Jump to content


  • Posts

  • Joined

  • Last visited

Everything posted by sevenperforce

  1. Its next encounter will be with Poseidon...
  2. Isn't that the same as saying T-4 in 0 minutes?
  3. They're talking about how the 40-second hold opportunity doesn't exist for Falcon 9? That's interesting. Still waiting for closeout of prop load on the first stage.
  4. They're getting very close. Closing out prop load on the header tanks. Starship main tanks already closed out and pressed. Still loading Superheavy. That up-close shot showing the booster vibrations at the frost line...wow. This thing is a beast.
  5. INSPRUCKER They've gotta assume this is getting a bunch of viewers who are much less familiar with rocket science.
  6. Well, there’s some question as to whether more mass or more speed does a better job. DART seems to suggest that energy is the primary driver, given the tremendous multiplier over the pure momentum exchange. The nuclear test ban treaty only forbids nuclear TESTING in space; it doesn’t prohibit the USE of nukes. If we were deflecting an asteroid, the use of nukes wouldn’t even be a technical violation of the treaty.
  7. The engines can ignite and start the flip at a higher altitude when people are on board. If all engines ignite nominally, then they just throttle down; if there’s a problem then there’s time to adjust.
  8. I will note that with transoceanic flights, the odds of survival on a ditch with total engine failure is uncomfortably low. There have only been three instances where a commercial aircraft was intentionally ditched in deep water due to engine failure; one resulted in total LOCV and the other two had about a 50% passenger rescue rate. And near-airport ditch events caused by engine trouble just after takeoff routinely result in loss of life. Total engine failure on Starship is essentially the equivalent of total engine failure over the open ocean. And keep in mind that numerous ocean ditches with multiple or total fatalities have resulted from a partial engine loss; Starship can land even with two engine failures. That seems excessive. Dragon flew - what? 20 flights before Crew Dragon was a thing? I see your point, but at the same time Falcon 9 had flown MANY times before Doug and Bob climbed into Dragon Endeavor. When the reliability of the underlying launch vehicle is a larger aspect of the LOCV calculation, it’s more appropriate to have a large number of launches before people hop on. Which just reminds us of the utter insanity and inanity that was the Shuttle. Sure, let’s throw human beings onto a vehicle that (a) has never flown before and (b) has zero contingency abort modes.
  9. I'd bet sooner. But of course SMART requires engines.
  10. How do you propose to make a reusable second stage? You have three options for reusing your orbital stage. First, you can have it enter butt-first with its own heat shield, like the Stoke Space design and the Chrysler SERV design, and perform a propulsive landing or a parachute landing. Second, you can have it enter head-first with its own heat shield, like the old Delta Clipper concept or the original reusable Falcon Heavy Upper Stage concept, then execute a 180° aerodynamic flip maneuver, then perform a propulsive landing. Third, you can spread your TPS across the side of the vehicle and have it enter sideways. With the third concept, you can either land it horizontally with wings or you can execute a 90° aerodynamic flip with a propulsive landing. Those are your options. There really isn't anything else on the table. The Shuttle also had heat tiles on moving joints -- in fact, it had heat tiles on the landing gear door seams. Why do you think the belly-flop maneuver is risky? The Shuttle had an incredibly thin range of allowable flight angles during re-entry, far less than what Starship can handle. Columbia didn't come apart directly due to heat shield failure; it came apart because the change in drag over the failure area became greater than what the control surfaces and RCS could handle and so it yawed out of the acceptable flight angle range. That's not how modern testing works. This is not KSP. SpaceX isn't just using 15 or 20 flights as single "well that looks safe" datapoints. Rather, every one of the tens of thousands of sensors all over Starship is firing at every single moment in every single flight. It's the sensor data that is most valuable. Besides, this thing is going to get a lot more than 20 flights before we put humans on board. At least for launch and Earth EDL. What airframe? The HLS lunar Starship is just a tube with engines. All rockets are tubes with engines. Do you have a better idea for a lunar airframe? As for Mars, yes: the concept was to have a vehicle which can go to Mars, land on Mars, take off from Mars, and land on Earth. If we want people to go back and forth between Mars reliably, that will become necessary. "Move fast break stuff" is the development strategy which is designed for fast iteration and finding faults faster. If you have a potentially fatal defect in your vehicle, then the more testing and more iteration you do, the more likely you are to expose that defect. Operational flights with people on board are not part of the development strategy.
