I think that is fair. However, as I have said, I believe there is a lot more behind the scenes at play here than is often given credit, not the least of which is how to sell the larger Ares program to Congress in a manageable way that will provide incremental progress to keep the money coming. In the end, isn't it better to proceed with a rocket that has money and political will to build it than a better rocket that doesn't? Let me also give an example of non-political "nitty gritty" details that are so easily ignored but directly contribute to the design of the rocket:(from http://www.safesimplesoon.com/mythbusters2.htm)QuoteIn ESAS and until last Spring, the Ares—I injected the Orion into a 30x160nmi transfer orbit and the Orion then circularized itself, to avoid the complexity of deorbiting the large upperstage. Working with Constellation and CEV project teams, the program elected to change to a -30x100nmi orbit to move the ocean impact of the CLV upperstage to the Indian Ocean from the South Pacific to stay away from populated islands. It's details like where the spent stage will land that can shape the rocket design, but drive the vehicle away from what the objective rocket designer would consider ideal.
In ESAS and until last Spring, the Ares—I injected the Orion into a 30x160nmi transfer orbit and the Orion then circularized itself, to avoid the complexity of deorbiting the large upperstage. Working with Constellation and CEV project teams, the program elected to change to a -30x100nmi orbit to move the ocean impact of the CLV upperstage to the Indian Ocean from the South Pacific to stay away from populated islands.
The inescapable truth is that a -30 nmi x 100 nmi orbit requires a pretty big delta-V from Orion or it's coming down in the ocean along with the upper stage. In other words, Orion is its own third stage because Ares I can't place it into a proper parking orbit.This is a design bug not a feature!
Perhaps a better alternative would have had the upper stage inject Orion into a circular parking orbit, followed by the upper stage doing a de-orbit burn to dump the upper stage into the best possible spot in the ocean.
But this simply would not have been possible with Ares I. It lacks the performance nessary.
The key with the strap-on SRB's is that any TO effects which do occur are easy to mitigate using existing and well-proven techniques.Every strap-on SRB in use, including the very large Shuttle and Titan SRB's, has been attached to the booster using a joint which is specifically designed to either safely absorb the forces of the SRB's oscillations, or to change the frequencies so that the TO frequency doesn't coincide with the resonant frequency of the vehicle any longer.
Quote from: kraisee on 12/10/2008 06:16 pmThe key with the strap-on SRB's is that any TO effects which do occur are easy to mitigate using existing and well-proven techniques.Every strap-on SRB in use, including the very large Shuttle and Titan SRB's, has been attached to the booster using a joint which is specifically designed to either safely absorb the forces of the SRB's oscillations, or to change the frequencies so that the TO frequency doesn't coincide with the resonant frequency of the vehicle any longer.I think this is not correct description what's going on with more solid boosters. TO is in fact reaction of vehicle to the forcing function. If this reaction coincides with vehicle's natural frequency you have a problem.Vehicles like STS, Titan IV, Ariane 5 and medium EELVs take advantage of having more than one forcing functions. Those functions interact and result in less organized superpositioned forcing function. As this function is less organized it is less likely that it can tune up with vehicle natural frequency and cause dangerous levels of vibrations.Notable difference is Atlas V 411 which has just one solid. It would be interesting to see what the change in observed vibration levels is. However, it's likely that the stack was designed to be insensitive to the forcing function of SRB (or vice versa) in the first place. On the other side interaction of more forcing functions can cause vibrations not only in axial direction but also in lateral direction. This is exactly what happening with space shuttle on solids when astronauts are shaken to the “sides”. Astronauts in Orion won't be shaken to the sides (in big extend) but rather experience variating force pushing them straight up.
Quote from: jeff.findley on 12/11/2008 02:24 pmThe inescapable truth is that a -30 nmi x 100 nmi orbit requires a pretty big delta-V from Orion or it's coming down in the ocean along with the upper stage. In other words, Orion is its own third stage because Ares I can't place it into a proper parking orbit.This is a design bug not a feature!The delta-V to circularize this orbit is only about 62 meters per second, which is less than 1% of the total delta-V provided by the upper stage. NASA could have designed the upper stage to provide this extra impulse (the total vehicle weight would have been less if it had), but it did not in order to drop the stage safely into the Indian Ocean. Shuttle is nominally suborbital after MECO. It takes a 50-ish meters/second OMS burn to circularize the orbiter's orbit. Is that also a bug? - Ed Kyle
Sure, it's debunked to the point where the current design won't see TO killing astronauts. It will only shake them bad enough that they won't be able to throw switches... (rolls eyes).
Your article talks about the ability to read a 10 point font on a display with an error rate of 10% at 1.0 g's of simulated thrust oscillation. How does this relate to throwing switches? Is it humanly possible to timely and accurately throw a switch under those conditions? Has this already been studied?I guess if astroanuts aren't expected to ever have to throw switches, they're passengers on Orion, not pilots.
