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

[ZachS09]

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?

 - Ed Kyle

Someone said that there's 40 kilograms of propellant in each satellite, which makes each sat 267 kilograms, and there's a deployer mechanism (not a dispenser) that adds up to 18,500 kilograms.

[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?

 - Ed Kyle

Someone said that there's 40 kilograms of propellant in each satellite, which makes each sat 267 kilograms, and there's a deployer mechanism (not a dispenser) that adds up to 18,500 kilograms.

Who is this "someone"?

[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

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

Nope. You're not "asking a question," you're right out saying it's a contradiction. The press kit does not list a total. As others have noted, there appears to be some sort of structure holding the satellites together (apparently not a dispenser per se). That could easily account for the discrepency.

To not even try to understand how the two could be consistent means you're trolling.

Skepticism is perfectly fine and healthy. But interpreting things specifically in a way that leads to a contradiction while intentionally ignoring another perfectly valid explanation that avoids contradiction is trolling.

EDIT: And I'm done here. No more needs to be said.
edit/gongora: You are done, and further posts like this will be deleted, as your next post was.

[ZachS09]

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?

 - Ed Kyle

Someone said that there's 40 kilograms of propellant in each satellite, which makes each sat 267 kilograms, and there's a deployer mechanism (not a dispenser) that adds up to 18,500 kilograms.

Who is this "someone"?

https://forum.nasaspaceflight.com/index.php?topic=47594.msg1946572#msg1946572

ZachF states his opinion about the wet mass in each sat.

[edkyle99]

ZachF states his opinion about the wet mass in each sat.

He may be right, but that clearly was just his opinion - a guess.   SpaceX is officially giving 227 kg with no other explanation.  Most launch providers - even SpaceX previously when it has done it - give the liftoff mass for the satellites they are launching.   

 - Ed Kyle 

[mandrewa]

I'm not sure if Robotbeat was estimating 40 kg of Xenon or Krypton, or he was simply saying a what if.

In fact, depending on how much propellant is loaded per satellite and how often the full constellation is replaced, SpaceX’s propellant demand could be greater than the entire world production capacity of Xenon.

12000 satellites replaced every 5 years with 40kg of propellant is 96 tons of propellant per year. 2017 world Xenon production was 88 tons. Kind of a problem, especially if you want to make the satellites any bigger.

But JH was definitely estimating 10 kg.

They shouldn't need anywhere near 40 kg of Krypton per satellite. Moving from 440 km to 550 km will take less than 100 m/s, and yearly station keeping should be less than 100 m/s as well. This gives a maximum total dv of 600 m/s. Musk stated the isp of the krypton HET's at 1500 seconds. With a wet mass of 227 kg, you end up with <10 kg of fuel use over the life of the satellite.

Given 12000 satellites replaced every 5 years, that's 24 tons of Krypton per year.

[edkyle99]

Nope. You're not "asking a question," you're right out saying it's a contradiction.

Because it is a contradiction.

The press kit does not list a total. As others have noted, there appears to be some sort of structure holding the satellites together (apparently not a dispenser per se). That could easily account for the discrepency.

The difference between the press kit and Elon's tweet (assuming he's talking metric tons) is 4,880 kg.  That makes no sense for an adapter+dispenser.

To not even try to understand how the two could be consistent means you're trolling.

I am trying to understand, as noted above.  I'm frustrated trying to report what this company is doing, because the company sends messages like this that don't add up all the time.

 - Ed Kyle

[mandrewa]

Elon Musk is a space enthusiast, much like many of the people on this board.  Unlike most of us he's doing the job of fifteen people.  He has very little time to spend on this. We are fortunate that Elon Musk enjoys communicating this information and talking about what they are doing, because due to that we know far more about what is going on in SpaceX than we do with ULA or Arianespace or Blue Origin.

But Elon Musk is very short of time.  He probably doesn't double check his figures.  His information is noisy.  It comes with errors.  This 18.6 tons is probably a mistake.

[matthewkantar]

I bet 18.6 tons is no mistake. Elon knows the details and rarely misses the numbers. All of the facts from SpaceX and Elon are consistent.

[Urx]

Possible contributing factors to the difference:
- Dry vs. wet mass of the satellites
- Imperial vs. metric tonnes
- PAF mass
- Fairing mass (2x 800kg IIRC?)

