SpaceX advances drive for Mars rocket via Raptor power

[CJ]

I'm very perplexed by reports that someone (Can't recall whom) at SpaceX's claimed it would be only for Mars launches. That really makes no sense to me. "Primarily" I could accept, but not "only". It just makes no fiscal sense; why wouldn't they accept business for it?

I believe someone else suggested on this forum that what that really means is that they're designing it for Mars only (not taking other possible uses into account in the design process, staying focused on Mars) not necessarily that they'd never sell launches of the rocket for any other purpose.

Sure, it's huge, but it'd be ideal for launching high-mass payloads, such as, say, a space station, or a really large Geo communications platform that just isn't feasible to launch today (for example, one requiring a lot of power and thus large solar arrays, such as to do direct broadcast).

Maybe space-based solar power, too, if reusability can lower costs enough.

Hrmmm. Designing it so it's optimized for Mars does fit... and it actually wouldn't necessarily harm their LEO and GEO prospects.
The example that comes to mind is the F-15 fighter. The design philosophy was "not one pound for air to ground", because they wanted it to be the best air-to-air fighter it could be. But... in spite of that design philosophy (or perhaps because of it) we now have the F-15 E, which is superb in both air-to-air and air-to-ground roles.

A solar power sat would be interesting, though I'm a bit skeptical; the radiation environment is such that you'd need gallium-arsenide cells, which are very expensive. My personal hunch is that with current tech, a case can't be made for a solar power sat to beam power to earth cheaper than generating it here. But... it might be very viable to build one to supply power to other satellites in Geo, as the cost dynamics are a lot different. There are all sorts of possibilities in GEO, or in other orbits, that low cost-per-pound would open up.

The reported thrust of Raptor (apparently over a million foot-pounds!!) is astounding. That's getting close to the Saturn 5's F-1, at 1.5 million - and the S5 first stage used 5 of them. Assuming current interpretations are correct, the Raptor-powered first stage will use 9, so considerably more thrust (and thus higher gross takeoff mass) than S5. Also, the F-1 wasn't great on ISP at 264. That's big, very big. And if they do a heavy version, 3 cores... I think they'll need to measure the launches on the Richter scale.

And @Martin, thanks for the source (Shotwell comments). Interesting... but as for SpaceX official comments regarding future plans, the more I think about it, the more I'm inclined to take them with a grain of salt. The reason is that, as with most any complex endeavor, things can change. I'm not suggesting they are lying, only that if things look like they should be done differently when the times comes, SpaceX is quite capable of disregarding past statements and adapting. And that IMHO is a good thing. (An example... they originally went with insulating the first stage to survive entry, but that didn't work, so they changed plans and did something else.)   

One thing I'd like to ask, and hope someone knows; has the possibility of a direct-ascent launch profile been discussed on the forums anywhere (Either for GEO or for earth-escape) in context of Raptor and the BFR? I know that, in contrast to going to LEO first, you get more gravity losses, but... how do the numbers work out for direct ascent when factoring in reusability (are the fuel costs less than for boostback? Direct ascent negates to downrange velocity issue, and that's a Delta/v savings.). I'm chagrined to admit that I can't figure out how to calculate the fuel needs (and thus payload impact) of grav losses for direct ascent profile vs. boostback from a LEO ascent profile.   
 
 

 

[CuddlyRocket]

[Gwynne Shotwell] could be trying very hard to avoid the impression that Raptor/MCT is a competitor to SLS.

You might very well be right there! If so, it's a stance they'll maintain until they've built their BFR; then they'll be arguing to be allowed to compete for the payloads!

Maybe space-based solar power, too, if reusability can lower costs enough.

A solar power sat would be interesting, though I'm a bit skeptical; the radiation environment is such that you'd need gallium-arsenide cells, which are very expensive. My personal hunch is that with current tech, a case can't be made for a solar power sat to beam power to earth cheaper than generating it here.

