RCgothic

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Everything posted by RCgothic

  1. Even without BFR or NG, sheer launch cadence and cost effectiveness allows Falcon Heavy (hell, even Falcon 9) to fill 90% of SLS's brief.
  2. Better to take a chance on ripping up the current design and trying again than to continue to spend money on a design that certainly won't.
  3. It's worth cancelling something when it's clear it's going to fail. The ongoing cash could be better spent on something else. The only mission for SLS that I highlighted that can't be done by another currently operational rocket is volume to LEO. That's a pretty niche requirement.
  4. Guarantee SLS is not landing on the moon or Mars. Doesn't have cargo space for a lander or a lander designed for it even if it had the throw weight to include one, which it doesn't. Doesn't have life support capacity to reach Mars, or cargo space for a hab module or a hab designed for it even if it had the throw weight to include one, which it doesn't. Doesn't have the on-orbit it linger time to construct a mothership in leo, even if it had a design for one, which it doesn't. By the time the next SLS upper stage gets into orbit in a year's time the original second stage's dregs will have evaporated, leaving the newly arrived upper stage unable to throw the weight of the combined mothership anywhere useful. SLS has precisely 3 uses: 1) Large probes on high energy trajectories. But NASA can't afford to build any large probes whilst operating SLS, and other rockets becoming operational can throw multiple smaller probes to the same places for much less. 2) Large cargos to LEO. Gets spanked on a $/kg basis by currently operational rockets. It's a matter of time before a cheaper rocket with comparable volume comes along. 3) Orion to LLO. But currently operational rockets have a high enough launch cadence to support rendezvous missions and even a landing. And it's not cheap. The components it uses haven't flown in their current specification before. It's too expensive to do an all up test for. It will get cancelled the moment the public starts laughing at it, which will be round about the time Blue Origin or SpaceX demonstrate their next gen launchers.
  5. So now you've got an engine specification that's never been flown before negating the safety argument and you've spent even more money on redesigning, stripping it down and rebuilding it. It was a Ferrari. Now it's a Koenigsegg. What would be appropriate is a Mercedes-Benz Actros.
  6. It's certainly impressive that they got so much performance out of the RS25. But did they do so economically? Does the application depend on squeezing every last drop of usable performance out of the engine? Why won't a cheaper, less efficient engine with a denser fuel or slightly larger tank do? There's no point in building a Bugatti Veyron if a Ford Transit will do. Maybe the RS25 was the closest they could get to a solution for shuttle, but even then it didn't quite work. For an expendable first stage engine it's wholly unsuited. And then treating the test due of an engine that probably wasn't even built this century as a milestone. SMH. SLS certainly isn't going to Mars. It can't loft enough mass in one go for an Apollo-style mission to the red planet, and it can't be constructed fast enough to enable on-orbit construction of a mothership. The upper stage propellant would simply boil off before the next launch was ready, and it would take more than one launch worth of upper stage propellant to perform the TMI. For the same reason it's questionable it can even land us back on the moon. Even if NASA had the funding to develop the landers and habs it would require. It's sad to see NASA reduced to this. It's not even NASA's fault.
  7. NASA test fired an RS 25 yesterday, and tried to dress it up as if it were an actual milestone achievement instead of an engine they've had in storage for over a decade based on even older technology and both hideously overcomplicated and expensive for a disposable stage.
  8. I think they have enough recovered Blk3 boosters that if they have to expend a few before Blk5 comes online in April it's no big deal. They won't attempt to use a Blk3 a third time in any case.
  9. April 15th, Iridium 51-55 according to Wikipedia. Date may vary.
  10. Interferometer. Reassembly not required.
  11. Poor dude. That wasn't footage of Falcon Heavy though.
  12. Think I heard this too. The opposite engine would immediately shut down to balance the thrust I reckon, leading to two engines out.
  13. After rewatching, the abruptness of the ASDS getting swamped and then cutting out fits with a nearby splashdown at 300mph. Nothing new beyond the outer engines ruining out of igniter.
