PakledHostage

Indeed. It was fun guys! I gotta go to a meeting so can't watch the rest of the climb to orbit. Post a video if anyone has the link?

I understood that the dropouts over Rf violated launch constraints, but they are going to stay on wire ("hard line") telemetry until T-0 minutes to avoid violating the constraints again. They are just recomputing their T-0 time and will pick up the count shortly. They believe that the problem was multi-path in the Rf signal. Edit: New T-0 time is 02:33 UTC (about 15 minutes from now)

Now the LD has commanded not to release the hold. Anyone know what's up? Edit: reset hold to 10 minutes until T-4 minutes. Something about dropouts in the telemetry from the SV

Exiting hold at T-4 minutes. Good luck guys!

T-10 minutes with just under 20 minutes to launch.

Something that I've always been curious about on the topic of Oort clouds is the Oort cloud surrounding Gliese 710. By some estimates, that star will pass through the outer reaches of our Sun's Oort cloud in just over a million years. How big is its own Oort cloud though? If it is of comparable size to our own Sun's, then it stands to reason that some of its Oort cloud bodies could pass through the inner solar system of our Sun.

Just down through T-45 minutes, and just short of an hour to launch.

Impressive. Thanks for sharing.

I have always assumed that it is the time step that the game uses when numerically integrating the forces that act on your spacecraft while it is on "physics" (rather than while on rails). Longer time steps in numerical integrations typically introduce more error because they represent a courser approximation. Think of it like a low resolution image; the longer the time step (i.e. the 0.12 second setting), the lower the resolution and the "grainier" the result. Shorter time steps can also introduce error, however, because computers have only limited precision in the numbers that they store. Rounding errors can accumulate to become very large over enough time steps. See Lies my computer and calculator told me for a good description of some of the pitfalls of performing calculations with computers. The article is a bit dated now but it is still relevant. I wish I could give a better answer than that, but I can't tell you which setting to use without knowing the details of how the game integrates the forces acting on your spacecraft while on physics. It is probably best to experiment with it. I have it set towards the low end on my game. Edit: Wow, uber sniped by three guys!

Thanks for clearing that up for us.

Please re-read my post. I did not advocate censoring discussions about project Orion. I advocated a single "megathread" that would be the forum for discussing all things "Orion". As it is, we currently have two threads where you are debating the merits of Orion, and the topic probably comes up in another half dozen threads every week. We've all heard your arguments and recognize that you are entitled to your opinions, but bringing it up over and over again just polarizes the discussion in this science forum.

I agree. It is getting a lot tedious. I know it is a bit of a stretch, but maybe we could ask the mods to sticky an Orion thread and make it a rule that all discussion about project Orion goes there and there only? I don't think the rule would affect a lot of people. After all, there's really only one member on these forums who keeps bringing it up and subjecting the rest of us to the same arguments over and over, ad nauseam.

Oh don't worry about it... Your English is far better than my Turkish and we can tell that you don't know what you're talking about even with the grammar mistakes.

You have to ignore the cheesy voice-over, but this video has some good footage of the GPS IIR-1 satellite launch failure in 1997, and associated property damage. Fortunately nobody was hurt.

Not directly space related, but I have always been impressed by Arthur C. Clarke's prediction in 1974 about how we would use computers... The only thing he failed to foresee in his prediction was that we wouldn't just use the computer as a phone, but that the computer he described would be the phone. http://www.youtube.com/watch?v=OIRZebE8O84

Have a read through the description of the Challenger accident sequence. The breach of the right-hand SRB wasn't obvious until the footage was reviewed by the accident investigators. The final destruction only started when the R/H SRB broke free of its lower attach fitting at 72.284 seconds into the flight. Evidence of the aft bulkhead of the external tank failing isn't seen until almost a second later. At 73.162 seconds, there is evidence that the right-hand SRB has pivoted into the upper section of the external tank and caused its rupture. The hydrogen tank had been leaking since about 66 seconds into the flight but there was no "explosion" until after the R/H SRB broke free and penetrated the liquid oxygen tank.

