SpaceX Tuesday...
Discussion
SpaceX is unusual in that they run a test fire several days before the intended launch. Albeit it's only a 3-4 second test usually. The Falcon Heavy test fire will be longer, as they'll be turning on the engines in matching pairs it seems.
Everyone else seems to be happy to just go for it on the big day. Of course Shuttle apart, their engines weren't designed to be reused and even the Shuttle's main engines had to rebuilt or at least given a major overhaul after each firing. The Shuttle's liquid hydrogen fuel wasn't very nice to metal components either. Some rocket could be re-lit (eg the J-2 engine on the Saturn 5 third stage), but most were and still are a one shot deal.
Instead they prefer to confirm function before commiting & lighting the solid rocket boosters (if fitted) & releasing the hold downs. The Shuttle's 3 main engines were started a full 6.6 seconds before lift off. If they didn't hit 90% thrust within 3 seconds, the computers would abort the countdown. This happened 5 times over the life of the Shuttle program.
E.g. STS-68 Endeavor back on 18th August 1994:
https://www.youtube.com/watch?v=Uaav5jgU_gA
They had to empty it, haul it back to the VAB and swap out all 3 main engines before they could try again. It went up eventually on 13th September 1994
Hopefully when SpaceX are happy with the Block 5 models, they'll be able to finalise the Falcon 9 design and no longer feel the need to do pre-launch test fires at all. I'm sure they'll still test fire them over in Texas though. It'll also mean the rocket development team can devote their full attention to the BFR.
Future Falcon Heavy rockets will use the Block 5 core.
Everyone else seems to be happy to just go for it on the big day. Of course Shuttle apart, their engines weren't designed to be reused and even the Shuttle's main engines had to rebuilt or at least given a major overhaul after each firing. The Shuttle's liquid hydrogen fuel wasn't very nice to metal components either. Some rocket could be re-lit (eg the J-2 engine on the Saturn 5 third stage), but most were and still are a one shot deal.
Instead they prefer to confirm function before commiting & lighting the solid rocket boosters (if fitted) & releasing the hold downs. The Shuttle's 3 main engines were started a full 6.6 seconds before lift off. If they didn't hit 90% thrust within 3 seconds, the computers would abort the countdown. This happened 5 times over the life of the Shuttle program.
E.g. STS-68 Endeavor back on 18th August 1994:
https://www.youtube.com/watch?v=Uaav5jgU_gA
They had to empty it, haul it back to the VAB and swap out all 3 main engines before they could try again. It went up eventually on 13th September 1994
Hopefully when SpaceX are happy with the Block 5 models, they'll be able to finalise the Falcon 9 design and no longer feel the need to do pre-launch test fires at all. I'm sure they'll still test fire them over in Texas though. It'll also mean the rocket development team can devote their full attention to the BFR.
Future Falcon Heavy rockets will use the Block 5 core.
Beati Dogu said:
Very likely so.
The Atlas V is on the pad nextdoor, only about 2 miles away and the ULA guys there need to get on with their job. It's also carrying a classified NROL satellite and splattering the launch site with chunks of flaming Falcon Heavy just wouldn't do.
At this rate I can't see F9H getting off the ground in January. The Atlas V is on the pad nextdoor, only about 2 miles away and the ULA guys there need to get on with their job. It's also carrying a classified NROL satellite and splattering the launch site with chunks of flaming Falcon Heavy just wouldn't do.
True on both counts! 
I can sense his concern.
A friend of mine was at Cape Canveral for the 2nd ever launch of the Space Shuttle (STS-2, early November 1981). The countdown was stopped at T-17 and then scrubbed. He had to go back home to Ireland the next day - so it was REALLY frustrating for him. It eventually took off a week later - but he was home by then.
A friend of mine was at Cape Canveral for the 2nd ever launch of the Space Shuttle (STS-2, early November 1981). The countdown was stopped at T-17 and then scrubbed. He had to go back home to Ireland the next day - so it was REALLY frustrating for him. It eventually took off a week later - but he was home by then.
What a sickener. You just can't rely on the buggers; Especially new rockets. They footled around with the Shuttle for months before they felt confident enough to launch it for the first time. Even then they hit a technical issue and had to rob a part off Challenger, which was still under construction in California at the time. It worked out though, as Columbia launched exactly 20 years to the day after Yuri Gagarin became the first human in space.
Here's a nice hazy shot of Falcon Heavy with the Atlas V in the background, to the left.
Here's a nice hazy shot of Falcon Heavy with the Atlas V in the background, to the left.
The Shuttle was more problematic than most rockets - right up to the time it was retired. Apart from all the usual constraints that face rocket launches, the Shuttle had additional ones that often called a halt to proceedings such as -
rainfall (the tiles could not be exposed to water droplets at high speeds),
crosswinds at the Shuttle landing runway (in case they had to perform a Return To Launch Site Abort)
bad weather or crosswinds at the trans-Atlantic abort landing sites (such as Banjul or Zaragozza)
lighting conditions at those abort sights
cold temperatures (ESPECIALLY, after the Challenger accident)
rainfall (the tiles could not be exposed to water droplets at high speeds),
crosswinds at the Shuttle landing runway (in case they had to perform a Return To Launch Site Abort)
bad weather or crosswinds at the trans-Atlantic abort landing sites (such as Banjul or Zaragozza)
lighting conditions at those abort sights
cold temperatures (ESPECIALLY, after the Challenger accident)
Flooble said:
Amazing to think that in twenty years things went from a converted ICBM and basic capsule to a reusable spaceplane. Then in the forty years after that ... um ...
The winged spaceplane idea predates the space capsule by at least 15 years. Eugene Sanger designed one in 1940. The US Air Force intended to start using one in 1965/66 (the Dyna -Soar).NASA conducted much lifting body research in the 1960s and early 1970s. The spaceplane was not an "advancement" on capsules, it was a parallel alternative that had to bide its time before one was finally commissioned. The fragility of the eventual Shuttle has somewhat dented enthusiasm for spaceplanes and the current thinking is that capsules (i.e. blunt body re-entry vehicles) are better and safer for manned use.
Having sad that, one spaceplane is currently making trips in and out of orbit (the X-37) and another is in development for use in the next 5 to 10 years,( the Dream Chaser).
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