No TO mitigation is not complete. Yes, further testing is required, and yes, they won't have the best data until after Ares I-Y, but the statement you made didn't fit with the current information. We're talking about less shaking you get in your car, when reading your SatNav.
Since when does the shuttle launch into a 100 nmi orbit? How much mass could Ares I put into a typical shuttle (i.e. ISS) orbit assuming that Orion does a 50 ish meter/second burn, just like the shuttle?
Ares I simply is not a viable launch vehicle without Orion performing like an upper stage. Again, this is a bug, not a feature.Jeff
Quote from: jeff.findley on 12/12/2008 03:12 pmSince when does the shuttle launch into a 100 nmi orbit? How much mass could Ares I put into a typical shuttle (i.e. ISS) orbit assuming that Orion does a 50 ish meter/second burn, just like the shuttle? If Ares I injected Orion into a typical post-MECO shuttle orbit (58 x 220 km, for example) it would only cost perhaps 0.4 tonnes of payload capability. And that assumes that the current Ares I design is used without alteration. It would very likely be possible to squeeze more performance out of Ares I for a higher orbit if NASA specified such an orbit. But there is already enough, or nearly enough, margin between Ares I capability and Orion's allocated mass to provide that capability if needed.But it isn't needed.
Are we talking more vibration than you see on a typical shuttle flight during SRB burn?
The in cockpit videos I've seen show the astronauts' seats bouncing around like they're in a Jeep going down a bumpy off-road trail. By comparison, when the SRB's separate, the ride gets noticably smooth, to the point that it's difficult to see any vibration of the seats on the video.
Quote from: Chris Bergin on 12/12/2008 05:03 pmNo TO mitigation is not complete. Yes, further testing is required, and yes, they won't have the best data until after Ares I-Y, but the statement you made didn't fit with the current information. We're talking about less shaking you get in your car, when reading your SatNav.Are we talking more vibration than you see on a typical shuttle flight during SRB burn? The in cockpit videos I've seen show the astronauts' seats bouncing around like they're in a Jeep going down a bumpy off-road trail. By comparison, when the SRB's separate, the ride gets noticably smooth, to the point that it's difficult to see any vibration of the seats on the video.
Quote from: jeff.findley on 12/12/2008 05:31 pmQuote from: Chris Bergin on 12/12/2008 05:03 pmNo TO mitigation is not complete. Yes, further testing is required, and yes, they won't have the best data until after Ares I-Y, but the statement you made didn't fit with the current information. We're talking about less shaking you get in your car, when reading your SatNav.Are we talking more vibration than you see on a typical shuttle flight during SRB burn? The in cockpit videos I've seen show the astronauts' seats bouncing around like they're in a Jeep going down a bumpy off-road trail. By comparison, when the SRB's separate, the ride gets noticably smooth, to the point that it's difficult to see any vibration of the seats on the video. I am curious too. Why astronauts never comment on that? It's "politically incorrect" at NASA to say anything remotely bad about ATK?
Quote from: edkyle99 on 12/11/2008 07:56 pmQuote from: jeff.findley on 12/11/2008 02:24 pmThe inescapable truth is that a -30 nmi x 100 nmi orbit requires a pretty big delta-V from Orion or it's coming down in the ocean along with the upper stage. In other words, Orion is its own third stage because Ares I can't place it into a proper parking orbit.This is a design bug not a feature!The delta-V to circularize this orbit is only about 62 meters per second, which is less than 1% of the total delta-V provided by the upper stage. NASA could have designed the upper stage to provide this extra impulse (the total vehicle weight would have been less if it had), but it did not in order to drop the stage safely into the Indian Ocean. Shuttle is nominally suborbital after MECO. It takes a 50-ish meters/second OMS burn to circularize the orbiter's orbit. Is that also a bug? - Ed Kyle Since when does the shuttle launch into a 100 nmi orbit?
Quote from: edkyle99 on 12/12/2008 05:38 pmQuote from: jeff.findley on 12/12/2008 03:12 pmSince when does the shuttle launch into a 100 nmi orbit? How much mass could Ares I put into a typical shuttle (i.e. ISS) orbit assuming that Orion does a 50 ish meter/second burn, just like the shuttle? If Ares I injected Orion into a typical post-MECO shuttle orbit (58 x 220 km, for example) it would only cost perhaps 0.4 tonnes of payload capability. And that assumes that the current Ares I design is used without alteration. It would very likely be possible to squeeze more performance out of Ares I for a higher orbit if NASA specified such an orbit. But there is already enough, or nearly enough, margin between Ares I capability and Orion's allocated mass to provide that capability if needed.But it isn't needed. Famous last words.Apollo program discovered that there _always_ is something useful you can do with extra upmass capability, and then you want more. Von Braun knew that, and designed Saturn V with _big_ performance reserve.Why NASA chose to forgot it? Von Braun is not famous enough in this field for you?
Maybe Ares I can lift Orion into ISS orbit, but at the max of its capabilities. There is zero growth potential.