like a 170mt expendable.  Which would be larger than Saturn INT-21, but not too much so.
I'd guess the booster would need around 15-19 Raptors to do that, with maybe 3 vacuum Raptors on the upper stage/MCT?
Or am I really off there?

Elon has said:
15% barge landing, upper stage expendable.
30% RTLS, upper stage expendable.
50% RTLS with upper stage reuse.

That is for Merlin 1D, Raptor will probably do a bit better because of its higher Isp.
If the MCT IS the upper stage, then there is no penalty for upper stage reuse (already need legs, TPS, landing thrusters to land on Mars, and Earth landing propellant comes from Mars).  This should make it possible to launch the MCT full of cargo.  Granted, most flights will be refueling flights, so there will be an upper stage reuse penalty for those.

Yes, if you look up thread this is exactly what I was saying.

Mike,
Thanks for that clarification.  I remembered the 30% number, but not the proper context.

Mike & Cyberpilot,
Yea, the more I think about it, and given Elon's Reddit comment about MCT being a "completely new architecture", that makes me think more and more like STS as in a "Space Transportation System", rather than a BFR/rocket with a reusable spacecraft (MCT) on it.  There's also this comment from Reddit:

Quote
In your recent MIT talk, you mentioned that you didn't think 2nd stage recovery was possible for the Falcon 9. This is due to low fuel efficiency of kerosene fuel, and the high velocities needed for many payloads (high orbits like Geostationary orbit). However, you also said that full reusability would be possible for the Mars Colonial Transporter launch vehicle.

What have you learned from flights of Falcon 9 that taught you

a) that reuse of its second stage won't be possible and

b) what you'll need to do differently with MCT to reuse its second stage.

[–]ElonMuskOfficial:
Actually, we could make the 2nd stage of Falcon reusable and still have significant payload on Falcon Heavy, but I think our engineering resources are better spent moving on to the Mars system.

MCT will have meaningfully higher specific impulse engines: 380 vs 345 vac Isp. For those unfamiliar, in the rocket world, that is a super gigantic difference for stages of roughly equivalent mass ratio (mass full to mass empty).

I get the impression here that MCT is analagous to a reusable F9US, not that it's being lofted by a 2nd stage as payload, as has been conventional wisdom previously.

And then this quote I cited to Gramps:

Quote
Emily Shanklin indicated in late 2013 that the Raptor would be the first of a "family of engines" designed for the exploration and colonization of Mars. Could you elaborate on her wording, i.e. was she simply referring to a vacuum version and standard version, or do you plan on building multiple methane-based engines with significantly different thrust and size specifications?

[–]ElonMuskOfficial
Default plan is to have a sea level and vacuum version of Raptor, much like Merlin. Since the booster and spaceship will both have multiple engines, we don't have to have fundamentally different designs.

This plan might change.

He speaks only of a sea level version of Raptor and "the booster" and a vacuum version of Raptor and  "the spaceship", without mentioning any sort dedicated 2nd stage, which would seem important if you are talking about the stages of MCT.  Otherwise I'd have expected him to have mentioned an upper stage and the spacecraft having the vacuum version of Raptor.

So yea, I'm really thinking there isn't "MCT" and "BFR", there's just "MCT".  MCT has two pieces, a reusable booster and a reusable spacecraft.   Just as STS had 3 pieces, the Orbiter, the ET, and the SRB's, but it was all just "STS".

And if you aren't counting MCT as payload, but as the part of the mass put into LEO, A 60mt dry spacecraft loaded with 100mt of cargo should only require a booster of approximately S-1C class], not 15Mlbf BFR class.  Saturn INT-21 could have put about that into LEO if you add it's ~120mt of payload plus the 45mt dry mass of the S-II.    Just picture the S-II as a spacecraft, that would have cabin area and cargo areas integrated into it, and then it's refueled in LEO.  It would have had quote a massive TLI or TMI capacity I would guess.

Perhaps MCT will essentially be a reusable Saturn INT-21 with the S-II being essentially a reusable spacecraft?