  14. Feedback is that the side cores are in good enough condition to fly again but they won't.
  15. I believe I was there in July 2001 when it happened the time before. I recall because the guide said it was unusual. I also recall getting annoyed at her for not having heard of the Enterprise.
  16. According to Wikipedia the first scheduled B5 launch is in April for Iridium Next 51-55
  17. Assume that thrust decays to zero at 10s when Saturn V clears the tower from 100% at t=0 at constant acceleration. Distance s=ut+0.5at^2 condenses to s=0.5at^2 Rescaling y=0.5mt^2 with y between 0 and 1 allows us to find the constant m as 0.02/s^2 Area under that curve is A =1/6 * mt^3, or 3.33s out of a total area of 1*10s =10s. The area not under this curve is the weighted thrust fraction, 6.66s The average thrust fraction is therefore 0.66. So with a total fuel consumption of 13.6 te per second, Saturn's average thrust per second is 9.0 te per second. This beats Falcon Heavy over 10s (90te Vs 82te) but not if Falcon Heavy gets an extra 2s test (98.4te). Falcon Heavy hold down static fire is therefore a more extreme test for the flame trench than Saturn V in terms of total propellant. And with a higher ISP and exhaust velocity it's likely to be a harsher test in that regard too.
  18. Falcon Heavy is something like 8.2 tonnes per second. Assuming Saturn V dumps negligible propellant into the flame trench after it clears the tower (exhaust slowed by distance, "aim" of exhaust wanders) then with a linear reduction it would need to take longer than 14.5s to exceed the Falcon Heavy's static fire. It doesn't take that long, so Falcon Heavy probably wins. But it's moving slowly to begin with. Assuming again zero as Saturn clears the tower and, 10s to clear the tower, and reduction proportional to distance ascended.... I'll do the maths later if nobody else beats me to it. I think it's close.
  19. It takes about 6-10 seconds for a Saturn V to clear the tower, so it's probably reasonable to say that a 12 second Falcon Heavy hold down burn is probably comparable in terms of energy delivered to the flame trench.
  20. I am also with Slashy. Yes, some risks you just have to suck up. There are failure modes you just can't prepare against. If the LM ascent stage springs a leak on the lunar surface there's just no way back from that. You can't pack additional fuel tanks when the margins are that fine. You design the LM so it's as reliable as possible and that's that. But some risks you don't have to just suck up. Was there an unavoidable need for cargo and crew to be on the craft following maturation of rendezvous technology? No. Was putting an orbiter on the side of a fuel tank that had to be insulated with foam the only way to put crew and or cargo in space? No. Were solid rocket boosters the only choice? No. Would a different architecture have allowed full abort capability for the duration of ascent? Yes. Would the airforce have bought in to a conventional rocket family without crippling it with barely-acheivable design requirements? Most likely. Shuttle was a bad design forced to work until it didn't. This isn't just in hindsight - there were articles at the time criticising the choices that were being made. There's no reason except for flawed design goals that NASA's post-Saturn vehicle(s) couldn't have had the reliability record of ATLAS at a fraction of the cost of shuttle.
  21. Fair points both. Capsule and Liquid boosters is still safest though.
  22. But it could have torn free completely, at which point it overtakes the stack and even a capsule with a rapid abort response is at risk. Liquid boosters can be throttled down. SRBs have no place on a manned launch.
  23. Yes, the SRBs could tear free and overtake the stack, LOCV even for a capsule. SRBs have no business on a manned rocket. LFBs could be throttled down to prevent this. SLS is not free from this failure mode. The other failure mode is being on the side of the stack in the path of falling debris. The orbiter was on the side of the stack to enable recovery and reuse of the main engines in a gliding recovery. That wasn't as cheap and effective as advertised, and procluded abort modes for substantial portions of the flight. The exposure of the orbiter to these risks was in hindsight entirely pointless, and it should have been with foresight following STS-1 if not sooner. Manned vehicles must have abort modes from 0-0.
  24. I believe the reason for the long delay this time is that the range needs to be clear for the prep for an Atlas launch today and tomorrow.