The mission requirement being discussed at the time the shuttle system was being built (as unrealistic as it sounds now) ran as follows. In a time of international tension (this was in the depths of the Cold War, after all) the US discovers the urgent need to deploy a reconnaissance satellite into polar orbit. Tensions are so high that the shuttle may be exposed to ASAT measures, being a much easier target to track than its payload. So they launch south across the Pacific, pop open the payload doors as soon as they reach orbit, deploy the satellite, close doors and hope there isn't a proble, do a deorbit burn, and angle the re-entry path hard to return to Vandenburg.
I think the question here is about the USAF polar orbit one-orbit profile, which partly drove the cross-range requirement, not the AOA.
It was AOA that drove the cross-range requirement. The one orbit mission was not realistic. http://forum.nasaspaceflight.com/index.php?topic=4998.msg79056#msg79056http://forum.nasaspaceflight.com/index.php?topic=18127.100
Was there a specific reason for 'one orbit'? Why not a slightly more relaxed schedule?
Quote from: Welsh Dragon on 06/14/2017 10:54 amI think the question here is about the USAF polar orbit one-orbit profile, which partly drove the cross-range requirement, not the AOA. It was AOA that drove the cross-range requirement. The one orbit mission was not realistic. http://forum.nasaspaceflight.com/index.php?topic=4998.msg79056#msg79056http://forum.nasaspaceflight.com/index.php?topic=18127.100
Since the HEXAGON satellites were short-lived, they didn't need to be sun-synchronous.
BRM-3B was hopeless right from the start. Whoever drew it up must not have known anything about orbital rendezvous.
An interesting feature of BRM-3 is that it specifies an inclination of 104deg which is not sun-synchronous. I have seen a track chart for BRM-3 and in the second half of the single orbit the Shuttle would have passed over the Middle East and Western Europe, just below the horizon of the Soviet spacewatch radars in Azerbaijan and Stevastopol. Clearly this was the reason for choosing this particular orbit. The Soviets didn't have IR launch warning satellites in those days, so the launch might have remained secret from them (unless you believe the rumors about KGB moles living in Lompoc). Since the HEXAGON satellites were short-lived, they didn't need to be sun-synchronous.BRM-3A might have been practical since all they had to do was open payload bay, eject the satellite, close the bay, and reorient for retrofire. BRM-3B was hopeless right from the start. Whoever drew it up must not have known anything about orbital rendezvous. Members of Nixon's inner circle claim that some USAF officers convinced him that Shuttle could capture Soviet satellites and that this alleged capability had a major role in approval of the Shuttle program. This story resurfaces from time to time but it makes no sense:-- Soviet spacecraft were designed to take launch loads in the vertical direction only-- we wouldn't know how to design the interface hardware-- we did know that many Soviet military spacecraft had demolition charges on board.But just because it makes no sense doesn't mean that it wasn't told to Nixon.
1. The really difficult intelligence requirement for STS was the 32,000lb to polar orbit payload. This was the tall pole in the program because a large proportion of the total "payload" orbited was the parasitic mass of the Orbiter. The decline in performance with inclination was proportional to the total orbited mass, but had to be subtracted from the much smaller actual payload. 2. Even the "production" shuttles didn't come close to meeting this requirement. How close is hard to say because there is surprisingly little data on masses in the shuttle literature. It seems that most of the performance deficit was extra weight in the Orbiters, which got much worse after ~4,000lbs of lead was added to their noses to fix an error in calculating the center of lift. 3 The USAF tried to fix the problem by A) going to 109% thrust on the SSMEs and B) developing lightweight "filament-wound" SRBs in which most of the steel was replaced by fiberglass. A) never worked and B) didn't work well enough. 4. By 1984 it was clear that the heaviest polar-orbit payloads (KENNEN and LACROS) couldn't be launched and the USAF was forced to break its treaty with NASA and start the CLEV>Titan IV program.5. The failure of STS to meet its cost and flight rate targets has gotten a lot of attention but the payload deficiency led directly to the intelligence community dropping its support for the program. Somebody should study this issue. It is mostly ignored in Dennis Jenkins' book.
If I remember correctly, it was the military that demanded the Space Shuttle be capable of returning to base after just 1 orbit, and this capability was never actually used in the history of STS.How much did this requirement impact the other capabilities and the safety profile of the Space Shuttle? How much better (or worse) would the vehicle have been without this design requirement?
The same reasoning applied to the "large" payload bay. This is often depicted as yet another Air Force stipulation. However one of the shuttle's key mission requirements was building a modular space station. You can't build a modular space station with a little orbiter.
Quote from: joema on 08/10/2017 04:51 pmThe same reasoning applied to the "large" payload bay. This is often depicted as yet another Air Force stipulation. However one of the shuttle's key mission requirements was building a modular space station. You can't build a modular space station with a little orbiter.The payload bay was sized for HEXAGON.There was no space station planned when STS was green-lighted.
Wrong. That was only the length. HEXAGON was only 10ft wise. The diameter of the payload bay was sized fire station modules and high energy upper stage, as stated many times before.
Quote from: Jim on 08/10/2017 07:21 pmWrong. That was only the length. HEXAGON was only 10ft wise. The diameter of the payload bay was sized fire station modules and high energy upper stage, as stated many times before.Apologies for forgetting the Book of Jim. http://forum.nasaspaceflight.com/index.php?topic=29244.msg921978#msg921978But, who would design a 6:1 aspect ratio bay? I think the 60 had a lot to do with the 15.