Quote from: Lee Jay on 10/04/2016 02:51 amFalcon 9 tankage is 3.7m in diameter.I keep saying this on this forum, but the road transportable limit is closer to 4.2-4.5m. I know this because I've personally managed the shipment of both 4.2m and 4.5m diameter cylinders across the country without doing anything particularly special (like closing roads or removing stop lights).Length factors in as well, I'm sure.
Falcon 9 tankage is 3.7m in diameter.I keep saying this on this forum, but the road transportable limit is closer to 4.2-4.5m. I know this because I've personally managed the shipment of both 4.2m and 4.5m diameter cylinders across the country without doing anything particularly special (like closing roads or removing stop lights).
People keep bringing up the Raptor first stage on Falcon 9. Most of the rocket scientists here have said, it can't and will not work. Raptor uses methane. It is far less dense than kerosene. It would require a wider first stage to hold enough to power 3 Raptors.
One SL Raptor engine gives 137N of Thrust in 20%, the SuperDraco gives 72N. So I think the idea can work, just find difficult that Spacex will use differents fuels on the first and second stages, just increases the complexities.
That said, I think the huge composite LOX tank that they showed off was probably built someplace other than Hawthorne, so maybe they've already started a large-scale composite fabrication shop in Texas or Florida.
People keep bringing up the Raptor first stage on Falcon 9. Most of the rocket scientists here have said, it can't and will not work. Raptor uses methane. It is far less dense than kerosene. It would require a wider first stage to hold enough to power 3 Raptors. It would not be road transportable. It would require rebuilding the ground infrastructure to handle it. Now a 5.2m vacuum Raptor upper stage the same length as the existing second stage might work. It would allow the first stage to return to launch site for most launches. It could also lift more payload to LEO. It would also work great on a FH. Now, they would have to add methane handling equipment at the launch pads. They would have to rework their strong back. It would also have to be made near water transport or a large airport for Super Guppy type air transport. This is why Saturn V and Saturn IB used kerosene for first stages. It has the most lift capability for size of any fuel short of maybe solids. Hope this helps.Having methane on a first stage would require a whole new rocket design. This is why the New Glen rocket of Blue Origin will be about 7m in diameter with 5 BE-4 engines which are similar in thrust to the Raptor.
......So in summary, a methalox Falcon 9 family built with small Raptor-like cousins can be the same size as the existing Falcon 9 family. It will however be even more reusable, carry more to orbit, mass less, damage the pad with less thrust, and be burning an even cleaner propellant mix. To me, this seems like it would be a worthy long-term upgrade to the Falcon 9 family. To others I’m sure it is not, so please sound off below about the math posted above, what you think of a methalox Falcon 9, and whether you think it would be worth the change.
Quote from: Lee Jay on 10/04/2016 02:51 amFalcon 9 tankage is 3.7m in diameter.I keep saying this on this forum, but the road transportable limit is closer to 4.2-4.5m. I know this because I've personally managed the shipment of both 4.2m and 4.5m diameter cylinders across the country without doing anything particularly special (like closing roads or removing stop lights).But how do you get a 4.5 m tank out of Hawthorne? When I've looked it appears there are a number of difficulties very close to the SpaceX facilities.I think the idea of SpaceX building rockets elsewhere should be met with skepticism. Major construction elsewhere will increase their costs. It would be good to stick with road-transportable stages.That said, I think the huge composite LOX tank that they showed off was probably built someplace other than Hawthorne, so maybe they've already started a large-scale composite fabrication shop in Texas or Florida.
I suspect they may have built it at the Brownsville location.
Quote from: Patchouli on 10/09/2016 04:30 amI suspect they may have built it at the Brownsville location.Where in Brownsville would they have built the tank? There's not any buildings there yet that SpaceX owns which would be that size ...
A combination fairing/heat shield would probably weigh too much for F9 causing a very low mass payload, and it would have to be carried all the way to orbit. Existing fairings eject before the payload reaches orbit. To me, the best solution for F9/FH is a metholox 5.2m upper stage to increase payload capabilities. It would have to be a sub scale Raptor. The stage might have enough fuel left to slow it down and drop through the atmosphere like Starship is going to do and parachute down, and be retrieved by maybe a helicopter. Even an expendable metholox upper stage at 5.2m in diameter can increase F9 to about 28 tons to LEO and FH to about 70-80 tons to LEO. Quite a boost in payload capability. However, SpaceX is not going to do anything to the F9/FH system as they are concentrating on Starship.
