SpaceX F9 : Starlink v0.9 : May 23, 2019 - DISCUSSION

[intelati]

Holy.

The Falcon will get quite a workout tonight

(shhhh, don't tell the people that claim that the upper stage and PAF can only handle 12 tons)

This also isn't a standard payload adapter. I'm assuming it's custom sized for Starlink only. (At least currently...)

[docmordrid]

18.5 tons.    (shhhh, don't tell the people that claim that the upper stage and PAF can only handle 12 tons) 

https://twitter.com/elonmusk/status/1128834111878193155

I saw that and sprayed iced tea all over the tablet, couch, and me  😨

[ZachF]

18.5 tons.    (shhhh, don't tell the people that claim that the upper stage and PAF can only handle 12 tons) 

https://twitter.com/elonmusk/status/1128834111878193155

The earlier press release stated 227kg each, which would be 13,620kg total.... must be wet weight vs dry weight I'm guessing?

[ZachS09]

I'm guessing that there's a big dispenser and the 13,620 mass EXCLUDES the dispenser.

[mandrewa]

18.5 tons.    (shhhh, don't tell the people that claim that the upper stage and PAF can only handle 12 tons) 

https://twitter.com/elonmusk/status/1128834111878193155

The earlier press release stated 227kg each, which would be 13,620kg total.... must be wet weight vs dry weight I'm guessing?

18.5 U.S. tons equals 16.8 metric tons.  16.8/60 = 0.28 metric ton per satellite.  The propellant is krypton.  I saw a low estimate of 10 kg of krypton and a high of 40 kg.  Assuming 227 kg is dry mass, wet mass would either be 237 kg or 267 kg.

Something is missing.  Or it's a typo.

[ZachF]

I'm guessing that there's a big dispenser and the 13,620 mass EXCLUDES the dispenser.

Probably, although 4880 kg just for a dispenser doesn't make much sense given that the entire setup was built to save mass in this area (stacking the satellites on top of each other, and spinning to release them)

I'd bet the 227kg is dry mass, and the 18,500kg is wet mass + dispenser.

Wet mass of 296kg and an ISP of 1500 would give the Starlink sats about 400m/s of dV.

EDIT- did not correct for gravity; would be about 3,920m/s of dV.

[docmordrid]

I'm guessing that there's a big dispenser and the 13,620 mass EXCLUDES the dispenser.

Probably, although 4880 kg just for a dispenser doesn't make much sense given that the entire setup was built to save mass in this area (stacking the satellites on top of each other, and spinning to release them)

I'd bet the 227kg is dry mass, and the 18,500kg is wet mass + dispenser.

Wet mass of 296kg and an ISP of 1500 would give the Starlink sats about 400m/s of dV.

Musk said there is no dispenser.

[ZachF]

18.5 tons.    (shhhh, don't tell the people that claim that the upper stage and PAF can only handle 12 tons) 

https://twitter.com/elonmusk/status/1128834111878193155

The earlier press release stated 227kg each, which would be 13,620kg total.... must be wet weight vs dry weight I'm guessing?

18.5 U.S. tons equals 16.8 metric tons.  16.8/60 = 0.28 metric ton per satellite.  The propellant is krypton.  I saw a low estimate of 10 kg of krypton and a high of 40 kg.  Assuming 227 kg is dry mass, wet mass would either be 237 kg or 267 kg.

Something is missing.  Or it's a typo.

40kg of prop, given a 227kg dry mass at an ISP of 1500 gives the sats 250m/s of dV.

If he is using US not imperial tons, and the total mass is 16,800, 60 x 267 = 16,020 kg, leaving 780kg for the dispenser/deckholder

EDIT- corrected for gravity/ISP definition again. dV is 2,450m/s

[ZachF]

I'm guessing that there's a big dispenser and the 13,620 mass EXCLUDES the dispenser.

Probably, although 4880 kg just for a dispenser doesn't make much sense given that the entire setup was built to save mass in this area (stacking the satellites on top of each other, and spinning to release them)

I'd bet the 227kg is dry mass, and the 18,500kg is wet mass + dispenser.