Your hunch is spot on. You get more Earth-based, even 24-hr, electricity with Earth-based photovoltaics than orbital, and at much less risk and money up-front! The relative difference has even been increasing for some time; but as far as I know, no-one's done a study with reusability taken into account.

One thing I'd like to ask, and hope someone knows; has the possibility of a direct-ascent launch profile been discussed on the forums anywhere (Either for GEO or for earth-escape) in context of Raptor and the BFR? I know that, in contrast to going to LEO first, you get more gravity losses, but... how do the numbers work out for direct ascent when factoring in reusability (are the fuel costs less than for boostback? Direct ascent negates to downrange velocity issue, and that's a Delta/v savings.). I'm chagrined to admit that I can't figure out how to calculate the fuel needs (and thus payload impact) of grav losses for direct ascent profile vs. boostback from a LEO ascent profile. 

Yep. Check the early pages of the MCT speculation thread or in the Missions to Mars (HSF) sub-forum. As far as I can recall, direct launch requires less delta-v; the purpose of going to LEO first is to refuel, thereby allowing more payload with smaller launchers. But I'm not an expert either!

[MP99]

And @Martin, thanks for the source (Shotwell comments). Interesting... but as for SpaceX official comments regarding future plans, the more I think about it, the more I'm inclined to take them with a grain of salt. The reason is that, as with most any complex endeavor, things can change. I'm not suggesting they are lying, only that if things look like they should be done differently when the times comes, SpaceX is quite capable of disregarding past statements and adapting. And that IMHO is a good thing. (An example... they originally went with insulating the first stage to survive entry, but that didn't work, so they changed plans and did something else.)   

NP.

And agree with that 100%.

Cheers, Martin

[Mongo62]

Maybe space-based solar power, too, if reusability can lower costs enough.

A solar power sat would be interesting, though I'm a bit skeptical; the radiation environment is such that you'd need gallium-arsenide cells, which are very expensive. My personal hunch is that with current tech, a case can't be made for a solar power sat to beam power to earth cheaper than generating it here.

Your hunch is spot on. You get more Earth-based, even 24-hr, electricity with Earth-based photovoltaics than orbital, and at much less risk and money up-front! The relative difference has even been increasing for some time; but as far as I know, no-one's done a study with reusability taken into account.

I would think that solar thermal power generation, perhaps using a Sterling cycle, would be more mass-effective than photovoltaic, mainly because the concentration mirrors could be made nearly arbitrarily thin. And since there would be no solar cells to degrade, the radiation environment would be far less of an issue.

This might be considered OT, but if SpaceX succeeds with their cost-to-orbit goals, I would not be surprised if space-based solar thermal electricity generation suddenly becomes financially competitive -- and a lot more carbon-friendly. So it's not really OT in my opinion, since space-based power generation could provide a major increase in demand for BFR-sized launch services, in addition to Mars colonization.

[docmordrid]

JAXA recently unveiled their roadmap to a 1GW solar power satellote system. Long IEEE Spectrum writeup

http://spectrum.ieee.org/green-tech/solar/how-japan-plans-to-build-an-orbital-solar-farm

[rst]

This might be considered OT, but if SpaceX succeeds with their cost-to-orbit goals, I would not be surprised if space-based solar thermal electricity generation suddenly becomes financially competitive -- and a lot more carbon-friendly. So it's not really OT in my opinion, since space-based power generation could provide a major increase in demand for BFR-sized launch services, in addition to Mars colonization.

Just as a reminder:  Elon hates solar power satellites.  I'm not sure he hates them enough to turn down money from someone else who has funding for them, but, well ... here's one public statement:

While Musk loves electric cars and spaceflight, there’s one thing he hates: space solar power. "You’d have to convert photon to electron to photon back to electron. What’s the conversion rate?" he says, getting riled up for the first time during his talk. "Stab that bloody thing in the heart!"