Which brings me back to my theory/speculation of a much smaller stack than has been conventional wisdom to this point, that Robotbeat has been challenging me on.
Robotbeat certainly makes a valid point about me not being able to prove this theory/speculation, but it's not idle speculation either.  Musk himself gave a few different hints in his Reddit interview, but nothing definitive.  And I may or may not be putting them together correctly.  :-)

Offline JasonAW3

  • Senior Member
  • *****
  • Posts: 2443
  • Claremore, Ok.
  • Liked: 410
  • Likes Given: 14
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #865 on: 04/13/2015 08:20 pm »
I seriously doubt ULA has any real intention on designing or building equipment to go to Mars.  Their main intent is to make as much money as possible by building throw away rockets for sat launches and cargl support of the ISS.

SpaceX started with the idea of going to Mars.  As hard as they are going, I have little doubt that they will succeed.
My God!  It's full of universes!

Online Robotbeat

  • Senior Member
  • *****
  • Posts: 39271
  • Minnesota
  • Liked: 25242
  • Likes Given: 12115
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #866 on: 04/13/2015 08:36 pm »
Yeah, ULA is more interested in the Moon. :)
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Lobo

  • Senior Member
  • *****
  • Posts: 6915
  • Spokane, WA
  • Liked: 672
  • Likes Given: 437
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #867 on: 04/13/2015 08:48 pm »
A few other random thoughts based on some of these clues by Elon:

Quote
[–]ElonMuskOfficial:
Actually, we could make the 2nd stage of Falcon reusable and still have significant payload on Falcon Heavy, but I think our engineering resources are better spent moving on to the Mars system.

MCT will have meaningfully higher specific impulse engines: 380 vs 345 vac Isp. For those unfamiliar, in the rocket world, that is a super gigantic difference for stages of roughly equivalent mass ratio (mass full to mass empty).

MCT is planned to be pretty darned light, if it would have a roughly equivalent mass ratio to a reusable F9US, which wouldn't have any systems or hardware associated with a crew as MCT will.    Hard to say how light that is, but if it's roughly the size of the S-II stage, which was 45mt dry, then ~60mt isn't an unreasonable guestimate at the spacecraft's dry mass, which has been thrown around here some.  (Although it's still only a guestimate).

Quote
[–]ElonMuskOfficial
Default plan is to have a sea level and vacuum version of Raptor, much like Merlin. Since the booster and spaceship will both have multiple engines, we don't have to have fundamentally different designs.

This plan might change.

The spacecraft will have multiple engines.    Let the speculation run on what that means exactly.  I wonder about four engines though.  Four would give pretty good power after a "low and slow" staging which will be desirable if the booster is to get back to the launch site.  That means the stack will need the spacecraft to have a lot of power at staging to take over.  Four Raptors is almost double the thrust of the S-II.  So it's a pretty good fit for ascent needs.
More importantly, a cluster of 4 on the surface of Mars means redundancy for liftoff.  I can't imagine more than two Raptors would be needed to lift off of Mars in it's 1/3g gravity.  That's 3Mlbs of equivalent lifting power.   So any pair of the four engines could be used to lift off.  I still think dedicated landing thruster engines will be used for safety and reliability (like Dv2), but this means an engine failure on Mars can be compensated for making a rescue contingency less likely.

And with MCT having just two pieces and LEO refueling, it should be able to handle NASA's desired HSF needs.   It can go to an L-point, and should be able to do a NEO without the need for development of a deep space Hab....it'll already be it's own deep space hab.  It can just go.  It just needs to keep enough fuel to get back to Earth.
It can do a Lunar mission easy enough, although it might need to be refueled in lunar orbit as it cannot be refueled on the surface.  That's easy enough, a 2nd MCT is fueled up in LEO along with it, and then both are sent to LOR to fuel up the lander, while the tanker does TEI and goes back to Earth.
But NASA's real goal is the Moon, and MCT will be designed from the start for that.  While there can be a lot of political resistance to cancelling SLS for MCT from purely a HLV standpoint, it becomes harder to justify when you add in the price tag for NASA do develop a Mars lander, Mars Ascent Vehicle, and Mars Transit Hab (Per NASA's conventional DRM's for Mars) on top of development and operation of SLS.   If the MCT LV itself isn't enough to cancel SLS, the fact it should pretty much be ready from the jump to handle NASA's BLEO HSF goals without much additional development might be what does.