[jcm]

Possible contributing factors to the difference:
- Dry vs. wet mass of the satellites
- Imperial vs. metric tonnes
- PAF mass
- Fairing mass (2x 800kg IIRC?)

Fairing mass is never, never included in statements about payload mass (since the fairing is dumped
relatively early).
It would be very surprising if the quoted mass was dry rather than wet, that is almost never the case in a context like this.
A PAF is likely to be significantly less than 500 kg.
Assuming imperial tons to be generous, there's still a 2.5 tonne discrepancy left.
I wouldn't say contradiction, but definitely a clarification would be be very helpful since this is a record-breaking flight and it would be good to get the numbers right (e..g so we can know when this new record
is broken by a later flight).

[smoliarm]

Ok, here is my take for this "227 kg vs 18.5 tons" business

1. I agree with Jonathan.
2. I agree with Ed Kyle.
3. Moreover, I strongly agree with NASA LSP Calculator
If we plug into its performance query - altitude of 440 km and inclination of 51.6°
then, for *Falcon 9 (Full Thrust, ASDS)* we get performance of ... 14300 kg
I can further refine this for actual inclination of 53.0° using extrapolation, and finally I get
14200 kg as performance for "Falcon 9 Full Thrust", with ASDS-type booster return.

As I understand how this system (Launch Services Program) works - the LSP calculator is a government issued document. With all associated legal *bells and whistles*.
It should be taken seriously.

The bottom line - there is a big discrepancy between
"227*60=13620 kg" and "18.5 tons",
which calls for ... CLARIFICATION.
Hopefully, Chris G will get it done

PS: IMHO, I see no trolling in Ed Kyle's posts, and I suspect that detailed discussion of *what should be called trolling and what should not* - it is OT for this thread.

[smoliarm]

...
Elon Musk ✔ @elonmusk
...

If all goes well, each launch of 60 satellites will generate more power than Space Station

...

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.

- here is a chance for another big discrepancy. Only a few people know this total (248 kW for all 8 wings, or 31 kW max power for a single wing).
Most will look ISS electric power in WIKI which says "Altogether, the arrays can generate 84 to 120 kilowatts".
And there is no "discrepancy" here, there is another word - redundancy

BUT - we do not know, what Elon was referring to in his tweet -
a. Max output of all 8 arrays combined (248 kW)
or
b. Max power generation by the ISS electric system (120 kW)

Therefore, just to be on a safe side, I would say Starlink nameplate has something like 2 kW.

Which is still - very impressive - for a sat with approx. dimensions of 3.5 m by 1.5 m

[speedevil]

I bet 18.6 tons is no mistake. Elon knows the details and rarely misses the numbers. All of the facts from SpaceX and Elon are consistent.

He may know it.
He has however typoed on twitter before.
(and if not been fined, been censured for it by the SEC)

[envy887]

Ok, here is my take for this "227 kg vs 18.5 tons" business

1. I agree with Jonathan.
2. I agree with Ed Kyle.
3. Moreover, I strongly agree with NASA LSP Calculator
If we plug into its performance query - altitude of 440 km and inclination of 51.6°
then, for *Falcon 9 (Full Thrust, ASDS)* we get performance of ... 14300 kg
I can further refine this for actual inclination of 53.0° using extrapolation, and finally I get
14200 kg as performance for "Falcon 9 Full Thrust", with ASDS-type booster return.

As I understand how this system (Launch Services Program) works - the LSP calculator is a government issued document. With all associated legal *bells and whistles*.
It should be taken seriously.

The bottom line - there is a big discrepancy between
"227*60=13620 kg" and "18.5 tons",
which calls for ... CLARIFICATION.
Hopefully, Chris G will get it done

PS: IMHO, I see no trolling in Ed Kyle's posts, and I suspect that detailed discussion of *what should be called trolling and what should not* - it is OT for this thread.

LSP numbers include NASA GR&As and probably additional margins. But when launching their own payload there is no reason for SpaceX to limit payloads to those assumptions. They could, for example, be using a MRS and make up the dispersions with the satellites onboard thrusters after deployment.

[envy887]

I bet 18.6 tons is no mistake.