Wet mass of 296kg and an ISP of 1500 would give the Starlink sats about 400m/s of dV.

Musk said there is no dispenser.

No, but there looks to be a structure to hold them in place.

[JH]

Wet mass of 296kg and an ISP of 1500 would give the Starlink sats about 400m/s of dV.

Pretty sure you forgot to multiply the isp by standard gravity to get the exhaust velocity. m0 = 296, m1 = 227, and isp = 1500 gives 3905 m/s.

[ZachF]

Wet mass of 296kg and an ISP of 1500 would give the Starlink sats about 400m/s of dV.

Pretty sure you forgot to multiply the isp by standard gravity to get the exhaust velocity. m0 = 296, m1 = 227, and isp = 1500 gives 3905 m/s.

 

Derp... rookie mistake.

[JH]

No worries. It happens.

[meekGee]

I think they showed how it will look like in the patch: The main body is half a square, and it will host the antennas (waves coming out of it), then a very big solar array (several times the area of the main body) is extended from one side.

Interesting!

Does the drag have to be evenly distributed to avoid applying torque?

Considering the satellites have to permanently rotate to keep their antenna pointed towards the ground ant the solar panel towards the sun, drag-induced torque isn't much of a worry.

I thought about that but I thought of some potential problems and I'm not entirely sure how they balance out.

Satellites have to rotate to point antenna and solar and so on, but they are able to do so using reaction wheels, without expending propellant. But if you get a net torque from drag reaction wheels wouldn't be able to cancel it. They'd be able to overcome it in the short term but eventually it would require the expenditure of propellant, that's when it would be an issue. So it seems like a satellite low enough to experience nontrivial drag would want to be mostly balanced in terms of drag and mass distribution to avoid a net torque, so the only issue they'd have to deal with would be reboosting and fine tuning their orbit.

If they're clever, then can actuate the panel so the net angular impulse accumulated over time is zero.

[Robotbeat]

18.5 TONNES?!? 😨

Elon Musk ✔ @elonmusk
Starlink mission will be heaviest @SpaceX payload ever at 18.5 tons. If all goes well, each launch of 60 satellites will generate more power than Space Station & deliver 1 terabit of bandwidth to Earth.
9:26 PM - May 15, 2019

https://twitter.com/elonmusk/status/1128834111878193155

ISS's 8 solar wings produced about 248kilowatts beginning-of-life (less than that now, and less also if averaged over the orbit). That implies these satellites do about 4kW nameplate apiece. Not bad for a 227kg satellite built for a song. The whole constellation (~12000 birds) will be 50 Megawatts or more, then.

[edkyle99]

So typical of this outfit.  Their press kit says one thing.  Elon says something completely different, and in "tons", whatever that means.

 - Ed Kyle

[Bubbinski]

They just scrubbed due to high altitude winds, try again tomorrow, as per SpaceX webcast which just ended

[Robotbeat]

So typical of this outfit.  Their press kit says one thing.  Elon says something completely different, and in "tons", whatever that means.

 - Ed Kyle

Seriously, Ed?


The press kit and Elon are not necessarily in contradiction. Troll harder.

[Bubbinski]

How are the upper level winds looking for tomorrow?

[Wolfram66]

They just scrubbed due to high altitude winds, try again tomorrow, as per SpaceX webcast which just ended

Yes, upper level shear is bad
http://tropic.ssec.wisc.edu/real-time/windmain.php?&basin=atlantic&sat=wg8&prod=shr&zoom=&time=

[edkyle99]

So typical of this outfit.  Their press kit says one thing.  Elon says something completely different, and in "tons", whatever that means.

 - Ed Kyle

You're trolling, Ed.

The press kit and Elon are not necessarily in contradiction. Troll harder.

Yes they are.  The press kit says 227 kg for each of 60 satellites for a total of 13,620 kg.  This is what the company told the press, which reported same.  Then Elon says "18.5 tons".  Contradiction.  Why the unnecessary obfuscation?  It is not "trolling" to ask this question!

 - Ed Kyle