Offline MikeAtkinson

  • Full Member
  • ****
  • Posts: 1980
  • Bracknell, England
  • Liked: 784
  • Likes Given: 120
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #868 on: 04/13/2015 09:54 pm »
MCT is planned to be pretty darned light, if it would have a roughly equivalent mass ratio to a reusable F9US, which wouldn't have any systems or hardware associated with a crew as MCT will.    Hard to say how light that is, but if it's roughly the size of the S-II stage, which was 45mt dry, then ~60mt isn't an unreasonable guestimate at the spacecraft's dry mass, which has been thrown around here some.  (Although it's still only a guestimate).

If we are right about the MCT being the spacecraft which is its own upper stage then one way of thinking about it is as having components:

1. Stage - tanks, main engine, TVC, landing legs, etc.
2. Fairing - structure to contain the payload, payload adapter, heat shield.
3. Long duration - solar panels, radiators, long range comms, cryocooler, etc. (possibly including SEL course correction).
4. Payload - hab or cargo.

I think it difficult to get all of the MCT components (not including payload - obviously) into 60 tonnes. I have yet to see a good bottom-up estimate of the MCT dry mass.

Offline Lobo

  • Senior Member
  • *****
  • Posts: 6915
  • Spokane, WA
  • Liked: 672
  • Likes Given: 437
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #869 on: 04/13/2015 11:21 pm »
MCT is planned to be pretty darned light, if it would have a roughly equivalent mass ratio to a reusable F9US, which wouldn't have any systems or hardware associated with a crew as MCT will.    Hard to say how light that is, but if it's roughly the size of the S-II stage, which was 45mt dry, then ~60mt isn't an unreasonable guestimate at the spacecraft's dry mass, which has been thrown around here some.  (Although it's still only a guestimate).

If we are right about the MCT being the spacecraft which is its own upper stage then one way of thinking about it is as having components:

1. Stage - tanks, main engine, TVC, landing legs, etc.
2. Fairing - structure to contain the payload, payload adapter, heat shield.
3. Long duration - solar panels, radiators, long range comms, cryocooler, etc. (possibly including SEL course correction).
4. Payload - hab or cargo.

I think it difficult to get all of the MCT components (not including payload - obviously) into 60 tonnes. I have yet to see a good bottom-up estimate of the MCT dry mass.

You could very well be correct.  I was just commenting on Elon's comment that MCT seems to be -planned- to be pretty light.  If it has the same mass fraction as F9US-R would have had, except F9US-R doesn't have #2, #3, or #4 from your list on it (except the heat shield from #2) then that'd be pretty light, relatively.

I don't think anyone has seen any bottom-up estimate of MCT's dry mass becuase SpaceX has been very tight lipped out it.  So anything is just a guess at this point.

I mention 60mt because....if our other assumtions about MCT/BFR being more Saturn INT-21 class in size, then the S-II should be at least a reasonable analog in size/mass.  At least from a basic structural standpoint.  However, if SpaceX were to make a new S-II stage today, I'd think it'd be a fair amount lighter, using today's manufacturing techniques and designs.  So the 45mt S-II maybe becomes a 35mt S-IIv2.0? 
The S-II was 40s more efficient than MCT would be, but used a much less dense fuel than LCH4, so it would be more volumous for the same propellant mass.  MCT will be less efficient, and will need more margin to overcome the reuse penalties like legs, landing engiens, and a TPS.  So it will need more propellant mass to make up for that.   Maybe back up to a rougly similar size to the more volumous S-II?  So I was just using the S-II as an anlogy for something that may be roughly similar in actual size and thus dry mass.  Assuming the basic stage today could be made a little lighter than the old S-II and add on that the mass of the TPS, legs, landing engines, crew cabin and ECLSS...60-ish tonnes doesn't seem like too bad of a SWAG number.  A cargo hold really shouldn't be too heavy unless pressurized.  It's just empty space otherwise. 
But if it needed to be 70 or 75mt, the MCT stack would just be a little larger.  Remember, INT-21 would have put almost 165mt into LEO including the S-II mass.  A 75mt MCT plus 100mt of cargo is only 10mt more than that.  So we're still in the same size class.




 

Offline Lobo

  • Senior Member
  • *****
  • Posts: 6915
  • Spokane, WA
  • Liked: 672
  • Likes Given: 437
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #870 on: 04/14/2015 05:19 pm »
One more thought.

When considering my Saturn S-II stage analog.  If it was in LEO, fully fueled, how much could it get through TMI?   

Someone could model that accurately, but to do just a quick and dirty comparative analysis.
 
