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SpaceX Discussion Thread

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With 60 under the fairing, they want to make sure everything is right, don't want a dedicated launch for 60 paperweights.

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11 minutes ago, Geonovast said:

These are satellites for internet, right?  Can't they run Windows update in orbit?

Only if they want to ruin them. :P

PREPARING FOR CRITICAL MANEUVER...
ENGAGE ION ENGINES IN 5... 4... 3-

Your system is rebooting to install important updates.

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Satellites based on windows 10? This cant be good :P

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Posted (edited)
7 hours ago, Raven Industries said:

I wonder what spurred their sudden desire to update software. 

Have you never had that issue before? When it comes to updating, the typical computer is like a six-month old baby who needs to pee. When it wants to, it does, and no force in Heaven or Hell can stop it. Doesn't matter if you're having an important presentation, the deadline is coming up to submit your thesis, or you're about to launch a rocket into space. Nobody can predict when an update will come, but when it comes, you can't stop it.

Edited by Codraroll

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Posted (edited)
12 minutes ago, Codraroll said:

When it comes to updating, the typical computer windows is like a six-month old baby who needs to pee.

Ftfy

 

On a more serious note, whatever software issue they found must have been very serious to cancel a launch - and do we know  if it was with the actual sats, or somewhere else? Has anyone heard a word on what it might have been?

Edited by kurja

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26 minutes ago, kurja said:

On a more serious note, whatever software issue they found must have been very serious to cancel a launch - and do we know  if it was with the actual sats, or somewhere else? Has anyone heard a word on what it might have been?

It is on the sats.

I wonder if this is related to the whatsapp hack...

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2 hours ago, Xd the great said:

It is on the sats.

I wonder if this is related to the whatsapp hack...

I wonder if they suddenly realized the satelites were still programmed for the previous days deployment, and they couldn't update the systems on the launch pad.

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21 minutes ago, Rakaydos said:

I wonder if they suddenly realized the satelites were still programmed for the previous days deployment, and they couldn't update the systems on the launch pad.

Deploying 60 sats at once, sounds like good old "60 decouplers and 600 explosion" days.

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I'd imagine that the sats don't run Windows 10, but there was a Windows 10 update late yesterday.

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58 minutes ago, Ultimate Steve said:

I'd imagine that the sats don't run Windows 10, but there was a Windows 10 update late yesterday.

Coincidence? I think not.

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Posted (edited)
Quote

at present multiple sources have indicated that the company is hoping to perform orbital test flights of the Starship prototypes through Single Stage to Orbit (SSTO) launches.

“multiple sources”, though. I'll wait for official confirmation. 

How much dv does it need to pull it off? 10k? (Launch + landing)

Theoretically possible with 10k m/s dV, Isp of 380s, 75t dry, 1100t wet mass.

Edited by sh1pman

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It's about 9.5k to LEO, so that doesn't leave much for reentry or landing.

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13 minutes ago, Flibble said:

It's about 9.5k to LEO, so that doesn't leave much for reentry or landing.

They could just alt+f12

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If Starship has SSTO capability, then it has the Delta-v, if refueled in LEO, to go to the Moon and back with no payload. 3 for TLI, 1 for LLO, 4 for landing and ascent, 1 for transfer, and 1 for landing, heat shielding, and boiloff. That's 10, close to the same as an SSTO. It's a useless capability, but an interesting one.

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Posted (edited)

Landing dv is whatever terminal velocity is (plus whatever the deorbit burn is). It looks like for a 100 tonne mass, with the drag coefficient of an airplane of about the right cross sectional area (sideways), it's a few hundred m/s at most. So landing will take something like 2-300 m/s dv.

Edited by tater

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15 minutes ago, tater said:

Landing dv is whatever terminal velocity is (plus whatever the deorbit burn is). It looks like for a 100 tonne mass, with the drag coefficient of an airplane of about the right cross sectional area (sideways), it's a few hundred m/s at most. So landing will take something like 2-300 m/s dv.

Right, and for most of the other numbers I was overestimating, so SS should be able to do it.

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1 hour ago, Ultimate Steve said:

If Starship has SSTO capability, then it has the Delta-v, if refueled in LEO, to go to the Moon and back with no payload. 3 for TLI, 1 for LLO, 4 for landing and ascent, 1 for transfer, and 1 for landing, heat shielding, and boiloff. That's 10, close to the same as an SSTO. It's a useless capability, but an interesting one.

Surely you could spare the mass of one Mystery Gootm. That's something.

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Posted (edited)

Well if they can refuel in LEO, then they should be able to refuel in a highly elliptical orbit (once they have enough operational tankers).  