This particular objection doesn't have much to do with your Stirling-cycle idea, and even on its own, it doesn't quite stand without further elaboration.  (The photon-to-electron-to-photon conversion in the powersats effectively shifts their frequency to a wavelength where the atmosphere aborbs less; you've got to figure that into the aggregate system efficiency as well.)  But he's certainly not brimming with enthusiasm.

http://www.popularmechanics.com/how-to/blog/elon-musk-on-spacex-tesla-and-why-space-solar-power-must-die-13386162

[ncb1397]

We already get plenty of space based solar power beamed to earth on a regular basis. No need to reinvent the sun.

[AncientU]

[Gwynne Shotwell] could be trying very hard to avoid the impression that Raptor/MCT is a competitor to SLS.

You might very well be right there! If so, it's a stance they'll maintain until they've built their BFR; then they'll be arguing to be allowed to compete for the payloads!

I think they'll simply sell a couple BFR flights per year to NASA so that NASA can actually afford to build some payloads and maybe --- wait for it --- explore.  The cost advantage of their BFR over SLS will make the EELV advantage look modest.

[Mongo62]

We already get plenty of space based solar power beamed to earth on a regular basis. No need to reinvent the sun.

You mean, other than the fact that Earth based direct solar power is:

1. only available for half the day
2. available for less than that when allowing for cloud cover
3. available at much lower solar power density than in space, around 50% at best (high noon with the Sun directly overhead) dropping to near zero when the Sun is near the horizon
4. with photovoltaic elements subject to weather-related degradation over time (space photovoltaic also degrades over time due to radiation, but not space thermal)
5. with a limit in combined power density that is considerably lower than is theoretically possible with microwave transmission, hence requiring more surface area on Earth to acquire than a microwave rectenna with the same power output

[Chris Bergin]

That's all smashing stuff lads, but how's about we concentrate on Raptor?

[ImUtrecht]

Chamberpressure of Raptor could be around 50 Mpa ?

[baldusi]

Chamberpressure of Raptor could be around 50 Mpa ?

My first calculation was 20.5MPa with an expansion ratio of 45:1. O/F 3.5.

[upjin]

This might be considered OT, but if SpaceX succeeds with their cost-to-orbit goals, I would not be surprised if space-based solar thermal electricity generation suddenly becomes financially competitive -- and a lot more carbon-friendly. So it's not really OT in my opinion, since space-based power generation could provide a major increase in demand for BFR-sized launch services, in addition to Mars colonization.

Just as a reminder:  Elon hates solar power satellites.  I'm not sure he hates them enough to turn down money from someone else who has funding for them, but, well ... here's one public statement:

While Musk loves electric cars and spaceflight, there’s one thing he hates: space solar power. "You’d have to convert photon to electron to photon back to electron. What’s the conversion rate?" he says, getting riled up for the first time during his talk. "Stab that bloody thing in the heart!"

This particular objection doesn't have much to do with your Stirling-cycle idea, and even on its own, it doesn't quite stand without further elaboration.  (The photon-to-electron-to-photon conversion in the powersats effectively shifts their frequency to a wavelength where the atmosphere aborbs less; you've got to figure that into the aggregate system efficiency as well.)  But he's certainly not brimming with enthusiasm.

http://www.popularmechanics.com/how-to/blog/elon-musk-on-spacex-tesla-and-why-space-solar-power-must-die-13386162

Excellent point.  Elon, for a Mars colony, will be looking for the best sources to get power and sustain growth.

It's not just a question of getting to Mars.  He wants to stay there.

[ImUtrecht]

Chamberpressure of Raptor could be around 50 Mpa ?

My first calculation was 20.5MPa with an expansion ratio of 45:1. O/F 3.5.

But that would be lower than the RD-180 that has 26.17MPa.
I thought that with full flow staged combustion higher pressures were possibele.
The expansion rate is higher then RD-180
I think they will use hydrostatic bearings for reusability and higher pressures.
Soon we will know more and i am quite curious to find out.
Thanks for your input Baldusi.