I don't think we are being trolled. GregroxMun is a regular on these forums. I don't have any sense of his/her age or background, but there are quite a few science minded kids here, and also several professional scientists and engineers. We do what we can to help out when someone has a question, even if it is a bit unusual (so long as they are polite about it).

Interesting photo of the propfan. Looking up the registration, the aircraft is an Antonov 70. Only two were ever built according to Wikipedia. It cruises slower than typical turbofan powered aircraft so it is operating under different conditions than they do. Something else that is interesting about it is that it appears to have counter rotating propfans. Propeller's accelerate the air that passes through them both axially and radially. The counter rotating props allow the recovery of some of the energy lost in radial velocity, thereby increasing the efficiency.

Like most respondents in this thread, I'm assuming that you're talking about mounting a propeller on the front of a turbofan engine. Something to keep in mind though is that turbofan engines are already optimized for peak efficiency over their typical operating range. To put things in perspective, a 747-400 has a fuel capacity of ~375 000 pounds. Compare that to the empty weight of 400 000 pounds and a useful payload (with full fuel) of only 100 000 pounds. Flying a 747 on a return flight from LA to Sydney will burn almost two full tanks of fuel costing close to half a million dollars. Whatever you save in fuel burn not only saves you money, but it also increases useful payload (because you have to carry less fuel to reach your destination and can carry payload instead). Fuel costs money and useful payload pays the bills, so clearly there is a huge incentive to increase the efficiency of engines. Engine/airframe manufacturers already do everything that is technologically possible to increase efficiency.

It seems that Gravity has been nominated for Best Picture at this year's Academy Awards... I guess I am wrong; it didn't suck. Mea culpa.

People who exaggerate... I must've heard it a million times this past week: "It is minus 60 in Saskatchewan!"

But that wasn't my point. My point was that even engineering designs such as commercial airliners that are less complex than spacecraft often require "hotfixes" (to use your word) in service. This despite the fact that they are built to operate in a somewhat more forgiving environment than spacecraft and are designed to comply with a large body of regulations that evolved as a result of decades of experience. I intentionally chose the example of AD 75-15-05 because it relates to a design problem that existed in all widebody aircraft designs at the time. In hindsight, it is pretty obvious that suddenly exposing the cabin floor to a differential pressure of 6-8 psi between its two sides could cause it to collapse, but nobody took the possibility seriously enough to mandate new design requirements until after the Turkish Airlines accident. This closely parallels the debate that is going on in this thread, which is why I mentioned it.

But this sort of thing happens in aviation all the time. Why should spacecraft be any different? Every single commercial aircraft type currently in service (including the new 787) has a long list of airworthiness directives. Airworthyness directives are a regulatory mechanism that allow regulatory authorities like the FAA to force operators to modify their in-service aircraft. Sometimes, the "worst case [accident]" that necessitated the airworthiness directive didn't even happen to the aircraft type that must be changed. For example, a lot of armchair aviation buffs like to hate on the DC-10 because of the Turkish Airlines crash, but subsequent to that crash, the FAA issued AD 75-15-05 that required operators of wide body Boeing, McDonnell Douglass, Lockheed and Airbus aircraft to install blow-out panels in the cabin floors so that the floors wouldn't collapse in the event that the aircraft depressurized above or below the floor. In other words, one of the design flaws that contributed to the Turkish Airlines DC10 crash existed in all wide body aircraft at the time, and all had to be modified after the problem was recognised.

This reminded me of a something, so I hunted around on YouTube for a bit. Hopefully some of you will enjoy it (just ignore the words at the beginning; they seem to be just translations of the credits).

We had a related discussion about a month ago. There was some debate about whether or not it was possible to see the moons with the naked eye. I won't speculate on whether it is possible or not, but Jupiter's moons do span up to about 1/3 of the diameter of the full moon depending on their orbital positions. I took the photo below with a standard DSLR camera with a 300 mm lens. I scaled the image down by 50% and cropped it for posting, but both the upper and lower images are the same scale.