Quote from: LouScheffer on 02/22/2018 01:14 pm... At MECO, the apogee is already at orbital altitude. So the second stage can just thrust horizontally while it coasts up to LEO, and does not need to fight gravity.At MECO, S2 is flying at best at one third of orbital velocity. To maintain its apogee at orbital altitude, while accelerating at only around 1g, it needs to fly with a substantial AoA, and hence cosine losses. You can see this for yourself in the webcasts. It can only fly horizontally and maintain altitude once it has reached orbital velocity.
... At MECO, the apogee is already at orbital altitude. So the second stage can just thrust horizontally while it coasts up to LEO, and does not need to fight gravity.
It doesn't - density is about 4.5 g/cm3. The three metals with densities less than water are lithium, potassium, and sodium, but building floating structures out of those would be, shall we say, problematic.
Quote from: LouScheffer on 02/22/2018 01:43 amQuote from: Lar on 02/22/2018 12:39 amWe have seen block 4 before so unless this is a 4.5 or something I don't see the higher thrust part as all that likely. I see no reason they need to switch the engines and the rest of the booster at the same time. If I were SpaceX, I'd start making only the uprated engines as soon as they were qualified. If that's before the rest of the block 5 is ready, no big deal. Just stick them on the model 4 core and enjoy the benefits. Exactly like they did with the titanium fins.What's the alternative in this case? Deliberately build less-useful engines? So my vote is a model 4.5 core.Here is why I think this is a model 4.5 booster. It's way out of family for any other GTO mission. (Data from stcks F9 to GTO page.[... chart deleted ...]
Quote from: Lar on 02/22/2018 12:39 amWe have seen block 4 before so unless this is a 4.5 or something I don't see the higher thrust part as all that likely. I see no reason they need to switch the engines and the rest of the booster at the same time. If I were SpaceX, I'd start making only the uprated engines as soon as they were qualified. If that's before the rest of the block 5 is ready, no big deal. Just stick them on the model 4 core and enjoy the benefits. Exactly like they did with the titanium fins.What's the alternative in this case? Deliberately build less-useful engines? So my vote is a model 4.5 core.
We have seen block 4 before so unless this is a 4.5 or something I don't see the higher thrust part as all that likely.
More evidence for a block 4.5 . If you draw a line through the latest expendable launches, and extrapolate to to GEO-1800, you get about 7300 kg to GTO with an expendable block 4. Add in the improvement we see in this mission, you get 8.1t to GTO. SpaceX claims 8.3t to GTO with block 5, so we are seeing almost all the improvement there is in block 5.Or conversely, a full block 5, according to SpaceX, could loft 8.3t to GTO, expendable. Derate that for recovery, at the observed rates, and a full block 5 could loft 6.3t expendable. This one is 6.1t, so if it's a stock GTO orbit, we're seeing very close to full block 5 performance.
Quote from: jabe on 02/22/2018 09:54 pmWith the stage looking like it has titanium fins, per https://forum.nasaspaceflight.com/index.php?topic=44695.msg1791981#msg1791981, may be worth doing salvage if they lose the stage.anyone know the cost of those fins?jbIt's not really their cost but more the time and labor needed to make them (So yes, cost is also a problem with those when you add in all the prices of the labor and machinery).Titanium doesn't float on water AFAIK, so if they lose the stage there's a really good chance they lose the fins too. If the fins land fairly intact on the deck of OCISLY they may be salvageable, but most of the past landing failures have involved a large portion of the vehicle falling off the ship.
With the stage looking like it has titanium fins, per https://forum.nasaspaceflight.com/index.php?topic=44695.msg1791981#msg1791981, may be worth doing salvage if they lose the stage.anyone know the cost of those fins?jb
Or conversely, a full block 5, according to SpaceX, could loft 8.3t to GTO, expendable. Derate that for recovery, at the observed rates, and a full block 5 could loft 6.3t expendable. This one is 6.1t, so if it's a stock GTO orbit, we're seeing very close to full block 5 performance.
The launch has been delayed past this weekend, they’re doing some additional testing on the fairing’s pressurization system. I thought the fairing issues were over with, the ZUMA launch had been delayed due to this. Is this related to fairing 2.0 or some other thing like a factory problem?
Standing down from this weekend's launch attempt to conduct additional testing on the fairing’s pressurization system. Once complete, and pending range availability, we will confirm a new targeted launch date.
Do we know how the pressurisation system works? Is it active or passive? If further tests are needed I guess this makes it more complex than the vents we see at the base of the fairing with the tear away covers on. If further tests are needed, it sounds like valves and things are involved.
QuoteStanding down from this weekend's launch attempt to conduct additional testing on the fairing’s pressurization system. Once complete, and pending range availability, we will confirm a new targeted launch date.Do we know how the pressurisation system works? Is it active or passive? If further tests are needed I guess this makes it more complex than the vents we see at the base of the fairing with the tear away covers on. If further tests are needed, it sounds like valves and things are involved.Paul
SpaceX Stats now lists the launch for Wednesday evening, no confirmation from SX or Musk twitter
March 1 Range Requested (pending Range Approval).
Quote from: Chris Bergin on 02/26/2018 01:14 pmMarch 1 Range Requested (pending Range Approval).Isn't GOES-S launching on March 1st?Can the range really support two launches on the same day?(I know they want to get there, but are they there yet?)
Quote from: mn on 02/26/2018 05:03 pmQuote from: Chris Bergin on 02/26/2018 01:14 pmMarch 1 Range Requested (pending Range Approval).Isn't GOES-S launching on March 1st?Can the range really support two launches on the same day?(I know they want to get there, but are they there yet?)Yes, it is confirmed when talking about 2 F9's on the same day from Florida due to AFTS being used on both launchers. As for 2 adjacent pads with different launchers that is the unconfirmed part, but the CCAFS range plan is to make it where type of launcher doesn't matter. AFTS would be the factor at play.