A history, over at Ars Technica. In addition to the balloon tanks, there were concerns with the common bulkhead between the LOX and LH2 tanks (though AFAIK this has never caused a Centaur failure).
As I’ve written before, there was an alternative approach, that NASA never considered.
I’ve never heard of the “Dry Centaur” concept until now. It’s mentioned in Rand’s second link. I wish I could find Pournelle’s article on it, but so far, no luck.
It’s a brilliant concept IMHO; it largely solves the safety problems with Centaur, plus it would have advanced the tech needed for refueling.
To be honest, I always felt that using a shuttle to launch an upper stage like that was both risky and pointless. You don’t need a manned rocket to launch sats, especially one that’s got what amounts to a 100,000 lb payload shroud.
I felt the push (during the early years of the program) to make Shuttle our only launch provider to be beyond comprehension, so much so that I suspected treason or other dark conspiracy (I was about 12 at the time.). Now I just think they were utterly insane.
Follow up to my post above; I think I’m misremembering; I now think I became aware (my family was involved in aerospace) that they were trying to make Shuttle the sole launcher just before Challenger (even though history indicates the policy had been in place for some time; I just was unaware), so take my recollections on the policies of the time with a huge grain of salt.
The Shuttle program was always premised that it would be the sole launcher for the nation (official name: National Space Transportation System). It was the only way they could get enough traffic to get the flight rate needed to hit the cost targets (it still failed). Fortunately, the Pentagon resisted.
Thanks for the info, Rand.
Any idea why they believed they could get the flight rate that high? Shuttle wasn’t designed for easy or fast servicing (a fact I find rather odd, given the plans for fast turnaround).
It’s a good thing the Pentagon resisted, or we’ve had had a far bigger mess.
At the time they made that philosophical decision, the decision makers didn’t understand the real issues with the program. There was a lot of denial about it, all the way until January 1986.
So, would the External Tank (ET) be orbited instead of dropped in the Indian Ocean, and the fuel transfer be on orbit?
Or would the transfer happen just short of orbit, when they are sure they can make orbit, while still thrusting to provide G-force to settle to liquids in the tank?
Paul, those are very interesting points. Taking the ET to orbit would have been a performance hit, on missions that were already very performance-marginal.
If the fuel transfer would have been speedy, maybe they could have done it during OMS-1 (which would have been a more lengthy than normal burn on those missions anyway). That would have solved the settling issue, and alleviated some of the performance hit, but it’d definitely put the transfer on a very tight schedule. IMHO, it’d be very technically challenging to do it pre-MECO, due to high fuel flow through the umbilicals, but if that was viable, your idea would result in the least performance hit.
Shut down 1 of the 3 main engines towards the end of the main-engine burn so you can get enough flow through the umbilicals to fill the Centaur?
I guess you don’t want to fuel the Centaur until you are sure you “made orbit” to avoid the hairy abort modes.
Aw, heck! Just put the Centaur on a Titan rocket . Why did we or anyone else think it to be a good idea to put a cryogenic rocket stage instead the Payload bay?
Because there was to be no Titan rocket. One Shuttle to rule them all.
What I’ve heard is that dumping the external tank used a dog-leg maneuver that cost enough delta-V that taking the tank to orbit wouldn’t hurt payload.
maybe they could have done it during OMS-1 (which would have been a more lengthy than normal burn on those missions anyway
You couldn’t do OMS-1 with tank attached, for numerous reasons. The transfer had to be completed prior to MECO, tapping off the flow through the umbilicals.
No OMS 1 with ET attached? Hrmm.
Oh, I see; the OMS couldn’t gimble enough to bisect the CG with the ET attached, when the ET had a lot more mass than when empty. Plus of course the issue of delta/v.
What confused me into thinking it might be possible was that they did, at least once, fire the OMS engines with ET attached. It was during the ATO – but, of course, two of the SSMEs were firing too, and those certainly could gimble through the CG.
If you look at the later missions, the OMS fired on several of them during the uphill climb. It may be the case that with the SSME’s not firing and the tank attached that there would be a CG issue but on many occasions as well they did a direct ascent to orbit with the SSME except for the circularization burn.
After writing the above, this also makes no sense as there were always plans to take the tanks to orbit which by definition means that they could fire the OMS with the tank attached.
There were a lot of things that they thought they could not do early in the program that they did toward the end. One of them was to do OMS burns during SSME powered flight. It bought some considerable improvement in payload to orbit.
My point wasn’t that you can’t burn OMS during powered flight, but that you can’t do it after MECO with tank attached.
That does not make any sense either as there were many proposals to use the ET in orbit which would have by definition required using the OMS after MECO.
Do you think that OMS had gimbal authority to fire through the CG with an ET attached? I don’t think so.
There were a lot of smart people, Including NASA that worked on plans to take ET’s to space. If there was no way to do it, wouldn’t that roadblock have come up during that time?
The latter.
This reticence to fly the Centaur has always baffled me. The Shuttle has a far less rocky ride to orbit than an ELV. This is especially the case with the keel pins along the cargo bay floor. They flew LOX/H2 tanks in the orbiter all the time for the fuel cells and later in the program flew cargo bay mounted extra tanks for the LDO missions.
The bottom line is that the folks that built the orbiters knew far more about the capabilities of the system than the people who later operated it.