From a 250 km LEO lunar transfer is about 3120 m/s, capture to low orbit about 820 m/s, landing 1720 m/s, ascent another 1720 m/s, then Earth return and landing should be another 820 m/s plus around 400 m/s to land. So they need around 8600 m/s.  

So assuming a fully refuelled Starship in LEO, and another fully refuel Starship as tanker (also starting from LEO).   1100 tons fully fueled mass and 75 tons dry mass for both ships.   ISP of 380.  (So the tanker version has 1025 tons of fuel and 10 km/s dV at this point.  The other ship has less because it has a payload).

Burn 2300 m/s with both ships.  That means each ship uses 507 tons of fuel.  Use the tanker to fully refuel the other ship.  That leaves the tanker with 11 tons of fuel, which is 500m/s.  Should be plenty to de-orbit and land.   

At this point a lunar landing and return needs about 6300 m/s.  That means the non-fuel mass of the lunar lander starship + payload can be a little over 200 tons, so on this sort of mission profile Starship can land (and return to earth) around 125 tons of payload.  Plenty of mass for a useful mission.

(dV numbers from an online RO/RSS dV chart, which might be wrong.  Calculations using an online rocket equation calculator plus windows calculator.  Quite possible I entered the wrong number somewhere.  An earlier version of this calculation assumed refuelling in elliptical Lunar orbit, which might need too many refuelling flights to be practical.  I'll leave it below). 

--------------------------------------------------------------------------------------------------------------------------------------------

From an elliptical Lunar orbit landing is about 2400 km/s, ascent another 2400m/s, then Earth return and landing should be about 500 m/s or so. So they need around 5500 m/s.  

Using a lot of tankers to refuel in elliptical lunar orbit, a starship with a dry mass of 75 tons with a payload of 175 tons (and returning that payload to earth to keep calculations simpler), a fully fuelled mass of 1100 tons, ISP of 3800, that looks like a dV of 5517 m/s.  That is definitely a useful payload capacity, but probably too many tanker flights to be practical.

Edited by AVaughan

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11 hours ago, Ultimate Steve said:

I'd imagine that the sats don't run Windows 10, but there was a Windows 10 update late yesterday.

So you are confirming Starlink sats are just unsold Windows phones filled with krypton?

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10 minutes ago, Nightside said:

So you are confirming Starlink sats are just unsold Windows phones filled with krypton?

And hooked to a solar panel and a phased array antenna 

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4 hours ago, Ultimate Steve said:

[good stuff]

 

45 minutes ago, AVaughan said:

[even gooder stuff]

...eat your heart out, Blue Moon. :cool:

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The issue with refilling in highly elliptical orbits becomes timing. Assuming they have launch site options, though, this might not be a huge problem.

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Posted (edited)
49 minutes ago, tater said:

The issue with refilling in highly elliptical orbits becomes timing. Assuming they have launch site options, though, this might not be a huge problem.

My calculations above required that both the lunar lander and the tanker were already refueled in LEO, so I'm not sure how multiple launch site options helps with the highly elliptical orbit rendezvous.   (It obviously could help with launch cadence, which could be an issue with 2 starships needing to be refueled at the same time.  Don't forget boil off.  You might even want to leave both ships docked to their last tanker for a last minute top-off about an orbit or so before they leave LEO).  

Yeah the elliptical orbit rendezvous could be an issue.  You probably also don't want 2 starships in similar orbits both doing the 2300 m/s burn at the same time.  If I was to try that sort of rendezvous in KSP, I would have one ship raise its apoapsis first, then as it approaches periapsis the other ship could burn to setup a rendezvous at apoapsis.  (They could even start at different orbital altitudes).  Timing everything would still be an issue, but one I expect SpaceX could solve.  You might also want to plan for a course correction burn to fine tune the rendezvous.   (You could also split the raise apoapsis burn of the first ship over 2 orbits, which would allow you to adjust the orbital phase angle between the two ships at that time.  That means that they only need to be in the same orbital plane, and the initial phase angle between them isn't critical).   Of course you still need to be able to execute subsequent burns according to plan.  

Also if you really want to avoid it, a fully fueled starship should have around 8929 m/s dV even with a 25 ton payload.  (1100 tons fuelled mass, 380 isp, 75 + 25 ton dry mass, works out to 8929 m/s of dV).  So enough for a useful lunar mission even if you avoid refueling in an elliptical orbit.  Of course all of this is highly dependent on assumptions about wet and dry mass, isp, and that they can solve any issues with refueling in orbit.

 

 

Edited by AVaughan

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