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SpaceX Discussion Thread

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48 minutes ago, PB666 said:

f it combines fuel from the first and second stages

then it's not an SSTO, it's a TSTO.

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I don't see how an expendable BFS SSTO would be practical at all. Its probably going to be more expensive than an F9.

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7 hours ago, tater said:

then it's not an SSTO, it's a TSTO.

In theory if no stage sep whats the diff.

I should add however such a vehical would unlikely return to the surface. So its not fully ssto

Edited by PB666

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32 minutes ago, PB666 said:

In theory if no stage sep whats the diff.

I should add however such a vehical would unlikely return to the surface. So its not fully ssto

Well, it's an SSTO, but it's not a reusable one, which defeats the purpose.

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I think a lot of the SSTO speculation w/r/t BFS came from this graphic:

refilling.png

This states that for payloads up to about 15 tonnes, the BFS is carrying 8.5-9 km/s of dV fully fueled, which should in theory be enough to reach orbit, right?

Trouble is, this graphic is about on-orbit refueling, which assumes the 375-second isp of the Raptor Vacuum engines. The first segment of the flight would need to use a much lower specific impulse. It would also need to deal with extremely high gravity drag due to low takeoff thrust.

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16 minutes ago, Technical Ben said:

From that graphic, is it one tanker to fully fill, or 5?

I don't think they ever said for sure, but it suggests five refuel flights. Probably about right. 

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43 minutes ago, sevenperforce said:

I think a lot of the SSTO speculation w/r/t BFS came from this graphic:

I think it came from Musk stating flatly that the BFS was an SSTO for small payloads. :wink:

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37 minutes ago, tater said:

I think it came from Musk stating flatly that the BFS was an SSTO for small payloads. :wink:

But he also said he's going to ship millions of people to mars.

@sevenperforceThe minimum orbital speed is 7824 @ 160km. lets just say , thats 31e6/kg + 9.5 * 160k and assume 2 g off the pad and no drag. .....7920 +  120 sec x 10 = 9120 dV without drag. On my larges flights i have drag in the 3 to 5 m/s range for about 30 seconds. So thats 9290 dV but from boca - 410 ......8880 minimum, at the rate hes gaining speed Max Q comes early and with more than a g- of drag. 

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1 hour ago, tater said:

I think it came from Musk stating flatly that the BFS was an SSTO for small payloads. :wink:

He said it could bairly make orbit, THEN he added a sea level engine that fixes some of the TWR problems.

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44 minutes ago, Rakaydos said:

He said it could bairly make orbit, THEN he added a sea level engine that fixes some of the TWR problems.

He needs better ISP on the sea level engine.

What they are using right now. Given his current numbers of 330 and 356 he needs a fuel to dry mass of >15:1.

I should point out that even for small PLs and a completely recyclable craft 150,000 kgs of of metholox is still expensive to carry a 'kilogram' into space (hyperbole intended). Particularly when two stage is completely recyclable and it can carry 100 times as many small payloads. With the age of light payloads and ION drives one really doesn't care where in orbit one is placed (as long as it is not in immediate risk of decay) it can achieve any orbit with respect to time.

Way back there wasn't I talking about a 8000 ft stratovolcano in Ecuador. If you are going to do high thrust SSTO, a very tall mountain at the equator is a good idea. You hit maxQ at 2500 meters lower and you can begin your push to downrange sooner and faster. Maybe kilamonjaro is a better place.

We sure do like arguing about improbable hypotheticals don't we.

Abstract: There is a marginal utility of gain pushing recycling and stage minimization to the extreme, particularly in the current launch market were no-one is actually doing it commercial, except SpaceX. Thus if you are offering a SSTO just to save the customers a few pennies (doubtful) its not really going to be that good for the business. In the case of SpaceX, once the TSTO BFS is good to go, you could put several hundred satellites in one rocket . . . . thats crazy cheap enough. The price worry is two pronged, will the be competitive and can that supply at the price. The problem in the short term is that spaceX needs to grow, they've got 150 orders and they need to launch many more rockets a month, if they cannot then they are going to increase the price because the labor force needs to grow, all the while they are building an assembly facility in LA and a launch facility in boca chica, and a Port facility in the port of brownsville at some point. So they do need cash flow to grow and thats hard if the margins are too low. On the flipside in order to get the holo-space business to grow the price needs to continue to fall, and I should add something needs to be started with regard to space junk, not involving harpons.

Consequently, you don't want to be offering services so cheap that demand begins to get inflexible, the price needs to stay high enough at least to allow the competition to catch up.

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For those who get 'Space' feeds from Facebook . . .change is in the air.

http://www.businessinsider.com/elon-musk-deletes-tesla-spacex-facebook-pages-2018-3

Many folk in tech industry treat Facebook like a new age plague, but thinks are beginning to spiral, and even some long time supporters are beginning to bail.

This latest spat apparently occurred because of what FB did with peoples personal data (alot of the discussion too political to mention here).

But it goes along with Facebooks longstanding problem of earning money and managing privacy (particularly personal data and third party usages).

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3 hours ago, tater said:

 

10,000 rep?   How!?!?!?

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1 hour ago, tater said:

 

 

Where the video of the static fire?  Come on, SpaceX! No pics, no clicks!  

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SpaceX doesn’t usually publish static fire videos.

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2 hours ago, cubinator said:

Don't hit Tiangong-1 on the way up! :sticktongue: 

Not a problem. Borrow Mr Steven's net, bolt it to the top of a Falcon Heavy and just catch that sucker on its way down. Bonus diplomacy points for handing it back to the Chinese.

#ItWorkedInKerbalSpaceProgram

 

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7 hours ago, cubinator said:

Don't hit Tiangong-1 on the way up! :sticktongue: 

IKR?

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8 hours ago, KSK said:

#ItWorkedInKerbalSpaceProgram

dew-it.jpg

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The company that made the sat, Thales, has a website, and their news section shows delivery of other sats to the various launch sites before they are sent to orbit, and there is no such news story for the Bangabandhu-1 sat I can see (I looked back a year to be sure). So I have a feeling the sat has not shipped from France yet.

 

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