SpaceX News

Point out news stories, on the net or in mainstream media, related to polywell fusion.

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TheRadicalModerate
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Re: SpaceX News

Postby TheRadicalModerate » Fri Oct 27, 2017 6:16 pm

paperburn1 wrote:But remember it has to fill 4 different jobs with the engine selection. Sub-orbital point to point, orbital point to point, LEO at least to space station range with 173 ton payload and MARS.
At least according to grand plan using only two different types of engine.


Note that, during the recent reddit AMA, Elon announced that the current (post-Adelaide) BFS design now has a third center engine with an expansion ratio between the sea-level and vacuum versions.

After running a few of these scenarios, I'm a lot less convinced that there's only going to be one version of the BFS. We know (also from the AMA) that they're planning on changing the payload structure substantially for the tanker versions, and the long-haul crewed version will also obviously be substantially different from the cargo version. If they're going to fool with payload structure, why not fool with the engines as well?

Here's the other use case that isn't covered with the current engining for the BFS: landing fail-safe on the Moon. Suppose you want to do a powered descent with only 10 tonnes of payload and enough fuel to return to Earth:

Delta-v from lunar surface to TEI (plus 500 m/s for landing): 3360 m/s
Assume dry mass of 85 t and no payload on return flight, and you get a mass ratio of exp(3360/(9.8*375)) = 2.49, which means you need 127 t of propellant. That makes mass to the lunar surface 85t + 127t + 10t = 222t.

For safe powered descent, you need to be able to hover, which means that thrust = lunar weight. Lunar weight = 222t * 1.62 m/s^2 = 360 kN. But a single SL Raptor running in vacuum is going to generate about 1830 kN (this is a bit of a SWAG, but it's definitely more than 1700 and less than 1900), so you can only land with a single engine throttled to 20%, which is right at the very bottom of the stated design range for the Raptor.

And you simply can't do it if you're adhering to the "two-engine fail-safe" criterion that Elon's been touting. To get to that, you have to have 444t of wet mass to the surface, which would be 232t of payload, which is more payload than you can launch to LEO.

My guess is that, if they really want to go after all of these markets (Earth orbital, Earth point-to-point, Martian interplanetary, lunar), they're going to need at least three variants:

1) The current plan of record: 4 Raptor vac, 2 Raptor SL, and the 1 Raptor intermediate that Musk talked about in the reddit AMA. This'll handle Earth orbital (both up and down) and Martian.

2) A single-stage-to-suborbit version with Raptor intermediate engines for Earth point-to-point, to make something safe enough to pass common carrier regulatory standards. Per the analysis up above, this is right on the hairy edge of feasible, and may require some additional structural compromises.

3) A lunar version, similar to #1, but with the three center engines replaced by a sub-scale Raptor that only generates about 800 kN of max thrust. That'll let it land light payloads on the Moon but still also handle a small amount of lunar down-mass (a crew, for instance) to land fail-safe on Earth.

If they can figure out how to do the SSTSO on only seven intermediate engines, they could use a single common thrust structure and just mix-and-match engines. Again, that needs a lot of analysis to figure if it's possible, but this whole idea of launching passengers on a regular basis with a booster that contains 31 fate-shared rocket engines and no launch escape is just silly. It's bad enough with only seven engines, but that's at least on the outer edge of sane.

TheRadicalModerate
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Re: SpaceX News

Postby TheRadicalModerate » Fri Oct 27, 2017 6:18 pm

Maui wrote:
TDPerk wrote:
hanelyp wrote:One problem with a lower G launch is increased gravity losses, increasing the delta-V the engines need to produce.


Eh, start at 1.3, ramp over 10 seconds to 2.5. Fuel is cheap.

Sure, but that's not the question. The question is does BFR have the fuel capacity to do so.


Per the analysis I did up-thread, the answer to that question is that it works. You've got multiple thousands of m/s of delta-v available to offset any additional gravity losses.

wizz33
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Re: SpaceX News

Postby wizz33 » Sat Oct 28, 2017 9:35 pm

dont forget the 10 tons vernier trusters

paperburn1
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Re: SpaceX News

Postby paperburn1 » Sat Oct 28, 2017 10:06 pm

Cheap orbital refueling would really be a game changer "halfway to anywhere"
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TheRadicalModerate
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Re: SpaceX News

Postby TheRadicalModerate » Sat Oct 28, 2017 10:22 pm

wizz33 wrote:dont forget the 10 tons vernier trusters


Where are you getting that number from? The only thing I heard about BFR thrusters was from Musk's recent reddit AMA:

The control thrusters will be closer in design to the Raptor main chamber than SuperDraco and will be pressure-fed to enable lowest possible impulse bit (no turbopump spin delay).


Maximum lunar landing mass with 10 tonnes-force (= 98 kN) thrusters would be 60.5 tonnes, which is considerably less than the 85 t dry mass of the BFS.

paperburn1
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Re: SpaceX News

Postby paperburn1 » Mon Oct 30, 2017 4:35 am

PAD 39A launch at 3:34 p.m. EDT (1934 GMT) Monday at the opening of a 144-minute window. The Koreasat 5A communications satellite.
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Tom Ligon
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Re: SpaceX News

Postby Tom Ligon » Mon Oct 30, 2017 10:17 pm

The landing was OK, but the video feed for both the barge and the first stage suffered major drop-outs, and clearly was a couple of meters off-center. The commentator noted that this one was a little "toasty." The judges deducted two full points. The Russian judge again deducted an extra point for boring, but as the high and low scores are disregarded, it doesn't matter to the score.

