not true. Merlin 1C (the previous engine) also dumped the turbopump exhaust overboard. the new Merlin 1D-VAC (vacuum optimized version, for upper stages, not what you're seeing here) is the only Merlin that dumps the turbopump exhaust through the engine bell, because it improves performance slightly at the expense of cost and weight.
13 posts • joined 27 Sep 2011
Re: Why compress helium...
from aeroscraft's own website:
Another way to understand VTOL is to compare the Aeroscraft to a submarine. For example, when a submarine needs to dive into the water, it takes on water to make it heavier. When the submarine needs to surface, it releases that water to become lighter. Similarly, the Aeroscraft can control its weight by releasing and taking on air, controlling the heaviness or lightness of the vehicle.
Re: Fifteen years earlier
DC-X was not 100 feet tall, nor would it ever be capable of getting to orbit. just because something was done before with a very different vehicle does not make this any less difficult, or impressive.
as far as "the recovered rocket motors, pumps etc. will need extensive refurbishment afterwards" - really? Elon Musk repeatedly tells anyone who will listen that that was the whole problem with the shuttle, too much refurbishment. EVERY SpaceX engine is designed to be used multiple (ten at least) times without any refurb, precisely because he doesn't want to repeat history.
Re: "made a close pass within 1.5 miles of the station"
"he could in principle up sticks to somewhere else and work for whoever he chooses on whatever projects take his fancy and suit the commercial ends of the company"
no, he can't. there is a complex law call ITAR which classes rockets and space vehicles as 'controlled exports'. that means, effectively, that you'll be thrown in jail if you try to do what you suggest. because SpaceX did all the development in the US, it has to *stay* in the US.
there have recently been some moves towards relaxing the law a bit on the 'space vehicle' side, but rockets would still be considered 'controlled' (not surprising really, since they bear a striking resemblance to missiles).
Re: Great but oversold?
actually what they are doing is 'berthing', not 'docking'. it is also quite a bit more difficult than docking, partly because of the position of the various ports on the ISS, and partly because they have to rendezvous with an empty point in space, instead of a nice hard space station that stops you in your tracks if you overdo it (there was some argument when the original COTS contracts were drawn up whether to require them to do this, since it is more difficult).
to 'dock' with the ISS, a spacecraft basically approaches the ISS along it's orbit. it has to match the orbit closely (complex), but once that is done, it is stable. then it is a case of forwards/backwards until it docks.
to 'berth' with the ISS, they have to approach from 'under' the ISS (between the ISS and earth). because they are 'below', they are in a different orbit than the ISS. that means that Dragon has to continually fire thrusters at precisely calculated levels as it approaches to keep it aligned with the ISS (imagine yourself balancing on a ball that is slowly getting bigger, and reaching up to change a lightbulb at the same time).
when it is in the precise spot 30 feet away from the station (still balancing using thrusters, remember) the ISS robot arm is positioned inches away from the spacecraft, then thrusters are cut and the robot arm grabs it before it 'falls' away. to complete the example, imagine someone kicks the ball out from under you, and you have to grab the lightbulb a split second later so you don't fall..
so, why did NASA want the commercial providers to berth, instead of dock? because these are cargo missions, and the berthing ports are much larger than the docking ports - so they can move big, bulky supplies to/from the ISS. there's also another benefit of the 'approach from below' to the berthing port: if Dragon (or Orbital's Antares) suddenly fails, just before berthing, it will simply fall away from the space station. if it were instead in the same orbit for docking, there's a pretty good chance the two would collide.
Re: IBM ROMP vs. ARM
the ARM1 chip had mo multiply (or multiply add) instructions. it was used in the Tube coprocessor for the BBC Micro that the article talks about (the £4500 one..). I actually got to use one briefly long after it was obsolete...
lack of multiply was discovered to be causing performance problems, so a slightly revised chip (ARM2) was used from then on (ie: all the Archimedes series) which had MUL/MLA implemented, although it was a bit of a hack - every instruction took a single clock cycle *except* MUL or MLA which could take up to 16 clock cycles (still way faster than emulating multiply in software).
the issue is that the NEO may not be easy to 'get a hold of'. it may be a loose collection of rubble, for example, or spinning wildly.
in that case your large 'gravitational attractor' (read: huge lump of moon rock with rockets attached) is already under your control - you 'just' park it near to the NEO you want to influence.
First stages burn out above the lower atmosphere - almost in a vacuum (very close). they also tend to burn out at extreme speeds (Mach 6 or higher). any parachute deployed at those speeds will just burn up in seconds as soon as the atmosphere is 'hit' on descent.
the parachutes you're talking about on planetary landers were specially designed for Mach 2-3 (at huge expense for 70s Mars landers), and are only deployed after the lander has aerobraked using a large, heavy, heatshield. SpaceX seems to be planning to relight one of the engines to substantially slow the stage before it hits the atmosphere, deploy parachutes, then possibly relight the engine again just before touchdown to reduce landing damage in the ocean, or even do a powered landing on eg a large ship.