The S-IVB could get 45mt plus it's own dry mass of 16mt, plus whatever residuals were left in it at separation, through TLI.  That's 61mt+ (depending on the mass of residuals).
And that would be more if the S-IVB didn't need to do the final part of the ascent burn that it needed to do while flying on the while Saturn V stack.  So it wasn't fully fueled while in LEO.  If so, maybe it's total TLI would be closer to 70mt?  Let's assume 70mt if fully fueled in LEO for an example.

The S-II carried about 4.2X more propellant than the S-IVB, and had a little better mass fraction.  So 4.2X the TLI capacty of the S-IVB (including it's own dry mass) would be about 294mt (assuming close to 70mt through TLI for a fully fueled S-IVB in LEO).  The S-IVB and S-II used the same engine with the same impulse, so I think that's a reasonable comparison.
And I think TMI capacity is around 80-82% of TLI?  So assuming 80%, that's 235mt through TMI.   That'd allow for a 135mt MCT and 100mt of useful payload.
Raptor will be about 40s less impulse than the S-II's J2 engines, so that 235mt would need to be derated for that, but for example if you derate say 20% (guess) for that lower impulse, that's still 188mt total.  An 88mt Spacecraft and 100mt of payload.  That's still very plausible.  The spacecraft could be lighter than that even.  The lighter the spacecraft and smaller MCT's booster needs to be to get it up into LEO with stowed cargo.


Offline RedLineTrain

  • Senior Member
  • *****
  • Posts: 2459
  • Liked: 2412
  • Likes Given: 10229
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #871 on: 06/22/2015 01:40 pm »
I notice that Jeff Thornburg is resurfacing after the ISDC 2014 cancellation.  He will be testifying before congress with a large group of heavies.

Offline Ben the Space Brit

  • Senior Member
  • *****
  • Posts: 7206
  • A spaceflight fan
  • London, UK
  • Liked: 806
  • Likes Given: 900
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #872 on: 06/22/2015 01:56 pm »
When considering my Saturn S-II stage analog.  If it was in LEO, fully fueled, how much could it get through TMI?   

I don't know how much research Steven Baxter did for The Voyage. However, his TMI/MOI stage was a four-engine S-II (powered by something similar to J-2S, IIRC) that also had two S-II-derived external tanks. That launched a total mass through TMI well in excess of 150t but required a Venus slingshot to make up a dV shortfall.
« Last Edit: 06/22/2015 03:10 pm by Ben the Space Brit »
"Oops! I left the silly thing in reverse!" - Duck Dodgers

~*~*~*~

The Space Shuttle Program - 1981-2011

The time for words has passed; The time has come to put up or shut up!
DON'T PROPAGANDISE, FLY!!!

Offline spacenut

  • Senior Member
  • *****
  • Posts: 5183
  • East Alabama
  • Liked: 2588
  • Likes Given: 2896
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #873 on: 06/22/2015 05:39 pm »
Does anyone know how far they have advanced working on the Raptor engine?  How soon will one be ready to test fire?  Seems like SpaceX is hush-hush about this.  Once the engine is built, tested, and we know the power, then we will know how many will be used on the BFR and the MCT. 

On a note.  If Elon Musk want's 15 million lbs thrust to get 100 tons to Mars, I still wonder why 12 million can't get 80 tons and he can use Kennedy and not have to build another launch facility.  Maybe he is thinking of using a launch pad slightly off shore in Texas and since the BFR will have to be barged to the launch pad from the manufacturing facility, then it could be offloaded right at the pad offshore.  Off shore pad could be built like a large oil platform with cranes for lifting the rocket up to the platform to be fueled and launched.  LOX and LCH4 could be piped to the platform for fueling from on shore or fueled from tanker ships.  The water would solve the flame trench problem. 

Offline mme

  • Full Member
  • ****
  • Posts: 1510
  • Santa Barbara, CA, USA, Earth, Solar System, Milky Way Galaxy, Virgo Supercluster
  • Liked: 2034
  • Likes Given: 5382
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #874 on: 06/22/2015 06:29 pm »
...

On a note.  If Elon Musk want's 15 million lbs thrust to get 100 tons to Mars, I still wonder why 12 million can't get 80 tons and he can use Kennedy and not have to build another launch facility.  ...
I can think of at least two advantages to building a new launch facility: (Potentially) more control and fewer conflicts with the range and it reduces the impact to the flow of the existing launch manifest.