Clearly they're getting picky.

https://www.space.com/38609-spacex-laun ... ocket.html

Taliesin
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Re: SpaceX News

Postby Taliesin » Mon Oct 30, 2017 10:37 pm

The barge was rocking and rolling enough in the tropical cyclone that it had trouble keeping it's satellite link alive.. and they still stuck the landing. Nice work! No additional points for style? ;-)

Tom Ligon
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Re: SpaceX News

Postby Tom Ligon » Mon Oct 30, 2017 11:30 pm

Taliesin wrote:The barge was rocking and rolling enough in the tropical cyclone that it had trouble keeping it's satellite link alive.. and they still stuck the landing. Nice work! No additional points for style? ;-)


The good news is, ten votes of boring erases one "rapid unplanned disassembly."

Landing under difficult conditions is a wonderful demonstration of robustness, but it does not make investors any happier about launching under difficult conditions.

paperburn1
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Re: SpaceX News

Postby paperburn1 » Tue Oct 31, 2017 5:30 am

Tom Ligon wrote:, and clearly was a couple of meters off-center. The commentator noted that this one was a little "toasty." The judges deducted two full points.

This makes me chuckle, the average error in the Apollo was 2.4 miles from intended point with the best landing at .55 nautical miles. The navy was prepared to recover from 5000 square miles if necessary.
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Tom Ligon
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Re: SpaceX News

Postby Tom Ligon » Tue Oct 31, 2017 5:34 pm

paperburn1 wrote:This makes me chuckle, the average error in the Apollo was 2.4 miles from intended point with the best landing at .55 nautical miles. The navy was prepared to recover from 5000 square miles if necessary.


Its a sign of the times. We've gone from hanging on the edge of our seats and holding our breath hoping they survive, to worrying about finesse.

We're not quite to the point where these operations are no more newsworthy than a 777 making a greaser landing, but its is the goal.

paperburn1
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Re: SpaceX News

Postby paperburn1 » Mon Nov 20, 2017 4:30 am

Nogo for launch
I noticed INDIA has a fail to deploy fairing and lost a satellite. They use a system very similar to what Musk falcon 9 uses to deploy fairing. They ran into a problem with the pneumatic pushers they use to deploy the fairing. I do not know if this was a local manufacture or something they have sourced out for spacex but basically it is the same system. Spacex is being very tight lipped on this problem, I do not know if it is because of the payload or other issues.
space.com
In terms of the next flight that SpaceX has under NASA’s Commercial Resupply Services contract, not much. The $1.6 billion agreement likely won’t be impacted as the cargo variant of SpaceX‘s Dragon spacecraft does not utilize a payload fairing (the rocket’s nose cone) when it travels to the International Space Station and the mission appears to still be a “go” for a December 4 launch date. When launched this will be the 13th flight under this agreement (CRS-13).

The payload fairing issue that SpaceX has encountered could mean that Zuma, as well as the Iridium NEXT 4 flight slated to take place on December 22, might not take place this year and the “unofficial” flight of the Falcon Heavy, which could have taken place later this year is unlikely to occur.



https://www.youtube.com/watch?v=TXYh4re0j8M
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TDPerk
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Re: SpaceX News

Postby TDPerk » Tue Nov 21, 2017 2:51 pm

paperburn1 wrote:Nogo for launch
I noticed INDIA has a fail to deploy fairing and lost a satellite. They use a system very similar to what Musk falcon 9 uses to deploy fairing. They ran into a problem with the pneumatic pushers they use to deploy the fairing. I do not know if this was a local manufacture or something they have sourced out for spacex but basically it is the same system. Spacex is being very tight lipped on this problem, I do not know if it is because of the payload or other issues.
space.com
In terms of the next flight that SpaceX has under NASA’s Commercial Resupply Services contract, not much. The $1.6 billion agreement likely won’t be impacted as the cargo variant of SpaceX‘s Dragon spacecraft does not utilize a payload fairing (the rocket’s nose cone) when it travels to the International Space Station and the mission appears to still be a “go” for a December 4 launch date. When launched this will be the 13th flight under this agreement (CRS-13).

The payload fairing issue that SpaceX has encountered could mean that Zuma, as well as the Iridium NEXT 4 flight slated to take place on December 22, might not take place this year and the “unofficial” flight of the Falcon Heavy, which could have taken place later this year is unlikely to occur.
https://www.youtube.com/watch?v=TXYh4re0j8M


You have no excuse for so much as suspecting India used the same part as SpaceX. SpaceX has to be tight lipped, the nature of the ZUMA payload is a national security secret. SpaceX did not perform the fairing integration for this payload, they likely are only doing their own checks on payload integration.

https://www.nasaspaceflight.com/2017/11 ... satellite/
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paperburn1
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Re: SpaceX News

Postby paperburn1 » Tue Nov 21, 2017 3:48 pm

Same system never said it was same parts I was wondering if they used same parts, so maybe they were just being careful. Roughly 80% of the parts in any SpaceX rocket are made on the company's own factory. The other twenty percent are purchased from outside venders Just an interested question. It would be foolish to think they are not in the business of selling parts and pieces. They could undercut most suppliers by huge amounts .

Yey , airbags go off in a car and cause damage to the occupant; other automotive makers check to make sure that the same flaw does not exist in their system because they use airbags too..
logical and safety orientated.

I do not know if it is because of the payload or other issues. you might have missed that part of the statement.
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paperburn1
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Re: SpaceX News

Postby paperburn1 » Fri Dec 15, 2017 8:35 pm

I am not a nuclear physicist, but play one on the internet.


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