I think we are going to lose only the weight of the fairing in payload about 1.9 (actual fairing weight) tons which is les than 9% loss for LEO, and less than 23% for GTO.If we can build a relatively light heatshielding capable fairing it would be doable.
But that 1.9 ton fairing isn't a real heat shield. The only reason they survive reentry as they do is because they weigh almost nothing relative to their cross-sectional area when oriented properly. If you added the dry mass of S2, none of it survives. So you need a heat shield, which adds weight, which directly cuts into payload. To just suggest "make a lighter heat shield" isn't particularly useful. The idea that they're going to make "fairing 2.0" that can also do double duty as a re-entry shield for S2 without any mass penalty is probably hopelessly optimistic. (never mind the added mass penalty of other recovery associated hardware).
So absolutely agree, it is not as easy as spacexfanatic seems to think. If it was, SpaceX would likely already have done so...
Quote from: spacenut on 10/04/2016 01:45 amPeople keep bringing up the Raptor first stage on Falcon 9. Most of the rocket scientists here have said, it can't and will not work. Raptor uses methane. It is far less dense than kerosene. It would require a wider first stage to hold enough to power 3 Raptors.Keep in mind that Raptors have over 18% more IsP than Merlins, so this could partially compensate the less denser propellant. Also 3 Raptors have a higher thrust than 9 Merlins and this can reduce gravity losses (and more if using >3 Raptors, which could possibly be accommodated since their size is not much bigger than the Merlins).
Quote from: cdebuhr on 04/26/2020 04:21 pmBut that 1.9 ton fairing isn't a real heat shield. The only reason they survive reentry as they do is because they weigh almost nothing relative to their cross-sectional area when oriented properly. If you added the dry mass of S2, none of it survives. So you need a heat shield, which adds weight, which directly cuts into payload. To just suggest "make a lighter heat shield" isn't particularly useful. The idea that they're going to make "fairing 2.0" that can also do double duty as a re-entry shield for S2 without any mass penalty is probably hopelessly optimistic. (never mind the added mass penalty of other recovery associated hardware).Not only that. As you say, the fairing is jettisoned as early as possible, typically just after main engine cut-off (MECO), which means that it reenters the atmosphere at a much lower speed than the S2 will. In the latest Starlink mission, for example, that was approximately at a speed of 8130 km/h. Compare that to the speed at SECO (second-stage engine cut-off), 26900 km/h, more than three times as high. Just that would subject you to much higher temperatures.So absolutely agree, it is not as easy as spacexfanatic seems to think. If it was, SpaceX would likely already have done so...
A 1kg object(1st stage) at 8000km/s has 2.5mj, at 2800km/s (2nd stage) has 30mj, that is why 2nd stage recovery is so much harder than 1st stage. Plus every 10kg of recovery gear added to 2nd reduces payload by 10kg, for 1st payload penalty is 1.2kg.https://www.calculatorsoup.com/calculators/physics/kinetic.php
Quote from: spacexfanatic on 04/26/2020 12:14 pmI think we are going to lose only the weight of the fairing in payload about 1.9 (actual fairing weight) tons which is les than 9% loss for LEO, and less than 23% for GTO.If we can build a relatively light heatshielding capable fairing it would be doable.But that 1.9 ton fairing isn't a real heat shield. The only reason they survive reentry as they do is because they weigh almost nothing relative to their cross-sectional area when oriented properly. If you added the dry mass of S2, none of it survives. So you need a heat shield, which adds weight, which directly cuts into payload. To just suggest "make a lighter heat shield" isn't particularly useful. The idea that they're going to make "fairing 2.0" that can also do double duty as a re-entry shield for S2 without any mass penalty is probably hopelessly optimistic. (never mind the added mass penalty of other recovery associated hardware).But it gets worse ...The fairing is jettisoned ASAP for good reason. As a rule, on any launch you want to shed dead weight as soon as it is practical to do so, so that the rocket engines can use what total impulse they've got left accelerating only that stuff that is still needed. Now you want to take the now heavier fairing-plus-heat-shield all the way to orbit. This is going to cost you massively in terms of mass to orbit. Much more than just the extra mass of the heatsheild, etc. I can't tell you what the mass to orbit penalty is in detail, because first you need to figure out how much this is all going to weigh, and then you need to do the math, but its not going to be pretty.To help illustrate the point, ask yourself this question ... Why do they drop S1 when its empty? Now, I realize that comparing a depleted S1 to a payload fairing is a bit extreme, but in both cases the you're shedding dead weight for precisely the same reason.