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Space Science Coverage / Re: Astronomy Thread
« Last post by Star One on Today at 08:27 PM »
Thought the astronomers on here might appreciate the sentiments expressed on this Twitter thread.

This thread might be interesting if you’ve ever wondered: “Could the govt be hiding knowledge of a killer asteroid from us?” Answer is no: we’d all be talking about it on Twitter. (Thread is about worrisome object that, with more data, turned out NOT to be a threat.)
SpaceX General Section / Re: NASA CRS-7 report released
« Last post by mn on Today at 08:19 PM »
Someone sent me this excerpt from the Metallic Materials Properties Development and Standardization. The source says it indicates that 17-4 PH should not be used in cryogenic service in tension in the way the strut was loaded. Cast parts always have flaws in them, which explains the factor of four recommended by supplier. The LOX at launch was about -297 F, probably a bit warmer when the tank blew. So, I was wondering what folks thought of that.

Also, here's another question: would SpaceX have had to change the struts in any event once they went to densified propellants? Wouldn't they have become too brittle submerged in a deeper state of cold?

The document refers specifically to 'Impact Strength', is that applicable to the the F9 use case?

The document also says that for 'Non impact' applications it's OK to use down to -320
Space Science Coverage / Re: Pluto-Planet debate discussions
« Last post by Star One on Today at 08:17 PM »

A new def of planet is being considered at #LPSC2018. In tweet exchange w @carolynporco @jeanlucmargot ((link:…), the big Q is how the dynamical properties (grav. influence) play in defining the term "planet" and  whether Pluto is plainly a planet. @AlanStern
Blue Origin / Re: New Armstrong Speculation and Discussion
« Last post by DJPledger on Today at 08:07 PM »
Since they mentioned 100ft diameter boosters, Blue Origin seems to believe you can more or less scale up from what they have now. Probably with much more efficient and powerful engines.

Or they're planning a much more squat, and possibly not cylindrical, vehicle. Or it was simply an off the cuff statement about how "things are totally gonna be huge eventually" with no actual engineering basis for that number.

At a perfectly linear scaling, a 100 foot wide NG would be 4.3x the height of the currently planned one. Total volume ~80x that of NG, assume mass increases approximately the same. 560 BE-4s. Even if they managed to match the ultimate growth target of M-1 (ie, the largest engine ever seriously designed, and an optimistic derivative of that), thats still well over a hundred engines
Even if BO could dev. engines of 30MN SL thrust each you would still need 45 engines on the booster, ain't going to happen. NA likely to be around the size of BFR maybe slightly larger. Dev. of any liquid fuel engine beyond around 8-10MN thrust will likely be extremely difficult. 7 engines of 8MN SL thrust for NA will give approx. BFR thrust. BO have never stated that BE-4 will power NA so I assume that it will have a new main engine.
Delta-V is Ascent+TEI+TCM+EOI+1% margin = (1890+1169+2+3185)*1.01 = 6308.5 m/s. RL-10C-2 ve = 4535.6 m/s. Mass ratio = exp(6308.5/4535.6) = 4.018. An 8 t vehicle would then have a dry mass of 1.99 t, including the cabin! Not going to work. Assuming a mc = 2000 kg cabin, one me = 301 kg engine, two crew at mh = 125 kg each and mr = 100 kg of samples, a stage dry mass model of ms = 0.46718*mp^{0.848}, I get ms = 1353 kg and mp = 12085 kg. Total mass is mc+2*mh+mr+me+ms+mp = 2000+2*125+100+301+1353+12085 = 16,089 kg, which is 4.1 t greater than the 12 t that can be landed!

Yes. We're talking about doing Apollo Direct Ascent with a launch vehicle that has under one third the TLI performance of the Nova-class Saturn C-8, and we're making what seems like a poor design trade by hauling about EOI propellant rather than a reentry heatshield. It makes sense that if you work this kind of architecture backwards to the mass of the crew cabin, we get something that's probably not sufficient for a two-person crew.

I think the best way to make this work is to do direct ascent / direct reentry with Dragon using Earth orbit rendezvous. The descent/lander stage would launch on an expendable FH. If the the ascent stage can't also fit on that FH, then that's an additional F9 launch.
Going direct ascent from the lunar surface with something like Dragon 2 rapidly makes mass growth untenable. Assuming you need pressure-fed storables for liftoff assurance, your best possible mass fraction is going to be on the order of 2.4:1, so with Dragon 2 as your payload, you're already looking at upwards of 25 tonnes landed mass. So you need to start with around 45-50 tonnes in LLO, which is pushing the limits of what an expendable Falcon Heavy can lift to LEO.

You'd have to launch a landing stage to LEO via FH, launch another FH for EOR to do a TLI (letting the landing stage perform LOI), then send up your ascent stage on FH, then send up your crew and Dragon 2 on a F9, then send up a fourth FH for the TLI. Then the ascent stage performs LOI, ascent and descent stage rendezvous in LLO, and the descent begins.

That's four Falcon Heavy launches (most of which will require expending the core) and a F9, just for a single expended flags-and-footprints mission. Only, no airlock, so that's even less useful.
General Discussion / Stephen Hawking has passed away
« Last post by Star One on Today at 07:58 PM »
Looks like Mr Hawking was determined to go out with a bang as he currently has a paper in peer review setting out the mathematics needed for detecting multiple big bangs from parallel universes within the CMB.

A final theory explaining how mankind might detect parallel universes was completed by Stephen Hawking shortly before he died, it has emerged.

Colleagues have revealed the renowned theoretical physicist’s final academic work was to set out the groundbreaking mathematics needed for a spacecraft to find traces of multiple big bangs.

Currently being reviewed by a leading scientific journal, the paper, named A Smooth Exit from Eternal Inflation, may turn out to be Hawking’s most important scientific legacy.
Of course it seems like the best way to pitch something like this would be to have the crew vehicle be CST-100 (includes more players).
This would be true if CST100 had ANY advantage over Dragon 2. It's way heavier. Does it have more onboard dV?

SpaceX and ULA are direct rivals so there are legal problem if they try talking to each other. A different company would have to be prime contractor. Although NASA could do be overall boss for government trips.
Chinese Launchers / Re: BeiDou Deployment
« Last post by VR2 on Today at 07:44 PM »
Is there a source where these graphs can be found, or are they your own work?
Source exists. I've been looking for him for a long time. :P
SpaceX Mars / Re: Development of a Martian export economy
« Last post by Robotbeat on Today at 07:43 PM »
Yeah, honestly I think we’re fine with the Outer Space Treaty making land ownership in space not feasible. Until Mars achieves independence, it’s not needed. De facto ownership by actually utilizing the land is fine, of course.
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