After all, they're hoping that the launch market expands and that they get a big chunk of the business.
Space is not Highlander.  There can, and will, be more than one.

Offline nadreck

...

On a note.  If Elon Musk want's 15 million lbs thrust to get 100 tons to Mars, I still wonder why 12 million can't get 80 tons and he can use Kennedy and not have to build another launch facility.  ...
I can think of at least two advantages to building a new launch facility: (Potentially) more control and fewer conflicts with the range and it reduces the impact to the flow of the existing launch manifest.

After all, they're hoping that the launch market expands and that they get a big chunk of the business.

And lower costs at a new facility. Legacy launch facilities have the baggage of legacy range, facilities, services costs. Something new could be designed to leapfrog that.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline symbios

  • Full Member
  • **
  • Posts: 246
  • Elon Musk fan
  • Sweden
  • Liked: 152
  • Likes Given: 739
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #876 on: 06/22/2015 08:45 pm »
Is there any advantage in throttling down at take-off in LV performance to 12 mlbf and at appropriate altitude throttle up to 15 mlbf?

I was thinking of range limitations of 12 mlbf that has been talked about a lot.
I'm a fan, not a fanatic...

Offline Owlon

  • Math/Science Teacher
  • Full Member
  • ***
  • Posts: 315
  • Vermont, USA
  • Liked: 167
  • Likes Given: 118
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #877 on: 06/22/2015 09:11 pm »
Is there any advantage in throttling down at take-off in LV performance to 12 mlbf and at appropriate altitude throttle up to 15 mlbf?

I was thinking of range limitations of 12 mlbf that has been talked about a lot.

I see this brought up a lot, and the problem is that right at launch is exactly when you need the most thrust. If you can get your rocket off the ground with a 1.2 T/W ratio using 12 mlbf of thrust you'll actually get better performance by leaving off the extra engines it would take to reach 15 mlbf.

Offline DAZ

  • Full Member
  • *
  • Posts: 162
  • Everett WA
  • Liked: 165
  • Likes Given: 1
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #878 on: 06/22/2015 11:35 pm »
Is there any advantage in throttling down at take-off in LV performance to 12 mlbf and at appropriate altitude throttle up to 15 mlbf?

I was thinking of range limitations of 12 mlbf that has been talked about a lot.

I see this brought up a lot, and the problem is that right at launch is exactly when you need the most thrust. If you can get your rocket off the ground with a 1.2 T/W ratio using 12 mlbf of thrust you'll actually get better performance by leaving off the extra engines it would take to reach 15 mlbf.

Can the rocket tolerate an engine failure at liftoff commit with a 1.2 T/W?  The rocket is only safer with multiple engines if it can tolerate an engine failure.  This is most important at liftoff with a rocket as large as being discuss here as if you lose the rocket at takeoff you will lose a lot of infrastructure.

Offline Owlon

  • Math/Science Teacher
  • Full Member
  • ***
  • Posts: 315
  • Vermont, USA
  • Liked: 167
  • Likes Given: 118
Re: SpaceX advances drive for Mars rocket via Raptor power
« Reply #879 on: 06/23/2015 06:23 am »
Is there any advantage in throttling down at take-off in LV performance to 12 mlbf and at appropriate altitude throttle up to 15 mlbf?

I was thinking of range limitations of 12 mlbf that has been talked about a lot.

I see this brought up a lot, and the problem is that right at launch is exactly when you need the most thrust. If you can get your rocket off the ground with a 1.2 T/W ratio using 12 mlbf of thrust you'll actually get better performance by leaving off the extra engines it would take to reach 15 mlbf.

Can the rocket tolerate an engine failure at liftoff commit with a 1.2 T/W?  The rocket is only safer with multiple engines if it can tolerate an engine failure.  This is most important at liftoff with a rocket as large as being discuss here as if you lose the rocket at takeoff you will lose a lot of infrastructure.

With 9 or so engines, yes--you still have a T/W over 1, you just probably lose your margin for recovery of the first stage. With the 30ish engines a 15 mlbf BFR would have you could probably lose more than one engine and still recover the stage.

Tags:
 

Advertisement NovaTech
Advertisement Northrop Grumman
Advertisement
Advertisement Margaritaville Beach Resort South Padre Island
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
1