  11. Assuming 3-4 years to set up and launch the mission and a pure impactor mechanism, we could reach 2021QM1 in under 5 years. The asteroid is smaller than Dimorphos, the target of the Dart mission, and so we could expect a fairly significant amount of deflection from a simple impactor. Another impactor like DART would change 2021QM1's orbital velocity enough that its path would diverge by half the diameter of Earth over a 10-year period. So we would have plenty of time. I suspect that in a real-world situation, we would use dramatic overkill and launch multiple megatonne-class nukes to make absolutely sure that it was deflected well out of Earth's path. Makes me think of a fictional setting where someone alters the detonation times of the nukes such that it is nudged into a collision course with a specific point on Earth....
  12. It's definitely big enough to be a city-killer, so it would absolutely be a worthy candidate for deflection if it was anywhere near dangerous to Earth. It takes 691 days to orbit the sun and goes from a perihelion of 0.5 AU (nearly as close to the sun as Mercury) all the way up to an aphelion of approximately 2.6 AU (well beyond Mars and inching into the asteroid belt). Its inclination, ascending node longitude, and argument of periapsis nearly matches that of Earth, although with enough variation that close passes are rare. From a ▲v perspective, it's not significantly more difficult to reach than, say, Ceres. Dawn took 7 years to reach Ceres, but that was with a flyby of Mars and a fourteen-month orbital vacation around Vesta, and it used ions which obviously are slow. We could reach 2021 QM1 quickly enough in a pinch. Because Earth's orbit has so little eccentricity, it doesn't matter where in our orbit we launch from. Leaving Earth orbit and going from 1 AU to 2.6 AU will cost around 4 km/s of ▲v BLEO and require a coast period of around 14 months, but that's if we want to do a minimum-energy Hohmann transfer and actually match velocity to 2021 QM1 to use some sort of gravity tractor. On the other hand, if we are hitting it with a simple impactor or a nuke, we can do a much faster transfer. It may or may not cost more ▲v for the fast transfer since 2021QM1's orbit is so eccentric.
  13. At launch. But 100t less dry mass will have an extreme impact on delta-v, resulting in an early burnout of the second stage. Either they will have lots of fuel left (which they propably cant vent during the half orbit they are doing) or they start with less than full fuel tanks, which will be more than just 2% of the mass at liftoff. In either event, the outcome will be well within the system's ability to compensate. For one thing, they're only running the Raptors on Superheavy at around 90%. And they can similarly throttle down Starship to compensate, or burn to a slightly higher orbit, or dump propellant. It's not just a half orbit. It's the equivalent of a full orbit -- a rather aggressive one -- just with a higher apogee and a perigee inside the Earth.
  14. The fully loaded Starship + Superheavy is over 5,000 tonnes. The impact of having or not having a 100-150 tonne payload will be an acceleration difference of 2%. Negligible. I think they at least try to recapture the methane. I certainly hope so, anyway. It's an extremely potent greenhouse gas, so just dumping a huge tank of it would be a big no-no environmentally. Oxygen is no big deal, as long as you don't dump it all at once, because that's obviously a fire/explosion hazard. Oh, they pump everything they can back into the tanks. Both LOX and methane.
  15. I wouldn't terribly mind seeing a kaboom -- anything past liftoff is a success -- but I'd prefer having it happen at T+ something rather than T- something.
  16. John notes that they begin lighting the engines over a six-second period rather than the ~2 seconds for Falcon 9.
  17. Sad that it won't be tomorrow, but at least that means I'll be at home again Wednesday for the next attempt.
  18. Maybe, maybe not. I don't know that we have seen them load prop into the updated header tanks.
  19. What about the re-entry observation over Hawaii? It can’t get that far west that fast.
  20. If it can hoover then I have a backyard that needs to be cleaned up
  21. I guess that allows them to expend more propellant on the second stage burn, but it's disappointing that they won't try.
  22. That's encouraging! Woke Starship is based. /s
  23. "For the benefit of Earth" Okay just stop talking and DO it.
  • Create New...