Well, he actually wrote 18.5, so 18.6 is definitely a mistake by someone

[Pete]

I wonder if they'll have to move up to argon. Krypton might be cheaper than Xenon but my understanding it's it's still pretty rare as gasses go.

Krypton is rare, but not *rare*

The earth atmosphere contains less than 6 trillion tons of the stuff.

It is easily (but expensively) obtainable by cooling air down to liquid, then carefully evaporating off the nitrogen and oxygen. The main cost driver is energy expense, not short supply.

Bulk cost is about $300 per kg.
("bulk" in this case being up to a ton. For the whole StarLink constellation over its lifetime, i expect this can be brought down quite a bit)

[envy887]

Possible contributing factors to the difference:
- Dry vs. wet mass of the satellites
- Imperial vs. metric tonnes
- PAF mass
- Fairing mass (2x 800kg IIRC?)

Fairing mass is never, never included in statements about payload mass (since the fairing is dumped
relatively early).
It would be very surprising if the quoted mass was dry rather than wet, that is almost never the case in a context like this.
A PAF is likely to be significantly less than 500 kg.
Assuming imperial tons to be generous, there's still a 2.5 tonne discrepancy left.
I wouldn't say contradiction, but definitely a clarification would be be very helpful since this is a record-breaking flight and it would be good to get the numbers right (e..g so we can know when this new record
is broken by a later flight).

Something else that I haven't seen noted yet: 227 kg is what you get when you convert exactly 500 pounds to kg and round to 3 significant figures. I think that the number started as "about 500 pounds" and magically acquired two more significant digits in the conversion to metric.

This doesn't entirely explain the discrepancy, though. Even if Elon is rounding fractions and using short tons, the lowest payload mass that could be reasonably described would be a little over eighteen and a quarter short tons = 36500 pounds, which would be a little over 600 lbm per satellite for each of 60 satellites. That doesn't fit with "about 500 pounds".

18.5 metric tons would be 40,800 lbm total or 687 lbm per satellite, quite a bit more than "about 500 pounds".

[DanseMacabre]

Ok, here is my take for this "227 kg vs 18.5 tons" business

1. I agree with Jonathan.
2. I agree with Ed Kyle.
3. Moreover, I strongly agree with NASA LSP Calculator
If we plug into its performance query - altitude of 440 km and inclination of 51.6°
then, for *Falcon 9 (Full Thrust, ASDS)* we get performance of ... 14300 kg
I can further refine this for actual inclination of 53.0° using extrapolation, and finally I get
14200 kg as performance for "Falcon 9 Full Thrust", with ASDS-type booster return.

As I understand how this system (Launch Services Program) works - the LSP calculator is a government issued document. With all associated legal *bells and whistles*.
It should be taken seriously.

The bottom line - there is a big discrepancy between
"227*60=13620 kg" and "18.5 tons",
which calls for ... CLARIFICATION.
Hopefully, Chris G will get it done

PS: IMHO, I see no trolling in Ed Kyle's posts, and I suspect that detailed discussion of *what should be called trolling and what should not* - it is OT for this thread.

Does the ASDS booster return factor in the fact that the ASDS is very far downrange?

[envy887]

Ok, here is my take for this "227 kg vs 18.5 tons" business

1. I agree with Jonathan.
2. I agree with Ed Kyle.
3. Moreover, I strongly agree with NASA LSP Calculator
If we plug into its performance query - altitude of 440 km and inclination of 51.6°
then, for *Falcon 9 (Full Thrust, ASDS)* we get performance of ... 14300 kg
I can further refine this for actual inclination of 53.0° using extrapolation, and finally I get
14200 kg as performance for "Falcon 9 Full Thrust", with ASDS-type booster return.

As I understand how this system (Launch Services Program) works - the LSP calculator is a government issued document. With all associated legal *bells and whistles*.
It should be taken seriously.

The bottom line - there is a big discrepancy between
"227*60=13620 kg" and "18.5 tons",
which calls for ... CLARIFICATION.
Hopefully, Chris G will get it done

PS: IMHO, I see no trolling in Ed Kyle's posts, and I suspect that detailed discussion of *what should be called trolling and what should not* - it is OT for this thread.

Does the ASDS booster return factor in the fact that the ASDS is very far downrange?

It's a maximum payload, so probably yes. But I don't think that the F9 numbers have been updated for Block 5.