Question: first calculation for how much thrust? One million or 1,6 million lbf ?

[baldusi]

The isp calculations weren't affected by the thrust level in the basic software I used. Regarding the chamber pressure, with full flow you can do high pressure or lower the turbine temperature. And 20.5MPa is nothing to sneeze at. SSME has that chamber pressure. The NK-33 has 14.5. And the amazing design for the RD-0164, 17.5MPa. So 20.5MPa would put it right up there with the big boys. The RL10 is just 4.5MPa.

[MP99]

Chamberpressure of Raptor could be around 50 Mpa ?

My first calculation was 20.5MPa with an expansion ratio of 45:1. O/F 3.5.

But that would be lower than the RD-180 that has 26.17MPa.
I thought that with full flow staged combustion higher pressures were possibele.
The expansion rate is higher then RD-180
I think they will use hydrostatic bearings for reusability and higher pressures.
Soon we will know more and i am quite curious to find out.
Thanks for your input Baldusi.

Question: first calculation for how much thrust? One million or 1,6 million lbf ?

BTW, there are no prizes for making difficult engineering challenges for yourself.

A lower chamber pressure should make the engine easier to design, and leave margins for multiple reuses. Remember the failure of M1C engine on one of the F9 v1.0 flights, and that will have been at lower pressure than this.

Cheers, Martin

[meekGee]

A bit of evening kremlinology.

Does anyone remember which conferences SpaceX used to make significant reveals at, in the past?

To those not from the U.S.:

ISDC is the more "enthusiastic" venue.  Anything from suborbital to Mars.
The Space Symposium is where the fat cats are.  100% what they call business.
Joint Propulsion Conference is where the tech is.  Not just rockets.

All three conferences are in the very near future.

As far as I can tell Elon is skipping the Space Symposium (Can you imagine the dinner tables if he were there?), and has an engineer (Jeff Thornburg) make a Raptor reveal at ISDC.  EDIT: In addition to his talk, that is.

Message?

[Llian Rhydderch]

A bit of evening kremlinology.

Does anyone remember which conferences SpaceX used to make significant reveals at, in the past?

To those not from the U.S.:

ISDC is the more "enthusiastic" venue.  Anything from suborbital to Mars.
The Space Symposium is where the fat cats are.  100% what they call business.
Joint Propulsion Conference is where the tech is.  Not just rockets.

As far as I can tell Elon is skipping the Space Symposium (Can you imagine the dinner tables if he were there?), and has an engineer (Jeff Thornburg) make a Raptor reveal at ISDC.

Message?

"First they ignore you, then they laugh at you, then they fight you, then you [ignore them]."

(I've slightly paraphrased Mahatma Gandhi's famous words to make them most applicable to Lars' question.)

[docmordrid]

Message? Fat cat meetings are for if you want to sell them something. Is there any indication SpaceX wants to sell Raptors? BFR's?

ISTM that Musk sees himself, and SpaceX, as more akin to the newspace advocacy groups than the button down groups. He'll gravitate there and to press events where SpaceX is the focus.

[meekGee]

It's not just that Musk is skipping the SS.  It's that in the entire agenda there are only two SpaceX appearances.

Shotwell vs. Gass on a panel (plus 4 other people nobody will care about), and something sponsored by SpaceX's VP for Government sales.   And SpaceX wants to sell them stuff.

Of course Musk is not the fat-cat type, and of course he has to talk at ISDC.  But a technical talk about the engine?  ISDC is not that kind of conference.


There's something about the mentality of a follower that wants to be "as good as the leader", and the mentality of a leader that just takes it for granted he's in front.  I think SpaceX outgrew the "I want to be a grown up" phase.

Never mind the award dinners - they'll sell their rockets even without trying to one-up Boeing in the size of the booth.

...

I'm trying to dig up past agendas to get a feel for a trend.  It's easier with ISDC than it is with SS.